My HAT! This has been the most difficult article to write. I just couldn’t figure out how to relay all the information in a way that was concise, relevant and accurate. And then, just when I thought I had cracked it and sent it off to the specialists to check, it came back with so many changes that I briefly considered throwing in the towel! I immediately understood why we are in such trouble when it comes to managing the ‘creatures’ eating the mac trees … yes, I am not even sure what to call them … to quote entomologist, Dr Elsje Joubert; “a butterfly is not a fly but a house fly is. A ladybug is not a bug but a stink bug is.” I had specifically avoided calling orchard insects PESTS as some of them aren’t, and was going with BUGS but have learnt that that is completely inaccurate so I have come full circle and will accept that the unwanted orchard insects are indeed PESTS.
Macadamia’s high nutritional content makes them valuable to both humans and insects. But waging an endless war would be expensive, exhausting and futile. So perhaps the first thing to decide is how much is worth fighting for – are we open to a little compromise? Perhaps the first step is deciding on an acceptable level of insect damage – and aim for that, rather than 0% Unsound Kernel Rate which could well be unattainable without creating a very sterile, unsustainable wasteland in the process.
If you are still deciding about whether you should compromise with Nature, consider these facts:
- If humans were to disappear from the planet tomorrow, it would not only go on living, it would improve – consider how COVID-19 has slowed us down and benefitted the natural environment. If insects disappeared tomorrow, all life would perish – just one of the important functions insects fulfil is being the base of almost all food chains.
- National Geographic refers to insects as the lever-pullers of the earth; their populations, migrations and presence influence what happens with the rest of life on the planet.
- Unlike humans, all insects add value, even if we don’t appreciate it. Just one of MANY examples: insects effectively rid our planet of waste (think of dung beetles and carrion beetles) – without them, we’d be in a world of disease.
Here’s a closer look at insects as a class:
|Strengths and Weaknesses of INSECTS|
|STRENGTHS||Numbers & high reproduction rates||It is estimated that there are 200 million insects for every 1 human on the planet.||Precision attacks are key in controlling reproduction.|
|Flight||This enables fast and frequent mobility.||Constant scouting to monitor insect movements, conserve resources and minimise collateral damage.|
|Small size & camouflage||Multitude of hiding places.||Highly trained and effective scouting is essential.|
|Masters of disguise||Change forms (through the life cycle stages).||Scout for insects in any of their life-stages. Train your scouts well on what the stages are and what the insects look like.|
|Different calendar||Insects view time in units of heat. Humans see time in terms of sunrises. This simple difference throws many humans off target.||Do not be thrown off and launch badly timed attacks. Effective scouting &record-keeping brings intelligence on what stage the insect is in on each day.|
|Ability to adapt||Insects can build resistance quickly. Much of their survival is built around this.||Avoid using the same tactic and chemical repeatedly. Insects will become resistant. Resources will be wasted.|
|High tolerance||Temperature, humidity, chemical levels etc. affect humans more than they do insects.||Insects are strong and built to survive. If the environment becomes perfect for them, it might be time for a white flag. i.e.: change crop.|
|Ability to work together||Insects are hard-wired to work en-masse, compensating for their small stature.||One insect is beatable. Thousands are a threat. Keep the numbers low enough so that crop losses are acceptable.|
|Weaknesses||Predictability||Through a relatively short study we are able to establish the stages of an insect’s life cycle.||Their cycles are known – with high-quality scouting we can be ready for the next stage with a suitable attack.|
|Vulnerabilities||Insects change structure throughout their life cycle. Some phases leave them more vulnerable than others.||We have the option to focus on one or more of the most vulnerable stages and become masters in controlling numbers through highly accurate attacks in that phase.|
|Fragility & size||Let’s face it, they’re not rhinos! E.g.: Insects lose water quickly due to their large surface area to volume ratio and are sensitive to high temperatures.||Insects are fragile – always be on the lookout for weaknesses – there are many. Patience & accuracy are key in exploiting these.|
|Being a part of a Food Chain||Humans can use food-chain levels below or above the target insects to help control numbers.||We have Allies! But they require protection, nutrition and the opportunity to grow their numbers.
Removing complete steps in the food chain can be disastrous – even our pests have a vital place. The key is to sustain balance!
Important to any large-scale operation are EXPERTS. I travelled to Mpumalanga and Limpopo in February this year, and consulted with these highly respected entomologists. The insight they bring to understanding bugs is vital in this war and my sincere thanks go to:
Left: Dr Colleen Hepburn, at work. Centre: Dr Elsje Joubert and her son Chrisjan (who was desperate to get to his Dad, standing just behind me). Right: Dr Schalk Schoeman
Now let’s look at the main PESTS in the MACADAMIA orchards:
We can further define stink bugs into Early- and Late-season stink bugs.
A FEW OF THE EARLY-SEASON STINK BUGS. Left: Bark stink bug, Centre: Yellow-edged stink bug Right: Green Vegetable bug
‘Early’ refers to the time in the macadamia season when these bugs are present in the orchards and cause damage. It was thought that Early-stink bug mouthparts were shorter and therefore only able to feed on the smaller, softer, immature nuts. At Kudu Farms, Colleen Hepburn did a comprehensive study of all stink bug species from scouting collections during the 2018-2019 growing season. Of the 24 species, which had enough individuals to dissect, only 5 species’ mouthparts were NOT long enough to penetrate the combined thickness of the husk and shell of the mature nuts of the 13 cultivars grown. Why then are they only present in our orchards early on in the season? Colleen explains that all insects ‘host-hop’ – move from crops to other plants depending on what is available and what they prefer feeding on. Schalk explains that the answer may also lie in dominance. Although yellow-edged stink bugs pose a significant risk to the macadamia crop, they are not fussy eaters and have a wide-range of host plants that they will go to, including the common castor oil plant. Possibly, because of this adaptability, they are easily pushed out by the two-spotted bugs.
The Late stink bugs to pay attention to are the Two-spotted stink bug and the Coconut bug.
LATE STINKBUGS: Left: juvenile 2-spotted stinkbug. Centre: adult 2-spotted stinkbug. Right: Adult Coconut bug
Of these, the two-spotted stink bug is undoubtedly the biggest challenge facing the South African Macadamia industry currently because of their dominance during the peak nut-bearing phase (when nuts are over 25mm in diameter. Schalk has recently been discussing dominance with Professor Johnny van den Berg from the University of Potchefstroom and explained that the law of nature says that, within a complex of insects competing for a single food source, one will always become dominant. They believe that Two-spots are attracted to the orchard by the scent of the macadamia flowers (although this was questioned by some experts who scout all year long and only find two-spots from January) and then emit a powerful odour to move the other stink bugs out.
Schalk thinks that the Coconut bug is probably the second biggest challenge in macadamias currently although this may differ per area.
We may think that eradicating two-spotted stink bugs will solve all our problems. In reality all it will do is make way for the next dominant stink bug to take its place. As long as we farm the perfect food source for stink bugs, we will be in competition with them.
In the war against stink bugs, an integrated programme is best:
- These are expensive.
- Insects build up resistance over time especially if chemicals of the same class are used constantly.
- They kill indiscriminately meaning that many other insects, like the parasitoids that can assist in controlling populations naturally, and the pollinators that directly help us get more nuts, will also die. By killing them we are adding to our problems.
- Introduce an alternate ‘feast’.
- Finding an alternate food source for stink bugs should be our primary focus right now, then we can migrate them all to a new feast and get on with farming macs. Two-spotted bugs have been found on Kei Apple which is a thorny shrub but Schalk is doubtful that it is a great host. There is another tree, related to the Macadamia, called Thoria speciose Faurea saligna or Boekerhout, that needs to be explored. It is important that the phenology of the alternate host coincides with the macadamia tree. Of concern to Schalk is that Faurea Thoria nuts are very small and stink bug mouthparts are very long so the logical deduction is that the indigenous food source would rather be a larger, thick shelled fruit. Perhaps a monkey apple?
- Biocontrol can be employed in three different ways:
- Classic exotic: a once-off release of a suitable exotic Biological Control Agent (an insect that destroys – through eating or laying eggs in it, or some other mechanism) that will control the exotic pest. N.B. This is proven feasible only when the pest is not indigenous (which the two-spotted stink bug is).
- Classic indigenous: Multiple, continuous, seasonal releases of an indigenous natural enemy that will control numbers of an indigenous pest.
- Conservational: This involves not destroying the ecological balances present, i.e.: no chemicals – let nature its own course.
- Stink bug disease … we need to use whatever nature has to offer to fight stink bugs naturally. (I suddenly have an image of myself as a stink bug and some greater life form celebrating the “success” of the Corona Virus in fighting the over-population of the human race) If we could find the stink bug version of COVID-19 …
- Soil-borne fungi. Although it has been thought that stink bugs are purely arborial (living exclusively in trees, with no soil-based phase in their life cycle) some studies have recorded high rates of naturally occurring infections in stink bugs after winter suggesting that there may indeed be a soil phase in their life cycle – as this fungus is most-likely soil-based. This unfortunately needs confirmation but may present an opportunity for new weapons and should be watched closely.
- Biocontrol can be employed in three different ways:
There are a number of moth species using macadamias as a host. Macadamia Nut Borer (MNB) and False Codling Moth (FCM) are currently the most damaging, with varying levels of prevalence in different mac-growing areas.
The greatest challenges when planning moth control measures are:
- The visual similarity of different types of moths; in mid-2019 Schalk hosted a professor from an American University. She collected some FCM larvae from Barberton whilst here and later discovered that almost half were actually Carob moth.
- All farms differ in terms of what alternate host plants are in the vicinity and the moth will host-hop in and out of your orchards. Without constant, expert scouting you will not know exactly what you are facing and when.
It is important that monitoring traps are set up using the specific hormone lures for each species so that you can establish what is present in your orchards. Proper identification is crucial as misidentification will result in incorrect chemicals being applied, which has major economic and ecological implications.
Again, integrated warfare is the best option:
- These are expensive.
- Insects build resistance to them.
- They kill indiscriminately meaning that many other insects, like the parasitoids that can assist in controlling populations naturally, will also die. By killing them we may just be adding to our problems.
- TIMING IS EVERYTHING: Almost all registered products are active on the recently hatched larva only and, as this little guy crawls out his egg and immediately begins his mission of boring into the nut, you have a very small window in which to spray EFFECTIVELY. Make sure you read the label and understand how the chemical works – some need to be sprayed directly on to the nymph, some have a short ovicidal life and can be sprayed shortly before hatching. Unless you get this timing spot-on, you’re wasting time, money, resources and beneficial life in the orchard.
- Introduce an alternate ‘feast’.
- Finding an alternate host for the moth’s larva stage should be our primary focus right now. If we found one that fruited before the macs and caught and killed them all in this ‘trap’ crop, it would save damage to the macs.
- Wasp species lay their eggs in the moth eggs and thereby destroy the larva. In Australia, these wasp eggs are sold on cards that are clipped to the macadamia tree.
- Introduce natural diseases into the orchard e.g: Insect viruses, Microbial (Entomopathogenic fungi that can attack the soil-based pupal stage of the moth life-cycle), nematodes, bacteria etc.
- Nature herself
- Pheromones are released by the moths to help them locate each other for mating. Scientists have been able to replicate these hormones BUT these chemicals are very specific; only the precise hormone will do the job. When it works perfectly, the pheromones released for control will completely confuse the moths, they won’t be able to locate each other; and no mating will take place.
- Other pheromones, made from plant extracts (aggregation pheromones or kairomones), can be used to attract moths to a trap, where they can be poisoned.
Here is a parasitic wasp emerging from a parasitized moth egg.
Macadamia FELTED COCCID
MFC arrived at an unfortunate time in the South African macadamia industry, when SAMAC left Subtrop and necessary systems were not yet up and running perfectly so the procedures that would have been part of a fully functioning biosecurity protocol weren’t functional and this allowed the insect to slip in and gain a secure foothold that is now making it challenging to control. The fact that it was also introduced to the country through a nursery further exacerbated the issue as widespread distribution happened very quickly.
An exotic parasitic wasp is being imported from Australia. It was supposed to be here in December last year but has been delayed, first in Hawaii, dealing with an infestation they are experiencing, and then by COVID. Before the journey to SA, it had to be ‘described’ properly. This publication is currently in with the relevant authorities. There are, of course, serious eco-challenges when introducing exotic insects and the wasp will be quarantined at Roodeplaat in Gauteng whilst it undergoes rigorous testing. A colony of MFC are already there, awaiting the wasps’ arrival. The MFC will be bred and host specificity testing will start. Our indigenous scale bugs will be exposed to the imported wasp and, if there is any effect on them, the wasp will not be released. Schalk is confident that everything will be fine and the exotic wasp will be cleared for use in the macadamia industry.
Commercial operators will then take over the breeding of the wasps and release them to the industry. It is classical biological control and a single release should sort the problem out. All sounds too easy …
The lifecycle of Thrips is very interesting as they most definitely have two stages spent in the soil; this makes them susceptible to nematodes and entomopathogenic fungi. Here is the link an interesting video on thrips https://www.youtube.com/watch?v=Yp2zXV0f-cQ courtesy of Koppert.co.za
Thrips damage is not limited to one part of the tree; they affect new flush, flowers and nuts. Schalk explained why he is only really concerned about the damage to new flush:
- He studied the impact of thrips on macadamia husks, which is often referred to as ‘bronzing’. He discovered that the higher the thrips damage, the thinner the husk and shell which, at the processor, results in a higher percentage crack out. He does not believe that the kernel size is affected and therefore concluded that ‘bronzing’ is not an issue in macadamia farming.
- Flower damage is an area that requires more study; under hot and dry conditions thrips will damage flowers but it is unclear what impact this has on the bottom line as beneficial thrips also help with pollination.
- The impact that new flush damage would have on the following season’s crop was where Schalk’s concern lay. He believes November dump is based on a calculation that the tree does to establish its capacity to carry a harvest and part of that calculation includes a “leaf count”. Under-developed and damaged leaves would then affect that calculation and result in a higher number of nuts dumped in November. One of the Universities is planning some further research into this theory.
Thrips are challenging because they tend to build up resistance to chemicals very quickly – mostly due to the mis-timed sprays everyone does. The implication of this is that you need to use a variety of active ingredients and plan your spray programme carefully. Poorly timed sprays may do no more than kill off any natural predators.
This concept was demonstrated for Schalk by a University contemporary who wanted to study onion thrips. He planted a patch of onions at the University and Schalk asked where he planned to get the thrips from. His friend smiled and said, “They’ll come.” He then sprayed a pyrethroid 3 or 4 times, effectively killing all the beneficials and the thrips infestation arrived! By annihilating the natural predators, he was left with the insect he wanted to study. Why then, do we do exactly that when trying to rid our mac orchards of thrips???
Now that we have a clear understanding of who the pests are, let’s explore the chemicals:
When it comes to using chemicals, we have to consider the THREE factors that are VITAL to making it a successful investment.
Each one of these elements – timing, application and choice of product is not only important but can be highly dangerous and irresponsible if not used accurately.
- Accurate timing can only be achieved by scouting. As we have already established – insects do not work by daylight calendars but rather by heat units. During hot periods they will develop far quicker than during cold periods. Insects also move in and out of orchards quickly. We also need to be acutely aware of what other insects (allies) are present in the orchard and what their susceptibility is. The only way to know all of this is to LOOK. Highly trained and effective scouts need to spend quality time in the orchards, and collect up-to-date data on which to base treatments.
- Accurate application is down to equipment and execution. Schalk advises that, right now there are no definitive standards, but in February this year, a meeting was held with the Pesticide Dynamics Team at the Agricultural Research Council in Pretoria to create a study that would establish highly accurate calculations of what to do with sprayers to get optimal efficacy in terms of chemical droplet size and positioning. It has taken so long to get to this point because a project of this nature is very expensive. The outcomes would establish firm and conclusive guidelines on spraying equipment and methodology. All the information available currently has been amassed by experience over time but has never been scientifically quantified. The scientists in the Pesticide Dynamics Team will ascertain deposition rates etc and be able to quantify, chemically and biologically, the results of various spray techniques. Schalk knows it is a daunting project, if it can even be pulled off as planned. The initial aspect to be tested will be equipment, keeping chemicals and tree shape and size constant. Later, in subsequent project phases, the other variables will be tested. In the meantime, there are things we can do to improve accuracy:
- Schalk feels that we have not yet learnt how to spray effectively in macadamias. This is one of our biggest impediments with insufficient pruning being the main culprit. Although pruning insights and methods are improving (see TropicalBytes article focussing purely on this topic – http://www.tropicalbytes.co.za/2020-5-pruning/ ) – there are still many farmers who are not paying enough attention to this practice. Spraying in a poorly pruned orchard renders the investment ineffective and exacerbates the escalation of the insect population. The specific pruning considerations are tree height, tree density and adequate passageways for the spray rig (if spraying is done with a tractor). Schalk advises that there should be a gap of at least 1m, preferably 1,5m, between the spray applicator nozzles and closest leaves. In most orchards he visits the tractor is brushing against the closest leaves – that’s NO distance! This means that the spray is not penetrating into the foliage and the insects are safe. Schalk also advises that 80% of the spray should be directed towards the top of the tree and only 20% to the bottom as most stink bugs hang out in the tree tops. Usually, with ineffective spray equipment, tree height and density issues, the amount of chemical reaching the top is so little that it is ineffective and, over years, will build resistance.
- Check effectiveness. I mentioned this in last month’s pruning article but it is worth repeating: hide a piece of litmus paper in the most difficult-to-reach part of the tree and then check to see whether your sprayers covered it effectively. Elsje and Stoffel Joubert have a great way of doing this by clipping a piece of litmus paper to a length of conduit.
- Accurate chemicals. It is the farmers responsibility to thoroughly research the chemical application rates, composition and registration, the insect he is targeting and the environment (what will fall as collateral damage) before using the chemical. Not only are chemicals expensive, they are also highly toxic. That toxicity is intentional but it is, generally, not specific. Other creatures – probably essential allies – above and below your target in the food chain, will be affected by whatever you spray. This is a loaded gun and the consequences are massive.
These are the chemical classes we currently use:
Purified pyrethrum, called pyrethrins, has been very useful in insect control. It kills a variety of insects and mites, knocking them off plants very quickly. For this reason, and because of its relatively low toxicity to humans, pyrethrins remain very popular today (think of Raid® Flying Insect Killer, and many others). Pyrethrins also have the desirable environmental characteristic that they break down quickly (minutes to hours) in the outdoor environment although, from a pest control perspective, this may not be an advantage.
Unfortunately for farmers, pyrethrum has always been expensive, and natural supplies are limited and often unreliable. For this reason, pesticide chemists considered it a high priority to search for ways to synthesize pyrethrins in a laboratory after WWII. The result, in 1949, was the first artificial pyrethrin-like insecticide called allethrin.
Once chemists figured out the techniques for synthesizing this class of insecticide, many different versions were created. In the 1960s a number of new, “second-generation” pyrethroids were patented, including tetramethrin, resmethrin, bioallethrin and phenothrin. These new compounds were many times as toxic to insects as natural pyrethrum and still have many uses today, including household insecticides. Since the 1960s, further advances in synthesis have created new, useful insecticides that resemble the original pyrethrin molecules less and less. These new pyrethroid insecticides have become more toxic to insects and last longer in the environment than the early compounds. Pyrethroids are toxic to beneficial insects such as bees, dragonflies, mayflies, gadflies, and some other invertebrates, including those that constitute the base of aquatic and terrestrial food webs.
It’s not too difficult to recognize a pyrethroid insecticide. Look at the pesticide label; Pyrethroid common names almost always end in either -thrin or -ate. Examples include allethrin, resmethrin, permethrin, cyfluthrin or esfenvalerate.
These are chemical substances produced by the process of esterification between phosphoric acid and alcohol. Besides being a key component of herbicides, pesticides, and insecticides, organophosphates are also the main components of nerve gas. Acute or chronic exposure to oganophosphates can produce varying levels of toxicity in humans, animals, plants, and insects and, because of this broad toxicity, these chemicals are being taken off the South African market as we speak. Europe has already banned their use. Our industry has been getting away with using them because there is not a lot of residue left once the nuts have been processed, so the chemical is not picked up in the export process. Examples of organophosphates are: Acephate and Chlorpyrifos.
Neonicotinoids (sometimes shortened to Neonics)
These products are based on the same chemical found in cigarettes; nicotine. They are neuro-active. They are also systemic, meaning that the chemical is absorbed into a plant and distributed throughout its tissue, remaining there for a full season. Application is through drenching the soil around the tree. Neonicotinoid use has been linked, in a range of studies, to adverse ecological effects, including honey-bee Colony Collapse Disorder (CCD) and loss of birds due to a reduction in insect populations. Some scientific findings regarding the harm caused to bees by Neonics have been conflicting and controversial. This is partly because bees exposed to lower levels of neonicotinoids do not die immediately. Some sources have proposed that neonicotinoids only reduce a bee colony’s ability to survive the winter. Examples of neonicotinoids are Imidacloprid, Clothianidin, Acetamiprid.
These pesticides are derived from carbamic acid and kill insects in a similar way to organophosphate insecticides; affecting nerve impulse transmission. They are widely used in homes, gardens, and agriculture. The first carbamate, carbaryl, was introduced in 1956, and more of it has been used throughout the world than all other carbamates combined. Because of carbaryl’s relatively low mammalian oral and dermal toxicity and broad control spectrum, it has had wide use in lawn and garden settings. Most of the carbamates are extremely toxic to foraging bees and parasitic wasps.
Avermectins and Milbemycins
These chemicals induce paralysis of invertebrate neuromuscular systems. Resistance to avermectins has been reported, which suggests moderation in use. These naturally occurring compounds are generated as fermentation products. Examples are Emamectin benzoate and Abamectin [syn. Avermectin]
Diamide insecticides have emerged as one of the most promising new classes of insecticide chemistry owing to their excellent insecticidal efficacy and high margins of mammalian safety. Chlorantraniliprole and flubendiamide, the first two insecticides from this class, demonstrate exceptional activity across a broad range of pests in the insect Order Lepidoptera (moths). This chemistry has been confirmed to control insects via activation of ryanodine receptors which leads to uncontrolled calcium release in muscles. The high levels of mammalian safety are attributed to a strong selectivity for insect over mammalian receptors. Coragen® insect control is a product many of you know well (sugarcane farmers for effectively combating Eldana and macadamia farmers for its control of False Codling Moths) and it belongs to this class of chemicals. You can therefore feel assured that you are not only using a progressive product but also one that limits fall-out and collateral damage. Personally, I am very grateful to FMC, the holding company, for investing in our learning and keeping this platform alive.
These chemicals act as insect growth regulators by inhibiting synthesis of chitin in the insect’s body. One of the more commonly used benzoylurea pesticides is diflubenzuron.
These chemicals are used effectively by inducing precocious molting. Recently, Diacylhydrazine derivatives have attracted considerable attention due to their simple structure, low toxicity, and high insecticidal selectivity. An example is Methoxyfenozide, used to control FCM.
Spinosyns are a family of broad-spectrum insecticides, including spinosad and spinetoram, isolated from a soil bacterium. Being of biological origin, they are considered to have a low environmental impact with low toxicity on non-target species. Thanks to their mode of action the resistance phenomena is uncommon. For all these reasons, they are currently one of the most interesting options. An example is spinetoram, used to control FCM, MNB and Thrips.
Its main mode of action is via blocking of neuronal sodium channels but should be used with caution since some insects can become resistant. An example is Indoxacarb used to control FCM.
Biopesticides are certain types of pesticides derived from natural materials like animals, plants, bacteria, pathogens and certain minerals.
Biochemical pesticides are naturally occurring substances that control pests by non-toxic means. Conventional pesticides, by contrast, are generally synthetic materials that kill or inactivate the pest.
- Pheromones. Biochemical pesticides include substances that interfere with mating, such as insect sex pheromones, as well as various scented plant extracts that attract insect pests to traps (aggregation pheromones or kairomones). Because nature is so complex and highly integrated, it is very difficult to manipulate and mimic – therefore pheromones enjoy limited success. It is certainly a field of study that warrants for more investment and focus.
- Microbial pesticides consist of a microorganism (e.g., a bacterium, fungus, virus or protozoan) as the active ingredient which is deployed to infect and debilitate the bug.
- Botanicals. Think strong smells like garlic – there are so many potential harmless resources out there, if only we could identify, and replicate, what gets up a bug’s nose!
The advantages of using biopesticides?
- Biopesticides are usually inherently less toxic than conventional pesticides.
- Biopesticides generally affect only the target pest and closely related organisms, in contrast to broad spectrum, conventional pesticides that may affect organisms as different as birds, insects and mammals.
- Biopesticides often are effective in very small quantities and often decompose quickly, resulting in lower exposures and largely avoiding the pollution problems caused by conventional pesticides.
- When used as a component of Integrated Pest Management (IPM) programs, biopesticides can greatly reduce the use of conventional pesticides, while crop yields remain high.
To use biopesticides effectively (and safely), however, users need to know a great deal about managing pests and must carefully follow all label directions.
I found a table, on the SAMAC website, that was very useful. It listed chemical classes, brand names, and some general information on what can be used in the mac industry war against pests. I thought it would be helpful to see what is available and what the active ingredient is. You can then decide what kind of war you are waging and which weapons you prefer. Here is a simplified version*:
|PEST||Options of active ingredients registered to treat it||Application method||Chemical Class|
|Bollworm||Emamectin benzoate||Foliar||Avermectins and Milbemycins|
|chlorantraniliprole + lambdacyhalothrin||Aerial; ground||diamides + pyrethroid|
|Helicoverpa armigera nucleopolyhedrovirus [syn. bollworm nucleopolyhedrovirus||Foliar; aerial||Microbial|
|False Codling Moth (FCM)||emamectin benzoate||Foliar||avermectins; milbemycins|
|acetamiprid + bifenthrin||Foliar||neonicotinoids + pyrethroid|
|chlorantraniliprole + lambdacyhalothrin||Aerial; ground||diamides + pyrethroid|
|Thaumatotibia (Cryptophlebia) leucotreta granulovirus [syn. false codling moth granulovirus]||Foliar||insect virus|
|Bacillus thuringiensis, subspecies kurstaki (strain SB4)||Foliar||microbial|
|acetamiprid + novaluron||Foliar||neonicotinoids + benzoylureas|
|Multiple varieties||Lure; mating disruption||pheromones|
|Multiple varieties + permethrin||Attract & kill||Pheromones + pyrethroid|
|Macadamia Nut Borer
|Multiple varieties||Mating disruption||pheromones|
|Multiple varieties + permethrin||Attract & kill||Pheromones + pyrethroid|
|emamectin benzoate||Foliar||avermectins; milbemycins|
|Stink bug||chlorantraniliprole + lambdacyhalothrin||Aerial; ground||diamides + pyrethroid|
|chlorpyrifos + cypermethrin||Foliar||organophosphate|
|pymetrozine||Foliar||pyridine azomethine derivatives|
Schalk voiced his concern about increasingly limited chemical options in the vicious war against macadamia pests as chemicals are being outlawed (eg: organophosphates) without less harmful replacements being developed.
Again, the solution has to come from adopting a programme that uses more than just chemicals. Schalk agrees and shared this relevant story to emphasise the point:
Fifteen years ago, the kids in Nelspruit found that all their silkworms were dying. Only when a brand-new silk factory in Bushbuck Ridge lost around a million silkworms did everyone start to investigate. A product had been used to control scale insects on citrus farms – it had a growth regulating effect on the silkworms and prevented them from maturing. The problem was that it had a very stable bond and when it landed on any organic material it did not break down at all. Drift trials were conducted and it was discovered that areas 8km away from the spray site were affected! The product was removed from the market but Schalk says we can take two important learnings from this disaster: 1. more trials need to be done to establish all the fall-out of the chemicals we are using 2. What are the invisible consequences of our chemicals? Things we will never know. If there was no silkworm factory in the vicinity of this chemical, would we have realised the level of toxins we were using? What other (indigenous) creatures were adversely affected?
Schalk attended a symposium in China recently and one issue was abundantly clear: we have to relook at everything we are doing before we wipe out the bottom of the food chain (insects). Between human activity and climate change, certain vital insects are facing obliteration. This was clearly verified in a study done in a forest in Germany. The results showed that 80% of the insects in this forest have disappeared over 30 years. What does this mean for the rest of the world – how fast are our insects disappearing, especially in agriculture?
Schalk insists that we cannot carry on spraying like we are now. For next 10 years, while the options are slim, we have no option but we do have to switch ultimately before we collapse the ecosystem. In battle terms, we have to start using sniper rifles rather than shotguns and atom bombs.
How does this look? For moths, Schalk says our chemicals are fairly soft and fit well into an Integrated Pest Management programme. Pheromones and the disruption they cause to mating will work and has many advantages. The work needed to progress in this field is being done. We also have a plethora of biologicals that can be unleashed to control moths. For example, there is an indigenous wasp, called Trichogrammatoidea cryptophlebiae. It is a small wasp that has successfully been bred and released. It parasitizes the moth eggs as shown in the picture under the Moth Wanted poster above but conventional spray programmes of 4 to 5 pyrethroid/organophosphate sprays in a season will wipe the wasps out.
For stink bugs, we have bats but unfortunately, they struggle to keep up with the volumes bred inside a mac orchard. Some farmers have built bat houses or kept bananas close to their mac trees (banana trees are excellent bat houses) and have consequently been able to cut back on their spray programmes.
Various bat house designs are available and it’s not difficult to build.
Schalk explains that the war against pests is like building a wall of unique bricks. Each measure you take is a brick in the wall but you cannot use the same type of brick throughout. It’s up to you how to build the wall but, ultimately, if your wall is working against nature rather than with it, it will collapse.
The sustainable solutions seem to lie in Biopesticides and pathogens. Right now, there are still considerable challenges to be overcome in these fields (e.g. entomopathogenic fungi, which are excellent in infecting and controlling many insects, are susceptible to UV light, meaning the spores become ineffective when exposed to sunlight. Colleen Hepburn advises the ways around this are: 1. to spray at night; 2. Apply as a soil drench and reapply at intervals to ensure the entomopathogenic fungi culture establishes itself; and 3. Use mulch under the trees which gives added protection to the spores.
The addition of a sunscreen is being investigated and will hopefully extend the lifespan of beneficial fungi in the orchard. Another exciting development is an enzyme that dissolves the cuticle (outside skin) of the insect, which was alluded to earlier in the article. As with all new products, the concern is always around selectivity; how do we protect good insects while eradicating harmful ones and sustaining the food chain?
THE IMPORTANCE OF SCOUTING
All the specialists I engaged were in agreement on one major point – spraying to a programme is the worst way to do things.
- Indiscriminate damage – if you haven’t scouted, spraying may be unnecessary. The expensive & indiscriminate killing is wasteful.
- Inaccuracy – Insect cycles work in heat units, not conventional days, so you may miss the sweet spot which is more wasted resources and unnecessary killing.
Schalk says scouting is the only way to do it but needs to be refined:
- When the nuts are young, under 20mm, go out and cut them open. See what is happening inside. See if there are stink bugs. If nuts are on the ground, there is usually a reason – most likely moth or stink bug damage. If you’re in an orchard in December and there are a lot of nuts on the ground, there is almost definitely an issue going on.
- Chemical scouting needs to be done responsibly.
- Do not use the same trees for every scout. Randomly select and change the trees -keep moving around. Insects move, you need to move. ‘Edge effect’ has been proven over and over again so make sure at least half of the trees scouted are on the edge of the orchard, especially if the orchard is close to natural bush area or some sort of insect-haven.
- Felted coccid congregates in pockets. Schalk says it is the weirdest distribution of any insect he has seen. They land on a single tree and “nuke it”.
SOME OTHER EXCITING DEVELOPMENTS ON THE HORIZON
- Alternative food sources are exciting for Schalk. He believes there are so many solutions in discovering the indigenous food for stink bugs.
- Push-pull is also interesting. Just like in sugarcane, where molasses grass is used as a push plant and BT-maize or certain watergrasses are used as pull plants.
- Pathogenic nematodes for Thrips & FCM control are showing a lot of promise. This is applied as a drench or in the irrigation. The nematodes feed on the larvae and Dr Willem Steyn from ARC-TSC is excited to see that it looks like it is going to work. He has just completed the first field trials. The data hasn’t been analysed yet but he is hopeful after what he’s seen.
- For Schalk, the most promise lies in mimicking the odour pests give off in dominance. He has recently been discussing the possibility of exploring this option with one of the world’s leading chemical ecologists who is busy quantifying the use of the defensive compound found in the 2-spotted stink bugs’ smell. i.e.: how to use that to keep all other stink bugs away. Although the two-spotted bug won’t outcompete itself, it will narrow our targets (and exclude the early stink bug issues) and enable us to focus on one stink bug exclusively later on in the season. Although it is currently only a concept initial testing should be done with Coconut bugs in avos where there is a big problem at the moment – especially as they are very limited on what they can spray and remain Global Gap Accredited. Once the concept has been proven, they can roll out into the mac industry. They do have a head-start in that they’ve identified a stink bug in the litchi orchards that seems to show dominance over the two-spot! Schalk warns that all this is very expensive work … but it may also be highly effective.
As he ran out the door, Schalk made sure I understood that the farmers need to know that all chemical applications have to be based on the outcomes of excellent scouting. And that farmers should always use a softer, integrated approach with environmental balance as the priority.
I recently visited a highly successful mac farmer on the South Coast and he showed me spray recommendation posters from a few agents. It took me a while to figure out that, although there were about 30 – 40 items on each poster, there were only 4 – 5 sprays. So the companies were recommending combination sprays. When we consider the highly targeted requirements of a spray programme, in terms of timing and methods – e.g.: where, in the orchard, to spray (moths are all over but stink bugs tend to hang out in the upper branches and scale insects are single tree specific) – I wondered how combination spraying could ever fulfil these requirements. And, I hope, by now, we’ve established the necessity of being highly specific. Nature is designed in a detailed and highly intricate way – how can we ever hope to implement sustainable, dominant control and keep the mac trees safe and productive when we go in with bulk bombs?
DR COLLEEN HEPBURN
Approaching Kudu Farms, I felt as if I was driving onto a movie set. It was a “gloomy” day in February with a storm threatening (the same rains that continued unabated for 4 days thereafter!!), the dusty roads of the remote settlement were empty. At least the insects here are not representative of the greater Mpumalanga region, given the isolation of the farms. Colleen is a full-time entomologist, employed by this progressive and successful macadamia grower and processor. Her skills help all the farmers supplying this amazing company (I will be doing an article on their journey – it is fascinating!) Colleen challenges and questions constantly and this has brought fresh and revolutionary insight to many aspects of pest control in our industry.
One of her current studies is to look more closely at the seasonal occurrence of the Two-spotted stink bug. Literature tells us that each stage of an insect’s development takes place over a certain number of days. Scientists have worked out a model which uses Degree-days which are measured in heat units, not days (as I have referred to a few times in this article). Researchers working on the Two-spotted stink bug model are still quantifying the data; the lower developmental threshold temperature is around 10,5°C and the upper developmental threshold 33°C; the number of heat units to complete a lifecycle is approx. 338. Outside these upper and lower thresholds, insect development slows down. Colleen has analysed five season’s worth of weather and scouting data collected at Kudu Farms and plotted the seasonal patterns of occurrence. The average number of days it takes a Two-spotted stink bug to complete a lifecycle in ‘ideal’ conditions, between those lower and upper temperatures, is around 21 days and NOT 44 days as is on the chart most people use as a reference. For those who employ calendar or rote spraying once a month, this means the first month the spray will be 1 week too late; second month 2 weeks too late; third month 3 weeks too late etc. so the timing of the sprays are way off target. We need to incorporate the latest technology and revisit what has been used as standard practice in the industry for years. Throughout the different mac growing areas, the temperature data (from a weather station) and the stink bug numbers (collected from regular scouting) will differ, but the number of heat units for the development of the Two-spotted stink bug remains the same. This information by no means proposes that spraying should take place every 21 days, quite the opposite in fact; a number of sprays can be eliminated as the number of stink bugs are nowhere near the threshold or even present.
As Colleen is responsible for controlling insect damage on Kudu Farms, she’s appreciative of the challenges faced by farmers. Key to her strategy is precision. She applies the initial spray as the stink bug nymphs reach their second stage. This knocks out both the adults and the nymphs (the next generation), which will increase the time before the next spray is necessary. Adults will continue to immigrate into the orchard which is why scouting is so vital. Always keep a record of when the first nymphs appear in a season and take note of the stages the nymphs are at when collecting the scouting catch; you will have a clearer picture of what is going on in the orchards. This way, she minimises the number of spray applications and costs. The strategy is to reduce the number of immatures before their mouthparts develop to a size where they can damage the kernel. She knows that large farms face the challenge of getting around large areas within a short period of time, whether for scouting or spraying, especially if there’s rain, mechanical breakdowns or a myriad of other challenges farmers face. It is important to get a spray round completed as soon as possible, starting with the farm with the highest numbers. If there is an outbreak in a confined area, perhaps near an area of natural bush, the solution is to ‘spot spray’ those hot spots, it may not be necessary to do a full spray round of all the farms. She emphasises that you have to control the initial ‘in orchard’ reproductive cycle before they reach adulthood, and this is one approach she has found effective.
When I asked about her strategy for thrips she advised scouting is also vital, not only on the big trees but the smaller trees too as all trees produce new flush. The scouting team collects data weekly. Colleen has analysed data from the past 5 years and can see the seasonal trends. When applying a chemical spray to suppress numbers, she suggests a double-tap (after the initial spray to apply another spray shortly thereafter) as thrips lifecycles are extremely short; take out the adults and subsequently the nymphs as soon as they emerge. This has helped her reduce numbers significantly. Small trees are only sprayed when damage to the new flush is noticed and not on a regular basis. It is important to monitor both old and young trees as if only one is done, the thrips numbers could be building up on the other.
In Colleen’s world, it is all about scouting and seeing what is in the orchards, where and in what densities. Her team scouts all year round, 4 days a week to get around all the farms! She stresses how important it is to find the indigenous food source of the Two-spotted stink bug; macadamias are exotic plants, brought in from Australia, they’ve only been here 90-odd years. Two-spots are indigenous, so what were they eating 100 years ago?
DR ELSJE JOUBERT
Elsje is young, energetic and passionate with an enquiring mind that never seems to sleep. She farms in Levubu and brings us broad insight from this well-established macadamia area:
- Her preference is for biocontrol and actively promotes the use of parasitoids to control both Nut Borer and Thrips. She also encourages the use of entopathogenic nematodes in the soil to infect and neutralise thrips during their soil-based stage. Fungi are affective with stink bugs but they are highly susceptible to sunlight and heat.
- There are parasitoids that use the stink bugs to hatch their young but, like the other creatures higher up the food chain – bats, geckos, birds etc, they just can’t keep up with the stink bug numbers produced in the mac orchards.
- She’s noticed that the cooler areas, higher up in the mountains, they do not have half the insect problems that the warmer valleys have. This is probably because they have more heat units and this increases their rate of production.
- Elsje warns against taking your eyes off the insects even when there is no fruit on the trees. Stink bugs over-winter in the orchards and by allowing this generation to breed, you start the next season off in the negative. She did this last year and her reluctance to spray resulted in substantial crop losses.
- Using a softer chemical approach, coupled with natural predators, requires patience and tolerance for short term losses that will result in long term benefits. She illustrates this by explaining that you cannot put lion into a game farm without there being enough buck. When the buck population is big enough, the lions will breed and natural balance will be maintained if humans resist the temptation to interfere.
- She helps me to understand the severity of the stink bug problem faced by the industry in Levubu; R240 million was lost by the South African industry to stink bugs last year and Levubu carries 45% of that loss although they only account for 22% of the country’s crop. See the table below from SourceBI for comparative costs.
- As our expenditures toward pest control increases, our profit margins are decreasing. Do the math: look at your losses and plan your control strategy accordingly.
So, how do we avoid going bankrupt? Again, I hear about the value of scouting and spraying with precision. For Elsje, spray calibrations are the greatest area of weakness. This results in inaccurate applications and we’ve already discussed the myriad of problems that causes.
Elsje’s farm uses ‘EM’ which is a mixture they create using natural bacteria. It is safe enough for a human to drink but packed with live goodness – up to 1 billion spores per teaspoon. The bacteria promotes healthy tree growth and is uncomfortable for the stink bugs to live with in the soil. It promotes healthy soil activity. Unfortunately, when the weather is insect-perfect (hot and dry), the bacteria dies so spraying is limited to cool, wet conditions. Elsje believes that climate change, which is showing a trend to hotter and drier conditions for Levubu, will undo a lot of macadamia farms as insects simply become unmanageable.
She said that the only way to farm sustainably, is to keep pests and diseases under control in an integrated way. This means that various strategies must be followed to control pests and diseases. General (cultural) practices, such as pruning and planting cultivars that are resistant to pests and diseases, are very important. The farmer must maintain tree and soil health as a standard practice. Cover crops may help indirectly to control pests through their function in the ecosystem.
Growers must know the major pests and diseases and monitor for these and new pests and diseases regularly. Growers must intervene in such a way that the pest and disease levels are kept low and damage does not reach economic thresholds. The biological integrity of the environment must be kept intact. Chemical control must be done in a way to combat resistance, i.e. by alternating chemical groups. The effect of chemical use on beneficial organisms must be studied and rectified. Biological control must always be considered as a first step of intervention and should be integrated into a chemical control program.
When it comes to new pests, you may be interested in reading this article I found recently: https://www.farmersweekly.co.za/crops/field-crops/protecting-south-africas-trees-from-the-shot-hole-borer/ I am not sure whether macadamias are good hosts but it is worth being informed and keeping your scouts educated.
After what I believe was a thorough investigation of the challenges pests pose to the macadamia industry, I can conclude that an integrated strategy shows the most promise for sustainable farming that will leave a situation worth handing over to your children.
Wasps can be beneficial allies
What Is Integrated Pest Management?
Integrated Pest Management, or IPM, is a strategy in which observations, including inspection and monitoring, are used to make pest-control decisions based on predetermined management objectives. IPM takes an ecological approach to selecting control methods, combining a variety of chemical and nonchemical control tactics in a way that minimizes risk to people and the environment. This process must include an evaluation and written records to document the procedure and results.
Although the basic components of IPM are always the same, the specific elements of an IPM program vary from one environment to another. IPM dictates that every pest situation be evaluated independently. In all cases, inspection and monitoring provide the necessary facts upon which to base decisions about whether or not to implement control procedures. After making the decision to implement controls, various control options must be carefully selected, based on effectiveness of the tactic and human and environmental safety. Finally, evaluation and record keeping promote informed decisions regarding how long to continue controls or whether or not to make changes.
These five main components of IPM are considered essential:
- Inspection (scouting)
- Monitoring and Tolerance Level Establishment (how much are you prepared to share with nature)
- Situation-Specific Decision-Making (what, how, when, where)
- Application of Pest Management Techniques (precision)
- Evaluation and Record Keeping (learnings)
No discussion on insects would be complete without a discussion on BEES but I am going to have to accept that this discussion is then, indeed incomplete! It’s already been a really long article and to add this, would be to waste your attention, which I may well have lost by now anyway. It is however important and, I believe, warrants a stand-alone article so, in the words of the Terminator himself, “I’ll be back …”
Given the highly technical nature of insect warfare, I relied heavily on research and need to give credit to the internet sites that assisted in compiling this article:
* NB: Disclaimer: TropicalBytes (or myself) is in no way qualified to make recommendations or suggestions with regards to anything related to pest management, particularly chemical use.