SATI Beyond The Bunch 4th Quarter 2025

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SATI Research Booklet

Quarter 4

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LIAAN JANSE VAN VUUREN

2 0 2 5

FOCUS ON: Mealy bugs

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A winged mealy bug male with a group of females. Note the size difference.

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About Beyond the Bunch This quarterly publication aims to serve as a science-based resource for the South African table grape industry. Each edition explores a topic or questions raised by industry, with links to related additional reading. Submit your topic or questions Producers and industry stakeholders are encouraged to suggest scientific or technical questions or topics of interest. We will strive to address as many of these as possible.

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MEALY BUG BIOLOGY

A 103-million-year-old fossilised leaf from Nebraska bears an imprint that would be instantly recognisable to any present day table-grape grower: a female mealy bug. These small sucking insects evolved over aeons to exploit a wide range of plants and are now ubiquitous agricultural pests.

BY ANNA MOUTON

Table-grape vineyards are suitable mealy bug habitats because the vines provide nutritious sap to support mealy bug reproduction during summer. Understanding their biology is the first step toward successful control.

What are mealy bugs? Mealy bugs are soft scale insects. Adult female scale insects are sedentary and depend on their waxy coating and cryptic habits for protection. Like all bugs, mealy bugs have piercing-sucking mouthparts to extract phloem from their hosts. Modern mealy bugs comprise more than 2 000 species, but this newsletter focuses on the vine mealy bug ( Planococcus ficus ), the most common species in South African table grapes. It is widespread internationally and exotic to South Africa.

Mealy bugs cause three problems The most common impact of mealy bugs is on grape appearance. Mealy bugs produce a sugary fluid called honeydew, which serves as a substrate for sooty mould. Unsurprisingly, consumers find mealy bugs, sticky honeydew, and the associated black mould off-putting. Heavy mealy bug infestations can also damage leaves and bunches, leading to browning, wilting, and desiccation. Premature leaf drop can occur. The vine mealy bug is the primary vector of grapevine leafroll-associated viruses. Infection with these viruses reduces grape yields and quality and shortens the productive lifespan of vineyards.

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A year in the life

LIAAN JANSE VAN VUUREN

Female mealy bugs don’t have a pupal stage. Adult female mealy bugs overwinter in cracks or under bark. Vine mealy bugs can also survive underground on roots. The females lay eggs that hatch into mobile first instars called crawlers. These energetic juveniles can scale a grapevine in a day. Female crawlers moult several times before adulthood. Vine mealy bug females can lay up to 750 eggs during a lifetime of several weeks to several months. Male crawlers also moult before pupating to become winged adults. Adult males only live a few days and don’t feed. Their only goal is to seek and mate with females. Vine mealy bugs require temperatures of ± 16–36 °C to

develop. The optimum range for development is 23–27 °C. The insects can complete their life cycle in 3–4 weeks during summer and have 3–7 generations per year. Crawlers start surging up the vine trunks in September or October. They prefer soft, nutritious tissues and start by targeting new stem growth, then move on to leaves, and finally bunches. Stem infestations of vine mealy bugs peak during January in Stellenbosch and Robertson and during February in the Hex River Valley. Peak crawler activity is associated with favourable weather, but females lay eggs throughout the year so that crawlers may be present in small numbers even in winter. Mealy bug populations tend to decline later in summer, even though temperatures are still favourable for reproduction. This may be partly due to increased activity by predators and parasitoids. Adult females also move to winter hiding places as sap flow slows.

Mealy bug females like to shelter in crevices and under bark.

Ants Mealy bugs can spread by hitching a ride on people and equipment, and crawlers can be carried by the wind. However, ants are largely responsible for transporting mealy bugs within vineyards. Mealy bugs and ants go together like coffee and rusks. Besides carrying mealy bugs to new locations, ants defend them against enemies. The mealy bugs reward this behaviour by excreting sticky honeydew that the ants consume eagerly. Ants form similar relationships with other sucking insects, including aphids and scales. Due to the close association between mealy bugs and ants, ant control is an essential component of mealy bug management, which is discussed in the following section.

GRAEME HATLEY

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BIOCONTROL OF VINE MEALY BUG Many table-grape growers worry that a shrinking pesticide arsenal will allow vine mealy bugs to overrun their vineyards. But there are several biological options for controlling these troublesome pests.

BY ANNA MOUTON

Integrated mealy bug management relies on four pillars: monitoring, biological control, chemical control, and cultural practices. This article focuses on non chemical approaches to vine mealy bug management. Growers wishing to integrate these practices in their crop-protection programmes must consult their crop-protection advisers.

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Scouts must be able to identify lacewing eggs.

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Scouting for ants in grape vines is an essential part of mealy bug management.

Monitoring There are three ways to monitor mealy bug infestations, and all of these should be used when deciding on appropriate management strategies. Vineyard history Classify vineyards according to the observation of bunch infestations in the vineyard and the pack house. A vineyard with very few or no infested bun ches shouldn’t need dormant spray applications or aggressive crawler control. Substantial bunch infes tations indicate a greater need for chemical control. Mealy bugs are frequently unevenly distributed within vineyards. If bunch infestations are at economically meaningful levels, it’s advisable to identify and address mealy bug hotspots in the vineyard rather than jumping to blanket spray applications. Scouting In-depth scouting should be done once during winter to find and eliminate colonies of adult females. Start summer scouting from bud break and continue until harvest. Every block must be scouted weekly, so farms need enough trained scouts to avoid missing infestations. Check for adults and crawlers. Crawlers are the easiest stage to control because they’re exposed: they aren’t hiding in cracks, and they haven’t yet developed protective waxy coatings. It’s also essential to target crawlers before they reach bunches.

Mark infested vines during the season so they can be used to assess the efficacy of control measures and to detect crawler activity early in the following season. Pheromone traps Winged mealy bug males can be caught with pheromone-baited traps hung in the vine canopy. Traps attract males powerfully, but males are not strong fliers. Therefore, the best place for traps is near suspected hotspots. Traps at the vineyard edges may attract males from outside the vineyard. Deploy traps in September and check them weekly. The lures should be replaced according to the manufacturer’s recommendations. Trapping should continue at least until harvest. In problem blocks, continue checking traps monthly after harvest. Male mealy bugs are very small (± 1.0–1.5 mm long) and must be identified using a stereomicroscope. Scout for crawlers once males appear in traps. There are no thresholds for mealy bug trap catches, but 65 males per trap in two weeks indicates that scouting for crawlers should intensify. Peak crawler movement tends to shift a week earlier or later every season, but mass crawler migrations usually occur 1–2 weeks after males are trapped. However, the relationship between male numbers and crawler movement is site-dependent, so trap catches and crawler activity must be correlated based on historical data.

Scouting protocol 1. Divide the block into 20 plots of equal size, each containing five vines. Plots should be evenly spaced but include suspected hotspots. 2. Check for adult females under the bark. Check for all life stages on stems, leaves, and bunches. Infestations tend to start on stems, move to leaves, and end up on bunches. 3. Examine all new growth on each vine using a hand lens. Adult females are easily spotted with the naked eye, but crawlers can be less than 0.5 mm long. 4. Chemical control to prevent economic damage is unnecessary if fewer than 2% of vines have infested

stems. A mass release of natural enemies should be considered instead. 5. Check for ant activity. Control ants if more than 20% of vines are infested.

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Biocontrol agents Predators and parasitoids are the foundation of successful mealy bug management. In many vineyards, it’s possible to suppress mealy bugs below economic thresholds using only these natural enemies and without the need for any chemicals.

Parasitoids versus predators The parasitoids used for crop protection are wasps that lay their eggs inside pests. The developing wasp larvae consume the host from the inside. Parasitoids tend to be host-specific – they only target one insect type or species. In general, parasitoids can survive at lower pest densities than predators because the adult parasitoids feed on pollen and nectar. Each parasitoid female can lay eggs in a relatively large number of hosts, although parasitism rates vary by parasitoid species and site-specific factors. The predators used for crop protection are insects or mites that eat pests. Both larvae and adults of most predators hunt and kill prey. Predators will often feed on different prey species but may have strong preferences for particular prey. Adult predators require high pest densities. The pickier a predator is, the higher the density of its preferred prey must be. Many predators are notoriously voracious, but they still kill pests one by one, so they tend to chalk up a lower body count than parasitoids. Common commercially available parasitoids Anagyrus vladimiri and Coccidoxenoides perminutus parasitise vine mealy bugs ( Planococcus ficus ). A. vladimiri prefers third instar and adult mealy bugs, but may have a limited impact on second instars. C. perminutus only lays eggs in first and second-instar mealy bugs.

C. perminutus is more heat-sensitive than A. vladimiri . Leptomastix dactylopii will parasitise more than 20 mealy bug species, including vine mealy bugs, but prefers citrus mealy bugs ( Planococcus citri ). Therefore, it may abscond to nearby citrus rather than remain in vineyards. L. dactylopii has limited commercial availability but occurs naturally in most grape-growing regions. Common commercially available predators Cryptolaemus montrouzieri is a diminutive beetle, affectionately known as the mealy bug destroyer. Besides eating all mealy bug stages, it lays its eggs in the egg sacs of vine mealy bugs, which are devoured by the beetle larvae.

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Mealy bug destroyers being unleashed on pests.

BRAHM JONKER

Nephus bipunctatus and other Nephus beetles are even tinier, so they can squeeze into crevices to find mealy bugs. However, because they are smaller, they eat less than C. montrouzieri and prefer smaller mealy bug life stages. Neither of these beetles is specifically a vine mealy bug predator, but adult beetles will fly away if food is scarce. They should be reserved for hotspots or severe infestations.

Mealy bugs parasitised by Anagyrus vladimiri.

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Adult lacewings feed on pollen and nectar but their larvae are generalist predators.

Green lacewings ( Chrysoperla species) differ from the beetles in that only larval lacewings are predators. Adult lacewings feed on pollen and nectar. However, lacewing larvae are indiscriminate feeders, eating many soft-bodied pests, including red spider mites, aphids, scales, and mealy bugs. They will even eat each other if other food is scarce. Timing of releases The timing of releases should be guided by the block’s history and monitoring data. Releases should ideally start once trap catches and scouting observations indicate that pests are present. Mark mealy bug hotspots to ensure optimal placement of parasitoid and predator releases. A rule of thumb for vine mealy bug parasitoids is three releases from November to January. There is no point in releasing parasitoids if there are no hosts for them, but stopping the first wave of crawlers is crucial to prevent mealy bug infestations in bunches, so conscientious scouting matters. Although early parasitoid releases are more effective than late releases, in practice, parasitoid releases will usually be delayed by thrips control programmes. Coordinating releases with the spray programme is essential. Reputable biocontrol suppliers assess the sensitivity of their parasitoids and predators to registered pesticides and can advise on the likely impact of applications and residues. Postharvest releases are potentially valuable, espe cially in problem blocks. Postharvest spray applica tions may seem an easier option, but keep in mind that these pesticides will also significantly reduce natural predators and parasitoids and can exacer bate some pest infestations. Releases become less effective once temperatures drop below about 20 °C.

Tips for successful releases Most suppliers provide the predators and parasitoids in small dispensers packed in a cooler box. Keep the box in a cool room. Do not refrigerate the box, but replace the ice pack if necessary. It’s obviously best to hang out the dispensers sooner rather than later, but they should keep for 3–5 days. During warm weather, place them out early in the morning or late in the afternoon rather than at midday. Spread the dispensers evenly throughout blocks, but target hotspots if present. Hang dispensers horizontally in the bunch zone. Avoid exposing them to direct sunlight. Remember to open the dispensers. Some have exit holes covered by a sticker, and others have lids. Remove the lids entirely as they can sometimes close again. Parasitoid and lacewing adults require pollen and nectar. Flowering cover crops are ideal but often absent during the season. Flowering plants at the head of rows can be a good substitute. Examples include alyssum and herbs in the mint family, such as basil, oregano, sages, thymes, and wild dagga ( Leonotis species). Plants on the vineyard floor or at the head of rows also provide shelter and potentially offer a slightly cooler microclimate during the hottest part of the day. Many pests tolerate dust, and some, such as red spider mites, seem to relish it. Parasitoids and predators, in contrast, avoid dust. Dust reduction is therefore essential for successful pest control. Leaf removal and summer pruning improve predator and parasitoid efficacy because it’s easier for these insects to find the mealy bugs. For the same reasons, correct bunch spacing facilitates mealy bug control.

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BRAHM JONKER

Besides the mealy bug husks, scouts should also observe that honeydew secretion has stopped. Scouts should see predators feeding, especially the larvae, as these can’t fly away. Be warned that larval Cryptolaemus look a lot like mealy bugs, highlighting the importance of well-trained and experienced scouts. Trouble-shooting Provided the guidelines above are followed, the most common reason for failure is the presence of ants in the vines. Ants love the honeydew excreted by mealy bugs and will guard them against predators and parasitoids. Ants also catch other insects for food and have even been known to invade parasitoid dispensers, de stroying the contents before a single wasp emerged. On the upside, ants do kill some pests, so ants on the vineyard floor are beneficial, but keep them out of the grapevines. Mixing parasitoid and predator releases with pesticide applications is another reason for failure. Integrated pest management is called integrated for a reason – growers should work with their crop-protection adviser to figure out how to combine biological and chemical control measures. Growers should also consult the parasitoid and predator suppliers about the suitability of biocontrol agents for their climate and crop. For example, ask about the temperature tolerance of different species. Biocontrol agents are not inexpensive, but trying to save money by reducing the number or dose of releases is a false economy.

Dead mealy bugs remain as empty husks after parasitoid adults emerge.

Is it working? Inspect the packaging and quality of your biocontrol agents on delivery. In addition to general scouting, mark at least one release spot and go back to check the hatching rate and control in the vicinity. The biocontrol agents will take at least two weeks to reduce pest populations. This should be evidenced by reduced trap catches, but evaluating predator and parasitoid activity through scouting is indispensable. Parasitoid wasps are minuscule. Scouts are unlikely to spot them. Instead, examine mealy bug colonies for signs of parasitism. Keep in mind that mealy bug colonies won’t disappear because parasitised mealy bug bodies remain behind as empty husks when the adult wasps emerge.

Ants are fierce predators in all sorts of ecosystems globally.

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Releases must be calibrated to the pest pressure. For example, in blocks with severe vine mealy bug infestations, early-season releases of both Anagyrus vladimiri and Coccidoxenoides perminutus , followed by repeated releases of A. vladimiri , may need to be augmented with predators such as Cryptolaemus or lacewings. Additionally, shopping around for the cheapest predators or parasitoids could end up being extremely costly. Not all bio control agents are created equal. Some products contain poor-quality insects, a suboptimal male-to-female ratio, or even incorrectly identified species. Stick to repu table suppliers and, where available, regis tered products. Work with suppliers to ensure they can prepare the correct volumes of fresh insects at the right time. Supply bottlenecks are common, especially during the November to January peak demand period. This can result in delays if growers haven’t communicated their requirements. Lastly, remember that predator and parasitoid releases aren’t one-and-done. Just as conventional pesticides are applied multiple times, every season, releases must be repeated. But in both cases, a long-term commitment to integrated pest management will gradually reduce pest pressure and create more resilient vineyards.

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Ant control Sticky stem barriers are highly effective at excluding ants (and weevils) from the canopy. Some markets even require sticky stem barriers. Although labour-intensive to apply, the barriers are long lasting, provided they are checked to ensure they stay clean. Ants have been known to build bridges over sticky barriers. Stem barriers must also be applied to posts and wires. Ensure that ants can’t access the vines by climbing up weeds or other structures. Attract-and-kill products are already registered for ants in other crops, so could become an option for table grapes in future. If all else fails, ant nests can be sprayed. These must be spot applications using a backpack-sprayer.

Entomopathogens Entomopathogens are microorganisms that attack and kill insects. Two entomopathogenic fungi ( Beauveria bassiana and Metarhizium anisopliae ) are available as products registered for mealy bugs. Fungal spores are applied as full-cover sprays and are most effective against crawlers. They are less effective against older life stages. However, they help control other insects, including thrips and weevils. Spray applications must land the fungal spores on the pests, as spore survival can be short, especially when exposed to sunlight. Repeated applications are recommended. Entomopathogenic fungi can also be applied as a soil drench to control mealy bug adults on vine roots. The fungi may also help reduce the soil stages of other pests, such as false codling moths. The compatibility of entomopathogenic fungi with various fungicides differs. Consult your crop-protection adviser when incorporating these fungi into your programme. Furthermore, remember that fungal spores only work if they’re alive, so store and handle them with care, avoiding exposure to high temperatures.

Acknowledgements The following specialists provided technical inputs:

• De Wet Du Toit. Technical marketing specialist. InteliGro. • Desi Fourie. Technical Adviser. Viking.

• Brahm Jonker. Managing Director. Fieldbugs. • Robert Wilsdorf. Technical manager. Viking.

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