Over 25 years of working in vineyards with my colleagues at Bio Ag Services, I have learned a fair amount about managing pests organically. What follows are my opinions; not always verified by scientific experiments.
I try to minimize use of dusting sulfur because I am convinced that it increases problems with mites, leafhoppers and mealybugs. Probably this happens in part because the sulfur interferes with predators and parasites. But I suspect, along with many others, that sulfur is also hard on the vines and makes them either more attractive or more conducive to pest increase.
Mildew control without dusting sulfur is a challenge because dusting can give better coverage than water based sprays, especially when the canopy and bunches are closing, as in June. Dusting sulfur is also cheaper than other methods and more quickly applied, using less labor and fuel.
Wettable sulfur might have the same drawbacks as dusting sulfur, but to a lesser degree. The amount of sulfur used is much less, fuming is probably reduced, and the treatment interval is longer (10-14 days vs. 6-10 days). Most of my organic growers use 2-3 lbs. wettable sulfur until bloom.
I recommend applying about 5 lbs. of wettable sulfur close at budbreak or just before. Dr. Doug Gubler has shown that this suppresses the overwintering chasmothecia on the canes just as they would be releasing spores to infect the new green tissue. Lime sulfur applied in late dormancy works almost as well. These treatments do not depend on temperatures in the mildew index, which models conidial spore production on the green tissue.
After bloom I recommend using a preventive material such as Regalia or Sonata, tank mixed with an exterminant such as M-Pede or Oroboost. Nu Film P also seems to work well as the tank mix. M-Pede should not be used after fruit set on table grapes. Oroboost and Nu Film P should be used with care. I have not seen much problems with the waxy bloom, but some of my growers think they have.
Coverage is the key to success with these materials. The interval is similar to wettable sulfur, 10-14 days depending on the mildew index.
Dr. Gubler has demonstrated good mildew control with highly refined oils such as Stylet Oil and Purespray. Some workers also have evidence that oil suppresses mites and leafhoppers if timing is correct. Personally I am reluctant to use oil on vines because I fear it might be hard on the vines. But I have talked to several people who use it and have not heard of any problems with raisin or juice grapes. Oil should not be used on table grapes after fruit set.
If mildew starts to show up so an outbreak is feared, use a wash with wettable sulfur or Kaligreen. Use a high volume such as 200-300 gallons. Be careful with Kaligreen- I have seen very serious damage to some table grapes in applications a few weeks before veraison.
Kaligreen can also be used safely just before bloom. It cleans up any mildew that has started, even if it is not evident yet.
Mildew control can be ended once veraison is reached, or a couple of weeks earlier if weather is very hot. This particularly applies to raisin and juice grapes. More care should be taken if mildew is starting to show up before veraison. On most varieties, I do not see stem mildew as much of a threat. On susceptible varieties resumption of treatments when weather cools off in the fall, perhaps with dusting sulfur, may be more effective than treatments in mid-summer.
Mite problems arise in grapes when vines are stressed. Causes may be lack of water such as in sandy streaks, dust and heat along roads, or sulfur dust. Growers should do their best to solve the underlying problems with such tools as soil amendments, dust suppression or washing vines, and using alternatives to sulfur dust.
The second line of defense is biological control. The most important agents are predatory mites and six-spot thrips, but lacewings, minute pirate bugs, big-eyed bugs, black hunter thrips, and some spiders may also help. Flower thrips, which are also pests, can contribute significantly to mite control. Trophic relationships are complex, as most of these predators also eat each other. Endemic biocontrol is best, but supplemental releases of predatory mites or six-spot thrips may also help if timing is good and the habitat is not antagonistic (i.e. too hot).
Predatory mites are the main reason that mites are difficult to find in many vineyards. They are able to maintain mite populations at very low levels. They can also survive on alternate prey such as Willamette mites or Tydeid mites.
Releases of predatory mites should be aimed at maintaining populations. If suppression of a mite outbreak is the goal, large numbers will be needed and success is still not guaranteed.
Six spot thrips tend to appear when mite populations start to increase, although that increase may be only a few leaves with 10-50 mites. Six spot thrips also seem to be more able than predatory mites to tolerate hot weather. Six spot thrips can be released to suppress mite outbreaks, but success is dependent on releasing them early in the outbreak. As with predatory mites, success is not guaranteed.
Organic miticides are not nearly as dependable as conventional miticides. At best they suppress the mites, and the same materials may work fairly well in one situation, but fail in another. Coverage is one important issue- the applicator should drive slowly. Weather may also be a factor. We are trying to learn more about how to effectively use organic miticides. Here are some options:
Oils or soaps that smother or desiccate: JMS Stylet, Purespray Green; M-Pede. Pyrethrum: PyGanic. Best tank mixed with M-Pede, Oroboost, or Nu Film P. Specialty plant oils: Biomite, GC Mite, Ecotrol.
Organic leafhopper management includes monitoring immigration, evaluating biocontrol, and correctly timing treatment if needed.
Grape and variegated leafhoppers usually do not overwinter on vines because they like green foliage in the winter. They may overwinter on weeds, or on neighboring evergreen crops such as citrus, or in people’s yards on evergreen bushes. They tend to leave these overwintering sites before grape budbreak and temporarily feed on earlier leafing plants such as stonefruit or almonds, or on late winter weeds. From there they move to grapes after budbreak. They feed on grapes for several weeks before they start laying eggs.
Later generations may migrate from other vineyards. Leafhoppers will move long distances, through orchards, fallow or weedy fields, or other crops until they reach a vineyard.
By monitoring sides and corners of vineyards during migration times, a scout can find out where to watch most closely for leafhopper hatch.
Leafhopper biocontrol comes from a complex of beneficials. In my opinion the most important are Anagrus egg parasites, certain spiders including the yellow sac spider (Cheiracanthium), and lacewings. Ants also play a role; possibly important but this has not been studied. Anagrus is more effective on GLH but is still a key to VLH control. Yellow sac spider populations can be judged by noting their 3 types of nests: overwintering, day-resting, and egg-nests. When they are abundant enough, the number of leafhopper nymphs will decline or at least not increase very fast. Moderate populations of leafhoppers with good biocontrol may not need any further treatment.
Leafhopper control is easier when little or no dusting sulfur is applied. Studies have shown that Anagrus parasites live shorter lives with sulfur. I also think that vine stress caused by sulfur gives the leafhoppers some advantage.
Lacewings are the only biocontrol available from insectaries that are likely to help with leafhoppers, and releases are only moderately effective at best. Lacewings happily eat leafhoppers, but seem to be more attracted to honeydew producing prey such as aphids and mealybugs. Usually eggs or new larvae are released, which is laborious since they need to be placed on or near every vine. Finally, ants often eat most of the released eggs, which are not on the protective stalks that the mother lacewings would make. One advantage of lacewings is that large numbers of eggs can be purchased cheaply from insectaries.
Organic leafhopper insecticides have little or no residual action, so it is important to time the application to minimize the number of eggs, which are protected, and adults, which are harder to kill than nymphs. The best time for this is when the first nymphs to hatch are close to turning into adults. Leafhoppers mature from hatch to adult in 3-4 weeks. This takes about 435 degree days, with min-max 50.5-95oF.
I have had best success with PyGanic tank mixed with Oroboost, M-Pede, or Nu Film P.
Some workers have also reported that oil applied during the egg-laying period helps to control leafhoppers.
The new material Venerate from Marrone also shows promise on leafhoppers.
Grape mealybugs are rarely a serious problem in organic grapes in the San Joaquin Valley. No one has been able to adequately demonstrate the reason for this; presumably many conventional growers are using some chemicals that disrupt mealybug biocontrol. Actually, most conventional raisin and wine growers and many conventional table grape growers have few GMB problems.
Interestingly, even though organic and raisin growers have traditionally used a lot of dusting sulfur for mildew, GMB has usually not been a serious problem. This is in contrast with vine mealybug (see below).
The key to GMB control is biocontrol, which is supplied mainly by predaceous midge maggots and parasites in the family Encyrtidae, with help from lacewings and the tiny lady beetle, Nephus.
Vine mealybugs are a big challenge. Their introduction drove many organic grape growers to give up and go conventional. But new tools and knowledge have made it possible, in most cases, to adequately control VMB for organic grapes.
The tactics available for organic VMB control are pheromone disruption, stopping use of sulfur dust, biocontrol- both endemic and insectary-reared, ant control, and pyrethrum sprays. Venerate might also be good.
Pheromone disruption works well if VMB populations are very low. This is often the case in organic vineyards in spring, because biocontrol tends to be most effective in the fall, leaving low overwintering populations. However it will not happen if many VMB are overwintering on roots or in the holes of carpenter worms, which both act as refuges from biocontrol. In these cases, pheromones are probably not worth their high cost.
Pheromones offer good protection against new infestation in vineyards that have few or no mealybugs. If a few crawlers come in, for example carried by birds, when they mature as females they will not attract males, which normally can fly in from a quarter mile away. The unmated females will not lay eggs and the tiny infestation will die off.
Some research suggests that in addition to confusing VMB males, the pheromones increase parasitism.
Pheromones should be placed by mid-April, before males begin to fly.
Stopping dusting sulfur is a very important tactic in the control of VMB. In many cases we have seen disaster turn into a minor problem by taking this step alone. As with mites and leafhoppers, we suspect that sulfur both interferes with biocontrol and makes the vine more susceptible through stress.
The most important VMB biocontrol agents are Anagyrus and Coccidoxenoides parasites, Nephus beetles, predaceous midge maggots, and green and brown lacewings. All but the midges are available from insectaries, although Nephus is in limited supply. All are also endemic and will come in by themselves.
The main problem with VMB biocontrol is that it often comes too late. Anagyrus typically dominates in the fall, and is a very good searcher for stray mealybugs, but it does not even emerge from overwintering until late May or June, after two VMB generations. The four predators start earlier but need at least moderate VMB populations to survive. Working together, the parasites and predators may reduce the VMB to a very low level by late August, but by then much of the crop may be lost.
Insectary releases of all of these insects are undoubtedly helpful, but evaluating the effect of releases compared to the endemic populations is difficult. Releasing enough to make a decisive difference is expensive, hundreds of dollars per acre. Releasing smaller amounts might get them started earlier, make significant improvements in their numbers, or speed up control by a couple of important weeks.
Nephus beetles are excellent at controlling VMB populations under bark. They are not effective on VMB on canes, canopy, or bunches. They also work poorly on young vines without much covering bark. Older vines may show wet bark from VMB, but upon examination few VMB are surviving and the canes and bunches are clean; the beetles ate the VMB before they could move up from the trunks. Nephus beetles can be released as soon as VMB can be found and the insectary is ready, in May or early June.
Midges also work best under the bark or between bunches and wood. They are more consistently present on GMB, but sometimes quickly clean up VMB infestations. Possibly they work better on VMB when GMB is also present.
Anagyrus parasites start late but build up over a couple of months and eventually clean up most of the VMB not eaten by parasites. In August and September bunches may look heavily infested, but most of the VMB are parasitized. Anagyrus continues to work at low VMB levels and is a key to very low overwintering numbers. Insectary releases may start in May before the endemic Anagyrus start to emerge, and continue at intervals through June and July.
Coccidoxenoides parasites are smaller than Anagyrus and work on smaller VMB instars, especially under bark. They also start earlier. The mummies are not well attached to the substrate, so they tend to fall off when bark is peeled. This makes them difficult to monitor. They are not available from insectaries. Some vineyards with releases by researchers showed marked decreases in VMB populations over a couple of years.
Green lacewings are strongly attracted to VMB honeydew. For VMB control, they can be released as adults, because they will find the vines with infestations. They can be released when honeydew becomes visible on the trunks.
Brown lacewings have been shown by researchers to be good mealybug predators. They probably play a bigger role than realized; they are easily overlooked because they are nocturnal, the eggs are not on obvious stalks like green lacewings, and the larvae are easily confused with green lacewing larvae. They are also available from an insectary.
Ants play a major role in mealybug problems. Ants protect VMB from biocontrol, move them from vine to vine, and make spaces for mealybugs around roots. In one study in Coachella Valley, VMB virtually disappeared when Formica field ants were controlled.
Almost all local ant species tend VMB. Gray field ants are the most common and fire ants are the worst. Other common tenders include pavement ants, pyramid ants, thief ants, odorous house ants, crazy ants, honeypot ants, little black ants, and Argentine ants. This last is rare in San Joaquin Valley vineyards but much more common in northern and coastal California districts. It can be very effective at protecting mealybugs. Harvester ants are the only common SJV species not tending mealybugs.
Ants are difficult to control, especially in organic vineyards. We have good fire ant baits, but they are not organic and do not control field ants. Seduce ant bait is organic and sometimes moderately effective on field ants. The pieces are too large for fire ants. Bait stations using sugar water with boron can be used on Argentine ants. Dry boron baits can also be devised that are attractive to either fire ants or field ants, but unfortunately they are not legal because Solubor is registered as a fertilizer, not an insecticide.
Ants can be temporarily kept off vines with sticky barriers. Obviously this is very labor intensive.
VMB is difficult to control with sprays because large portions of the population are always protected in hidden places under bark, inside bunches, or on roots. The best to be hoped for is to slow down large migrations of small crawlers to the canopy. The same PyGanic tank mixes that control leafhoppers will also kill younger stages of VMB if they are exposed.
Caterpillars are usually not too difficult to control in organic vineyards. They typically have good biocontrol by spiders, lacewings, parasites, and other beneficial insects. Ants probably also play an important role, so if ants are controlled, watch carefully for increasing caterpillar problems.
Well-timed B.t. sprays are effective on OLR and leaffolders. They may need to be repeated two or more times to equal insecticides with longer residual. Skeletonizers are less susceptible to B.t. but repeated BT Dust applications will control the first 3 instars. Entrust (spinosad) is very effective on all of these worms, but should be avoided where possible because it is disruptive to biocontrol, especially to mealybug parasites. It is less disruptive if used early, before the middle of May. Venerate might also work well.