Japanese beetles (Fig. 1) have now been observed last weekend around Dane county, but not yet at any of the vineyards we are monitoring for research or at the West Madison Agricultural Research Station (WMARS). As they begin to emerge from the ground, it is important to be ready by finalizing your management plan. Japanese beetles are very voracious defoliators—and sometimes fruit feeders—on most of our fruit crops. There are many different practices that can be applied to mitigate the impact of Japanese beetles in our fruit crops and these were discussed in the Cold Climate Grapes Webinar Series hosted by UW-Madison and UMN on June 2, 2021 and you can watch the webinar recording here: https://youtu.be/zpDa6dmYphk. At this time, it is important to remember that monitoring does not require traps and can be done visually, that will save you from purchasing traps and lures, and will not attract more Japanese beetle than you would have without a trap. It is important to think about how to prevent Japanese beetles that are moving into your fruit crops from laying eggs in your patch or orchard. To do this you can withhold irrigation of the grass in the alleyways to prevent newly emerged females from laying eggs in the grass on your farm. You can also raise the cutting height of the grass to more than 3” to deter females from laying eggs as well. Finally, applying a soil insecticide such as a neonicotinoid in late June can target the newly hatched larvae that will be there in early July. For adult management, there is no economic threshold for any of our fruit crops to help determine when to spray.

In grape, a MSU study found that grape plants can tolerate at least 30% defoliation (Fig. 2) without having any impact on plant growth parameters. In apple, it is likely possible to tolerate around 20-30% defoliation without any impact on tree health. Research is ongoing at the UMN on the impact of Japanese beetle on apple and grape and more info will be coming soon from these projects. If you decide to apply an insecticide for adults, it is important to think that more beetles will fly in after the initial knock down so products with longer residual activities will be helpful to knock down the new influx of beetles. For conventional production, several insecticides are effective at controlling Japanese beetle which include different modes of action: carbamates (e.g, Sevin), pyrethroids (e.g., Danitol, Baythroid, Mustang Maxx), organophosphates (e.g., Imidan), and neonicotinoids (e.g., Assail, Belay, Admire Pro). In organic production, fewer products are available but have good efficacy such as Bacillus thuringiensis (BeetleGone!), kaolin clay (Surround), and insect growth regulators (e.g., Neemix).

Rose chafer are also polyphagous, feeding on many of our fruit crops and can damage plants by eating large amounts of foliage and sometimes feeding on buds and flowers as well. Rose chafers feeding on leaves can be mistaken for that of the Japanese beetle, as both skeletonize the leaves by feeding between the leaf veins. Rose chafer can be most damaging when the early-emerging adults feed on and destroy flower buds and flowers. Rose chafers overwinter as larvae in the soil and similar to Japanese beetle the larvae feed on the roots of grass and other plants. Adults emerge, seemingly all at once, in late May to early June, and there is only one generation per year throughout the Eastern United States. They congregate on plants to mate and feed for about three weeks. Rose chafers prefer to lay eggs in sandy soil and farms on or near sandy soil sites are advised to monitor earlier in the season and more carefully.

Monitoring and trapping

Monitoring for the conspicuous adult beetles should begin in late May and continue until they are no longer found in the vineyard. Because feeding on flower buds can cause crop loss, an economic threshold as low as two beetles per vine is recommended for chemical controls. When monitoring, it is best to inspect 25 vines near the edges and corners of the vineyard, and 25 from within the vineyard block. By inspecting vines throughout each block, you can determine if the entire vineyard is affected, or if infestations are localized and a spot treatment could be applied to control these beetles.

Traps can also be used to monitor population emergence and can be purchased online at places such as Great Lakes IPM. Mass trapping by using a large number of traps either on the perimeter or inside the vineyard is often thought about but this approach has not yet been assessed to determine whether it attracts more beetle or actually decreases the population within a vineyard.

Non-chemical control

When few beetles are present in the crop or are present in isolated patches, hand picking is a an effective control method. Naturally-occurring biocontrol agents present in fruit crops can attack rose chafer either as larvae in the soil or as adults on plants; for example shield bugs can feed on adult rose chafers. It is important to foster natural populations of biocontrol agents on your farm by providing natural habitat around the farm and reducing pesticide inputs, but, by themselves, these natural enemies may not be able to control rapidly emerging populations or large populations of rose chafers.

Chemical control

While most fruit crop can tolerate some defoliation from beetles, it is important to monitor regularly to detect fast increases in population levels that could lead to extensive defoliation and/or flower or fruit damage. Young plants with fewer leaves are more at risk and should be monitored more frequently and protected. If chemical control is warranted, it should be implemented from pre-bloom until around pea-sized berries in grape. Several insecticides are available for rose chafers and include neonicotinoids (e.g., Assail), pyrethroids (e.g., Danitol, Baythroid), carbamates (e.g., Sevin), and organophosphates (e.g., Imidan). For organic production, pyrethrins (e.g., Pyganic), azadirachtin (e.g., Aza-Direct), and kaolin clay (Surround) can provide control for rose chafers.

Other pesticides registered on the different fruit crops for control of rose chafers and their efficacy can be found on the Midwest Fruit Pest Management Guide. As always, please read the label carefully and check that the pesticide you intend to apply is registered on the crop you plan to spray. More information on where to check if a pesticide is registered in Wisconsin on your specific crop can be found in this Tank Mixing 101 article.

Grape phylloxera continues to increase at WMARS and leaves are starting to curl up from the high number of galls per leaves (Fig. 3). Timing using degree days was discussed in a previous article and it is important to treat to avoid such high level of injury to the leaves during the first generation of grape phylloxera. It is not recommended to spray once grapes have started to bloom according to the Midwest Fruit Pest Management Guide. If you notice that galls continue to appear on new growth, you should flag the affected vines or area and remember to carefully monitor these areas early next spring. At the first signs of gall formation in the spring, you should consider applying imidacloprid (e.g., Admire Pro) as a soil-applied insecticide for systemic control from bud swell until you see the first expanded leaves, in the areas of the vineyards that have experienced high levels of infestation the previous summer. The active ingredient imidacloprid needs to be available as soon as the grape roots begin to uptake water for the chemical to get all the way to the leaves and protect them.

Happy growing season!

This article was posted in Grapes, Insects and tagged Christelle Guédot, grape phylloxera, grape phylloxera galls, Grapes, insects, Japanese Beetles, Rose chafer.