Preparing for rose chafer management in vineyards
Rose chafers can quickly damage vines. To better manage this pest, know the biology and lifecycle, and available options for control.
In the past few years, populations of the rose chafer beetle, Macrodactylus subspinosus, have been abundant in some regions of southwest Michigan. These beetles can be found in grape growing regions across Michigan and beyond; however, outbreaks in the Lawton, Mich., region in recent years have been causing some high levels of damage to clusters during the bloom period. With this recent history, it is a good time to review the biology and lifecycle of this pest and review the available options for control.
The rose chafer is a light-tan beetle with a darker-brown head and long, spiny legs. It is about 0.5 inches long. The adult beetles have only one generation per season with emergence from the soil starting in late May and June, and with the beetles living for up to a month. While grapes are a preferred host, there are also many other plants it will feed on including roses, strawberries, peaches, cherries, apples, raspberries, blackberries, clovers, hollyhocks, corn, beans, beet, peppers, cabbage, peonies and many more plants, trees and shrubs.
This vineyard pest is distributed throughout the eastern United States with greatest abundance in areas with sandy soils and grass. This is because the female beetle, once mated, selects grassy and sandy areas for laying her eggs. Those eggs hatch into larvae that feed on grass roots through the summer, moving down away from the frost line during the winter. In spring they feed again, pupate, and then emerge in late May and June. Emergence of adult beetles typically coincides with bloom of grapevines. The beetle's ability to skeletonize leaves until only the midribs are left, and consume the young tender clusters, makes it an economically-significant pest of grape production
Rose chafer management
The rapid arrival of rose chafer beetles and the potential for high populations in hotspots underscores the need for regular vineyard monitoring. By scouting areas that have had this pest in the past, growers can protect clusters when the beetles start emerging rather than waiting until severe damage has occurred. Establish a route for checking vines and travel this route looking for the beetles on vines, ideally twice a week. The beetles are easy to see and direct counts on vines are possible. There is also a trap developed and marketed for rose chafer monitoring or trapping-out, but Michigan State University Extension does not recommend using this except as a single trap for monitoring in a location away from vineyards as the trap can draw beetles to the vineyard.
There is no formal economic threshold developed for this pest, but Ohio State University recommends an average of two rose chafers per vine as a working action threshold for initiating a control program. Below this there is likely to be only a small amount of damage that doesn’t warrant the expense of a spray. However, as mentioned above, the population of this pest can rise rapidly, and I have observed over 200 rose chafers per vine in one winegrape location in northwest Michigan, and this is clearly going to cause damage to that vine. Rose chafers can also be very locally distributes such that one corner or one edge of a vineyard has high populations, usually adjacent to a grassy area. This highlights the need to sample different areas of a vineyard to know the pest distribution. If there are hotspots, a targeted spray may be sufficient to control the beetles without needing a blanket application across the whole vineyard.
As mentioned above, rose chafer beetles are attracted to sandy and grassy areas during their egglaying period. It may not be feasible, but if areas that are obvious sources of the beetle can be changed into a non-grass cover crop or can be fallow for the period of late May until early June, this might force the beetles to seek egglaying sites elsewhere. Small numbers of beetles can also be hand-removed and placed into soapy water if you have a small enough vineyard that this manual control is possible.
For chemical control, there are a number of options to consider. Assail, Sevin and Danitol are all ranked as providing excellent control of this pest. These have some different properties with the neonicotinoid insecticide Assail providing protection due to it knocking down the beetles and also because it is a systemic insecticide that is taken into the vine making it resistant to wash-off and providing good residual activity.
In a 2003 MSU research trial in Leelanau County, we found that Assail provided longer control than Sevin. The carbamate insecticide Sevin and the pyrethroid insecticide Danitol both have contact activity against rose chafers, providing knockdown of the beetles on contact and with Sevin also having some activity as a stomach poison after being eaten by the beetles.
Additional broad spectrum insecticides such as the pyrethroids Baythroid and Mustang Max are expected to also have good activity, as is the organophosphate Imidan. Under the high spring temperatures we have been having recently, the residual control of pyrethroids is expected to be shorter than under cool conditions. However, we also expect there to be a shorter period of rose chafer activity during hot conditions, allowing for a shorter period needed for vine protection against this pest.
The timing of rose chafer activity also can overlap with early season grape berry moth activity and early potato leafhopper infestation. The insecticides mentioned above will also provide some control of these other insect pests at the same time.
Dr. Isaacs' work is funded in part by MSU's AgBioResearch.