Japanese beetles (JB; Figure 1) started to emerge about 2 weeks ago, probably about a week later than in the past couple of years. As expected, numbers have been increasing in fruit crops in the last two weeks. However, populations, at least in grape at the West Madison Agricultural Research Station, are far lower than they were at the same date in 2017. Japanese beetle can feed on over 300 plant species and last year, there were concerns in parts of the Midwest of seeing a lot of JB in fruit crops, including apple. While there is no economic threshold for JB in fruit crops, we recommend using a 30% defoliation (Figure 1) threshold in grapes before applying an insecticide. In berry crops or tree fruit, more modest defoliation thresholds may be more appropriate. It was suggested that for apple, 15% defoliation will not affect mature fruit trees or yield but higher levels of defoliation may stress trees and reduce crop yield and quality (Growing Apples in Wisconsin).
Bark, hardwood chips, and rubber mulches applied to row middles decreased JB larval populations in vineyards with rubber mulch resulting in zero JB larvae (Maier, 2016).
Tilling row middles in blueberry reduced larval populations of JB by 72% compared to grassy row middles and JB adults were less abundant in tilled fields. The timing of tillage (Spring vs. Fall) was not consistent in providing reductions of JB larval populations over the two-year study but overall reduced populations by 50-70% in blueberry fields (Szendrei and Isaacs, 2005).
Below is a list of available insecticides registered in Wisconsin to control Japanese beetle. Please make sure to read the label to insure that the product you are considering to spray is registered for the specific crop you intend to protect. There are many other tradenames available, and we do not recommend these that are listed above other options. All product recommendations can be found in the 2019-2020 Midwest Fruit Pest Management Guide. Additionally, you should always fully read and follow the label before spraying any pesticide.
IRAC Code: Insecticide Resistance Action Committee Mode of Action group code
Happy growing season!This article was posted in Apples, Berries, Grapes and tagged Berries, Japanese Beetles.