This article was written to complement Celeste Welty’s blog on Japanese beetle insecticide selection last week (http://u.osu.edu/vegnetnews/2018/06/30/insecticide-notes/).
One of Ohio’s most recognizable leaf feeders, the copper-colored and metallic green Japanese beetle, is on the rise. According to scattered reports across the state, this beetle has been leaving a trail of skeletonized leaves on an array of landscape plants, field crops, vegetable and fruit crops.
While specific thresholds do not exist for most crops, below are listed a few guidelines that should help growers manage Japanese beetles in general.
Sweet Corn – During the early-silking stage, examine 50 ears in small plantings (< 2 acres) or 100 ears in large plantings (> 2 acres). Treat by spraying insecticide directed at the silks to prevent clipping by beetles during the early-silk stage if the average number of beetles is 2 or more per ear. If pollination has already occurred, silk clipping will not harm kernel development or ear, therefore control is not necessary.
Hops – At this time there is no established treatment threshold for Japanese beetles in hops. Growers should consider that established, unstressed and robust plants can likely tolerate a substantial amount of leaf feeding before any negative effects occur. Those managing hopyards with small, newly established, or stressed plants should take a more aggressive approach to Japanese beetle management, as plants with limited leaf area and those already under stress will be more susceptible to damage. It is also important to carefully observe beetle behavior in the hopyard; if flowers, burrs or cones are present and being damaged, growers should consider more aggressive management as yield and quality are directly affected (excerpted from https://www.canr.msu.edu/uploads/234/71503/Hop_JapaneseBeetle.pdf).
Fruit crops and Grapes – For most fruit crops, there is no economic threshold on the number of beetles or amount of damage that requires treatment. If a susceptible cultivar is being grown and growers previously have experienced high populations of Japanese beetles, an insecticide should be applied when beetles emerge and thereafter as needed.