Question:
How do I manage Japanese beetles on my sweet corn?Answer:
Japanese beetles feed on many different types of plants. They can be problematic on sweet corn as they frequently feed on green corn silks, inhibiting pollination and leaving incomplete kernel filling in the ears. Silks must be clipped to less than ½ inches before damage is noticed. This can lead to smaller, incomplete, or "gap tooth" looking ears.
Handpicking
Control in this situation is difficult. Handpicking can be done in the home gard
en. Beetles feed in clusters and can be knocked into a bucket of soapy water. Handpicking must be done frequently (sometimes daily, depending on the population size). Once dead, the beetles can be buried in the garden or discarded. Japanese beetles produce pheromones that attract more Japanese beetles, so start handpicking early before the population on the plants gets large.
Insecticides
Most garden insecticides will control the beetles present at the time of application and offer some residual protection. Common examples include permethrin, bifenthrin, or cyfluthrin. Multiple applications at regular intervals will be needed for complete control as new beetles are always flying in from somewhere else. Read and follow label directions concerning rate and timing of application, the maximum number of treatments per year, and the interval between sprays or between spraying and harvest. Do not spray when bees and beneficial insects are present.
Ineffective Control Methods
Methods that do not effectively prevent damage to silks include screening, which is typically impractical on sweet corn and traps/lures. These products will bring more Japanese beetles to your garden, exacerbating the problem.
Cultural Control Options
Since Japanese beetle emergence is only during a limited period during the summer, succession planting can help provide good quality crops before or after beetle emergence. Additionally, silk clipping is not an issue if pollination is complete, or nearly so, before beetles arrive. Pollination is complete if silks are brown or pollen is no longer being shed from the tassel. Pollen shed starts in the middle of the central tassel spike and progresses outwards. So if tassles have pollen shedding from the tips of lower tassel spikes, pollination is nearly complete, and silk damage will not be a significant issue.
Learn more in this article: Japanese Beetle.
Photo by Dan Fillius