Japanese Beetles Ahead of Schedule in 2026

Japanese beetle development is about two weeks ahead of schedule this spring, which is not too surprising with the warm May temperatures. Japanese beetle adults begin emergence when approximately 1,030 growing degree days (GDD; base 50°F) have accumulated since January 1 and will continue emerging until 2,150 GDD have accumulated. Japanese beetle adults likely began emerging in the southern portion of the state last week, and emergence will occur within the next week in northern Iowa (Figure 1). 

Japanese beetles have a wide host range that includes many species of fruit and vegetable crops, ornamentals, and field crops. Feeding will look a bit different depending on the host plant, but since beetles have chewing mouthparts, they consume plant tissue and cause defoliation. Injury can appear severe in areas where Japanese beetles aggregate, which includes field edges. A combination of sex pheromones, aggregation pheromones, and feeding-induced plant volatiles leads to clusters of beetles feeding in one place. For more information on Japanese beetle identification, sampling, and management in corn and soybean, read our encyclopedia article or review this article in the Journal of Integrated Pest Management.

Japanese beetles are known to occur throughout most of Iowa, but there are 14 counties that have never reported Japanese beetle. If you see Japanese beetle in a county not highlighted in this map, let us know by emailing bugtraps@iastate.edu so we can update the distribution record.

Be aware of look-alikes. The adult sand chafer is often confused with the Japanese beetle and typically emerges around the same time. Sand chafers are dull in comparison to the Japanese beetle; they have brown bodies and brown hairs on their abdomen, while Japanese beetles are bright green and coppery brown with white hairs on the abdomen. See this video for more information.