I received several questions about blister beetles in alfalfa hay over the weekend. I thought it might be helpful to review what they look like and provide a few management tactics to minimize the negative effects for animals.
Just last week, Ashley Dean predicted overwintering mortality of bean leaf beetle in Iowa. It looked pretty grim for this soybean pest, with over 77% mortality predicted for central Iowa. I didn’t have high hopes for a new insecticidal seed treatment study going in at the ISU Johnson Farm just south of Ames. While we were getting ready to plant today, it started to rain just a bit, too.
Thanks to ISUEO Field Agronomist Meaghan Anderson and Extension Entomologist Ashley Dean, I had a great field scouting adventure in central Iowa. First visiting the field for poor germination and other issues, Meaghan was digging in the soil in search of more information and found grubs! So of course, she invited Ashley and me for a closer look. I have been hearing about grubs in cornfields, particularly north of I-80; for about a week. With people assessing germination and checking stand counts, it is also a good idea to look for early-season pest activity --- like grubs!
Several reports from ISU Field Agronomists have indicated Japanese beetles are emerging in southern Iowa. The emergence is about 7-10 days behind the last few years, due to slowly accumulating degree days in 2019. Literature shows Japanese beetle adults need about 1,030 growing degree days (base 50°F) to complete development and will continue emergence until around 2,150 degree days. Based on accumulating degree-day temperatures in 2019, Japanese beetle adults should be active in some areas of southern Iowa this week (Figure 1).
In this video Ed Zaworski of the ISU Plant and Insect Diagnostic Clinic discusses pine wilt and shares tips and management practices. Check out their website: https://hortnews.extension.iastate.ed... Pine wilt causes rapid wilting and dying of pine trees, particularly Scots (Scotch) pines.
Bean leaf beetle adults (Photo 1) are susceptible to cold weather and most will die when air temperatures fall below 14°F (-10°C). However, they have adapted to winter by protecting themselves under plant debris and loose soil. Each spring, adult beetles emerge from overwintering habitat and migrate to available hosts, such as alfalfa, tick trefoil, and various clovers. As the season progresses, bean leaf beetles move to preferred hosts, like soybean. While initial adult activity can begin before soybean emergence, peak abundance often coincides with early-vegetative soybean.
This week, I’ve had a number of people tell me they spotted Japanese beetle. I was initially surprised, because I track degree days to predict adult emergence every summer and it seemed a bit early. According to the ISU Agronomy Mesonet, adults could be emerging in southern Iowa and I would expect adult emergence in central Iowa next week. See my recent ICM News article showing a degree-day map for 2018.
Japanese beetle is an invasive insect that feeds on corn and soybean plus many other plants. This pest has been in Iowa since 1994 but its distribution in field crops is considered sporadic around the state. Statewide populations in field crops have been variable since 2014 and it is unclear if pressure will be significant this year. Several reports around Iowa indicated high numbers of grubs within fields, but it is not clear if they were Japanese beetle or another closely-related species. Adult emergence well before corn silking is noteworthy.
Over the weekend, someone let me know they saw a western corn rootworm adult. Remember this pest overwinters as an egg that hatches in June! They get confused with closely-related species every spring: striped cucumber beetle. Striped and spotted cucumber beetles overwinter as adults and become active when spring temperatures warm up. Most scouts are able to distinguish northern corn rootworm and southern corn rootworm (also known as spotted cucumber beetle) fairly easily. However, western corn rootworm and striped cucumber beetles can be distinguished by the stripes on the forewings.
This year, I’ve had a handful of people ask me about managing Colorado potato beetle (CPB) in Iowa. Read more about CPB identification and biology here. These conversations were with producers growing over 5 acres of potatoes and having a difficult time reducing CPB pressure. With the help of Dr. Ian MacRae at the University of Minnesota, I put together an IPM plan for this devastating pest. Colorado potato beetle (CPB) is a major pest of potato that is native to America and Mexico.
