Last week the discussion was on bagworms with the promise to follow up on Japanese beetles when they became a problem. Based on calls this week from the southern parts of Clay and Owen counties, they are here!
Bagworms and Japanese beetles seem to be the most common horticultural insect call during the summer. Both can completely defoliate a tree.
Japanese beetles can cause problems in both the grub and adult beetle state. Many want to apply pesticides to lawns thinking that they are controlling these beetles. However, timing is critical for control.
Application outside of late July is simply throwing money away and adding unnecessary pesticides to the environment where you live. Both granular and liquid products to control grubs in turf should be watered in to improve efficacy. The grubs hatch from eggs in late July or early August. Due to the fact that these young grubs are most susceptible to the insecticide and that turf damage can be prevented, timing is key for success. Also check to see if grubs are present before treatment occurs.
A history or grub problems or finding five or more grubs per square foot justifies treatment. Otherwise save your money!
The adult Japanese beetles are major defoliators. They often don't have a lot of rhyme or reason as they may decide to congregate or swarm a particular area. If adults are a problem, typically one will need two insecticide treatments during the peak flight period. The first application should occur when beetles are abundant and damage is becoming intolerable.
That will likely be occurring this week. Secondary applications can be determined by monitoring plant damage and beetle numbers. Neem products containing Azadirachtin can be effective repellants that can reduce defoliation when applied at weekly or slightly longer intervals. Soil application of imidacloprid or acetamiprid can reduce the amount of defoliation caused by adults when applied to soil at the base of a tree. Applications for future reference should occur in late May so trees have enough time to take up the materials into the leaves.
Avoid using pheromone Japanese beetle traps as they attract more beetles and do not aide in controlling damage. If traps are used, place them a considerable distance away from infected plants. For food plants, control with carbaryl, permethrin and malathion are safe. But be sure to follow harvest restrictions as these products have wait periods following application.
Purdue publication E-75 entitled Japanese Beetles in the Urban Landscape is free of charge and available at your local office. In addition to providing information about Japanese beetles, it lists products for controlling the beetles. It also lists plants to avoid due to beetle problems as well as plants that typically remain free of Japanese beetle feeding.
You can contact the local Purdue Extension Office by calling 829-5020 Ext. 14 in Owen County or 448-9041 in Clay County for more information or publication copies regarding this week's column topic or to RSVP for upcoming events. It is always best to call first to assure items are ready when you arrive and to RSVP for programs. While most publications are free, some do have a fee. All times listed are Eastern Time.
July 6-12 -- Owen County Fair
July 8 -- Purdue Weed Day, West Lafayette
July 11-18 -- Clay County 4-H Fair
Aug. 6-17 -- Indiana State Fair