I could list a number of pest situations such as the three I just described. As we begin the growing season, and our annual battle with plant pests (weeds, diseases and insects), two key factors to effective control are to positively identify the cause of plant problems; then determine when the most effective time is to use control measures, especially pesticides.
White grubs overwinter as larvae, which are the cream colored, c-shaped grubs with reddish heads. In spring, mature larvae move closer to the soil surface to pupate and it’s common to find white grubs during spring. However, these grubs do very little to no feeding at this time of year and are not a concern to lawns or garden plants.
Applying insecticides to kill overwintering grubs in the spring is not justified. Mature grubs are difficult to kill and killing these grubs will not prevent new adult beetles from laying eggs in the lawn. Hence, killing white grubs now will not prevent damage later this summer. Also, insecticides containing imidacloprid will not kill mature white grubs.
For insecticide applications targeting only white grubs, the ideal time to apply products with imidacloprid, such as Merit or Grub X, is between the 3rd week of June and mid-July. If applied at this time, the next generation of white grubs will be controlled. This is the generation that causes late summer damage.
If imidacloprid is applied earlier, such as mid to late May for control of bluegrass billbugs; this application can provide control of white grubs in August. However, early applications do not always work as well in controlling grubs. Unless you have a history of billbug damage, it is best to wait until mid June to mid July to apply Merit for white grubs. If applied earlier, closely monitor lawns in August for white grubs.
Dandelions are a perennial broad-leaf weed whose taproots survive from year to year. Spring applications of herbicides are not as effective in reducing dandelions and killing individual plants. Flowering and seed production has already taken place; and while herbicides will kill foliage at this time of year, dandelions tend to regrow from their roots during summer.
At this time of year, remove flowers as they appear to reduce seed production and dig dandelions to weaken them so turfgrass can fill in the area and compete with weeds. If herbicides are applied in spring, remove flowers first; then spot spray weeds with a liquid herbicide. Do not apply weed and feed products for dandelion control.
Damage to evergreens from bagworms has been rapidly increasing in our area with trees being severely defoliated and even killed. Now is the time to take a close look at evergreen trees and shrubs to check for bagworms. When checking evergreens, look for one to two inch long, brown, cocoon-like bags tightly attached to twigs. Each bag contains 300 to 1000 eggs which will soon hatch from late May into June. If you only find a few bagworms, clip them off and destroy them. If you find numerous bags, keep checking the tree for signs of egg hatch. You may see tiny caterpillars hanging down from a small web, or you may see young bagworms as one-fourth inch, triangular shaped bags on top of twigs.
The most effective time to control bagworms with insecticides is after eggs hatch and when young bagworms are about one-fourth inch long. Apply insecticides such as permethrin, carbaryl, or Bacillus thuringiensis, usually in late May or early June.
Again, if you observe a lawn or plant problem this season, take time to positively identify the cause of the problem and determine when the best time is to use control measures, especially pesticides. These two steps can increase control, save money, and reduce unnecessary applications of pesticides.
Source: Kelly Feehan, Extension Educator
Ann Fenton, Extension Educator
University of Nebraska-Lincoln
