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Pest Watch

September 18, 2002

Scattered reports of white grub injury have been coming in. Damage is likely, particularly during dry periods, for the next month or two in Illinois. If the fall is cold early, this time will shorten; under warm fall conditions, damage is possible in southern Illinois until Thanksgiving. Trichlorfon, sold as Dylox, is very effective where damage is already occurring. It provides control in 3 days, allowing the turf to recover quicker and the client to no longer find live grubs. Heterorhabditis bacteriophora, sold as Hb nematodes, is also effective against damaging grubs. Control should take 7 to 10 days and will probably be around 60%, versus 95% for Dylox. With either Dylox or Hb nematodes, water after application with at least 1/2 inch of water to flush the insecticide or worms into the root zone where the grubs live.

Zimmerman pine moth can be effectively controlled at this time. The eggs hatch in late August, but the larvae wander across the tree for a few weeks before retreating into a hibernaculum under bark for the winter. Permethrin (Astro, Pounce) should be effective, as well as other long-lasting pyrethroids. Spray the trunk and base of major branches on Scotch, Austrian, and other pines.

Mimosa webworm is obvious, with heavy damage on honey locust throughout the state as well as on silk tree (mimosa) in southern Illinois. This insect tends to be more numerous after warmer winters because the overwintering larvae are killed by extreme conditions. Numerous insecticides are effective for control, but treatment this late in the season is usually not warranted. This late-season damage is unlikely to harm tree health, and the damaged leaves will hang on the tree whether or not the caterpillars are still there. Thus, the aesthetic damage will remain whether or not it is treated.

Dogwood sawfly has been reported from The Morton Arboretum in northeastern Illinois. Young larvae are covered with a white, waxy flocculent and are typically found curled up on the leaf. Older larvae do not have the white flocculent and are bluish green, with yellow undersides. They feed on the edges of dogwood leaves, causing some defoliation when populations are high. As with other late-season defoliators, they cause little to no damage to the health of the plant so treatment is usually not needed. Being a sawfly, it is controlled with many insecticides but not Bacillus thuringiensis kurstaki.

Protect yourself from West Nile virus. Although many mosquitoes carry the virus, the northern house mosquito, Culex pipiens, is the most likely culprit. This is an evening and morning biter that is small and brownish. It is a quiet biter, meaning that it typically does not buzz by your ear, nor do you usually feel the bite. Protect yourself with an insect repellent containing about 30% DEET, such as Off or Cutters, particularly in the evening and early morning. This container-breeding mosquito utilizes the putrid water in clogged gutters, old tires, tin cans, abandoned swimming pools, wading pools, birdbaths, pet water bowls, and tree holes. Dumping and cleaning outdoor containers of water weekly greatly reduces the numbers of this mosquito.

Author: Phil Nixon


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