Purdue Extension Service

Summer doesn't officially start for another 22 days, but some of our summer pests should be making their first appearance very soon.

Bagworms should be hatching out right about now. Bagworms are caterpillars that live inside spindle-shaped bags which they construct to protect themselves against birds and other enemies. These bags, composed of silken threads and bits of foliage, look so much like a part of the tree that they may go unnoticed until extensive damage has occurred.

Early in June, the insects hatch from eggs which wintered in the old bags attached to tree branches. As soon as the young worms appear, they start to spin bags. They can cause a lot of defoliation by the end of summer if they aren't controlled.

Hand-picking the old bags before the new generation hatches is an excellent control method, but doesn't work well for large plants or those with heavy infestations. Bacillus thuringiensis (BT, Dipel) is a bacteria that only kills caterpillars; it can be sprayed on the plants in the first few weeks of June. Starting in July, the bagworms are too large and mature to be controlled with BT, so you'll need to switch to a rescue treatment of one of the following: malathion, Orthene (acephate), Sevin (carbaryl), or Spectracide Bug Stop (permethrin).

Japanese beetles should also be emerging any time now. There is no sure-fire way to protect your plants. The best advice I can give is to have your plants treated early in the season with a soil drench of imidacloprid (Bayer Tree and Shrub Insect Control, Merit), which will give you protection for the entire year. You'll still see some feeding damage, because the beetle has to eat the leaf to be poisoned. Avoid using beetle traps, unless you can place it a few hundred feet from the garden, as they bring in more beetles than would have been there normally.

Speaking of beetles: it's still a little early to be getting your grub control chemicals applied. We should probably hold off until late June or into July before we start these treatments. Only apply grub control products if your lawn has more than 7 or 8 grubs per square foot, to protect the lawn. Controlling grubs is not an effective way to protect your garden from adult beetles.

I've been seeing a lot of rose slug damage this spring. These are not true slugs, but are the larvae of sawflies (an insect in the same order as bees and wasps). The larvae are green and look a lot like caterpillars, but they are not true caterpillars. They eat ragged holes in the center of the rose leaf. Usually, the damage is minor and won't hurt anything, but if you need to control them, use malathion, Sevin, or permethrin, being sure to spray the undersides of the leaves.

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Landscape Insects for Early Summer

By Larry Caplan, Extension Horticulture Educator, Vanderburgh County, IN

For the Evansville Courier and Press, May 31, 2009