Herbicide drift, soldier beetles and bagworms

By John Fulton

[June 09, 2009]  As if trees didn't have enough leaf problems with diseases, herbicide drift has shown up in a big way this past week. In all cases I have seen, the herbicides involved have been members of the growth regulator group. This group includes products such as 2,4-D and Banvel. Both products are used in agricultural production, right of way maintenance and home lawn care.

Leaf symptoms usually appear as some sort of abnormal growth. This can include twisting, cupping, elongation and rolling. Since the chemicals are systemic growth regulators, they move throughout the trees (or shrubs or flowers) and then show the most damage on the newest growing points. Think of what a dandelion looks like after it has been treated with 2,4-D and you get the general idea.

Where the products come from on your trees is generally a big mystery. They can drift during the actual spraying process (called spray drift), or they can come back up off the ground as a vapor and move with winds (called vapor drift). The difficulty with vapor drift is that it can occur for up to a week and a half after the application and then can drift for up to a mile and a half.

Some species of trees are more susceptible than others, and the full-size leaves are less likely to show symptoms. Redbuds, oaks and lilacs are among the most susceptible trees. Grapes and tomatoes are among the most susceptible garden plants.

If you do have damage from herbicide drift, the end results can vary. Generally, on established perennials, the damage is ugly leaves for at least part of the growing season. You can also have some "wave" to the ends of branches and possibly the loss of some small branch ends. On younger stock, transplanted in the last year or so, the damage may be fatal. It usually takes several weeks to get an indication of the amount of damage done, but a year is even better.

As for treatment, water when the weather stays dry. Don't fertilize at this time. Remember that growth regulator herbicides make things "grow themselves to death." You have to walk a fine line between keeping the tree healthy and making matters worse.

Insects to watch for

Soldier beetles will be appearing shortly. They look like pale lightning bugs without the light and are very common around pollinating linden trees. Since soldier beetles are beneficial, it is inadvisable to kill them. They feed on small insects such as aphids. However, they do qualify as a nuisance pest in much the same way as the Asian ladybugs. Weatherstripping and caulking will help keep them out of your house. A vacuum cleaner will safely remove soldier beetles that are found inside.

After some very severe infestations of bagworms the past few years, the calls have been coming in all year on the correct treatment times for bagworms this year. Year in and year out, the correct treatment time for bagworms is June 15. You can mark this date on your calendar for next year and be within a few days of the correct treatment time. With a very cool spring, a week later may be a possibility, but this season's yo-yo temperatures really even out. The idea is to have all the eggs hatched before treatment.

The traditional treatment has been Sevin, but the Bt products such as Dipel and Thuricide have really taken the majority of the market. Many other products will work, but the Bt products have several good points, including safety to mammals and toxicity to larger bagworms.

If you are in doubt about whether you have bagworms, check your trees and shrubs around June 15. You can actually see the small bags as the larvae build them. They become very noticeable at about one-sixteenth of an inch long. Treat bagworms early, since larger ones are more difficult to control, but try to ensure the eggs are all hatched out.

[By JOHN FULTON, University of Illinois Extension, Logan County]