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Herbicide drift, West Nile virus    Send a link to a friend 

By John Fulton

[MAY 24, 2006]  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 dicamba. Both products are used in agricultural production, right of way maintenance and in 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. The chemicals 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.

Different 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 this 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.

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West Nile virus

West Nile virus has, unfortunately, become a household phrase. The virus was first isolated in Uganda, Africa. It can harm humans, birds and other animals. It is transmitted by infected mosquitoes, primarily the northern house mosquito. The mosquito becomes infected after biting wild birds that are the primary host of the virus. The mosquito is actually able to transmit the virus after 10-14 days after biting the infected bird.

The mosquito life cycle has four life stages: egg, larvae, pupa and adult. The female mosquito lays eggs on water or moist soil. Most of the larvae hatch after 48 hours, and the larvae and pupae live in the water. The females need a blood meal before they can lay eggs, so only the females bite. They bite every few days during their adult lives, which may last several weeks.

Preventing mosquitoes is a first step. Homeowners can best accomplish this by eliminating standing water. Tires and old containers are obvious places to start. Drill holes in the bottom of recycling containers, clean clogged gutters, don't allow stagnant water in anything such as birdbaths, change landscape slopes to eliminate standing water, and use larvacides in standing water that can't be eliminated. Bt Israeli is the strain that is effective against mosquito larvae -- not the Bt variety commonly used on trees and gardens! The mosquitoes have already begun hatching, so treatment time is at hand.

Also protect yourself from bites. Mosquitoes can travel up to three miles from their breeding sites! Make sure that screens and doors are tight, use proper outside lighting such as fluorescent lights, stay indoors at dawn and dusk when mosquitoes are most active, wear long-sleeved shirt and long pants when you must go outside, and use insect repellents properly applied. Exposed skin should be sparingly treated with a repellent containing up to 30 percent DEET, or up to 10 percent for children. Make sure to treat thin clothing as well, since mosquitoes can bite through the thin clothing.

[John Fulton, unit leader, University of Illinois Extension, Logan County Unit]


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