Herbicide injury and time to
By John Fulton
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[June 07, 2014]
As if trees didn’t have enough leaf
problems with the diseases, herbicide drift has shown up in a big
way this past week or so. Particularly noticeable is drift damage on
tomatoes and grapes. 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 (Banvel.) Both products are used
in agricultural production, right-of-way maintenance, and in home
lawn care. Just check the label on your favorite broadleaf weed
control product, and if you can get by the technical chemical name,
it will usually end with salt of dicamba as one of the ingredients
in the three-way combination products.
Leaf symptoms usually appear as some sort of abnormal growth.
This can include twisting, cupping, elongation, and rolling.
Since these 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 and gardens 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 one and one-half weeks after the application, and then can
drift for up to a mile and a half. This vapor drift problem is
more common with esther formulations of the chemical (basically
oil based) as compared to the amine formulation (basically water
Different species of plants are more susceptible than others,
and the full-size leaves are less likely to show symptoms. Red
buds, oaks, and lilacs are among the most susceptible trees.
Grapes and tomatoes are among the most susceptible garden
plants. The chemicals concentrate in the newest growing tissues
such as the buds, tips, and newest leaves.
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.
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As for treatment, water plants 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 plant healthy and making
If you haven’t sown pumpkins for fall decoration, usually around
Father’s Day is the correct timing. Vining pumpkins need at
least 50 – 100 square feet per hill, with the larger pumpkins
requiring the larger area. Hills should be five to six feet
apart and rows of hills should be 10 – 15 feet apart. Each hill
should have about four seeds per hill, planted about an inch
The miniature varieties such as the Jack-Be-Little are sometimes
grown in rows with seeds planted every eight to twelve inches,
then thinned to about two feet apart in the rows. Fall
decoration pumpkins should be cut from the vine before the vine
dries in order to have a good stem attached to the pumpkin, but
after the color is acceptable.
[By JOHN FULTON, COUNTY EXTENSION
DIRECTOR SERVING LOGAN, MENARD, AND SANGAMON COUNTIES]