Signup to receive email updates

or follow our RSS feed


John Fulton

John Fulton
Former County Extension Director

Blog Archives

732 Total Posts

follow our RSS feed

Blog Banner

In The Backyard

Horticulture columns and tips done on a timely basis
tomato affected by herbicide

Misshapen Leaves = Herbicide Damage

Posted by John Fulton -

If you happen to have severely misshapen leaves on plants ranging from tomatoes to red bud trees, growth regulator herbicides may be the culprits. We have seen an increase in herbicide damage this past few weeks. Particularly noticeable is 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. Spray drift, vapor drift, runoff, and movement in water are all possible ways to damage desirable plants.

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 plants, 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 damaging product came from 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 based). Treating your lawn for dandelions or henbit, then getting an inch rain on it can move the chemicals in the rainwater into the root zone of unintended victims (meaning your plants). This is actually somewhat common when lawn areas surrounding highly susceptible trees are treated for broadleaf weeds.

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. When it comes to annuals, the damage is dependent on how much of the chemical is in play, and growing conditions.

As for treatment, water plants if it turns 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 matters worse.

Please share this article with your friends!
Share on Facebook Tweet on Twitter Pin on Pinterest