Question: “My tomatoes’ leaves are curling, distorted, and twisting up. They almost look as though they are unfurling like the fiddle head of a fern frond. The plants are also stunted and not producing many fruit.”
Answer: There are two common reasons why the leaves of a tomato plant do this. First, a minor or slight leaf rolling on the outer edges of the leaves can often be a symptom of stress on tomatoes. This stress could be related to heat, lack of water, or too much water. Be sure to water your tomatoes deeply and less frequently. An established tomato should be thoroughly watered only once or twice a week and then allow the soil to dry a few days before watering again. If we get an inch of rain, then they probably won’t need any more water for the next week. Consider using drip irrigation or soaker hoses around your plants. These methods will help conserve moisture and avoid getting the foliage wet, which can cause disease.
If the leaves of your tomatoes are more extreme in their leaf curling or twisting, then this is often associated with herbicide injury. Unfortunately, those who have the best intentions of avoiding herbicides often don’t realize that there are several ways you can indirectly introduce these chemicals to your garden. Some of the more common routes involve the use of soil amendments such as cow manure and horse manure. Although these may seem like good “organic” sources of nutrients and compost to add to your garden, they often can carry over herbicides residues from products used to control weeds on pastures and hayfields grazed by livestock. Even the use of hay or straw as a mulch can sometimes have enough residue to cause damage to sensitive plants such as tomatoes.
Therefore, be sure you know the source of your manure or straw before using them in your garden. Even if you think you are buying from a farm that doesn’t use herbicides, they could be buying and feeding hay to their animals from another location that does use them. These herbicides are safe to use in pastures and hayfields. They selectively kill the weeds without hurting the forage grass and can be feed to livestock without any harm to the animals. However, depending on the chemical used, it can pass through the animal and remain active in the manure for several months. Tomatoes are one of the most sensitive vegetables and make a good indicator plant to test your manure source.
Herbicides can also carry over in lawn clippings that are gathered for composting or garden use. Many chemicals that you use for weed control on your lawn have the same effect as those used in pastures and hayfields. It is possible that even blowing the grass clippings from your lawn mower into your garden could carry over enough chemical residues to damage tomato plants. Unfortunately, if your tomatoes or other vegetables have herbicide injury, there is nothing you can do to reverse the damage. The best course of action is to start new plants in a different location and try to get a late crop in before the season is over. It should be safe to plant back into any affected areas the next season. For more information on any gardening topic, visit UGA Extension’s website at http://www.columbusga.org/cooperative_extension/coop_ext.htm. Click on the publications tab and search via keyword—So go get gardening!
Jennifer Davidson is the Agriculture & Natural Resources Extension Agent for Muscogee County Cooperative Extension, a partnership of The University of Georgia, The U.S. Department of Agriculture, and Columbus Consolidated Government.