Plant Pathology Infobytes
May 8, 1997
Too Much Fertilizer Can Cause Gardening Problems
Successful gardeners know that a good fertility program is essential before top yields of tomatoes, peppers, corn, squash, and other traditional vegetable favorites can be produced.
However, too much of a good thing can also have an adverse affect on vegetable production. This means you need to be careful how you make additional applications of fertilizer to your garden crops. Over application of ammonium nitrate, triple thirteen, or just about any fertilizer material added to plants as a side-dress can easily lead to soluble salts injury.
Cucurbits such as squash, cucumbers, cantaloupes, pumpkins, watermelons, pumpkins are especially sensitive to soluble salts injury, as are other vegetables including tomato, peppers, beans, and corn.
Excessively high soluble salts hurt garden plants by causing root burn. The burning reduces the ability of roots to absorb water and nutrients. Roots of properly fertilized plants are able to carry out these essential functions without problem, but it's a different story with over fertilized plants. In fact, instead of being able to pick up water, water may actually flow out of the roots of these plants.
As a result, your squash plant may wilt and show symptoms of dehydration. The high salts accumulate in the plant and together with the reduced water uptake, cause yellowing and scorching of tips of new leaves and shoots. One of the most common symptoms of toxic accumulations of salts is burning around the leaf margins. Affected plants are usually stunted and produce reduced yields.
High soluble salts weaken or stress plants. Plants under stress become increasingly vulnerable to root and foliar diseases. For example, root which are burned by high salts are more easily invaded by root rot fungi than healthy roots.
Gardeners who suspect they may have soluble salts buildup because of application of too much fertilizer should check with their county Extension office about the procedure for collecting a soil sample for nutritional analysis. The Soil Testing Department at Mississippi State University can conduct a test to determine if you have excessive salts buildup in your garden soil and offer suggestions for correcting the problem.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.