Plant Pathology Infobytes
March 16, 1999
Take it Easy With that Fertilizer
Whatever the season or crop, familiarity with fertilizers pays off. Successful gardeners know that a good fertility program leads to healthier and more productive plants and is essential before top yields of tomatoes, peppers, corn, squash, and other traditional vegetable favorites can be produced.
But it's important use the right amount of fertilzer, since "too much of a good thing" may quickly harm your plants. Here's the best advice: collect a soil sample for analysis to determine how much fertilizer you should add to your soil at the beginning of the gardening season. The results of the soil fertility analysis will also tell you how much fertilzer should be added to your particular crop as the season progress. For information on the procedure for collecting a sample, check with your county Extension office.
This means that you once you get your garden going this spring, add additional applications of fertilizer only as recommended (and in recommended amount). Remember - over application of ammonium nitrate, triple thirteen, or just about any fertilizer material, added to plants as a side-dress can easily burn roots and foliage through accumulation of soluble salts in the soil.
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. Severely stressed plants may die from over fertilization.
Fertilize, but fertilize wisely. Gardeners who suspect they may have soluble salts buildup because of application of too much fertilizer should check with your 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.