That rotten spot on the bottom side of tomatoes is all too familiar to home vegetable growers. The same problem can be seen on melons, squash and cucumbers, but is most often seen on tomatoes.

PHOTO PROVIDED BY THE CLEMSON EXTENSION SERVICE Blossom end rot is caused by a calcium deficiency - not a disease - and is brought about by extremely wet or dry soil. Many growers feel they have a disease problem, but actually this condition is a mineral deficiency. The common name for this problem is "blossom end rot" and it is caused by a lack of calcium in the fruit.

Once a grower understands that a lack of calcium is causing the problem, they automatically assume that their garden must need lime. Since the problem is a lack calcium and lime is a calcium source that seems to be a fair assumption. Well, not so fast. Lime alone will not insure that your vegetables will not have blossom end rot.

Calcium, like any other other plant nutrient, is picked up in the water that the plant's roots absorb. If garden soil is allowed to dry out, there is less water to be absorbed, and likewise, fewer nutrients are absorbed. A layer of mulch around the plants will help keep soil moist and nutrient uptake at a more constant level. Irrigation during dry periods is a must.

Don't misunderstand. Liming is a very sound practice and should be done a regular basis. A soil test can give you accurate lime and fertilizer recommendations. Just remember that liming is not a cure-all.for blossom end rot,

Even if you have followed soil test recommendations and kept your plants moist and mulched, it is still possible for you to have blossom end rot problems. Don't panic. You just need to do a little corrective spraying. Several commercial products are a available, under trade names like "Stop Rot." These prod- ucts contain either calcium chloride or calcium nitrate. Many growers prefer to use the home remedy of Epsom salts. Dissolve a couple of tablespoons of either product in a gallon of water and spray the mixture directly on the leaves and fruit of the plant. Repeat on a 7- to 10-day interval. This will not "heal" existing spots, but it will keep those spots from getting worse and will limit the formation of new spots.

Vegetables don't

cross pollinate

We often get this question from home gardeners: "Do vegetables crops pollinate?" Gardeners get some oddly shaped, off tasting, poor quality vegetables and are concerned that vegetables may be "crossing," especially cantaloupes and cucumbers.

Put simply, this just does not happen. If you are getting some type of odd looking vegetable, look at your growing conditions. Plant disease, insects, low fertility and adverse weather can all cause problems with vegetable quality. Many of these are related to poor pollination. Extremely hot, dry or still weather can cause pollination problems. So can a lack of honeybees. Poorly pollinated vegetables often produce misshapen fruit. Insect or hail damage can also produce a fruit that has an odd shape. In those cases, a small area of the fruit may be killed or scarred, but the fruit will continue to grow and mature, fibbing a fruit with a rough or depressed area on the surface.

Disease can cause a number of conditions that lower vegetable quality and appearance. Keeping the leaves of the plant healthy is critical. The leaf is the power factory of the plant, taking energy from the sun and turning it into energy for the plant. The sugars produced in the leaf of the plant effect the taste of the vegetable.

There are two important points to remember in keeping the leaves healthy. First, keep in leaves as dry as possible. Use drip irrigation or soaker hoses instead of overhead irrigation if possible. Second, fungicides (the family of chemicals used to control diseases) are protectants. These products are used to prevent the disease from occurring, not to treat symptoms of the disease. It is very similar to a person using a sunscreen. Once the fungicide has worn off or broken down from sunlight and weather, there is no protection. Fungicides should be applied on a 10- to 14-day interval. If your garden has history of disease problems, start a preventive spray program at bloom time and continue though harvest.

It is not unusual, especially with hybrid varieties of vegetables, to see off type plants come up in a row. These plants will most often produce poor quality vegetables. If that happens in your garden, the best course of action is to destroy the off type plant.