Growing tomatoes in the coastal South is always a gamble. Throughout the summer you play the odds against insects, diseases, heat, or drought ruining your crop. Until a few weeks ago, growing conditions this season had been nearly ideal, resulting in some of the healthiest tomato plants I have seen in years. Recent heavy rains are likely to change this trend, raising the stakes against a bumper crop this season.
Splitting and cracking
Side splitting and cracking up are terms you want to hear in reference to a joke you just made, not about your tomatoes. Heavy rain, especially when preceded by dry weather, is the leading cause of fruit cracking and splitting in tomatoes. This type of damage is most likely to occur as tomatoes begin to ripen and you are anxiously anticipating harvest, though green fruit can be affected as well.
Cracking and splitting occur when rapid changes in soil moisture levels cause fruits to expand quicker than the tomato skin can grow. There are two different patterns this damage may take. Vertical splits along the sides of fruits are known as radial cracking and are the most serious. This pattern of splitting commonly occurs during hot, humid weather. Cracking that occurs in a circular pattern at the top of tomato fruits, ringing the stem end, is known as concentric cracking. When cracking of either type occurs in green tomatoes, fruits are likely to rot before they fully ripen if left on the vine.
With both radial and concentric cracking, your best option is to harvest fruits immediately, before they begin to rot. These fruits are edible and can be allowed to finish ripening indoors, though any fruit that develops a sour smell or begins to ooze should go straight to the compost pile. Fruits that ripen off the vine, as well as those that ripen on the vine during cloudy, rainy weather will be less flavorful than those that mature fully on the plant during sunny weather.
Blossom end rot
In addition to cracking and splitting, fluctuations in soil moisture level are the most common cause of blossom end rot. This disorder occurs when there is not enough calcium available within developing fruit, causing the lower end of the fruit to turn tan or black. Other factors that can cause blossom end rot include extreme heat or cold, over fertilization, and low soil pH (acid soil). If you have tomatoes that have started to develop blossom end rot, remove them from the vine and compost them. They will not develop or ripen normally.
There are several issues that can cause tomato leaves to curl, including wet weather. Leaf curling as a result of wet conditions is not a serious concern and will not damage plants or reduce yields. Some varieties are more prone to leaf curling than others. When excessive moisture is the cause of leaf curling, leaves curl upward starting from the bottom of the plant first. Leaves that curl as a result of wet soil conditions may take on a leathery appearance, but otherwise remain green and healthy.
The most important thing you can do to minimize fruit cracking, blossom end rot, and leaf curling in tomatoes is to maintain even soil moisture levels by watering during drought. Most vegetables require around one inch of water per week to remain productive. Soaker hose and drip irrigation systems are the best way to provide this water to vegetable and ornamental plants because these systems apply water directly to the soil. This reduces water loss through evaporation and keeps plant leaves dry, which helps limit the spread of leaf diseases. Mulching your vegetable garden will also help keep the soil evenly moist and minimize moisture related problems.
Other tomato problems associated with rainy weather and wet soils include wilt diseases and leaf diseases such as early blight. If you suspect your tomatoes have a disease or insect problem, have the cause correctly diagnosed before taking any action. Visit Texas Cooperative Extension’s Tomato Problem Solver website, aggie-horticulture.tamu.edu/vegetable/tomato-problem-solver/, to diagnose your tomato problems or contact your local Extension office for assistance. Locate your local Extension office or post your questions to be answered online through the ‘Ask an Expert’ link at ces.ncsu.edu.
Charlotte D. Glen is the horticulture agent with the Pender County Cooperative Extension of NC State University, College of Agriculture & Life Sciences. She can be reached via e-mail at Charlotte_Glen@ncsu.edu.