Late Blight is a fungal disease that usually occurs toward the end of summer when cooler, wetter weather arrives. The initial symptoms are dark greasy-looking spots on the leaves that then progress to the stems and fruit. The vines may succumb in a matter of days and infected green fruit rots before it can ripen. Preventive and corrective action: avoid overhead watering; promote good air circulation by staking and pruning; remove leaves touching the ground; remove infected plants; rotate crops.
Blossom End Rot (BER) causes a soft, dark lesion on the bottoms of ripening tomato fruit. It is most prevalent in Roma-type tomatoes, but can occur with many varieties. BER is considered a nutritional disorder due to lack of calcium uptake, but in a practical sense the cause is usually irregular watering. To avoid problems, have your soil tested to ensure that it contains appropriate nutrients and pH and keep plants adequately watered. Use a thick organic mulch around plants to help maintain soil moisture.
Physiological Leaf Roll is a common cosmetic issue seen early in the season, but does not impact fruit production or the health of the plant. Some varieties are more susceptible than others. Ensure adequate watering, and avoid over-fertilizing and over-pruning of young plants.
Catfacing is a development disorder that causes fruit to appear puckered, lumpy, or zippered. It is usually limited to early fruit or fruit developing during cool periods. High levels of nitrogen may increase the problem: Do not over-fertilize.
Cracked Fruit is most common when significant rainfall follows a period of dry weather. Sudden, rapid growth during fruit ripening causes the tomato to outgrow its skin. Mulching and regular, even watering can reduce cracking. Harvesting fruit in advance of forecasted rain is also advisable.
Sunscald causes soft white or yellow spots on fruit exposed to south-facing sun. Some varieties are more susceptible, simply because they produce less abundant foliage. Avoid pruning of upper leaves from tomato plants and cover plants or fruit with lightweight shade cloth if needed.
