There are numerous diseases that affect tomatoes, but I’m only going to focus on three. As far as I’m concerned they are important, since few common cultivars have been bred for resistance.
Because of our hot humid climate in eastern Carolina, bacterial wilt is a disease of great importance. Bacteria live in the soil and enter plants through wounds, usually from transplanting.
Once plants contract the disease they wilt but leaves stay green temporarily. If you are sure this isn’t water stress, remove these plans from the area immediately. There is no feasible chemical control. The only variety I have encountered that shows even partial resistance is Kewalo.
The most common tomato disease prevalent with our sandy soil is blossom end rot. It is more properly considered a disorder, as the problem is not caused by a pathogen. Water soaked spots develop at the ends of the fruits and they expand and eventually become black. This rotting is caused by a secondary infection.
What initially causes blossom end rot is a calcium deficiency in the soil and sandy soils are usually low in calcium. Often fluctuating soil moisture plays a part too. So does excessive ammonia nitrogen fertilization. Calcium nitrate is probably the best nitrogen fertilizer to use.
Soil calcium must be kept high, but sometimes this can cause soil pH to become too high. On sandy soils I would recommend using gypsum in conjunction with lime to keep the pH stable and calcium levels sufficient.
A handful of varieties show some resistance to blossom end rot. The only ones that are also well adapted to the heat and humidity we have in the coastal plain are Ravello and Manalucie. Ravello is a paste type resembling Roma. Manalucie is a large heirloom type.
The latest tomato plague to this area is the tomato spotted wilt virus (TSWV). This disease is causing increased frustration locally. TSWV is spread by thrips, tiny insects similar to the ones found on wheat at harvest time. These insects contract the virus from weeds and carry it to the tomato plants.
After several weeks some plants may look stunted. Younger ones usually wilt and die. Some leaves develop dark spots and/or purple veins. Often the foliage looks twisted almost resembling herbicide injury. Fruits usually have yellow spots.
The first step in combating this disease is sanitation. Keep the area as weed-free as possible and make sure adjacent places are mowed. Crop debris from the previous year’s growth may be contaminated with thrips, so remove old crop residue and mulch the area for the winter. This will discourage weeds. Promptly remove any plants which show symptoms of TSWV.
Several newer varieties show promise. The first cultivar with TSWV resistance was Amelia, an attractive bright red tomato. My problem with this selection is that it is too firm and crunchy. One promising cultivar is Bella Rosa, a large round tomato that looks a lot like Amelia but is not as crunchy. BHN 444, BHN 640, Talladega and Top Gun are also becoming popular. Plum Regal is a paste-type that also shows resistance to Fusarium and Verticillium wilts.
Ted Manzer teaches agriculture at Northeastern High School.
