As usual during this time of year, a lot of problems are showing up on tomatoes, in part because we’ve had so much rain since the first of June. Constantly wet foliage on the tomato plants leads to diseases. Leaf wetness to a disease is sort of like gasoline to a fire.
What are the problems I am seeing and hearing about the most? Let’s start first with the diseases. All of these problems start with the older, bottom leaves and move up the plant
Early blight is a disease that can be somewhat controlled. Small, irregular, brown dead spots appear on the leaves. Spots enlarge to about ½-inch in diameter in a bull’s-eye pattern. Leaf tissue around the brown spots begins to yellow. With severe spotting the entire leaf may turn yellow. The greatest injury occurs as the tomatoes begin to mature. Daconil 2787 or any copper- based fungicide, sprayed at seven-day intervals, can help control early blight.
Septoria leaf spot is one of the most common tomato diseases and one of the most destructive. It usually becomes most evident after the plant begins to set fruit. Septoria spots are small and round, with a tan center and dark brown border. When conditions are like we’ve had, there is a progressive loss of foliage. Monday a lady brought one of her plants to my office that was eaten up with septoria.
Bacterial leaf spot symptoms may be similar to other leaf spots, although the spots are generally smaller and more numerous. You can also use Daconil or copper based fungicides for septoria and bacterial leaf spot control.
At the first sign of leaf spot diseases, one the best things you can do is pick the infected leaves off as soon as possible to help prevent the spread of the diseases.
To also help with these and other leaf spot diseases, water tomatoes with a hose directed at the base so you will wet as little foliage as possible. If you must use overhead irrigation, water early in the morning and not late in the afternoon so the foliage will dry as quickly as possible.
Tomatoes that are planted really close together tend to get these leaf spot diseases worse than those farther apart. Why? Because of air circulation. I ask people if they have ever seen these big fans on bentgrass golf greens. They are there to provide air circulation and cut down on diseases. I know it is not practical for the most part, but your plants would probably have very few diseases if you set up a big fan to blow air across your garden.
Bacterial wilt is the problem when the entire plant wilts, almost overnight. There is no association with yellowing or spotting on the leaves. The plant will come back somewhat during the night but completely wilts during the heat of the day. The only thing you can do is to pull up the plant and get rid of it. You can cut into the stem of the plant and you will see that the stem center becomes water-soaked or brown and is sometimes hollow. Bacterial wilt prevents water and nutrients from being transported through the plant. This is a soil-borne disease and you should not plant tomatoes or any other solanaceous crop (peppers, potatoes, eggplant, etc.) in that spot for the next five years, if not longer. Having this problem in the soil is why many people have to plant their tomatoes in pots, filled with potting soil.
On Tuesday, I had a couple bring in a plant that had obvious herbicide damage. When I told them what my diagnosis was, the lady told me they had not sprayed anything in or near the garden, so that couldn’t be the problem. I then asked her if she mulched the tomatoes, and if so, with what. She had, and used grass clippings. She had used a weed-n-feed on her lawn, so that was the culprit. Never use grass clippings as mulch on tomatoes if a herbicide has been applied to the lawn.
Sometimes tomato leaves will curl. If no leaf spots or insects are associated with the curling, then there is nothing to worry about. The symptoms are usually seen when plants have a heavy fruit load. Environmental factors reported to promote symptoms include high temperatures, drought, and prolonged periods of wet soil conditions.
As tomatoes get close to ripening, you will see a lot of growth cracks if we continue to have a lot of rain. The fruit just grows too fast for its own good. Rapid growth is frequently promoted by a period of dry weather followed by heavy rain. Cracking is more severe in hot weather.
You cannot control the rain, but do your best to maintain even soil moisture with regular irrigation when it doesn’t rain.
If your tomato leaves are eaten or your tomato fruit is bored into by a worm, you may have tomato hornworms or fruitworms. Hornworms can strip a plant in one or two days. This is why it is important to monitor your garden daily.
Hand-picking of both of these worms is usually the easiest control.
If you cannot find them, Sevin, esfenvalerate, bifenthrin, or cyfluthrin also will provide good control.