Tomato plants need care, but not too much

Published 12:00 am Sunday, June 7, 2009

There are two calls we have been receiving in abundance over the last two weeks. One involves tomato problems and the other the annoying gnats that are consuming our area recently. Both of these issues deserve full attention, but unfortunately the tomato calls have been a little more abundant, next week we will target gnat control but hopefully they start declining by then.

Q: How much should I fertilize my tomato plants?

A: Tomato plants are in the production phase now and all sorts of problems are showing up. All the rain we had in May has leached nutrients, particularly nitrogen, out of the soil and some plants are pale, small, and prone to diseases. Many tomato plants will respond to additional fertilizer, but don’t overdo the rates. Overdosing fertilizer only causes a multitude of additional problems. Two pounds of calcium nitrate or ammonium sulfate per 100 feet of row is sufficient. This translates to approximately one tablespoon per plant for those of us with only a few plants.

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Q: Why aren’t my tomato plants putting out any fruits?

A: When we start to have big healthy plants with no fruit on them we often have reason for concern. However, the problem sometimes comes from to over management. When you over fertilize tomatoes with high nitrogen fertilizers such as Miracle Grow you often see this problem. The plant remains in the vegetative state longer than usual and continues to grow stems and leaves but no fruit. Tomatoes are self pollinators so they do not require bees to pollinate unlike the vine crops such as cucumbers or watermelons. Just be patient and slow down on the fertilizer and the tomatoes will come.

Q: How can I tell if my tomato has a disease, fungus or insect problem?

A: Bacterial wilt is caused by a soil dwelling bacteria and it causes a sudden collapse of the tomato plant. The plant may show a few drooping new leaves one day and totally collapse within two or three days. Verifying bacterial wilt as the culprit is done by cutting the stem and placing it in a clear glass of water. The bacterial will stream out of the cut stem within five minutes and look like milky steam. Bacterial wilt organism are extremely difficult to remove from soil since they attack over 200 species.

Southern stem blight has also been found throughout the county. To test for southern stem blight, find a fading plant and cut off the stem and look inside it. If the stem is hollow you have it. This is a fungus and spraying a fungicide on remaining plants can help control this from reoccurring.

Septoria leaf blotch, bacterial speck and bacterial spot are all characterized by black lesions or spots on the leaves. The bacterial diseases have round black spots, while leaf blotch has larger spots that typically have dark edges and light centers. Fortunately they are all managed with applications of copper based fungicides.

If the plant looks like one leaf or one side is yellowing, you may have Fusarium fungi. These live in the soil and attack the plant’s roots and crown. One test for Fusarium is to cut the stem at an angle just above the soil surface and look for dark brown discolorations. Fading leaves may also be Verticillium fungi. The plants wilt during the day and recover at night, but the lower leaves become light green to yellow and splotchy between the veins, while Fusarium is an overall yellowing of one leaf. Once the plant show signs of infection, it takes a minimum of seven years for the population of fungi in the soil to decline enough to plant susceptible tomatoes there again. Thankfully, many modern tomato varieties have tolerance to Verticillium and Fusarium fungi, so changing varieties to ones with F’s and V in the string of letters behind the name can allow you to continue growing tomatoes.

Don’t confuse Fusarium, bacterial and Verticillium wilt with the other wilt we talk about with tomatoes. These organisms live in the soil and attack the root and vascular systems. Tomato Spotted Wilt is caused by a virus spread by thrips.

David Carter is the director of the Adams County Extension Service. He can be reached at 601-445-8201.