Archive for Thursday, July 31, 2008

Struggling tomato plants may still prosper

July 31, 2008


If you are having difficulties growing tomatoes this year, you are not alone. The weather is the largest factor in the tomato problems, playing a role in the overall health of the plants and influencing insects and diseases.

Cool, wet days in May and early June encouraged the plants to grow lush tops without developing much of a root system. Water was abundant; roots did not need to grow deep into the soil in search of moisture.

As soon as the rain stopped, most tomato plants realized that their root systems were insufficient to support their tops. Their leaves may have even rolled up in an attempt by the plant to reduce leaf surface area. The best remedy when something like this happens is to water deeply and infrequently and often enough to keep the soil moist but not saturated.

Next, the plants began to grow roots and recover from the shock of hot, sunny days, but the heat and humidity provided the perfect growing environment for fungi that colonize in the leaves of tomato plants. Since the plants were already stressed, they had a harder time than usual fighting off the disease known as Septoria leaf spot. Septoria spreads with splashing water, so limit overhead watering and use a mulch around the base of the plants to break up the water droplets.

Another disease, early blight, looks similar to septoria leaf spot but is less commonly a problem in our area. Both diseases are characterized by brown spots on the leaves that eventually make the leaves turn yellow and fall from the plant. Early blight spots often have concentric rings and may infect fruit or stems, while Septoria leaf spot is limited to leaves and is characterized simply by brown spots on the lower leaves. If infection continues to increase even with mulch and drip irrigation, a fungicide is necessary to control the diseases.

Once the fruit began to ripen, the bottoms began to rot. A brown or black spot begins right in the center of the bottom, then spreads outward, growing as the tomato ripens further. Known as blossom end rot, this decay is also physiological. The rot indicates that the plant is deficient in calcium, most likely because of moisture fluctuations in the soil. Adding calcium is unlikely to help at all - the plant simply cannot absorb the nutrient. Water deeply and infrequently to keep the soil moist but not saturated.

Just when the tomatoes had had almost enough, stink bugs and spider mites moved in and started picnicking. Stink bugs are shield-shaped, smell terribly when crushed between your fingers and leave very small white or yellow spots on the outside of the tomato fruit. The damage is purely cosmetic, and the spotted fruit is still safe to eat fresh.

Spider mites are harder to see and identify. They feed on the leaves, leaving the leaf surface with a slightly mottled or flecked appearance. Hold a white piece of paper under the leaves and shake the plant. If mites are present, you will likely see tiny spots running about on the surface of the paper. Even though they are tiny, spider mites suck the juices from the leaves and cause serious damage to the plant.

The tomato plants that have withstood all of the insect and disease pests so far are reluctant to set fruit now because of nighttime temperatures. When the temperature stays over 75 degrees at night, the plants lose water constantly. They have little energy to put into fruit production.

Although I may have made tomato production in Kansas sound like a miracle, growers are still producing a few. I have a feeling that in a few weeks production will reach the normal truckload proportions, but if you have tomatoes right now, consider yourself one of the lucky ones.

If you have questions about your tomatoes or other gardening matters, call a Douglas County Extension Master Gardener at 843-7058 or send e-mail to Master Gardeners run the hot line from 1 p.m. to 4 p.m. MondayFriday, but you can leave a message anytime.

- Jennifer Smith is the Douglas County Extension Agent-Horticulture for K-State Research and Extension.


lounger 9 years, 10 months ago

Our Tomato's are doing pretty good here in east Lawrence. The Potato's have been hit with blight though.

Chrissy Neibarger 9 years, 10 months ago

My cherry tomatoes are going crazy. I planted about 6 plants and am pulling off about 25 every other day. I guess I'm one of the lucky ones.

Richard Heckler 9 years, 10 months ago

Thanks Jenifer. The other day I placed a shade screen over the tops of our container grown plants which seems to be helping. Rather than staking our tomatoes, allowing them to sit on one side of our picnic table while the plants grow over the top seems to be working thus far. Experimental science.

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