Archive for Thursday, August 2, 2007

The Green Thumb

August 2, 2007

Plants were late to bloom and even later to set fruit this season. Now as the red and green globes emerge, I cannot wait for my first BLT sandwich. There seems to be a problem, though. Some of the leaves near the base are turning brown, and some of the green leaves have black spots on them. The fruit, too, looks unusual. There are yellow splotches on the red fruit and black spots on the green fruit. What is wrong with my tomatoes?

The first thing is water. Make sure the tomatoes have a good and regular supply of water. One to 1 1/2 inches per week applied on the same day of each week is great. Amend that if we get rain, but measure the rain in your area, as Lawrence is known for spotty showers and surging downpours.

A brown leathery patch on the bottom of the tomato is called "blossom end rot." This is the most common problem you'll see right now. It is caused by a calcium deficiency, and no amount of chemical application will stop it. It is a physiological disorder, resulting from a shortage of available calcium. End rot grows quickly and allows the invasion of secondary organisms, completely rotting the fruit.

Warm temperatures cause rapid top growth and limited root growth. The calcium that is taken up goes to the growth and not the fruit. Secondary fruiting is not usually affected. This is why regular watering, to encourage and maintain strong roots, is advised. The good portion of the affected fruit still can be used.

There are diseases, fusarium and verticillium wilt, that live in the soil and enter the plant through the roots. The symptoms are all but the same. Older leaves and those closest to the ground dry up first. This may progress to either kill the plant or only provide you with small fruit at best. There is no corrective control. The disease is in the ground and now in your plants. Next year, buy disease-resistant varieties and rotate your crop. Rotation means planting 15-20 feet away and not returning to the diseased area for 4 to 6 years. Remove and destroy diseased plants, and fertilize correctly to suppress the disease.

Walnut wilt is common. Tomato, potato, alfalfa and several other herbaceous plants are affected by the chemical in walnut trees -- juglone. If your plant is in an area that has, or did have, walnut trees, this many be an issue. The wilt appears as stunted growth, wilted leaves and small fruit. Note, too, that if you used walnut leaves or hulls as mulch, the juglone is present.

Just after blossom set, blight and septoria leaf spot may affect the plant. Browning leaves with strong lesions is blight; green leaves with black spots is septoria. These overwinter in plant debris, even that tilled into the ground. Sanitation is the best control. Fungicides such as a bordeaux mixture, mancozeb or chlorothanlonil are recommended. These fungicides require repeated application every 7-10 days throughout the growing season.

Good sanitation practices always are important with fruiting plants. Clean up and remove all debris when the plants die back. Tilling in destroys some, but certainly not all, of the diseases that are present. Tomato cages (any vine support) may have disease spores on the rusted wire surface, wood crevices or bits of remaining vine left on the cages. Cages left out in the open usually will be subject to the disinfecting properties of sunlight and weather extremes. A 60:1 Clorox water mix is a great disinfectant for cages and tools.

Low-hanging fruit also is a target for small animals such as squirrels or rabbits. Pick these first. Make it a challenge for the squirrels, and give the rabbits NO opportunity.

-- Stan Ring is the horticulture program assistant at K-State Research and Extension -- Douglas County. He can be reached at 843-7058 or Sring1@oznet.ksu.edu.

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