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10/23/2008

Tomato Diseases

Ozarks Gardening
Jim Long

Tomato Problems and Some Solutions

It’s been a banner year for diseases on everything from tomatoes and roses to peppers and fruit. All of the excess moisture has cultivated fungal problems in the soil, on the leaves and on fruit such as plums and peaches. Readers who normally don’t have such problems on these crops in a normal year, say they have had lots of problems this season.

On tomatoes, as I’ve written before, tomato verticillium wilt begins in early spring, but is spread rapidly by aphids. I’ve described in this column and on my garden blog how I control the aphids, which slows down or stops the progression of this most common tomato disease.

Verticillium wilt causes the leaves to turn yellow and dry up, starting at the bottom of the plant and working upward. It’s caused by a soil-bourne fungus and can affect many different vegetables, and can stay in the soil for many years. It’s why crop rotation is important, meaning not growing tomatoes and peppers in the same soil bed for more than four or five years. Verticillium wilt inhibits the plants ability to take in water and nutrients, which eventually kills the plant.

There are some treatments that seem to help tomatoes, at the same time helping other soil borne fungal problems. This treatment is reported to help black spot on roses as well as damping off of plant seedlings early in the year and is beneficial for some kinds of lawn grass fungal problems, as well. What’s the magic formula? Just good old cornmeal.

Researchers at Texas A & M Research Station in Stephenville, Texas noticed that a peanut crop planted following a crop of corn didn’t suffer the expected fungal diseases they usually encounter with that crop. Additional research showed that cornmeal contains beneficial organisms that are as effective, possibly more, as are chemical fungicides. Evidently cornmeal attracts a member of the Trichoderma fungus family, which is a beneficial fungus that kills off disease causing fungi in the soil.

According to their research, and others who have used this method, you should work 2 pounds of cornmeal into the soil for every 10 ft. by 10 ft. area, then water well (or, in the Ozarks, wait two days before it rains again). There’s considerable discussion on the web about whether you should use horticultural cornmeal or food grade cornmeal from the grocery store.

The differences are these: Food grade cornmeal from the grocery store is only the interior, starchy part of the corn kernel, without the hard, outer shell. It’s slightly more expensive and some sources say it just doesn’t work as well as horticultural cornmeal.

Horticultural cornmeal is cheaper to buy, can be found in feed stores and any other stores that sell soil amendments and garden supplies, and includes the entire corn kernel. People who have used this say the addition of one or two pounds of dry molasses (available at feed stores) per 100 square feet area works even better.

So here’s what I plan to do in my tomato and pepper beds this fall and winter. After frost and after I’ve removed all the dead plant debris, I’m plan to scatter horticultural cornmeal and some dry molasses on the soil and till it in. Then during the winter, I’m going to use Alden Hembree’s tomato disease control method (which I believe came from garden guru, Jerry Baker): Mix 1 tablespoon of shampoo and 1 tablespoon of Clorox into 1 gallon of water. Mix and spray the soil of your tomato bed monthly until spring planting time.

Next spring, when I’m ready to till up the tomato beds once more before planting, I plan to spread more horticultural cornmeal and dry molasses on the soil just before turning it over. I’m also going to use that method around my roses that suffer from fungal diseases and see if it helps. If Texas A & M says it works as good or better than chemical controls, I’m all for it. (Most sources say one application per year is enough, but that a second application isn’t harmful).

Both methods hold great promise and lots of people swear they work, so I’m going to use both and see what happens. One benefit of the cornmeal addition is that it adds a bit of nutrients to the so, as does the addition of dry molasses.

Cornmeal also works to eliminate algae in water and speeds up the decomposition in compost piles. Just don’t confuse horticultural cornmeal with corn gluten meal. Corn gluten meal is used as a weed control and prevents weed seeds from germinating and is a different product altogether.