Seven Factors Help Reduce Diseases that Plague Tomatoes

First posted on 05-11-2010

While tomatoes are popular and easy to grow, both the home gardener and commercial grower find it challenging to maintain productivity throughout the growing season.

Diseases such as Septoria leaf spot and early blight affect the lower portion of the tomato plant and shorten productivity.

Environmental conditions play a role in presence and severity of certain diseases. Abundant rainfall and high humidity pose a threat to severe blight conditions.

Little resistance to blight is available through variety selections, so proper cultural management techniques are important for control.

“Disease management must start early in the season. Once you have the problem, control is difficult,” said Patrick Byers, horticulture specialist, University of Missouri Extension.

One key factor is site and ground selection. If possible, a three to four year rotation with crops outside of the Solanacea family should be followed. Potatoes, tomatoes, peppers, and eggplant are within the same family and these crops should not be included in the rotation planting cycle.

Second, to help manage blight, disease free plants should be planted in fertile soil based on the proper planting dates.

“Plants stressed prior to planting or following planting may lead to disaster,” said Byers.

Third, it is important to avoid ground contact with plant foliage.

“Stake tomato plants and mulch underneath them to reduce the incidence of blight transfer from the soil to the plant,” said Byers.

Blights are soil borne diseases and anything that inhibits the transfer of spores from the ground to the plant will help increase the chances for control, according to Byers.

Fourth, good air circulation around the plants (aided by proper spacing and pruning) will reduce blight infections. If room allows, 30 inches between staked indeterminate plants is suggested. Basic pruning is the removal of side shoots or suckers when they are three to four inches long.

Fifth, avoid overhead irrigation during the evening. Trickle irrigation or bottom irrigation is best to avoid moisture contact with the leaves reducing conditions ideal for disease.

Sixth, if all procedures fail to control blight, be prepared to replant transplants about the middle of July for a fall crop. Typical summer conditions of heat and dry weather result in less incidence of disease thus providing productive plants until frost.

Seventh, chemical fungicide application is often needed but application timing is crucial. Home gardeners may use chlorothalonil (Daconil) at seven to 14 day intervals.

For more information, or answers to your specific lawn and garden questions, contact Byers or the Greene County Master Gardener Hotline at (417) 862-9284. Guide sheet 6203, “Common Diseases in the Home Garden” is also available online at extension.missouri.edu.

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