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Give your tomatoes TLC to combat disease, minimize pests

June 4, 2016
Anne-Marie Walker

Reaching to harvest a few tomatoes for dinner, I heard the unmistakable warning rattle of a rattlesnake. Quickly I withdrew my hand and stepped back. It had been a hot day and undoubtedly, the dense foliage of tomato plants afforded cool relief for the reptile. In that rather dramatic moment, I learned the importance of close observation of the wide array of inhabitants in our gardens.

Here’s a primer to increase awareness of what needs to be done to grow healthy tomatoes, combat diseases and minimize pest problems.

Remember the fun of selecting your tomato plants in April, planting in May and suddenly June arrives. Transplanted tomatoes grow quickly and need applied fertilizer every four to six weeks. If you planted in containers, remember that because you water more frequently, you need to fertilize even more often as nutrients wash out.

The University of California recommends fertilizing tomatoes with fertilizer containing Nof 3.5 to 5 percent (nitrogen for growth), P of 3 to 4 percent (phosphorus for root growth, flowering and fruiting) and K of 1.5 to 3.5 percent (potassium for overall growth).

Water your tomato plant properly at ground level to minimize foliar diseases. As fruit sets and is 1 inch and growing, you need to water as required for plant growth. New transplants should be watered 2 to 3 inches deep. When plants have matured they can develop roots as deep as 4 feet, so it is important to water them once every 10 days. Soil probes can help insure you are watering sufficiently.

By June, your tomato plant is classified as “bloom to early fruit set” and should be tied every 12 inches to a central stake, surrounded by a cage or additional poles. The transplant probably has plenty of side shoots; the growth that occurs at every node between the stem and the leaves. Allowing suckers to develop can help increase yield and lower the incidence of sunscald and large cracks on fruit that can occur during periods of high temperature and sunlight. Avoid a tangled mass of vines by pruning some suckers to allow air circulation that can decrease potential for disease.

Begin monitoring for stinkbugs, the beetles that suck on fruit and stink. The best defense against stinkbugs is to weed and clean all debris from your property. Another pest often striking at this stage is a russet mite, causing leaf and stem bronzing. Encouraging ladybugs and/or use of insecticidal soap gets rid of mites. Also, watch for more serious problems, including verticillium wilt and fusarium wilt — both are fungal diseases causing a general yellowing of foliage. The best defense against wilt is selection of disease-resistant tomato varieties; F means resistant to fusarium, V means resistant to verticillium and N is resistant to nematodes — tiny worms that work at plant roots retarding healthy growth.

If you see bronzing leaves and chlorotic blotches on fruit, thrips blown by wind have infected your tomatoes with tomato spotted wilt virus. Defensive measures include weeding your garden and removal of infected plants. Finally, watch for aphids and hornworms (pick them off) and fruitworms that are caterpillars (larvae) of brown moths. Naturally occurring beneficial insects such as pirate bugs, praying mantises and wasps are the predators of fruitworms.

Tomatoes mature on average within 60 to 80 days, finally rewarding you with healthy, tasty tomatoes. Do continue to watch for diseases, including wilts and late blight and keep a record of pests and diseases for better harvest this year and planning for next year.

To learn more about combating tomato diseases, go online to the UC Integrated Pest Management Program at www.ipm.ucdavis.edu and type “Tomato IPM” into the search box.

Growing tomatoes may not be problem-free, but the taste of a homegrown tomato makes all your work and vigilance worthwhile.

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