How to care for your tomatoes during the hot summer days | The Fresno Bee

Central San Joaquin Valley gardeners are justifiably proud of their bountiful tomato crops. Our tomato season goes into full swing at the end of June and the first weeks of July when both early- and late-ripening varieties are ready to eat – and when problems become obvious.

Here are a few common summertime tomato problems you may find in your garden.

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Cracking and cat-facing – As temperatures rise above 90 degrees in summer, tomato flesh expands faster than the skins, causing the skin to crack; the cracks immediately heal, leaving narrow scars. The cracking is normal and does not usually affect the fruit quality, just its appearance. Keep the soil consistently moist – tomatoes need at least 2 gallons of water a week.

Cat-facing is caused by low temperatures, below 50 degrees, during flowering and fruit set. We did have cooler than normal spells this spring so you may see tomatoes in your garden that have large cavities and cracks at the bottom or blossom end of the fruit. (To some the deformations resemble a cat face – hence the term). The cavities and cracks can make the bottom portion of the fruit inedible.

Sunscald and solar yellowing – Tomatoes that receive too much sun exposure can turn yellow and leathery on the sun side. The unaffected portions of the fruit are still edible. Maintain sufficient leaf cover by increasing levels of nitrogen (slightly) in fertilizers and by not removing smaller branches that grow in the axils or branch junctions.

Summer’s high-intensity light is the cause of solar yellowing. The red pigment fails to develop when tomatoes are grown in open areas where they can receive up to 14 hours a day of sunlight.

Provide shade for scalding or yellowing tomatoes, especially during midday and hot afternoons, with shade cloth structures or moveable market umbrellas. Monitor sun and shade patterns since tomatoes need at least six hours of full sun.

All vine, no fruit – Tomatoes, especially vine or indeterminate varieties, are sensitive to nitrogen in fertilizers and will rapidly produce more vine than flowers if nitrogen levels are too high. Switch to lower nitrogen (less than 5 percent) or apply higher phosphorus (the second number on the label) foods or compost until green growth slows and flower production resumes. Vine-type tomatoes continue to produce over the long summer season; bush or determinate tomatoes have a shorter productive season but are less sensitive to excess nitrogen.

Lower leaves dying – Verticillium wilt is a soil-borne fungus that infects tomatoes as well as many other plants. The fungus blocks water and nutrient uptake. Lower leaves turn brown and die; then the entire plant dies from the bottom up. Symptoms become more severe when plants are water- and heat-stressed.

Buy tomatoes that are labeled as being resistant to verticillium wilt. Look for the letter V on the label. Rotate summer vegetable crops every year to prevent the buildup of the fungus in the soil and pull out dying plants as soon as the disease is obvious.

Soil solarization, using the heat of the summer sun, can significantly reduce the numbers of fungal spores in the soil. Check the UC Integrated Pest Management website (ipm.ucanr.edu) under soil solarization for complete, easy instructions.