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What’s bugging your tomatoes?

July 11, 2015
Nanette Londeree

Plucking big, ripe, juicy tomatoes right off the vine is a joy of summer. As one of America’s favorite vegetables — though botanically a fruit — this seemingly simple to grow plant can provide you with a bountiful crop of sweet, delicious tomatoes or challenge your gardening skills with variety of weird problems.

So, what’s bugging your tomatoes? Is it a pest, a disease or something completely different?

Tomatoes are South American natives that grow best with at least four to six hours of full sun and relatively consistent warm, not hot, temperatures. They’re also particularly sensitive to low night temperatures. We’ve had an overall cool spring punctuated with intermittent sizzling days. The roller coaster-like temperature swings can play havoc with your crop, and problems arising from environmental conditions are common.

Do you have healthy looking plants with no fruit? Temperatures below 55 degrees or above 90 degrees can cause tomato flowers to fall off or fail to set fruit; too much shade can also result in no fruit. Lush dark green abundant leaves with no flowers may be a result of too much nitrogen.

Good fruit production with poor color development is also linked to temperatures. Optimum color occurs between 65 and 70 degrees. Temperatures that are too high speed up ripening so fruits are more orange than red. Prolonged cool temperatures slow down ripening so tomatoes stay green. Sudden exposure to direct sunlight in hot, dry weather can produce sunscald — white, yellow or leathery brown patches on the sides of fruit.

Circular, concentric or radial cracks from the stem end of the fruit appear when differences between day and night temperatures are significant. Catfacing (misshapen or malformed fruit at the blossom end) causes fruit to pucker and have deep crevices; it can show up after abnormally cool or hot conditions. A small water-soaked spot near the blossom end of the fruit (blossom end rot) may be apparent when calcium is not readily available to developing fruit because of fluctuations in soil moisture.

Lots of critters enjoy tomatoes as much as we do, from tiny aphids and whiteflies to slimy slugs and enormous hornworms. A number of diseases also attack tomatoes; ones like early blight can decimate a plant.

So what’s a gardener to do?

While there’s not much you can do about the weather, you can provide your plants with plenty of sun and adequate, consistent water. Protect precious fruit on particularly hot days with shade cloth or screening material and avoid over-pruning the plants, allowing leaf cover to shield fruit.

And pests? Identify the culprit, then try the least-toxic approach to control. Aphids and whiteflies are sucking insects that cause curling, yellowing and distortion of leaves and produce sticky honeydew that attract ants. Prune out infested leaves and stems and discard. Knock the bugs off the plant with a strong stream of water. If you need something more, treat with insecticidal soaps or neem oils.

If slugs are a problem, remove their daytime hiding places, trap and dispose of them daily. Reduce moist surfaces by switching to drip irrigation or watering in the morning rather than later in the day.

Hornworms are huge (about the size of an adult’s thumb) and with their excellent camouflage, are often easy to miss. Their calling card is a plant nearly stripped of foliage. If you find them, hand pick and drop them in some soapy water.

Early blight is the most common fungal disease of tomatoes. Black or brown spots appear on leaves (usually older leaves first), stems and fruit. Avoid overhead irrigation; copper fungicides applied at the first sign of infestation and repeated every seven to 10 days may provide control.

Understanding common tomato problems can help you keep your plants happy, healthy and productive. If environmental conditions produce less than perfect looking fruit, don’t fret — just cut out the undesirable portion and indulge in summer’s tasty treat.

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