The first tomatoes of this season are ripening in our gardens just as pest insects attack, diseases take their toll and nutritional deficiencies become obvious. Home gardeners love their tomatoes. Fortunately, most of the problems are easily solved, allowing worried gardeners to enjoy the crop.
Pest insects attack stressed plants. Our summer heat stresses tomatoes which are then prone to infestations of whiteflies and aphids. Curling leaves on tomatoes are a sign of whitefly and aphid damage. Sticky yellow traps will catch whiteflies; aphids can be washed off plants.
Use insecticidal soap to reduce heavy populations but avoid applying chemical pesticides which kill beneficial insects including green lacewings and small striped syrphid flies that feed on many pest insects, their eggs and their larvae.
Leaffooted bugs are a type of stinkbug and are fairly recent pests. They are large, up to one-inch long, with funny-looking leaf-shaped rear legs. Leaffooted bugs suck out the juices of ripe tomatoes leaving star-shaped yellow spots behind. Hand pick leaffooted bugs, wearing gloves and clean up weedy areas where they lay their eggs. The damaged fruit is still edible.
The UC Davis website, www.ipm.ucavis.edu, has good photos of leaffooted bugs to help with identification.
Tomato hornworms are big, green, scary-looking caterpillars that can defoliate a tomato plant overnight. Monitor your plants, looking for chewed leaves and black frass or hornworm droppings.
Handpick tomato hornworms at dusk when they are feeding or apply Bt or Bacillus thuringiensis which is a very effective control of all caterpillars. Bt is nontoxic to vertebrates; the fruit can be eaten immediately after spraying. Brand names include Safer’s Caterpillar Killer and Monterey’s Bt.
Tomatoes need consistent fertilization and consistently moist soil. Reduce stress on tomato plants by deep watering when the top inch or two of soil is dry and by monthly feedings of a couple of tablespoons of a low number granular fertilizer which releases nutrients slowly over a longer period of time.
Blossom end rot in tomatoes causes the bottom of the fruit to turn grayish black. A lack of calcium (and inconsistent irrigation) lead to blossom end rot. Add bone meal when planting or fertilizing or use a fertilizer that contains extra calcium – at least 3 percent. The fruit is edible – just cut out the discolored areas.
Both fusarium and verticillium wilts are fatal fungal diseases which cause the lower leaves of tomatoe plants to turn brown and die. The leaf browning continues up the plant, often on only one side, and the plant eventually dies.
The wilts are caused by soil-born fungi that plug up the water and nutrient flow inside the stems. Diseased plants should be removed and put into the green waste bin; home compost piles seldom get hot enough to kill the fungal spores.
Before buying tomato seeds or transplants, check labels for the letters V and F which indicate that the plants are resistant to the wilts.
Rotate tomato crops within the planting bed yearly to avoid a buildup of disease pathogens in one area. Solarizing the soil in planting beds where wilts were evident will kill the fungal spores.
Send Elinor Teague plant questions at email@example.com or firstname.lastname@example.org (“plants” in the subject line).