By Guest Columnist Bonnie Coblentz
Successful Mississippi gardens are filling up with beautiful tomatoes, but unless gardeners stay alert and act, these plants can succumb to summer insect pests and diseases.
Blackened areas at or near the bottom of the fruit are most likely blossom-end rot. While not a disease, this problem can ruin fruit. The solution is to make sure plants get enough calcium and never let them dry out between waterings. Mulch helps with water retention. Wilted plants can be caused by a number of diseases, but make sure plants are getting enough water -- an inch to an inch and a half each week, whether from the hose or natural rainfall, advises Rick Snyder, MSU Extension vegetable specialist working from the Truck Crops Branch Experiment Station in Crystal Springs. When wilt is not caused by a lack of water, it can indicate Southern blight, bacterial wilt, tomato spotted wilt virus or several other diseases. One of the most common diseases on tomatoes is early blight indicated by brown spots on lower leaves that have concentric rings in them, with lower leaves turning yellow and eventually falling off as it progresses. Left unchecked, it will move up the plant with spots, yellowing and leaf drop. To prevent the diseases and keep insects at bay as well, gardener Blake Layton, also an entomologist with the Mississippi State University Extension Service, recommends spraying with a mix of three common chemicals -- permethrin, chlorothalonil and copper octanoate. Mix the ingredients with water in a hand pump sprayer and apply to vegetable gardens, spraying on tomato plants starting one to two weeks after transplanting and continuing every seven to 10 days through the season.
“Pick first, spray later that day, wait two to three days before picking again, and wash or peel fruit before eating,” Layton says. “As long as I maintain this spray schedule, we enjoy good insect and disease control. Once I start missing a few sprays, pest problems increase and fruit quality declines drastically.”
Tomatoes are primarily wind-pollinated, but bees do visit tomato blooms. So spray as late in the day as possible to protect them, as bee activity usually declines near dusk.
The products containing ingredients recommended by Layton are readily available at local seed and feed stores. Layton says to read labels carefully to be sure the product you buy is for tomatoes, and mix and apply according to directions. Permethrin controls fruitworms, hornworms, stink bugs and leaf-footed bugs, while the other products are for disease control. Each of the ingredients has a zero-day pre-harvest interval, but Layton suggests allowing a couple of days to pass before resuming harvest. Layton says it is wise to alternate the products used to maintain effective disease and insect control. This practice helps prevent the development of resistance. “Mancozeb is a good alternative for chlorothalonil, but because it has a 5-day pre-harvest interval, it is best used in early season,” he says. “If caterpillar pests are your only insect concern, Spinosad is an effective alternative for permethrin, but Spinosad does not control stink bugs and is best used in early season when stink bugs numbers are low.” For those interested in gardening organically, there are several organic fungicide products. Organic insecticides that contain Spinosad do a great job controlling fruitworms and hornworms, but there are no effective organic options for controlling stink bugs or leaf-footed bugs, other than hand-removing the pests. The MSU Extension Service offers information at http://extension.msstate.edu/publications. Search for Extension Publication 2347, “Insect Pests of the Home Vegetable Garden,” or Extension Publication 3175, “Common Diseases of Tomatoes.” EDITOR’S NOTE: Bonnie Coblentz is a writer for the Mississippi State University Extension Service.