Whether the fruit is destined for salsa, a salad bowl or the "T" in a BLT, tomatoes are the most popular crop grown by backyard gardeners.

They are also prone to a variety of diseases and pests. One look at the list of tomato ills, and you'll get the impression that all manner of nasty little fungi and insects are lurking in the soil and air, ready to ambush roots, stems, leaves and fruit. Good cultural practices, such as crop rotation, mulching, proper spacing, removing and destroying infected plant debris as well as planting resistant cultivars can prevent their attack.

Septoria leaf spot

What it is: The most common foliar disease occurring in Iowa, according to Iowa State University Extension horticulturists. This fungus appears as small water-soaked spots that become circular spots that are light in the center with dark edges. Spores look like black specks that rain or watering can quickly spread to other leaves. Heavily infected leaves turn yellow, dry and wither, then fall off. It can attack any time during the growing process.

How to control/prevent: Plant disease-resistant varieties; leave plenty of room between plants to improve air circulation at maturity; water at base of plants in morning hours to allow drying time; rotate crops; don't mess around with plants when foliage is wet or damp to avoid spreading spores; remove plant debris; fungicides also are available.

Early blight

What it is: This fungus appears as black or brown spots that may merge to form blotches, and sometimes concentric circles form inside the spots. Spots first appear on lower leaves, which turn yellow and dry up. The fungus may attack fruit, causing black, sunken areas. It spreads rapidly in warm, damp weather, especially after fruit is set.

How to control/prevent: Plant resistant cultivars; harvest all ripe tomatoes daily; follow same practices as preventing septoria leaf spot.

Anthracnose

What it is: Caused by the fungus Colletotrichum coccodes, anthracnose is another common Iowa disease. Green fruit can become infected, but usually symptoms can be seen on ripe or ripening fruit as small, circular indented spots in the skin. Expanding quickly, spots develop dark centers or rings of dark specks, which are spore-producing bodies of the fungus. In wet, humid conditions, these bodies produce large numbers of spores and give the diseased areas a creamy to salmon-pink color. This means decay has penetrated deeply into the tomato flesh and may rot completely.

How to control/prevent: Destroy discarded plant material (fungus survives on diseased vines, in soil and seeds); spores establish themselves on leaf spots caused by early blight or insect damage and can easily spread by rain splash. Wet, warm weather causes the disease to spread. Control measures are the same as septoria leaf spot and early blight.

Fusarium wilt

What it is: A soil-dwelling fungus, attacks only certain tomato cultivars. Infected plants have yellow, wilted leaves that progress upward from the stem. Frequently, early symptoms are seen on one side of the plant. Leaves drop, and affected plants usually die without producing much fruit.

How to control/prevent: Plant resistant cultivars; look for letter "F" after the variety name; even resistant varieties may be infected, but not severely enough to reduce harvest; follow good cultural practices such as crop rotation.

Verticillium wilt

What it is: V. wilt can attack more than 200 plant species, including potato, pepper, eggplant, strawberry, watermelon and radish. Lower leaves are first affected and the disease progresses upward. Yellow blotches appear on lower leaves, the leaves then wither and drop off. Infected plants may survive the growing season but the plant is stunted and yield is reduced.

How to control/prevent: Plant resistant varieties (look for "V" after cultivar name); follow good cultural practices, particularly crop rotation.

Late blight

What it is: Not common in Iowa, late blight can occur in mid- to late August if there is persistent wet, cool weather or nights that cause heavy dew, and it will devastate plants.

How to control/prevent: Same as septoria leaf spot

Blossom end rot

What it is: It's ugly, for one thing, and first appears as black spots on the fruit's blossom end. The spot gradually increases in size, causing only localized injury, but it opens the door to other organisms that infect and rot the fruit. It often shows up in hot, dry weather on early fruit.

How to control/prevent: It is caused by a calcium deficiency, but adding more calcium isn't the proper response. To prevent, horticulturists say a steady growth rate and consistent, ample moisture will maintain a steady flow of calcium in the soil to the fruit. Mulch to conserve moisture. Avoid heavy applications of nitrogen-rich fertilizers. Remove infected fruit.

Weather/chemical damage

What it is: Cracking, thin or tough skin is due to weather conditions; poor and blotchy yellow/orange color occurs when temps rise above 95 or below 60. "Cat-faced" fruit occurs when cold weather at fruit set distorts and kills cells, causing deformities, most common in beefsteak-type tomatoes. Sunscald occurs when green fruit is exposed to the sun, killing tissue and setting up invasion by other organisms which rot fruit. Tomato plants are sensitive to broadleaf weed killers and can cause warped, thicker fruit.

How to control/prevent: You can't control the weather, but consistent watering, prevention of foliar diseases and other good practices can help. Chemically damaged fruit should be discarded.

Failure to set fruit

What it is: High day and night temps reduce flower production in tomato plants. If night temps are above 70, flower production and pollination is impacted. The most ideal temps for fruit set are 58 to 68 at night.

How to control/prevent: Just roll with the punches.

Insects

Biggest pests: Cutworms and tomato hornworm. Cutworms are nocturnal and not exclusive to tomatoes. Make a cutworm collar from a plastic milk carton or paper cup. Cut off both ends and turn upside down over the plant, buried 1 1/2 inches in the soil.

The sphinx moth deposits the eggs which hatch into hornworms, which immediately begin eating foliage and tomatoes. Inspect plants daily and remove the little buggers.

Source: Iowa State University Extension