Extension Educator, Horticulture
The first hint of spring brings visions of voluptuous vegetables to our dreams -- armloads of tomatoes and truckloads of zucchini. However unlike our dreams all is not perfect in the summer vegetable garden.
Our cooler July weather meant slow ripening tomatoes. In contrast dry windy days with temperatures above 95 degrees F causes tomato and pepper flowers to fall off and therefore no fruit develops.
Our weather has been perfect for many fungal leaf spot diseases. Common diseases of tomatoes are septoria leaf spot and early blight. Both start as spots on lower leaves which can quickly yellow and then die but remain attached. Septoria causes small water-soaked spots. These spots become circular to angular with dark margins and grayish white centers. Early blight causes small brown leaf spots with a target-like series of concentric rings in each lesion. Vine crops such as cucumbers and melons may also have leaf diseases such as powdery mildew and anthracnose.
Although we can't control the weather, we can control our garden practices. Here are some basics for controlling disease in the vegetable garden:
Plant resistant varieties – Not all diseases can be lessened with resistant varieties, but it's worth researching possibilities before planting.
Feed the soil – Add compost at the beginning and end of the season.
Improve air circulation – Most infectious diseases need surface moisture on the leaf or stem. Anything we can do (short of a giant fan) to dry the leaves will help such as caging or trellising. Give plants plenty of space. After my tomatoes and I suffered through years of tomato diseases, I finally quit planting seven tomato plants in an area fit for only four plants. I've seen a marked decrease in tomato diseases. I guess old gardeners can learn new tricks.
Water plants properly – Most plants need one inch of water a week through irrigation or rain. Consistent soil moisture is key to healthy plants and good vegetable production. For example tomato cracking and blossom end rot can be more severe with fluctuations in watering. Water the soil and not the plants. Keep leaves as dry as possible through soaker hoses and watering early in the day.
Use mulch - Mulch vegetable plants with most any organic material such as straw, compost or thin layers of grass clippings to a depth of 2-3 inches. Mulch reduces weed seed germination, helps to retain soil moisture, alleviates high soil temperatures, and adds organic matter.
Practice garden sanitation – Some leaf disease can be managed or at least their progress can be slowed by removing infected leaves as soon as the spots appear. To lessen disease spread do not work around plants when leaves are wet. Since many diseases can hang out on old leaves and stems to infect plants next year, remove and destroy infected leaves, stems and unharvested fruit at the end of the season. Bury in an unused part of the garden or start a compost pile specifically for ornamentals and not vegetables.
Use fungicides appropriately - Most fungicides are preventatives so they have to be applied before infection occurs or early when disease first appears. Not all fungicides are labeled for edibles and not all fungicides will control all diseases. One fungicide application rarely helps. Applications are usually needed at 5- to l0-day intervals during humid or wet weather. Be sure to read and follow all label directions especially the days between application and harvest.
If diseases are plaguing your plants, contact your local UI Extension office for proper disease identification and appropriate management strategy. Samples can also be taken to UI Plant Clinic 1401 W. St. Mary's Road Urbana, IL 61802 PH: 217-333-0519
For more info on vegetable problems: http://urbanext.illinois.edu/vegproblems/
Gardeners have to be patient optimists. Of course there is always the local Farmers Market. http://www.agr.state.il.us/markets/farmers/