Plant Pathology Infobytes
June 15, 1999
Disease Control Tips for the Home Garden
Don't let blights, leaf spots, and other diseases get the upper hand on your vegetable crop. Home gardeners should observe their plants daily for evidence of diseases. If problems are spotted quickly enough, control action can often be taken in time to keep diseases at low levels, thus preventing major losses in vegetable crop yield and quality.
Preferably, a fungicide application program should be started before symptoms of disease are noted on tomatoes, beans, peppers and other garden crops. However, if you've neglected this chore, start a spray program with a recommended fungicide at the first sign of disease symptoms.
If several days of rainfall occur, fungicide application becomes even more important, since most garden diseases are favored by rainy conditions and extended cloudy weather. Anthracnose, rust, mildew, and other blights develop rapidly when plants are wet, and regular applications of a foliar fungicide are necessary for effective control of these diseases.
Several types of sprayers can be used in the home garden for fungicide application. Hand atomizers are inexpensive and are well suited to smaller gardens. They vary in capacity up to about three quarts. One type operates with a hand plunger and another with a squeeze handle. You can even use a discarded and well-rinsed Windex bottle if only a few plants need spraying.
Hose-on applicators fit on the end of a garden hose. As the water comes out, a suction mixes the material with water. Considerable water and a concentrated fungicide solution are required, which makes liquid fungicide formulation more suited to this type sprayer. Wettable powder formulations don't work as well when applied with a hose-on applicator.
Knapsack type sprayers are carried on the back. The sprayer has a pump with a large air chamber and agitator mounted in two- to five-gallon tank. The handle of the pump extends over the shoulder or under the arm, making it possible to pump with one hand and spray with the other.
Compressed-air sprayers range in capacity from one to five gallons. Many are made from galvanized steel, but those made of plastic or stainless steel are noncorroding and will last for years if properly maintained. When applying a wettable powder fungicide, shake the sprayer frequently to keep the fungicide in suspension.
After each use, rinse the sprayer with water, and never apply a fungicide in a sprayer that has been used for herbicide application. It is very difficult to completely remove herbicide residues, and frequently enough are carried-over in the sprayer to cause later plant damage. Thus it's best to use one sprayer for fungicides and insecticides and a different one for herbicides.
What about applying fungicide and insecticide combinations? Most fungicides and insecticides are compatible. This means they can be mixed and sprayed onto plants at the same time, thus avoiding the need for separate applications. But there are exceptions, so check product labels closely for statements that warn against this practice.
To obtain the best coverage, use a cone type nozzle and spray the upper and lower surfaces of leaves, and spray from several directions. Adding a teaspoonful of spreader-sticker (available at most garden supply stores), will help in spreading the spray solution to improve coverage and reduce fungicide wash-off during spring and summer showers.
The key to successful foliar disease control with fungicides is (1) early application to prevent early season plant infection and rapid spread of disease, (2) selection of the proper fungicide (not all fungicides will control the same diseases), (3) through coverage of all foliage and other plant parts, and (4) repeated application.
Several fungicides can be used in the home garden, but those containing chlorothalonil as the active ingredient control a wider range of garden diseases and are cleared for use on more crops than other types of fungicides. Read product labels to make sure that you are purchasing a fungicide with the desired active ingredient. Mancozeb and maneb containing fungicides also offer "broad spectrum" disease control and are cleared for use on many garden vegetables. Copper-based fungicides are gaining in popularity, and are popular with organically minded gardeners. Fungicides, like all agricultural chemicals, should be handled with caution. Read the label on the container carefully and follow the directions closely. Store pesticides in cool, dry places away from children and pets and in the original container. Containers when disposed of, should be crushed, and disposed of according to label directions.
If you have other questions about ways to control garden pests, feel free to check with us at your county Extension office.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.