Garden Disease Prevention Basics

Learn about these garden disease prevention basics that can help prevent diseases often attacking your vegetable garden.


| August/September 2007



Use a sprayer such as this to apply plant disease treatments.

Use a sprayer such as this to apply plant disease treatments.


Illustration by Elayne Sears

These garden disease prevention basics can prevent many of the diseases that plague your vegetables.

Garden Disease Prevention Basics

It happens in the best of gardens. Your plants are growing beautifully, and then you notice some of them are being consumed by pathogenic (from the Greek pathos, meaning suffering) microorganisms. The good news is you don’t have to be a plant pathologist to prevent many of the diseases that threaten a food garden, because disease-resistant varieties that are grown in soil enriched with organic matter usually stay healthy when the going gets tough.

Cured compost helps plants prime themselves to better handle challenges from diseases while improving the soil’s tilth. Providing enough water to avoid drought stress helps, too. Many gardeners include seaweed sprays in their garden’s preventive health care program, which provide nutrients for both plants and beneficial microorganisms.

Still, some leaves will shrivel and entire plants may sometimes suddenly collapse. To offer the best help to troubled plants, first you’ll need to know how different types of diseases tick. Seeing is believing. In late summer, most gardens offer some examples of common garden diseases, such as leaf blemishes and fruit rots, stem and root infections, and viral diseases spread by insects.

Garden Fungal Follies

Let’s start by looking at your tomatoes, especially the leaves closest to the ground. That area stays damp longer than the plant’s high branches, and the leaves down there are getting old — two factors that make them prime victims for early blight (dark brown patches) or several other leaf spot diseases, including gray leaf spot and Septoria leaf spot. All are caused by fungi that busily release millions of spores, which spread to new leaves by the time the colonies become big enough to see. If those new leaves are damp and temperatures are right, the spores germinate and penetrate the leaf using enzymes to melt entryways into plant cells, and a new leaf spot is born.

Leaf blemishes come in a variety of colors. Among your squash, you may see some white patches of powdery mildew, which is caused by spore-producing fungi that weaken plants by robbing leaves of their ability to perform efficient photosynthesis. You might see streaks of cinnamon-like rust in your corn, or patches of orange rust powder on bramble fruits or beans — more examples of spore-producing parasitic fungi. If you grow fruits, the velvety brown patina on your shriveled peaches or plums is caused by brown rot and Botrytis. Other spore-producing fungi turn strawberries and grapes into moldy mummies.





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