Fungicides A Primer for the Home Gardener

“Fungicide” is a mysterious word to many home gardeners. Insecticides kill insects and herbicides keep weeds in check… but what does a fungicide do? In a broad sense a fungicide is any chemical which protects plants against attack by disease producing fungi.

But how important are plant diseases caused by fungi?

In the United States, crop losses due to ten of the most important diseases produced by fungi amount to billions of dollars annually. Plant diseases, and the chemicals used to prevent them, are big business. Diseases do their share to keep our grocery bills high.

Fungicides can be conveniently divided up into four groups, depending on their action:

Protective fungicides

Are applied as foliage sprays or dusts and as seed treatments to stop disease producing fungi from entering plants. These chemicals provide protection but will not cure a disease once the fungus has become established within the growing plant or seed. Practically all fungicides used today are in this category.

Eradicant fungicides

Applied as foliage sprays or seed treatments to kill or check disease causing fungi after they have penetrated into plants and become established. For examples chemicals used on certain types of seeds to kill seed rot and seedling blight producing fungi hiding under the seed coat. These fungicides have limited uses and are often quite dangerous to many types of growing plants.

Chemotherapeutants

Are chemicals taken up and distributed within a plant to control certain diseases.

Fumigants

These chemicals usually break down in the soil to produce a gas toxic to soil-borne fungi and nematodes. Many fumigants also kill certain weed seeds, insects and other animal life in the soil. Farmers in some areas of the world fumigate yearly to control root knot nematodes and other soil pests.

New Ones Prevail

In the past few years many new fungicides have been introduced to control plant diseases. These chemicals are rapidly replacing the older materials. Many of these older materials were messy to handle, corrode the insides out of spray equipment, cause spray injury and reduce the quality and quantity of the fruit or vegetable crop they are designed to protect - on top of that they may not have been too environmentally friendly.

An unfortunate thing is that many garden centers, nurseries and big box stores do not stock modern fungicides. All a home gardener can get in many cities and towns is very general fungicides to control limited diseases in the “modern” home garden and landscape.

The chemical names (called active ingredients) of the new fungicides are difficult to remember or even pronounce, yet they are printed on many package labels. These chemicals are marketed under a bewildering assortment of “trade names.” This caused so much confusion that “common names” have now been adopted nationally and are being increasingly used in place of the chemical name on package labels.

In the past few years a large number of fungicide-insecticide combinations (like the printer, copier, scanner for home computer user) for fruits, vegetables, flowers (especially roses) as well as trees and shrubs have been offered to the home gardener in small packages.

These all-purpose or one-pack mixtures, although more expensive, have been eagerly accepted. They have largely eliminated the necessity of stocking a large assortment of garden medicines. Many chemical manufacturers now have identical or very similar mixtures. But be sure you read the fine printing on the label! Certain plants can be injured by sprays particularly if the weather becomes hot and dry. Many new fungicides are currently being evaluated by agricultural experimental stations and manufacturers.

Always read the label and follow the directions when applying any chemicals.

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