Types of Herbicides
A chemical must be toxic to plants before it can be effective as an herbicide. An herbicide that is effective against most kinds of plants is called a nonselective chemical. Such chemicals are useful in areas where complete control of vegetation is needed. On the other hand, herbicides that are more toxic to some plants than others are called selective chemicals. Most herbicides for use on lawns and crops are selective; using the proper rate of these herbicides can remove susceptible weeds from tolerant plants. If excessive rates are used, however, the tolerance may be exceeded, resulting in injury to desired plants. Each kind of flower, fruit, and vegetable varies in its tolerance to a specific herbicide. In the small orchard, this means that not all herbicides can be used around all plants and that many plants do not have tolerances for any of the herbicides available on the market. A limited number of selective herbicides can be used in the home garden and around the home grounds.
Before selecting an herbicide, the fruit grower should consider the available weed-control alternatives. The weed should be identified and its growth habit--annual, biennial, or perennial—should be determined.
Herbicides generally are applied at different times, depending upon the emergence time of the weeds and upon the type of fruit plants.
Soil-applied herbicides are effective against germinating seeds or young seedlings.
To be effective, herbicides applied to foliage must remain on the foliage long enough to penetrate into the leaf, move within the plant to an active site, and cause a toxic effect.
TitleTypes of Herbicides
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