Foliar Herbicides

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. Foliar herbicides can either kill or burn the foliage on contact, or be translocated within the plant to its growing points. The nontranslocated herbicides may not completely eliminate the weed problem but will kill any aboveground parts. The translocated chemicals are effective in killing both aboveground and belowground parts of the plants. Such translocated herbicides are effective against many of the perennial weeds with vegetative reproductive parts below the soil surface.

Weed response to selective herbicides depends upon the retention, uptake, or translocation of the chemical through the plant's foliage, as well as upon the reactions of the herbicide within the plant. The selectivity of an herbicide can result from slight differences in the plant's structure, the quality of the foliage, the depth of the root system, or the location of the growing points.

Substantial time, effort, and money have been invested in the development of pesticides designed to do a specific job. Each pesticide label must specify the intended use of the product, as well as the pests controlled and on which plants it can be applied safely. Chemical weed control, in its simplest form, involves matching a specific problem with the herbicide that will safely solve that problem.

For more information on the use of hand sprayers in applying herbicides, see the Fungicides, Herbicides, and Insecticides section of this chapter.