It has been said, a weed is simply a plant growing out of place. For some people a watermelon may be called a weed if it is growing in a rose garden. I for one would simply eat the watermelon while looking at the roses.
A “true weed” is many times unsightly, competes with desirable plants for light, water and soil nutrients. Weeds also are hosts for pests such as plant pathogens, nematodes and insects. Certain weeds are also irritants to humans. Example of a plant with irritants would be poison oak.
Controlling weeds with chemicals should be carefully planned instead of being a hit-or-miss event that many times either does not work or kills the plants you want to save.
Herbicides may be classified according to the chemistry of the chemical and also the method of application. Herbicides may be selective, non-selective, systemic or contact.
A selective herbicide controls or suppresses certain plant species without seriously affecting the growth of another plant species. Non-selective herbicide control plants regardless of species.
Systemic herbicides may be selective or non-selective. Systemic herbicides are extensively moved in the plant’s vascular system. Most systemic herbicides require several days or even a few weeks to work.
Contact herbicides only affect the portion of green plant tissue contacted by the herbicide spray. With contact herbicides the underground part of the plant is not killed and, in many cases, repeat applications of the chemical are needed.
Contact herbicides may be classified as selected or non-selective.
Herbicides are also classified as preemergence or postemergence depending on the time the chemical is applied. Preemergence herbicides are applied prior to weed seed germination and form a barrier at, or right below, the soil surface. Weeds that already have emerged at the time of application are not controlled consistently by preemergence herbicides.
Postemergence herbicides are applied directly to emerged weeds. In contrast to preemergence herbicides, this group of herbicides provides little, if any, soil residual control of weeds.
If you decide to use a herbicide to control weeds, it is important to read and follow the chemical label. In order to determine which chemical is best for your weed problem, you may contact the extension service.
Herbicides are only one tool you may use to control weeds. The use of mulch, as well as equipment, may be used to effectively control weeds.
Last and not least, remember, pulling weeds by hand or the use of the old hoe has killed countless weeds.
Clark Beusse is the Dawson County extension agent. For more information, call (706) 265-2442.