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Index : Plant Care
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- 16. El Nino Brings Lots of Weeds - Top
- Lots of rain over the last two months has brought with it a bumper crop of weeds. Gardens and landscapes are literally being choked with London rocket, shepard's purse, foxtail and a host of other undesirable species, recently sprouted from seed.
It's too late for pre-emergent weed control, but control is necessary because maturing weeds will soon produce seed for next year's crop of weeds.
Mechanical control is probably the best method to eliminate weeds know, especially for weeds that have grown large. Many of the weeds growing now are annuals and only come up from seed. Unlike perennials, these annual weeds will not re-grow from the roots. So killing the above ground, leafy portion, of the plant will eradicate the weed.
Cutting weeds off with a sharp garden hoe is most effective. Simply shave the weeds off at the soil surface. If your careful, powered string trimmers can also be used to cut down weeds. String trimmers should not be used in rock mulched areas however. Gravel and rocks can be dangerously thrown by the flailing string line.
Hand pulling weeds is effective when weeds are young. Larger, more mature weeds, however will have an extensive root system very difficult to pull out of the soil. And if you do, the roots from nearby desirable plants will be damaged. Also young weeds will pull much easier if the soil is moist.
Powered tillers, both large and small can be used to cut down weeds in cultivated gardens. A shallow setting of the tines is best. This will cut or shave off the weeds without turning too much soil over and exposing more weed seed.
Chemical control of weeds may be used in leu of mechanical control measures. Because a majority of weeds growing now are of the annual variety, as with hoeing, only the above ground portion of the weed need be killed. Chemical weed killers that can accomplish this fall into the category of contact or locally systemic herbicides, such as diquat or finale. They can be purchased in liquid form at most garden centers and nurseries. It's important when using either of these products to spray the entire weed. It is most effective to treat actively growing weeds. Don't wait until the weeds get large and mature. At that point, it will be more difficult to kill them.
When using any chemical, weed killers included, follow all label directions. Mix the concentration of spray recommended. Mixing a stronger, or weaker solution of spray than that recommended will result in poor control. Wear a long sleeve shirt and pants, use chemical resistant gloves, and wear goggles or safety glasses as a minimum. If the label calls for further protective equipment, wear it!
When spraying weed killers, use only a sprayer designated for that use. Even when sprayers are properly washed, some chemical residue may remain. If you then mix an insecticide in that same tank to spray, lets say, tomatoes for aphids, the tomatoes can be injured.
Spray post-emergent herbicides when the air is calm. Early morning is a good time because temperatures are cool and the wind is generally down. Never spray under windy or breezy conditions! Spray may drift onto valuable plants and cause damage. If you must spray weeds close to valuable plants, use a shield made of a large piece or cardboard to place between the weeds and surrounding plants.
Finally, to prevent weeds from re-growing, consider using pre-emergent herbicides. Amaze, Surflan XL, and Portait herbicides all come in easy-to-use granular forms. They provide control of weeds for four to six months. To be effective pre-emergent herbicides are best applied prior to rainy periods in the summer and winter. They also must be watered into the top layer of soil.
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Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161.
Material originally appeared in Arizona Daily Star gardening column, on June 9, 1996
- Updated: June 9, 1996
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