|
Hannah Mathers, Ohio State University Extension, Horticulture and Crop Science |
Rudyard Kipling wrote, "We have 40 million reasons for failure, but not a single excuse." In nursery weed control, there are countless reasons why the herbicides or other control practices we choose may not work in various situations; however, we can gain knowledge of what will work, and we can learn from our successes and failures. Oscar Wilde wrote, "Experience is the name everyone gives to their mistakes."
Weed control in ornamentals can take many forms. There are more options in field culture than in containers and container yards. In nursery fields, possible control methods include physical, biological, cultural, chemical, and combinations of these methods. Physical control failures may occur if cultivation is done during wet, cool, shady, low wind conditions allowing disturbed weeds to reestablish themselves; hand weeding is done after seed is produced; or the soil is dry and the reproductive plant parts are left behind. Cultivation and hand weeding can also fail if the piles of pulled or hoed weeds are not cleaned up and certain weeds continue to flower and ripen seeds after having been hoed or uprooted. Shifts of weed populations can occur when any type of control is used exclusively. Repeated mowing will result in a predominance of prostrate weeds.
Total reliance on cultivation will lead to a predominance of perennial weeds. Despite these examples of failure with physical control programs, failures in the chemical control program are probably the ones most managers often remember.
Herbicides are very effective tools for controlling weeds while reducing costs associated with physical weed removal. Herbicide selection depends on the weeds you are trying to control, the stage of the planting, the plant material in the planting and the stage of the weed growth. Other factors influencing herbicide selection include timing of the herbicide application; classification and persistence in the soil; the chemical mode-of-action; soil type; temperature; soil pH; organic matter content; available soil moisture; whether the weeds or crop plants are under stress; spray pattern; equipment calibration; chemical retention on leaf or soil surface; uptake in the weed; and spray water quality. Some of these factors will be discussed here.