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Herbicide Application
Herbicides generally are applied at different times, depending upon the emergence time of the weeds and upon the type of fruit plants. Herbicides that are applied at specific times include the following:
- Preplant herbicides are used before the crop is planted to control germinating weed seeds, and are usually mixed into the top 2 to 3 inches of soil. No preplant herbicides are labeled for fruit plants.
- Preemergence herbicides are used after the crop has been planted, but before the weeds or crop emerges. Restrictions on the age of plants to be treated must be followed.
- Postemergence herbicides are used after the crop and/or weeds have emerged from the soil surface and are growing. The most common of these is Round-Up®, which can be purchased without a pesticide license.
Herbicides usually are more effective when temperatures before application have favored uniform germination and rapid weed growth. Rapidly growing weeds are easiest to kill. High temperatures at the time of application also tend to increase the activity of the herbicide but also increase the possibility of crop injury. Moderate temperatures between 70 and 85°F are the most favorable for spraying.
Wind can also be a factor in herbicide application. It can cause improper distribution over the weeds, reducing herbicide effectiveness while increasing the danger of drift onto desirable plants. Fewer problems occur if sprays are used when the wind velocity is low and the wind is blowing away from desirable plants.
The activity of herbicides applied to the soil is improved by moderate rain or irrigation shortly after application. The water helps to move the chemical into the weed zone and aids in the germination of the weed seeds. When herbicides are applied to the foliage, rain or irrigation should not occur until several hours after the material has been applied. After this time, most herbicides will have been taken into the foliage of the plant where they are not affected by rainfall.