There is no substitute for good cultural and crop management practices, for these constitute the backbone of any weed control program. Dependence upon herbicides alone does not always provide the most economical weed control. Herbicide performance is strongly related to environmental conditions, so not even the best herbicides are equally effective from year to year. The most desirable weed control program is one that will control existing weeds economically and prevent a buildup of weed seed or tubers, rhizomes, etc. in the soil. Such a program includes integrated use of several practices which may include any of several crop management practices in addition to chemical weed control.
Crop rotation is one of the most effective cultural practices for improving long-term weed control. Crop rotation aids in controlling weeds by: 1) allowing rotation of herbicides as well as crops, and 2) providing the opportunity to plant highly competitive crops which prevent weed establishment. Many herbicides that are available for use in corn, for instance, are extremely effective in controlling weeds for which there are no adequate controls in soybeans or sugarbeets. Rotation to a densely planted crop such as alfalfa or small grains helps prevent most annual weeds from becoming established and producing seed with little, if any, chemical input. Some production systems which utilize rotation to small seeded legumes (including alfalfa) or other densely grown perennial grass-legume forage mixtures are effective in reducing populations of some perennial weeds.
Any practice that provides optimum conditions for early and vigorous growth of crops helps give them a competitive edge over weeds. Following are some of these practices:
Following are several other preventative cultural practices that do not allow weeds to become established and spread:
Mechanical weed control is still an important component of many weed control programs. Primary tillage operations involve moldboard plowing or some type of reduced tillage that destroys existing vegetation and allows adequate seedbed preparations. Secondary tillage is performed for final seedbed preparation, and is usually done with a tandem disk, field cultivator, or similar implement. The third category of tillage is selective cultivation, which is used to control weeds after the corp has emerged from the soil. Selective cultivation may be performed with a rotary hoe, rolling cultivator, shovel (sweep) cultivator, or similar implement.
Conventional tillage systems involve primary and secondary tillage. These operations may be followed by selective cultivation, depending on the crop and its row spacing. Conventional tillage is effective for reducing populations of many biennial and perennial weeds that may arise from rhizomes or rootstocks. Annual weeds that reproduce only from seed will most likely still be a problem and require additional controls.
If selective cultivation is used, it should be done early. Rotary hoes are effective for controlling small weeds (less than 1 inch tall) and should be operated at relatively high speed (7 to 10 mph) and on fairly dry soil. For maximum effectiveness, a rotary hoe should be used when weeds are in the "white stage", or just emerging from the soil. Cultivation with a shovel, sweep, or rolling cultivator is more effective on larger weeds than a rotary hoe, but should still be operated when weeds are very small. Cultivations should be shallow (1 to 2 inches deep) to prevent excessive root damage to the crop. Deeper cultivation also depletes soil moisture and can cause excessive ridging, creating problems at harvest for some crops.
Conservation or reduced tillage systems do not involve moldboard plowing and maintain some previous crop residue on the soil surface. Primary tillage in a reduced tillage system consists of using a disk, field cultivator, or chisel plow and may be the last operation before planting. No-till crop production involves no primary or secondary tillage, and the crop is planted directly into a sod or the previous year's crop residue. Conservation tillage systems generally rely more heavily on chemical weed control than conventional tillage systems. For additional details on reduced tillage systems, refer to other sections of this chapter.
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