Part 2, Section 1: Pest Management
Pest Management
Weed Control
Cultural and mechanical controls
Cultural practices that aid in the control of weeds include anything that make the crop more competitive against them: proper seedbed preparation, planting date, fertilization, crop rotation, row spacing, seeding rate, and variety selection.
Date of planting can influence the type and number of weeds present. In general, optimum soil temperature at planting time will help the crop emerge quickly and out-compete weeds that emerge with or shortly after the crop. Planting corn as soon as possible after the risk of frost has passed may allow the crop to better compete against later-emerging weeds. In contrast, planting later (after June 1 to 15) generally reduces the types and intensities of weeds encountered. Early plantings run the risk of cool-wet soils, frost, and a greater possibility of plant disease and herbicide injury, while delayed plantings generally do not yield as well as earlier seedings. The weed species present in a field along with its potential severity may help determine the best time for planting.
Few producers appreciate the benefits of crop rotation. Crop rotation interrupts pest life cycles, allows alternative tillage and herbicide options, and can provide a "window of opportunity" in attacking particular problem pests such as perennial weeds. For example, rotation to perennial forage crops, such as alfalfa or grass, allow mowing as a weed-management tool. By following corn with a fall- or spring-seeded small grain, summer annual weeds such as velvetleaf and foxtail may never emerge, compete, or set seed the year of the cereal grain. After small grain harvest in midsummer, perennial weeds including hemp dogbane and Canada thistle are reduced more effectively with a late summer systemic herbicide application and/or tillage. Even a simple rotation from corn to soybeans can allow both additional tillage and herbicide opportunities.
Mechanical weed control includes the use of preplant tillage such as plowing, disking, and field cultivating. These primary and secondary tillages can help reduce the rate and spread of certain perennial weeds. Postplanting operations such as rotary hoeing, row cultivating, and hand hoeing can help reduce dependence on herbicides.
Rotary hoeing is a popular weed-management tool in parts of the midwestern United States. If preemergence or preplant herbicides are not performing adequately because of a lack of rainfall or some other reason, a rotary hoe can be effective when used after weed germination, but before weed emergence. Operate it at 10 to 12 miles per hour with enough drag to stir the soil and displace the small seedlings.
Row cultivators should be used when weeds are small. Shallow cultivation helps prevent injury to crop roots. Newer innovations in cultivator design make the use of row crop cultivators more possible in reduced tillage systems.
Finally, herbicides provide a convenient, economical, and effective way to help manage weeds. They allow fields to be planted with less tillage, allow earlier planting dates, and provide additional time to perform the other tasks that farm or personal life require. Herbicides may not be a necessity on some farms, but without the use of chemical weed control, mechanical and cultural control methods become that much more important.