Crop Rotations

Crop rotations help to reduce weed problems in corn or other subsequent crops in the rotation. Another benefit is reduction of insects, diseases, and nematodes in corn and succeeding crops.

Crop Competition

Crop competition is one of the most significant but often overlooked tools in weed control. A good stand of corn, which emerges rapidly and uniformly and shades the middles early, is very important in reducing weed competition. This involves utilizing good management practices, such as choosing a well-adapted hybrid, ensuring good fertility, maintaining proper soil pH, and using adequate plant populations. These good management practices are necessary for controlling weeds and producing high yield. The plant that emerges and grows most rapidly is usually the plant that will have the competitive advantage; therefore, everything should be done to ensure that the corn has this competitive advantage instead of the weeds.

Know Your Weeds

Know your weeds and choose an appropriate and effective herbicide for the specific weed problem. Generally, for preplant and preemergence applications, the weed problem must be anticipated based on the previous year's weed history because the weeds have not emerged at the time of application. Observe the field in the fall and record which weeds are present and where they occur. These "weed maps" can refresh your memory and help in herbicide purchasing decisions in the following spring. Once the weed problems have been identified, Tables 4 and 5 can be used to determine the most effective herbicide(s).

Cultivation

Cultivation is still a good and economical means of weed control. However, few benefits other than weed control have been attributed to it. Disadvantages of cultivation include enhanced soil erosion, disruption of corn roots, greater moisture loss from soil, and increased weed seed near the surface. If herbicides have resulted in good weed control, then the need to cultivate is questionable.

Herbicides

Herbicides are one of the most effective tools for successful weed control in corn. Preplant or preemergence applications combined with the previously discussed management practices are important for ensuring that corn has the initial competitive advantage. If corn is taller than the weeds, then postemergence directed applications can be utilized to extend the weed control through the season. This option is not available if the weeds are as tall as the corn. Late-season, over-the-top applications can aid in harvest efficiency. However, this will not be needed in most cases if good weed control is achieved throughout the season and the corn is harvested when mature.

The herbicides in Table 1, Table 2, and Table 3 have performed well in UF/IFAS research. When choosing an herbicide, consider the crop that will follow in a rotation and the risk of herbicide carryover and injury. Read the label and follow all instructions and precautions. Accurate sprayer calibration is extremely important because insufficient rates may not provide adequate weed control and excessive rates may injure the crop or result in carryover and injury to succeeding crops. Herbicides, like any pesticide, should be handled with care. Store herbicides behind locked doors in the original containers with the label intact. Keep them separated from seed, fertilizers, and other pesticides.

Weed Control in No-Till Corn

No-till production practices virtually eliminate the effect of cultivation, thus placing greater importance on effective chemical weed control.

Chemical weed control in no-till corn is similar to that in conventional corn with two basic differences:

1. Existing vegetative growth must be killed or suppressed with an herbicide at or before planting by burndown application. See Table 1 for these herbicides.

2. Herbicides requiring mechanical soil incorporation cannot be effectively used. All other herbicides listed for preemergence or postemergence application below can be used in no-till corn just as in conventional corn.

Tables