Uncontrolled weeds continue to be a major limiting factor in Delmarva corn production. To be successful in controlling weeds in corn, the weed control program must be well planned and well executed. Consideration should be given to cultural, mechanical, and chemical methods of weed control with reference to specific weed infestations. The major elements of a successful weed control program in corn are summarized below.
The first step in an effective weed control program is proper weed identification. Only by knowing the exact identities and relative infestations of weeds on a field-by-field basis can the proper weed control strategy be developed. Continued use of the same program, or use of reduced tillage practices, can result in changes in weed infestations. Keep an accurate field record of the weeds in each field on a yearly basis, and use this record to plan your weed control program.
Several aspects of cultural weed control should be considered in planning a corn weed control program. These include weed-free seed, cover crops, and crop rotation. Crop rotation is a valuable tool in our corn/soybean rotations because perennial broadleaf weeds that cannot be controlled in soybeans can be effectively controlled in corn. Take advantage of this opportunity to control these tough weeds with mechanical methods and herbicides.
Mechanical weed control is still one of our most useful weed control tools. Both primary tillage and cultivation should be considered for specific weed problems. Perennial broadleaf weeds are an increasing problem in no-till corn production. In some cases, these weeds cannot be controlled without tillage to disrupt underground perennial parts. The use of the moldboard plow is an effective method of control and, for some weeds, represents the only practical method of control.
Many options are available in terms of herbicidal control of weeds in corn. Both preplant incorporated and preemergence combinations are available that offer broad spectrum weed control. Preplant incorporated treatments ensure activation of the herbicide and minimize the risk of crop injury. Preemergence treatments require rainfall for activation, but offer good weed control when rainfall occurs within the first 2 weeks after application. Consider postemergence and directed postemergence applications. These are some of our strongest options in corn weed control. Identify the weed and select the herbicide program that best fits your specific weed infestation.
The following tables give general ratings of relative herbicidal activity. Activity varies with weather conditions, soil type, and application method. Under nonoptimal conditions, activity may be less than indicated.
