Weed Management in Dry Edible Beans:
(From Dry Bean Production and Pest Management, 2nd Edition)
Weeds can have a major impact on dry bean seed yield and quality. Weeds that grow above the crop canopy will cause greater yield loss than weeds that remain below the canopy. For example, common sunflower, common cocklebur, redroot pigweed, barnyardgrass, and hairy nightshade at densities of one plant per three square feet can reduce cry bean seed yields by 66, 50, 24, 24, and 22 percent respectively. As weed density increases, crop yield reduction generally increases until weeds begin to compete with themselves.
Time of weed emergence has a significant impact on weed competitiveness -- weeds emerging with the crop cause greater yield losses than weeds emerging after the crop. To minimize crop losses, dry beans need to be kept weed free until the crop reaches the sixth trifoliolate leaf stage or about six weeks after planting. After this period, the dry bean canopy should be competitive enoughh to surpess the growth of newly emerging weeds. Poor stands, crop stress, and wide rows may preclude bean foliage from covering the row and late-emerging weeds may be troublesome.
Planning a Weed Management Program
Several factors should be considered when planning a weed management program for dry beans. Factors such as a weed species, cover crop, preplant tillage, herbicide incorporation, crop rotation, crop cultivar, row spacing, rotary hoeing, cultivation, and herbicides all need to be integrated to develop an effective weed control strategy.
- Accurate weed identification should be the first step in any weed management program, and is important for selecting the most effective and economical treatment. View photos of weeds common to western Nebraska (PDF file, 1.8 MG, 8 pages)
- Tillage associated with seedbed preparations has a major impact on weed spectrum and population. In general, non-inversion tillage (I.E. chisel plowing) methods leave a greater proportion of weed seed near the soil surface than do inversion tillage methods (moldboard plowing). This increases the potential for weed germination and establishment.
- The use of a fall-planted cover crop can reduce weed emergence the following spring.
- Many herbicides used for weed control in dry beans need to be incorporated into the soil to reduce their loss from volatilization and photodecomposition. This necessitates preplant application. The performance of herbicides such as Eptam, Treflan, Prowl, Sonalan, Dual Magnum, Lasso, and Outlook respond to preplant incorporation.
- Dry bean cultivar and row spacing are important factors in determininng the amount of late-season weed pressure. If bean plants have a large leaf canopy to intercept sunlight, the soil surface will receive only small quantities of light and weed growth and seed germination below the canopy will be restricted. Dry bean cultivar and market calss influence plant architecture.
- Producers need to select herbicides or herbicide combinations based on weed spectrums in each field. this requires producers to have records of previous weed infestations or to identify weed seedlings. Mappinng weed infestations in a field can aid weed-management decisions.
- Herbicides applied at planting may not provide adequate weed control because of inadequate moisture or mechanical incorporation after planting. There are several possible tools such as rotary hoeing, cultivation, and postemergence herbicide application, which could be utilized to control weed escapes. Field scouting immediately after the crop and weeds begin to emerge is important to identify weeds and provide the information necessary to choose a postemergence herbice program that matches the weed spectrum.
Herbice resistance occurs from repeated use of a herbicide or herbicides with the same mode of action. Repeated herbicide use eliminates susceptible weeds and allows resistant weeds to increase inn the absence of competition. Plants that have developed herbicide resistance are kocha, pigweed/water hemp, cocklebur, nightshade, marestail, sunflower, foxtail and wild oats. To minimize herbicide resistant weeds, consider the following strategies:
- Use herbicides only when necessary.
- Follow manufacturers' labeled rates.
- Apply herbicides as tank mixes or use sequential treatments that contain multiple modes of action.
- Rotate herbicides with different modes of action.
- Rotate crops with different life cycles, such as winter annual crops (winter wheat), perennial crops (alfalfa), and summer annual crops (corn or dry bean).
- Combine mechanical and chemical weed control practices.
- Scout fields regularly to identify weeds that escape herbicide treatments.
(Article by Robert G. Wilson, Steve D. Miller, and Scott J. Nissen)
Other Extension Resources:
2015 Guide to Weed Management in Nebraska, EC130
Research results and recommendations on weed management in Nebraska crop production. A print edition of this 204-page Extension circular is available at Nebraska extension offices or can be ordered. This publication has a chapter on weed response to Herbicides in dry bean, as well as other useful information about weed management, selecting and using herbicides, and other topics.