Agricultural pest management
Special Weed Problems
(Reviewed 8/07, updated 12/08)
Fields with heavy infestations of these weeds are generally not suitable for dry bean production until the infestation is brought under control by rotating to other crops and using herbicides that are registered in these crops.
ANNUAL MORNINGGLORY. The dense foliage of annual morningglory can engulf a stand of dry beans. Seeds germinate down to a depth of 4 inches (10 cm) or more, much deeper than most annuals. Most seedlings emerge following irrigations, but they may also appear when surface soil is too dry to allow germination of other annuals. Seeds remain viable in soil for long periods.
Control of annual morningglory is critical from crop emergence to harvest. Destroy seedlings while they are small, because once they have twined up stems they are difficult to control without injuring the crop. Vine types of bean varieties that cover the entire soil surface will outcompete this weed and reduce its growth. In rotation crops such as corn, herbicides that effectively control this weed are registered.
FIELD BINDWEED. If possible, avoid growing beans in fields infested with field bindweed as there are no herbicides registered for postemergent application in beans in California that controls this weed.
Bindweed is a persistent perennial weed and control should be an ongoing program. For annual crops like beans, take control measures before planting to reduce the population. Fall treatments in September or October of glyphosate (Roundup) or 2,4-D will reduce spring populations and help beans to get a head start. If bindweed has emerged before planting, tillage or glyphosate treatments are suggested.
NIGHTSHADES (BLACK, HAIRY). Avoid planting seed contaminated with nightshade seed or especially planting to a nightshade-infested field. Both nightshade species are tall and therefore major competitors with beans for sunlight. They also cause serious harvesting problems. During threshing berries rupture releasing pigmented and sticky juice that stains crop seed and causes dirt and nightshade seed to stick to it. Nightshades are prolific seed producers, have seed that are viable for many years in the soil, and are tolerant to many herbicides. Therefore, successful nightshade control requires preventing them from producing seed.
Plan a crop rotation with a crop that has registered herbicides that are effective for nightshade control, such as corn. Winter cereals may be good choices because of the herbicides that are registered in these crops. In blackeyes/cowpeas, early suppression or control can be achieved with s-metolachlor (Dual) or high rates of ethalfluralin (Sonalan). High rates of ethalfluralin, however, may damage crop seedlings if the temperatures turn cool after planting. There are no herbicides that will give long enough control that when the beans start to senesce towards the end of the season and light reaches the soil prevents the nightshades from growing and setting seed before the field can be harvested.
NUTSEDGES. Both yellow and purple nutsedge are serious problems in dry bean fields and should be controlled in rotation crops. To suppress these weeds, use EPTC (Eptam) or s-metolachlor (Dual Magnum) in a preplant incorporated application. Several cultivations can also be made until the bean plants cover the rows to suppress populations.
Plant winter cereals as a rotation for summer fallow and chemical control with glyphosate.
UC IPM Pest Management Guidelines: Dry
W. M. Canevari, UC Cooperative Extension, San Joaquin County
Acknowledgment for contributions to Weeds:C. A. Frate, UC Cooperative Extension, Tulare County