Fields with heavy infestations of any of the weeds below are generally not suitable for dry bean production until the infestation is reduced by rotating to other crops and using effective herbicides, tillage, and cultural practices.
Annual Morningglory. The dense foliage of annual morningglory can engulf a stand of dry beans. Plants emerge during spring and summer from seed at a depth of 4 inches 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 the soil for long periods of time.
It is critical to control annual morningglory from crop emergence through harvest.
- Destroy annual morningglory plants while they are seedlings, because once they begin twining up bean plant stems they are difficult to control without injuring the crop.
- Apply a pre-harvest herbicide if necessary. Annual morningglory plants are a problem during harvest time because they can completely cover the bean canopy, preventing windrowing and bean harvest.
- Consider planting vine-types bean varieties that cover the entire soil surface and can out-compete this weed and reduce its growth.
- Plant rotation crops such as corn or cotton to use herbicides that effectively control this weed but are not registered in dry bean.
Field Bindweed. If possible, avoid growing beans in fields heavily infested with field bindweed, as there are no herbicides registered for postemergence control in California and preemergence herbicides give only temporary suppression.
Bindweed is a persistent perennial weed with roots extending many feet down in the soil profile. Control should be an ongoing program. For annual crops like beans, take control measures before planting to reduce weed numbers. Fall applications (September or October) of glyphosate at high rates, 2,4-D, or dicamba will reduce spring weed numbers and help beans to get a head start. If bindweed has emerged before planting, till or apply glyphosate. In-season applications of postemergence directed herbicides will provide some suppression but will not provide complete control.
Nightshades (Black, Hairy). Avoid planting seed contaminated with nightshade seed or planting in a nightshade-infested field. Nightshade berries are toxic. There is zero tolerance of nightshade berries for canning beans—they must be completely removed. Since berry removal is not always possible at the warehouse, beans maybe rejected.
Both nightshade species grow tall, competing with beans for sunlight. They also cause serious harvesting problems. During threshing, berries rupture, releasing a pigmented, 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 the prevention of seed production.
Plan a crop rotation with a crop that has registered herbicides that are effective for nightshade control, such as corn or winter cereals. In most dry bean varieties, early suppression or control can be achieved with s-metolachlor, ethalfluralin, or often a combination of both herbicides. High rates of ethalfluralin may damage crop seedlings if the temperatures turn cool after planting. There are no herbicides that provide control throughout the season. When the beans start to senesce towards the end of the season and light reaches the soil through the thinning canopy, nightshades and other weeds can grow and set seed before the field can be harvested.
Nutsedges. Both yellow and purple nutsedge are serious problems in dry bean fields. They should be controlled in rotation crops using s-metolachlor or EPTC in a preplant incorporated application. EPTC is not registered on blackeyes. S-metolachlor will not work on purple nutsedge, but it will partially control yellow nutsedge. Several cultivations can be made to suppress nutsedge until the bean plants cover the rows. Bentazon, a postemergence herbicide, has a limited-use registration for dry beans grown under sprinkler irrigation. Check label for local use.
Plant small grains as a rotation followed by summer fallow and employ repeated tillage, herbicide control with glyphosate, or both.