Bermudagrass is a very competitive plant species; however, weeds will reduce seed yield if populations are high—especially if the crop is growing poorly. Additionally, weeds make harvesting more difficult because they do not dry as readily as the crop. Succulent weed plants do not pass through harvesting equipment easily and can clog up combines. Another problem with weeds in bermudagrass production is that cleaning undesirable seed out of the crop after harvest can greatly increase processing costs.
Weeds are controlled best in the seedling stage; therefore, it is important to be able to identify them. A good pictorial reference, such as the UC ANR Publication 4030, Grower's Weed Identification Handbook, or the weed photo gallery will help assist in identifying weeds. It is important to keep a log of summer and winter weeds by field for a comprehensive management system.
Examine the bermudagrass field frequently throughout the year but especially after the first irrigations following harvests. Bermudagrass seed can be harvested twice during the year, once in late spring or early summer and again in late fall. After each harvest, fields are often burned to get rid of thatch, harvest residues, and fungal spores. Following the burn, fields are irrigated to stimulate regrowth of the bermudagrass. Winter annual weeds, both grasses and broadleaves, will germinate after the fall harvest. After the summer harvest, summer grasses and nutsedges are most common. The entire field should be examined to determine which species of weeds are present. Economic thresholds have not been developed for estimating the impact of weed populations on bermudagrass seed yields, but growers report significant yield losses from moderate levels of weeds.
Cultural practices play an important role in bermudagrass weed management because a vigorous crop is very competitive against annual weeds. Bermudagrass is a multi-year crop, so weed problems that occur at the beginning of the production cycle will persist until the field is rotated to another crop. Preplant cultural practices are especially important because bermudagrass is broadcast planted rather than seeded in rows, so mechanical cultivation is not an option for postplant weed control. Bermudagrass is flood irrigated between raised borders. Fields should be precisely leveled before planting the crop to ensure even water distribution. Adequate phosphorus fertilizer should be applied before planting to encourage proper root development. Seed certified by the California Crop Improvement Association is slightly more expensive than common seed, but it is a good investment to ensure potential for higher yield, increased germination, and reduced risk of introducing a new weed species. Monitor nitrogen levels in the crop frequently to plan fertilization schedules that will ensure proper crop growth. On the other hand, excessive nitrogen fertilizer can lead to crop disease problems and increased weed growth. Insect and disease pests should be controlled to maintain crop growth. Thoroughly cleaning harvest equipment before entering or leaving a field is an important practice that prevents spreading weeds within and between fields. Field burning generally does not kill many weed seeds but does make weed monitoring easier.
Growers cannot rely on herbicides to solve weed problems in bermudagrass fields, especially when the fields are poorly managed. This is because of very limited herbicide options for this crop and because the thick thatch of stolons and dead plant material prevent herbicides from reaching the soil where they can work properly. Other problems with herbicide use in bermudagrass are that a variety of products (seed, hay, and straw) will be harvested and livestock will occasionally graze in these fields. Growers, PCAs, and pesticide applicators need to be in regular communication to ensure that the specific herbicide used is allowed for the harvested product.