Written by Darrell Deneke, former SDSU Extension IPM Coordinator.
Fall is a good time to assess your range and pasture condition as we go into the winter season. This is especially important when it comes to your weed management strategies. Identifying the weeds of concern can take place in the fall and control plans for the next growing season can be determined. A good weed inventory in the fall will tell ranchers what the predominant weed species are in the pasture.
When scouting your pastures check for the type of weeds present. Many perennials and biennials will have new growth in the fall especially with adequate fall moisture. Perennials may have new shoots or seedlings from seed banks or, like biennials, the rosettes may be found. Annual weeds may have remnants of mature growth or in the case of later emerging annuals lush growth and new seed formation will be present. Some weed species can be grazed in the fall, but be sure the weed species present does not represent toxicity risks for livestock. The other management concern is to make sure the weeds are not allowed to go to seed and further increase the soil seed bank.
Fall is also a good time to assess the range and pasture grass conditions. Overstocking will contribute to stressing grass species and give weed species a competitive edge thus increasing trouble spots in a pasture. This is a good time to consider adjusting your grazing management plan to increase the overall competitiveness of your forage mix. The best weed control program for pastures and range is a competitive healthy grass stand.
When conducting your weed inventory identify the weed species in abundance and develop a pasture map that shows where the weeds are located and the general weed population size using a rating system of few, many, or scattered. Also, note if the weeds are broadleaf, woody or grass species. Accurately identifying the weed species will make planning control options much easier.
Consider an Integrated Pest Management (IPM) approach to your weed management plans. Look at all options available; herbicides, mowing or clipping, grazing management, biological control and other cultural and mechanical controls. If weed populations are noted in the inventory as being scattered in areas, a plan for spot treatment is a good way of cutting costs and reducing the amount of herbicide to the land.
Annual weeds are normally treated in the late spring and early summer with mid-June being the target for many pasture weeds. Perennial and biennial weed species can be treated in late spring and early fall with good results. Fall is a great time to spray some perennial and biennial weeds as the plants are translocating sugars and starches to their roots to prepare for winter. This will aid the herbicide treatment getting to the root system and give more effective results. If there are perennial brushy weed species present, specific herbicide products will need to be considered. Always remember to be aware of desirable forbs and broadleaf plants in the pasture and range and note them in your inventory as well. Try to avoid contact with the herbicide treatment so you can maintain them as part of your healthy pasture and rangeland plant community.
For pasture and range weed management information refer to the SDSU Extension Noxious Weed publication.