"Identifying the weeds of concern can take place in the fall to determine control plans for the next growing season," he said. "A good weed inventory in the fall will tell ranchers what the predominant weed species is in the pasture."
When scouting your pastures, check for the type of weeds present. Deneke explained 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. Although some weed species can be grazed in the fall, Deneke encouraged livestock producers to scout to ensure the weed species present do not represent a toxicity risk to livestock.
"The other management concern is to control the weeds so they do not go to seed and further increase the soil seed bank," he said.
Deneke said fall is also a good time to assess range and pasture grass condition. "Overstocking will contribute to stressing grass species and give weeds a competitive edge thus increasing trouble spots in a pasture," he said.
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," Deneke said.
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 size of the weed population using a rating system of few, many, or scattered. Also, Deneke said to note if the weeds are broadleaf, woody or grass species. "Accurately identifying the weed species will make planning control options much easier," he said.
Consider an Integrated Pest Management (IPM) approach to your weed management plans. In other words, look at all options available whether that be 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, Deneke said a plan for spot treatment is a good way of cutting costs and reducing the amount of herbicide applied to the land.
Annual weeds are normally treated in 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," Deneke said. "Fall is a great time to spray some perennial and biennial weeds as the plants are moving sugars and starches to their roots to prepare for winter."
He added that this will aid the herbicide treatment to get to the root system and give more effective results. If there are perennial brushy weed species present, Deneke said 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," he said. "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.