Late summer, fall and harvest are good times to check out where you may have a problem with specific weeds or where a new weed is invading or possibly even herbicide resistance is developing. By identifying the weed, extent of any infestations and locations of weed problems, you will have a better strategy for managing these weeds in the future, maybe even this fall. Marestail or maybe more specifically, glyphosate resistant marestail has become a major problem in Nebraska. In traveling around southeast Nebraska, marestail control and weed control in general appears to be much better overall this summer compared to previous years. Once marestail bolts from the rosette state it is hard to control. It can emerge in the fall, so keep an eye out for it. Several growers have actually found that cereal rye has been very effective in control of marestail. This may be another option and at the same time provide erosion control and potentially improve soil health. Fall control of winter annuals should improve field conditions next spring for planting and weed control in next year’s crop. Another very tough weed to control is field horsetail or scouring rush (Equisetum). This is the weed that looks like a small bamboo plant and it grows in wet areas, especially along railroad right-of-ways and ditches. Unfortunately, it many times is invading more into fields and is very tough to control. The University of Nebraska-Lincoln has conducted research in controlling this weed. They found Chlorsulfuron, labeled as Glean for use in wheat, or as Telar for use in non-crop areas, was very effective at controlling scouring rush for more than one year when it was applied at 3 oz /A. Chlorsulfuron has a long soil residual and can cause significant injury to corn and soybean. The maximum use rate in wheat is 0.33 oz/A (approximately 10 times less than what was applied in noncrop areas, and the rotation interval to corn or soybean is 24 months. If chlorsulfuron were used to control a scouring rush patch that is expanding from a non-crop area into a corn or soybean field, individuals should only consider planting an IR-corn or STS soybean in the treated area in the subsequent 3-5 years, and may still suffer some crop injury from herbicide carryover.
Another major concern in Nebraska is palmer amaranth. While I have not seen infestations of it in the area, I know there are fields in southeast Nebraska that have it. In southwest Nebraska glyphosate resistant palmer amaranth is causing all kinds of problems. The best method of controlling these resistant weeds is to limit their seed production by alternating herbicides, combining herbicides with glyphosate in treating weed problems or even hand-walking fields. It is important to recognize fields that have herbicide resistant weeds so you can prevent them from producing seed. If you think you may have palmer amaranth in a field, do whatever you can to limit seed production. Recent research at Kansas State University, shows promise for the use of cereal rye as a cover crop in slowing down early spring emergence and growth of Palmer Amaranth. If it becomes a problem in southeast Nebraska it may be a valuable tool to use.
Finally be aware of the noxious and invasive weeds in the area, specifically musk thistle and Sericea lespedeza. It is important if you can identify these weeds in pastures or CRP before they become major problems. Unfortunately Sericea lespedeza is showing up more in CRP, pastures and grasslands. I actually had a farmer bring in a sample of Sericea lespedeza he found in his pasture today. There have been reports of it being in grass seed mixes, spread by deer, birds and the wind. Other weeds that are showing up in southeast Nebraska and could cause problems include: phragmites, common teasel and cutleaf teasel. Phragmites can be found growing along some of the wet ditches and wetland areas in southeast Nebraska. Teasel can be found in non-cropped areas and in pastures or CRP. It is a problem in the neighboring states Kansas and Missouri. If you have questions about any of these weeds or need assistance in identifying a weed, feel free to contact me at the Nemaha County Extension office at 402-274-4755 or (402) 274-9639 (cell).