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What's up with weeds?
If someone could figure out a market for waterhemp or giant ragweed, these plants could form almost a recession-proof market for many Missouri farmers. (Then again, these weeds likely would battle weeds themselves!) Here’s what’s going on in the world of University of Missouri (MU) weed research at last week’s MU Pest Management Day at MU’s Bradford Research and Outreach Center.
There’s lots of promising soybean weed technology coming on the market in the next few years, notes Kevin Bradley, MU Extension weeds specialist. They include tolerance to growth regulator herbicides like 2,4-D and dicamba (now used in herbicides like Banvel and Clarity).
Drift and volatility concerns accompany growth regulator herbicides, though. This concern also encompasses herbicides now used to control weeds in pastures. Since current soybean varieties on the market are highly sensitive to growth regulator herbicides and are often sandwiched between Missouri pastures and hayland, Craig Solomon, MU weed scientist graduate student, notes it’s important to know how herbicides can impact them.
Growth regulator herbicides evaluated included in the MU trials include 2,4-D amine, Clarity, Tordon 22K, Milestone, Remedy Ultra, Stinger, aminocyclopyrachlor, and Starane. “Surprisingly, 2,4-D amine showed no height or yield reductions,” says Bradley. Milestone herbicide showed the greatest height and yield reductions, he adds. The trial showed soybeans were more likely to recover from misapplications of growth regulator herbicides made earlier (V3, third trifoliate) than later ( R2, full flowering).
A challenge in using new growth regulator technology will be proper cleanout of sprayers between use of different herbicides. “If a co-op sprays 2,4-D on 2,4-D tolerant beans one day and dicamba on dicamba-tolerant beans the next, it will be a big issue making sure the sprayer is properly cleaned out,” says Bradley.
Several companies are promoting one-pass treatments of strobilurin fungicides, slow-release nitrogen, and postemergence herbicides early on during the V5 to V6 growth stage. Solomon reported on a study that compared postemergence herbicide treatments laced with fungicide and slow-release nitrogen vs. treatments not containing them.
Fungicide did decrease gray leaf spot levels in the irrigated continuous corn plots. However Solomon and Bradley note neither fungicide nor the slow-release N boosted corn yields. Chlorophyll content and stalk strength were similar between treatments containing a fungicide and those that did not include one. Adding a slow-release N fertilizer to the mix also was shown not likely to boost corn yields. It’s important to note, though, that this data comes from one site in one year. The test is being repeated this year.
Another new soybean technology likely to debut by mid-decade include HPPD inhibitor soybeans. HPPD-inhibitor herbicides, such as Balance Pro, are now used on corn. “Tolerance to 2,4-D and dicamba are solutions to glyphosate resistance,” says Bradley. “In some areas of Missouri, waterhemp has developed resistance to several modes of action to where the only solution is Liberty Link soybeans.”
Still, it will be important to use these technologies in rotation with others. “The big thing is not to go Callisto/Callisto/Callisto or Balance/Balance/Balance or 2,4-D/2,4-D/2,4D all the time,” says Bradley. “If we abuse them, their effectiveness will go down.”
Weed scientists recommend the use of preemergence herbicides to take the heat off postemergence herbicides like glyphosate or glufosinate. Rotation also adds modes of action, which helps deter resistance to any one herbicide. This year, farmers may have soured on preemergence chemicals, as a number failed to activate due to drought. The end result is an extra herbicide bill and little weed control.
“This year, guys got sour on preemergence herbicides, but we have to stay with them,” says Bradley. “Year in and year out, preemergence herbicides will give you control better control.”
You’ll also see better yields minus the grass and broadleaf competition. “We are losing yield by waiting too long to treat,” says Bradley. On average, 2.4 bushels per bushel were lost in 2011 Missouri trials when just a postemergence chemical was applied.
Bradley notes an overlapping residual program can work well by first applying a preemergence residual herbicide followed by a postemergence mix of glyphosate and a residual herbicide. “Cost increases, but you get better weed control from it,” says Bradley.
Early treatment is particularly important for waterhemp with existing and future technologies. “If you apply dicamba to dicamba-tolerant soybeans on waterhemp at this height, you will not be happy,” says Bradley.
See the latest from weed research in Missouri.