Wet conditions slowing the control of weeds in some fields

Tag : nonionic surfactant

Most of the early-planted soybeans should have already been treatedwith post-emergence (POST) herbicides at this point. The results ofweed-crop interference studies show that weeds should be treatedwith herbicide before they exceed a size of 6 to 8 inches. Weedsmay not have reached this size in later-planted soybeans, or wherepre-emergence herbicide activity-reduced weed populations andgrowth. Some points to consider in the management of post soybeanherbicides:
1. It is possible to apply post-herbicides too soon after plantingin early-planted soybeans, and the end result can be the need for asecond post-herbicide application to control later-emerging weeds.However, the risk of applying too early decreases when soybeans areplanted in late May or in June, since weed emergence tends to peakabout this same time.
2. Glyphosate rates should generally be based on weed size and age,environmental conditions, and the previous history of glyphosateeffectiveness. If is possible to use the lowest labeled rate ofglyphosate, 0.75 lba ae/A. Our research with glyphosate resistanceclearly shows that in any situation where glyphosate activity couldbe reduced (large weeds, drought stress, low level resistance),most effective control results from using a high glyphosate rate inthe first post-emergence application, and following with a lowerrate in a second application if needed. Using a low rate in thefirst application and then trying to "bail out" the resulting poorcontrol with a second application at a higher rate will have a muchlower rate of success.
3. Where a second post-emergence glyphosate application is neededto control plants that survived the first application, our researchindicates that about three-week intervals between applications mayresult in the best control. This provides time for plants to resumegrowth after the first application so that glyphosate can haveactivity in the plant, but does not allow time for plants to regrowto a large size. Waiting until enough regrowth occurs so thatplants can be seen above the crop from a road survey is not thebest approach. Applying the second glyphosate treatment too soonafter the first is also not optimum, since plants that have notrecovered from the first application cannot respond to the second.
4. Deciding how to manage glyphosate in soybean fields with ahistory of poor glyphosate performance can be more involved thanjust increasing rates. It is possible for glyphosate to provideadequate control of populations that have a low level of glyphosateresistance. This can be achieved by making the first application of1.5 lbs when plants are small, and following with a secondapplication at 0.75 lb about three weeks later. Weed populationswith a higher level of glyphosate resistance (fields whereglyphosate has largely failed on at least part of the weedpopulation in a previous year) will require treatment with a fullrate of an alternative to glyphosate.
5. In situations where conditions are less than ideal for herbicideactivity, full rates of true AMS (ammonium sulfate) may be moreeffective than AMS substitutes or products than contain reducedrates of AMS. The same holds true when mixing glyphosate andmanganese in foliar applications.
6. Glyphosate activity can increase when applied in low sprayvolumes, but this has to be balanced against the need forpenetration of spray into dense weed/crop canopies or to obtainbetter coverage of large weeds. For the latter situations, it'spossible that spray volumes of 15 to 20 gpa may be more effectivethan 10 gpa or less. Be cautious also of using too manydrift-reduction measures, such as combinations of low drift nozzlesand drift-reducing agents. This can result in too few droplets oftoo large a size, which can reduce control.
7. Increasing the rate of a glyphosate product applied will usuallybe more effective than adding nonionic surfactant. Most glyphosateproducts already contain a relatively high concentration ofsurfactant. Increasing the rate of product applied results in theapplication of higher rates of both glyphosate and the surfactantsthat are part of the formulation.
8. The time of day of application affects herbicide effectiveness.Previous research by OSU and other universities has shown thatactivity can be reduced when herbicides are applied in earlymorning or in the evening (or at night).
What are those purple things along the interstate?
The Ohio Department of Agriculture's (ODA) Emerald Ash BorerProgram began placing purple detection traps in or near ash treesacross Ohio in April. Researchers have developed a purple trap andlure that is attractive to EAB adult beetles. State and federalofficials are using these manufactured traps for the first time inOhio and throughout the country, replacing the former detectiontree survey method. Department surveyors have placed nearly 7,500traps in or near ash trees in parts of Ohio (including MuskingumCounty) where the insect has not yet been detected.
Calendar of Activities
No Ag Breakfast this month
July 12- Ohio Sheep Day, Kline Farm in Athens County. Call theoffice for flier
Mark Mechling is an extension agent with The Ohio State UniversityExtension Office and can be reached at 740-454-0144 or mechling.1@osu.edu