All posts by Larry Steckel, Extension Weed Specialist

Best Management Practices for Liberty Applications

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The beginning of June is always a busy planting and spray window.  It will be more so this spring with most of last week a wash to get much field work done. Of course, there will be a good deal of glyphosate and dicamba sprayed this week and likely some Liberty as well. With Liberty in such short supply every quart must count.  This is just a quick reminder that the time of day that Liberty is applied has a large determination on the success or failure of that application.

From 2012 to 2017 we conducted a good many studies examining Liberty performance on Palmer amaranth as affected by the time of day the application was conducted.  All the studies pointed to the same conclusion, that Liberty applied in the middle of the day provided better and more consistent control of Palmer amaranth than either early morning or evening applications (studies conducted in warm weather). As an example, one study (Figure 1.) from 2015 showed good control of 4” tall Palmer amaranth if the Liberty application was applied at noon compared to applications made at dawn or sunset.

Figure 1. Palmer amaranth control from Liberty herbicide as effected by application timing.

In general, the best Liberty performance can be achieved when applications are made from 8:00AM to 6:00PM.

Other environmental factors also greatly effect Liberty’s weed control performance.  It controls weeds best if applied on days where the high temperatures for the day are in the 80s or 90s.  Also, it works best at higher humidity’s as well.  In other words, a typical June or July day.

Seedling Cotton Burn from Early Post Applications

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Picture 1. Cotton growing through Dual Magnum + Roundup PowerMax Burn

Weather permitting, this week will be the start of the early POST applications in cotton. These applications are often critical to not only curtail weed competition but to combat thrips injury as well.  The biggest concern with these applications is injury to the young cotton plants.  Traditionally, the main pesticides applied are a mixture of glyphosate plus either Dual, Outlook or Warrant plus Intrepid Edge or acephate. Those herbicides which contain a good surfactant in glyphosate with the oil formulations of the chloracetamide herbicides will always burn young cotton leaves. The typical cotton injury from those mixtures will range from 10 to 20% (Picture 1). Continue reading

Corn Maturity Cutoffs for Herbicides

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How large can corn be before glyphosate could potentially cause injury? The glyphosate label states it can be applied up through the V8 corn growth stage. My experience has been if glyphosate is applied to corn larger than that it can at times cause ears to be barren.  This phenomenon is difficult to predict ahead of time as it can vary due to maturity of the corn at application, hybrid and weather. Continue reading

Ryegrass and Johnsongrass: Where do we go from here?

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Picture 1. Ryegrass infestation in wheat escaping Osprey
Ryegrass in corn escapes glyphosate + dicamba burndown

Ryegrass has moved from being an aggravation 10 years ago to a significant weed issue in our row crops.  In wheat at this point, the yield loss caused by the weed has occurred (Picture 1). In cotton and soybeans, clethodim can be used now to push this weed on to maturity. In corn, there is no real solution to controlling it other than spraying the typical POST corn premix and hoping that pushes the ryegrass on to maturity (Picture 2).

The wheat fields that were consistently clean of ryegrass were those treated with either Anthem Maxx, Zidua or Axiom last fall.  A good bit of the ryegrass population in the state is resistant to ALS-inhibiting herbicides which renders herbicides like Osprey, Finesse, and Powerflex harmless to ryegrass. Axial Bold has shown improved ryegrass control in spring applications over those ALS-inhibiting herbicides but it does not offer the consistent ryegrass control as those delayed PRE-applications of Anthem Maxx, Zidua or Axiom.

Johnsongrass is also a consistent problem in a good many cornfields. Glyphosate is just not providing any traction in the burndown on Johnsongrass and the POST in-crop applications are no better.  Our most recent research funded by the Tennessee Corn Checkoff program has shown that Steadfast Q or Accent Q can still provide good control of Johnsongrass when glyphosate fails.

Mitigating Herbicide Mixing Issues

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There have been numerous reports of mixing issues when either Roundup PowerMax 3 or Gramoxone is added to the tank with residual herbicides like atrazine, Cotoran, Caparol, fomesafen or a pyroxasulfone containing product.  What happens is the white herbicides will often clabber up and stop up screens and strainers in the sprayer. Continue reading

Still Seeing Good Control with Liberty on Palmer amaranth

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Picture 1. Good Palmer amaranth control with 32 oz/A Liberty on Lauderdale county populations

Results from our greenhouse screens of Palmer amaranth to Liberty has been very encouraging.  We feared that the Liberty resistance documented in Arkansas had crossed the river.  The good news is that we have seen good control with a 32 oz/A rate of Liberty on all the Palmer populations tested (Picture 1). Continue reading

Poor Burndown Performance

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There have been a number of reports on disappointing burndown applications that were applied during that cold stretch, 3 to 4 weeks ago, when nighttime temperatures were in the 20s.  The herbicides that performed poorly were some combination of systemic herbicides glyphosate, dicamba, clethodim and Leadoff. Continue reading