All posts by Larry Steckel, Extension Weed Specialist

When Dicamba Fails…

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Picture 1. 3 to 6″ Palmer amaranth escaping Engenia + glyphosate in XtendFlex cotton. Picture taken 12 days after application

Just when it appears that ryegrass has become our most problematic weed, Palmer amaranth goes into “hold my beer and watch this” mode.  In the last 10 days we have fielded numerous reports on dicamba failures to control Palmer amaranth.  Just this past week we were able to visit a number of these fields. Continue reading

Crunch Time for Weed Control

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Picture 1. Goosegrass escaping multiple glyphosate applications. Tipton County. Mid-June 2022

As the calendar turns to June weed management concerns change from ryegrass and horseweed to the summer annuals goosegrass, junglerice and Palmer amaranth.

Tennessee growers are in a real crunch time to control these three summer annual weeds. Big percentages of the corn, soybean and cotton crops all need some kind of POST application right now. The planter technology that can plant three different crops across large acreages very quickly has one drawback. The sprayers often cannot keep up to most every acre needing to be sprayed just as quickly. Continue reading

Herbicide Stewardship

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It is crunch time for weed control in our row crops.  When every minute counts to get herbicide applied it is tempting to cut corners on herbicide stewardship.  The forecast would suggest that Tennessee will be entering a bit of a dry spell.  Herbicide drift is even harder for crops to recover from when drought stressed so please take time to use best management practices applying all herbicides but particularly products that contain dicamba and 2,4-D. Continue reading

Corn Herbicide Maturity Cut-Offs

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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.

Crop stage and/or crop height is used to determine the cutoffs for a given herbicide.  Often the label states the limits at whichever (crop stage or crop height) comes first.  Crop stage can easily be done by counting the number of leaf collars that are fully exposed (ex.  4 collars = 4 leaf) (Picture below).

4 leaf (collar) corn – V4 stage

Postemergence Corn Herbicides Crop Height Cutoff Crop Stage Cutoff
Accent 20 inches 6 leaf
Atrazine (Bicep, Degree Xtra, Acuron, etc.) 12 inches
Buctril 8 leaf
Callisto* 30 inches (without atrazine)
Capreno* 20 inches 7 leaf (without atrazine)
Corvus 2 leaf
Dicamba (Banvel, Clarity) 8 inches (1 pt/A) or
36 inches (1/2 pt/A)
5 leaf

Distinct 24 inches
Glyphosate – RR corn only 30 inches 8 leaf
Halex GT 30 inches 8 leaf
Hornet 24 inches
Armezon/Impact 8 leaf
Laudis 8 leaf
Liberty (Ignite) – LL corn only 24 inches 7 leaf
Diflexx 36 inches 6 leaf
Realm Q 20 inches 7 leaf
Resource 10 leaf
Resolve Q 20 inches 7 leaf
Roundup PM – RR corn only 8 leaf
Status 36 inches 10 leaf
Steadfast Q 20 inches 7 leaf
2,4-D 8 inches

*Note that if atrazine is added to herbicides such as Callisto or Capreno for example, the cutoff would be reduced to 12 inches.

Ryegrass Issues Persist and Johnsongrass Management

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Ryegrass Infestation in Corn

Ryegrass infestations still persist in some fields.  In cotton and soybeans, clethodim can be used now to push this weed on to maturity. In corn, other than just going out and spraying the typical POST corn premix and hoping that pushes the ryegrass on to maturity there is no real solution to controlling it. Continue reading

Early-Season Weed Concerns in ThyrvOn Cotton

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Picture 1. Palmer amaranth and goosegrass that emerged at 1 to 2 lf cotton and then escaped Post Application of Engenia + Glyphosate fb/Liberty + Glyphosate. Picture August 2022. Madison County TN

My understanding is that some cotton planted this year will contain the ThryvOn trait.   According to UT entomologist Sebe Brown these varieties will likely not require any POST foliar insecticide application for thrips.  This is great as far as management for that pest but from a weed management perspective this could be a problem. Continue reading

Mitigating Potential Herbicide Mixing Issues

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This time of year as we move to burndown behind the planter we typically get some reports of mixing issues when either glyphosate or Gramoxone is added to the tank with residual herbicides like atrazine, metribuzin, 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

Thinking ahead: Vine Control in Corn

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2022: Burcucumber growing over top of mature corn

Practically every September some growers are dismayed at the vine infestations present at corn harvest.  Often, these weed infestations emerged after PRE applied or early POST applied herbicides had played out.  They grew very little until August and as the corn dried down and light became more available those established weeds started rapidly growing. Continue reading