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
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 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
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
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
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
There were a number of reports of ryegrass escaping burndown in fields that either will soon be planted to corn or just had been planted to corn. Thankfully this issue seems less of a problem than a year ago. In most cases the ryegrass escaped glyphosate + dicamba early burndown. Paraquat application has the best probability of controlling ryegrass that has escaped early burndown. Continue reading
With the planting season started, many people are thinking about using Gramoxone (paraquat) as a burndown for many weeds present at planting. Gramoxone is a very good broad-spectrum herbicide that has been the go to for burndown of many winter and summer annual broadleaf weeds. With Palmer amaranth starting to emerge, Gramoxone is the only sure thing that will control it. However, it is less consistent controlling some weeds like horseweed (marestail). Continue reading