Last fall there was a notable amount of Palmer amaranth in many corn fields in areas of the state where we had confirmed dicamba resistance. As a result, we have recently conducted some field screens on these pigweed populations to herbicides used in corn and soybean.
Figure 1
From late April and throughout the month of May, many parts of Middle and West TN have received persistent rainfall that is well above the average for this period. These rains have produced persistently wet soil conditions and have coincided with sidedress N fertilizer application where most or all of the recommended N is applied. With this much rain, there is potential for N loss. Continue reading
Carryover injury from fomesafen (Flexstar, Prefix, Reflex, Intimidator, Marvel, Dawn, Rhythm, etc.) is starting to show in a few corn fields. This is because some applications in late June and July in 2023 coupled with a very dry fall allowed the herbicide to persist into winter. Recent rains then allow any herbicide carryover to more completely get into the soil solution.
Fomesafen carryover injury in corn and grain sorghum looks similar. Expect to see stunting and interveinal chlorosis as pictures below sent from crop consultants clearly shows.
Due to little time and very few good spray days, some corn fields have yet to have their layby application. Corn is putting on a new leaf every 3 days with all the heat and water. Therefore, time is short before it will be too mature to apply many herbicides safely over the top.
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). If tankmixing, cutoff is always determined by the most limiting factor.
Johnsongrass Escaping Glyphosate Burndown
| Postemergence Corn Herbicides | Crop Height Cutoff | Crop Stage Cutoff |
| Accent | 20 inches | 6 leaf |
| Acuron GT | 30 inches | 8 leaf |
| Atrazine (Bicep, Degree Xtra, Acuron, etc.) | 12 inches | – |
| Callisto* | 30 inches (without atrazine) | – |
| Capreno* | 20 inches | 7 leaf (without atrazine) |
| Corvus | 2 leaf | – |
| Dicamba (Clarity, etc.) | 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 |
| Armezon/Impact | – | 8 leaf |
| Laudis | – | 8 leaf |
| Liberty – LL corn only | 24 inches | 7 leaf |
| Diflexx | 36 inches | 10 leaf |
| Realm Q | 20 inches | 7 leaf |
| Resicore | 11 inches | – |
| Resolve Q | 20 inches | 7 leaf |
| Roundup PM – RR corn only | – | 8 leaf |
| Shield Ex | 20 inches | 6 leaf |
| Status | 36 inches | 10 leaf |
| Steadfast Q | 20 inches | 7 leaf |
| Storen | – | 8 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.
Large patches of Johnsongrass that have gotten through glyphosate burndown are now very prevalent in many fields. This is particularly noticeable in several southeastern counties of West Tennessee where some of the Johnsongrass has shaken off burndown and now is almost waist high in some cases. The main threat with Johnsongrass is in corn where there are few POST applied options. Continue reading
I’ve received a few calls in the past couple days on cutworms appearing in seedling corn. Below are some take home points on cutworms:
By Nutifafa Adotey, Assistant Professor & Soil and Nutr. Magt Specialist, Forbes R Walker, Professor & Envt. Soil Specialist, and Frank Yin, Professor & Cropping System Scientist, University of Tennessee
Poultry litter has become readily available to producers in Tennessee. However, poultry litter cannot supply all the nitrogen needed for corn and thus supplemental N is required to obtain optimal yield. The amount of supplemental N can be estimated using the Pre-Sidedress Nitrate Test. The Pre-Sidedress Nitrate Test is recommended only for corn producers using animal manure, poultry litter or biosolids, who want to estimate and fine-tune their sidedress N fertilizer applications following manure/poultry litter application. This article provides a guide for Tennessee corn producers using poultry litter on how to estimate sidedress N rate using the Pre-Sidedress Nitrate Test. Continue reading
A good many reports from the field reflect what our research this spring has shown. In short, clethodim is the herbicide of choice to control ryegrass. Often clethodim tankmixed with glyphosate can improve the probability of better overall control. Ryegrass control with glyphosate alone is much more hit and miss both in our research and in many fields this year (Picture 1). Continue reading