The weather forecast, if accurate, suggests next week will dry up enough where we all can get back in the field. Everyone will need to be running sprayers as weeds have not stopped growing. I know everyone will be in a rush, but please, please take the time to be good stewards and apply herbicides as directed by the labels. Continue reading
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. Continue reading
JACKSON, Tenn. – The University of Tennessee Institute of Agriculture will host the annual Weed Tour June 18 at the West Tennessee AgResearch and Education Center. The guided tour will feature 60 weed management research tests in cotton, corn and soybean.
Weed Tour runs from 9 – 11:30 a.m., with registration opening at 8:30 a.m. Continue reading
What began in March as a quick start to the planting season has with the many frequent rain events turned into a very slow struggle. The question of the hour is on how to burndown fields that are grown up messes before planting soybeans (Picture 1 and 2). There are strategies that can tackle fields that are heavily infested with 3’ tall goosegrass, Palmer amaranth, horseweed and volunteer corn. They typically require some kind of sequential application to be successful.
Paraquat, the usual “go to” for late spring burndown, will not control grasses with size, horseweed or even pigweed that has gotten so far out of hand. As such, the best approach is aggressive tillage. That unfortunately is not an option on our highly erodible fields.
In those cases, a tankmix of a high rate of Liberty plus clethodim is the best approach to try to control the grass weeds, horseweed and set the pigweed back. Then, if possible, a couple days later apply paraquat. This approach would have the best chance of success with herbicides.
In fields where the soybeans may emerge before a follow-up paraquat application could take place then Liberty tankmixed with Enlist should take out any escaped broadleaves. If grass seems to be recovering then apply Liberty plus clethodim.
The UT Cotton Scout School is scheduled for Wednesday, May 21st, at the West Tennessee Research and Education Center (605 Airways Blvd, Jackson). There is no fee, and preregistration is not required. Registration begins at 8:00 AM with the program starting at 8:30. Pesticide points in categories 1, 4, 10 and 12 will be offered and a BBQ lunch will be provided. Content will include classroom and hands-on training with an optional go-to-the-field session after lunch. Topics covered will include cotton development and identification and symptoms of insect pests, plant diseases, and weeds.
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 REV | 24 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.
Italian ryegrass is still a significant problem in many Tennessee fields due to failed herbicide burndown applications.
Our recent research suggests that there are two critical factors in burning down ryegrass. First, timing of herbicide application is extremely critical to gain the most consistent ryegrass control. The second is herbicide choice.
Timing is a very important component in ryegrass control. Our recent research has shown that burndown applications applied in early February provide better control than the same application in March and is worlds better than applications in April (Picture 1.)
In general, clethodim is the most consistent choice to control this weed. Glyphosate at best will only provide ryegrass suppression. The tankmix of the two often will enhance the consistency of ryegrass control.
There have been calls this spring about ryegrass that has escaped multiple clethodim applications. The concern of course is that resistance has developed as it has in Louisiana and Mississippi. We plan to conduct a survey this year to determine if resistance to clethodim is present in Tennessee ryegrass.
Results from our greenhouse screens of Palmer amaranth to Liberty have 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