Warm weather this winter has many wheat fields progressing at a faster than normal pace. Several questions have been asked recently if we are setting up for a repeat of the 2007 Easter freeze. In general wheat across Tennessee is still in the tillering phase of growth and according to the table below we are just at a slight risk for yield impacts if temperatures are fall into the low teens for an extended time. Having a crop that has broken dormancy this early sets up the potential for damage once jointing occurs. The key to any damage is what the weather conditions will bring in late March and early April.
Do I need to apply my topdress nitrogen now, or should I wait to keep the wheat from progressing too fast? First, remember that if you are using a urea based nitrogen fertilizer it needs warm temperatures and microbial activity to convert to nitrate (plant available form of nitrogen) which causes a lag from application to plant uptake. Second, if we have field conditions that will allow us to get across the field without causing ruts with equipment we should go ahead and get nitrogen out. Third, you do not control the weather. Once wheat begins to joint nitrogen demand increases rapidly, if top-dress nitrogen is delayed until late jointing, yields can be negatively impacted. We need to manage our wheat for high yield potential by having nitrogen available when it is needed. The Easter freeze of 2007 was a rare event, if we did not have the freeze that year we would have had a record wheat crop. So, should I apply my nitrogen now? The answer is yes, we should manage this crop for high yield potential and hope the weather pattern cooperates.
The following table was adapted from a Texas A&M publication.
|
Growth stage |
Injury temps. (2 hours) |
Primary symptoms |
Yield effect |
| Tillering |
12 F |
Chlorosis, burnt leaf tips, silage odor, blue hue to field. | Slight to moderate |
| Jointing |
24 F |
Growing point death, burnt leaf tips, odor | Moderate to severe |
| Boot |
28 F |
Floret sterility, spike trapped in sheath, burnt leaf, odor | Severe |
| Flowering |
32 F |
Floret sterility, whit awns or heads, damage to stem | Severe |
| Milk |
28 F |
Floret sterility, whit awns or heads, discolored kernels | Moderate to Severe |
| Dough |
28 F |
Shriveled, discolored kernels | Slight to Moderate |
Little off the subject, but still dealing with wheat. Should we be looking at any early fungicide applications, along with an insecticide?? Have a fair amount of what I call winter burn in this wheat, from the severe up/down temp swings we have seen. Not real sure this crop ever did go dormant. Also has not helped with the fields being extremely wet, we are at full ground saturation in my particular area. Savannah, TN. River bottoms. Would probably take close to 2 weeks of no rain to get fields crossable.
The University of Tennessee does not recommend using foliar fungicides on wheat prior to Feekes scale 10.1 (beginning of head emergence). In general, we do not find economic returns from applying fungicides prior to head emergence.
We will probably experience some foliage burn from the predicted lows in the mid-teens this weekend (2/11/12). While this will appear ugly, it will help slow crop development to delay maturity and help the avoid a late freeze when heads do emerge in early April.
For high yield potential, how much N would you recommend? Would you recommend one or split applications? Does the 2 week window herbicide to N application window (or vice versa) apply to all wheat herbicides or just to Osprey? Thanks.
UT Recommends applying a total of 90 pounds actual N (90 units) for small grains. While often time higher N rates make more bushels of wheat, the return on your nitrogen investment decreases substantially. Applying more than 120 units of N leads to higher incidence of wheat diseases and lodging problems at harvest.
Split applications of N are good if you can get some separation between applications. Ideally applying 1/3 of you N in mid-January then coming back in mid to late February with the rest helps reduce N losses in the environment.
The two week window with N applications and herbicides applies to Osprey, Powerflex, Axial and Finesse. It is ok to tankmix Harmony and/or dicamba with top-dress nitrogen.