C.O.R.N. Newsletter: 2017-12

HEADING: https://www.youtube.com/watch?v=Q6Da1HRlmV8

After being slowed down by cold temperatures over the last 7-10 days, the wheat crop is now heading-out or flowering in some parts of the state – do not be deceived by the fact that plants still look short in some fields. Heading and flowering will continue over the next few weeks. These are very important growth stages from the standpoint of disease management, since it is critical to maintain the health of the heads and the leaves during grain fill to enhance yield.

1. Examine primary tillers at multiple locations in the field – remove them if it makes it easier for you to examine;
2. Identify the flag leaf, which is the uppermost (last) leaf, and look at the position of the head in the leaf sheath of the flag leaf;
3. If the flag leaf is fully emerged and the head is still encased and swollen in the leaf sheath, then you are still at Feekes 10, the boot stage;
4. If the first few spikelets are out of the leaf sheath then you are at Feekes 10.1;
5. If about 25% of the head is out of the leaf sheath then you are at Feekes 10.2;
6. If about 50% of the head is out of the leaf sheath then you are at Feekes 10.3;
7. If about 75% of the head is out of the leaf sheath then you are at Feekes 10.4; and
8. If the head is fully emerged (the entire head is out of the leaf sheath) then you are at Feekes 10.5;
9. Once the heads are completely out, it may take another 3-5 days, and sometimes longer if it’s cool, for it begin to flower.

FLOWERING: https://www.youtube.com/watch?v=ybZVW_YbhxY  

This stage is marked by the extrusion of anthers from the spikelets; the reason for which this process is also referred to as anthesis. The identification of this growth stage is very important for the management of Fusarium head blight (head scab) with fungicides.    

10. Closely examine the heads (also called the spike) of primary tillers at multiple locations in the field for the presence of anthers – often seen as a yellowish (or other color) part of the flower hanging from the spikelet;
11. If no anthers are seen, then your wheat may still be at the heading growth stage, Feekes10.5;
12. If the first few anthers are seen hanging from florets/spikelets in the central portion of the spike, your wheat is at Feekes 10.5.1 - early flowering or early anthesis;
13. If anthers are seen hanging from florets/spikelets in the central and top portions of the spike, your wheat is at Feekes 10.5.2 - mid-flowering or mid-anthesis;
14. If anthers are seen hanging from florets/spikelets along the entire length of the spike, your wheat is at Feekes 10.5.3 - late-flowering or late-anthesis;

Note: When trying to identify flowering growth stages, based your assessment on the presence of fresh (brightly colored) anthers, since dried, discolored, and spent anthers may remain hanging from the spikes well after Feekes 10.5.3. This can be misleading. Fungicides are most effective against head scab and vomitoxin when applied during Flowering.

HEAD SCAB RISK: http://www.wheatscab.psu.edu

Head scab and vomitoxin become our biggest concerns at this time of the wheat season. For wheat flowering today, May 8, the risk of scab is low across most of the state (the map is green), but moderate in parts of the west (yellow areas close to the Indiana border). The risk is also moderate-high in the northeast corner if the state, but the wheat in that region is not yet flowering. Several fields across Southern and Central Ohio will reach anthesis during this week. The risk will likely remain low if it stays cold, in spite of the rains, but continue to keep your eyes on the weather and the scab forecasting and alert systems over the next few weeks, and be prepared to apply a fungicide (Prosaro or Caramba at full label-recommended rates) at flowering if the risk increases.      

As a result of the warm winter and early spring, weed growth in no-till fields is ahead of schedule.  Fields not treated with burndown herbicides last fall or during the earlier drier period this spring can have some large weeds at this point.  Many fields need time to dry out following the most recent rains before they will tolerate traffic, which will allow weeds to get even larger and more challenging to kill.  Large marestail can be especially problematic due to the combination of glyphosate and ALS resistance in most populations.  Cool weather can reduce the activity of the herbicides that have activity on marestail.  The standard “glyphosate + 2,4-D” burndown is not likely to control large marestail plants based on recent history, and increasing the 2,4-D rate or adding metribuzin won’t necessarily result in effective control of these plants either.  The issue here is that 2,4-D is carrying the entire load with regard to control of emerged marestail, and it’s not effective enough to control large plants, even with the addition of metribuzin.  While Sharpen is more effective than 2,4-D, a mixture of glyphosate plus Sharpen can also become more variable in effectiveness as marestail get larger.  In no-till fields that have not yet been treated with herbicides, consider making changes to burndown programs to ensure complete control of large marestail prior to emergence of nonGMO, Roundup Ready, and LibertyLink soybeans.  Postemergence application of glufosinate in LibertyLink soybeans is most effective on marestail plants that emerge after planting, not for control of plants that survived the burndown herbicide treatment.  Suggestions follow.

- Burndown treatments should contain at least two active ingredients with substantial activity on marestail.  The most cost-effective of these still include 2,4-D, which will require a 7-day wait to plant.  Examples:  glyphosate + 2,4-D + either Sharpen or Zidua PRO; Gramoxone + 2,4-D; Glufosinate + 2,4-D.  The inclusion of metribuzin is recommended for all of these mixtures, and should absolutely not be omitted for the mixtures of 2,4-D with Gramoxone or glufosinate. 

- where it’s not possible to wait to plant, choices can be less effective or more expensive.  Best approaches here, ranked from most to least effective:  1) glufosinate + metribuzin + either Sharpen or Zidua PRO; 2) glufosinate + Sharpen or Zidua PRO; 3) Gramoxone + metribuzin +  Sharpen or Zidua PRO.  

- Switching to a program that includes Sharpen can result in the need to modify the residual herbicides as well.  Mixtures of Sharpen with residual products that contain flumioxazin (Valor etc), sulfentrazone (Authority), or fomesafen (Prefix, etc) must be applied at least 14 days before soybean planting.  Waiting this long to plant may not work as we move later into May.  Alternative residuals that can be used in mixtures with Sharpen, and applied anytime prior to soybean emergence include:  Canopy Blend or Cloak DF + metribuzin;  Matador + metribuzin; metolachlor/metribuzin premix products (Boundary etc).   Total metribuzin rate for all of these should be the equivalent of 8 to 10 oz of metribuzin 75 DF (possibly less on sandy soils low in organic matter).   

- In fields planted with Xtend soybeans, there is obviously the option to use XtendiMax, Engenia, or FeXapan in the burndown, and then also as a postemergence follow up if necessary.  Dicamba is generally more effective then 2,4-D on marestail, especially larger plants, and the combination of glyphosate plus dicamba may be effective enough in the burndown.  We have observed reduced control of larger plants in mixtures or dicamba with residual products that contain flumioxazin (Valor etc) or sulfentrazone (Authority).  Increasing the dicamba rate may reduce problems in these mixtures. 

- be sure to optimize spray parameters and adjuvants.  Mixtures containing Sharpen and Zidua PRO should be applied with MSO.  Gramoxone should be applied with COC.  Gramoxone, glufosinate, and saflufenacil (Sharpen, Zidua) are contact herbicides, which require 15 to 20 gpa spray volumes and nozzles that optimize coverage.  Check labels for specifics.

This information is summarized in a short video, which can be found on our blog (u.osu.edu/osuweeds) or on our Youtube channel https://youtu.be/orhtPNcn9GU.  We have also started a Facebook page for information disseminated by OSU specialist, “OSU Agronomy and Pest Management Specialists”, and the video is posted there as well.