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Weed management for slow-developing winter wheat.

Amanda de Oliveira Silva, Small Grains Extension Specialist and Misha Manuchehri, Weed Extension Specialist

November has been cooler than normal and that has limited wheat growth across the state. Most of fields where wheat was planted earlier have the crown roots slowly developing and top growth is lower than expected. Many of these fields have very thin stands and will probably not have enough forage to feed the cattle. In many areas, planting was delayed due to either lack or excess of moisture. Most of fields that were planted late are at 1-2 leaf stage with seminal roots developing. Plants are showing signs of cold injury but should grow out of it well.

Slow developing wheat due to cold temperatures.
Photo taken on December 2, 2019 in Stillwater, OK by Amanda de O. Silva
Symptom of cold injury on wheat planted on November 4th, 2019.
Photo taken on December 6, 2019 at Kingfisher County by Amanda de O. Silva.

Fall or Spring Herbicide Application for a slow-developing wheat?

Moisture has been plentiful in many areas in Oklahoma this fall. As a result, several winter annual weeds have emerged. These weeds are competing well with our wheat crop, which is behind in many areas due to cold temperatures. If you are investing in a herbicide application this year, you may be thinking “when should I apply”? The answer is not always simple but there are several things to consider before making this decision.

A 2019 winter wheat field heavily infested with Italian ryegrass.
Photo taken by Misha Manuchehri.
Henbit seedlings in a November 2019 planted wheat field in Stillwater.
Photo taken by Misha Manuchehri.

1. Is your wheat at an approved growth stage per the herbicide label?

Many postemergence herbicides labelled for use in wheat recommend the crop be at 2 or 3 leaves. Be sure to check these requirements to ensure crop safety.

2. What are your target weeds?

Many producers chose to apply a postemergence herbicide in the spring when top-dressing N to limit the number of passes made across their fields. This often makes sense for weeds that have multiple flushes, as two applications often are not financially feasible. For example, Italian ryegrass that is not managed with a delayed preemergence herbicide (Anthem Flex, Axiom, or Zidua) may be sprayed in the late winter vs. fall to target multiple flushes. On the other hand, early emerging, difficult-to-control grasses like rescuegrass, are best managed in the fall before entering “dormancy”.

3. What are daytime temperatures like? Are your wheat and weeds actively growing?

All postemergence herbicides labelled in wheat move in living tissue. Herbicide application will be most successful when your wheat AND your weeds are actively growing.

4. Have you applied this product before? Was it successful at that timing?

We can learn a lot from field history. If a product wasn’t successful in the past, we need to learn why so that we can make the necessary changes to increase its success or perhaps it is time to use a new weed management method. Finally, selection for herbicide resistant weed biotypes can occur quickly. If you are unsure if you have resistance, please send in a seed sample to the weed science lab.

It is time to scout wheat fields for fall armyworm!

By Amanda de Oliveira Silva, OSU Small Grains Extension Specialist and Tom Royer, Extension Entomologist

We are receiving reports of fall armyworms infestations and wanted to alert producers to check their wheat fields every day after seeding emergence. The worms can be very tiny and difficult to see it. Symptoms like “window pane” in the leaves indicate feeding from fall armyworm. Also, check under crop residue as they might try to hide from the heat.

Symptom of “window paned” leaves shows severe feeding from the fall armyworm. Photo taken on October 2, 2019 at Canadian County by Amanda de O. Silva.
Fall armyworms may be found under crop residue during the day. Photo taken on October 2, 2019 at Canadian County by Amanda de O. Silva.

Replanting decisions need to be made on field by field basis. Replanting might be best for producers taking the crop to a grain-only system. Also, allow some time to replant to avoid having infestations back again.

“We will not get relief from fall armyworms until we get a killing frost, so keep vigilant!” Tom Royer

Several helpful resources are available for producers. Contact your local county Extension office. For additional read refer to Pest e-alerts Reports of Seedling wheat Infested with Fall Armyworm 2019. Consult the newly updated OSU Fact Sheets CR-7193 Management of Insect Pests in Rangeland and Pasture and CR-7194 Management of Insect and Mite Pests of Small Grains for control suggestions.

Follow-up to “What can I expect from wheat just now emerging?”

By: David Marburger, former OSU Small Grains Extension Specialist

 

Wheat that was dusted-in or late-planted during the fall 2017 and resulted in spotty stands or no stands at all from a lack of soil moisture was a frustrating and common occurrence for many Oklahoma producers. Unfortunately, the first water some wheat seed imbibed did not occur until after a late-February rainfall. When the remaining seed started germinating and emerging, many were begging the question, “What is a realistic expectation for this late-emerging wheat crop?” In a March 2018 blog article titled, What can I expect from wheat just now emerging? I tried addressing several related questions:

  • Will these plants produce a head?
  • How cold and for how long do the seedlings need to be exposed to cooler temperatures to vernalize?
  • Is vernalization completely temperature dependent?
  • Do we have information on varietal differences?
  • What forage or grain yield potential do I have?

 

I also mentioned in that article that we were working on gathering more variety-specific information. We had a small, unused space next to the variety demonstration plots at the Stillwater agronomy farm. In that small space we were able to plant more than 30 varieties that were entered in the OSU variety trials last season (Figure 1). These plots were established on March 6 and managed similarly to the “grain-only” demonstration plots located immediately to the north of this area. The “grain-only” demonstration plots were established on October 31, 2017 with a seeding rate of 60 lbs/acre. In-furrow DAP at 50 lbs/acre was also applied. Therefore, the intention was for the planting date to be the only difference.

figure 1

Figure 1. Planting wheat on March 6, 2018 at the Stillwater agronomy farm.

 

figure 2

Figure 2. Picture taken on April 26, 2018 of the wheat varieties planted 51 days earlier. The “dual-purpose” and “grain-only” variety demonstration trials are those located to the right of this area. Every wheat variety entered into the variety trials (n = 56) was planted on September 19, 2017 to represent a dual-purpose planting date (background) and on October 31, 2017 to represent a grain-only planting date (foreground).

 

figure 3 top

figure 3 bottom

Figure 3. Photos taken on May 16, 2018. The top photo shows the progress of the wheat varieties planted on March 6, 2018. The bottom photo shows the area where the same varieties were planted on October 31, 2017. You can see how some of the varieties in the bottom photo are beginning to “turn.”

 

figure 4

Figure 4. Photo taken on June 9, 2018. Some of the varieties planted on March 6, 2018 produced heads while others did not. The right side of the photo shows a few of the varieties from the dual-purpose demonstration trial that were a few days from being harvest-ready.

 

figure 5

Figure 5. Photo taken on June 21, 2018. This shows the differences in the number of heads produced or lack thereof among varieties planted on March 6, 2018. Varieties within both planting date demonstration trials to the right were harvest-ready for some time by this date.

 

What did we find?

In the previous blog article, I mentioned that variety-specific vernalization requirements are not fully characterized, but winter wheat varieties adapted to the southern Great Plains may need between 120 to 1080 hours (5 to 43 days) at air temperatures below 45° F to vernalize. Dr. Brett Carver feels three weeks (504 hours) of exposure to constant temperatures below 45° F should be sufficient for most varieties in Oklahoma, but reducing that to two weeks (336 hours) may cause vernalization issues for some varieties.

 

After this demo was established, we experienced a cool March and April overall. In fact, April 2018 ended up being the second coldest on record. Hourly weather data provided by Wes Lee from the Stillwater Mesonet station showed that we accumulated 368 hours after March 6 where the average air temperature was less than 45° F. The last calendar day which had at least one hour with an average temperature below 45° F was April 28.

 

As a result of these conditions, we found 28 of 35 varieties (80%) produced heads. The heading dates for those varieties are provided in Table 1. For the 28 varieties which produced heads, we collected samples from the plots planted on March 6, 2018 and October 31, 2017 in order to make comparisons for a few plant characteristics. Two subsamples were collected from each plot within both planting dates. Each subsample consisted of 1 m of row. Plant height, head number, total biomass, total grain weight, harvest index, and seed weight were measured from each subsample. The data for each plant characteristic was averaged from the two subsamples within each planting date, and the results are presented in Tables 1 and 2.

 

table 1

 

table 2

 

Results Summary

  • 28 of 35 varieties (80%) produced heads to some level. The varieties which did not produce heads were Doublestop CL Plus, Duster, Iba, Joe, Showdown, Stardust, and TAM 114.
  • Compared to the same varieties planted on October 31, 2017, the 28 varieties which produced heads and were planted on March 6, 2018 on average:
    • headed 40 days later (range of 28 to 50 days later);
    • were 36% shorter in plant height (range of -20% to -48%);
    • produced 49% less number of heads (range of -17% to -78%);
    • produced 76% less total biomass (range of -47% to -93%);
    • produced 80% less total grain weight (range of -49% to -98%);
    • had reduced seed weight per 50 seeds by 39% (range of -16% to -58%);
    • had reduced harvest index by 24% (range of +44% to -70%)

 

Other Observations

A couple producers also shared some of their findings from late-emerging fields. Fred Schmedt near Altus, OK mentioned that some of their Bentley and Smith’s Gold which was planted into cotton stubble and emerged in the first week of March did produce grain. The yields they had were pretty similar to those for the same varieties in our demonstration. Jimmy Kinder near Walters, OK also had some Bentley which produced grain, and his yield was slightly better than yield for Bentley in our demonstration.

 

As a comparison to Stillwater, Wes Lee also provided me the hourly weather data from the Altus and Walters Mesonet stations. The number of accumulated hours beginning after March 6 where the average air temperature for the hour was below 45° F was 277 for Altus and 245 for Walters. The true number of accumulated hours though depended on the time when the seed of these varieties in these fields imbibed water and sprouted.

 

 

Final Thoughts

Hopefully Oklahoma winter wheat producers will never run into this problem again, and we can just put these data on the shelf to collect dust. If it does happen again though, these observations can at least give us a starting point to help aid in making more confident and timely decisions on how to move forward. However, it does not look good for forage or grain yield potential any way you slice it (as likely expected), and contacting your agent if you have crop insurance to discuss your options is highly advised. Also keep in mind that these results are from one location in one year under the cultural practices used. Seeding rate is an example of how cultural practices may influence the results. Using a higher seeding rate in attempt to compensate for less tiller production in a late-planted wheat scenario may not reduce total biomass and grain yield as dramatically compared to the observations in our demonstration.