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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.