Amanda de Oliveira Silva, Small Grains Extension Specialist
As the weather warmed up last week the damage from the latest freeze event (on April 15) is starting to show in some areas of Oklahoma. A lot of wheat fields were at the flowering stage when the freeze came in, and the near the wheat is to flowering the more sensitive it is to freezing temperatures.
We split up in a group of people to look for potential freeze damage at different counties in South Central and South West Oklahoma last week. Most of the damage we are seeing is death of the flower parts followed by head discoloration (Figure 1). Temperatures got cold enough to kill the flower parts but not the cells in the green tissue, so it is taking a little bit longer for the rest of the plant to start showing the damage. The male parts (anthers) have a pale color and are dead inside of the glume (Figure 2), they are supposed to be green and turgid. In cases where pollination had already occurred when the freeze came in, we could see berries being formed, but those berries are shriveled and dried out (Figure 3).
I went to Chickasha on Monday (April 20) and found a few varieties lodged and with head starting to turn colors. I went back on Friday (April 24) with the Senior Agriculturalist of our program Robert Calhoun, and wow, we got hit! Mesonet station reported that our field spent 5 hours at 30F, and that was more than enough to harm our blooming wheat. There was a visual difference between early vs. late maturing varieties in our trial (Figure 4), but we will be able to truly assess differences from freeze-damage among varieties in the coming days. Other symptoms we found on severely damaged plants was lodging followed by enlarged nodes and split stems (Figure 5).
We found a few wheat fields with up to 100% loss from freeze damage at Garvin county. According to Mesonet, the county experienced about 6 hours at 29F. Secondary tillers were also damaged.
Caddo county spent 6 hours at 27F and wheat fields are just now starting to turn, but the heads are blank with no grain being formed and anthers are dead. At some those fields, secondary tillers were less affected than the heads from the main tillers and were blooming (Figure 6).
We were not able to find freeze injury in wheat fields at Kingfisher and Canadian counties as of April 23, but we will certainly look at more fields in those areas again this week.
Gary Strickland checked about 15 fields on the west side of Jackson county and found from 40 to 70% damage. He also reported more severe damage on the east side of the county ranging from 70 to 100% in the fields checked.
Dr. Todd Baughman checked about 30-40 fields in the Tillman County area and reported an average of 50% wheat loss due to freeze damage, but some fields were at 100% loss. I have also heard from producers that some wheat fields are severely damaged at Cotton County.
Injury symptoms should become more easily identifiable by the end of this week and growers can assess damage to individual fields. I recommend opening the wheat spikelet and taking a look at the flower parts to see if they continue to be viable. Low-lying areas of the field seems to show more severe damage than higher areas of the field. So, look at different areas throughout the field to help determining the % injury. If injury is extremely variable, increase sample size.
Talk to your insurance adjuster before making any decision. If you are not so sure about the damage give it a few more days until you can have a more clear picture of possible losses due to the freeze. If you decide to cut your wheat for hay see the recommendations from our Forage Extension Specialist Alex Rocateli below.
Freeze injury seemed to be worst in a combination of fields in lower areas planted with early maturing variety that was right at the flowering period when the freeze came in. Wheat is way more advanced in growth this growing season than usual and that is why we are seen lots of damage due to freeze this year. There is no “recovery” treatment that can be done at this point. For next seasons, producers could consider planting varieties with different maturity range to spread the freeze-injury risk.
We think in a couple days we will have a more clear picture of possible damage in different areas. While it is fairly easy to determine the extent of injury on individual fields, the hit or miss nature of freeze injury this year makes it difficult to estimate the total impact on the Oklahoma wheat crop as a whole.
Considerations for haying freeze damaged wheat by Alex Rocatelli, OSU Forage Extension Specialist
Haying wheat for forage is an option for wheat that was affected by the latest freeze event. However, before making any decision, producers should evaluate the freeze loss in their entire wheat field. Therefore, a field may have severe damage and very low grain yield potential in some areas. At the same time, minor freeze injury may allow worthwhile grain yields in other areas. To date, most of the wheat fields are within late boot to flowering stages. At these growth stages, forage yield is almost maximized, while forage quality remains good (19-15% crude protein/68-66% total digestible nutrients). In other words, this is good hay! However, freeze-damaged wheat degrades very rapidly; therefore, it is recommended to cut, cure, and bale it as soon as possible. Unfortunately, we have chances of rain statewide in the next days, which may cause some rain damage during the curing process. The severity of rain damage in curing wheat hay will depend on rainfall amount and intensity. High rainfall amount pouring for a long time can cause more damage than low amounts pouring in a short time. Finally, freeze-damage kills the wheat head; however, the plant is still alive, taking up nitrate from the soil. Under this condition, wheat plants will not utilize nitrate to produce grain, accumulating it into the stems. High amounts of nitrate in forage can be toxic to livestock; therefore, nitrate forage testing is highly recommended for freeze-damage wheat hay. For more information on nitrate toxicity, follow the link: https://extension.okstate.edu/fact-sheets/nitrate-toxicity-in-livestock.html
Thanks to all field collaborators for this post:
Aaron Henson – Tilman County Extension Educator
David Nowlin – Caddo county Extension Educator
Gary Strickland – Jackson County Ext Center
Kyle Worthington – Canadian county Extension Educator
Melissa Koesler – Garvin County Extension
Robert Calhoun – Senior Agriculturalist Small Grains Program
Sumit Sharma – Assistant Extension Specialist Goodwell
Todd Baughman – Weed Scientist and Research Professor