Night 3
“Weather Trends Affecting Ohio Ag”
Aaron Wilson, Assistant Professor
Ag Weather & Climate Field Specialist
OSU Extension
Frost
Yes, Another Article About Freeze Symptoms in Winter Wheat
Source: Dr. Laura Lindsey, OSU
After a (short) second round of winter last week, there has been some concern regarding winter wheat. As a reminder, the magnitude of freeze damage depends on: 1) temperature, 2) duration of temperature, and 3) wheat growth stage. During the cold snap last week, the majority of winter wheat in Ohio was at the Feekes 6 to 8 growth stage. In northern Ohio, temperatures were in the low 30s to upper 20s. In Southern Ohio, temperatures were mostly above 30°F with a dip to 26°F on April 23, recorded by the CFAES weather system in Pike County. Underneath the snow, temperatures were warmer (Figure 1 records the temperature under the snow on April 21).
A few years ago, we conducted a freeze chamber experiment to examine the effect of low temperature on winter wheat at several growth stages (Table 1). Keep in mind, actual yield reductions in the field can be quite variable depending on the weather for the remainder of the growing season. At Feekes 6 growth stage, temperatures >20°F caused no damage. However, by Feekes 8 growth stage, temperatures of 25°F to 28°F caused a 10 to 25% reduction in wheat yield. These temperatures were from the crown of the wheat plant, not air temperature.
What to look for: After a freeze event, wait one to two weeks after active growing conditions resume to check for visual signs of freeze injury. Make sure to examine several areas of the field as landscape features influence the micro-climates within fields. Small differences in temperatures can cause large differences in damage and grain yield.
At Feekes 6 growth stage, damage from freezing will cause discoloration of the leaf tissue, with leaf tips or edges exhibiting symptoms first (Figure 2). However, discoloration does not necessarily indicate a reduction in grain yield. At Feekes 6 growth stage, damage can also be assessed by carefully cutting the wheat stem lengthwise to expose the developing spike at the first node. Damaged spikes will appear discolored and shriveled. A healthy, developing spike should be rigid and whitish-green (Figure 3).
Figure 2. At Feekes 6 growth stage, freeze damage causes yellowing of browning (necrosis) of the leaf and stem tissue. Wheat plants pictured (left to right) were exposed to temperatures of 3, 14, 21, 28, and 39°F corresponding to death of 100%, 80%, 50%, 25%, and 0% death of the plant tissue.
Figure 3. At Feekes 6 growth stage, freeze injury causes damage to forming wheat spike within the stem. Wheat spikes pictured (left to right) were exposed to 39, 28, 21, 14, and 3°F temperature treatments. At 3°F, the wheat spike appears discolored and deformed.
At Feekes 8 growth stage, damage from freeze may include yellowing or browning of the flag leaf. The flag leaf may appear twisted or in a spiral (Figure 4). As the plant continues to grow, the wheat spike may get stuck in the leaf sheath, causing a crooked appearance at heading (Figure 5). (Although, this phenology can also be associated with spikes that emerge quickly due to warm temperatures.)
Overall, I think freeze damage should be minimal from this most recent cold snap. At Feekes 6 growth stage, wheat is still fairly tolerant of cold temperatures. In the southern portion of the state, where wheat stage was more advanced, temperatures tended to be warmer. However, the best way to assess for potential damage is to scout your field after active growing conditions resume this week. For more information, see our new ‘Freeze Symptoms and Associated Yield Loss in Soft Red Winter Wheat’ FactSheet: https://ohioline.osu.edu/factsheet/anr-93
Figure 4. Twisting or spiral appearance of the flag leaf can be caused by low temperatures. Photo credit: Greg LaBarge.
Figure 5. At Feekes 8 growth stage, damage may include yellowing or browning of the flag leaf. The wheat head may get stuck in the leaf sheath causing a crooked appearance at heading.
Should you expect any freeze damage to winter wheat? Most likely, no.
Source: Laura Lindsey, Alexander Lindsey, OSU Extension
The incoming cold temperatures are not likely to impact winter wheat. The magnitude of freeze damage depends on: 1) temperature, 2) duration of temperature, and 3) wheat growth stage.
Prior to the Feekes 6 growth stage, the growing point of wheat is below the soil surface, protected from freezing temperatures. Most of the wheat in Ohio is at the Feekes 4 (beginning of erect growth) or Feekes 5 (leaf sheaths strongly erect) growth stage and should be unaffected by the incoming cold temperatures, predicted to be mid- to low 20s on Wednesday and Thursday.
At Feekes 6 growth stage, our research has shown only a 5% reduction in wheat yield at a temperature of 20°F for 15-minute duration and 50% reduction in wheat yield at a temperature of 12°F for 15-minute duration. (Although, it should be noted, there is a great deal of variability in response due to environmental conditions for the remainder of the growing season. Additionally, greater soil moisture levels can help buffer against short-term temperature fluctuations.)
For more information on Freeze Symptoms and Associated Yield Loss in Soft Red Winter Wheat, please see our new FactSheet: https://ohioline.osu.edu/factsheet/anr-93
We Now Turn Our Attention to Autumn Harvest Season
Source: Jim Noel
The cooler than normal blob of water in the eastern Pacific Ocean near the equator tends to push the first autumn freeze later than normal in our region. Therefore, there is no indication of an early freeze in September this year. It appears the first freeze for Ohio will not come until October either on schedule or a bit later than normal.
September looks to have the first half start cooler than normal followed by a return to normal temperatures for second half of the month. Precipitation will be normal or sightly above normal for September. Normal rainfall is currently 1-1.5 inches per two weeks dropping to about an inch per two weeks for the second half of September. Even though we expect rainfall at or slightly above normal in September, there is a great deal of uncertainty due to the tropics and where those systems will travel. So you will want to pay attention to later outlooks at: https://www.cpc.ncep.noaa.gov
Rainfall for the first half of September will average 0.50-2.00 inches. The heaviest rains will likely surround the state of Ohio in most directions.
October into part of November looks to resume the above normal temperatures which should create an extended autumn this year. Rainfall remains highly uncertain but it appears near normal is the most likely outcome for October and November as we have some climate models showing above normal and some below normal rainfall.
The early outlook for winter calls for above normal temperatures first half and below normal temperatures second half. Precipitation is likely to become above normal with potential influences from the tropical Pacific Ocean.
Frost Damage to Soybeans
Source: Charles Hurburgh, Rebecca Vittetoe, Meaghan Anderson, Iowa State University
Figure 1. Frost-damaged soybeans with shriveled and discolored leaves. Photo courtesy of Rebecca Vittetoe.
Temperatures fell into the low 30’s and upper 20’s in most of Iowa over the weekend of October 11-13. Because of the very late planting season, some crops were immature enough to be injured by the freezing temperatures. This ICM Blog will address frost damage concerns to soybeans.
Frost normally forms early in the morning, driven by radiation cooling especially on clear cold nights. The visual impact of the frost damage is most evident the next day (Figure 1).
Temperatures below 32°F can damage soybean leaves, and temperatures below 30°F for an extended time periods can damage the stems, pods, and seeds. A killing freeze is considered to be 28°F for soybeans.
The severity of frost damage to soybeans depends on the following: how low the temperatures dropped, the duration of the cold temperatures, and the growth stage of the soybeans. Soybean fields with at least one mature pod on the main stem of each plant (R7 growth stage) are likely to be minimally affected by frost. Soybean plants with green pods will be more affected by frost. If the frost just damaged soybean leaves, particularly in the upper canopy, pods and seeds will continue to develop with yield minimally affected.
If the frost was more severe and damaged the stems, pods, and seed, the potential for reduced yield and quality is higher. In addition to reduced yield and quality, severely frost-damaged soybeans will dry down more slowly and be more likely to shatter at harvest. Farm moisture meters and older elevator meters will read about 1.5-2% points low until moisture and color have equalized. The new 150 mhz meters used by many elevators are more accurate.
Handling frost-damaged soybeans