Kansas Wheat: How Has Cold Weather Affected Crops?

Well, here we go again with Mother Nature not cooperating with us! Several areas of the state, including northcentral Kansas, experienced some rather cold temperatures! So you might be wondering if that may have affected the wheat.

Minimum air temperatures across Kansas reached very low levels during April 3-4, 2018 and then again this past weekend, April 7, 2018. The minimum temperature observed (April 3-4) across the state was 11 degrees F. reported at the K-State Mesonet station in Scandia along with another station in southern Kansas.

The Post Rock District weather stations ranged from 13-14 degrees F. For the April 7 temperatures, the minimum observed was 5 degrees F. reported in Hill City while our Post Rock District weather stations indicated 8-9 degrees F. at each of the three in Jewell, Mitchell and Osborne counties.

Different stages of wheat development vary in their sensitivity to cold temperatures and this year, wheat development is quite delayed relative to the past two years in Kansas. So the delayed wheat development is good in regard to potential damage to the wheat here in north central Kansas from the cold temperatures.

While it is late in the year for these observed temperatures, most of the wheat that I have examined, in our Post Rock District, the wheat growing point is below the ground, so is more protected than wheat that would be more advanced in the development.

However, since the wheat has been greening up, you may have noticed that some of your fields may have experienced some winter-kill or winter damage especially with the significantly dry conditions.

According to the most current Kansas Drought Monitor map, parts of northcentral Kansas, including our Post Rock Extension District, are in the moderate to severe drought.

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According to Mary Knapp, K-State Research and Extension, State Climatologist, “It is important to consider that air temperatures reported by our meteorological monitoring stations are often measured 5 feet aboveground, and may not fully reflect the microclimate to which the wheat canopy is actually exposed.”

For example, a lush wheat canopy will tend to reduce the extent of freeze damage as the warmth of the soil will radiate up into the canopy. In addition, moist soil buffers temperature changes better than dry soils and therefore less freeze injury may occur at a given temperature when soils are wet.

Unfortunately, we really don’t have either of these two conditions for our wheat crop.

A dry soil will cool down faster than a moist soil, thus increasing the chances of low temperatures at the crown level. The circumstances for concern with the crop’s ability to make it through these recent cold days include:

• Extremely dry soils with poor root development
• Late-sown crops with delayed development (less than 4-5 leaves and 1-2 tillers)
• Shallowly-sown fields where the crown is closer to the soil surface
• Heavy-residue situations which may have precluded good seed soil contact

So let’s take a look at the reported soil temperatures during this time. As a result of so many interacting variables, evaluating solely air temperatures may not completely reflect the conditions experienced by the wheat crop. Soil temperatures can help determine the extent of cold stress at the crown and lower canopy levels.

According to the Kansas Mesonet Library (here), 2-inch soil temperature depths at the Jewell, Mitchell and Osborne County weather stations dipped down to 34-38 degrees F. with the 4-inch soil temperature depths at 38-41 degrees F. for both weather events.

As you can see in the chart below, wheat in the tillering stage (Feekes 3, 4 or early 5) can sustain 12 degrees F. (air temperatures for at least 2 hours) with minimal potential damage. But, as mentioned earlier, the three weather stations in our Post Rock Extension District recorded air temperatures of 8-9 degrees F.

So a “wait and see” game on the potential damage that the wheat may have experienced!

Click Image to Enlarge

Where most of the wheat in the northcentral part of Kansas still has the developing head (growing point) below ground and insulated from cold air temperatures (Feekes 3, 4, or early 5), there is a low risk of potential damage that may be expected from the cold temperatures from the first part of April at this time.

But with the temperatures expected to warm up for the next few days, wait a few days and the wheat may start to show symptoms if damage has occurred. It would be a good idea to actually go out in the field and dig up some plants and split the wheat stems to find the growing point (developing head) and see the condition.

A healthy growing point will be whitish, greenish and firm while a damaged growing point will be yellowish, brownish and somewhat mushy.

Other than the above circumstances, most of the damage at this stage (Tillering – Feekes 3, 4 or early 5) should occur to leaf tissue, which might give the crop a rough look for a few weeks. The chart provides you with the symptoms and the yield effect on the wheat at certain temperatures and at specific growth stages.

The first apparent sign of freeze injury will be leaf dieback and senescence (death) which should occur regardless of damage to the actual growing point. This will occur more quickly if temperatures warm up after low temperatures.

Existing leaves will almost always turn bluish-black after a hard freeze, and give off a silage odor. Those leaves are burned back and dead, but is not a problem as long as newly emerging leaves are green.

Provided that the growing point is not damaged, the wheat will recover from this damage in the spring with possibly little yield loss.

K-State Research and Extension has an excellent publication, “Spring Freeze Injury to Kansas Wheat” that is available either online or at one of our Post Rock Extension District Offices in Beloit, Lincoln, Mankato, Osborne or Smith Center. The publication, at NO COST, is an excellent resource that explains the potential injury to wheat at different growth stages and at different temperatures along with color pictures.

If you have more questions on wheat freeze, give me a call at any of our Post Rock Extension District Offices in Beloit, Lincoln, Mankato, Osborne or Smith Center.

Post Rock Extension District of K-State Research and Extension serves Jewell, Lincoln, Mitchell, Osborne, and Smith counties. Sandra may be contacted at swick@ksu.edu or by calling Smith Center, 282-6823, Beloit 738-3597, Lincoln 524-4432, Mankato 378-3174, or Osborne 346-2521. Join us on Facebook at “Post Rock Extension”. Also remember our website is www.postrock.ksu.edu and my twitter account is @PRDcrops.

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