Determining Freeze Damage in Wheat
for Grain, April 2020
We
are certainly in some crazy times this week.
Adding to the situation, we had a hard freeze event earlier this week in
the Hale and Swisher areas that even blanketed much of the area with snow. Air temperatures dropped into the 20’s for
much of us. This did much more than drop
our soil temperatures to levels even too cool to plant corn, let alone cotton. This
certainly put our wheat, much of which is jointing and shooting heads upward a
bit ahead of and ‘average’ schedule, at high risk for freeze damage. With a substantial amount of ‘cover’ wheat in
the area being kept for grain with wheat being just about the stable commodity
crop through the crazy times and markets lately, we need to know if these, and
our ‘intended’ grain fields remain a viable fields, or if the damage is too
severe. With wheat, at least, we can
salvage our inputs so far and alter the fields purpose to cover, hay, or even
silage before too much expense is lost
So, did your wheat
receive damage? We will need to dissect several
wheat heads from each field to be certain.
First
off, determining freeze damage is not rocket science, but it does help to have
a bit of experience in growing point dissection and damage identification. While I encourage producers to make these educated
determinations personally, having a trusted ag agent, crop consultant, coop
agronomist, or company representative with a bit more experience to get a
second eye on the field or send a quality photo to would be a good idea.
Next
you need to understand that you cannot evaluate a field the day after the
potential injury occurred. It will take
a bit of time for the damage to truly show.
This will avoid miss identification and ease confusion. Ideally, 3-5 days of good growing weather
should be enough for any dead tissue to show signs of rot or sterility in seed
locations.
You
will need a sharp knife, but a good razor blade will do. While it is not necessary, having a hand lens
for magnification can prove useful. From
the field, harvest one jointed wheat stem at a time from ground level for dissection. Several per field will be needed. I like to stay in the field and make my dissections
fresh. I usually hunker low where I harvested
the stem to reduce wind and make each dissection immediately following stem
harvest. This helps me keep up with
where in the field damage has occurred, but you can transport dissections back
to a pickup, barn, lab, or other sheltered area for comfort. Just do not let the samples wait long before dissection
and damage determination as a desiccating plant will muddy results.
To
make your dissection, start splitting carefully with your knife from the base
of the stem the plant into even halves moving upward. If you are only interested in head health, it
is possible to determine the location of the head / growing point within the
stem and begin your dissection there.
Dissecting the whole hollow stem area up to the growing point will allow
you to also determine overall plant health, asses potential for stem collapse
and future lodging issues, and disease lesions inside the stem/stalk area. Any major discoloration, off colored spots, weak
vascular tissue, or wet appearing spots along the inside of the hollow stem
could be indications of future issues with lodging, grain fill, or fungal
disease that could also limit yield potential or even initiate fungicide treatments. For all fungal and wheat disease ID and
recommendations, please consult the Texas A&M AgriLife Small Grain Guide.
Once
your dissection has finally reached the growing point, you can either slice
through the future wheat head, or slice around it. You will likely want to do some of both from
the same area to identify differing issues and severity. With the future head and some of the future leaves
above the head now exposed, make careful observations of the head itself.
 | |
| Healthy wheat head and growing point dissected perfectly. Photo by Tim Ballinger, Ballinger Innovative Agronomics |
After
3-5 days of good growing conditions, any tissue killed by freezing weather will
start to show some obvious signs. Sometimes
leaves still in the ‘whorl’ could be damaged. They could take on a white, desiccated
appearance. Don’t let this startle you
too much. Sometimes the leaves extending
from the growing point will be damaged, but the all-important growing point and
head can remain undamaged. Upon
inspection of the future head area, any killed tissue will take on a yellowish-green
tent turning brownish-green over time that quickly turns mushy. The consistency of this killed area will take
on the consistency of gel, and not the crisp consistency of healthy tissue.
It
is also very common for the growing point tissue to survive freezing temperatures
but sustain head damage. Plant hormones
exposed to cold temperatures tend to do very odd things in the young growing
points and on future fruiting sites because they do not move properly. In this case, the future fruiting sites on
the head currently have many plant hormones in precise and minute amounts
developing all the structures that will make up the all the flower elements and
eventually the grain sites. There is no
need to get into too much detail in understanding all of the multiple problems
that could be happening here. The end
result and the clues to cue us in, should be the same, if the head was impacted
in this way.
The seed area will
turn a bleached looking white. Perhaps some
small, developing vascular tissue was damaged, perhaps the ova were impacted,
or maybe even the pollen area was killed, but the result is always tell-telling
white upon close inspection. The head
area can always appear greenish-white, but any freeze damaged area will be
whiter. These sites are not dead and
will not rot as described earlier. They
should continue to grow and seem to develop in their slightly off way, but they
are sterile sites and the impacted area will look different as it continues to develop. Sometimes, the entire head will be impacted this
way but usually it is only a portion of the head. If allowed to continue, these areas will be remaining
a bleached white once the head emerges and can be spotted easily form across
the field. This could also be a sign of
a specific fungal disease but the differentiation between freeze damage and
fungal is that the fungal cannot be determined as long before boot stage. Again, please consult our Texas A&M
AgriLife Small Grain Guides for early ID and management of this type of fungal
issue also.
Now armed with a
how to identify freeze damaged wheat, hopefully you can make an educated decision
about how to manage your specific fields.
The amount of yield you are willing to sustain from a freeze and
continue to make inputs for grain yields remain up to you, the market, and
input costs. I would suggest that a 20%
head loss or overall grain loss, from either the white sterilization or head
killing, would be a good measuring stick this season. While many plants will start anew and produce
secondary heads, these heads are starting over.
If they are relied upon for yield replacement, remember that these heads
will contain roughly half the yield potential and will lag behind in maturity.
Blayne Reed
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