Warren County Agriculture

On April 15, temperatures in Warren County dropped below freezing. Since that time I have had some questions about damage and some inquiries about how to estimate damage. I have compiled some information put together by our UK Extension Specialists. As you can see in the tables below provided by Matt Dixon with the UK Weather Center, temperatures did get below 31 degrees for around 5 hours. 

Scouting for Wheat Damage

Carrie Knott, Extension Agronomist-Princeton, University of Kentucky

Published on Kygrains.info

Tuesday night temperatures dipped to or below 24°F for several hours at many locations throughout Kentucky. For winter wheat that has reached the jointing (Feekes 6) growth stage, or beyond, damage can occur to the developing wheat head at these temperatures.

In general, we think that injury can occur if temperatures are at or below those listed in the table below for 2 or more hours.

Some areas across the state already had wheat that was beginning to head. This will make scouting field for freeze damage very important.

To assess wheat freeze damage:

1. Wait until high temperatures are at least 40°F for 5 to 7 days. According to the projected weather forecast, we will have high temperatures greater than 40°F all week, therefore assessing freeze damage Monday or Tuesday will likely provide an good estimate of freeze damage.

2. Scout fields

A. For fields that have not yet headed and look for yellow, chlorotic growing points and    limp leaves. There will likely be yellow leaf tips, but as long as the growing point is not affected, there will likely be minimal to no damage.

B. For fields that are in the ‘Boot’ (Feekes 10) growth stage, dissect out the heads and look for damage.

C. For field that have headed or beyond, inspect heads and florets for damage.

3. An additional concern for wheat stands and yield potential is heaving.  If extreme temperature changes occur the freezing and thawing cycle may push wheat plants out of the soil.  This will result in reduced stands and could ultimately affect yield if heaving occurs on a large percentage of the field.

Accessing Corn & Soybeans Freeze Damage

By: Dr. Chad Lee, University of Kentucky Grains Crop Specialist

We need about 5 days of warm weather before freeze damage symptoms are evident. You may see hints of damage earlier than 5 days, but you won’t be able to identify the extent of damage in most fields.  

Soybeans:

We need about 5 days of warm weather before the freeze damage is evident on the crop. Any freeze damage below the cotyledons will kill the plant. If the cotyledons survive, then the soybean plant has full to nearly full yield potential. 

Soybeans in the crook stage, where the plant is just emerging and the stem looks like a shepherd’s crook, are extremely sensitive to freezing weather. We can almost assume that soybeans at this stage are killed from the freeze. If the majority of the field was at this stage, then the farmer should plan to replant. Scouting the field about 5 days after the freeze is warranted, but one should expect to need to replant in these fields. 

For soybeans that had not emerged or soybeans with at least unifoliate leaves, the soybeans have a better chance of surviving. Sometimes, the upper leaves will insulate and protect the lower leaves. As long as the node at the cotyledon survives, the plant should survive. 

Corn: 

We need about 5 days of warm weather before the freeze damage is evident on the crop. I expect minimal yield loss on corn. I do expect nearly all aboveground growth to be frozen and dead, but I expect corn plants to survive. For corn planted at the proper depth, the growing point is at least a half-inch below the surface. As long as that growing point survives, corn has 100% yield potential, even if all aboveground growth dies. The soil often buffers the freezing temperatures and insulates the growing point. Look for areas in the fields where: 

1. seeds are shallow – shallow seeds put the growing point closer to the soil surface
2. furrows are not fully closed – open furrows allowing freezing to get to the seed quickly. 
3. areas of the field that are saturated: the higher water content will often freeze deeper in the soil than fields as field capacity
4. expect there to be more damage in tilled fields, including “vertical tilled” fields. The reside from no-till provides a temperature buffer. I expect fields with cover crop residue to be buffered as well. 

Other Thoughts on Scouting and Assessing Damage

When scouting either crop about 5 days after the freeze event, look for plants or plant structures that have turned brown or black. Look for signs of loss of turgor pressure. I think most aboveground damage will be easy to see in a few days. 

For corn, take a shovel and dig up a few plants to evaluate the growth above the seed. If there are no signs of brown/black areas on the plants, and if turgor pressure is good, then the seedlings are very likely to survive. 

As you scout, please send us some images. 

Forages:  Alfalfa & Red Clover

Dr. Jimmy Henning, UK Forage Extension Specialist

In Scouting Alfalfa stands in Lexington, Dr. Henning noticed some variable damage in Alfalfa stands but thinks that most will grow out of it.  Red clover is much less affected in the instances he has witnessed.  However, if you have seen damage or have more questions.  AGR-236 Managing Frost Damaged Alfalfa Stands

Fruit and Vegetables

We will not know damage to fruit trees until they have had a chance to grow and develop more.  Blooms were damaged but will not know the full extent of the damage for a bit. Small fruit crops like strawberries if they were not covered suffered damage.  Crops like asparagus that were not able to be covered or harvested experienced a loss.

If you have any questions or photos to share, please contact us at the extension office.