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Potential Effect of Weekend Freezes on Corn and Soybean
Chad Lee, Conner Raymond, and Carrie Knott; University of Kentucky
Freezing temperatures were recorded across Kentucky Monday morning, April 24, 2023. The coldest temperatures were mostly in central and eastern Kentucky, but freezing temperatures were as far west as Trigg and Webster counties. Temperatures fell to or slightly below freezing in the following counties from Sunday to Monday: Butler, Caldwell, Carroll, Christian, Crittenden, Graves, Grayson, Hardin, Logan, Meade, Ohio, Taylor, and Webster counties (Table 1, at the end of this article). Webster and McLean County were the coldest at 30°F. Frosts likely occurred west of these counties. The good news is that soil surface temperatures likely stayed in the low 50’s to mid-40’s. This is based on soil surface temperatures measured at UKREC in Princeton, KY.
About 36% of corn acres and 20% of soybean acres were planted as of April 23, 2023, according to the USDA-NASS.
Corn and Soybeans at Risk
Corn and soybeans are at more risk to death from the freeze events at specific growth stages and in certain conditions. The following scenarios go from greatest risk to least risk of plant death from the freeze events.
Soybeans at the “crook” stage where the stem is emerged and bent over like a shepherd’s crook were the most susceptible to the freeze (Figure 1). These plants were most likely to be killed by the freeze or frost. At crook stage, typical damage is along the stem with some yellowing of the cotyledon. This will be followed by plants snapping off where damage was observed (Figures 2 and 3).
Corn and soybean seeds and seedlings in furrows that were not fully closed are at risk of being killed by the freeze.
Corn or soybean seeds that were planted shallow had a slight risk of freeze damage, although plant death from the freeze is unlikely.
Corn plants emerged may have tissue above the soil surface die off from the freeze, but the growing points should have been insulated beneath the soil surface. Those corn plants should recover well. No yield loss is expected.
Soybean plants that have FULLY emerged and are at the VE growth stage (emergence) should survive the freeze event, based on observations during freeze events in late April 2021 and early May 2020. If the soybean cotyledons survive, the soybean plants will survive, and no yield loss will occur. If the cotyledons do not survive, the plant will not survive, either.
Corn and soybean seeds at proper planting depths are at very little risk from the freeze. Corn and soybean radicles (the shoots emerging from the seeds) that are still below the soil surface likely were insulated and will survive.
We need about 5 days of warm weather before symptoms are easy to see. Based on current forecasts, it may take six or seven actual days to get the 5 days of good growing conditions. Plants or plant parts that have turned black or brown and have lost turgor pressure are easy to identify.
Corn plants need to be examined from the seed upward. We are assuming that the roots are deep enough to not be a concern. Dig up some corn plants and look for any signs of brown/black areas from the seeds upward. If plants are white to yellow beneath the soil and turgor pressure is good, then the seedlings are likely to survive.
Maybe Just a Chill
Corn and soybean seeds that are in the process of germinating during the freeze are at risk of taking in cold water (imbibitional chilling) within the first 24 to 48 hours after planting. If the soil temperatures were below 50F for an extended period during those 24 to 48 hours, then the seeds are more likely to be damaged. There is some debate about how long the soils need to stay below 50F before severe damage is done from the imbibitional chilling. We can say those seeds are at risk. At this point, either the seeds were damaged, or they were not from imbibitional chilling. Emergence will be slower in these fields. The fields can be scouted in about five days or so to determine the health of germinating seeds and/or emerged plants.
Table 1: Low temperatures recorded across the state from 4/21/23 through 4/24/23. Freezing temperatures are highlighted in light blue. Weather data from the Kentucky Mesonet.
|Low Temperature °F||3 Day|
|KY Mesonet Site||4/21-22||4/22-23||4/23-24||Average Low|
Coulter, Jeff. 2021. Spring Freeze Injury in Corn. University of Minnesota Extension. https://extension.umn.edu/growing-corn/spring-freeze-injury-corn
KY Climate Center. 2023. Kentucky Mesonet. https://www.kymesonet.org/ accessed April 24, 2023.
Lee, C.D. Evaluating early season frost damage to corn. AGR-192. Univ. of Kentucky Cooperative Extension Service. http://www2.ca.uky.edu/agcomm/pubs/agr/agr192/agr192.pdf
Nielsen, R.L. 2020. Assessing Frost/Cold Temperature Injury to Young Corn. Corny News Network. http://www.kingcorn.org/news/timeless/FrostedCorn.html
Nielsen, R.L. 2020. Cold Soils & Risk of Imbibitional Chilling Injury in Corn. Corny News Network. Purdue Univ. https://www.agry.purdue.edu/ext/corn/news/timeless/ImbibitionalChilling.html
Staton, Michael. 2021. Assessing frost/freeze damage to emerged soybeans. Michigan State University Extension. https://www.canr.msu.edu/news/assessing-low-temperature-injury-to-soybeans
Taylor, M., A. Nygren, J. Rees., J. Specht and A. Timmerman. 2020. Evaluating freeze and chilling injury in corn and soybeans. Nebraska Cropwatch. https://cropwatch.unl.edu/2020/evaluating-freeze-and-chilling-injury-corn-and-soybeans
USDA-NASS. 2023. USDA-NASS. Crop Progress and Condition. https://www.nass.usda.gov/Statistics_by_State/Kentucky/Publications/Crop_Progress_&_Condition/cw23/CW042423.pdf
Important Time to Sample for Alfalfa Weevil
Ric Bessin, UK Extension Entomologist
The UK Ag Weather Center’s degree day model for alfalfa weevil indicates that many counties in Kentucky have exceed 190 DD used as a starting point to begin scouting by the third week of March. In fact alfalfa weevil damage has appeared in some fields. Once temperature accumulations reach 190 DD, growers are advised to look at their alfalfa fields and conduct weekly alfalfa weevil larval counts and compare those to the economic thresholds listed below.
Figure 1. When degree-day totals reach 190 Degree Days, it is time to begin scouting for alfalfa weevil larvae. Scouting continues on at least on at least a weekly schedule until regrowth after the first cutting. Treat the DD totals for the counties as estimates.
Fall laid alfalfa weevil eggs are the first to hatch in the spring. These eggs hatch earlier than those laid in the spring and 190 DD approximate when first leaf feeding damage becomes noticeable. Temperatures extremes during the winter help to limit the survival of alfalfa weevil eggs that were laid in stems in the fall. Damage by the young larvae will first appear as tiny pin holes in the leaves.
To scout for alfalfa weevil, we use the stem sampling method. While walking in a “U” or “Z” pattern through a field, collect 30 alfalfa stems, carefully cup the top of each stem in one hand and break it off the crown with your other hand and place it bud end downward in a plastic bucket. Be sure your samples are at least 20 feet from the edge of a field so that they are representative of the entire interior of a field. Knock the stems groups of 4 or 5 stems at a time against the inside of the bucket to dislodge the larvae. Count the number of larvae. Measure the length of 10 random alfalfa stems. If the field is close to harvest, harvest can be an alternative to spraying, but producers need to watch for damage to the regrowth, there are similar scouting tables for regrowth after the first cutting.
Alfalfa Weevil Larvae Thresholds for Spraying 190 to 225 Degree Days (Check your degree days)
|Average stem height (inches)||Number of alfalfa weevil larvae on 30 stems|
- Apply a long residual insecticide if the number of larvae is greater than the number in the table for the average height of alfalfa sampled.
- Sample again in 2 days if the number is above 15 but less than the number in the table.
- Sample in 7 days if the number is less than 15 in your sample of 30 stems.
Alfalfa Weevil Larvae Thresholds for Spraying 226 to 275 Degree Days
|Average stem height (inches)||Number of alfalfa weevil larvae on 30 stems|
- Apply a long residual insecticide if the larval number per 30 stems is greater than the number in the table above for the height of alfalfa sampled.
- Sample again in 7 days if you find less than the number of larvae for the appropriate alfalfa height.
For degree day accumulations above 275, use the economic threshold tables in ENTFACT 127 or ENT-17 to determine the need to spray the field for alfalfa weevil.
If you de need to treat for alfalfa weevil larvae, keep in mind that insecticide resistance has been an issue in some areas. The best strategy to manage resistance is to use an insecticide only when necessary and to rotate modes of action each year. For many other pests we would rotate more often, but alfalfa weevil has only one generation per years. To rotate modes of action, select insecticides that have a different IRAC group number on the label.
Use Winter to for Preventive Maintenance
on Your Sprayers
Ric Bessin, UK Extension Entomologist
As winter begins to wind down, we need to get our equipment ready for the coming growing season. When it is time to begin spraying and planting, we don’t want to spend precious time to fix and repair equipment. It is during this down time when we should do some routine maintenance on our sprayers. Spray equipment in poor repair can lead to poor application which will cost you money.
Look for Leaks
Before your start, put on a pair of gloves to protect yourself from pesticide residues. Begin by filling your sprayer with clean water, but before you engage the pump, look for leaks from around the pump, hoses, strainers, and nozzles. Pay particular attention to the hoses, as these often show signs of wear sooner than other more durable parts. Besides obvious leaks from hoses, inspect hoses for cracking and signs of dry rot as these can burst when pressurized. Places where hoses might crimp with folding booms are prone to cracking as hoses age. Engage the pump and look again for leaks. Check the pressure gauge and test the cutoff valves to be sure they are working.
The job of strainers is to keep gunk from reaching and plugging nozzles. With just routine use there can be significant debris buildup with the inline strainer from the tank or the individual strainers in front of each nozzle. Sometimes these can be cleaned with a soft brush, other times they need to be replaced.
Next, the Nozzles All nozzles wear over time. This leads to increasing and irregular flow rate from nozzles and poor spray patterns. In place of uniform applications across a field, there may be streaks due to places of over and under applications. While some nozzles materials, such as ceramics and stainless steel, may be more resistant to wear, all nozzles will show signs of wear eventually. Sprays containing abrasive materials such as wettable powders and flowables cause more wear to nozzles. Before conducting a catch test, be sure each of the nozzles are of the exact same type and are not mismatched. Start your sprayer with the clean water and observe the pattern from each of the nozzles, look for streaks and clogs. The pattern from each nozzle should be the same. Run a 30-second or 1-minute catch test for each nozzle, output from each nozzle should be within 5% of the average output from all nozzles. Nozzles that are worn or cannot be unclogged need to be replaced and the catch test repeated.
Now that your sprayer is working properly, it needs to be recalibrated. As new strainers and nozzles can change the spray output. Calibration should be done at a minimum once a year, but for those that use a sprayer more frequent or after changing to different nozzles (going from flat fan to hollow cone for example) recalibration must be done more often. For instructions for calibrating a sprayer are in the Recordkeeping Manual for Private Pesticide Applicators.
Winterize Your Trees
Written by Lindsey Purcell, Urban Forestry Specialist, Department of Forestry and Natural Resources, Purdue University
As trees in our urban and suburban landscapes prepare for winter dormancy and cold, they could use a little extra care from you to ensure a good start in the spring. As the seasons change, trees prepare to overwinter in a dormant state. Dormancy is not death; it is a natural state in which trees prepare and adapt to cold conditions with physiological and structural adjustments. Even though the leaves are changing colors and falling to the ground, trees are still active, making necessary preparations for winter.
Winter conditions will make finding moisture a challenge—and keeping plant cells hydrated in winter is critical for survival. Potential sources of winter water include unfrozen soil; internal reservoirs; and the area above the ground, but just under the snow cover (the subnivean zone). If trees cannot find needed water in these areas, expect poor health and growth the following spring.
Summer and fall drought conditions can place trees in an overall water deficit, predisposing them to pest issues and poor health the next growing season. Likewise, spring and summer weather affects the trees’ ability to survive winter weather. Young or newly planted trees will require more attention because of limited abilities in obtaining water in their growing environment. The key to survival is giving trees adequate moisture before winter freezes the world around them.
Good cultural practices and proper plant health care make a difference in how much water is available to your trees in winter and how well they survive.
Tips for winter preparation include:
Trunk wrapping. Smooth or thin-bark trees like honey locust, crabapples, linden, and especially maple, are susceptible to sunscald and frost cracks because of the temperature fluctuations from sun exposure in the winter. The wounds caused by temperature fluctuations can leave the tree exposed to fungal organisms, which cause decay in the tree. Prevention includes guarding the trunks of younger and smooth-bark trees up to about the first branches using a flexible, white tree wrap. Leave the wrap on until after the last freezing temperatures. Remove tree guards in the spring to reduce potential damage from disease and insects.
Mulching. Mulch benefits trees all year long, not just during the summer months. Refresh the mulch layer placed in the spring so that there are about 2–3 inches of wood chips, bark, or other organic mulch over the root zone of the tree. Start at the base of the trunk, but not against it, and extend mulch to the edge of the outer branches or dripline. This will reduce soil evaporation, improve water absorption, and insulate against temperature extremes.
Pruning. Late fall and early winter are acceptable times for limited, functional pruning of most tree species. Prune trees to remove dying, diseased, or dead branches, or to improve branching structure. This also is a good time to remove water sprouts and basal sprouts. However, limit the amount of green wood pruning going into winter to reduce the amount of energy reserves the plant must use to heal the pruning wounds. Be sure to use proper pruning practices as outlined in Trees Need a Proper Start: Prune Them Right (FNR-FAQ-19-W) found at Purdue Extension’s The Education Store.
Fertilizing. If trees are not stressed from moisture deficits, apply a complete fertilizer with micronutrients. Use a low-nitrogen formulation (5-10-10 or similar ratio/ combination) to prevent a late flush of new growth. Be sure to broadcast the material uniformly over the root zone and with sufficient water so that roots can absorb nutrients. You can apply water-soluble fertilizers during watering to provide nutrients as well. Follow label directions. Providing trees essential elements just before winter will enhance next season’s growth.
Watering. Whenever rainfall is insufficient for extended periods, supplemental water is needed, especially on newly planted and less-established trees. Follow the “5 + 5 rule,” which says to provide 5 gallons of water plus another 5 gallons for every diameter-inch of tree trunk. This should provide plenty of water to help a tree during times of inadequate rainfall. For mature and well-established trees, 1 inch of supplemental water applied to the root zone every week should keep soil moisture adequate. Continue to water through the fall until the ground is frozen, so that trees have ample moisture to survive the winter months and are ready for spring growth. If limited rain or snowfall in winter indicates drought, it may be necessary to water in the winter. The best time for winter watering is a warm day, when the temperature is above 40 degrees. Refer to Drought? Don’t forget the trees! (FNR-483-W) for more information on watering trees.
These simple guidelines will help trees get off to a good start after the long winter, when we are ready to transition from snow white to growing green.
Combating the Spread of Fire Ants
Source: Joe Collins, Kentucky Deputy State Entomologist
We know that fire ants have been in the state since 2000. They have typically been an invasive species only in Western Kentucky; however, earlier this year, Kentuckians discovered them in the eastern part of the state. These ants can pose a risk to human, animal and crop health. While the U.S. Department of Agriculture doesn’t currently list Kentucky as an “invaded” state, you should still know how to prevent, spot, report and treat fire ants in case you do encounter them.
So far fire ants have been confirmed in southeastern counties like McCreary and Whitley counties along the Tennessee border, but the survey is ongoing to determine the boundaries of the infested area. If you are in or around an area where fire ants have been reported, it is important to report suspected fire ant mounds. Fire ants can spread to new areas of the state through the movement of certain agricultural products. For example, fire ants can infest round bales stored in the field or on the ground, so be wary in purchasing these types of bales.
Fire ants are known for their mound-like nests. These nests vary in size but can be as large as 18 to 24 inches tall, and the mound has a fluffy soil appearance. You’ll typically find these mounds in open sunny areas on level ground or on a southern facing slope, and you won’t usually find them in wooded areas.
If you suspect fire ants on your property, do not approach the mound as fire ants are very aggressive and may sting if you disturb the mound. To report a mound, contact your local extension agent or submit a report to ReportAPest@uky.edu including a photo or video and address or GPS coordinates of the mound.
If fire ants are identified on your property, you may use fire ant baits such as Advion, Amdro and Extinguish to eliminate the ants. Read and follow the directions on the product label. Do not use gasoline, diesel or other flammable products as a control tactic.
For more information about fire ants, contact the Warren County office of the University of Kentucky Cooperative Extension Service.
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Equine: September Tips & Tidbits
UK College of Agriculture, Food and Environment
“High Traffic Area Pads for Horses” ID-164
Some Early Thoughts On This Fall’s Soil Fertility Management
UK College of Agriculture, Food & Environment Corn & Soybean News (August 2022)Dr. John Grove, Professor of Agronomy/Soils Research & Extension
SOIL TESTING for the next crop is important this fall. The summer season’s drought, after spring wetness (with compaction issues), is causing lower, more variable, corn and soybean yields. Lower grain yield means lower nutrient removal, but this is not perfectly predictable from a yield monitor. Drought affected grain is usually nutrient rich compared to rainy season grain. More corn acres will be harvested for silage rather than grain and nutrient removal is greater with silage. Soil test ‘problem’ fields/areas identified earlier this season. If you don’t do your own soil sampling, you might want to book sampling services early – this year there are more questions that need samples to inform deci-sion-making.
SOIL ACIDITY hurts root activity – a bigger problem in droughty seasons. Once soil test results are in, take a close look at soil pH. If needed, and if weather permits, lime should always be applied in the fall. Good quality lime takes time to dissolve and cause the carbonates to neutralize soil acidity.
DECIDING WHETHER TO APPLY fall nutrients, especially for corn and soybean, is more difficult this year. The decision generally depends on the target crop (wheat/forages vs. corn/soy); economics/value of fertilizer, time, and equipment; and the soil test value (low values mean higher recommended rates – better nutrient use efficiency when needy soils are fertilized to better match crop demand = spring for summer crops like corn and soybean). Fertilizer prices are lower (except for potash) now, but still high relative to prior years.
WHEAT follows corn in many areas. This year, most wheat will not need fall nitrogen (N). Lower corn yield causes less N removal. Tissue N will be higher in corn residues, giving greater N availability as residues decompose. Many grain producers have fields in forage production. Likely under fertilized this year, these crops/fields may really need some fall fertility to improve stand health, winterhardi-ness, and both forage quality and stand competitiveness with weeds next spring.
A WINTER COVER CROP can contribute. In addition to protecting against soil erosion (especially with less full-season soy residues this year), cover crops cause greater nutrient retention against fall-winter losses. One ton of rye dry matter (good stand, 12 to 18 inches tall) contains about 35 lb N, 45 lb K2O, and 10 lb P2O5. These nutrients won’t all be immediately available with rye termination next spring, but $32(N) + $33(K2O) + $7(P2O5) = $72 worth of nutrients, considering the most recent aver-age retail fertilizer price levels (https://www.dtnpf.com/agriculture/web/ag/crops/article/2022/08/02/summer-slump-retail-fertilizer), are retained.
FALL NUTRIENT SOURCE DECISIONS might also be difficult. This fall, the need for fertilizer N will be significantly lower. Fall application of N, regardless the nutrient source, will be less economical and losses are more likely, given likely greater fall background soil N levels. Nutrient sources containing N and other important nutrients (DAP, 18-46-0; MAP, 11-52-0; poultry litter) are usually priced consid-ering their N content, making them less desirable for fall application to wheat, corn, and soy acres this fall. DAP, 18-46-0, is a popular fertilizer P source and the most recent DTN survey average retail price (the URL just above) was $1005/ton. Urea, 46-0-0, was $836/ton ($0.909/lb N). This means that the 360 lb N in one ton of DAP was worth about $327, and the phosphate value was $678/ton DAP ($0.737/lb P2O5). About a third of the price of DAP is in the value of N it contains – N that is less likely to be needed this fall. You might ask your fertilizer retailer to bring in triple super phosphate (0-46-0) so that you can meet your fall phosphate needs without losing money on unnecessary N.
FERTILIZER PLACEMENT (banding) improves fertilizer P and K use efficiency, relative to broadcast fertilizer. AGR 1 (http://www2.ca.uky.edu/agcomm/pubs/agr/agr1/agr1.pdf) indicates that in spring, if soil test P and/or K are very low or low, one-third to one-half the recommended rates of P2O5 and/or K2O for corn can be used if it is banded 2 to 4 inches from the row. Relevant research for Kentucky soils is not available, but I’d estimate that precision (GPS guided) banding fall applied P and K would similarly improve their use efficiency relative to fall broadcast P and K. Precision fall banding would likely be superior to spring broadcasting, though not as good as spring banding, as long as corn is planted 2 to 4 inches from the banded P and K. Precision fall placement anticipates precision spring planting.
SBA Deadline Approaching for Working Capital Loans in Kentucky for Secretary of Agriculture Disaster Declaration for Tornadoes
Source: U.S. Small Business Administration
ATLANTA – The U.S. Small Business Administration (SBA) is reminding small businesses, small agricultural cooperatives, small businesses engaged in aquaculture, and most private nonprofit organizations that Sept. 19 is the filing deadline for federal economic injury disaster loans in Kentucky resulting from Tornadoes on Dec. 10-11, 2021.
Low-interest disaster loans are available in the following counties: Allen, Barren, Butler, Edmonson, Grayson, Hart, Logan, Simpson and Warren in Kentucky.
Under this declaration, the SBA’s Economic Injury Disaster Loan (EIDL) program is available to eligible farm-related and nonfarm-related entities that suffered financial losses as a direct result of this disaster. Apart from aquaculture enterprises, SBA cannot provide disaster loans to agricultural producers, farmers, and ranchers.
The loan amount can be up to $2 million with interest rates of 2.83 percent for small businesses and 1.875 percent for private nonprofit organizations, with terms up to 30 years. The SBA determines eligibility based on the size of the applicant, type of activity and its financial resources. Loan amounts and terms are set by the SBA and are based on each applicant’s financial condition. These working capital loans may be used to pay fixed debts, payroll, accounts payable, and other bills that could have been paid had the disaster not occurred. The loans are not intended to replace lost sales or profits.
Applicants may apply online using the Electronic Loan Application (ELA) via the SBA’s secure website at DisasterLoanAssistance.sba.gov/ela/s/ and should apply under SBA declaration # 17321.
Disaster loan information and application forms may also be obtained by calling the SBA’s Customer Service Center at 800-659-2955 (if you are deaf, hard of hearing, or have a speech disability, please dial 7-1-1 to access telecommunications relay services), or by sending an email to DisasterCustomerService@sba.gov. Loan applications can be downloaded from the SBA’s website at sba.gov/disaster. Completed applications should be mailed to: U.S. Small Business Administration, Processing and Disbursement Center, 14925 Kingsport Road, Fort Worth, TX 76155.
Submit completed loan applications to SBA no later than Sept. 19, 2022.
Feeding of Japanese Beetles on Soybean also Cause Injuries to Blooms
UK College of Agriculture, Food & Environment Corn & Soybean News (August 2022)
Dr. Raul Villanueva, Extension Entomologist
Japanese beetles, Popillia japonica (Coleoptera: Scarabaeidae) are native to Asia. This species was first detected in the early 1900s in New Jersey, but now occurs throughout many areas of the United States. This is a well-established pest in Kentucky.
Japanese beetles have only one generation per year. Its larval stage lives underground feeding on roots, with adults emerging in early-July through mid-September. The larval form of this carabid is called white grub.
Adult beetles are considered destructive pests of many ornamentals, turf, and landscape plants. In soy-bean fields, it has been observed feeding on leaf tissue between leaf veins; in many cases this feeding leaves a lace-like, skeletonized appearance. Figures 1A and 1B show initial feeding and advanced skele-tonized leaf, respectively. Leaf damage in soybeans can appear severe as leaves can be completely skel-etonized, and many beetles may be found aggregating on plants in a patchy distribution of the field. However, this injury seldom requires control measures.
At this time, I am reporting a not as well-known feeding habit of Japanese beetles in soybeans. I had heard that this insect was causing some damage to soybean blooms in the North Central region of the U.S. While conducting tallies for insects in soybeans, I observed that a couple of beetles were aggregat-ed under the foliage, and they were feeding on the blooms (Figure 2). Injury to soybean blooms may reduce pod development; however, studies to evaluate the impact of this feeding behavior have not yet been conducted. Feeding on flowers or fruit by Japanese beetles is typical for fruits or ornamental plants.