C.O.R.N. Newsletter: 2022-34
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October Usually Brings Our First Fall Freeze
The calendar has turned to October, and with it, harvest and fall activities will accelerate over the next few weeks. We have already experienced a few chilly nights this past week with patchy frost in some areas, but when do we typically see our first freeze conditions? This first (last) official freeze is defined as the first fall (spring) day where the overnight low reaches 32°F.
The Midwest Regional Climate Center (MRCC) has developed a new Freeze Date Tool (https://mrcc.purdue.edu/freeze/freezedatetool.html) that relies on historical temperature data at the county level back to 1950 and allows users to select a freeze temperature threshold between 20°F and 40°F to visualize the earliest, average, and latest fall or spring event. For instance, many of us are interested in the hard freeze threshold of 28°F, the temperature at which our corn and soybean growing season comes to an end.
Figure 1 shows the average first fall freeze date for areas of the eastern corn belt for the period 1950-2021 using the 32°F threshold. The online version allows users to hover their mouse over a county of choice to view the average freeze date for that county. For instance, the Knox County average is October 8, October 11 in Darke and Fulton Counties, and October 17 in Fayette County. Areas near bigger cities like Cleveland and Cincinnati have first freeze dates closer to the end of the month.
Temperatures are expected to flirt with 32°F on Tuesday morning and again Saturday and Sunday mornings. Still, most of the earliest dates and even the earliest 10% of dates on record occurred in late September, so we are beyond those thresholds. More recent first freeze dates have been occurring later in the year, with some counties reporting a trend of more than 3 days later per decade (~21 days later over the full period). The Freeze Tool also allows users to view these trends as well as more detailed analysis for individual counties.
Other MRCC climate related tools are available with cli-MATE. For instance, Figure 2 shows the probability of an earlier freeze in the fall for the Wauseon Water Plant in Fulton County using data over the last 30 years. Note that 50% of the time, a hard freeze (28°F) occurs by October 30th (green line) for this site. These graphs can be generated for stations across the state.
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Weather Update: Cool, Dry Weather Continues
After making landfall as a destructive Category 4 storm with winds to 155 mph along the southwest coast of Florida last week and another landfall in the Carolinas, the remnants of Hurricane Ian skirted across our far southeastern counties over the weekend with generally light rain and gusty winds (Figure 1). Elsewhere, lake-effect rain showers earlier in the week impacted counties in the northeast, but much of the state was dry. Temperatures have been running 3-10°F below normal for the past 7 days as well. Cool temperatures are limiting impacts from an overall drying trend across much of western and southern Ohio, but this is a good environment to continue drying crops ahead of harvest. The situation should be monitored in the coming weeks though for the potetnial for field and combine fires as the forecast indicates continued dry condtions. For the latest up-to-date conditions, seasonal outlooks, and monthly climate summaries, please visit the State Climate Office of Ohio.
Forecast
High pressure will keep fair skies and calm winds locked over the state for Tuesday through Thursday. After a chilly start in the 30s on Tuesday morning with scattered frost, temperatures will moderate throughout the week with highs in the mid to upper 60s (north) to mid to upper 70s (south). A series of cold fronts will sweep through late in the week with spotty showers possible on Friday. Cooler air will filter into the state with highs on Friday and Saturday only likely to reach the upper 40s to mid 50s, with overnight lows well down into the low to mid 30s. This raises the possability of some areas of Ohio (e.g., NW and NE) reaching their first fall freeze conditions (temperatures < 32°F); though at this time, upper 20s are not likely. For more informaton on historical fall freeze conditions, check out October Usually Brings Our First Fall Freeze also in this week’s C.O.R.N. Newsletter.The Weather Prediction Center is forecasting less than 0.10 of an inch of precipitation in Ohio this week (Figure 2).
The Climate Prediction Center’s 6–10-day outlook for the period of October 9 - 13, 2022 and the 16-Day Rainfall Outlook from NOAA/NWS/Ohio River Forecast Center show temperatures and precipitation are leaning toward below normal levels (Figure 3). Climate averages include a high-temperature range of 68-72°F, a low-temperature range of 46-50°F, and average weekly total precipitation of about 0.70 inches.
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Harvesting and Handling Ear Rot-Affected Corn
Ear rots and mycotoxins: Ear rots are beginning to show up in pockets across the state, leading to concerns about mycotoxin contamination of grain. So far, we have received images and samples with Gibberella, Diplodia, Fusarium, and Trichoderma ear rots, four of the most common ear rots in the state. Of these, Gibberella (GER) and Fusarium ear rots are of greatest concerns, since grain harvested from affected fields will be contaminated with mycotoxins, particularly vomitoxin in the case of GER. Vomitoxin is a concern for the livestock and ethanol industries. Feed made from heavily contaminated grain may lead to vomiting and low weight gain in animals; pigs are particularly sensitive. Vomitoxin is not destroyed during ethanol production, nor is it removed in the ethanol fraction, but rather becomes concentrated in the grain fraction. This leads to three-fold higher levels of the toxin in DDGS, a nutrient-rich co-product of ethanol production that is commonly sold as an ingredient for animal feed. Consequently, ethanol plants may reject GER-affect grain with high levels of vomitoxin. Slow grain dry-down, late-season rainfall, and delayed harvest will increase ear rot severity and mycotoxin contamination.
Harvesting: Severely diseased and toxin-contaminated grain are usually smaller than healthy grain, and are covered with fungal mycelium (mold). Compared to healthy grain, diseased grain break easily during harvest, transport, and other forms of grain handling, increasing the number of fine particles and the amount of dust in the grain lot. Fines and dust usually consist of pieces of cobs that are often more contaminated with mycotoxins than the grain itself. Fields with ear rot problems should be harvested as soon as possible and handled separately from healthy fields, even if it means harvesting those field at a higher-than-usual moisture content. Adjusting the combine to minimize damage to the grain and increasing the fan speed will help to remove lightweight grain, fines, and dust particles, and as a result, reduce the overall level of mycotoxin contamination of the grain lot.First consider using combine settings that are as gentil on the cobs as possible to minimize cob breakage. To do this, start at the concaves and rotor speed. You want to set your concave clearance to match your average cob diameter. On newer machines that are zeroed correctly, take a few shelled ears and find the metric wrench that just fits over the cob; this will be your concave setting in mm. For other machines, measure the diameter of the average cob and the distance from your rasp bars to the concave. Once your concave setting is correct, run your rotor as slowly as you can to get the grain shelled off. If you are still having problems with cob breakage, consider changing the type of concaves you are using. In general, round bar concaves shell wet corn and corn with rotten cobs better than large wire concaves. If you change concaves to round bar, be sure to recheck the clearance to rasp bars.
Once your threshing system is set correctly, turn your attention to air speed and separator. Run your air speed as fast as you can. Some producers even install rubber flaps and special kits to stop the air from escaping in places it should not. Next open your bottom sieve all the way to allow maximum air to reach the top sieve/chaffer. For wet or moldy corn, do all of your separation and cleaning on the top sieve. Generally, the initial top sieve setting is 5/8 inch open on the front and middle sections, open it more if you have corn coming out the back and close it to clean up your grain tank sample. Another option is to reconsider how open the back foot that goes directly into the reclean system is; often we open this more than the main separation area, but with moldy corn, this may not be the best practice. Using the same distance opening as the main sieve or less, down to even closing this section all the way, helps the air float the fines out instead of being lost. When vomitoxin levels are unacceptably high, close your reclean all the way and even block it off so that no air escapes. This helps with cleaning.
The last step is to put perforated screens under the augers and elevator doors on the combine. These perforated screens are often used for dry beans, and from our research, help to separate the fines. One quick test this fall showed vomitoxin levels around 26 ppm in samples of the screenings coming from our perforated screens, while the grain tank sample was 5 ppm. We are still running tests to determine how effective this approach is for reducing vomitoxin, but some work out of Canada showed a 40% vomitoxin reduction through perforated screens on all combine auger and elevator bottoms. One important thing to keep in mind is that this works best once corn is below 25% moisture. Above these levels, the perforated screens can create more fines as they cause a grinding action on the wet corn.
There is a YouTube Video form Pete Johnson that has be circulating which shows many of these adjustments https://youtu.be/Wt7tZHmZHM4 However, remember that adjusting the combine to reduce vomitoxin is a careful balancing act between reduce the vomitoxin levels and not loosing good corn from the machine. Screening, cleaning, and harvesting strategies will reduce vomitoxin contamination by removing lightweight kernels and fines, but will not get rid of vomitoxin that is inside the grain.
Sampling, Testing, and storage: Grain samples should be pulled from field suspected of having ear rots problems and tested for mycotoxins. As we mentioned in our factsheet (https://ohioline.osu.edu/factsheet/plpath-cer-04), moldy kernels are usually not evenly distributed in a grain lot, and as a result, toxin-contaminated grain are usually found in pockets (hot spots). Consequently, poor sampling and/or testing technique may lead to incorrect estimates of vomitoxin in the grain lot. For instance, a sample pulled from a hot spot may lead to an overestimated of the overall level of contamination on the load. To obtain better estimates of contamination, pull multiple samples from the grain stream during harvest or from the grain truck/wagon. When testing at grain elevators, you may request a second sample be drawn if you feel the first sample was not representative of the entire lot. Following vomitoxin testing, you have the right to reject the grain buyers’ results and ask the handler to send the second sample to a federally licensed grain inspector for a re-test. Refer to Ohio Code 926.31 for details.
Grain should be dried down to below 15% moisture and storage in a clean dry bin. If multiple bins are available, consider testing and segregating different fields based on vomitoxin test levels. After drying there are usually more fines that may separate out. These can be removed using rotary screen separators and slant screen separators. We are still studying to determine the level of vomitoxin reduction you can expect to see with screening methods, but we have seen it significantly reduce very high vomitoxin numbers.
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Elvis Has Left the Building
After nearly 35 years of employment and service, Dr. Mark Loux, Professor and Weed Science Extension Specialist, has retired from The Ohio State University.
In his time at Ohio State, Mark led an applied research and extension program focused on weed management in agronomic crops. Known for his quick wit and no-nonsense attitude, Mark was a foundational part of OSU’s Agronomic Crops Team. Mark traveled all over the state delivering weed management information at field days and workshops. His ability to relate to growers and deliver information that was both educational and entertaining was admired by many of us in extension. His research evaluating herbicide efficacy and weed management best practices led to timely recommendations for growers. Mark led the editing and production efforts for the Weed Control Guide for Ohio, Indiana, and Illinois, along with countless contributions to the CORN newsletter, fact sheets, and media features. Over the course of his career, he earned several awards including honors for outstanding papers and service to our weed science societies. Beyond his research and extension duties, Mark was a dedicated employee and contributed a great deal of time and effort to service on various committees for the department and college.
Mark has served as my boss, academic advisor, and mentor for nearly a decade. I will miss having him just down the hall for a cup of (high quality) coffee and a chat. Lucky for me and unfortunately for him, I have his number. On behalf of the OSU weed science program, I’d like to say thank you to Mark for being our fearless leader and friend, and backpack spraying with us until the very end. We wish you the best and offer sincere congratulations on your retirement. P.S. Mark only agreed to let me write this article under the condition that he got to choose the title. We always thought he more closely resembled Brian May of Queen, but that doesn’t quite have the same ring to it.
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Wheat Planting When the Soil is Dry
For the germination process to begin, wheat seeds need to imbibe (take in) water. With dry soil in some areas of the state, there may be concerns about delayed germination and emergence after planting. In previous years, when wheat was planted into dry soil, emergence occurred approximately 4 weeks after planting when soil moisture was restored with rainfall. Some key points to keep in mind:
- If soil is dry, conserve soil moisture by planting wheat without the use of tillage if possible. In addition to soil moisture conservation, excessive tillage may also result in soil crusting and emergence problems following a rainfall event.
- Wheat seed should be planted into soil moisture, but no deeper than a 1.5-inch depth.
- If you anticipate wheat seed germination and emergence will be delayed (>2 weeks after your county’s Hessian fly-safe date), you may want to consider increasing your seeding rate to 1.6 to 2.0 million seeds/acre.
- Even with delayed planting (or delayed emergence), wheat can yield near normal up to three weeks after the Hessian fly-safe date. In some years, wheat planted late October or early November may only have a slight impact on grain yield if freezing weather is delayed until late November or early December.
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Feeding Frosted Forages
I am beginning to get questions about toxicities that can develop after forages are frosted. There is potential for some forage toxicities and other problems that can develop after a frost. Prussic acid poisoning and high nitrates are the main concern with a few specific annual forages and several weed species, but there is also an increased risk of bloat when grazing legumes after a frost.
Nitrate accumulation in frosted forages. Freezing damage slows down metabolism in all plants, and this might result in nitrate accumulation in plants that are still growing, especially grasses like oats and other small grains, millet, and sudangrass. This build-up usually is not hazardous to grazing animals, but greenchop or hay cut right after a freeze can be more dangerous. When in doubt, send in a sample to a forage testing lab and request a nitrate test before grazing or feeding a forage after a frost.
Prussic Acid Toxicity
Several forage and weed species contain compounds called cyanogenic glucosides that are converted quickly to prussic acid (i.e. hydrogen cyanide) in freeze-damaged plant tissues, or under drought conditions. Some labs provide prussic acid testing of forages (see a partial list at the end of this article). Sampling and shipping guidelines should be carefully followed because prussic acid is a gas and can dissipate during shipping leading to a false sense of security when no prussic acid is found in the sample. Call the lab to confirm what guidelines they suggest and that they are still doing the test.
Plant age affects toxicity. Young, rapidly growing plants of species that contain cyanogenic glucosides will have the highest levels of prussic acid. Pure stands of Indiangrass (a native prairie grass) can have lethal levels of cyanide if they are grazed when the plants are less than 8 inches tall.
Species with prussic acid poisoning potential. Forage species that can contain prussic acid after frost are listed below in decreasing order of toxicity risk:
- Grain sorghum = high to very high toxic potential
- Indiangrass = high toxic potential
- Sorghum-sudangrass hybrids (“sudax”) and forage sorghums = intermediate to high potential
- Sudangrass hybrids = intermediate potential
- Sudangrass varieties = low to intermediate in cyanide poisoning potential
- Piper sudangrass = low prussic acid poisoning potential
- Pearl millet and foxtail millet = rarely cause toxicity
Species not usually planted for agronomic use can also develop toxic levels of prussic acid, including the following:
- Johnsongrass
- Shattercane
- Chokecherry
- Black cherry
- Elderberry
It is always a good idea to check areas where wild cherry trees grow after a storm and pick up and discard any fallen limbs to prevent animals from grazing on the leaves and twigs.
Frost affects toxicity. Cyanogenic glucosides are converted quickly to prussic acid (i.e. hydrogen cyanide) in freeze-damaged plant tissues. Prussic acid poisoning potential is most common after the first autumn frost. New growth from frosted plants is palatable but can be dangerously high in prussic acid.
Drought stress can affect prussic acid poisoning risk. Drought-stunted plants can contain or produce prussic acid and can possess toxic levels at maturity. Prussic acid poisoning can be associated with new regrowth following a drought-ending rain. Rain after drought plus young stages of plant maturity can combine to cause toxic levels of prussic acid in forages.
Fertility can affect poisoning risk. Plants growing under high nitrogen levels or in soils deficient in phosphorus or potassium will be more likely to have high prussic acid poisoning potential.
Fresh forage has more risk. After frost damage, cyanide levels will likely be higher in fresh forage as compared with silage or hay that is wilted in the field. This is because cyanide is a gas and dissipates as the forage is wilted and dried for making silage or dry hay.
Prussic Acid Toxicity Symptoms
Animals can die within minutes if they consume forage with high concentrations of prussic acid. Prussic acid interferes with oxygen transfer in the blood stream of the animal, causing it to die of asphyxiation. Before death, symptoms include excess salivation, difficult breathing, staggering, convulsions, and collapse.
Ruminants are more susceptible to prussic acid poisoning than horses or swine because cud chewing and rumen bacteria help release the cyanide from plant tissue.
Grazing Precautions Against Nitrate & Prussic Acid Poisoning
The following guidelines will help you avoid danger to your livestock this fall when feeding species with nitrates or prussic acid poisoning potential:
- Do not graze on nights when frost is likely. High levels of toxic prussic acid are produced within hours after a frost, even if it was a light frost.
- Do not graze after a killing frost until plants are dry, which usually takes 5 to 7 days.
- After a non-killing frost, do not allow animals to graze for two weeks because the plants usually contain high concentrations of prussic acid.
- New growth may appear at the base of the plant after a non-killing frost. If this occurs, wait for a killing freeze, then wait another 10 to 14 days before grazing the new growth.
- Do not allow hungry or stressed animals to graze young growth of species with prussic acid potential. To reduce the risk, feed ground cereal grains to animals before turning them out to graze.
- Use heavy stocking rates (4-6 head of cattle/acre) and rotational grazing to reduce the risk of animals selectively grazing leaves that can contain high levels of prussic acid.
- Never graze immature growth or short regrowth following a harvest or grazing (at any time of the year). Graze or greenchop sudangrass only after it is 15 to 18 inches tall. Sorghum-sudangrass should be 24 to 30 inches tall before grazing.
- Do not graze wilted plants or plants with young tillers.
- Under drought conditions, allow animals to graze only the upper one-third to one-half of the plant or the leaves of coarse-stemmed forages if the nitrate levels in these plant parts is safe. Monitor animals closely and remove them quickly when the upper portion of plants is grazed off.
- Generally, forage nitrate levels drop significantly 3 to 5 days after sufficient rainfall, but it is always safer to send in a sample for testing before grazing or feeding forage soon after drought stress periods. I have seen where frosts after drought ending rains seems to maintain the high nitrate levels in forages (high nitrates can be maintained all winter in the forage0, so don’t assume frosts will reduce the nitrate levels. Keep testing the forage and only graze or feed it when and IF the nitrate levels drop to safe levels!
- Making hay does not reduce nitrate levels in the forage, but the hay can be tested and diluted sufficiently with other feeds to make it safe for animals.
- Ensiling forage converts nitrates to volatile nitrous oxides, or “silo gases”. These gases are highly toxic to humans. Safety practices include removing tarps from a portion of the silo a day or two before removing the silage from the bunker and wearing respirators designed to filter out nitrous oxides.
Greenchop
Green-chopping will not reduce the level of nitrates and is not likely to greatly reduce the level of prussic acid present. However, green-chopping frost-damaged plants will lower the risk compared with grazing directly, because animals are less likely to selectively graze damaged tissue. Stems in the forage dilute the high prussic acid content that can occur in leaves. However, the forage can still be toxic, so feed greenchop with great caution after a frost. If feeding greenchopped forage of species containing cyanogenic glucosides, feed it within a few hours of greenchopping, and do not leave greenchopped forage in wagons or feedbunks overnight.
Hay and Silage
Prussic acid content in the plant decreases dramatically during the hay drying process and the forage should be safe once baled as dry hay. The forage can be mowed any time after a frost if you are making hay. It is rare for dry hay to contain toxic levels of prussic acid. However, if the hay was not properly cured and dried before baling, it should be tested for prussic acid content before feeding to livestock.
Forage with prussic acid potential that is stored as silage is generally safe to feed. To be extra cautious, wait 5 to 7 days after a frost before chopping for silage. If the plants appear to be drying down quickly after a killing frost, it is safe to ensile sooner.
Delay feeding silage for 8 weeks after ensiling. If the forage likely contained high levels of cyanide at the time of chopping, hazardous levels of cyanide might remain and the silage should be analyzed before feeding.
Species That Can Cause Bloat After Frost
Forage legumes such as alfalfa and clovers have an increased risk of bloat when grazed one or two days after a hard frost. The bloat risk is highest when grazing pure legume stands and least when grazing stands having mostly grass.
The safest management is to wait a few days after a killing frost before grazing pure legume stands – wait until the forage begins to dry from the frost damage. It is also a good idea to make sure animals have some dry hay before being introduced to lush fall pastures that contain significant amounts of legumes. You can also swath your legume-rich pasture ahead of grazing and let animals graze dry hay in the swath. Bloat protectants like poloxalene can be fed as blocks or mixed with grain. While this an expensive supplement, it does work well when animals eat a uniform amount each day.
Frost and Equine Toxicity Problems
(source: Bruce Anderson, University of Nebraska)
Minnesota specialists report that fall pasture, especially frost damaged pasture, can have high concentrations of nonstructural carbohydrates, like sugars. This can lead to various health problems for horses, such as founder and colic. They recommend pulling horses off of pasture for about one week following the first killing frost.
High concentrations of nonstructural carbohydrates are most likely in leafy regrowth of cool-season grasses such as brome, timothy, and bluegrass but native warm-season grasses also may occasionally have similar risks.
Another unexpected risk can come from dead maple leaves that fall or are blown into horse pastures. Red blood cells can be damaged in horses that eat 1.5 to 3 pounds of dried maple leaves per one thousand pounds of bodyweight. This problem apparently does not occur with fresh green leaves or with any other animal type. Fortunately, the toxicity does not appear to remain in the leaves the following spring.
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AVOID A NIGHTMARE NEXT SPRING!!!!!!!!
Scout Forage Stands for Winter Annuals NOW. Last week Mark Loux reminded us to control cressleaf groundsel and other winter annual weeds now. If you haven’t read that article, go read it right now, Our Annual Article to Nag about Fall Herbicides and Cressleaf Groundsel, and read the other articles linked in that one.
Scouting hayfields and pastures and applying controls this month, especially in NEW FORAGE STANDS seeded this summer and early autumn, is absolutely critical to AVOID A NIGHTMARE NEXT SPRING.
JUST DO IT! We really don’t want to say next spring, “WE TOLD YOU SO LAST FALL” ---that would bring us no joy at all and your regret will be painful if you don’t listen to this advice…
I am being blunt because we really want to avoid the nightmares we have seen in fields the past few springs. We have good tools to use this fall to avoid nightmare weed problems next spring that will require throwing the forage away because of toxic weeds in the stand.
Thank you for taking this warning to heart!
Weed ID and Control Resources
OSU has resources to help with the identification and control of these problematic weed species. In the abovementioned article, dandelion, wild carrot, poison hemlock, cressleaf groundsel and annual bluegrass were highlighted. Identification of these and other problematic species is covered in the Common Ohio Winter Annual Weed Identification video. We also have a collection of digital books that can be helpful for weed ID on the go.
These and other winter annual species are most easily controlled with herbicides in the fall. Control efforts implemented now through November will reduce issues with these weeds come spring when they are harder to kill. The best resource for weed control recommendations is the Weed Control Guide for Ohio, Indiana, and Illinois; many of these species are featured in the “Control of Problem Weeds” section. The forages and grass pasture sections of this guide cover herbicide options for weed management in these systems.
An ounce of prevention is worth a pound of cure. Fall herbicide applications help to ensure a clean start next spring and are the best management strategy for some of the most difficult to control winter annual species.
Crop Observation and Recommendation Network
C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.
Contributors
Disclaimer
The information presented here, along with any trade names used, is supplied with the understanding that no discrimination is intended and no endorsement is made by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
CFAES provides research and related educational programs to clientele on a nondiscriminatory basis. For more information, visit cfaesdiversity.osu.edu. For an accessible format of this publication, visit cfaes.osu.edu/accessibility.