C.O.R.N. Newsletter: 2015-34
-
Sampling for Soybean Cyst Nematode – It’s time!
This year’s early harvest provides the perfect opportunity to take a look at the SCN populations in your fields. We know that the state is now “polluted” with SCN, fortunately most of those fields are at very low levels – which is where they should be kept. However, there are some surprising locations where individual fields are getting or have gotten into trouble with very high populations. So let’s review the loss levels for SCN for the majority of soil types here.
Levels of SCN and concerns
SCN egg Count/100 cc
Cyst count
Population Level
0-40
0
not detected
40-200
1
trace
200-2000
1-4
low
2000-5000
3-20
moderate
5000 & over
15-20
high
If your SCN report in the past has come back as:
1. Not detected: this is not surprising. Remember that SCN sits in pockets and can be quite variable (Figure 1). Continue to monitor your fields.
2. Trace: May begin to measure some yield loss on susceptible varieties, especially on lighter soils.
3. Low: Plant SCN resistant varieties or rotate to a non-host crop (corn or wheat).
4. Moderate: Rotate to a non-host crop and follow with SCN resistant varieties the following year. We have planted susceptible varieties in fields with this level of SCN and have recorded 20 to 50% yield loss.
5. High: rotate to a non-host crop for two to three years, then sample SCN to determine if populations have declined to a level where soybeans can be planted again.
SCN is picky about what it feeds and reproduces on but it does like a few weed hosts and cover crops as well as soybean. If you have SCN in your fields , it is important to also control winter annuals such as purple deadnettle, but also avoid cover crops such as several of the clover’s, cowpea and common & hairy vetch.
So it is time to sample! We recommend sampling in the fall – because in most cases this is what the population will be in the spring. With the warmer weather this year and hopefully no frozen ground should give ample time to collect and process the samples in plenty of time for spring planting. Processing of samples does cost time and money, so here are a few thoughts on how to sample or how to target your sampling to get the best information for your money. Through funds from the soybean check-off, we have completed several targeted surveys over the past 5 years. My group tended to target those fields where yields were stuck or below 30 bu/A. Or when we sampled we hit those pockets in the field where the soybeans tended to be shorter or where they matured earlier and always yielded less that the rest of the field. We were able to detect SCN in almost all of these situations, so these are the ones that should have the top priority for sampling.
Updated information on where to send the samples:
OSU C. Wayne Ellett Plant and Pest Diagnostic Clinic
8995 E. Main St. Bldg 23
Reynoldsburg, OH 43068
Phone: 614-292-5006
www.ppdc.osu.edu - follow this link to download forms to go along with the samples
Brookside Laboratory Inc.
200 White Mountain Dr.
New Bremen, OH 45869
417-977-2766
Spectrum Analytic Inc.
1087 Jamison Rd. NW
Washington Court House, OH 43160
740-335-1562
For some additional information on Management of SCN – always check Ohio’s SCN fact sheet and several other resources as well:
http://soybeanresearchinfo.com/ - link to the 5th edition of the SCN guide developed through the North Central Soybean Research Program.
Link to recent findings and sampling protocol for SCN: https://www.youtube.com/watch?v=FQgg-UPQdcs&feature=youtu.be
-
Higher western bean cutworm feeding may lead to mycotoxins
Although western bean cutworm (WBC) flight counts have been relatively stable compared to last year, several growers and extension educators have sent in pictures of western bean cutworm infestations and damage in corn. Obviously it is much too late to do much at this point, as the larvae are either still protected, or more likely, have dropped to the ground to overwinter. However, the holes and damage that remain could lead to secondary infestations from mold and fungi, and some of these infestations may also be a source for mycotoxins, including fumonisins and deoxynivalenol, AKA vomitoxin.
In some cases, damaged kernels will likely be colonized by opportunistic molds, meaning that the mold-causing fungi are just there because they gain easy access to the grain. However, in other cases, damaged ears may be colonized by fungi such as Fusarium, Gibberella and Aspergillus that produce harmful mycotoxins. Some molds that are associated with mycotoxins are easy to detect based on the color of the damaged areas. For instance reddish or pinkish molds are often cause by Gibberella zeae, a fungus know to be associated with several toxins, including vomitoxin. On the other hand, greenish molds may be caused by Aspergillus, which is known to be associated with aflatoxins, but not all green molds are caused by Aspergillus. The same can be said for whitish mold growth, some, but not all are caused by mycotoxin-producing fungi.
So, since it is not always easy to tell which mold is associated with which fungus or which fungus produces mycotoxins, the safe thing to do is to avoid feeding moldy grain to livestock. Mycotoxins are harmful to animals – some animals are more sensitive to vomitoxin while others are more sensitive to fumonisins, but it is quite possible that multiple toxins are present in those damaged ears. Mycotoxin-producing fungi are also opportunistic. If you have damaged ears and moldy grain, get it tested for mycotoxins before feeding to livestock, and if you absolutely have to use moldy grain, make sure it does not make up more than the recommended limit for the toxin detected and the animal being fed. This link provides more information on ear molds and mycotoxin contamination:
-
Precautions for Harvesting Forages After a Frost
Several forage species can be extremely toxic soon after a frost because they contain compounds called cyanogenic glucosides that are converted quickly to prussic acid (i.e. hydrogen cyanide) in freeze-damaged plant tissues. Others species have an increased risk of causing bloat when grazed after a frost, those are discussed at the end of this article.
Species that can develop toxic levels of prussic acid after frost include annual grasses in the sorghum family, Johnsongrass, shattercane, chokecherry, black cherry, indiangrass, and 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.
The potential toxicity after frost varies by species as follows:
· Sudangrass varieties = low to intermediate in cyanide poisoning potential
· Sudangrass hybrids = intermediate potential
· Sorghum-sudangrass hybrids and forage sorghums = intermediate to high
· Grain sorghum = high to very high
· Piper sudangrass = low prussic acid poisoning potential
· Pearl millet and foxtail millet = rarely cause toxicity
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.
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. After frost damage, cyanide levels will likely be higher in fresh forage as compared with silage or hay. This is because cyanide is a gas and dissipates as the forage is wilted and dried for making silage or dry hay.
Young, rapidly growing plants of species that contain cyanogenic glucosides will have the highest levels of prussic acid. After a frost, cyanide is more concentrated in young leaves and tillers than in older leaves or stems. New growth of sorghum species following a non-killing frost is dangerously high in cyanide. Pure stands of indiangrass can have lethal levels of cyanide if they are grazed when the plants are less than 8 inches tall.
Grazing Precautions
The following guidelines will help you avoid danger to your livestock this fall when feeding species with prussic acid poisoning potential:
· Do not graze on nights when frost is likely. High levels of toxic compounds 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 toxic compounds.
· New growth may appear at the base of the plant after a non-killing frost. If this occurs, wait for a hard, killing freeze, then wait another 10 to 14 days before grazing the new growth.
· Don’t 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.
Greenchop
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. Also, always feed greenchopped forage of species containing cyanogenic glucosides within a few hours, and don’t leave greenchopped forage in wagons or feedbunks overnight.
Hay and silage are safer
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 anytime after a frost if you are making hay. It is very 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.
Freezing also slows down metabolism in all plants that might result in nitrate accumulation in plants that are still growing, especially grasses like oats, millet, and sudangrass. This build-up usually isn't hazardous to grazing animals, but green chop or hay cut right after a freeze can be more dangerous.
Species That Can Cause Bloat
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.
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 an accessible format of this publication, visit cfaes.osu.edu/accessibility.