A bi-monthly news publication of The Ohio State University Extension, Editors: Clif Little and Mark Sulc
This newsletter is made possible with support from the Bob & Jewell Evans Foundation
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Contents:

• Frost Damage & Prussic Acid Poisoning Potential
• 2006 Forage Performance Trials Coming Soon
• Identify Pasture Renovation Needs
• Apply Herbicides Now to Stop the Yellow Weed Next Spring in Forages in Eastern Ohio
• Fog Fever - A Fall Pasture Problem
• Should Tall Alfalfa Be Cut Before Winter?

[top]Frost Damage & Prussic Acid Poisoning Potential- Dr. Mark Sulc, The Ohio State University

Prussic acid poisoning can occur when feeding frost-damaged sudangrass, sorghum-sudangrass hybrids, forage sorghum, or grain sorghum. These species contain cyanogenic glucosides, which are converted to prussic acid (hydrogen cyanide) when the plants are damaged by frost.

When animals consume forage with high levels of cyanide-producing compounds, prussic acid is absorbed into the bloodstream, where it binds hemoglobin and interferes with oxygen transfer. The animal soon dies of asphyxiation. Prussic acid acts rapidly, frequently killing animals in minutes. Symptoms include excess salivation, difficult breathing, staggering, convulsions, and collapse. Ruminants are more susceptible than horses or swine because cud chewing and rumen bacteria help release the cyanide.

Sudangrass varieties are low to intermediate in cyanide potential, sudangrass hybrids are intermediate, sorghum-sudangrass hybrids and forage sorghums are intermediate to high, and grain sorghum is high to very high. Piper sudangrass has low prussic acid poisoning potential, and pearl millet is virtually free of cyanogenic glucosides.

Plants growing under high nitrogen levels or in phosphorus or potassium deficient soils will be more likely to have high cyanide potential. After frost damage, cyanide levels will likely be higher in fresh forage as compared with silage or hay, because cyanide is volatile and dissipates as the forage cures and dries.

Follow these precautions when grazing or greenchopping sorghum species this fall:

• Do not graze on nights when frost is likely. High levels of the toxic compounds are produced within hours after a frost.
• Do not graze after a killing frost until the plants are dry. Wait 5 to 7 days to allow the released cyanide to dissipate.
• After a non-killing frost, do not allow animals to graze because the plants usually contain high concentrations of toxic compounds. Once the first frost has occurred, grazing should not begin until 5 to 7 days after a killing frost.
• Graze or greenchop only when sorghum grasses are more than 18 inches tall.
• Do not graze wilted plants or plants with young tillers.
• Green-chopping the frost-damaged plants will lower the risk compared with grazing directly, because animals have less ability to selectively graze damaged tissue. However, the forage can still be toxic after greenchopping, so feed with great caution.

When making hay or silage from sorghum species this fall, consider the following:

• Frost-damaged annual sorghum grasses can be made into hay with little or no risk of cyanide toxicity. When plants are wilted enough to make dry hay, most of the volatile cyanide gas will have dissipated.
• Normal silage making allows most of the cyanide to dissipate from frost damaged annual sorghum grasses. Delay feeding of silage for 6 to 8 weeks after ensiling.
• Silage made from forage that likely contained high cyanide levels at harvest should be sent to a lab and analyzed for cyanide content before feeding.

[top] 2006 Forage Performance Trials Coming Soon Mark Sulc, Extension Forage Specialist

The results from the 2006 Ohio Forage Performance Trials will be available by mid-November. Check with your local county Extension office, or visit the performance trials website at www.ag.ohio-state.edu/~perf/. The results will also appear in a special insert of Ohio’s Country Journal in December.

Results will be published on varietal performance of alfalfa, red clover, orchardgrass, tall fescues, perennial ryegrass, and annual ryegrass varieties. Trials were conducted at North Baltimore, Wooster, South Charleston, and Jackson.

[top] Identify Pasture Renovation Needs- Rory Lewandowski, Extension Educator, Athens County

One of the tasks that can be done this fall by graziers is to evaluate the need for pasture renovation. This year’s drought and high temperatures when combined with over-grazing, can result in both severe root dieback and death of grass crowns. The effect of this is a pasture that will be slow to recover and resume normal production. In some cases there may be areas that die out, or where the sod thins and allows more weed growth. Another situation I have seen this year is where productive pastures, improved by years of frost seeding clover, became overgrown with annual broadleaf weeds and summer annual grasses even though the pasture had not been over-grazed during the growing season.

In this second situation, weather combined with management decisions resulted in the paddock’s decline. I wouldn’t be surprised to find any number of experienced graziers with the same problem. The wet fall and winter of 2004-2005 started the paddocks decline when this over wintering paddock was subjected to excessive hoof action, especially in areas where hay was fed. Typically in previous years, grazing stockpiled fescue off this paddock created a situation favorable to frost seeding clover in early spring, and the fescue sod recovered by summer to create a good fescue/clover pasture. However, the frost seeding in the spring of 2005 didn’t seem to catch and the fescue sod in the heavily trampled areas was slow to recover, opening the way for annual weeds like pigweed and ragweed as well as a host of the warm season annual grasses such as goose grass and barnyard grass. Due to the very wet soil conditions, the winter grazing basically destroyed the sod base and allowed weeds and grasses to become established that are normally seen in a cultivated situation and in heavy traffic areas like barnyards. Soil compaction may have played a role in the failure of the frost-seeded clover to establish, as well as hindering the recovery of the fescue sod. Another contributing factor was the summer drought and high temperatures, which would have made it difficult for a struggling seedling to survive.

The type of damage done to a paddock will determine how renovation should be handled. For those pasture paddocks that were overgrazed this summer and slow to recover, there are several options. If fall rains return, a late fall application of nitrogen fertilizer after top growth has ceased can help the root system of the grass plant to recover. Once daytime temperatures are in the 40-degree range, there will be little top growth, but soil temperatures will still be warm enough that roots can grow. Applying 40 to 50 pounds of actual nitrogen in November is an option, but economics should be considered since there will not be an immediate return on this investment. Another option is to make an early spring application of nitrogen at about a 20-lb/acre rate to try to stimulate the stressed plants to start growth and recovery a little sooner. A third option, not involving fertilizer, is to accept that this over-grazed paddock will recover slowly, and must be managed more carefully by reducing the stocking rate and paying close attention to leaving half the plant and giving adequate rest periods.

For those paddocks or areas that might have been overtaken with annual weeds and annual warm season grasses, frost seeding may not be enough to re-establish a good sod. Consider doing some soil preparation and conventional drilling if the topography permits, or if not, no-till seed in early spring, before mid-April if possible. Drilling the seed will ensure better seed/soil contact and will also result in better stand establishment when grasses are being planted. Make sure to allow 6 to 8 weeks before grazing or clipping to allow the grass plants to establish. On a positive note, this renovation will allow the producer to introduce new and improved orchardgrass or tall fescue varieties into the pasture. This fall can be used to research possible varieties and to take soil tests, if it has been more than 3 or 4 years since the last soil test, so that everything will be ready to go by early spring.

In a perfect world, weather would cooperate with pasture management so that pastures would continually improve and cattle would always have enough to eat. The reality is that pasture management involves pasture renovation.

[top]Apply Herbicides Now to Stop the Yellow Weed Next Spring in Forages in Eastern Ohio- Jeff Stachler, Mark Loux, Anthony Dobbels

The yellow flowering weed becoming more prevalent in forage fields in Eastern Ohio in April to May is most likely wild turnip. It may also be birdsrape mustard, however, because the two species appear identical and are so closely related, it is hard to separate them. Wild turnip is sometimes confused with yellow rocket in the spring. However, yellow rocket starts to flower later than wild turnip, and wild turnip will reach heights of up to 3 to 4 feet tall while yellow rocket usually gets no more than two feet tall.

There are limited research data on the control of wild turnip in forage production. However, based upon limited research conducted by The Ohio State University, Dr. Don Myers, and Melvin Lahmers, herbicides MUST be applied in the fall to achieve effective wild turnip control. For alfalfa production, apply 2,4-DB (2 qt/A), Pursuit 70 DF (1.08 to 1.44 oz/A) plus 2,4-DB (1 qt/A) plus crop oil concentrate plus AMS, or Raptor (6.0 oz/A) plus crop oil concentrate plus AMS. Raptor will control most grass species, 2,4-DB will not control any grass species, and Pursuit's activity on grass species is intermediate between the other two products. Treatments containing 2,4-DB will provide some control of purple deadnettle, but almost no control of common chickweed unless applied with 2.16 oz/A of Pursuit.

In grass pastures, fall application of dicamba (1 pt/A) plus 2,4-D ester (1 pt/A), 2,4-D ester (1 qt/A), Cimarron (0.2 oz/A), Cimarron plus 2,4-D ester (1 pt/A) or dicamba (0.5 pt/A), or Crossbow (2 pt/A) effectively controls wild turnip. Tall fescue may be injured by the Cimarron application. Among these herbicides, dicamba plus 2,4-D ester, or Cimarron, provide the most broad-spectrum control of other weeds.

[top]Fog Fever - A Fall Pasture Problem- Clif Little, Extension Educator, Guernsey County

Fog Fever is a rapidly developing, respiratory disease of cattle. Fog Fever is also called Acute Bovine Pulmonary Edema and Emphysema (ABPEE). Conditions and growth in our fall pastures has been perfect for this disorder to show itself. The onset of this disease occurs very quickly when hungry, adult cattle have been on dry feed or scarce summer pasture and are moved to green pasture or hay fields that are rapidly growing and lush. . This rapidly growing pasture can be fescue, grass-clover mixture, alfalfa, or other annual forages. The key factors are mature cattle that have been in a scarce dry summer pasture for some time and moved to rapidly growing, lush green grazing area.

Cattle suffering from Fog Fever become affected shortly after the move to lush grazing usually in less than 10-14 days. Affected adult cattle will have a rapid onset of respiratory difficulty. Cattle may have a normal temperature, or they may have an elevated temperature (> 103). Bovine respiratory syncytial virus (BRSV) can be mistaken for “fog fever”. Contact your veterinarian for diagnosis and as soon as you see unusual symptoms in the cattle.

Fog fever appears to be brought on by an abrupt change in diet. As the diet changes so does the rumen of the cattle. When we move cattle from a summer pasture to a stockpiled pasture or hayfield there can be a significant change in the nutritional quality of the forage. It is this change to lush green pasture and the increased consumption of the amino acid tryptophan that seem to cause the adverse health reactions. The excess tryptophan in the forage is converted by rumen bacteria to 3-methylindole (3-MI) at an unusually high rate. 3-MI is absorbed through the rumen into the blood stream and circulated to the lungs. 3-methylindole appears to cause the toxic changes in the lungs of cattle. There is no antidote for “fog fever” and cattle may not respond to symptomatic treatment and may die within a couple of days. Avoid any unnecessary stress of sick cattle. Your veterinarian may prescribe Banamine® or the use of ionophores such as Rumensin® or Bovatec® before turning the cattle onto the lush pastures.

There are some pasture management tools, which may help to prevent “fog fever”. Gradually introduce lush pasture to grazing livestock. Limit the time animals can graze the new area and feed some hay before turning them out. Gradually increase the time on the lush pasture so that at the end of ten days you can keep then out. Another strategy would be to allow a lower risk class of livestock such as yearlings or sheep to graze the new pasture first. Rotate pastures more quickly so that there is not a large difference in forage quality.

[top]Should Tall Alfalfa Be Cut Before Winter? - Dr. Mark Sulc, The Ohio State University

Earlier in the C.O.R.N. newsletter (September 6, 2005) I wrote about the risks of fall cutting alfalfa, and how to minimize that risk. With the temperatures and good moisture this fall, alfalfa has grown exceptionally well. I have received many questions as to whether this amount of growth going into the winter can harm the stand. The fear is that the alfalfa will smother itself out this winter.

The excessive alfalfa growth will NOT harm the stand. I have let stands of alfalfa go into the winter with as much growth as we see this fall, and I have never experienced a problem or seen the crop “smother out”.

Think about this…75-80% of the alfalfa crop this time of year is water. In other words, the dry matter content is around 20-25%. So divide what you see out there by 4, and that will be how much residue remains after a couple of hard frosts. There will be much less residue left than it appears right now.

Perhaps if it were to snow early on warm soils covered with lush alfalfa, and the snow were to stay there all winter long, we just might see some snow mold on the alfalfa. But that would be a very rare occasion in Ohio, with the exception of the lakeside snowbelt. In southern Ohio, its possible that alfalfa weevils could lay eggs in the alfalfa stand, potentially increasing weevil populations early next spring. That could happen even with a lot less growth, and other factors influence weevil populations in the spring.

There really is no need to take a cutting now in order to remove the large amount of alfalfa growth. In fact, considering all factors, cutting this week probably holds more risk to the stand than not cutting. If we cut this week, we are likely to have enough good growing weather left for the alfalfa to regrow over the next 2-3 weeks. Regrowth will burn up precious root reserves that are needed for the winter and early spring. There won’t be enough time to replenish those root reserves if the alfalfa is cut now.

If the forage is really needed, a LATE fall harvest can be considered, IF the soil is well drained. By LATE, I mean as close as possible to a killing frost of alfalfa, which is 25 F for several hours. This often does not happen until sometime in November in Ohio. I know that the weather is usually lousy in November for cutting forage, but waiting another 2 weeks to get closer to the killing frost will prevent regrowth and loss of energy reserves, and will reduce the risk of less vigorous stands next spring.

A late fall harvest should only be considered if the soil is well drained and there is no history or risk of heaving on that particular soil. Without residue cover, the temperature of the soil will fluctuate much more and heaving is more likely. This happened in a study at Wooster, when a November 1 cutting resulted in heaving of up to 50% of the plants. Where no fall cutting was made, less than 10% of the plants heaved.

Fall management of alfalfa is one of the few controllable factors that will potentially influence the health of your alfalfa stand next spring. If you don’t need the forage, walk away from it and let it insulate your stand this winter. It won’t smother out because of excessive alfalfa growth.

If you need the forage, then take a cutting the last week of October or early November, and only on well-drained soils. Also leave a 6-inch stubble. If you do cut this fall, leave some strips or areas that you do not cut within the same field. You might learn something interesting next spring about fall cutting on your farm by having those side-by-side comparisons!