Monthly Archives: February 2016

Risk Of Grass Tetany

With warm weather back, UGA Extension Beef Scientist Dr. Lawton Stewart warns us about potential for grass tetany. Here is an article by Dr. Deidre Harmon and Dr. Stewart:

I’m putting out High-Mag mineral, but cows are still going down?

What is grass tetany and why is magnesium important?

Grass tetany, also known as grass staggers, magnesium (Mg) tetany, hypomagnesemia, and wheat pasture poisoning, is a nutritional disorder caused by either 1) an inadequate amount of dietary Mg, or, 2) other mineral related factor that is preventing (antagonizing) dietary Mg from being properly absorbed or utilized.  Magnesium is considered a macro mineral and is needed in beef cattle diets to insure proper growth, reproduction, and metabolic function.  When dietary Mg is low or utilization is inhibited, neuromuscular function becomes impaired and leads to the clinical symptoms of staggering, muscle twitching, convulsions, and in severe cases, can lead to death.  This disorder is most common during cool, cloudy, and rainy weather, and frequently occurs when cool weather is followed by a warm period.

Why is magnesium an issue during this time of year?

  • Mg is essential, especially during lactation – Spring calving cows are highly susceptible to grass tetany because they reach peak lactation (require increased amounts of Mg) during the same time as the spring green. This onset of abundant lush forage is associated with decreased amounts of forage Mg. Older cows are more susceptible because they cannot mobilize Mg from reserves in the bone as quickly as younger cows.
  • High potassium (K) content is also associated with lush, growing forages. Although K is essential, in large amounts, it can work as an antagonist to reduce Mg uptake from the soil and Mg absorption in the rumen.

I’m putting out High-Mag mineral, but I am still losing cows?

  • Not consuming enough – There may be a palatability issue, especially when Mg is increased in the mineral.  However, cows typically do not voluntarily consume as much mineral this time of year.
  • High-Mg mineral if fed year-round – Sometimes, the strategy is to put high-Mg mineral out all year as an “insurance policy” – High-Mg mineral is only needed during the short period of time that grass tetany may occur.  Feeding the miner year-round may condition cattle to not consume enough during the time they really need it.
  • Not enough salt – Magnesium transport across the rumen wall can be reduced if 1) there is not enough salt in the diet, and, 2) if there is too much K in the diet. Collectively, too much K and too little salt can cause grass tetany, even if Mg intake is adequate.

What can I do?

  • Know exactly what cattle are consuming – Do the math based on how much mineral you’re putting out, how many cows, and how fast it is being consumed. Calculate the mineral on an oz/hd/d basis and determine whether or not their consumption meets requirements. Table 1 illustrates calculated consumption based on different feeding rates and herd sizes.
  • Increase intake (if need be) by mixing with feed and/or salt.  Again, do the math to ensure the correct intake.  OVER CONSUMPTION WILL NOT FIX THE PROBLEM.
  • Add salt – In addition to increasing the mineral intake, additional salt will ensure that the sodium requirement is being met and thus, help to maximize absorption of Mg. DO NOT DO THIS IN PLACE OF HIGH MAG, rather in addition to. This can be as simple as putting out plain white salt blocks.
Table 1. Calculated weekly consumption amounts for different feeding rates and herd sizes.

Table 1. Calculated weekly consumption amounts for different feeding rates and herd sizes.

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Avian Influenza Prevention


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February 3, 2016 · 8:14 PM

Time To Set Ambrosia Beetle Traps

Evidence of ambrosia beetles appear as "toothpicks" on the bark

Evidence of ambrosia beetles appear as “toothpicks” on the bark

Last year was a big year for ambrosia beetles. These beetles live all around us and in the woods. They generally attack stressed or injured trees. The pecan trees they affect are young trees, maybe 5 years and younger. They are identified by “toothpicks” on the outside bark. This is the boring dust pushing out of the tree. UGA Extension Entomologist Dr. Will Hudson says there is not a preventative management of these beetles. Treating is essentially a “shotgun” approach. Ambrosia beetles are hard to predict since they also attack other woody tree species.

The one thing growers can do to limit losses is trap adult beetles to pin point their first flight. Based on previous studies, February 1st is the best plan for South Georgia to set out traps. The traps are something producers can do to pin point when the first flight originates.

Trap Design

Dr. Hudson explains how to design the trap:

The simplest and most efficient (trap) is made from a bolt of wood with a hole drilled down the center.  Any hardwood will work, and a branch 2” – 4” in diameter about 2 feet long will do the trick. Drill a ½” (+/-) diameter hole down the center as far as you can (but not all the way through) and fill it with ethanol (grain alcohol, not rubbing alcohol; denatured is OK).  Put a stopper of some sort (a cork, for instance) in the hole and then hang the bolt about waist high at the edge of the orchard.  It will probably take several traps per edge, but edges along woodlines are most likely to catch beetles first.

Photo by Dr. Pete Schultz, VPI&SU.

Photo by Dr. Pete Schultz, VPI&SU.

Photo by Dr. Pete Schultz, VPI&SU

Photo by Dr. Pete Schultz, VPI&SU

Once attacks are detected on the trap, close-interval scouting can be initiated (check the trees every day or so for signs of beetles).  If you see toothpicks on the trees, apply a pyrethroid spray quickly to minimize damage and losses.  Unfortunately, barrier sprays applied as a preventative measure for other borers are not effective on these beetles.  They will provide protection for a few days or a week, depending on the weather, but ambrosia beetles do not eat the wood or bark so once the volatility of the insecticide has faded a bit they are not affected.

You can also reduce losses by removing the irrigation pipe collars that protect young trees from herbicides. Ambrosia beetles will attack inside the pipes where they can’t be seen.  This adds work, and means you have to delay herbicide application until they can be reinstalled once the trees leaf out completely. But, collars have definitely contributed to extra losses for a number of growers. The spring green-up period is when the trees are most vulnerable, and once they have leafed out completely the risk of attack drops to almost zero unless there is some stress factor for the trees.

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Forage Update & Winter Fertilization Considerations

Triticale 026

We’ve been looking at more and more forage issues the past few weeks. Rust is evident in some fields. We’re also seeing evidence of N efficiency as lower leaves show chlorosis. Here is an update on our forage crops from UGA Extension Forage Scientist Dr. Dennis Hancock:

Yet again, the weather is making farming a high stakes game of chance. We had a very wet end to the summer growing season (in most areas) and this resulted in the leaching out of almost all of the residual N in the soil. Then, we’ve had lots of warm weather lately, and this has encouraged disease issues to severely limit the growth potential of winter forages. The warm weather has also allowed for some additional N mineralization to occur, but this N hasn’t stuck around long enough to provide N to our winter forages. That is because we’ve had quite a bit of rainfall in the past several weeks (pretty much the whole state) and what little available N was released has quickly been leached away. Many (if not most) of our winter forage crops are starving for N at the moment. Even fields with good stands of clover are suffering because these legumes aren’t yet fixing much N (because the soils have been so water-logged that they can’t fix N).

To make matters worse, the weather projections are not particularly positive. The models suggest a lot more of the same on the near-term: mild to cool temperatures and above normal rainfall through March-April. They also project a short end of spring: above normal temps fairly normal rainfall in late April – June.  This means that the remaining bit of the production season is likely to be compressed from what is normally a February – May growing season in a good year to what may be just March – April in some areas.


Standard soil test recommendations are that one should put out 50 lbs of N/acre on ryegrass and small grains in late winter (late January – February) and another 50 lbs of N/acre on ryegrass in early spring (mid-March – mid-April). Applications of N at these rates are likely to result in more than 15-20 lbs of DM per lb of added N for the late winter application and more than 20-25 lbs of DM per lb of added N.  As a general rule of thumb, N response rates greater than 15-20 lbs of DM per lb of added N will result in an economical response.

This year, timely action with the winter applications will be absolutely crucial. Even if adequate N was applied at planting, it is likely that little or none of that is still available at the time of this writing.

The response to N (lbs of DM gained per lb of added N) has to be considered in context. To illustrate this, let us consider three scenarios:

Scenario 1) Ryegrass or small grains that have been slow to grow, either because of bad weather or N deficiency (and, sometimes, a late planting). These winter annual forage crops will often respond very aggressively to a winter application (20-30 lbs of DM per lb of added N assuming N rates are 40 – 60+ lbs of N/acre).  It is analogous to compensatory gains in growing livestock. It is the same basic principle: an organism that has had growth limitations will often grow at extraordinary rates whenever those factors are no longer limiting.

Scenario 2) Ryegrass or small grain plantings that have been growing strong. Winter annual forage crops in this scenario are unlikely to respond as aggressively to N at this time. For example, they may barely provide 15 lbs of DM per lb of added N during the few weeks following N application. However, this N is still crucial, as it keeps the plant growing at least at a healthy rate. Therefore, it is important to fertilize them at the same or nearly the same rates because they will need the fertility during the remainder of the season.

Scenario 3) Winter annual forages that have been moderate to severely damaged by disease (Helminthsporium leaf spot, grey leaf spot/blast, leaf rust, or barley yellow dwarf virus, etc.). These forage crops are unlikely to respond to N application. For example, tillers that are exhibiting physical symptoms of barley yellow dwarf (BYD) infection will die quickly, especially following a hard freeze. Therefore, if more than 30% of the tillers in a stand of oats have been damaged by barley yellow dwarf, those plants are unlikely to respond well to N. Each producer will have to determine if they are willing to take the risk, but if it were my oats, I doubt I would put any more N into those areas/fields.


Another consideration is the growth cycle of the crop. Here again, oats provide us a good example. Oats generally grow very well in the fall and in the spring, but not very well in the winter. The N recommendations for small grains as winter grazing states “…these crops can utilize about 100 (lbs of N) per acre during the growing season. Split the (N) application, applying 50 (lbs of N) per acre at planting and 50 (lbs of N) per acre in late winter before spring growth begins.” The instruction to apply 50 lbs of N/acre in late winter for small grains applies to oats, as well as to rye, wheat, and triticale. However, the operative part of this recommendation is the final phrase “in late winter before spring growth begins.” The spring growth of rye, wheat, and triticale have already begun or will do so imminently.  The spring growth of oats really won’t begin until early March.  Therefore, one would be wise to delay the late winter application of N to oats until the end of February.

Which Form of N?

Last, but certainly not least, one should consider the form of N being applied. If a producer applies ammonium nitrate, the fertilizer quickly dissolves into the soil moisture. Consequently, this source of N is almost immediately available to the plant. However, most of our producers no longer have access to ammonium nitrate.

Many of the N products that are most readily available are based on urea.  Urea and urea-based N formulations are, chemically speaking, organic forms of N. Urea must be broken down via a biological process to form nitrate, which is the form of N that plants predominantly absorb. Because this process is dependent upon the activity of microorganisms in the soil, weather can effect how rapidly this N becomes available to the plant. Cool and wet weather slows down the conversion of urea to a form of N that is available to the plant. Many producers will put on a significant amount of urea only to find that their crop fails to green up. This is NOT because they received “bad fertilizer.” It may be the result of the cool, wet weather.

Poultry litter is a great source of N… in the summer months. But, in the winter months, it is marginal at best. The reason for the difference is that most of the N is in an organic form. Just like the urea, the N in poultry litter has to be broken down by biological activity (bacteria) in order for it to be made available to the plant.  Further, putting poultry litter out now (February) is likely to pose an environmental risk such as the contamination of runoff water and therefore contaminating the water in your ponds, streams, and other freshwater resources. Of course, that assumes that poultry litter is even available to put out now or that one could get one of those trucks in the field at present, given how wet the soil is at present. Many producers apply poultry litter in the fall whenever they plant their winter grazing. This gives it a little bit of N to get off to a good start. But, it doesn’t provide much during the winter.

There are three reasonably good alternatives to these aforementioned N sources. The first one to be considered is liquid N (UAN), which is approximately half urea and half ammonium nitrate. Because of the ammonium nitrate portion, it is more readily available to the plant than many other N sources.

One should also consider using either Agrotain Plus-treated urea or SuperU. Both of these products are urea-based, but are sold under different trade names. Both are treated with a urease inhibitor (N-butyl-thiophosphoric triamide), which prevents loss as ammonia, and a nitrification inhibitor (dicyandiamide), which prevents N loss to leaching.  These still have the challenge of urea’s slow release, but they are less likely to be lost to the environment as ammonia gas or nitrate leaching into the groundwater.

Last, but not least, one should consider using the 18%N 19E product, which is a liquid N product. This product is essentially liquid calcium ammonium nitrate with sulfur and a few other micronutrients.  The N from this product, like ammonium nitrate, is almost immediately available to the plant. Further, it is often quite economical compared to other N sources because it is locally produced.

N deficiency in triticale

N deficiency in triticale. Lower (older) leaves turn yellow since N is mobile in the plant.

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