Winter 2002
- Barley Yellow Dwarf Virus in Oats and other Small Grains
- Are You Feeding Your Cattle Enough? Body Condition Scoring
- Plateau: A New Herbicide for Grass Weeds in Hayfields
- Forage Notes: Managing Winter Pastures & Hayfield Preparation
Barley Yellow Dwarf Virus in Oats and other Small Grains
Source:Ann Blount, Dick Sprenkle, & Ron Barnett NFREC; Alabama Extension Circular ANR-1082
A number oat and other small grain pastures in Jackson County have been hit hard by barley yellow dwarf virus (BYDV) this past fall and winter. Barley yellow dwarf virus is the most widely distributed and destructive viral disease that affect small grains.Yield losses of up to 60% have been attributed to this disease.
Symptoms of the disease include leaf discoloration, which begins at the tip and progresses downward.Leaf discoloration can range from yellow to orange to purple.These diseased plants often occur in circular patches within the field. Symptoms of BYDV are often confused with various nutritional disorders or cold damage. Unfortunately, by the time the symptoms are visible it is too late to take action.
BYDV is spread by aphids. Epidemics occur when aphids carry the virus from wild and cultivated hosts. Seedling infections reduce yields the most. Plants infected as seedlings in the fall of the year may not survive the winter, or are severely stunted and discolored when growth resumes in the spring.
The virus persists in small grains (oats, rye and wheat), in corn, and in over 80 species of perennial and annual grass species. Late-season infections occur as the aphids migrate from early-planted small grains, as well as wild grasses.Oats are particularly susceptible to BYDV. Early-planted oats often are heavily infected and serve as a source for migration of aphids carrying the virus into adjacent wheat.
Aphids acquire BYDV by feeding on infected plants. It normally takes 24 to 48 hours of feeding to acquire the virus but, once done, the aphid remains a carrier for life. Spread of BYDV depends entirely on aphid movement. Damaging outbreaks of BYDV are most likely if hosts are exposed to migrating aphids over extended periods of cool weather that favor small grain growth and aphid development. Infections can occur throughout the season and are most abundant where high populations of aphids survive the winter. Barley yellow dwarf virus is specialized in its relationship with the aphid carriers and is not transmissible through seed, plant sap, or by other insects.
There are three ways to reduce yield losses due to BYDV. The first method is to delay planting. Since oats are generally planted early in the fall to provide winter grazing ahead of ryegrass, planting at a later may defeat the purpose of using oats. The second method is to apply the insecticide Gaucho (imidacloprid) as a seed treatment. This systemic insecticide does not necessarily kill the aphids, but does alter their feeding habits and has been shown to be effective up to 90 days after planting. The drawback is the $12-14 per acre additional cost. Insecticide treatment of spring grains to control BYDV is rarely justified. The third approach is to control the grassy weeds within and near small grain fields, to reduce the potential for virus introduction. Currently, there are no small grain varieties with resistance to this disease available, but researchers are attempting to select for this trait.
Are You Feeding Your Cattle Enough? Body Condition Scoring
How do you know if your feeding program is as good as it needs to be? The best indicator is cattle performance. The main thing that a cow must do year in and year out is to breed and raise a calf. The most limiting factor for reproductive performance is adequate nutrition. Diseases and the genetic traits inherited also affect a cow’s ability to rebreed on a timely basis but the vast majority of cows do not rebreed because of the lack of quality feed 50 days prior to, and 90 days following calving.
Since this is true, how can you tell if the cows are getting what they need? The simplest way to monitor your feeding program and to make sure your cattle are getting enough quality feed is to make regular observations of body condition or fat cover over specific areas of a cows body. The diagram below shows the main areas on a cow used to determine body condition scores.
Body condition is important because it is an indication of body reserves. Fat cows can afford to lose some body condition through the winter and might be fed 1-2 pounds of a high protein supplement verses a thin cow which might require 4-6 pounds of a high protein and energy feed. Body condition scores (BCS) have been developed (1-9) to help people compare their observations with a standardized system. Body condition score 1 & 2 cattle are extremely thin with nothing but their bone structure and muscle showing. Body condition score 9 cattle are extremely fat with no bone structure showing. Body condition score 5 is neither fat nor thin and is ideal for both performance and profitability. There is normally a difference of only 75-80 pounds between eachbody condition score.
Cattlemen normally deal with cattle that are condition score 3-6. Condition score 3 cattle have very little fat but have no muscle loss. Condition score 4 cattle have some fat cover but the last two ribs and hip bones are still visible. Condition score 5 cattle are smooth with no bone structures clearly visible. Condition score 6 cattle are building fat layers over all structures but is more noticeable over the ribs, back and hips. These scores can be used in combination with records to develop probable pregnancy rates for cattle as seen in the graph below. Notice the dramatic differences in the average pregnancy rates as cattle get thinner. Young cattle and heifers may need to be a full condition score higher than mature cows during the breeding season to get the same results below.
Body condition scoring is simply a tool to use to ensure that the herd is not losing too much weight after calving. Using a scoring system allows you to keep records to monitor change. It also provides a method that can be used to sort cattle after weaning or at some other point, to separate thinner cattle needing more and better feed from the fatter, usually more aggressive cattle. This is one way to possibly reduce feed costs and yet increase your breeding percentage. Want to learn more? Go to Effects of Body Condition on Productivity in Beef Cattle.
Plateau: A New Herbicide for Grass Weeds in Hayfields
Joyce Ducar, University of Florida Extension Weed Specialist
BASF received a federal registration on Plateau for use in Bermuda grass pastures and hay meadows on 12/26/01. A state label was granted in January 2002. The active ingredient in Plateau is imazapic, which is also the main ingredient in the herbicide Cadre, which is used in peanut production.
Plateau is labeled at rates of 4 to 12 oz per acre for control of annual and perennial grasses. There are no grazing restrictions. There is a 7 day haying restriction. It is a non-restricted use pesticide. Plateau may be used on common and coastal varieties of Bermuda grass including Tifton 44, 78, and 85, Alicia and Russell. Jiggs shows more sensitivity. Do not use it on World Feeder varieties. You can expect Bermuda grass growth to slow/suppress for about 30 to 45 days. Do not apply to Bermuda grass under stress. Do not apply Plateau until the Bermuda grass has reached full green-up. Plateau will injure Pensacola or Tifton 9 bahia more seriously than Bermuda. Hay producers will have to compare the value of weed control versus yield reduction.
Research trials in the southeast using Plateau have shown it to have excellent control on sand spur (sandbur), crabgrass, signal grass, and nut grass (nutsedge) at the 4 oz/acre rate. In trials with Plateau for vassey grass control, researchers had 85% control of this weed after two months at the higher rates of 6-10 oz/acre.
Forage Notes
Carrol Chambliss, University of Florida Extension Forage Specialist
Cool Season Forage Management
Ryegrass, small grains, tall fescue, cool-season legumes, and mixtures of these forages may need extra attention in February and March. Due to the extended period of dry weather in the fall, growth has been minimal, but with recent rains and warmer temperatures these forages have grown rapidly.Additional nitrogen may be needed at this time, especially on ryegrass in order to keep it producing into the spring.
Nitrogen - The cool season grasses need nitrogen for sustained vigorous growth. Apply an additional 50 to 65 lb/acre of N after the first or second grazing period. Two hundred pounds of ammonium nitrate contains approximately 67 lb of N.Ammonium sulfate is 21% nitrogen and 24% sulfur. Three hundred pounds per acre would supply 63 lb of N. If possible, apply the N after a grazing cycle when the grass has been grazed down and after the dew has dried.
Grazing Management - Cross fencing and rotational grazing (stocking) provides the opportunity to prevent overgrazing. Allow pastures to grow 6 to 10" tall before grazing. When cool season forages have been grazed down to a 2 to 3" stubble height, move the animals to a new pasture. Overgrazing slows the rate of recovery and reduces future growth. Cross-fencing a large pasture with electric fencing will provide the subdivisions needed for rotational grazing. Rotational grazing promotes uniform grazing and maximum use of the forage.
Hay Field Preparation
Prepare for the coming season: Burn frosted Bermuda grass stubble to reduce spittlebug infestation, certain fungal diseases and to remove trash. Burning also seems to allow the sun to warm the ground and stimulate growth. Do not burn too soon. Wait until a few green shoots are present, indicating that the Bermuda grass is breaking "dormancy". If a hard freeze follows shortly after growth is stimulated, the stand could be damaged. This is especially true for a non-cold tolerant Bermuda such as Coastcross - 1. Coastal and other Bermuda grasses that have rhizomes have greater cold tolerance and will likely survive a hard freeze.
Study soil tests and consider last year’s growth. Are there areas in the field where growth appeared to be reduced or where the stand is thinning?Bermuda grasses use a lot of potassium. Over time there may be excessive "drawdown" of the potassium in the soil profile if only minimal amounts have been applied. Thinning of the stand is a common symptom of insufficient potassium.Fertilize the new growth with 80 pounds of N per acre and the recommended amounts of potassium and phosphorus based on soil tests.
Be prepared to control winter weeds in the first growth period, if needed. Burning will kill many of the weed seedlings, but a herbicide may be needed to kill weeds that escape the fire or that germinate later. Kill the weeds early in the season so that they will have enough time to dry and disintegrate before the first harvest is taken.
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