Pasture and Forage Minute: Grasshopper Control, Safe Grazing Guidelines And Blue-green Algae Poisoning
Grasshopper and Alfalfa
Summer heat brings insect pressure in alfalfa stands. One pest that you may see in increasing numbers are grasshoppers.
With dry conditions statewide, natural grasshopper population controls that thrive in warm, humid weather are not as effective and the growing nymphs are seeking out high energy food as they mature. If conditions stay dry, they will only get worse as the year continues and control may be needed.
Control begins with scouting to determine if insecticides are economically useful. I can’t give you an exact economic threshold because of variables like the value of the alfalfa, and the growth stage of both alfalfa and grasshopper are factors that need consideration. Still, if the grasshopper population in an established field is higher than five hoppers per square yard throughout the field or 15 hoppers per square yard in field margins, insecticides should be considered. Newly planted fields may need treatment if the grasshopper population is even lower.
Around many alfalfa fields, grasshoppers have just started moving in from the field margins. Treating just the outside 150 feet or so may be sufficient in these situations. However, if the entire field already is infested, it usually is best to first harvest the alfalfa and then apply insecticide to protect the regrowth.
With second cutting occurring or happening shortly, we can reduce the cost and amount of insecticide used when treating an entire field. Harvest alfalfa but leave several small, uncut strips across the field. The remaining grasshoppers will quickly congregate in these strips, enabling you to just treat these smaller areas.
Remember to carefully read and follow all label directions and be especially careful to avoid injuring bees and other important pollinating insects.
If you have many grasshoppers in your alfalfa, control them soon. As they grow larger, they’ll only get worse and control may be less effective.
Grazing Summer Annual Forages
Summer annual forages such as sudangrass, sorghum-sudan hybrids and pearl millet planted this spring soon could be ready to graze. There are some grazing guidelines to help avoid potential hazards.
The first guideline is too never turn hungry animals into sudangrass or sorghum-type pastures. The reason why is because they may eat so rapidly that they could get a quick overdose of prussic acid and die. All sudangrass and sorghum-type hybrids can produce a compound called prussic acid that is potentially poisonous. Prussic acid — which also is called cyanide — is nothing to fear though, as long as you use a few precautions to avoid problems.
The highest concentration of prussic acid is in new young shoots, so let your grass get a little growth on it before grazing to help dilute out the prussic acid. Let sudangrass get 15 to 18 inches in height before grazing. Sorghum-sudan hybrids usually have a little more prussic acid risk, so wait until they are 18 to 24 inches tall.
Pearl millet does not contain prussic acid, so if you planted millet these grazing precautions aren’t needed. Pearl millet can be grazed when it reaches 12 to 15 inches tall.
Nitrates also can accumulate in these grasses, particularly when there may be droughty conditions and/or excess nitrogen fertilization. However, as long as you avoid grazing too short, nitrates should not be a problem — especially since nitrate concentration is highest in the lower parts of the stems.
Summer annual grasses respond best to a simple, rotational grazing system. Divide fields into three or more smaller paddocks of a size that your animals can graze down to about eight or so inches of leafy stubble within seven to 10 days. Repeat this procedure with all paddocks. If grass in some paddocks gets too tall, it could be cut for hay.
A well-planned start, a good rotation and a little rain can give you good pasture from these grasses all the rest of the summer.
Water Quality and Blue-green Algae
When cattle are on pasture, grass growth and quality is important. Just as important for livestock is the water quality and amount. Surface water problems, such as blue-green algae, salinity, mineral concentrations or nitrates, will affect performance and health of cattle.
There are several factors that may cause livestock water to be less than ideal for quality. Salinity, or mineral, levels can become high enough to become toxic and when too high will cause livestock to refuse consumption. Dissolved salt concentrations increase with dry conditions. Typically, this is not an issue for most water sources in Nebraska.
High nitrates can occur in ponds and lakes in Nebraska. Some of this may be attributed to run-off when proper fertilizer application is not used in pastures or crop fields. While not always a concern in themselves, elevated nitrate levels in water coupled with feed sources that are high in nitrates could accelerate nitrate toxicity symptoms in cattle.
Blue-green algae is a very common occurrence in still water during the summer months. If the conditions are right, a bloom of growth can occur quickly, contaminating the water. Consumption can kill livestock within 24 hours. Blue-green algae can be treated with copper sulfate in ponds and lakes but be sure to follow instructions on rates and exclusions.
Assuring water is good quality will go a long way toward making summer grazing better and healthier cattle.