Important Links
Key to Wyoming Grasshoppers
Grasshopper Field Guides and Identification Resources
Grasshopper Outlook
Predicting grasshopper numbers at this time of year is impossible. Last year at least 1 million acres of Fremont County was infested with numbers in excess of 10 grasshoppers per square yard. If half were female and they laid an average amount of eggs, that would result in 500 eggs or more per square yard. Only 2% would need to survive to maintain the population at outbreak levels. Many areas of the county had between 30 and 50 hoppers per square yard. Certainly the potential exists for a continued outbreak.
Grasshopper populations are mainly limited by disease. While none of the diseases are dramatically or rapidly fatal in and of themselves, they serve to weaken the insect, reduce reproductive capacity, and in combination with spring and early summer weather patterns can contribute to a near total collapse of the population. Spraying very large blocks of land, greater than 10,000 acres, often results in significant population declines and ends outbreaks where single species of grasshoppers are at outbreak levels. Thus, in 2010, there were millions of acres of rangeland sprayed in the United States over half of which was in Wyoming. This was due to the fact that Wyoming Weed and Pest Districts are well organized and funded while similar programs are absent in the rest of the north central states. Some of the blocks treated were in excess of 200,000 acres without any exclusions and hopper control should be very good. However, in many of those blocks there were still enough grasshoppers left after the treatment to re-establish high populations in 2011 and we will not know how effective they were until the middle of June.
Grasshopper Treatment with Insecticides
These large blocks were all treated using an insecticide called Dimilin, which interferes with insect molting. Once the grasshopper eats the chemical, it is unable to make chitin, the compound that makes up its hard exoskeleton and gut lining. Those insects are malformed after molting and if still alive, eat little if any, and they are easy prey for birds. Dimilin works slowly over a period of weeks. The chemical is applied by air with very little carrier. For each acre 0.75 ounces of Dimilin is mixed with 16 ounces of water, a little concentrated crop oil as an emulsifier, and 8 ounces of canola oil which acts as a bait, attracting grasshoppers from as far away as 50 yards. Thus, the plane can spray a strip of land 100 feet wide, then skip a strip 100 feet wide before it makes its next pass. This Dimilin treatment is referred to as Reduced Agent and Application Treatment or RAATs. This practice works very well on range land. The application is made when the earliest of the grasshoppers are about half grown, in the 3rd instar or molt, and because of its 6 week residual, continues to kill hoppers as they hatch for the next month. The small hoppers are killed before they eat much grass. Thus the forage is protected for grazing and the cost is very low. The federal government, USDA/APHIS pays for all federal land and part of the state land and part of the private land. The state typically pays the balance on state land, and the landowner pays the balance on his private land, usually in the neighborhood of $1.75/protected acre. That is a reasonable price to pay to protect that grass on an acre of rangeland. The economic threshold for rangeland is 14 grasshopper per square yard, and very little of Fremont County rangeland had that high a count. The only rangeland treated in 2010 was 7,000 acres above Hidden Valley which USDA/APHIS justified as a crop protection application due to irrigated crop land on three sides.
A RAATs application is not useful for crops for a number of reasons. First, in a high value crop, we want the feeding to stop immediately and Dimilin works slowly over a period of weeks. Secondly, the grasshoppers in crops are different species for the most part than on the range and some of them exhibit an extended emergence over a period of a month or more. Third, most crops have a lot of foliage which requires lots of water as a carrier to penetrate and coat the plant surface. That means the plane will need to apply at least 2 gallons of spray per acre, or 20 gallons of spray per acre with a ground rig. Dimilin is applied in 26 ounces of spray mixture per acre. A plane load of Dimilin using RAATs will treat ten times as many acres as the plane can using conventional application methods. That reduces turning and provides other efficiencies that keep the costs low. Fourth, irrigated crops are producing lots of new foliage every day and all new growth is unprotected. This allows grasshoppers an opportunity to feed all day on fresh tender leaves without ever running into any insecticide. Fifth, nearly every insecticide has waiting periods between treatment and harvest making timing of the application difficult. Add to all of this few insecticides are approved for all crops and there are few farms that could spray all their fields at the same time due to different crops and harvest dates. It is impossible to put a 10,000 acre block together in cropland, maybe impossible to even treat 50% of the land at any one time. The result is that grasshoppers re-infest the treated fields very rapidly.
Treatment Economics
Crop losses do occur. Each landowner must assess for himself the degree of damage in the crop and the value of the loss. A general rule of thumb in agriculture is that for any practice to be economically justified, it must return more that 2 to 1 for the investment. So, if it costs you $15.00 to spray alfalfa for grasshoppers, the treatment must result in a $30.00 increase in yield. And that is not $30.00 worth of baled hay. It is hay standing in the field at harvest time. That might be reasonable in a very good alfalfa field, but not in one with average yields of 3 to 4 tons per acre in two cuttings. One place where spraying will have the greatest impact will be on second cutting. In 2010, many alfalfa fields had hatching grasshoppers following 1st cutting. Numbers were so high that the tiny grasshoppers were able to stop all regrowth in the field and many folks lost their second cutting, or at least had no regrowth for about three weeks when the grasshoppers started to decline. A chemical treatment applied through a sprinkler during the 1st irrigation of the second cutting will allow for quicker recovery of the alfalfa and should pay dividends because of the reduced application cost. This will not eliminate all the grasshoppers by any means, and there will still be lots of feeding damage, but once 2nd cutting greens up well, the hay will keep ahead of the grasshoppers. In 2010, many growers still had normal yields in two cuttings in spite of the grasshoppers even without treating by following some of the cultural practices below.
Small grains can also be heavily damaged by grasshoppers. In late July, as the grain is maturing and drying up, the last green area on the plant is the base of the head. Feeding below the head weakens the stem and the head breaks off. Straw yields are normal, but there is no grain. Normally in crops, The University of Nebraska suggests that it take over 14 grasshoppers per square yard to economically justify chemical treatments, but just a few grasshoppers can significantly reduce yields in barley. However, the best solution is to windrow the barley rather than to spray. As soon as the barley is down, the grasshoppers will stop feeding on it. Waiting to combine the crop standing will result in major losses. Spraying will not work well enough to justify the cost. It is a timing issue.
Cultural Practices
Cultural practices probably are the most cost effective. Plowing makes a big difference. Grasshopper eggs are laid in the upper inch of the soil profile. When the ground in plowed or deeply disked, the eggs are buried too deeply for the baby grasshoppers to emerge. No till planting encourages grasshopper hatching success. Some growers feel that running over their alfalfa fields in the spring with a harrow reduces hatching success and results in fewer grasshoppers later in the season. The grasshopper eggs are theoretically exposed on the surface where they are easily damaged or consumed by other insects and animals.
Heavy grass sod with good standing stubble after grazing reduces grasshopper egg laying in the late summer and fall. There is little open dirt for them to lay eggs in and the ground temperatures are cool. A pasture that is heavily grazed opens many egg laying sites and promotes reproduction. Grasshopper experts advocate twice over grazing of pastures. This is intensive management. The pastures are grazed late spring to take half of the most palatable grass. Then the livestock are removed for about three weeks allowing for irrigation and regrowth. Then the pasture is grazed again to take just half of the grass. Then, it is irrigated and allowed to recover in the fall. Few eggs will be laid under this practice. Pastures that are poorly irrigated are at greater risk because the grasses are already struggling to dominate the land and a lot of bare ground is exposed. Bunch grasses like crested wheat seem to support high grasshopper numbers, likely due to the fact that no sod exists, just individual plants with lots of bare soil in between. Thus, a long range grasshopper control strategy would be to avoid the use of bunch grasses for field borders, roadsides and waste areas.
Irrigation practice appears to be important to reducing damage from grasshoppers in alfalfa. Alfalfa is a deep rooted plant. If there is good spring moisture, there is a temptation to not irrigate first cutting. However, the deep roots will have depleted soil moisture even though the plants appear to have enough water. When the hay is cut, the plants go dormant and stay that way until that deep moisture is replaced by irrigation. In some years the alfalfa does not really wake back up until the second irrigation after the 1st cutting. That gives the grasshoppers and advantage. The sun warms the soils and causes them to hatch all at once and the new little hoppers are able to keep all the new growth trimmed off for several weeks. So, in anticipation of high insect damage, it makes good sense to make sure that the crop is never stressed for nutrients or water. That assures an immediate recovery after cutting and the grasshoppers are never able to get ahead of the crop. Good water management will help a lot to reduce crop losses.
Early harvest helps to get the first cutting in before there is significant damage and allows for a quicker recovery of the crop, possibly getting ahead of the grasshopper growth curve.
Spraying
It is hard to decide what value insecticides have in crop land. Sevin, or carbaryl, kills grasshoppers pretty well and has about a one week residual. For many crops there is a harvest interval of 10 to 14 days. Thus with grasshoppers free to move from untreated areas the treated fields are quickly overtaken. The residual is a little misleading. Any new foliage produced after the chemical treatment is unprotected. Since hoppers prefer the new tender growth, they can feed all day long without encountering any treated plant material. The same is true for Lorsban which has an even longer residual. Expect to pay $7.00 to $8.00 per acre for these products and an additional $8.00/acre for custom application.
Malathion, Mustang Max and Warrior are contact insecticides. The spray really needs to hit the grasshopper to kill it and the residual is very short, a day at the most. The waiting period to harvest is often shorter than Lorsban and Sevin. The costs per acre are similar. A new insecticide has just been registered for alfalfa. It is called Coragen and works in a completely different way tying up nutrients needed by the insect. It is also is systemic in the plant. That means the whole plant is toxic to the insect and there is good residual effect. This product has been used to control many insect species in vegetable crops for a number of years. There is no waiting period to harvest. It sounds really great, but we have not actually seen a new label as of March 21, 2011, and we have no indication of price.
There are two bait formulations that use Sevin or carbaryl as active ingredient. The advantage of using bait is that grasshoppers are attracted to the bait and most other insects are not. So, you can treat for grasshoppers without hurting bees and butterflies. It also means that much less active ingredient is applied per acre. EcoBran is effective at as little as 5 pounds per acre with only 2% active ingredient. The total amount of insecticide is less than an ounce per acre. The other bait is a 5% granule with a higher application rate. The baits theoretically have a 5 to 6 week residual, the material gets covered by dust, rain covers it up and irrigation washes it away. With any of these products reapplication is a reality if total grasshopper control is the goal.
One spraying practice that does pay out easily is to treat the fence rows and waste area around the fields. Plowed fields do not need to be treated. The border treatment usually eliminates significant damage to the crop from grasshoppers hatching there. The cost of treating the borders of a field is much less that treating the entire field. Many producers saw the most damage in the first 10 to 20 feet of the field.
Insurance
Last year Fremont County was declared a disaster area due to the grasshopper outbreak. That designation expands USDA/FSA options. If funded, most producers will receive damages for crop losses via some type of crop insurance.
Cost sharing
Cost sharing on chemical will be available. In 2010, Fremont County Weed and Pest was the only county in Wyoming to offer cost sharing on crop land. We will cost share on chemical for grasshopper control again in 2011. We plan to cost share on carbaryl, liquid and bait, malathion, and Dimilin prior to July 1st. After July 1st we will also cost share on Lorsban, Mustang Max and Warrior. The District does not want to compete with private business, but will work to make sure that adequate pesticide is available at a reasonable price and that there are ways to get it applied.
Aerial application should be more available in 2011 that it was in 2010. At least in March many applicators were soliciting for business in 2011 while none were to be found in July and August last year. The issue is that in the spring the big spray jobs are just being put together around the state, but no contracts have been let. All the ag pilots in 10 states are looking for a piece of the business. By the end of May, they will all be under contract and have more work than they can do and it will be hard to get anyone to come to Fremont County to treat small individual fields when there are the big block programs going full bore. Sky Aviation based in Worland intends to have a plane in Riverton all summer and Alan Lebsack, Wind River Ag hopes to have his plane for more of the summer. At this time the District does not plan to line up the work for these private applicators and producers should contract with them directly. Sky Aviation can be reached at 307-347-6138 office, 307-277-3822 cell, and Alan’s phone is 307-850-8544.
Feel free to call us for assistance. Please keep in mind this grasshopper outbreak involves at least 7 different species all with different hatching dates and crop preferences. It is a natural disaster. It is not a lot different than hail, or drought. There are actions that will mitigate the economic impact in part, but regardless of what we do there will still be losses. No treatment program will eliminate the grasshoppers and the crop damage entirely. The population will eventually collapse under its own weight due to a combination of disease and weather conditions. That maybe that will be this year, or 2012. Statistically, Fremont Count has one general grasshopper outbreak every 25 to 30 years. So, the law of averages suggests we are done with this mess. But, what we saw last year was not at all typical of a grasshopper outbreak, and there is no one willing or able to predict an end to the grasshoppers. We will only be able to tell what the summer will bring by mid-June. And that leaves little time to mobile a response unless we begin planning in March.
|
