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The arid climate and open spaces of our western states are the perfect combination for providing low disease pressure, which allows us the ability to produce high quality forages. 

However, this arid climate does not protect our hay crops from other pests, and one in particular is the alfalfa weevil, Hypera postica.  The alfalfa weevil is the most destructive insect pest to alfalfa hay in the intermountain plains of the West. 

According to Colorado State University, alfalfa weevil has been a problem in their alfalfa production since the early 1900s. 

Alfalfa weevil 101

So what is an alfalfa weevil? Adult alfalfa weevils are snout beetles, approximately one-quarter inches in length and brownish-grey with a dark brown band down the back. Adult alfalfa weevils over-winter in the crowns of alfalfa plants and become active in the spring once average temperatures warm above 48° Fahrenheit. 

During the spring, female weevils are busy laying eggs by chewing holes in new and dead alfalfa stems, then depositing the lemon-yellow colored eggs in clusters of five to 40 eggs inside these cavities.  Each female will lay between 400 and 1,000 eggs a season.

Prior to hatching, the eggs turn from the yellow-lemon color to a dark brown.  The young larvae emerge from the stem seven to 14 days after the eggs are laid. The weevil larvae are a grub that are yellowish-green with a shiny, black head and curved bodies that are one-twentieth of an inch. 

The newly emerged larvae feed on terminal alfalfa leaves prior to unfurling, while mature larvae feed on unfurled mature leaves. Alfalfa weevil larvae develop through four instar stages. 

By the third instar stage, a white stripe is visible down the center of the curved body.  It takes approximately three to four weeks for the larvae to develop from first instar to fourth instar, at which point the mature larvae then moves to the crown of the alfalfa plant to pupate into a loosely woven cocoon. 

  After seven to 14 days in the cocoon, depending on temperatures, the weevil emerges as an adult or snout beetle.  The adult beetles reduce their feeding on alfalfa plants for the rest of summer and focus on mating and surviving the winter. The complete life cycle is typically one generation per year in the intermountain plains of the west.


For the record, alfalfa weevil populations do not always reach economic thresholds that warrant control. Therefore monitoring your fields is advantageous. 

It has been found that a density of one larvae per 30 plants 12 inches tall can reduce yields by about three pounds per acre. However, alfalfa weevil impact on yield decreases with plant height so the same density of larvae on 16-inch tall plants was approximately 0.75 pounds per acre. 

Typically, alfalfa weevil larvae do the most damage to the first cutting through defoliation of the leaves, and they are typically out of the fields for second cutting.  However, if the damage to first cutting is significant enough then there could be major influences on the vigor of second cutting resulting in further yield loss. 

Since alfalfa weevil larvae grow and develop incrementally at almost a constant rate, which is directly related to the increasing spring temperatures above 48 degrees Fahrenheit, a growing degree day calculator can be utilized to determine the approximate date to monitor for growth stages and infestation or population. 

Estimating growth

A growing degree day calculator estimates the amount of accumulative days that have reached or exceeded 48 degrees Fahrenheit utilizing a high-low temperature gauge by adding the maximum temperature to the minimum temperature, dividing the total by two and subtracting 48.

The degree days are then totaled to represent cumulative degree days (DD) that can be correlated to development stage of the larvae – egg hatch at 310 DD, first instar at 350 DD, second instar at 425 DD, third instar at 500 DD, fourth instar 580 DD, adult emergence at 850 DD. 

Correlating the degree days to calendar days projects a date that can be utilized to concentrate monitoring efforts to determine economic threshold of an alfalfa field.

Once a date is determined utilize the six-stem count method, outlined in the sidebar, to monitor the different developmental stages of the alfalfa weevil larvae.  Since weevil populations can be spotty to uniform within a field, which is influenced by terrain, weather and soil conditions, field sampling should be done by predetermined patterns set by acreage and distinctive field sections. 

The fourth instar larval stage causes the most damage through defoliation than prior stages, therefore detection of earlier growth stages are suggested.

The economic threshold for controlling the alfalfa weevil infestation in your field is determined by the size of plants, the value of the hay, the cost of insecticide treatment, and the infestation levels or number of larvae per stem.  Contact your local extension office for current data on yield loss in your area and to discuss management options.

New development

The use of the cumulative growing degree day calculator has given our alfalfa growers a useful tool to help them better monitor and manage alfalfa weevils in their fields. Researchers and extension personnel have set average dates for the various larval growth stages by locations throughout their states.  These average dates are determined using the past 30-year daily temperature averages. 

Unfortunately, this method does not project accurate dates for unusually warm or cold springs, which can influence the development stages several weeks earlier or later.  To become more precise, calculations are encouraged to be done annually with current weather conditions. 

Current research in Wyoming is working on developing an electronic method to set the cumulative growing degree day calculator to local weather stations to give fast, accurate and local dates to keep monitoring efforts to a minimum while focusing the collection times to productive dates. 

Through this development, there is hope to benefit producers by making the monitoring and decision process more efficient and accurate.

Torrington – The mountain pine beetle ravaged forests across Wyoming in the last decade, and natural resource managers across the state have worked to address the concerns surrounding forest management to improve forest health and ensure long-term viability of the resource.

“We are on a mission to promote forest health and resilience in our area to provide a large-scale landscape that is ready to take on the challenges of fire, insect and disease,” said Sarah Mason of Crook County Natural Resource District. “We also see the need in harvesting the timber in these areas. It also keeps the economy going.”

Mason and Lacey Gurien of Weston County Natural Resource District talked about programming to address mountain pine beetle impacts in northeast Wyoming during a May 23-24 meeting of the Wyoming Legislature’s Joint Agriculture, State and Public Lands and Water Resources Committee.

Local-led efforts

Mason and Gurien have led a partnership of groups in the Black Hills to address pine beetle infestations.

“Pine beetles flight occurs in August,” Gurien said. “After that, we all get together, look at aerial photography and see where the pine beetles have hit. We collaborate and conduct training and education on pine beetle infestation.”

She noted that the districts utilize both spotters and sawyers to eliminate the affected trees and reduce the spread of bark beetles.

“We have spotters who go through and grid the forest. They physically walk the forest step-by-step, using GPS to mark individually impacted trees,” Gurien explained. “Then, our sawyers go in and cut down the infected trees. Our sawyers are trained and educated to help us improve our program.”

Inspectors then double-check their progress to make sure all infested trees are treated.

Treatment practices

The teams implement cut-and-chunk practices to stop beetles from spreading.

“Once we get in and cut down the trees, the bark heats up and the larvae die,” Gurien said. “We also use thinning practices.”

Thinning spreads out the trees to reduce competition for resources. Mason likened the previous state of forests to having dinner with a friend and eating off the same plate.

“Both people end up with not enough food and a little angry,” she said. “Trees are the same. They don’t have enough resources when they are too close. When we thin, it allows the trees to have more access to those resources and become stronger, healthier trees.”

Mason added, “When the beetles come back around, they have a better chance at fighting them off.”

Success story

“We have spent $4.3 million on this effort,” Gurien added. “We’re about 63 percent private ownership, with 36 percent federal and one percent state lands.”

Since 2012, of the 500,000 acres of forest in the Black Hills, 200,000 have been affected by pine beetles.

“In the Bear Lodge district, 40,000 acres have also been walked by our spotters. They walked 4,050 miles of forest, marking trees. They have  marked 8,000 trees,” she said. “We have trained over 80 individuals to walk and identify affected trees.”

To date, approximately 1,000 acres have been thinned, and an additional 1,000 acres are anticipated to be thinned by 2017.

Working together

Mason noted that the process of treating forests in the Black Hills has been a cooperative effort, both in terms of funding and management.

“We work very closely with the government in our area,” she said. “We work with our federal partners on targeted areas.”

While the federal government does not contribute much financially, Mason said, “In the longer-term, they help with timber sales and to keep timber sales sustainable.”

She also noted, “I do feel that our efforts are a partnership and a collaborative effort.”


Wyoming State Forester Bill Crapser commented that funding for the project has come through several sources, including the Wyoming Bark Beetle Response funding, which comes from a federal grant.

“That grant says $300,000 should specifically be targeted for use on private land,” he said. “The folks in Newcastle are working with conservation districts.”

Some money from the U.S. Forest Service is also incorporated for thinning projects, in particular.

“The Forest Service hasn’t been absent in this funding,” Crapser said. “The state has put a lot more money in than the Forest Service, but the Forest Service is trying to coordinate their timber sale program to complement what we’re doing on the ground.”

Future work

“Unmanaged forests and the state our forests were in got us here today. If we choose not to manage our forests, we have impacts,” Mason said, noting that dense forests are more problematic than just related to bark beetle.

“It’s harder to fight fires when the trees are crown-to-crown, and the dense stands don’t allow sunlight to the forest floor, so we don’t have forage on the ground,” she continued.

Mason also noted that the groups are seeking additional funding to pursue their efforts.

“We would like to pursue consistent funding to maintain this momentum going forward,” she said.

Committee Chairman and Washakie County Sen. Gerry Geis commented, “How can we say something against a program like this?”

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..

Worland – There are a number of key measures to take for the prevention of pests in farm-stored grain, according to University of Wyoming Extension Assistant Entomologist Scott Schell, who spoke at WESTI Ag Days in Worland on Feb. 19.

“Harvesting grain at the proper moisture level is important. If we put grain into storage and it has too much moisture, the grain could get mold and is also attractive to some of the pests of stored grain,” he commented.

It is recommended to store corn at less than 15 percent moisture, and most other grains should be stored at 12 percent moisture or less.

“We need to maintain the moisture in our target range for as long as we have the grain in storage,” he mentioned, adding that if grains need to be dried, the process should be done in stages to prevent damage.

Handling grain properly during harvest can also help to prevent infestations, as damaged grain is often more desirable to certain pests.

“Grains can be broken or cracked during harvest, handling or in the augers. Even if we dry out a grain too severely, it can sometimes crack and potentially be the start of a problem,” he said.

Special cautions should be taken with malting barley so cracked or damaged hulls do not impact the brewing process.


“We have to store grain in clean, dry, treated bins, meaning that we need to clean the bins out thoroughly and treat them with a preventative spray before we store a new crop,” Schell continued.

New grain should also be put into empty containers if it will be stored long-term, as mixing new and old grain crops can increase the likelihood of pest infestations.

Schell also warns that contract buyers may have specific regulations about which products can be used to treat storage bins for pest prevention before grains are added.

“Keeping bins clean and repaired is very important to prevent problems. Certainly, we can use older bins, but we need to keep them clean, repaired and as tight as possible, except for aeration systems,” he added.

Schell also noted that grain bins should be filled properly to maintain good airflow. If bins are too full or loaded improperly, moisture and temperature levels can be disrupted, and grain can get encrusted within the bin.

“The point of aeration is to maintain the quality of the grain product, managing it at a proper moisture and heat,” he remarked.


Once the crop has been put up, it’s also important to monitor the grain on a regular basis to ensure moisture and temperatures levels are being properly maintained and the aeration system is working well at all times.

“We can put it on our smartphone calendar or write it on the wall in the house, but we need to check and monitor our bins,” Schell stated.

If preventative measures fail and pests appear, he suggested identifying the pest first and foremost.

“Is it one that we brought in from the field? Is it one that is multiplying in the grain? Or do I have an insignificant insect that showed up in my bin by accident?” he asked.

Once the pest is identified, the best way to manage the population can be identified.

“The goal is to keep damages below the economic injury level. In most cases, we can’t always prevent all damage or all pests as it may not be economically feasible to do so,” he commented.


Fumigation, for example, is one control method that may be effective yet costly.

“Most all fumigation takes special equipment, training and licensing to apply. It’s probably not going to be cheap, and it’s probably best left to the people who have been trained. For our safety and because fumigants are quite toxic, we don’t want to make a mistake,” suggested Schell.

Again, it is also important to review any contracts that may exist with buyers as some companies have strict regulations about products applied to their grains.

“If we contract with a company, we need to find out what fumigants are acceptable to use,” he mentioned.

After measures have been taken to control pest populations, the grain should be re-evaluated for infestations.

“After our reentry period, once the treatment has had time to work, we need to resample and see what our results were. We need to make sure we had a good result and determine what steps we can take in the future to prevent the problem from happening again,” he said.

Multiple techniques

Grain pests can include many different kinds of organisms, from rodents, insects and mites to weeds, molds or other pathogens. Schell recommended using multiple methods to reduce pest problems in grain storage.

“We want to combine many approaches to deal with pests and not rely on only one thing because pests have the ability to become resistant to almost any method of control,” he remarked.

Different kinds of pests can also cause different types of damage, such as insects that grow inside of grains and are not immediately visible, pests that prefer to eat damaged grain and even pests that feed on mold growing on grain stored with too much moisture.

“Again, we need to harvest our grain at the proper moisture level, ensure that our machinery isn’t damaging the grain, store our crop only in clean, dry bins, never put new grain in with old grain and bring moisture levels down to recommended levels in stages. Also, monitoring is very important,” stated Schell.

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at This email address is being protected from spambots. You need JavaScript enabled to view it..

Last year, researchers at the University of Wyoming Sheridan Research and Extension Center began to investigate the possibilities of creating weevil-resistant alfalfa varieties for commercial growers.

After working with grapes for nearly 12 years, Assistant Professor of Horticulture Sadanand Dhekney believes that similar genetic engineering technology from grape research can be translated to producing alfalfa with weevil resistance.

“This is a pilot project. We have to establish a cell culture for alfalfa. Once we establish a cell culture system, we will have a means of inserting genes, and we can engineer plants,” Dhekney explains.

Some alfalfa varieties respond well to growing in a cell culture, but others are more difficult, and the project is currently trying to identify which varieties will be ideal for the research.

Commercial crops

“We are testing commercial varieties that are grown in Wyoming,” he notes. “Once that is optimized, we can start inserting genes for insect resistance.”

So far, one model variety has shown a lot of promise for the project but researchers hope to be able to use commercial varieties that are important to Wyoming growers as well.

Surprisingly, Dhekney is finding quite a bit of variation in how alfalfa varieties respond to growing in the cell culture.

“I would expect to see some difference, but it’s interesting to see that some varieties respond right away and other varieties take more time. That might be a potential challenge if we have to spend a lot of time optimizing the cell culture system and the engineering system to where we can have plants that growers are actually interested in,” he comments.

Growing cell cultures

Other variables can also affect how plants respond to the cell culture, such as seasonal factors like light and temperature.

“When we get material from plants growing in the greenhouse for cell culture, our plants might respond really well in the summertime but really poorly in the wintertime,” he cites as an example.

To create weevil-resistant alfalfa, researchers are hoping to use genetics that cause the plants to produce a protein called lectin, which binds to carbohydrates in the gut of the insect, making the carbohydrates unavailable for digestion. Known as antifeedants, these particular proteins essentially cause the weevils to starve and die.

“Genes for insect resistance come from different plant sources. We are currently getting them from rice, and we have some genes from maize. We also have lectin genes from bulbs that typically produce these antifeedants,” remarks Dhekney.

Eventually, if researchers see positive results, they may be able to isolate genes from the alfalfa itself to be used in future engineering.

Similar genetic information may also prove to be useful for controlling other pest problems, such as stem nematodes, which have also caused large problems for growers in Wyoming.

More questions

“We are just starting to scratch the surface. The first step is identifying those genes that show resistance and identifying the right plants. From there on, the options become unlimited, and it opens up a whole new world,” he says.

Once weevil-resistant plants are identified, a series of new questions will arise, such as how resistant plants impact livestock that consume it as forage.

“One of the reasons we chose to work with lectins from bulb plants is there have been some studies that have shown minimal effects on higher animals, but ultimately, we will have to study the effects of feeding the resistant plants on animal growth and development,” Dhekney says.

Pollination mechanisms will be another factor to consider if weevil-resistant alfalfa becomes a reality. Organic alfalfa is common in Wyoming and growers may be concerned about genetic contamination of organic crops.

“How far does the pollen of a modified plant blow away? What are the agents of pollen dispersal? What are the effects on beneficial insects that might feed on the pollen?” he asks. “There will be more questions if we come up with a solution for the weevil.”

Potential benefits

Success in creating weevil-resistant alfalfa could be one more tool in an integrated pest management strategy, adding to the effectiveness of other biological or chemical control methods, he adds.

Resistant varieties could also reduce the use of other pesticides that are currently being used to manage weevils in Wyoming.

At one of the large ranches in Sheridan County, Dhekney comments, “They spend thousands of dollars each year on aerial spraying of pesticides for weevils. It would take time, but if we had a variety that was resistant to the weevil, it would essentially mean less spraying, less labor and less use of the plane. This is one strategy that could significantly bring down costs of production.”

The current project is funded for three years of research, with support from the Wyoming Department of Agriculture and the University of Wyoming Agricultural Experiment Station.

“If results look encouraging, we might write a grant for a bigger agency and expand the work. We just have to see what kind of results we get and how quickly, and then we’ll go from there,” notes Dhekney.

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at This email address is being protected from spambots. You need JavaScript enabled to view it..

Casper – The mountain pine beetle epidemic has subsided across much of Wyoming, but Wyoming State Forestry’s Forest Health Specialist Les Koch said the state has another challenge on the horizon.

“Emerald ash borer is going to be important to Wyoming,” Koch said during the Wyoming Weed Management Rendezvous on Jan. 21. “We have not seen the bug in Wyoming yet, but it was detected in 2013 in Boulder, Colo. It has not been detected beyond the corporate limits of Boulder County yet.”

Regardless, the prominence of ash trees in the state of Wyoming means the bug could have significant impacts if it reaches Wyoming.

Impacting trees

“Green ash is native to the eastern side of the state, and every community in Wyoming has Green ash trees,” Koch explained. “It is widely planted in the state.”

Emerald ash borer invades trees similarly to how pine beetles kill pine trees.

“Literature tells us that adults emerge in mid- to late-May and peak in June,” he said, adding that until the bug appears in Wyoming, its exact habits in our environment will be unknown. “Everything is different in Wyoming.”

In outbreaks across the country, Koch said that emerald ash borer travels throughout contiguous stands of trees. The larvae of the beetle feed on the inner bark of the ash, disrupting the tree’s ability to transport both water and nutrients, subsequently killing the tree.

According to Koch, trees infected with emerald ash borer often exhibit sparse leaves and branches in the upper part of the tree during the growth season. Vertical splits in the bark are also common when dealing with emerald ash borer.

“New sprouts on the lower trunk and in the lower branches are another sign,” Koch said. “If we see a sparse crown as well as branches on the lower trunk, it might be wise to see what is causing the problem.”

Beetle lifecycle

Similarl to pine beetle, the emerald ash borer larvae winter under the bark of the tree.

“The segments of the larvae look like small bells,” Koch said. “It is pretty easy to identify.”

In addition, indicates that woodpeckers tend to like to eat the larvae, and heavy woodpecker damage may be a sign of infestation.

As the larvae emerge from the tree as adult beetles, they leave “D” shaped exit holes in the bark.

The adult beetle is metallic green and about one-half inch long.

Similar bug

Another bug, the ash bark beetle, may be confused for the emerald ash borer, but Koch explained the bark beetle is native to Wyoming, which makes it less of a concern.

In differentiating the bark beetle from the emerald ash borer, Koch explained that the bark beetle bores holes that are perpendicular to the main gallery of the tree, rather than parallel.

Green ash bark beetles also make small, pinhead-sized holes in the tree.

“If we see perpendicular tunnels and breathing holes, we do not have emerald ash borer,” he said.

Spreading pest

Wyoming is fortunate in that the large distances between cities mean that emerald ash borer would likely be unable to fly between communities to spread.

“How would it likely spread? Firewood,” Koch said. “If we have firewood with the insect underneath, we are going to have problems.”

He also noted that in Michigan, where the outbreak was first detected in 2002, emerald ash borer made an immense impact because of firewood movement.

Koch recommended that people seeking firewood should cut it in local areas.

“Anyone who does cut firewood should get it from a local forest so the native insects are present,” he said. “Firewood that is cut from national forest system land with a permit or that is transported should have the needles removed and make sure the bark has fallen off.”

If the bark is still intact, Koch recommended removing bark to make sure there are no larvae present.

“The insects can survive even in one-foot bolts of stacked firewood,” he added. “They will find the next available pine tree – whether that is on our property, the neighbor’s property or in a city park.”

Other recommendations

Koch added that, while emerald ash borer may become a threat, he wouldn’t go so far as to recommend against planting ash trees.

“I recommend the 10, 20, 30 rule,” he explained. “If we are going to plant Green ash trees, make sure no more than 10 percent of a stand is Green ash.”

He further adds that no more than 20 percent of the ash species should be planted, and no more than 30 percent of the same family of tree should be planted in a stand.

“We shouldn’t plant more than 10 percent of a species, 20 percent of a genus or 30 percent of one family in a stand,” Koch said. “We can still plant ash, but we need to diversify and plant other trees as well.”

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at