Alfalfa

U.S. Secretary of Agriculture Tom Vilsack recently announced the USDA Pandemic Assistance for Producers initiative. USDA is dedicating $6.5 billion in funding to reach a broader set of producers than in previous COVID-19 aid programs, with a specific focus on strengthening outreach to underserved producers and communities and small and medium agricultural operations. The original application period for CFAP 2 ended Dec. 11, 2020. However, USDA reopened CFAP 2 signup beginning April 5, 2021, for at least 60 days. A signup deadline will be announced at a later date.

See full post for more information on the USDA Pandemic Assistance Program for alfalfa farmers.

Dated: May 25, 2021

Many growers, PCAs, and Extension specialists are challenged by the task of determining unknown causes of poor crop growth in a field of alfalfa. Sometimes we can determine the causes, others we cannot achieve a quick conclusion, but often the actual causes of the problem are not known immediately. In alfalfa, several factors can interact to reduce crop growth, making diagnosis more problematic. Examination of field indicators and plant symptoms may provide clues as to the reason for poor growth or plant injury.

During one of the Western alfalfa symposiums, the late Steve Orloff, Steve Norberg, and Tim Hays of UC put an excellent program on "Diagnosing Problems in the Field". The links to this session are available as PDF and PowerPoint slides.

Dated: May 4, 2021

We started to see some cowpea aphid in one of our alfalfa experiments. We received some reports of cowpea aphid populations in small number of fields in central Arizona, as well as from alfalfa production area along the Colorado river. For information on cowpea aphids and how to manage them in your field, please see the full post. 

Dated: September 2020

Because of the economic consequence of alfalfa weevil, growers and PCAs use control measures against this serious pest. There are a variety of insecticides that can combat alfalfa weevil; however, almost all these insecticides are broad-spectrum. Our surveys of growers and pest control advisors showed that the efficacy of current broadspectrum insecticides against alfalfa pests, particularly alfalfa weevil, is declining. We have evaluated the efficacy of an alternative selective chemical that could be used to replace broad-spectrum pesticides; however, the pace of registrations of novel insecticides is dilatory. In the meantime, we need to be good stewards of the current and available chemicals to control this insect. One of the few available insecticides to manage alfalfa weevil is lambda-cyhalothrin (Warrior II™). With reports of potential resistance developed against this product from neighboring states, we investigated lambda-cyhalothrin (Warrior II™) against alfalfa weevil to test for any resistance by comparing the dose-response of field populations of alfalfa weevil from several states, including many sites in Arizona, using feeding assays. The results of these experiments will be helpful to growers and the agriculture industry in the western region and around the nation as they decide which insecticides to use on their crops and which ones are most effective. CLICK HERE for the UArizona Cooperative Extension publication that illustrates the results of these assays.  CLICK HERE for more general information on Alfalfa Weevils and how to test threshold.

Dated: Feb. 2019

Alfalfa must be dried or cured for safe storage as hay, generally we do not have problems reaching this dryness in Arizona. Normally, field and harvesting losses of hay are as high as 20 to 30% due to cutting and curing. Rain can increase these yield losses and reduce quality. 

For More in formation please see full article.

Dated: Oct. 2018

With the cooler temperatures of fall and optimum planting times for alfalfa approaching, winter weeds will soon be germinating in established alfalfa fields.  Now is a good time to be thinking about preemergence herbicide options for established alfalfa fields. Some winter weeds, such as common groundsel (Senecio vulgaris), are toxic, while others impart off-flavors to milk when fed to dairy cows.  For more information see the full article.

Dated: Oct. 2017

The decision to replace alfalfa stands is based on stand establishment costs, hay prices, the yield of the alfalfa stand in question, and other factors.  The economic benefit of replacing an alfalfa stand increases as the cost of establishment decreases, the hay price increases, and the yield reduction due to the poor stand increases.  For more information, see full article.

Dated: Sept. 2017

There have been many cases of cutworm infestations in alfalfa in central Arizona. Cutworms are frequent pests in the low desert of Arizona. The granulate (Feltia subterranea) and the variegated (Peridroma saucia) cutworms are the two most common species in alfalfa.  For more information, see full article. 

Dated: Aug. 2016

Alfalfa in the southwest ecosystem provides many environmental benefits: it is a rich habitat for wildlife, provides an insectary for diverse beneficial insects, improves soil characteristics, fixes atmospheric nitrogen, traps sediments and takes up nitrate pollutants, mitigates water and air pollution, and provides aesthetically pleasing open spaces.  For more information, see full article. 

Dated: May 2015

Over the last few weeks, we have received reports of sluggish mummified aphids in many alfalfa fields across central Arizona.  After visiting and collecting samples, it appeared the aphids are infected with a fungal disease that can eventually kill aphids in these fields.  This phenomenon is not usual in the desert.  Fungi depend on high moisture to grow and propagate.  The last rains we received created a favorable condition for the growth of this fungus and allowed its infection to alfalfa aphids.  We are monitoring this phenomenon, which we believe can give some relief from the alfalfa aphid problem we have been dealing with for the last few years.  Watch for similar aphids in your field and, if you believe your fields may have aphids with fungal infections, please let us know.

Dated: Feb. 2015

Stand Replacement: The decision to replace alfalfa stands is based on stand establishment costs, opportunities in other crops, hay price, and yield of the alfalfa stand in question. Historical yields for the farm can provide a good idea whether or not a stand should be replaced. A stand should be replaced if plant density is less than 4 to 6 plants per square foot or if the number of stems is less than 40 per square foot. Stands may need replacement regardless of average plant or stem density if plants are not uniformly distributed or if many bare spots exist where the sun at noon hits the soil surface. Renovating alfalfa stands by over-seeding with alfalfa is usually not effective except in bare spots greater than a 12-18 inch diameter. To avoid autotoxicity, delay seeding alfalfa into a field previously in alfalfa by at least 2 weeks after tillage or 3 weeks after herbicide-kill of the old stand.

Weed Control: Now is the time to apply pre-emergence herbicides for winter annual weed control in established stands. It’s better to be a month early than a day late with pre-emergent applications.

Dated: Oct. 2015

Many growers, PCAs, and Extension specialists are challenging by the task of determining unknown causes of poor crop growth in a field of alfalfa. Sometimes we can determine the causes, others we cannot achieve a quick conclusion, but often the actual causes of the problem are not known immediately. In alfalfa, several factors can interact to reduce crop growth, making diagnosis more problematic. Examination of field indicators and plant symptoms may provide clues as to the reason for poor growth or plant injury.

During the 2013 Western alfalfa symposium in Reno, Steve Orloff, Steve Norberg, Tim Hays of UC put an excellent program on “Diagnosing Problems in the Field”.   All the videos and written material from this conference can be seen at: http://alfalfa.ucdavis.edu/+symposium/2013/index.aspx

Dated: May 2014

Aphids, a key pest complex of alfalfa, are mostly controlled by broad-spectrum insecticides such as organophosphates and pyrethroids, leading to devastated natural enemy populations, other negative environmental impacts, and posing risks to insecticide applicators. It is therefore urgent to investigate the efficacy of lower-risk, selective insecticides against aphids.

The University of Arizona Cooperative Extension has started a project addressing the development and implementation of IPM practices directed at economically important pests of alfalfa hay. We wish to identify effective and environmental solutions that could improve current insect pest management practices in the low elevation desert southwest. One objective of this project is to investigate the efficacy of various insecticides for the control of alfalfa aphids. Lower risk, selective insecticides are available for sucking insects such as aphids in other crops, but their efficacy against the alfalfa aphid complex has not been investigated.  Currently, we are conducting two trials to study the efficacy of new and currently registered compounds at the University of Arizona Maricopa Ag Center. Several active ingredients are being tested in these trials, either as premixes or in tank mixes: dimethoate, malathion, chlorpyrifos, lambda-cyhalothrin, zeta-cypermethrin, chlorantraniliprole, and thiamethoxam, and experimental chemistries like sulfoxaflor, flonicamid and flupyradifurone.

PCAs and growers have expressed to me the many challenges in managing the aphid complex in alfalfa over the last two seasons. Many PCAs have reported different levels of control for the same product or tank mix. It is fair to say that our current arsenal of remedies to combat alfalfa aphids contains many old, broad-spectrum chemistries of diminished, declining or otherwise insufficient efficacy against today’s populations. The introduction of new products, like Transform® and Sivanto® for alfalfa would be welcomed; however, the actual date for the availability of these products remains uncertain. The alfalfa aphidicide trials we are conducting could help facilitate future special EPA emergency exemption requests (i.e., Section 18) in case they are needed for next year.

In order to learn more about the current situation of pest management in alfalfa and future opportunities, we would like to hear from more of our clientele: PCAs, growers, ag professionals, and ag industry representatives. We will have a breakout session during the upcoming Desert Ag Conference (DAC) on May 8, 2014, 3:00 – 4:30 pm to communicate with each other regarding the issues of alfalfa pest management this season.

Dated: March 2014

Talking with PCA’s, I found them using different techniques to deal with aphid populations in alfalfa. Some of them had aphids approaching the economic threshold level in their fields, so they decided to cut the hay a little early instead of applying an insecticide. Others had fields that were at threshold long before harvest and decided to apply a treatment. Another situation is the occurrence of higher populations of beneficials, which may make it possible to hold off spraying with the expectation that predation will keep aphids in check. Some folks go with the approach of pre-spraying, shortly after cutting. Whatever approach you take, everyone must adhere to the label limits for these products and active ingredients. For example, the specific use restrictions on Lorsban® Advanced label for alfalfa stated that “Do not make more than four applications of Lorsban Advanced or other products containing chlorpyrifos per season or apply any product containing chlorpyrifos more than once per alfalfa cutting.”

Conditions have been favorable for aphids to build up their populations in many areas of the low desert region. Our friends to the west in California also face high levels of blue alfalfa aphid. Similar to their observations, we are finding the heaviest densities to be very localized.

Efficacy trials for several aphicides are currently being conducted in the lower elevation desert in Arizona and California.
The Western Farm Press has this article about the current situation of aphids in alfalfa. Click Here to read this article.

Dated: March 2014

I received some questions about the values for forage quality parameters. Some forage quality parameters such as ADF (acid detergent fiber), NDF (neutral detergent fiber), and protein, are measured. ADF refers to cell wall portions in the silage that are made up of cellulose and lignin and NDF refers to the total cell wall (ADF + hemicellulose). Low values of ADF and NDF are desirable because ADF and NDF are inversely related to the digestibility of silage and dry matter intake (the amount of silage the animal can consume). Total digestible nutrients (TDN) is the sum of digestible nutrients in the forage which includes crude protein, fat, sugars, starch, and digestible fiber. TDN can be measured directly but is most often calculated from a mathematical formula using ADF (acid detergent fiber) as the sole measured value. Although TDN and ADF are related to each other, the relationship varies by region and is subject to different formulas and interpretation by the individual nutritionist. Another important parameter is Relative feed value (RFV) is a calculated index of forage quality that is very useful in comparing different types of forages. RFV provides an indication of digestibility of forage as does total digestible nutrients (TDN), but also includes intake potential. RFV is calculated from both ADF and NDF, whereas TDN is calculated from ADF only.

Dated: Feb. 2014

While scouting a number of alfalfa fields across central Arizona, I found that populations of Egyptian alfalfa weevil (EAW) and aphids are variable across the area. Some fields have high populations of both pests; some fields have high populations of one or the other, while others have very low populations of both EAW and aphids.
It is critical to correctly distinguish EAW larvae and adults from other insects which could be in the field at this time of year. We developed a short 1-page publication to help with that, Insect Pests of Desert-Grown Alfalfa: Egyptian Alfalfa Weevil. Remember that varieties with rapid spring growth may be more tolerant of weevil damage, and early harvesting can mitigate damage, but surviving larvae under windrows may reduce subsequent growth.
We have four different species of aphids in alfalfa: pea aphid, blue alfalfa aphid, cowpea aphid and spotted alfalfa aphid. To help with proper ID of these four species of aphids, the Arizona Pest Management Center has a short, 1-page piece on the diagnostics for the alfalfa aphid complex, Insect Pests of Desert-Grown Alfalfa: Alfalfa Aphid Complex.  It is important to ID these species, as each of them has different economic thresholds. CLICK HERE for information about alfalfa aphids monitoring and thresholds.

Dated: Feb. 2014

Using the right pattern of sweep net sampling is equally important. After many observations of sweep net sampling in alfalfa, I noticed that different “swing patterns” of the net resulted in different insect pest counts. Currently, all economic thresholds we use to monitor and justify treatments for alfalfa insect pests are based on 180° sweeps. Using other sweeping techniques may give different results and may lead to either spraying too late or unnecessary spraying.

Resistant varieties can tolerate aphid damage aided by proper irrigation scheduling which eliminates stress on the plant that makes it more susceptible to aphid infestations. Natural enemies can keep the populations of these insects in check. Strip cutting provides a refuge for natural enemies to help combat pests later in the season. With populations of the alfalfa aphid complex on the rise, it is crucial to make pest management decisions based upon positively distinguishing the four different species of aphids that are in alfalfa in the low desert: pea aphid, blue alfalfa aphid, cowpea aphid and spotted alfalfa aphid. It is important to ID these species as each of them has different economic thresholds http://www.ipm.ucdavis.edu/PMG/r1900611.html.

Dated: Feb. 2014

During this time of year, pest control advisors (PCA’s) and growers are dealing with a variety of insect pests in the two major field crops in central Arizona, alfalfa and cotton. In alfalfa, leafhoppers are major pests during this time of year. While scouting several fields this week, I noticed that hoppers [Potato Leafhopper and Three-cornered Alfalfa Hopper] were not as abundant as last year, but they approached levels that warrant management decisions in certain fields. The following two links from UC [http://www.ipm.ucdavis.edu/PMG/r1301211.html & http://www.ipm.ucdavis.edu/PMG/r1301611.html] provide information on description, damage, monitoring and management of these leafhoppers.

Leafhoppers are not the only insect pests we can find in alfalfa during the summer. Caterpillars are another group of insect pests that can be harmful to alfalfa during the summer. Mainly, we have three species of Lepidopteran larvae in alfalfa, Beet Armyworm: Spodoptera exigua, Western Yellowstriped Armyworm: Spodoptera praefica and Alfalfa Caterpillar: Colias eurytheme. Cutting the hay can mitigate caterpillar damage. Proper identification of these species is important because they have different economic thresholds. Using the economic threshold is crucial when the crop is too early to harvest and you decide to apply a treatment.

The following links from UC http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=10907, http://www.ipm.ucdavis.edu/PMG/r1300711.html, http://www.ipm.ucdavis.edu/PMG/r1300811.html, http://www.ipm.ucdavis.edu/PMG/r1300611.html provide information on description, damage, monitoring and management of these caterpillars.

Dated: Aug. 2013

“Summer slump” is a decline in growth of alfalfa usually beginning in July in hot summer areas, such as the low elevation deserts of Southwestern U.S. Alfalfa hay yield averaged over 2 years at Maricopa. Hay yield decreases after the beginning of July, characteristic of “summer slump”. Unpublished data from M. J. Ottman. In more temperate regions, there is a gradual decrease in alfalfa yield in successive harvests throughout the year, but the yield decline in the summer is not as sharp as in hot summer regions. The term summer slump has also been applied to reduction in growth of perennial cool season grasses such as tall fescue during the summer. For information see the full article about the alfalfa summer slump.

In Arizona, we have many species of stink bugs; that can be encountered in cotton, alfalfa, and other crops.  Some are occasional or potential pests of cotton.  See full post for more information on identification and effects of different stink bugs.

Dated: July 2013