Alfalfa Diseases: Symptoms and Management

  • Alfalfa diseases can reduce alfalfa tonnage, quality, and feeding value. 

  • Alfalfa disease management begins with the selection of locally adapted alfalfa products that have high levels of tolerance or resistance to the prominent alfalfa diseases in the area. 

  • Alfalfa diseases can occur when causal agents (fungi, bacteria, insects, nematodes) are present in the field, the alfalfa product is susceptible to the disease, and the environment is favorable for the disease. 

Alfalfa growers have the common goal of producing high tonnage, excellent quality, and high feeding value alfalfa for their livestock or for commercial sale. Some 50 or more alfalfa diseases can compromise that goal.1 Many alfalfa products have identified levels of tolerance or resistance to some, but not all, of these diseases. Therefore, it is important to know the most prevalent alfalfa diseases within the local area and then select the best adapted products to help manage potential disease outbreaks. Crop rotation may not be a viable management option because many alfalfa disease pathogens can survive within the soil or on residue for several years. 

Depending on the disease, plant infection can occur through soil water, splashing rain, wind, and possibly insect feeding. During the growing season, crop scouting should be conducted weekly to become aware of any disease development. Plant examination should be thorough as disease symptoms can mimic damage from insect feeding, herbicide burn on leaves, fertility deficiencies, environmental stress, and other issues. 

Disease management is also a product of plant establishment. At planting, fields should be weed-free, well-drained, fertile, and have a pH between 6.5 and 8.0.1 To help maximize germination and stands, seeds should be treated with fungicides and be planted at a depth of 1/2 inch, regardless of soil type.2

Foliar fungicides may or may not be economical to help manage foliar diseases. The use of foliar fungicides may be the most beneficial for the first cutting each year because spring weather is more favorable for foliar alfalfa disease development, the yield potential for the first cutting is usually higher, and the growing period is usually longer for the first cutting.3 Hay price, the stage of alfalfa growth, the amount of disease development, and the cost of the fungicide must be considered to help determine if a foliar fungicide application may be warranted.  

Most alfalfa diseases can be characterized by how the disease affects the plant - damping off, root rot, crown rot, and foliar diseases. However, many alfalfa diseases have a combination of symptoms.  

 

 

Seedling Alfalfa Diseases

 

Root Rots 

 

Crown and Stem Rots

 

Foliar and Stem Rot

 

Foliar Diseases 

Sources: 

1 Samac, D. 2011. Alfalfa diseases 101: Diagnosing common & emerging disease problems. Forage Focus. United States Department of Agriculture.  

2 Wells, M.S., Holen, D., and Sheaffer, C. 2018. Alfalfa establishment: Steps to maximize yield. University of Minnesota. https://extension.umn.edu/.

3 Lang, B. Is it profitable to use foliar fungicides in alfalfa production? Iowa State University. https://www.extension.iastate.edu/

4 Aphanomyces root rot in alfalfa. Integrated Pest Management Programs. University of Kentucky. https://ipm.ca.uky.edu/.

5 Samac, D. 2009. Mycoleptodiscus crown and root rot of alfalfa: An emerging problem in Minnesota and Wisconsin. United States Department of Agriculture.  

6 Groves, C. and Smith, D.L. 2013. Damping off and root rot of alfalfa caused by Phytophthora and Pythium. Integrated Pest and Crop Management. University of Wisconsin-Madison. https://ipcm.wisc.edu/.

7 Bessin, R. Phytophthora root rot in alfalfa. Integrated Pest Management Programs. University of Kentucky.  

8 Wegulo, S.N. Phytophthora root rot of alfalfa. NebGuide G2078. University of Nebraska-Lincoln. https://extension.unl.edu/.

9 Vincelli, P. 2008. Alfalfa diseases caused by Rhizoctonia fungi. Plant Pathology Fact Sheet. PPFS-AG-F-06. University of Kentucky Cooperative Extension Service. https://plantpathology.ca.uky.edu/

10 Babadoost, M. 1988. Bacterial wilt of alfalfa. Reports on Plant Diseases. RPD No. 300. University of Illinois.  

11 Diseases of alfalfa wilts and rots. 2014. Management Guide. New York State Integrated Pest Management Program. Cornell Cooperative Extension. Cornell University. https://ecommons.cornell.edu/.

12 Wegulo, S. N. and Anderson, B.E. 2011. Alfalfa anthracnose. G2081. NebGuide. University of Nebraska-Lincoln. https://extension.unl.edu/

13 Malvick, D.K. 2002. Sclerotinia crown and stem rot of alfalfa. The Bulletin. University of Illinois Extension. University of Illinois.  

14 Malvick, D.K. 1988. Leaf and stem diseases of alfalfa. Report on Plant Disease. RPD No. 301. University of Illinois. https://ipm.illinois.edu/

15 Wegulo, S.N. Spring and summer black stem and leaf spot diseases of alfalfa. NebGuide G2079. University of Nebraska-Lincoln. https://extension.unl.edu/

16 Davis, R.M., Frate, C.A., and Putnam, D.H. 2017. Stemphylium leaf spot. Alfalfa. UC Pest Management Guidelines. How to Manage Pests. University of California. 

Additional Source:

Samac, D.A., Rhodes, L.H. and Lamp, W.O. (Editors). 2015. Compendium of Alfalfa Diseases and Pests, Third Edition. The American Phytopathological Society (APS).  

Web sites verified 2/19/21.  4023_S1

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