The Richmond Register

August 13, 2013

Disease risks in late summer alfalfa seeding

By Brandon Sears
Extension Agent

RICHMOND — Later-summer plantings of alfalfa offer several agronomic advantages over spring seedings, particularly when soil moisture is adequate.

However, these seedings are also much more susceptible to the fungus that causes Sclerotinia crown and stem rot. This fungus is distinct from the Sclerotinia white mold disease that attacks many crops including tobacco. The Sclerotinia fungus that attacks alfalfa becomes active in mid to late autumn, and young alfalfa seedlings are often highly susceptible to the disease. The stand losses it can cause vary from minor to very severe.

There are a few alfalfa varieties that show partial resistance to this disease. Complete resistance is not available in commercial varieties, but partial resistance can reduce stand loss caused by this disease.

If considering a late-summer seeding, it is important to use a variety that has been shown to exhibit partial resistance under field conditions in Kentucky. This is important because some of the worst disease pressure from Sclerotinia crown and stem rot in the nation is in Kentucky. 

Variety evaluations conducted in other states are useful, but if a variety hasn’t been tested for resistance under Kentucky conditions, it hasn’t been adequately tested for use in Kentucky.

The variety Phoenix has been shown to have a significant level of Sclerotinia resistance under Kentucky conditions, so that is certainly one to consider for late-summer plantings. 

Cimarron SR is also a good choice from the standpoint of Sclerotinia.

Beyond that, I am unaware of other varieties that have held up against the severe disease pressure we sometimes get in Kentucky.

Be aware that these varieties can still suffer stand loss from the disease, but they will suffer considerably less stand loss than the many susceptible varieties on the market.

The best prevention against sclerotinia is to plant by mid-August if fall seeding or plant in the spring. If seeding in the fall, sclerotinia-resistant varieties can provide additional insurance.

Some of the top performing Alfalfa varieties in the 2012 UK Alfalfa variety trials include:  Evermore, Genoa, WL 357 HQ, WL 327, Phoenix, ABT 405, Cimarron SR.

Look for one of these varieties if you are seeding  alfalfa this fall.

Phase I Board meets Aug. 20

The Madison County Phase I Board will meet 7 p.m. Tuesday, Aug. 20 at the Central Kentucky Ag Credit Office, 1000 Ival James Blvd., across from Kohl’s on the Eastern Bypass. This meeting is open to the public.

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