February 18, 2004 | By: Aimee D. Heald
LEXINGTON, Ky.

Alfalfa stand loss is a natural occurrence. From the time the crop emerges from the ground, losses begin. In fact, each year fewer plants survive than the year before. However, the good news is that healthy alfalfa plants continue to grow and produce larger crowns and more shoots per crown, and that makes up for missing plants. 

“Although alfalfa stand loss is a fact of life, there are ways to minimize the amount lost,” said Paul Vincelli, plant pathologist at University of Kentucky College of Agriculture. “Stand losses in winter can occur as a result of several diseases. One that occurs in 10 to 20 percent of Kentucky alfalfa fields is Phytophthora root rot.”

Vincelli said this root rot disease doesn’t often show obvious symptoms above ground and diseased plants only show general stunting and slow growth. So, often a producer doesn’t know his stand is affected until the damage already is done. The diseased plants can die in the winter and that can result in substantial stand losses in susceptible varieties.

“Another disease that can predispose plants to winterkill is called crown rot complex,” Vincelli said. “Crown rot fungi invade and cause decay in the upper half of the alfalfa taproot, which is where the plant stores food reserves for winter survival.”

Although some alfalfa plant loss is inevitable, there are ways producers can minimize their losses. Vincelli said producers should select high-yielding, adapted, disease-resistant alfalfa varieties. 

“The UK Alfalfa Variety Trial results are always an excellent source of information to help producers choose varieties,” he said. “The report provides great information about yield performance, as well as disease resistance for each variety used in Kentucky. Always select a variety with an R (resistant) or HR (high resistant) rating to PRR (phytophthora root rot). These levels of resistance will keep this disease from being a serious limitation to yield and stand maintenance.”

It is important to realize that producers cannot select alfalfa varieties specifically resistant to crown rot complex since this complex actually is a collection of diseases with similar symptoms but many causes.

“Producers can reduce the activity of crown rot complex by selecting varieties well-adapted to our growing conditions and by maintaining them under good agronomic practices,” Vincelli said.
 

Contact: 

Writer: Aimee D. Heald 859-257-4736, ext. 267
Source: Paul Vincelli 859-257-7445, ext. 80722