Dodder is an expensive pest for seed alfalfa producers, and prevention is foremost in a combination of control strategies, according to Shannon Mueller, Fresno County farm advisor.

Reporting at the Alfalfa Seed Production Symposium held recently in San Joaquin, Calif., Mueller said once the matting of the yellowish, stringy parasite becomes attached to the crop, the problem can persist for as long as 20 years, requiring season-long control each year.

The extended viability is because only a fraction of the total seed population in the soil germinates during a single season.

Prevention hinges on eradication of patches of dodder before they can spread, and burning or clipping and removing infested plants. When spot treatment alone is not sufficient, the entire field must be treated.

Fields heavily infested with dodder, which can be spread from field to field by equipment or grazing animals, may require rotation to non-host crops.

Another approach is pre-emergence control, and applications of granular Treflan TR-10 or Prowl, both registered for use in California, provide very effective control, Mueller said.

“Proper timing is of critical importance in dodder control,” she said. “Application of either of these materials must be completed prior to emergence of the dodder, which varies depending on the year, location, temperature, and moisture. Dodder seed can germinate when the soil is moist and temperatures are higher than 60 degrees.”

Post-attachment control is being researched to identify a material that will control the pest without harming the host crop. Some progress has been reported, but results tend to indicate only temporary control.

Another front is removing dodder from alfalfa seed and destroying it. However, dodder seed resembles alfalfa seed and requires re-cleaning with a magnetic separator, resulting in a 2 to 15 percent loss of alfalfa seed.

“If a gap in the continuous process of control occurs, the cost of the program, which is high, is largely wasted,” Mueller said.

E-mail: dan_bryant@intertec.com