Using alfalfa to help cotton IPM

Preventing Lygus bugs from coming into a cotton field is the next best thing to not having the pest at all. Since cotton is embedded in a complex cropping mosaic, bugs building in neighboring fields can move to cotton. While cotton is not a preferred crop for this insect to set up a household, it will, nonetheless, settle in if nothing else is available.

Alfalfa hay, on the other hand, is a crop in which Lygus would prefer to stay and can serve as an important ally in managing Lygus in cotton. The vigorous growing plant with its attractive vegetative growing tips is ideal for Lygus development but does not suffer yield loss by this pest’s feeding. Thus, alfalfa hay can act as a  sponge, soaking up Lygus from the surrounding area. Finally, alfalfa is one of the few crops produced for its vegetative structure rather than its fruit, seed or tuber.  Therefore, Lygus feeding and development is not affected by any plant stress, such as change in physiological condition during reproduction phase.

Since there is no indication from the plant that harvest is imminent, there is no urge to leave the alfalfa field. Our studies have shown Lygus will remain in a harvested alfalfa field for up to 24 hours before leaving.

However, if given a choice, such as an uncut strip of alfalfa, Lygus will stay longer in the alfalfa field and may not leave at all. Additional trials  at Kearney Ag Center demonstrated that the population density within a strip can triple compared to density prior to harvest. In other words, they will stay on their familiar host as long it is available.

In the next 8 weeks, it is critical to leave uncut strips of alfalfa near cotton to minimize Lygus movement. Mass movement into neighboring cotton field can be prevented by leaving as little as two and half percent of the field left uncut. Providing a little bit of habitat will provide increased diversity during the critical period of early fruit set in cotton. Leaving habitat in the alfalfa field for only two cutting cycles in June and July can provide great return to the cotton grower in Lygus treatment savings, protection of beneficial insects and reduced risk to secondary pest outbreaks.

Throughout the San Joaquin Valley, alfalfa strips have become common and according to farmer testimonials, resulted in substantial savings in cotton treatment costs. These green islands provide a refuge for a reluctant pest and have been incorporated into the cotton IPM programs of thoughtful and progressive farmers.

For more information, see:

The IPM website page on managing Lygus in alfalfa

An impact statement on management of forage quality in strip-cut alfalfa