Alfalfa Pest Control: Celebrate the 50th Anniversary of a BPM That’s Still Good as Gold

With summer around the corner, alfalfa farmers are already in the middle of their third cutting of the season. This is an important pest management milestone for cotton.

A grower leaves a strip of uncut alfalfa to create a habitat
 for pests and help keep them out of a nearby cotton field.

That’s right. And if alfalfa growers have listened to their neighboring cotton growers and University of California IPM advisors as well as our field scout Carlos Silva, they will be leaving strips of uncut alfalfa in the fields.

Lygus is a big threat to cotton plants.

We talked about the importance this practice three weeks ago. If you forgot, here’s a quick summary: Leaving strips of alfalfa creates a habit to attract natural predators as well as pests, including lygus, a serious pest threat in cotton.

Here’s what other UC ag experts say:

“Lygus can re­produce on a variety of wild and culti­vated plant species. However, in many areas alfalfa is the key breeding place and overwintering habitat. During favorable periods, lygus populations increase to great numbers in this crop.

“An important feature of the lygus prob­lem is that they are very rarely a pest of alfalfa hay. However, when the alfalfa is cut, the adults fly to adjoining crops and to prevent crop loss, chemical treat­ments are often necessary to suppress the invading pest.

“Since alfalfa is a key crop in California agriculture, it would be impossible to eliminate alfalfa as a means of reducing lygus populations. The problem then is how to stabilize the alfalfa hay environ­ment to prevent or lower the probability of lygus adults leaving the alfalfa habitat where they do little or no damage.”  

“Lygus bug control is possible by strip cut­ting alfalfa to keep the bugs in the alfalfa where they do little harm, and allow sur­vival of natural enemies. The end result could well be a very considerable saving to California farmers, and perhaps even more importantly, a significant reduc­tion in pesticide hazard problems.”

Insightful words – from a 1964 article published in a UC publication called California Agriculture.

Indeed, pictured above are a strip cutting diagrams pulled from a 1963 field study called “Alfalfa Control.” That research by trio of UC Berkeley, Davis and Riverside entomologists      a half century ago is certainly paying dividends today. Happy Golden Anniversary.

Carlos will keep us updated on the how well the alfalfa strips are doing to keep the bad bugs out of cotton.

So far, he has found only one field with concerns about lygus during his recent sample taking. In that field, he netted four lygus bugs per 50 sweeps along one row of the field. The grower pulled six to eight pests per 50. UC IPM thresholds are less than two lygus per 50 until June 15 and more than 2 from June 15 to 30. After consulting with his pest control advisor, they decided to hold off with any treatment and continue monitoring the field.

For the most part, cotton plant development is faring well. Carlos says plants have three to six fruiting branches. We’ll talk more about plant mapping next time.