This is a great article on Stem Nematode management in the West.  Stem Nematode has been a severe pest in some years throughout California's Central Valley and high mountain valleys.

Stem nematode causes severe stunting, shortened internodes, and low first cut yields and can cause severe stand loss if infections are high.  It's transferred by irrigation water and equipment.  It is typically seen in very late winter or early spring.

Article by Ag Writer Vicky Boyd, in the Crops and Soils Magazine, available at:  

This Grade Chart represents the average Insecticide Efficacy Grade against alfalfa weevil larvae from experiments conducted in the Palo Verde Valley over the past five years, with applications being approximately 18-20 gallons/acre to ensure excellent foliar coverage. Some products and rates are represented by only a single data point, while others have multiple year/rates of data. Data shown are from experiments which had weevil larvae numbers at or above economic threshold levels, providing high confidence in data.

Efficacy of pyrethroid insecticide products has changed through this period due to the development of insecticide resistance in this area's alfalfa weevils. Resistance has shifted multiple pyrethroids from...