Lygus bugs (Lygus species) are serious pest of strawberries in California even present at moderate densities. Due to the emergence of pesticide resistance, it is essential to better time the few pesticides that are registered to control this pest. The timing of pesticide applications is solely dependant upon a close monitoring of Lygus bug population dynamics and its developmental biology. The sprays must be timed to kill the youngest immatures because the registered pesticides are not very effective against the adults.
Lygus bugs feed on many host plant species. In the Central Coast, they feed on strawberries and many flowering weed species and alternative crop hosts such as mustards, pepper weed, wild radish, vetch, alfalfa, and fava beans. The adult bugs usually overwinter in these weed species and second-year strawberries. They start to migrate to fall plantings in the spring, but only the adults can fly from one host to another. In second-year strawberries, overwintered eggs are major sources of Lygus populations. Our study showed that Lygus adults still lay eggs during December.
Monitoring to detect Lygus bugs on strawberries and the alternative hosts is the first step towards successful management of this pest. Our monitoring program recently detected that the first generation of Lygus nymphs started hatching during the week from February 7 to February 11 in many second-year strawberry fields in the Central Coast region. The cool weather and rain will slow down the Lygus emergence in these second-year fields but once the temperature starts to exceed 54 F for most of the day hours the emergence will again increase. We suggest that growers check their second-year fields for the presence of small Lygus nymphs and apply treatments if the threshold is reached.