Lygus bugs (Lygus species) damage strawberry fruit by puncturing individual seeds. This, in turn, stops development of the berry in the area surrounding the feeding site causing fruit distortion called “cat-facing”. Even at moderate densities, Lygus bugs cause economic loss to strawberry growers. Lygus bugs feed on many host plant species. In the Central Coast and Santa Maria Valley, they feed on strawberries and many flowering weed species and alternate crop hosts such as mustards, pepper weed, wild radish, vetch, alfalfa, and fava beans. The adult bugs usually overwinter in these weed species while some overwinter on second-year berries when present. They start to migrate to fall plantings in the spring, but only the adults can fly from one host to another. Therefore, an understanding of Lygus bug ecology and developmental biology on strawberries and the alternative hosts will help develop effective management strategies.
Pesticides remain the primary tool for suppression of Lygus populations. Due to the emergence of pesticide resistance, it is essential to better time the few pesticides registered to control this pest. The sprays must be timed to kill the youngest immatures because the registered pesticides are less effective against the adults. This will become even more critical as IGRs and other newer products become registered that have activity against more specific life stages of Lygus.
Monitoring to detect Lygus bugs on strawberries and the alternative hosts is the first step towards successful management of this pest. The rate of Lygus bug development is directly related to the amount of heat the bugs are exposed to, so measuring the amount of heat accumulation over time can be used to tell when different developmental stages in the Lygus bug life cycle will occur. A degree-day model was developed to measure the amount of heat accumulation over the season and is an effective tool to predict the Lygus bug development, but this method has not been widely adopted by strawberry growers and their PCAs.
The specific objectives in this project are: (1) to monitor the population dynamics and developmental biology of Lygus bugs in the Central Coast and Santa Maria Valley, (2) to identify the migration pattern of Lygus bugs to/from strawberries in the Central Coast and Santa Maria Valley, (3) to establish biofix dates for the Lygus bug degree-day model at multiple sites, and calculate degree-days throughout the sampling season, and (4) to disseminate timely information to the strawberry growers and PCAs to improve their Lygus bug management decisions.
Methods:
Seasonal Lygus bug life cycles are determined by systematically sampling strawberry fields and nearby flowering weed species starting early February 2010 to determine age structure (number of adults, small nymphs – 1st – 3rd instars, and large nymphs 4th – 5th instars) of the Lygus population on each host. We are currently sampling four sites in the Central Coast and two sites in the Santa Maria Valley. These sites cover a variety of climate.
Sampling in the strawberries is being done using a beating tray. The sampling unit is 10 plants that have been “beaten” to dislodge any Lygus bug present onto the tray on each sampling date. A suction sampling machine could be substituted in practice. Five areas in each field are sampled in this manner. Weeds are sampled by a sweep net, using 10 sweeps through the foliage or flowers as a sample unit and at least 5 units are sampled to determine number and age structure of Lygus bug present. Weeds that are flowering or have seeds present are preferred.
Ambient temperatures at sampling sites are recorded at hourly intervals during the sampling season using micro data loggers (HOBO temperature recorders, Onset Computer Corporation, Bourne, MA). The recorded temperature data are collected weekly for the degree-day calculation. Biofix for the degree-days is the first adult captured in strawberry plantings, and first nymph on weeds or other alternative hosts. These data are used to validate and demonstrate the Lygus bug degree-day model.
The resulting data are entered at the UC IPM Pest Monitoring web site and the web site is updated frequently. The web site address is http://www.ipm.ucdavis.edu/PM/. The username is LDDmem and the password is Membugs.
Monitoring Location information:
- Boronda Road, Salinas
- Blackie Road, Castroville
- Old Stage Road, Salinas
- San Juan Road, Pajara
- Mahoney Road, Santa Maria
- Foxen Canyon Road, Santa Maria