Central Coast strawberry crops are susceptible to Lygus hesperus damage, according to University of California integrated pest management specialists.
The pest can cause irregularly-shaped, cat-faced strawberries. Lygus damage fruit by puncturing individual seeds and that stops berry development around the pest feeding site. Straw-colored seeds that are large and hollow are a good indication of lygus damage.
damage is more a problem in strawberry-growing areas where there is continuous fruit production.
Winter weeds host lygus before they move into strawberries in the spring. Sprays must be timed to kill the earliest instars of nymphs for best results.
Begin monitoring weed hosts around fields in February for lygus nymphs to determine when these plant hosts should be destroyed and to establish the first biofix for a degree day model.
Begin monitoring strawberry plants mid-April to detect when adults first appear. Establishing when adults first enter the field also serves as the biofix for part of the degree day model. Monitor fields regularly during the production season for economically important lygus densities and treatment thresholds.
Threshold levels for lygus depend on the monitoring method used. When a beat sheet (12-inch embroidery hoop with muslin, or other device of similar size) is used, divide the field into blocks and sample four 200-foot lengths of row in each block. Sample one plant in each 20 feet of row by placing the beating tray under the plant and beating it with your hand. Apply sprays when one lygus nymph is found in 20 plants sampled.
A bug vacuum that sucks lygus from plants into a screen or net placed within the device is a more efficient sampling device. The threshold to be used when sampling with a vacuum is one lygus per 10 plants. Continue weekly monitoring as long as fruit is being harvested.
Calculating degree days (DD) can determine the time of egg hatch, which occurs just before best treatment times for lygus nymphs. This information can greatly improve the timing of lygus sprays and weed abatement in central coast areas, where damage from lygus is an annual problem.
Accumulate degree days for lygus using a lower threshold of 54 degrees F. There are two primary periods when lygus migrate from weeds into strawberries. Use degree days to determine when peak egg hatch occurs following each migration. The first migration is by overwintered adults; it usually occurs in April.
If treatment thresholds are exceeded, apply the first spray 252 DD from the date you find the first adult in the field after April. This will generally be from late May to early June.
The second treatment period is at 799 DD (late June/early July) from the date the first nymphs are found in strawberries.
A third treatment period corresponds to the emergence of nymphs that come from adults that have established in the field and those that have migrated to strawberries during the summer — about 799 DD (early August) after the first spray.