Managing Lygus Bugs in Strawberries Production Guideline by Frank Zalom, Jianlong Bi & Pat Thompson Issue 3.1 June 2011 The California Strawberry Lygus bugs are a serious Commission Production pest in coastal production Guidelines are produced in cooperation with scientists who areas from Camarillo to conduct research related to Watsonville. In central coast strawberry production. These fields where strawberry guidelines are a tool for growers, fruit are harvested past providing critical scientific May, lygus populations background information on continue to build through diseases and pests common to strawberry production in the summer months. More California. For copies of this recently, lygus have become guideline or others in the series, well established in summer- visit www.calstrawberry.com. planted off-cycle strawberry systems found in Ventura County, reaching damaging Production Guideline by: levels on both summer and Figure 1. An adult lygus bug. (These photographs are by Jack Kelly Clark, and Frank Zalom are copyrighted by the Regents of the University of California. They are provided by the Department of Entomology fall plantings. UC Statewide IPM Program for use in this publication.) University of California, Davis [email protected] Identification p. 530.752.3687 Adults (Figure 1) have Jianlong Bi wings, and are about 0.25 Cooperative Extension inch long, oval, and rather Monterey County flattened. They are greenish [email protected] or brownish and have p. 831.759.7359 reddish brown markings on their wings. Near the center of their back is a distinct, but small, yellow or pale green triangle. Eggs are not easily seen because they are small and are inserted into plant tissue including Figure 2. Lygus bug nymphs showing spots on back. (These photographs fruit and leaves. First and are by Jack Kelly Clark, and are copyrighted by the Regents of the University of second instar nymphs California. They are provided by the UC Statewide IPM Program for use in this publication.) are pale green and look similar to aphids, but move faster, have red tips on their antennae and lack the paired cornicles or tubes located near the tip of the abdomen of aphids. The larger third and later instars (Figure 2) are green and have five black dots on their © 2011 California Strawberry Commission back - two on the segment immediately behind the head, two on the next segment, and one in the middle of the abdomen. A common nonpest species that may be confused with lygus is Calocoris spp. (Figure 3). They have two prominent black dots on the back, just behind the head, and dark wing tips. Lygus adults have no black dots on the back. Nymphs and adults of Calocoris are longer and narrower than lygus. Other related species that may be confused with lygus are big-eyed bugs (Geocoris spp.) and false chinch bugs (Nysius spp.). Life history and damage In central coast areas, adult lygus bugs typically overwinter from September to January on flowering Figure 3. Calocoris looks similar to a lygus bug, but does not damage strawberries. (These photographs are by Jack Kelly Clark, and are plants and legumes outside of strawberry fields copyrighted by the Regents of the University of California. They are provided by the UC (Zalom et al. 1990). Cover crops including clover, Statewide IPM Program for use in this publication.) fava beans and vetch are good lygus hosts. Some lygus overwinter on summer-planted strawberries that become infested during the fall migration and on second-year strawberries which had become infested during the first year. Only the adults can fly from one host to another since the nymphs lack wings. Three seasonal populations of nymphs occur on central coast strawberries, the first in May or early June, the second in late June or early July, and the third in late July or August, depending on location and temperature conditions. Adults from the third generation overwinter, and will lay eggs in the spring contributing to the next season’s problem. In the Oxnard area, lygus populations cycle throughout the year. Adults readily move between Figure 4. Cat-facing caused by lygus bug feeding. (These photographs are strawberry plantings and from alternate hosts such by Jack Kelly Clark, and are copyrighted by the Regents of the University of California. They are provided by the UC Statewide IPM Program for use in this publication.) as flowering ornamental plants, beans, weeds, and possibly caneberries. Lygus has sucking-type mouthparts, which it uses to feed on the developing strawberry seeds. When a seed is damaged, the flesh behind it does not develop properly. This creates the characteristic discoloration and malformation called “cat-facing” (Figure 4). Poor pollination also causes cat-facing, which is one reason that cat-facing symptoms alone should not be used as the basis for applying insecticides. Damaged strawberry fruit will not recover. It is necessary to suppress lygus before the damage occurs. Both nymphs and adults will damage fruit. 2 California Strawberry Commission Production Guideline Monitoring and Management adults do not tend to feed or reproduce. There Successful lygus management requires an are two primary periods when lygus migrate from understanding of its biology and life cycle, and is weed and host crops into strawberries, and DD can best achieved through a combination of control be used to predict when peak egg hatch occurs approaches and careful monitoring both within following each migration. strawberry fields and on its alternate hosts. Monitoring is particularly important to determine On the central coast the migration of the if and when to take a control action. The most overwintered adults often begins in April. Not all effective treatment timing targets nymphs soon after fields will have damaging levels of lygus at this time. egg hatch after overwintering adults have invaded If treatment levels are exceeded, apply the first the strawberry field when the greatest percentage spray 252 DD from the date you found the first adult of the lygus present are nymphs. Monitoring should (biofix #2) in the strawberry field. This will generally begin in February to detect the first appearance of be from May to early June. The second treatment lygus nymphs on possible host plants around the period is at 799 DD (late June/early July) from the field to establish the first biofix for the lygus degree- date the first nymphs (biofix #1) were found in day (DD) model. These alternate hosts include weeds. A third treatment period corresponds to second year strawberry fields and summer plantings the emergence of nymphs that come from adults in Ventura County. Monitoring in fall planted established in a field and those that have migrated strawberry fields should begin in February in south to strawberries during the summer and it is about coast growing areas to early April in Santa Maria and 799 DD (early August) after the first treatment the central coast to detect when adults first appear. period. After this time in a typical season, lygus Summer plantings should be monitored for adults populations will include large numbers of all life at the initiation of flowering. Establishing when stages, so use of degree-days has little value. The adults first enter a field also serves as the second lygus model is on the UCIPM Program website: biofix for the lygus DD model, and is an indicator http://ipm.ucdavis.edu/WEATHER/ddretrieve.html. that nearby infested weed hosts must be destroyed Degree-days can also be easily calculated by hand or immediately. Monitoring the field regularly after this with commercially available data loggers using local time will establish whether or not lygus densities are weather information. economically important and require treatment. In Ventura County, migrations of adults occur to both The lygus DD model is designed to predict when the summer plantings and fall plantings at some lygus nymphs will be present in strawberries. time after initiation of flowering. Apply the first Controlling lygus nymphs is preferred because they spray at 252 DD from the date you find the first adult can’t migrate from the weed or alternate crop hosts in the strawberry field. The second treatment period being destroyed and they are also more susceptible is at 799 DD from the date the first nymph was to control using insecticides. “Degree-days” are units found in the strawberry field. On summer plantings representing heat accumulation and they can be that have been chopped, a treatment at 252 DD used to predict the time required for some event after chopping is warranted if lygus were present the to occur in the life cycle of lygus and other insects previous fall. after the occurrence of some biofix (a specific event which establishes that point at which DD calculation Monitoring for the presence of lygus in weed and should begin). In any 24 hour period, the amount many alternate hosts can be conducted using a of heat above a minimum developmental threshold sweep net by vigorously pushing the net through can be expressed as DD for that day, and these DD the upper third of the plant canopy and examining are summed over time. Lygus requires a minimum its contents for the presence of lygus nymphs and temperature of 54O F to develop, and this is the adults, or shaking the upper portion of the plants temperature above which DD are calculated. Below over a beating tray. To quantify the abundance 54O F, lygus eggs and nymphs do not develop, and of lygus in the strawberry field, it is necessary to systematically use either a beating-tray or a Managing Lugs Bugs in Strawberries 3 hand held vacuum device described in University for lygus can also detect infestations of aphids and of California Publication 3351, Integrated Pest worms which are dislodged onto the tray.