- Author: Shimat Villanassery Joseph
- Author: Mark Bolda
Lygus bug (Lygus herperus) (Figure 1a) continues to be a major pest of strawberry in northern Central Coast of California. The feeding injury on the young developing fruits results in catfaced fruits (Figure 1b) rendering them unmarketable. Management of lygus bug in strawberry is always been a challenge because of lack of effective insecticides with desirable attributes such as short pre-harvest intervals (PHIs). Moreover, the insecticides registered on strawberry for lygus bug control have been used over and over in the same season and it is likely that lygus bug developed resistance to those insecticides.
In 2015, an insecticide trial was conducted to evaluate the efficacy of newer insecticides registered on lygus bug. The details on insecticide products, active ingredients and rates are shown in Table 1. The newer insecticides tested were Sivanto and Sequoia. Sivanto is registered on strawberry with the maximum rate 14 fl oz per acre. Sequoia is not registered at this moment and rate tested is 2.88 fl oz per acre which is lower than 4.5 fl oz or 5.75 fl oz per acre tested in the previous years. The study was a replicated (5 replications) and the treatments were randomized. The plot size was ten 65-feet long beds which is fairly large for insecticide trial in a commercial strawberry field. First broadcast-spray application of insecticides was done on 13 June 2015 followed by a second broadcast-spray application on 20 June 2015. The insecticides were applied using commercial tractor mounted sprayer. The water volume used for both the applications was 200 gal/ acre. Dynamic (surfactant) was added at 0.25% v/v.
Beat-trays were used to sample insect populations (Figure 2). Twenty strawberry plants were sampled and the sampling consists of five strikes per plant with the lid of a regular sized Rubbermaid container. Sampling was done a day before application then at 3 and 7 days after first application then 3, 7, 14, 21, and 28 days after second application. The insect samples were bagged, transported to the laboratory and stored in the freezer for later evaluation in the laboratory. The samples were evaluated for all nymph stages and adult of lygus bug, thrips, predators (damsel bug, minute pirate bug, bigeyed bug, rove beetle, and spiders) (Figure 3) and parasitoids. In addition, 100 fruits were randomly sampled from each plot at 28-days after second insecticide application. The fruits were evaluated for lygus bug injury or “catface” and other unmarketable symptoms such as rot, spit strawberries etc.
When all the data were combined, number of lygus bug nymphs were lower in the higher rate of Sivanto and Sequoia than in untreated check treatment (Figure 4). Lower number of lygus bug adult was captured in higher rate of Sivanto and Beleaf than in untreated check. Similarly, number of predatory bugs was lower in the higher rate of Sivanto than in other treatments. Spiders captured were similar among treatments (Figure 5).
On fruit evaluation, there was no difference in number of fruits with catface injury or those marketable fruits among the insecticide treatments, although numerically, number of fruit with catface injury was lower in the higher rate of Sivanto treatment than in other treatments.
Overall, it appears that Sivanto at 14 fl oz per acre performed better than other treatments against lygus bug. Sequoia and Beleaf also showed evidence of lygus bug suppression. However, Sivanto at 10 fl oz per acre did not suppress lygus bug. The representative industry standard -- combined treatment of Actara and Danitol did not show any evidence of lygus bug suppression in this study.
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- Author: Shimat Villanassery Joseph
Lygus bug (Lygus herperus) (Figure 1), usually a sporadic pest on vegetable crops, is now a major pest of several vegetables this year especially on celery, lettuce, and radicchio in the Salinas Valley.
On celery, the feeding injury appears as lesions toward the base of the mature stock and young foliage in the center (Figure 2-3). On lettuce and radicchio, lygus bug feeding injury appears toward the bottom mid-rib area of the leaf (Figures 4-8).
Lygus bugs are highly mobile meaning they can move from field to field until they find a resourceful food source. Perhaps, lettuce and celery are not the nutrient rich diet to lygus bugs but these crops could provide much needed moisture and refuge. High populations of lygus bug could develop on weed hosts in the unmanaged areas such as ditches, side of the roadways etc. Also, alfalfa or beans could serve as hosts. When weed plants dry out or mowed, lygus bug adults tend to leave those hosts seeking food and water elsewhere and even seek temporary refuge in the lettuce or celery fields. Those female lygus bugs settled in the vegetables not only cause feeding injury but also lay eggs. A lygus bug female can lay on average 150 eggs for its life time in an ideal laboratory conditions. This suggests that a few lygus bug females settled in lettuce or celery can develop into colonies. Any disturbance to the favorable hosts such as mowing the weeds in the unmanaged areas or mass cutting of alfalfa could trigger lygus bug adult movement. It is important that alfalfa growers pay attention when they cut the alfalfa crop. Sequential or staggered alfalfa cutting is advisable because any area wide cutting will disturb them and will cause lygus bug adults flee the alfalfa field. Maintaining the alfalfa crop succulent with adequate water and fertilizer is advisable.
Management of lygus bug involves repeated use of insecticides particularly pyrethroid insecticides and Lannate (methomyl). Among those registered insecticides on celery such as Vydate (oxamyl) and Malathion have comparatively longer pre-harvest intervals (PHIs) than pyrethroid insecticides; thus, they are used during the early phase of the plant development. Among the pyrethroid insecticides registered on vegetables, Mustang (zeta-cypermethrin), permethrins and lambda-cyhalothrin (Warrior II) are widely used. Growers restrain from using Mustang because of maximum residue level (MRLs) restrictions imposed by certain export markets. There are several generics of pyrethroid insecticides available in the market. Repeated use or exposing pyrethroid insecticides to same generation of lygus bugs may lead to insecticide resistant lygus bug populations. Lack of insecticide coverage could also result in ineffective spray results. As indicated earlier, lygus bug adults are highly mobile and they could move as the spray equipment approaches. If nymphs exist in the field, they could easily hide in the crown areas of the plant. This suggests that there could be several reasons behind inadequate control of lygus bug. Monitoring the field is critical to reduce the establishment of lygus bug colony in the field for timely management.
- Author: Shimat Villanassery Joseph
- Author: Shimat V. Joseph
Lygus bug, Lygus hesperus feeding could cause economic damage to celery. Like any other true bug, lygus bug has a piercing and sucking mouth part which appears as a snout-like structure or beak on the head. Within the beak, four stylets are housed which come out while the bug feeds on the plant. In the process, stylets puncture the cells and leave a feeding sheath within the plant (Figure 1a and b). As time progresses, these injured tissues, depending on the severity, turn into sunken or elongated lesions or callus on the stem making the celery unmarketable (Figure 2).
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.
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