Description of the Pest
Western tarnished plant bug, which is commonly referred to as lygus bug, is a serious pest in Central Coast and Oxnard strawberry-growing areas where strawberries are typically grown past May and through the summer months, but they rarely become a pest in Southern California and the Central Valley where fresh market berry harvest is generally complete by the end of June. However, lygus bug is an occasional problem in these areas on second-year plantings and berries held through the summer.
Adults are about 0.25 inch (6 mm) long, oval, and rather flattened. They are greenish or brownish and have reddish-brown markings on their wings. In the center of their back is a distinct, but small, yellow or pale green triangle that helps distinguish them from other insects. The immature forms are pale green and look similar to an aphid. They can be distinguished from aphids by their more rapid movements.
Nymphs of the third and later instars are green and characterized by five black dots on the back – two on the segment immediately behind the head, two on the next segment, and one in the middle of the abdomen. A similar nonpest species that may be confused with lygus bug, Calocoris, frequently is found when monitoring weed and legume crop hosts for lygus bug. Calocoris has two prominent black dots on the back, just behind the head, and dark wing tips. Lygus bug adults have no black dots on the back. Both nymphs and adults of Calocoris are longer and narrower than lygus bug.
False chinch bug (Nysius spp.), an occasional minor strawberry pest that migrates into strawberry fields from weedy hosts, can also be confused with lygus bug. However, false chinch bug adults are smaller [0.1–0.2 inch (2.5-5 mm)], and grayish brown with a slender body. They have silvery gray wings that lack a cuneus (small triangle on the apical area of the forewings, typical of lygus bugs) and have four to five parallel veins on the membranous part, while lygus bug has closed cells (veins that loop and don't go to the end of the wing) on the membranous part of the wing. Nymphs are brownish gray with orange or reddish markings, and the front of the head (when viewed from above) is more triangular and pointed than lygus bug. There are no management guidelines for this pest except for good weed management.
Damage
Lygus bugs are one of the causes of irregularly shaped, cat-faced strawberries; another cause may be poor pollination, which results in small undeveloped seeds. Lygus bugs damage fruit by puncturing individual seeds; this, in turn, stops development of the berry in the area surrounding the feeding site. Straw-colored seeds that are large and hollow are a good indication of lygus bug damage. Lygus bug damage is more of a problem in strawberry-growing areas where continuous fruit production occurs.
Management
To successfully manage lygus bug
- Control weed hosts in winter.
- Monitor for the appearance of lygus bug nymphs on weed hosts and adults on strawberries in spring.
- Time insecticide sprays to control lygus bug nymphs before they cause significant damage. Sprays must be timed to kill the earliest instars of nymphs because registered insecticides are not very effective on adults.
It is important to limit the number of treatments for lygus bug, because most of the insecticides that are effective against lygus bug disrupt natural enemies of spider mites. Control actions for lygus bug in strawberries generally are needed only in growing areas of the Central Coast and Oxnard, and the management activities described below apply to these areas. Once flower development begins in Central Valley strawberries, you can watch for the appearance of lygus bug adults during other routine monitoring activities.
Biological Control
Anaphes iole is a naturally occurring parasitic wasp. It can be found in strawberry fields and surrounding lygus bug habitat, but because thresholds for this pest are very low, economically acceptable results are not achieved. A nymphal parasitoid, Peristenus relictus, is also found in some strawberry production areas.
Naturally occurring predators that feed on the nymphal stages of lygus bug include bigeyed bugs (Geocoris spp.), damsel bugs (Nabis spp.), minute pirate bugs (Orius tristicolor), and several species of spiders.
Cultural Control
Controlling weeds along roadways, ditches, and field borders near strawberry fields to help prevent spring buildup of lygus bug numbers is fundamental to lygus bug management in strawberries. Overwintered lygus bugs lay eggs in weeds in January that hatch in March. Carry out weed control measures in March and early April while lygus bugs are still nymphs. Once adults are present on weeds, they will migrate into strawberries when the weeds dry or are removed. Spraying adults or weeds to prevent movement is not very effective. To avoid adult migration in spring, mow or disc under cover crops, especially legumes, before they flower and while lygus bugs are still in the nymphal stages.
One cultural approach is to grow flowering plants in or adjacent to fields to attract lygus bug adults, but this approach requires careful monitoring and management to prevent an even greater problem from occurring. Adult lygus bug will lay eggs on the flowering plants, and nymphs will emerge from late March through April. The nymphs must be controlled at this time before they become adults and move to the strawberry plantation. Destroying the plants by discing or mowing is the most effective method of removing the infested, flowering plants. It is also possible to apply insecticides registered for use on strawberries for control of nymphs; however, none of the registered insecticides will provide complete control of the nymphs. If the plants are allowed to flower later into the season, carefully monitor the plants for the presence of lygus bug nymphs and take appropriate actions to prevent their movement into strawberries. This approach generally targets local populations of lygus bug and does not adequately impact longer-range lygus bug migration from drying foothill weeds.
Some growers have used suction devices (bug-vacs) to control lygus bug for many years. Research has shown that an efficient bug-vac can reduce adult numbers by 75% and nymphs 9 to 50%, but efficiency can vary considerably depending on the machine. Consistent vacuuming 1 to 2 times weekly can manage low to moderate numbers of lygus bug. If lygus bug numbers are moderate to high, use of vacuum machines alone will not reduce damage to the acceptable level. In the absence of effective fungicide programs, vacuums may increase problems with powdery mildew and gray mold by spreading the pathogens that cause these diseases. Additionally, they may remove a large portion of the general predator population.
Organically Acceptable Methods
Use biological and cultural controls and insecticidal soap sprays on organically certified strawberries.
Monitoring and Treatment Decisions
In February, monitor for the first appearance of lygus bug nymphs on plant hosts around the field to determine when these plants should be destroyed and to establish the first biofix for the degree-day model. Important plants and the key times to monitor them are outlined in the following table:
| Important Plant Hosts of Lygus Bugs | ||||
|---|---|---|---|---|
| Common name (scientific name) | Time of Year | |||
| Feb. | Mar. | Apr. | May | |
| California burclover (Medicago polymorpha) | l | l | ||
| California poppy (Eschscholzia spp.) | l | l | ||
| chickweed (Stellaria media) | l | L | ||
| common groundsel (Senecio vulgaris) | L | L | ||
| curly dock (Rumex crispus) | L | |||
| filaree (Erodium spp.) | l | l | l | l |
| lambsquarters (Chenopodium album) | l | |||
| little mallow (cheeseweed) (Malva parviflora) | L | |||
| lupines (Lupinus spp.) | L | L | ||
| milk thistle (Silybum marianum) | l | L | ||
| mustards (Brassica spp.) | l | l | L | L |
| pineapple-weed (Chamomilla suaveolens) | L | |||
| redmaids (Calandrinia ciliata) | L | |||
| shepherd's purse (Capsella bursa-pastoris) | L | |||
| wild radish (Raphanus raphanistrum) | L | L | L | L |
| l = lygus bug present | L = lygus bug present in higher numbers |
Begin monitoring the strawberry plants in mid-April to detect when adults first appear in the field. Establishing when adults first enter the field also serves as the biofix for part of the degree-day model described later. Continue monitoring the field regularly after this time to establish whether or not lygus bug densities are economically important and exceed the treatment threshold. Record your results (example survey form .
Threshold levels for lygus bugs 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 every 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.
- Continue weekly monitoring as long as fruit are being harvested for fresh market or freezer pack.
Currently registered insecticides are most effective against young first- and second-instar nymphs. Insecticides applied to later nymphal stages and adults are not very effective. Adult lygus that are not killed by sprays may migrate from the field to nearby weeds when pesticides are applied but can return.
Calculating degree-days (DD) is an effective way of determining the time of egg hatch, which occurs just before the 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 bug using a lower threshold of 54°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 the overwintered adults; it usually occurs in April. Not all fields will have damaging levels of lygus at this time.
- If treatment thresholds are exceeded, apply the first spray 252 degree-days 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 degree-days (late June–early July) from the date the first nymphs are found in weeds (typically in March) and targets nymphs from the second migration of lygus bugs into strawberry fields.
- A third treatment period corresponds to the emergence of nymphs that come from both adults that have established in the field and those that have migrated to strawberries during the summer; it is about 799 degree-days (early August) after the first spray.
To learn more about how to use degree-days to time insecticide applications, see Using Degree-Days to Time Insecticide Applications in Fruit and Nut Orchards. For assistance in calculating degree-days for lygus bug in your location, see Degree-days: Lygus Bug in Strawberries.
| Common name | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used. | ||||
| A. | FENPROPATHRIN* | |||
| (Danitol 2.4 EC) | 10.67 fl oz | 24 | 2 | |
| MODE-OF-ACTION GROUP NUMBER1: 3A | ||||
| COMMENTS: Synthetic pyrethroids are the most effective pesticides currently registered for lygus control in strawberries. However, very high levels of resistance to this pesticide have been identified in some growing areas. Therefore, although this pesticide can suppress spider mites, it should be used primarily to control lygus. Use of this pesticide is limited to two applications per year, but to reduce the pressure for resistance development, make no more than two applications of all pyrethroids to the crop each year. To delay resistance and to avoid the severe spider mite outbreaks that result from application of pyrethroids, it is preferable to target the summer generation of lygus in areas where fruit is produced throughout the summer. See label for harvest restrictions. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| B. | BIFENTHRIN* | |||
| (Brigade WSB) | Label rates | 12 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: 3A | ||||
| COMMENTS: Synthetic pyrethroids are the most effective pesticides currently registered for lygus control in strawberries. However, very high levels of resistance to this pesticide have been identified in some growing areas. Therefore, although this pesticide can suppress spider mites, it should be used primarily to control lygus. Use of this pesticide is limited to two applications per year, but to reduce the pressure for resistance development, make no more than two applications of all pyrethroids to the crop each year. To delay resistance and to avoid the severe spider mite outbreaks that result from application of pyrethroids, it is preferable to target the summer generation of lygus in areas where fruit is produced throughout the summer. See label for harvest restrictions. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| C. | FLONICAMID | |||
| (Beleaf 50SG) | 2.8 oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: 9C | ||||
| COMMENTS: Apply when lygus bug first appear, before high numbers appear. For resistance management, do not apply more than two sequential applications without first rotating to an insecticide with a different mode of action. | ||||
| D. | FLUPYRADIFURONE | |||
| (Sivanto 200SL) | 14 fl oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: 4D | ||||
| E. | NOVALURON | |||
| (Rimon 0.83EC) | 12 fl oz | 12 | 1 | |
| MODE-OF-ACTION GROUP NUMBER1: 15 | ||||
| COMMENTS: Apply when adults are first observed in the field. Target initial application prior to egg hatch. | ||||
| F. | NALED | |||
| (Dibrom 8E) | 1 pt | 48 | 1 | |
| MODE-OF-ACTION GROUP NUMBER1: 1B | ||||
| . . . PLUS . . . | ||||
| THIAMETHOXAM | ||||
| (Actara) | 4 oz | 12 | 3 | |
| MODE-OF-ACTION GROUP NUMBER1: 4A | ||||
| COMMENTS: Do not apply Dibrom when temperatures over 90°F. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same active ingredient. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. Review and follow the California neonicotinoid regulations effective January 1, 2024. Permissible application rates of this insecticide may be lower than label rates if applying more than one neonicotinoid active ingredient or using more than one application method in the same season. |
||||
| G. | ACETAMIPRID | |||
| (Assail 70WP) | 1.7–3 oz | 12 | 1 | |
| MODE-OF-ACTION GROUP NUMBER1: 4A | ||||
| COMMENTS: Gives better control of nymphs than adults. Can be tank mixed with fenpropathrin (Danitol) or bifenthrin (Brigade); however, to delay the development of insecticide resistance by lygus, aphids, and whiteflies, (especially where imidacloprid [Admire] is used), this tank mix should be reserved for situations where acetamiprid is not effective by itself. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum active ingredient on any label when tank mixing products that contain the same active ingredient. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| H. | THIAMETHOXAM | |||
| (Actara) | 4 oz | 12 | 3 | |
| MODE-OF-ACTION GROUP NUMBER1: 4A | ||||
| COMMENTS: Gives better control of nymphs than adults. Can be tank mixed with fenpropathrin (Danitol) or bifenthrin (Brigade); however, to delay the development of insecticide resistance by lygus, aphids, and whiteflies, (especially where imidacloprid [Admire] is used), this tank mix should be reserved for situations where thiamethoxam is not effective by itself. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same active ingredient. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. Review and follow the California neonicotinoid regulations effective January 1, 2024. Permissible application rates of this insecticide may be lower than label rates if applying more than one neonicotinoid active ingredient or using more than one application method in the same season. |
||||
| I. | NALED | |||
| (Dibrom 8EC) | 1 pt | 48 | 1 | |
| MODE-OF-ACTION GROUP NUMBER1: 1B | ||||
| COMMENTS: Do not use when temperature exceeds 90°F. Because naled is an organophosphate like malathion, it is not effective in some growing areas because of resistance. Do not apply more than 5 pt/acre per season. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| J. | MALATHION | |||
| (Malathion 8E) | 1.5–2 pt | 12 | 3 | |
| (Malathion 5EC) | 1.5–3 pt | 12 | 3 | |
| MODE-OF-ACTION GROUP NUMBER1: 1B | ||||
| COMMENTS: Only effective against first three nymphal instars. Very high levels of resistance to this pesticide have been identified in some growing areas. Check the California Strawberry Commission pink sheets for annual information on this. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| ORGANIC OPTIONS (Efficacy research may be lacking on these products) | ||||
| A. | AZADIRACHTIN# | |||
| (Neemix 4.5, AzaGuard) | Label rates | 4 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: un | ||||
| COMMENTS: An insect growth regulator. | ||||
| B. | ISARIA FUMOSOROSEA # | |||
| (PFR-97 20% WDG) | Label rates | 4 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: — | ||||
| C. | BEAUVERIA BASSIANA# | |||
| (BotaniGard ES) | Label rates | 4 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: — | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest. |
| * | Permit required from county agricultural commissioner for purchase or use. |
| # | Acceptable for use on organically grown produce. |
| 1 | Rotate insecticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers for insecticides and miticides (un=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). |