Bagrada Bug

Bagrada bug adults are 0.2 to 0.3 inch (5–7 mm) long, shield-shaped stink bugs. Adults are black with orange-and-white markings. They resemble harlequin bugs, but are smaller at about one-third to one-fifth the size. The wingless Bagrada bug nymphs develop through five instars. Newly molted nymphs of all ages are orange-red, but the legs, head, and thorax darken to black as nymphs get older. Male bugs are slightly smaller than females. Females lay cream-colored, barrel-shaped eggs in or on the soil surface, as well as on leaves and stems. Eggs turn orange-red as embryos mature inside.

Bagrada bugs feed on a wide variety of different crops, including cotton, legumes, strawberries, melons, potatoes, peppers, tomatoes, and grains (wheat, corn, sudangrass, and millet). They typically move into cole crops from surrounding weeds in late spring to summer, and up to fall in some regions. Specific timing of these infestations can vary between years and between regions.

Bagrada bugs insert their needlelike mouthparts into plant tissues and suck the sap. They can kill germinating seeds, seedlings, or young transplants when they feed on the apical meristem (terminal bud). White, starburst-shaped lesions and stippled areas develop on leaves and stems, which may wilt and die. Such damage on leafy cole crops such as mizuna and other non-cole crop Brassica greens such as arugula can render the crop unmarketable. When bug feeding damage causes meristematic tissues to die, heads do not form (also known as blind terminals). Other damage from Bagrada bug feeding may include forked buds, multiple heads, or leaves with brown or white dead blotches. It can also cause stunting on broccoli, cabbage, and cauliflower and render them unmarketable.

With high numbers of Bagrada bugs, young plants and germinating seeds that are left unprotected can be significantly damaged within a day. Even with multiple insecticide applications on a 3- to 5- day schedule, migrating adult bugs can cause up to 20 or 30% damage to emerging seedlings and young transplants, depending on the severity of the infestation. Damage can be severe in both organic and conventional crops.

Because adults and nymphs move from weeds into direct-seeded and transplanted cole crops, damage from the Bagrada bug may be initially visible in the perimeter of the field. However, the infestation can rapidly progress throughout the field, as the adults are highly mobile. Fields that are near grassy areas, weedy areas (especially with cruciferous weeds), lush desert habitat, and residential areas with preferred hosts have a higher risk of being damaged by Bagrada bug.

Rely on monitoring, cultural controls, and insecticide applications to manage Bagrada bug. Frequently monitor susceptible crops and vegetation (including weeds) around fields or weak or stressed plants in the field. Monitor for Bagrada bug in the midday hours if possible, as these bugs tend to hide in cracks or crevices, or on the undersides of leaves, when temperatures are cooler. If using cross-vane traps, use black traps, as these attract the most adult bugs. 

No natural enemies are known to effectively reduce Bagrada bug numbers in California or Arizona. Rove beetles and predatory ants may feed on Bagrada bug eggs in the soil, but these insects are not likely to keep Bagrada bug below damaging numbers.

Depending on your region, consider using crop rotation to manage Bagrada bug. In coastal areas, rotate to a non-Brassica crop, preferably a nonhost such as lettuce or spinach. In the southern desert, crop rotation for Bagrada bug is not usually necessary.

If using crop rotation, keep in mind that Bagrada bug can survive on many other crops, especially solanaceous crops like tomato, pepper and potato, though they do not reach the same numbers in those crops as they do in cole crops and other Brassica crops. Management with crop rotation may differ between regions. For example, rotating to pepper or tomato after a Bagrada bug infestation in cole crops does not pose a problem in the southern desert but may encourage Bagrada bug survival in other regions.

The following cultural controls can also be used to prevent yield loss from Bagrada bug:

• Remove weed hosts, especially perennial pepperweed, shortpod mustard, wild radish, and volunteer weeds in the Brassicaceae family.
• Cultivate to destroy bugs and their eggs in the soil.
• If using transplants from an infested area, ask the producer about their Bagrada bug control program.
• Examine transplants in the trays and ensure they are free of Bagrada bugs and damage before planting.
• Monitor transplants regularly after planting.

Exclusion or row covers may prevent damage, but research on their effectiveness has not been done. Make sure the row covers are deployed immediately after direct seeding or transplanting, especially for cauliflower and broccoli. Overhead irrigation does not reduce Bagrada bug numbers.

Use cultural control in an organically certified crop, as well as organic insecticides.

Combinations of organic insecticides are more effective compared to standalone pesticide applications (see the treatment table for more information). Organic insecticides such as insecticidal soap and azadirachtin may be useful in combination with other organic insecticides but are not effective in standalone applications. Entomopathogenic fungi products such as those containing Beauveria bassiana are also available for Bagrada bug control and are most effective when used in combination with other insecticides.

Though sweet alyssum is sometimes planted along the edges of organic cole crop fields and later vacuumed to remove Bagrada bugs, this practice often leads to higher Bagrada bug numbers and greater damage, and does not provide reliable control.

Neonicotinoid-treated seeds are the most effective control method of Bagrada bug in areas that are regularly infested with Bagrada bug. If transplanting in areas that harbor high numbers of Bagrada bug, apply an insecticide before or immediately after transplanting to protect transplants from migrating Bagrada bug adults. In the low desert, it is often necessary to apply a systemic insecticide to the soil before transplanting, or to use a foliar application of a pyrethroid after transplanting to prevent excess damage from Bagrada bug.

Look for Bagrada bug the morning following transplanting, when sprinklers are off. For direct-seeded cole crops, begin looking for bugs as soon as one day after planting. If you find Bagrada bugs, apply an insecticide to the transplants or apply insecticide when direct-seeded cole crops emerge. Continue monitoring two to three times per week until the 5- to 6-leaf stage. After this time, most plants tolerate Bagrada bug feeding without significant injury or yield loss.

Use the following monitoring methods:

1. Monitor during the warmer times of the day (near or above 80°F).
2. Look for bugs on the undersides of cotyledons and leaves.
3. Look for damage on cotyledons and young leaves.
4. Look for weaker or drooping plants in the field.
5. Keep your eyes on the soil underneath plants, on stems at the soil surface, and in cracks in the soil.
6. Apply an insecticide if there are one or more Bagrada bug adults per 3-foot row of seedlings or transplants.
7. After insecticide application (if necessary), look carefully on the soil for dead bugs; bugs blend in with the soil and play dead when disturbed.

During stand establishment, apply a foliar insecticide in a narrow band (4 inches wide) over the seedlings. Apply over a short period of time at the end of an irrigation run to prevent dilution and avoid pushing the insecticide too deep into the soil.

When stands are established, apply an insecticide when bugs or fresh damage are readily observed. Use foliar sprays, especially those with residual efficacy, such as pyrethroids, methomyl, or neonicotinoids (such as clothianidin or dinotefuran, which also protect against whiteflies) for extended Bagrada bug control.

Duration of control depends on application frequency, coverage, rates, whether tank-mix combinations are used, and the extent to which Bagrada bug continues to migrate into the field. Apply foliar insecticides during afternoon and early evening (only as is consistent with the pesticide label restrictions on times of application), when Bagrada bugs are most active. To help avoid the development of insecticide resistance, rotate applications among different insecticide modes of action.