Field Scouting Guide: Bagrada Bug
Invasive bragada bugs (Bagrada hilaris, aka painted bug) can cause a great deal of damage to brassica crops. For this edition of American Vegetable Grower‘s Field Scouting Guide series, we’ve reached out to pathologists to learn how to spot and treat B. hilaris.
This month, our contributors are John C. Palumbo, University of Arizona, and Ian M. Grettenberger, University of California, Davis.
- Scientific name: Bagrada hilaris
- Common name: Bagrada bug, also known as the painted bug
- Geographical Range: Presently known to cause issues in Arizona, California, New Mexico, Texas, and Hawaii.
- Crops affected: All brassica crops (e.g., broccoli, cabbage, cauliflower, kale). It has also been reported to damage a number of crops when populations are extremely high and its preferred hosts are not available.
Grettenberger: When populations are reasonably high, bagrada bugs can cause substantial damage. In some cases in Arizona, they have caused 60% yield loss to cole crops like broccoli. In some salad fields in the Salinas Valley, the damage was so great that the product would not have been marketable, and fields were simply disked in.
Bagrada bug can cause substantial damage to seedling stage crops. They can kill or stunt these plants. For heading crops like broccoli or cauliflower, bagrada bug can damage the apical meristem, causing the plant to produce multiple small and unmarketable heads or to not produce a head at all. All stages of bagrada bug can damage plants, although adults are typically the most problematic because they are the stage most likely to show up quickly in fields as they are dispersing and to damage plants.
Palumbo: The bagrada bug is a plant-feeding stink bug recently introduced into the U.S. The pest first invaded the desert Southwest growing regions of Arizona and Southern California in 2009, and by 2012 had quickly spread to all the coastal growing regions in California.
Bagrada populations have been very light in the past three years, but they’re still a threat to cole crop production in these regions. In 2015, the pest was found damaging brassica crops in Hawaii and is still considered a major problem.
Adults are quite mobile and can quickly invade newly established plantings. If adults are not controlled in the field, developing nymphs can cause significant damage as well.
Palumbo: Bagrada bugs look very similar to harlequin bugs, a common pest of brassica crops in some areas. They are both black with orange and white markings, but the Harlequin bugs are about three to four times larger than bagrada bugs.
They both cause similar damage to plants. Symptoms of feeding damage to cotyledons and young leaves are likely the most important things scouts should look for. Our action thresholds are based on damage rather than bug presence.
Palumbo: Preventing the adults from feeding on plant terminals and small cotyledons is critical to establishing and maintaining a quality stand and often requires timely control. A nominal action threshold has been established for bagrada bugs that triggers insecticide treatments when the number of plants with fresh-feeding damage exceeds 5%.
Once stands have become established, foliar insecticide sprays can effectively prevent feeding damage to plant foliage and terminal growth; length of control will likely depend on rates, coverage, spray frequency, tank-mix combinations, and duration of adult migration from outside the field.
Research has shown that once heading brassicas plants (i.e., cauliflower, broccoli, cabbage) reach the six-leaf stage, they are not be susceptible to damage to the terminal growing point. However, leafy brassica crops may be susceptible to cosmetic damage to leaves as a result of bagrada feeding for much longer periods.
Palumbo: Control in organic brassica crops can be very difficult. Using transplants can improve stand establishment, but you’ll still need to control adults to prevent terminal damage until plants reach the six-leaf stage. The use of row covers and trap crops has provided inconsistent protection of seedling plants.
Grettenberger: Organic management options are fairly limited, and efficacy has been variable. Management of weedy mustard hosts surrounding fields and quickly cultivating in harvested crops can help prevent population buildup.
Cropping System Considerations
Palumbo: Sanitation around production fields can help reduce bagrada bug abundance. In desert growing areas, grasses and cotton may be considered key sources of Bagrada bug infestations for fall cole crop plantings. In coastal growing regions, weedy brassicas (e.g., shortpod mustard and Indian mustard) are known hosts of bagrada bug populations. Observations suggest that cole crops planted adjacent to or near these crops and weeds may be at a high risk from bagrada bug infestations.
Monitoring and Scouting
Palumbo: When sampling for bagrada bugs, look for fresh-feeding signs on cotyledons and young leaves. Bagrada bugs are a small stink bug with piercing-sucking mouthparts that remove plant sap. You can spot leaf tissue feeding damage by circular or star-shaped chlorotic lesions that later become necrotic. Inspecting plants for adults can be misleading, as adults are generally most active in fields from mid-morning to late afternoon. During warmer times of the day, you’ll find adults on, or adjacent to, plants with recent feeding damage. Sprinkler irrigation appears to repel the adults somewhat, so begin sampling soon after sprinkler irrigation.
In transplanted cole crops, begin scouting for Bagrada bug the next morning following transplanting. Sprinklers can make it difficult to spot the bugs. So only scout before or after irrigating, preferably at night or early morning, until after irrigation. Carefully inspect all the leaves for the presence of fresh-feeding symptoms and adults.
In direct-seeded cole crops, begin scouting immediately upon seedling emergence. Bagrada bugs have been observed feeding on broccoli seedlings just as the cotyledons are appearing. Feeding can cause damaged or desiccated seedlings that appear wilted. On larger seedlings, at the one to two leaf stage or larger, fresh damage often appears on the young leaves.