- Author: Shimat Villanassery Joseph
Bagrada bug, Bagrada hilaris (Fig. 1) continues to be a major pest of brassica crops in the Salinas Valley and Hollister causing severe crop losses for both organic and conventional growers alike. Organic growers are struggling because there are very limited options at disposal to suppress the bagrada bug populations in the field. Conventional growers on the other hand are relying heavily on pyrethroid and neonicotinoid insecticides and are going with more number of applications than normal during early stages pf crop development (Cotyledon to four true leaves stage). This tactic (multiple applications) benefit the young seedlings as insecticide residues protect the plants from bagrada bug feeding especially, on the growing point or apical meristematic tissue. Feeding injury to meristematic tissue would cause “blind” head (no head) and multiple shoots on heading brassica crops such as broccoli, cauliflower or cabbage. With couple of insecticide applications at early stages of brassica crop, conventional growers are facing 5-30% loss from bagrada bug feeding injury. Some growers finding noticeably high mortality of cotyledons forcing them to skip thinning operation to maintain a decent crop stand.
Bagrada bug is taking a huge toll on leafy brassica crops such as Chinese cabbage (Pak Choi or Bak Choi), Arugula, Mizuna, Totsoi and Kale. These crops become unmarketable from direct feeding injury on the leaves (Fig. 2). These crops are like “magnets” for bagrada bugs. Bagrada bugs can precisely detect the seeds planted in the soil and most of the seedlings emerge with bagrada bug feeding injury. Sometimes, severe feeding at young stages cause plants die upon emergence (Fig. 3).
Two field trials were conducted in Hollister seeking organic insecticide options for bagrada bug management. The insecticide products chosen were Surround (Kaolin clay), Pyganic, Aza-direct, Entrust and M-pede. Surfact 50 was added when the Pyganic and Aza-direct were used alone. These organically approved insecticides were combined with other insecticides based on certain assumptions. For example, when insecticide Surround is sprayed, it forms a thin particle film on the leaf surface without affecting light transmission or photosynthesis. As bagrada bugs crawl on the Surround treated surface, the particles could stick to their body possibly cause irritation and force them to crawl off from the treated surface. This phenomenon if occurs, it could reduce the incidence of bagrada bug feeding injury. Moreover, it is possible that combining insecticides such as Pyganic and Aza-direct with Surround may increase insecticide exposure as bagrada bugs groom to remove the clay particles stuck on their body using their legs or wings.
The field where the trials were conducted had enormous bagrada bug pressure. Bagrada bugs were everywhere that one would easily kill “thousands of bugs” just by walking over the beds. All stages of bagrada bug were present in the field at the time of insecticide applications. The applications were targeted to protect the plants from feeding injury and not particularly to kill the bugs. The first trial was conducted in Mizuna field and the second trial was conducted in Arugula field. In both the trials, the products were applied four times at three-day interval until harvest between 7 AM and 9 AM. The water volume used was 40 gal per acre. The products were applied using the pneumatic sprayer or back pack sprayer. The details of the products, active ingredients and the rates used for the trials are shown in the Tables 1 and 2. The design of experiments was Completely Randomized Block Design with four replications (Fig. 4). Plant samples were collected twice a week and were evaluated for bagrada bug feeding injury on the true leaves (Fig. 5).
In trial 1, the bagrada bug feeding injury was numerically lower on Mizuna plants that received higher rate of Surround (alone) and Surround combined with Pyganic or Aza-direct than on untreated plants (Fig. 6). When the percentage change in bagrada bug injury on true leaves was calculated (taller the histogram, better the product performance), the plants treated with higher rate of Surround, and Surround combined with Pyganic or Aza-direct had greater reduction of bagrada bug feeding than untreated plants (Fig. 7). In trial 2, none of the treatments showed any indication of suppression when compared with untreated plants (Fig. 8).
Basically, these studies did not provide definite answers to the questions posed or problem but provided some trends. It appears that combining Pyganic or Aza-direct with Surround may have some value rather than applying alone. The Surround rate 20 lb per 40 gal of water is maximum rate for this product. Because Surround could clog the spray tanks, it requires rigorous agitation before application. Also, because Surround easily comes off from the leaf surface with sprinkler irrigation, reapplications are warranted if irrigated at closer intervals especially during the early stages of the crop. The rate of M-pede used in the study was 2% of the water volume. Typically, 2% of M-pede is considered as a high rate and increasing the rate (> 2%) may cause phytotoxicity (burning of leaves).
Then, can we manage bagrada bug?
Few thoughts:
- Perhaps, we should approach this problem differently. Bagrada bug is a landscape scale pest that they could reproduce and build-up to huge populations if the food is available in plenty, and warm and dry conditions persist. So far, we learned that their population build-up starting late July to December in the Salinas Valley and Hollister. The warmer conditions favor rapid reproduction and several overlapping generations of bagrada bug would develop in short period.
- We observed that their population pressure vary across landscapes and is a serious problem where the control options are limited. For example, bagrada bug problem is less severe when the management is aggressive such as conventional fields where growers have effective products that could suppress or knock down their populations at least in the crops grown. Organic growers on the other hand have limited options to fight bagrada bug and its population rapidly grows into uncontrollable size.
- We also noticed that initially these bugs invade the plants in the edge of the field from the surrounding fields or risk zones (e.g. ditches).
- These facts suggest that this is a landscape level problem rather than a field level problem. Bagrada bug management approach probably should include the management of various kinds of hosts that function as reservoir (e.g. brassica weeds) and aid to sustain their populations (brassica crops).
- Cultural management: Avoid planting brassica crops back-to-back pattern or staggered pattern. This would provide opportunity for bagrada bug to utilize the continuous supply of food to reach uncontrollable population size in short period of time. If somehow, the growers could disrupt the ecology of bagrada bug by not growing brassica crops in succession for a period instead rotate with non-brassica hosts, their population might crash and reach to a controllable levels.
- Weed management: Aggressive weed management especially brassicaceous weeds along with tight cultural management would disrupt the food supply and prevent escalation of population size.
- Bagrada bugs have demonstrated the ability to survive on non-brassica hosts especially solanaceous crops such as tomato, potato or pepper but would rarely reach to the levels we are seeing in brassica fields.
For further reading on bagrada bug please click on the following links (UC IPM pest note or blog articles).
http://www.ipm.ucdavis.edu/pestalert/pabagradabug.html
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=14915
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11632
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11591
Please contact me (Shimat Joseph) by email at svjoseph@ucanr.edu or phone at 831-229-8985 if you have any questions or comments.
- Author: Shimat Villanassery Joseph
Bagrada bug (Bagrada hilaris) (Figure 1), an invasive stink bug species native to old world countries of southern Africa, Middle East and Asia, was first detected in North America from Los Angeles Co, California in 2008, and is now established in brassica crop production regions of central coast of California.
Bagrada bug prefers cruciferous hosts (Family: Brassicaceae) including broccoli, cauliflower, cabbage, kale, arugula, or collards. Also, bagrada bug could survive on cruciferous weeds such wild radish, London rocket, short pod mustard, and shepherd's purse, as well as the insectary plant, sweet alyssum. Mustard weed species are very common in ditches, roadsides, and along the edges of agricultural fields in the central coast of California. Mustard cover crops such as white mustard and Indian mustard in particular, could harbor bagrada bug populations, which are not often monitored for insect pests.
Damage to brassica crops varies but can be severe. Severe economic loss has been reported when injury occurred during early developmental stages of the crop such as cotyledon or < 4 leaves stages. Injury on leaves appears initially as small puncture marks, which turn into white patches as leaves expand. In broccoli and cauliflower, the economic injury occurs when the bug feeding kills the apical meristematic tissue of young seedling, which later results in “multiple heads” or sometimes “blind head” (without a head). Severe feeding also depletes the nutrient reserves of the plant leading to desiccation or wilting. Other leafy brassica crops such as mizuna mustard or arugula are especially at risk from direct feeding damage of bagrada bug.
At this time, no baseline information on bagrada bug abundance, seasonal activity, or generations has been established in the coastal brassica crop production regions in California. Limited information exists to determine threshold based pest management decisions for bagrada bug. Monitoringfor bagrada bug during mid-day hours might increase the probability of finding them as the bugs typically hide and stay in the cracks and crevices or on the underside of leaves when the temperature is cooler. Strong attraction to specific color could be utilized when developing selective traps for monitoring bagrada bug in the field. Yellow traps are most commonly used for monitoring true bugs such as false chinch bugs, plant bugs, psyllids or stinkbugs. Yellow pyramid traps were used to monitor brown and dusky stink bugs.
This study was conducted to determine the influence of trap color on catches of bagrada bug. In fall 2013, an organically-managed broccoli field in San Ardo, CA was chosen for the study. Planting sweet alyssum is a common practice among organic growers in the Salinas Valley to harbor beneficial insects such as syrphid flies (hover flies) and lady beetles within the cole crop field. Strips of sweet alyssum were planted within the broccoli field. Cross-vane traps were constructed using corrugated plastic sheets and were painted with white, yellow, red, purple, or black paint (Figure 2). All the trap-base containers used in this study were light green colored. Traps were placed within the sweet alyssum plants (Figure 3).Bug captures were recorded for up to 5 weeks.
In total, 10,654 bagrada bug were captured and were predominantly adults (95%). Adult bagrada bug captures were influenced by trap color (Figure 4a). Black traps captured almost twice the number of adult bagrada bug than purple traps; however, adult catches were similar among purple, white or red traps. Catches of adults were higher in purple than in yellow traps. Similarly, the numbers of bagrada bug nymphs collected among various colored-traps were higher in black traps than other colored traps (Figure 4b). Future research will investigate the potential use of color preference with plant host odor to develop traps for field monitoring of bagrada bug
For those of you, who are interested to read more on it, please find the published article after clicking the link (below) and feel free to contact me (Shimat Joseph) at svjoseph@ucanr.edu or 831 759 7359.
http://cemonterey.ucanr.edu/files/195965.pdf
- Author: Tunyalee Martin
UC IPM’s new Pest Alert helps you identify Bagrada bug, an invasive stink bug spreading through western Arizona and southern California causing severe crop, nursery, and landscape losses. In agriculture, Bagrada bug is a pest of cole crops and other mustard family plants. In home gardens it feeds on these same vegetables and on ornamental plants such as sweet alyssum and candytuft.
Bagrada bugs use their needlelike mouthparts to pierce and feed on plants and their seeds. Damage includes leaf spotting, wilting, stunting, multiple branches or crowns, and death of the whole plant.
The Pest Alert was produced by UCCE advisors Eric Natwick and Surendra Dara, John Palumbo from the University of Arizona, and the UC IPM team.
Preliminary agricultural management information is also available.
- Author: Shimat Villanassery Joseph
- Author: Richard Smith
Bagrada bug, Bagrada hilaris is now well established in the southern region of the Salinas Valley. This invasive stink bug, if left unmanaged, could become a serious pest of brassica crops. We studied their occurrence on cover crop, a mustard cover crop blend, broccoli and surrounding weed species, and would like to report few observations.
1. Cover crop, mustard
We observed significant populations of bagrada bug on 4-5 week-old mustard cover crop blend (Brassica juncea and Sinapis alba) in San Ardo. Interestingly, the adjacent field was also cover cropped with mustard but was disced few weeks ago. It is likely that the previous adjacent mustard crop might have had a bagrada bugs infestation and they moved to new planting when it was disced. When we walked into mustard stand from the disced field, we noticed that number of bagrada bug numbers declined from the field edge to the interior of the field. To understand better, a border zone (edge of the field), interior zone (90 feet into the field), and intermediate zone (between border and interior zones) were designated. Within each zone, six spots (~ 5.6 feet) were randomly selected and number of bagrada bugs was quantified after spending two minutes per spot. Similarly, two weed species and one native shrub surrounding the mustard field were randomly selected and number of bagrada bugs on them was counted after spending about one minute per plant.
Bagrada bugs tend to be more abundant on the edge of field than interior zones of the field (Fig. 1). It seems that bugs settled on the border plants of the field rather aggressively moving into the field. All life stages were detected. Most of the adults were in the mating position (connected by the rear ends) but very mobile. The adults tend to hide into the soil or under the leaves when we approached the infested plants.
Among the weed species investigated, bagrada bugs were only found on short pod mustard (Fig. 2 and 3). Other weed species investigated were shortpod mustard (Hirschfeldia incana), common purslane (Portulaca oleracea), lambsquarter (Chenopodium album), and the native shrub coyote bush (Baccharis pilularis). It is interesting to note that shortpod mustard plants were senescing, yet we found bagrada bugs on them.
2. Broccoli
The broccoli field was located in San Ardo adjacent to the Salinas River. The riparian plant community along the river contained stands of perennial pepperweed (Lepidium latifolium) as well as other species. Bagrada bug infestation was severe on pepperweed (Figs. 4a, and b).
Bagrada bug feeding injury symptom on broccoli plants was clearly visible on plants along the edge of the field. Feeding injury symptoms on broccoli include leaf distortion, chlorotic patches along the leaf margin and stunting (Fig. 5). Again, feeding symptoms drastically declined and/or plant vigor improved as we walked few steps (~ 10 feet) into the broccoli field from river side. Both nymphs and adults of bagrada bug were active along the edge of the field.
These preliminary observations indicate that some plants in the mustard family are highly attractive to bagrada bug. Shortpod mustard is a common summer-growing species that is commonly found on roadsides, in vineyards and in rangeland. Perennial pepperweed is an invasive plant that is commonly found in the riparian strip along the Salinas River. Both plants provide sufficient food resources for bagrada bug to successfully breed. After the onset of the winter rains, other mustard family weed species such as field mustard (Brassica rapa), black mustard (B. nigra), London rocket (Sisymbrium irio) and wild radish (Raphanus sativus) will begin their growth cycle. These plants are very common along roadsides and in ditches and may also provide over wintering habitat for bagrada bug.
- Author: Shimat Villanassery Joseph
Bagrada bug, Bagrada hilaris is an invasive stink bug and is moving North from the Southern Counties of California, rapidly than anticipated. In the past weeks, I have detected huge populations of these stink bugs on Indian mustard (cover crop), broccoli raab and kale in the King City and San Ardo areas. It is more likely that low populations exist in the other parts of the Salinas Valley.
It is well known that bagrada bug prefers cruciferous hosts (Family: Brassicaceae) including broccoli, cauliflower, cabbage, kale, arugula, collards, and Indian mustard. Major crops, lettuce and spinach are NOT a suitable host for bagrada bug. Also, these bugs can survive on cruciferous weeds such as mustard species (Brassica sp), wild radish, London rocket, short pod mustard and shepherd’s purse, as well as the insectary crop sweet asylum or sunflower. Mustard weeds species are very common in the Salinas Valley along ditches, roadsides and even along the edges of agricultural fields. Mustard cover crops such as white mustard (Sinapsis alba) and Indian mustard (Brassica juncea) in particular, could harbor bagrada bug populations which are not often monitored for pests.
Bagrada bug adult could be easily confused with harlequin bug. Adult of harlequin bug is orange with black and white marks, whereas bagrada bug adult is black with orange and white marks; and adult harlequin bug is about 3 times larger than bagrada bug. Eggs of harlequin bug are white with horizontal, black strips, whereas bagrada bug has no strips but has a “dirty” white appearance.
Damage to brassica crops is varied but could be severe. Severe economic loss has been reported when injury occurred during early developmental stages of the crop such as coldyledon or < 4 leaves stages. Injury on leaves appears initially as small puncher marks, which turn into white patches as leaves expand. In broccoli and cauliflower, the economic injury occurs when the bug feeding kills the apical meristematic tissue of young seedling, which later result in “multiple heads” or sometimes “blind heads” (without a head). Severe feeding also depletes the nutrient reserves of the plant leading to desiccation or wilting.
At this time, monitoring for bugs is the key. Monitoring for bagrada bug during mid-day hours might increase the probability of finding them as the bugs typically hide and stay in the cracks and crevices or on the underside of leaves when the temperature is on the cooler side. Cruciferous weeds in the drains, river bottoms, edges of the field or near residential area increase the risk of establishment. Do not forget to check the brassica cover crops for bugs as well.
Based on the insecticide efficacy studies conducted in University of Arizona, bifenthrin and methomyl were most effective in reducing bagrada bug infestation and injury on broccoli. For organic growers, none of the products were efficacious but pyrethrin and azidirachtin are suggested.
If you detect bagrada bug in Monterey, Santa Cruz and San Benito Counties, please do not hesitate to contact me (Shimat Joseph) at svjoseph@ucdavis.edu or (831) 759-7359.
Further reading:
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9023
Video (by Surendra Dara): http://youtu.be/gSj3AZoJIRM
