Impact of Bagrada Bug on Desert Cole Crops in 2010-2011
The Bagrada bug, Bagrada hilaris, has been major problem in desert cole crops the past two fall growing seasons. In 2010, widespread infestations were reported throughout the desert growing area in September and October where stand losses and yield/quality reductions to broccoli, cauliflower, cabbage and other Brassica crops were considered economically significant in some growing areas. In 2011, Bagrada populations did not appear until early October, but certainly caused crop losses and required control with insecticides. In an attempt to document the impact of these outbreaks on desert production, a survey of growers and PCAs from Yuma and Imperial Valley was recently conducted to estimate the severity of Bagrada bug infestations on direct-seeded and transplanted cole crops during 2010. A summary of the survey results can be found at Impact of the Bagrada Bug on Desert Cole Crops: A Survey of PCA/Growers in 2010 and 2011. In general, the results of surveys in 2010 and 2011 showed that more than 93% of direct-seed cole crop acreage (e.g., broccoli) was treated for Bagrada adult infestations with insecticides compared to transplanted cole crops (e.g., cauliflower) where about 86% of the acreage was reported to be treated. Similarly, estimates showed that direct-seeded cole crops sustained greater stand losses and plant injury from Bagrada feeding than transplanted crops. When averaged over both years, estimated stand losses and plant injury caused by Bagrada bug feeding exceeded 10 % in direct-seeded crops. PCAs also provided information on insecticides that provided effective control through both chemigations and foliar sprays. In general, they reported that products that have contact activity (i.e., Pyrethroids, OP/Carbamates) appeared to provide the most effective control against Bagrada adults on both direct-seeded and transplanted cole crops. Overall, the results of the PCA survey are consistent with results obtained in research trials conducted at the Yuma Agricultural Center last year. In addition, access to the 1080 database showed that insecticide usage on cole crops has nearly doubled since Bagrada outbreaks first occurred in the fall of 2010.
The soft-rot bacterium, Erwiniacarotovora subsp. carotovora (syn.= Pectobacteriumcarotovorum subsp. carotovorum), enters through growth cracks or wounds caused by cold temperatures, insects, other disease organisms, or by mechanical means. Under warm, humid conditions, uninjured tissue may become infected through natural openings. Prolonged moisture from rain or irrigation and mild temperatures encourage disease development. Insects, tools, rain, clothing, or affected plant tissue can spread the bacteria. The bacteria survive in soil and plant debris.
Symptoms appear as small, water-soaked areas and enlarge rapidly. Tissue becomes soft and mushy, and within a few days the affected plant part may collapse. An offensive odor usually is present.
Management:
Cultural:
Set out plants in rows to allow good air drainage.
Cultivate carefully to minimize injuring plants.
Control frequency and source of irrigation water.Avoid frequent irrigation during head development. Time irrigation to allow the head to dry rapidly. Avoid stagnant water sources.
Clean and spray storage walls and floors with copper sulfate solution (1 lb/5 gal water). Bactericides such as Clorox, Lysol, and quaternary ammonium products also are effective.
In storage, use a buffering material such as straw or paper to prevent injury to the heads.
Keep storage house humidity between 90% and 95% and the temperature between 32°F and 39°F.
Chemical control
Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry.
Cease at 3 to 6 quarts in 100 gal water. For greenhouse plants only. Preharvest interval is 0 days. 4-hr reentry.
Band-Steam Applicator for Controlling Soilborne Pathogens and Weeds in Lettuce
Steam sterilization of soils is commonly used in plant nurseries and greenhouses for effective control of soilborne pathogens and weed seeds. The technique, however, is highly energy intensive as the entire soil profile is heated. This is too costly and slow to be practical for field scale vegetable production. To reduce energy consumption and cost, use of band-steaming, where steam is applied only in the area where it is needed – in the plant root zone, is proposed. In this method, narrow strips of soil centered on the seed line are treated with steam rather than the whole bed.
Over the course of the last year, we developed a prototype band-steam and co-product applicator that is designed to raise soil temperatures in a band 2” deep by 4” wide to levels sufficient to control soilborne pathogens (140 °F for > 20 minutes) and weed seed (150 °F for > 20 minutes). The device is principally comprised of a 35 BHP steam generator and a co-product applicator mounted on top of a bed shaper (Fig.1). The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper. An exothermic compound can be co-applied via shank injection and/or a banding spray nozzle. The rationale behind co-applying an exothermic compound with steam is that exothermic compounds react and release heat when combined with water, thereby reducing energy requirements and increasing travel speed.
Preliminary testing of the device this spring in Yuma, AZ were very promising. Trial results showed that application of steam alone effectively raised soil temperature in the center of the seed line to levels required for effective pest control (140 °F for more than 20 minutes). Use of the exothermic compound increased soil temperature by about 10 °F. A video of the device in action can be found at the link provided below.
We are currently evaluating the device in field trials with lettuce in Salinas, CA. Target pests in these experiments conducted in collaboration with Steve Fennimore, UC Davis, are soil pathogens which cause Sclerotinia lettuce drop and in-row weeds. Future articles will report the findings of this research.
This fall, we will be replicating these tests in Yuma, AZ and also investigating the effectiveness of band-steam for controlling Fusarium oxysporum f. sp. lactucae which causes Fusarium wilt of lettuce. Heat has been shown to effectively kill Fusarium oxysporum spores and control Fusarium wilt disease. As an example, soil solarization, where clear plastic is placed over crop beds during the summer, raises soil temperatures to 150-155˚F at the soil surface, effectively killing the pathogen and reducing disease incidence by 45-98% (Matheron and Porchas, 2010).
These projects are sponsored by USDA-NIFA, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support.
If you are interested in seeing the machine operate or would like more information, please feel free to contact me.
See the band-steam and co-product applicator in action!
References:
Matheron, M. E., & Porchas, M. 2010. Evaluation of soil solarization and flooding as management tools for Fusarium wilt of lettuce. Plant Dis. 94:1323-1328.
Sprangletop has become increasingly widespread in Arizona mostly because of its growth habits and tolerance to many commonly used herbicides. It is in the Leptochloa genus which is derived from the Greek words leptos (thin) and chloa (grass). There are more than 150 species of sprangletop worldwide but only three in Arizona and two in Yuma County. The two that are the most common in the low desert are Mexican Sprangletop, which is Leptochloa uninervia and Red Sprangletop, Leptochloa filiformis. A third species, Bearded Sprangletop, Leptochloa fascicularis, is more common at higher elevations of 1500 feet or higher. It is not uncommon to find both Red and Mexican Sprangletop in the same field and it is not hard to distinguish them when they are side by side. Red Sprangletop has a light green leaf blade which is similar in width to watergrass and barnyardgrass. It has very fine hairs and very small and fine branches and spiklets. It also has a long membranous ligule. The name Red refers to the leaf sheath, which is characteristically red, rather than the seed head. Mexican Sprangletop has a thinner leaf blade which is darker green or grayish in color and similar in appearance to common bermudagrass. The seed head is distinctly coarser than that of Red Sprangletop. Side by side, leaf color and size of the seed make it easy to distinguish these two. Both of these grasses are classified as summer annuals, but they grow more like perennials in the low desert. Sprangletop does very well in the hottest part of the summer and typically germinates from seed during the hottest period between July and September. Once established, however, it often survives through the cold winter months. It grows into clumps that often appear to be dead during the winter. New shoots commonly grow from these established crowns the next season. When this occurs, preemergent herbicides such as Trifluralin or Prowl are ineffective. Some Sprangletop plants stay green and grow through the winter. Many of the postemergence, grass specific herbicides that control many grasses are ineffective on Sprangletop. This also has contributed to the spread of these weeds. Sethoxydim (Poast) and Fluazifop (Fusilade) do not control either Red or Mexican sprangletop. Only Clethodim (Select Max, Select, Arrow and others) is the only one of these grass herbicides that is effective and only at the highest labeled rates. Two applications are often necessary to achieve season long control.