Impact of Diamondback Moth on Arizona Cole Crops: 2017 Survey Results
In Arizona, the diamondback moth (DBM) is typically considered a minor pest that occasionally builds up to damaging levels in the winter and spring. In most years, growers can easily control the pest with 1-2 well timed insecticide sprays. However, beginning in October 2016 outbreaks of an invasive DBM population occurred throughout all vegetable growing regions in Arizona and continued throughout the remainder of the spring growing season. Cole crops that were affected included broccoli, cauliflower, cabbage, kale, mizuna/arugula, Napa cabbage, bok choy, Brussel sprouts and Brassica seed crops. It was quickly determined that the source of the DBM populations originated from infested transplants grown in local desert greenhouses. Within weeks of transplanting, PCAs and growers found that they could not adequately control the DBM infestations. To further complicate the situation, it was later discovered that the invasive DBM population was very resistant to the anthranillic diamide insecticides that are commonly used to control Lep larvae. After the first transplanted fields began to harvest in November, several growers reported that seriously infested fields suffered significant yield reductions, and incurred extremely high control costs. By late December, DBM populations began to spread from the infested transplanted fields to direct-seeded crops throughout the region, causing further losses. By February, reports of infested broccoli, cabbage and cauliflower fields were routine. The DBM infestations experienced by Arizona growers in 2016-17 were not anticipated, and the resistant population that entered the desert caused serious losses in cole crops. It has been suggested that the DBM outbreaks this year were comparable in severity to the early sweetpotato whitefly outbreaks in 1992. In an attempt to document the impact of the DBM outbreaks on Arizona cole crops, we conducted a two-part survey of growers and PCAs from Yuma and Maricopa Counties in April 2017 to (1) estimate the severity of yield losses to DBM on direct-seeded and transplanted cole crops, and (2) the intensity of chemical management required to control DBM, and associated level of control provided by each insecticide product used. To download a copy of the survey results, please go to Impact of Diamondback Moth Outbreaks on Arizona Cole Crops in 2016-17.
In Arizona, the diamondback moth (DBM) is typically considered a minor pest that occasionally builds up to damaging levels in the winter and spring. In most years, growers can easily control the pest with 1-2 well timed insecticide sprays. However, beginning in October 2016 outbreaks of an invasive DBM population occurred throughout all vegetable growing regions in Arizona and continued throughout the remainder of the spring growing season. Cole crops that were affected included broccoli, cauliflower, cabbage, kale, mizuna/arugula, Napa cabbage, bok choy, Brussel sprouts and Brassica seed crops. It was quickly determined that the source of the DBM populations originated from infested transplants grown in local desert greenhouses. Within weeks of transplanting, PCAs and growers found that they could not adequately control the DBM infestations. To further complicate the situation, it was later discovered that the invasive DBM population was very resistant to the anthranillic diamide insecticides that are commonly used to control Lep larvae. After the first transplanted fields began to harvest in November, several growers reported that seriously infested fields suffered significant yield reductions, and incurred extremely high control costs. By late December, DBM populations began to spread from the infested transplanted fields to direct-seeded crops throughout the region, causing further losses. By February, reports of infested broccoli, cabbage and cauliflower fields were routine. The DBM infestations experienced by Arizona growers in 2016-17 were not anticipated, and the resistant population that entered the desert caused serious losses in cole crops. It has been suggested that the DBM outbreaks this year were comparable in severity to the early sweetpotato whitefly outbreaks in 1992. In an attempt to document the impact of the DBM outbreaks on Arizona cole crops, we conducted a two-part survey of growers and PCAs from Yuma and Maricopa Counties in April 2017 to (1) estimate the severity of yield losses to DBM on direct-seeded and transplanted cole crops, and (2) the intensity of chemical management required to control DBM, and associated level of control provided by each insecticide product used. To download a copy of the survey results, please go toIn Arizona, the diamondback moth (DBM) is typically considered a minor pest that occasionally builds up to damaging levels in the winter and spring. In most years, growers can easily control the pest with 1-2 well timed insecticide sprays. However, beginning in October 2016 outbreaks of an invasive DBM population occurred throughout all vegetable growing regions in Arizona and continued throughout the remainder of the spring growing season. Cole crops that were affected included broccoli, cauliflower, cabbage, kale, mizuna/arugula, Napa cabbage, bok choy, Brussel sprouts andBrassicaseed crops. It was quickly determined that the source of the DBM populations originated from infested transplants grown in local desert greenhouses. Within weeks of transplanting, PCAs and growers found that they could not adequately control the DBM infestations. To further complicate the situation, it was later discovered that the invasive DBM population was very resistant to the anthranillic diamide insecticides that are commonly used to control Lep larvae. After the first transplanted fields began to harvest in November, several growers reported that seriously infested fields suffered significant yield reductions, and incurred extremely high control costs. By late December, DBM populations began to spread from the infested transplanted fields to direct-seeded crops throughout the region, causing further losses. By February, reports of infested broccoli, cabbage and cauliflower fields were routine. The DBM infestations experienced by Arizona growers in 2016-17 were not anticipated, and the resistant population that entered the desert caused serious losses in cole crops. It has been suggested that the DBM outbreaks this year were comparable in severity to the early sweetpotato whitefly outbreaks in 1992. In an attempt to document the impact of the DBM outbreaks on Arizona cole crops, we conducted a two-part survey of growers and PCAs from Yuma and Maricopa Counties in April 2017 to (1) estimate the severity of yield losses to DBM on direct-seeded and transplanted cole crops, and (2) the intensity of chemical management required to control DBM, and associated level of control provided by each insecticide product used. To download a copy of the survey results, please go to
In response to the recent outbreaks of Diamondback moth (DBM) , Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur this fall.
This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches between bed centers. All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.
Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.
Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.
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.
In response to the recent outbreaks of Diamondback moth (DBM) , Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur this fall.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
