We continue to trap diamondback moth (DBM) in traps throughout the area. We currently have 57 pheromone traps stretched from Texas Hill to San Luis. In the past few weeks we’ve seen moth activity decrease in general in traps at Texas Hill, Tacna Roll, Wellton, Dome Valley and Bard/ Winterhaven. In contrast, we’ve recorded increases in trap captures in some traps in the Gila and Yuma Valleys. (See DBM Trap Network).
One trap located at the Yuma Ag Center captured more than 28 moths /trap per night last week. That trap is adjacent to several acres of untreated broccoli that are infested with DBM larvae. However, most traps throughout the Yuma area are not catching anywhere near those numbers of moths, and not surprising, the fields adjacent to these traps have little to no DBM larvae. Furthermore, to date no PCAs have reported failures in controlling DBM like they experienced last fall. On the Yuma Ag Center, we have had plenty of DBM in our cole crops. This allowed us to conduct a number of efficacy trials with both soil and foliar applied insecticides. In our Verimark tray-drench trial in cauliflower, we observed DBM control for almost 40 days. Soil shank applications of Verimark in broccoli provided DBM efficacy for ~ 30 days. Our foliar spray trials consistently showed that the all conventional insecticides we evaluated provided significantly better control of DBM larvae compared to the untreated check following multiple spray applications (for results see Efficacy of Foliar Insecticides Against Diamondback Moth, Fall 2017 andEfficacy of Foliar Insecticides Against DBM and Whitefly). On the other hand, we found it more difficult to control DBM with organically-approved biopesticides (see Organic Insecticide for DBM Control on Broccoli, Fall 2017).
An important lesson was learned from these studies. This fall DBM was not an issue, unlike last season. We’re obviously dealing with a different population this year. It is highly likely that the present DBM populations found at the Yuma Ag Center and throughout the Yuma area moved into the area via monsoon/tropical storms. I base this on the fact that the DBM have been easy to control with our standard insecticides (unlike last season), and we have been trapping moths adjacent to direct-seeded broccoli fields since early September. We’ve also been trapping them next to fallow fields. This clearly suggests that the DBM in Yuma this fall did not exclusively arrive on transplants, nor did last season’s resistant population over-summer here. I believe this explains why DBM is seldom a problem for Yuma PCAs. DBM populations have to migrate in and over the past 20 years or so, they have been susceptible to our industry standards. The exception would be last year, where the DBM outbreaks we experienced were associated with a resistant population that moved into fields from infested transplants. One last thing to consider: it is possible we may see additional DBM move into the area via winter storms from the coast. Hopefully we can pick up such movement with our traps.
This study was conducted at the JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers. Rest of the irrigation 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, which contained two 25 ft rows of lettuce. Plants were thinned on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.
Month
Max
Min
Avg
Rain
September
100
71
86
0.71 in
October
93
61
77
0.00 in
November
80
51
65
0.08 in
December
71
44
57
0.82 in
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in 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.
Corn earworm:
CEW moth increased the Dome Valley area last week, but areawide below average for early October.
Beet armyworm:
Trap counts highest in Tacan, Wellton and Dome, but below average for early fall.
Cabbage looper:
Cabbage looper numbers remained low consistent with late-September.
Diamondback moth:
DBM moths beginning to appear in traps in Wellton/Dome Valley, trending on average for early fall..
Whitefly:
Adult movement down in the past week, above average for late-September.
Thrips:
Thrips adult activity beginning to increase, and trending about average to previous years.
Aphids:
First winged adults captured for the season, consistent with heavy winds from W-NW last week. Can anticipate aphid flights to increase in the coming weeks.
Leafminers:
Adult activity tending downward in most locations, average for late-September.