Foxglove Aphid:
Foxglove aphids continue to colonize lettuce here at the Yuma Ag Center. In untreated lettuce plots here at YAC, the population is spotty, but when we do find them they can be quite abundant. In one field location, we have found more than 400 aphids on a single plant with a fair number of winged adults present. As lettuce acreage continues to decline, you should expect to begin finding more winged aphids in the last few fields. This is typical for this aphid species since it tends to be more biologically active under warmer temperatures. However, foxglove aphid is important because it has a tendency to colonize on younger leaves. This often translates into contamination of the heads or hearts of iceberg lettuce, romaine and celery. The key to effective foxglove aphid (and other aphids as well) management with foliar insecticide is to initiate sprays at the time apterous (wingless) aphids begin to colonize. Of course, this requires diligent scouting and sampling. On older lettuce, make sure you thoroughly examine developing heads/hearts. Fortunately, PCAs have alternatives for foliar aphid control. For more information on insecticide alternatives please visit the Foxglove Aphid on Desert Lettuce Crops.
Sivanto:
On January 16, 2015 the USEPA announced that Sivanto (flupyradifurone) received a section 3 registration on various commodities and will be available to local PCAs sometime pending state approval from the Arizona Department of Agriculture. According to the EPA, the new insecticide is safe on bees, and is expected to be an alternative to more toxic products including certain pyrethroid, neonicotinoid, and organophosphate insecticides. EPA further stated that laboratory-based studies indicate that the compound is practically non-toxic to adult honeybees. This and more information on Sivanto’s biological attributes can be found at http://www.epa.gov/oppfead1/cb/csb_page/updates/2015/alt-neonicotinoids.html In my opinion, Sivanto will be a good addition to our IPM program and will provide PCAs another alternative for managing sucking insect pests produce and melon crops. For a description of its attributes and fit in desert crops see New Insecticide Chemistry_Sivanto 2015
Methomyl:
USEPA also recently announced that the manufacturers of the insecticide methomyl (Lannate, Nudrin) have agreed to cancel some uses, and limit use on certain crops (lettuce, celery and peppers) to reduce risks to drinking water. Fortunately for desert growers, these changes should not have much of an impact on IPM on our produce crops. According to EPAs Risk Mitigation Decision, the number of applications of methomyl allowed on head lettuce will be reduced from 15 applications to 12, on leaf lettuce will be reduced from 8 to 6 applications, and on celery will be reduced from 10 to 8 applications. Based on our Lettuce Insect Losses Survey data over the past 5 years, methomyl is used on an average of about 40% of the Arizona lettuce acres and applied fewer than twice per field (seeTends in Lettuce Insecticides 2014). Thus, for now PCAs will not be affected by this label change for methomyl. However, I will be the first to support the importance of methomyl in our desert IPM/IRM programs crops because of the need for broad spectrum insect control, and the products role as a key alternative for western flower thrips control. For more information please go to http://yosemite.epa.gov/opa/admpress.nsf/bd4379a92ceceeac8525735900400c27/d2eccc5646af82d685257ddc0062b6df!OpenDocument
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 counts remained low over the past 2 weeks across all locations and about average for this time of the season.
Beet armyworm:
Trap counts decreased in most locations, and well below average for late-November. Most activity in Yuma Valley.
Cabbage looper:
Cabbage looper trap counts remained low in most areas but increased in the Yuma Valley. Activity below average for late November.
Diamondback moth:
Adults peaked in Bard, Gila and Yuma Valleys and slightly above average for this time of year. Traps located adjacent to cauliflower seed crops had the highest trap captures
Whitefly:
Adults remains active in Dome Valley and Roll consistent with melon crops completing harvest, but below average movement for this time of season.
Thrips:
Thrips adult movement decreased in most locations last week, and most active in Dome Valley, Wellton, and Tacna. Activity about average for mid-November.
Aphids:
Aphid movement peaked so far this season with highest activity in Dome Valley, Bard, N. Yuma Valley and N. Gila Valleys over the past 2 weeks. Activity average for this time of year.
Leafminers:
Adult activity increased sharply in the Dome, Yuma, and Gila Valleys, about average for this time of season.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
