With the above normal temperatures we’ve been experiencing for the past several weeks, it’s no wonder that western flower thrips numbers in the Yuma Valley are almost 4X times higher than this time last year (see graph below). Given these ideal temperatures, you can expect thrips numbers to continue to increase, and based on historical data, if temperatures remain moderate and rainfall is light we can expect thrips numbers to reach very high levels by the end of the month. Another factor PCAs should be concerned with this time of the year is thrips "bioconcentration" which annually occurs in late February and March as lettuce acreage declines. Each time a lettuce field is harvested and disked, adult thrips disperse from these areas into the next available lettuce field. This is generally coincident with our seasonally warm temperatures that are suitable for thrips development. As the number of lettuce acres becomes reduced near the end of the season, this creates a bottleneck effect that concentrates high numbers of thrips adults on the remaining fields under production. This can often make chemical control very difficult, particularly in March, as thrips adults may continually re-infest fields following spray applications (similar to battling whitefly adults on fall melons). When lettuce production is finished, these populations can pose a threat to seedling cotton, and even alfalfa. Note: the key to preventing thrips from significantly scarring leafy vegetable plants is to prevent immature populations from becoming established. The cryptic or thigmotactic behavior of thrips often makes them difficult to find on lettuce plants. Research has shown us that if you can see a few adults and larvae on the plant, it likely means that as many as 8-10 fold more thrips are actually on the plant (hiding near the base of the plant between midribs). This behavior also means that spray coverage is important, particularly with contact insecticides like Lannate, Torac and pyrethroids. For more information on the identification, biology, ecology and management of thrips on desert produce please visit Western Flower Thrips Management on Desert Produce
Western Flower Thrips Management on Desert Produce. Did you know: The word thrips is used for both the singular and plural forms of this lettuce pest; for example "there may be many thrips on a lettuce plant or a single thrips”.
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%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 18, 2024 on beds with 84 in. between bed centers and containing 30 lines of seed per bed. All irrigation water was supplied by sprinkler irrigation. Treatments were replicated four times in a randomized complete block design. Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed. Treatments were applied with a CO2backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles.
Month
Max
Min
Average
Rainfall
January
68
42
54
1.14 in
February
73
47
59
0.50 in
March
77
50
63
0.31 in
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 19 and final reading was taken on February 26, 2024. Spray date for each treatments are listed in excel file with the results. Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft2 areas within each of the four replicate plots per treatment. The number of spinach leaves in a 1-ft2 area of bed was approximately 144.
The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. No phytotoxicity was observed in any of the treatments in this trial.
Controlling Disease and Weeds with Band-Steam – Yuma Trials Show Good Promise
In previous articles (Vol. 11 (13), Vol. 11 (20), Vol. 11(24)), I’ve discussed using band-steam to control plant diseases and weeds. Band-steaming is where steam is used to heat narrow strips of soil to temperature levels sufficient to kill soilborne pathogens and weed seed (>140 °F for > 20 minutes). The concept is showing good promise. This past season, three trials were conducted examining the efficacy of using steam for disease and weed control in Yuma, AZ. In the studies, steam was applied in a 4-inch-wide by 2-inch-deep band of soil centered on the seedline using a prototype band-steam applicator (Fig.1). The band-steam applicator is principally comprised of a 35 BHP steam generator mounted on top of an elongated bed shaper. The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper.
Trial results were very encouraging as the prototype applicator was able to raise soil temperatures to target levels (140°F for >20 minutes) at viable travels speeds of 0.75 mph. Steam provided better than 80% weed control and significantly lowered hand weeding time by more than 2 hours per acre (Table 1). Results also showed that Fusarium colony forming units (CFU) were reduced from 2,600 in the control to 155 in the 0.75 mph and 53 in the 0.5 mph treatments, respectively (a more than 15-fold reduction). A significant difference in Fusarium wilt of lettuce disease incidence was not found, however disease infection at the field site was low (< 2%) and differences were not expected. At 0.5 mph, fuel costs were calculated to be $238/acre which was considered reasonable and consistent with the values reported by Fennimore et al. (2014).
An unexpected finding was that plants in steam treated plots appeared to be healthier and more vigorous than untreated plots (Fig. 2). This trial is still in progress and it will be interesting to see if this improved early growth translates into increases in crop yield.
In summary, early trial results are showing good promise for use of band-steam as a non-herbicidal method of pest control. We plan on conducting further trials in this multi-year study. If you are interested in evaluating the device on your farm and being part of the study please contact me. We are particularly interested in fields with a known history of Fusarium wilt of lettuce and/or Sclerotinia lettuce drop that will be planted to iceberg or romaine lettuce.
As always, if you are interested in seeing the machine operate or would like more information, please feel free to contact me.
Acknowledgements
This work is supported by Crop Protection and Pest Management grant no. 2017-70006-27273/project accession no. 1014065 from the USDA National Institute of Food and Agriculture, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
A special thank you is extended to Mellon Farms for allowing us to conduct this research on their farm.
References
Fennimore, S.A., Martin, F.N., Miller, T.C., Broome, J.C., Dorn, N. and Greene, I. 2014. Evaluation of a mobile steam applicator for soil disinfestation in California strawberry. HortScience 49(12):1542-1549.
Click link below or picture to see the band-steam and co-product applicator in action!
Carryover of Vegetable Herbicides to Wheat Grown in Rotation
Almost all the herbicides used on lettuce, cole crops and melons have restrictions on how soon wheat can be planted in rotation after they have been used. Experience has demonstrated, however, that safe intervals can vary considerably based upon many factors and are almost always much longer than they need to be. The most important factors are rate applied, irrigation practices and tillage. For example, when Kerb used to be banded at 2 to 4 lbs. per acre after planting and incorporated with furrow irrigation, it was common to see treated strips across wheat fields which followed. This is uncommon now that lower rates are Chemigated. We still see some Balan injury at ends of fields or in overlaps especially when sudan is planted. Wheat it not very sensitive to Prefar and carryover injury is uncommon.
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
