Now that the produce season has begun, one of the first pests you’re likely to encounter is adult whiteflies. However, thus far, adult numbers have been surprising light on fall melons compared to previous years. Whitefly populations sampled in our untreated experimental plots during the last week in August at the Yuma Ag Center, show that adult numbers are the lowest we’ve observed in August since 2008 (see graph below). However, several melon fields in the Wellton/Roll were found to have very high numbers this past weekend. In each case, the fields with high adult numbers were either adjacent to or within a ½ mile of cotton that had not defoliated yet. Once the cotton is defoliated, whitefly movement generally declines. Nonetheless, you can bet whiteflies will eventually show up in one of your fields. It is important that PCAs pay particular attention to early whitefly control on their newly planted produce crops. Prolonged feeding by heavy numbers of adults on seedling lettuce/cole crop plants can cause stunted plant growth. If you observe honeydew on leaves in the absence of nymphs then there are way too many adults on the seedling plants. There are likely too many eggs being laid as well. PCAs have a few options for effective residual control of adults, but good knockdown can be achieved on lettuce and cole crops with combinations of 1) pyrethroids tank-mixed with Orthene, 2) Venom, Assail, Scorpion (neonicotinoids), 3) Exirel (diamide), and 4) the newly registered Sivanto (buteolide). All of these products will provide 3-7 days or adult knockdown. To assess adult control under heavy migrations, try monitoring young leaves for the presence of light-colored eggs (newly laid) using a hand lens. Absence of newly laid eggs can be an indication that adults are not actively feeding on leaves or are dying before they can lay eggs. Furthermore, allowing adults to remain unchecked on small plants generally results in the development of large nymph populations that can cause significant growth/yield reductions in all produce crops. It is strongly recommended that growers apply a soil insecticide on lettuce and cole crops throughout September, and if the weather remains warm into mid-October. Soil applied imidacloprid (0.38 lbs. AI/ac) (e.g., Alias 2F-24 oz; Wrangler 4F-12 oz; Admire Pro- 10.5 oz) can provide control through thinning stage. Verimark applied at 13.5 oz/ac can provide excellent control of nymphs when applied at planting similar to the neonicotinoids to lettuce and cole crops. Once plants get larger, products like Movento, Exirel, Venom, Scorpion, Assail, Knack and Courier/Vetica can provide effective control of nymphs. For more information on whitefly biology, management and insecticide alternatives see these reports: Whitefly Management in Fall Produce-2015 and Insect Management on Desert Vegetables and Melons: Whitefly.
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.
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.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
