Prior to the cold snap that occurred in the low desert last week, green peach aphid populations were steadily colonizing untreated lettuce plots here at the Ag Center. Very few winged forms were found, but small colonies of 5-6 nymphs could be found on about 10% of the plants. However, temperatures in the Yuma Valley dropped below 32° F several nights during that period. Past experience has shown that aphid populations tend to significantly slow down under these “cold” desert temperatures. That is essentially what we observed this weekend; population growth had stalled out and aphid numbers were the same as they were 2 weeks prior. However, past experience has also shown us that aphid population growth begins to increase again once the weather warms up. Our local forecast suggests that temperatures will be in the mid-70’s for the next 10 days. Assuming the weather service is correct, these conditions may be ideal for aphid population growth. Thus far, in the Yuma Valley we have been finding mainly green peach aphid nymph colonies, and we have been picking up winged aphids on our yellow sticky traps. However, we have found winged Foxglove aphids in our celery. As temperatures increase foxglove may become more abundant (they tend to be more biologically active under warmer temperatures; that is when avg. temps > 60 F). If the field has been treated with imidacloprid at planting, then chances are you are in pretty good shape. But, continue to monitor as imidacloprid doesn’t generally last all season, and the neonicotinoids are marginally effective against foxglove and lettuce aphids. Regardless of whether you find green peach aphid or foxglove aphid the key to effective aphid 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 and Aphid Identification please visit Aphid Management in Desert Produce Crops – 2015 andAphid Identification in Desert Produce Crops So keep your eyes open for new aphid colonies and plan accordingly. As Thomas Edison once said “Good fortune is what happens when opportunity meets with planning”.
Prior to the cold snap that occurred in the low desert last week, green peach aphid populations were steadily colonizing untreated lettuce plots here at the Ag Center. Very few winged forms were found, but small colonies of 5-6 nymphs could be found on about 10% of the plants. However, temperatures in the Yuma Valley dropped below 32° F several nights during that period. Past experience has shown that aphid populations tend to significantly slow down under these “cold” desert temperatures. That is essentially what we observed this weekend; population growth had stalled out and aphid numbers were the same as they were 2 weeks prior. However, past experience has also shown us that aphid population growth begins to increase again once the weather warms up. Our local
Prior to the cold snap that occurred in the low desert last week, green peach aphid populations were steadily colonizing untreated lettuce plots here at the Ag Center. Very few winged forms were found, but small colonies of 5-6 nymphs could be found on about 10% of the plants. However, temperatures in the Yuma Valley dropped below 32° F several nights during that period. Past experience has shown that aphid populations tend to significantly slow down under these “cold” desert temperatures. That is essentially what we observed this weekend; population growth had stalled out and aphid numbers were the same as they were 2 weeks prior. However, past experience has also shown us that aphid population growth begins to increase again once the weather warms up. Our local
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.
Corn earworm:
CEW moth counts continued to decline 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, but well below average for late-October. Most activity in Yuma, dome and Gila Valleys.
Cabbage looper:
Cabbage looper trap counts declined in most areas but increased in the Bard and Yuma Valley. Activity below average for early November.
Diamondback moth:
Adults peaked in Gila and Yuma Valleys and above average in all locations for this time of year. Traps located adjacent to cauliflower and broccoli transplants had the highest trap captures
Whitefly:
Adults remains active in Dome Valley, Wellton, and Roll consistent with melon crops completing harvest, but below average movement for this time of season.
Thrips:
Thrips adult movement increased in most locations last week, particularly in Dome Valley, Wellton, and Tacna. Activity about average for early November.
Aphids:
Aphid movement increased sharply in 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 Gila Valley, Roll and Wellton; about average for this time of season.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
