Winter Weather: Impact on Produce Pests this Year 2011
Now that spring has officially arrived, one question I've been contemplating is how did the cold weather this past winter impact pest pressure on our winter vegetables. There is no doubt that temperatures throughout Yuma County were considerably cooler this winter relative to last year, particularly during January and February. Based on my observations at the Yuma Ag Center, I would say that aphid and thrips numbers were lower than what we typically see during this period. It is quite reasonable to assume that the lower winter temperatures, coupled with lower rainfall amounts, likely kept aphid numbers relatively low. These cooler temperatures may also explain why, in some cases, Movento appeared to provide inconsistent activity against aphids. The systemic activity of the compound is influenced by the growth of the plant, and with the cooler temperatures and multiple freezes experienced this winter, both lettuce plant growth and aphid activity were likely negatively influenced. Thrips numbers are beginning to rapidly increase now, but during Jan and Feb, their numbers remained very low. Although we saw less rainfall this winter, the cooler temperatures clearly suppressed population growth. In addition, it appeared to be a little windier this winter, but average wind speeds varied within Yuma County. Wind can influence insect movement, several abiotic/biotic factors, and of course, the ability of PCAs to spray crops. Finally, the hard freezes we experienced this winter certainly impacted plant growth, quality and insect management. This was especially evident in the Gila Valley for instance where the AZMET weather station recorded 7 days when temperatures dropped below 32°F for an average of about 5 hours per freeze. This is significant when you consider that no freeze events were recorded all of last growing season. In contrast, Roll had 30 days of below 32°F temperatures, compared to 19 last year. Looking forward, what impact these freezes have had on key pests of spring melons (i.e., whiteflies, cabbage loopers) remains to be seen. For a detailed summary of the winter weather data described above, please go to Winter Weather Conditions Yuma. For a more detailed discussion on the impact of weather on insects refer to the article Weather and Insects.
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%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches between bed centers. All other water 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. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.
Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.
Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for 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.
Area wide Insect Trapping Network (October 30, 2024)
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm:CEW moth counts down in most traps over the last week; about average for early October.
Beet armyworm: Trap counts increased in several areas last week, and about average for early October.
Cabbage looper: Cabbage looper trap counts increased in most locations, but still below average for this time of the season.
Diamondback moth: Adult activity spiked 2 weeks ago, particularly in the Yuma and Dome Valleys, but down over the past week. Average for this time of season.
Whitefly: Adult movement increasing Tacna consistent with melon harvests; overall about average for early October.
Thrips: Thrips adult movement peaked 2 weeks ago but down ovr the past week, overall activity above average.
Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; below average for October.
Leafminers: Adult activity increased significantly last week in several locations, above average for this time of season.
