The recent break in the weather suggested to me that insect activity in general should begin to significantly decline throughout the region. For instance, in the Yuma Valley during the past 10 days temperatures have been on average about 7 degrees cooler than normal and particularly the nighttime temperatures which have been as much as 12 degrees cooler. However, based on insect activity we’re observing in our experimental plots here at the Yuma Ag Center (YAC), as well as reports from PCAs - this is not the case. In September whitefly, beet armyworm and bagrada bug activity was heavy in most areas. We saw a small decline in whitefly activity following the rains we had a month ago, but adults are still actively moving in some areas. Here at YAC, whiteflies on untreated melons are causing significant plant mortality from heavy immature colonies and CYSDV. Beet armyworm pressure started heavy in September and remains heavy in our untreated blocks. We’re still observing overlapping egg lays of both egg masses and cabbage looper eggs. As is typical, cabbage loopers are very active now, as witnessed by large larval populations in our plots and an area wide increase in trap captures of moths (see Area Trap Network). We’re also beginning to pick up a significant increase in leafminer activity on untreated lettuce plots which is consistent with this time of the year. Bagrada bug have been heavy this year and pressure remains high in experimental plots at YAC (see Graph below). Their movement has not yet subsided, as reports are coming in from PCAs that they are still actively battling Bagrada in cole crops, especially in Bard, and the Gila and Yuma Valleys. A new planting of broccoli this week (Oct 10) at YAC was heavily infested with adults upon plant emergence. On our older plantings, nymph and adult populations are widespread. Based on past experience, we don’t expect a significant decline in Bagrada activity until average temperatures drop below 70 degrees. Finally consistent with the heavy N/NW winds experienced last week, we are beginning to pick up winged-aphids in our sticky traps, albeit in low numbers, in the Gila and Yuma Valleys. We have not detected winged aphids or colonies on winter vegetable plants yet. Temperatures this week so far are average for this time of the year, and are expected to be slightly higher than normal for the next 7 days or so. Thus, don’t be surprised if insect activity continues at the same pace until the next break in the weather which is historically around the opening of deer season (Nov 1). Life is good!
2023-2024 Powdery Mildew of Lettuce Fungicide Trial
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%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. 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, which contained two 25 ft rows of lettuce. Plants were thinned Jan 17, 2024 at the 3-4 leaf stage to a 12-inch spacing. 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.
Month
Max Temp (°F)
Min Temp (°F)
Average Temp (°F)
Rainfall
November
80
51
65
0.08 in
December
71
44
57
0.82 in
January
68
42
54
1.14 in
February
73
47
59
0.50 in
Powdery mildew (caused by Golovinomyces cichoracearum) efficacy trial treatments were made on February 15,2024, February 23, 2024, March 4, 2024, and March 12, 2024and .Disease was first seen on February 26,2024. Disease rating was done on March 15, 2024. Disease severity was determined by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 0.5 = one to a few very small powdery mildew colonies on bottom leaves; 1 = powdery mildew present on bottom leaves of plant; 2 = powdery mildew present on bottom leaves and lower wrapper leaves; 3 = powdery mildew present on bottom leaves and all wrapper leaves; 4 = powdery mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = powdery mildew present on entire plant. These ratings were transformed to percentage of leaves infected values before being statistically analyzed. Yield loss due to rejected lettuce heads would likely begin to occur on plants with a powdery mildew rating above 2.0 (percentage of leaves infected value of 40).
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. The most effective fungicides were Rhyme, Merivon, Quintec, Cevya, Luna Sensation, Luna Experience, and Elisys.
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 remain low across all locations; average for this time of the season.
Beet armyworm:
Trap counts decreased in all locations, and below average for late-January.
Cabbage looper:
Cabbage looper trap counts remained low in all locations; below average for early February.
Diamondback moth:
Adult activity increased slightly in some locations, particularly fields where trap is adjacent to with nearby brassica seed crops. Overall, activity is below average for this time of year.
Whitefly:
Adult movement remained low in all locations consistent with previous seasons.
Thrips:
Thrips adult movement beginning to increase slightly in most locations. Activity a about average for mid-February.
Aphids:
Aphid movement increased in many locations, particularly in Yuma Valley. Trap captures about average for this time of year.
Leafminers:
Adult activity increased in most areas, below average for this time of season.