Lettuce Insect, Disease and Weed Losses Workshop 2016
Next week the UA Vegetable IPM Team will be holding the 2016 Lettuce Insect, Disease and Weed Losses Workshop on Wednesday, April 20 at the Yuma Agricultural Center beginning at noon (lunch is provided at no cost). Since 2004, we have annually surveyed PCAs and growers to document local pest activity and pesticide usage in Arizona lettuce through this interactive workshop. In my opinion, this is one of the more important meeting we hold each year. Not only do we gather your input on pest activity and pesticide use from this past produce season, but we also provide information on last year’s results and new information on vegetable IPM. The survey information provided by PCAs and growers during these workshops is very useful to the local produce industry. First, the data can be extremely helpful in addressing state and federal regulatory issues by providing “real world" information on insect pest status and insecticides usage. In the past data generated from the surveys has been used to support registrations of key insecticide products (i.e., Movento and Lannate) and is currently being used to support the registration of flubendiamide. Secondly, from an academic perspective, the results of these surveys provide us with a historic record of pest occurrences and allows us to prioritize some of our research and educational activities. The insecticide usage data has also provided valuable support for many of the grant programs we request funding from. Finally, and perhaps most importantly for PCAs, it translates your efforts into economic terms for growers and shippers, and confirms the PCAs value to the lettuce industry by showing the importance of key pests and their cost-effective management in desert lettuce production. For example, survey results from the over the past 10 years show that on average, 1) costs associated with pest management fees have increased steadily where the cost of scouting and making management decisions by PCAs are well over $20/acre, 2) Leps, aphids and thrips are the most important economic pests in fall and spring lettuce, and 3) the use of older, broadly toxic insecticides (OP/Carbamates/Endosulfan) has dropped significantly, whereas use of the newer, softer reduced-risk chemistries (e.g., Radiant, imidacloprid, and diamides) continues to increase. Results from last year’s insecticide use surveys can be found in this report: 2014-15 Insecticide Usage on Arizona Lettuce For the most part PCAs already know this, but these surveys document this information for those less involved with the day-to-day activities of IPM in desert lettuce. Hopefully PCAs and growers see the value in this process and will join us next week at the 2016 Lettuce Insect, Disease and Weed Losses Workshop. See you there!
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 Fusarium Wilt of Lettuce Using Steam Heat – Trial Initiated
Earlier this week, we initiated a trial examining the use of band steam for controlling Fusarium wilt of lettuce. The premise behind this research is to use steam heat to raise soil temperatures to levels sufficient to kill soilborne pathogens. For Fusarium oxysporum f. sp. lactucae, the pathogen which causes Fusarium wilt of lettuce, the required temperature for control is generally taken to be > 140°F for 20 minutes. Soil solarization, where clear plastic is placed over the crop bed during the summer, exploits this concept. The technique raises soil surface temperatures to 150-155˚F, effectively killing the pathogen and reducing disease incidence by 45-98% (Matheron and Porchas, 2010).
In our trials, we are using steam heat to raise soil temperatures. Steam is delivered by a 35 BHP steam generator mounted on a custom designed elongated bed shaper (Fig. 1). Preliminary results were encouraging. The device was able to increase the temperature of the top 3” of soil to over 180°F at a travel speed of 0.5 mph as shown in this video of the machine in action (shown below). These temperatures exceed that of those known to control pathogens responsible for causing Fusarium wilt of lettuce (> 140°F for 20 minutes).
Stay tuned for final trial results and reports on the efficacy of using steam heat to control Fusarium wilt of lettuce.
If you are interested in evaluating the technique on your farm, please contact me. We are seeking additional sites with a known history of Fusarium wilt of lettuce disease incidence to test the efficacy and performance of the device.
References
Matheron, M. E., & Porchas, M. 2010. Evaluation of soil solarization and flooding as management tools for Fusarium wilt of lettuce. Plant Dis. 94:1323-1328.
Acknowledgements
This project is sponsored by USDA-NIFA, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support.
A special thank you is extended to Cory Mellon and Mellon Farms for allowing us to conduct this research on their farm.
Weeds are one of the most visible of all agricultural pests. They can’t move or hide and once established often stick up over the crop. Just one weed in a 10 acre field is annoying to look at. With insects and diseases, the damage is often more visible than the pest. That is not the case with weeds. A moderate weed infestation is approximately 10 weeds per square foot. If a herbicide produces 90% control, that leaves 1 weed per square foot or 43 weeds per acre. Without an untreated check, this can look like the herbicide failed! It is easy to leave an untreated spot in a field and it is well worth doing. Many applicators do so unintentionally because of skips, powerlines and other causes. They help determine crop injury and weed control. Here are some examples of what various levels of control looked like from one of our cole crop trials:
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
