Bindu Poudel-Ward, Martin Porchas, and Jason Furr
Yuma Agricultural Center, University of Arizona, Yuma, AZ
Bindu Poudel, Martin Porchas, and Jason Furr
Yuma Agricultural Center, University of Arizona, Yuma, AZ
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 ‘Magosa’ was seeded, then sprinkler-irrigated to germinate seed on Nov 16, 2020 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 four times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. 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 |
Min |
Avg |
Rain |
November |
80 |
49 |
64 |
0.00 |
December |
69 |
41 |
55 |
0.01 |
January |
70 |
42 |
56 |
1.31 |
February |
75 |
44 |
60 |
0.00 |
March |
77 |
46 |
63 |
0.00 |
Powdery mildew (caused by Golovinomyces cichoracearum) efficacy trial treatments were made on February 3rd, February 17, and March 2dn 2021. Disease rating was done on March 8, 2021. 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. All treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. The most effective fungicides, that held the percentage of leaves that were infected to 20% or less, included UA Experimental-1, Luna sensation, Quintec, and Torino. Phytotoxicity symptoms were not noted for any treatments in this trial.