Efficacy of Pyrethroid Insecticides for Cabbage Looper Control in Head Lettuce, 1997

David L. Kerns and Tony Tellez

Abstract

Mustang 1.5EW, Ammo 2.5EC, Pounce 3,2EC, Scout X-TRA, and three formulations of Karate were compared for efficacy to cabbage loopers infesting head lettuce in Yuma, AZ. Karate and Pounce provided the most consistent cabbage looper control followed by Mustang and Scout X-TRA. Ammo appeared slightly inferior to the other pyrethroids tested. There did not appear to be any obvious differences in the efficacy of the three Karate formulations.

Introduction

During 1997, Arizona pest control advisors (PCAs) and growers had the opportunity to utilize Success (spinosad) and Confirm (tebufenozide) for control of beet armyworms Spodoptera exiqua (Hübner) in leafy vegetables. However, over the past two years, cabbage loopers have been the most common lepidopterous pest infesting Arizona lettuce. For resistance management purposes, the University of Arizona recommends that traditional insecticide combinations be utilized in rotation with Success and Confirm. Most of these combinations consist of Lannate or Larvin for beet armyworm control, and a pyrethroid for cabbage looper control. Because pyrethroids are still extremely important insecticides for lepidopterous pest control in leafy vegetables in Arizona, it is important that efficacy of these products be continually evaluated. The objective of this study was to evaluate pyrethroid insecticides for control of cabbage loopers, beet armyworms and Heliothinae in lettuce.

Materials and Methods

Head lettuce, ‘Empire’ was direct seeded into double rows on 42-in beds on 26 August at the Yuma Valley Agricultural Center, Yuma, AZ. Plots were 4 beds X 25 ft, bordered on each side by 2 blank beds and on each end by 8 ft alleys. The test was a randomized complete block design, with 4 replicates. Treatments included Mustang 1.5EW (zeta-cypermethrin), Ammo 2.5EC (cypermethrin), Pounce 3.2EC (permethrin), Scout X-TRA (tralomethrin) and three formulations of Karate (lambda-cyhalothrin). The current emulsifiable formulation of Karate was compared to two CS formulations intended to reduce dermal irritation. Applications were made on 22 Sept and 3, 10 and 25 Oct, and 12 Nov. Two rate regimes were used in this study. On 22 Sept and 3 Oct, high rates were used because significant beet armyworms were present, while lower rates were used during subsequent applications. All treatments included Kinetic spreader sticker at 0.05% v/v. Insect densities were estimated by counting the number of small and large cabbage looper, beet armyworm and Heliothinae larvae per 15 plants per plot. The percentage of plants infested with eggs of each species was also estimated.

Treatments were sprayed using a tractor mounted sprayer. The boom covered 4 rows, with 3 hollow cone TXV-4 nozzles per row, one centered over the bed and two on angled drops on each side of the bed. The sprayer was calibrated to deliver 20 gallons per acre at 40 psi. The tractor traveled at 3 mph.

At harvest on 20 Nov, ten plants were randomly selected from the middle two beds of each plot and rated for damage and marketablility. Damage ratings were based on a 1-5 scale was used where; 1 = no damage, 2 = minor damage to the wrapper leaves, 3 = minor damage to the head, 4 = significant damage to the wrapper leaves and 5 = significant damage to the head.

All data were analyzed using a general linear model, and an F protected (P < 0.05) LSD for means separation.

Results and Discussions

The lettuce in this research trial was thinned on 15 Sept and the first insecticide application was made on 22 Sept. At that time, both beet armyworms and cabbage loopers were extremely numerous. However, Yuma was hit by hurricane Nora three days later resulting in a high volume of precipitation and high winds. We were not able to enter the field to make evaluations until 3 Oct, 11 DAT (days after treatment). Because of the wash off and physical impact on the worm populations we could not detect any differences among treatments (Table 1). Additionally, although beet armyworm and Heliothinae population densities were estimated in the trial, there were never any significant differences among treatments. Following hurricane Nora, beet armyworm densities were low, and although Heliothinae numbers were high in mid-October, they were spotty in distribution and extremely variable among plots. Thus this data is not presented.

Six days following application 2, all treatments except Ammo contained fewer small cabbage loopers than the untreated, and none of the insecticide treatments differed from each other (Table 2). All insecticide treatments contained fewer large loopers than the untreated, however Pounce and the Karate formulations appeared to be slightly superior to the other treatments. Application 3 was made at lower rates targeting primarily cabbage loopers. Three days following this application there were no significant differences among treatments (Table 3). By 6 DAT, only Mustang and Ammo failed to contain fewer cabbage loopers than the untreated and at 12 DAT, there were no significant differences among treatments.

Following application 4, Scout X-TRA did not differ from the untreated in large loopers at 5 DAT, but did by 12 DAT (Table 4), and all insecticide treatments were equally effective following application 5 (Table 5). Overall, at the rates we evaluated, Karate and Pounce appeared to provide the most consistent cabbage looper control followed by Mustang and Scout X-TRA. Ammo appeared slightly inferior to the other pyrethroids tested. There did not appear to be any obvious differences in the efficacy of the three Karate formulations. At harvest, all of the insecticide treatments had lower damage ratings and higher percentages of marketable heads than the untreated, but did not differ from each other (Table 5).


This is a part of publication AZ1101: "1998 Vegetable Report," College of Agriculture, The University of Arizona, Tucson, Arizona, 85721.
This document located at http://ag.arizona.edu/pubs/crops/az1101/az1101_24.html
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