© 2011 Plant Management Network.
Influence of Adjuvants and Spray Timing of Movento on Aphid Contamination and Crop Injury in Baby Spinach
John C. Palumbo, University of Arizona, Department of Entomology, Yuma Agricultural Center, Yuma, AZ 85364
Palumbo, J. C. 2011. Influence of adjuvants and spray timing of Movento on aphid contamination and crop injury in baby spinach. Online. Plant Health Progress doi:10.1094/PHP-2011-0630-01-RS.
Movento (spirotetramat), a new tetramic acid derivative insecticide, has shown to provide excellent activity against sucking insects through acropetal and basipetal systemic activity following foliar application on some vegetable crops. Studies conducted from 2007-2010 clearly showed that the addition of a penetrating adjuvant (i.e., Dyne-Amic) with Movento sprays significantly enhanced its efficacy against green peach aphid in baby spinach and prevented aphid contamination on marketable spinach plants. Aliette, a systemic fungicide, also significantly enhanced aphid control when combined with Movento. In the absence of a penetrating adjuvant, Movento sprays did not provide commercially acceptable control of green peach aphids in spinach, regardless of spray timing. Addition of other spray additives commonly used in spinach production did not significantly enhance Movento's aphicidal activity. Trials in 2009 and 2010 suggested that a single spray application of Movento with Dyne-Amic on older spinach plants (4-leaf stage) provided control comparable with the same mixture applied twice on smaller (2- and 4-leaf stages). Although growers are generally reluctant to apply oil-based chemicals on baby spinach crops due to risk of crop injury, no phytotocixity was observed with application of Movento/Dyne-Amic mixtures in any of the trials.
The production of spinach, Spinacia oleracea L., in Arizona has increased in value and production over the past several years, and baby spinach grown for the fresh-cut, bagged salad market was valued over $45 million dollars in 2009 (4). Marketing of fresh-cut baby spinach and other leafy vegetables requires that growers produce leaves that are essentially free of insect contaminates such as aphids (11). The green peach aphid, Myzus persicae (Sulzer), has generally been considered the most important aphid species of leafy vegetables in the southwestern United States because of its relative tolerance to some older insecticides (2) and its ability to reach high population levels (6) (Fig. 1). Feeding by this aphid can severely distort and curl the tender marketable sized leaves, and contamination of leaves in spinach can render the crop unmarketable (3). Since baby spinach is a relatively rapid growing crop that can be ready for harvest in as little as 35 days, spinach growers routinely make weekly, prophylactic insecticide applications to prevent aphid contamination at harvest. However, because of the potential for phytotoxic crop injury (marginal necrosis and chlorotic spotting) from chemicals sprays on tender leaf tissue, they are reluctant to apply oil-based insecticides or spray adjuvants on baby spinach. In many cases, this can limit the choice of insecticides available for aphid management on this crop.
Movento (spirotetramat) is a newly registered tetramic acid derivative insecticide for use for aphids and other sucking pests in leafy vegetables. It has a novel mode of action which inhibits lipid metabolism in sucking insects, and has unique systemic properties (5). Following foliar application and uptake through leaf tissue, the insecticide is translocated acropetally and basipetally within the entire vascular system (1). Once the compound penetrates leaf tissue, metabolites of the compound are mobile within the vascular tissue of the plant and toxic to sucking insects. Due to this systemic activity, new leaf tissue developed after a spray application of Movento will also be protected and can provide good residual activity against a number of aphid species on a leafy vegetables (7,8) Efficacy studies in lettuce have shown that Movento formulations were significantly more efficacious against aphids when applied with a penetrating adjuvant (9,10). Because of its systemic activity, Movento it a good candidate for aphid control in rapidly growing crops such as baby spinach. However, whether it can be used efficaciously in spinach without the addition of an adjuvant is unknown. The objective of this study was to determine the ability of Movento/adjuvant mixtures applied at various spray timings to prevent aphid contamination and crop injury on baby leaf spinach grown for the fresh-cut market under desert growing conditions.
Field Plot Experiments (2007-2010)
From 2007-2010, complementary small plot experiments were conducted at the University of Arizona, Yuma Agricultural Center in Yuma. Spinach (variety ‘Interceptor’) was direct seeded on beds (84-inch spacing) in 18 seed lines per bed at an approximate seeding density of 1.5 million seeds per acre on 30 January 2007, 22 January 2008, 24 January 2009, and 2 February 2010. All trials were managed similarly to local growing practices and were irrigated as needed with solid set, overhead sprinklers. Individual plots measured 1 bed (84 inches) by 35 ft with 6 ft unplanted buffer between each plot.
Each experiment consisted of applications of several Movento/adjuvant mixtures, an industry standard insecticide (Assail and/or Beleaf) and untreated control (Table 1). The foliar spray treatments were arranged in a RCB design and replicated four times in each experiment. The number of applications in each trial varied by treatment, and applications were triggered based on plant size (2-leaf and/or 4-leaf stage) (Fig. 2). In the 2008 trial, 2 applications were made to all treatments at the 2 and 4 leaf stages. Formulations, rates and spray timing for each insecticide and adjuvant are provided in the Tables 2 to 5. Rates for adjuvants used with Movento are expressed on a percent volume/volume basis (v/v), or in amount of product/ac. The foliar spray treatments were applied with a CO2 operated sprayer that delivered 22.0 GPA at 40 psi through four TX18 ConeJet nozzles at 19-inch spacings per bed.
Table 1. Insecticides and spray adjuvants evaluated for aphid contamination and product quality losses at harvest in baby spinach , 2007-2010.
Evaluation of Aphid Contamination and Statistical Analysis
To evaluate the economic efficacy of the insecticide treatments at various spray timings, aphid contamination was evaluated at harvest each year. Green peach aphid was the only species present during the trials. When spinach reached fresh-market harvest stage (7 or 8 leaves/plant), 30 plants were randomly selected from each plot and placed individually into large 5-gal tubs. Each plant was individually sampled by visually examining all marketable plant foliage and petioles, and counting the number of alatae and apterae aphids present. Phytotoxicity to marketable-sized leaves was also evaluated by examining 20 randomly selected leaves from each plot and reporting the occurrence of marginal leaf necrosis and chlorotic spotting resulting from chemical injury.
Experimental data for aphid contamination (mean aphids per plant) were analyzed separately for each year using analysis of variance with insecticide/spray timing treatments as the classification variable (PROC GLM, SAS Institute Inc., Cary, NC). To stabilize variances, means were transformed for aphid numbers [log(x+1)]. When significant F-values were reported, means were separated by protected least significant difference test (PROC GLM, SAS Institute Inc., Cary, NC). Untransformed mean values for aphid contamination are presented in the tables. To summarize the influence of the addition of Dyne-Amic with Movento sprays on aphid efficacy over the 4-year study, the percent reduction in aphid numbers at harvest relative to the untreated check were calculated. Means for the Movento, Movento/Dyne-Amic mixture, and Industry Standard treatments (applied at the 2 and 4 leaf stages only) were averaged over the four annual trials (n = 4). Data were transformed from percentages by arcsine √ before analysis of variance was performed, and means were separated by a protected least significant difference test (PROC GLM, SAS Institute Inc., Cary, NC). Means presented in Figure 1 were converted back to their original percentages.
Adjuvants and Spray Timing on Aphid Contamination
In 2007, aphid numbers were relatively low, but measurable differences among the insecticide treatments were observed. The harvest evaluation showed that the addition of a penetrating adjuvant, Dyne-Amic, enhanced Movento's efficacy against green peach aphids relative to all other treatments (Table 2). Aphid numbers were very low on Movento/Dyne-Amic treated leaves and were considered commercially acceptable for the fresh-cut baby spinach market. Movento applied to spinach without the addition of the adjuvant, regardless of spray timing, did not reduce aphid contamination relative to the untreated check. Because of the low tolerance of aphid infested spinach leaves by spinach buyers and shippers, those plots treated with only Movento (without an adjuvant) were infested with too many aphids to be considered commercially marketable. The industry standard had fewer aphids than the untreated control, but would have been considered only marginally acceptable for the fresh market due to aphid numbers. No phytotoxicity to treated leaf tissue was recorded. In 2008, several foliar additives were evaluated as spray adjuvants with Movento to determine if they could enhance the insecticides efficacy similar to the Dyne-Amic mixture observed the previous year. These products are foliar additives commonly used in commercial and organic spinach production (Table 1). At harvest, aphid contamination in the untreated control was very high (Table 3). Similar to the 2007 trial, the addition of the penetrating surfactant Dyne-Amic with Movento improved insecticide efficacy against green peach aphids compared with the untreated check. Contamination of marketable spinach leaves treated with the Movento/Dyne-Amic mixture was negligible and considered commercially acceptable for the fresh-cut market. Although all the other spray treatments reduced aphid numbers compared to the untreated check, green peach aphids were found on the marketable-sized spinach leaves at levels that were not commercially acceptable. No phytotoxicity was observed in any of the treatments.
Table 2. Green peach aphid contamination on baby spinach plants at harvest, 10 March 2007.
x Means followed by the same letter are not significantly different (P > 0.05, F-protected LSD).
y Assail (4 oz/acre) at the 2-leaf stage; Beleaf (2.8 oz/acre) applied at the 4-leaf stage.
Table 3. Green peach aphid contamination on baby spinach plants at harvest, 2 March 2008 (all spray treatments were applied at the 2- and 4 lf stages).
x Means followed by the same letter are not significantly different (P > 0.05, F-protected LSD).
y All spray treatments applied at the 2- and 4-leaf stages.
z Assail (4 oz/acre) at the 2-leaf stage; Beleaf (2.8 oz/acre) applied at the 4-leaf stage.
Aphid numbers were low in 2009 when applications were first initiated, but rapidly increased thereafter. At harvest, all treatments had lower aphid numbers than the untreated control, but aphid contamination among the Movento treatments varied with spray timing. The Movento/DyneAmic mixtures applied at the 2- and 4-leaf stages, and at the 4 leaf stage only, as well as the Movento+Aliette treatment applied at the 2- and 4-leaf stages provided the most commercially acceptable aphid control. Plants treated with Movento minus an adjuvant, as well as the industry standard, had fewer aphids than the untreated. However, leaves examined from these spray treatments were contaminated with green peach aphids at levels that were not considered marketable. No phytotoxicity was observed in any of the treatments.
In 2010, a final trial was designed to evaluate the efficacy of different Movento/adjuvant mixtures and spray timings on green peach aphid contamination on baby spinach plants. Aphid numbers were very heavy throughout the trial, and similar to 2009 trial, plants treated with the Movento/adjuvant mixtures had less aphid contamination than the untreated control (Table 5). Spray timing also influenced control, and again showed that the Movento/Dyne-Amic mixture applied at the 2- and 4-leaf stages, and at the 4-leaf stage only, as well as the Movento+Aliette treatment applied at the 2 and 4 leaf stages, provided the most commercially acceptable control. Aphid contamination on plants treated with Movento without an adjuvant and the industry standard was not different from the untreated control. No phytotoxicity resulted from any of the spray treatments.
Table 4. Green peach aphid contamination on baby spinach plants at harvest, 2 March 2009.
x Means followed by the same letter are not significantly different, AOV; protected LSD (P > 0.05).
y Beleaf (2.8 oz) applied at the 2-leaf stage; Assail (4 oz) applied at the 4-leaf stage.
Table 5. Green peach aphid contamination on baby spinach plants at harvest, 10 March 2010.
x Means followed by the same letter are not significantly different, AOV; protected LSD (P > 0.05).
Conclusions and Recommendations
These experiments clearly demonstrate that the addition of a penetrating adjuvant (i.e., Dyne-Amic) with Movento spray applications significantly enhanced its insecticidal activity against green peach aphids in fresh-market, baby spinach. Because Movento is primarily toxic to sucking pests through ingestion and has minimal contact toxicity (5), we presume that the addition of the methylated seed oil (MSO) enhanced the rapid entry of Movento into spinach leaves and its subsequent systemic movement within the plant's vascular system. Furthermore, the acropetal and basipetal systemic activity allowed the toxin to move to older, infested plant growth as well as to newly expanding leaf tissue. This likely explains why aphid contamination at harvest was negligible in plants treated with a single application of the Movento/Dyne-Amic mixture later in plant growth on larger plants. For example, in two of the trials the application of the Movento/Dyne-Amic mixture at the 4 leaf stage provided the same level of commercially acceptable control as the same mixture applied at both the 2- and 4-leaf stages. It is also important that no crop injury resulting from phytoxicity to marketable baby spinach leaves at harvest was observed on any of the spinach treated with the Movento/adjuvant sprays throughout this study.
In contrast, Movento applied to baby spinach without an adjuvant resulted in unacceptable levels of aphid contamination in each trial, regardless of spray timing. None of the other Movento/ adjuvant mixtures, with the exception of Aliette, provided commercially acceptable aphid control. Aliette was included in these evaluations because of the compounds known systemic properties (12). When used in combination with Movento in 2009 and 2010, aphid control was significantly enhanced but spray timing appeared to be important for this mixture. Significant aphid control with the Movento/Aliette mixture was only accomplished when two sprays were applied compared to a single spray with the Movento/Dyne-Amic mixture.
The industry standard insecticides Beleaf and/or Assail applied at the 2- and 4-leaf stages did not provide commercially acceptable protection from aphid contamination in these studies. Although these products are effective against green peach aphids with both contact and ingestion activity through translaminar activity in leaf tissue (8,9), sustained control on spinach was not observed. Because the baby spinach plants can quickly outgrow treated leaf tissue, control of green peach aphids with non-systemic compounds generally require repeated spray applications prior to harvest. Typically, growers apply 4-6 sprays applications to prevent aphid contamination in baby spinach crops grown in the desert southwest during the spring (Eric Dreidger, Crop Protection Services, Yuma, AZ, personal communication). This level of spray intensity with the industry standard insecticides has been required due to the extremely low tolerance for aphid contamination allowed on marketable leaves under current grower and shipper demands (2). For example, in some cases, shippers may require growers maintain a zero tolerance for aphids on the final product.
It can be reasonably concluded from this study that the addition of a penetrating adjuvant with Movento spray applications can significantly enhance its systemic activity against green peach aphid in baby spinach (Fig. 3). Without a penetrating adjuvant, aphid control with Movento was marginal at best and not commercially acceptable. Thus, given the consistent results of this study, as well as the lack of crop injury observed, it is recommended that growers use Movento with a penetrating adjuvant (e.g., MSO/OS blend at 0.25 to 0.375 % v/v) and apply the mixture after the development of the 2nd to 3rd leaf stage when aphid colonization is detected. This appears to be a significantly more cost-effective management approach to preventing aphid contamination in baby spinach relative to the prophylactic spray routine currently used by the industry. Ultimately however, spinach growers must decide whether the perceived risk of crop injury using a MSO or other penetrating adjuvant outweighs the benefit of economic aphid control provided by Movento/adjuvant mixtures in baby spinach.
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