- Author: Christian Nansen, Elvira de Lange, Alison Stewart, Department of Entomology and Nematology, UC Davis
- Author: Mark Edsall, California Strawberry Commission
- Author: Surendra K. Dara
The western tarnished plant bug (or lygus bug) and different species of spider mites are major arthropod pests in California strawberries. While predatory mite releases are very popular for controlling spider mites in both organic and conventional fields, a significant amount of chemical pesticides are used for arthropod pest management in conventional fields. Nearly 280,000 pounds of active ingredient of at least 30 chemical and botanical pesticides were used in 2016 in California strawberries (USDA-NASS, 2016; CDPR, 2017) and malathion, bifenazate, naled, acequinocyl, and fenpropathrin were the most common of about 79,000 pounds of chemical pesticides. A uniform and thorough coverage of pesticide sprays is essential for effective pest management and also for reducing excessive pesticide use that could lead to resistance and environmental health issues (Shi et al., 2013). Evaluation of pesticide spray applications and their performance will help improve current pest management strategies in strawberry as they did in other crops (Nansen et al., 2011; Nansen et al., 2015).
Several factors such as the tractor speed, spray nozzles, spray volume, boom height, adjuvants, pressure, canopy characters, micro and macroclimatic conditions influence the spray coverage. A better understanding of these factors will help improve the pesticide use and efficacy, optimize the cost, and reduce pesticide drift and other associated risks (Nansen and Ridsdill-Smith, 2013).
A study was conducted during 2016 and 2017 to evaluate multiple spray configurations under varying weather conditions where more than 4000 data points were collected. Data for only two spray configurations, using Albuz ATR 80 Lilac and Albuz ATR 80 Green nozzles, are shown here.
Configuration 1: Albuz ATR 80 Lilac nozzles were used in 144 experimental applications delivering 32-80 gallons of spray volume per acre. Water-sensitive spray cards (TeeJet, Wheaton, IL) were clipped to the petioles of strawberry leaves in horizontal and vertical orientation (1 card per application for each orientation). They were placed in the strawberry canopy prior to spray applications and the coverage was determined based on the pattern on the cards using the SnapCard smartphone application. Data suggested that spray volume does not always translate into a good spray coverage (Fig. 1). There was a wide variation in the coverage that ranged from 0-55% at 33 gpa and 5-80% at 80 gpa suggesting the influence of other factors. Taking the operational and weather conditions into account, a multiple linear regression analysis was conducted to measure the relationship between predicted and observed spray coverage which appeared to have a linear correlation (Adjusted R2=0.27; F+52.6; P < 0.001) (Fig. 2). Wind speed, wind gust, ambient temperature, pressure, and tractor speed were used as explanatory variables in this analysis. Based on this regression model, four possible scenarios were developed with predicted spray coverage values (Table 1). A 2 mph increase in the wind speed from 6 mph to 8 mph could reduce the spray coverage from 61 to 45% when the tractor runs at 1 mph or from 30 to 13% when the tractor runs at 2 mph.
Configuration 2: Albuz ATR 80 Green nozzles were used in 276 experimental applications delivering 180-440 gallons of volume per acre. Since the droplet size from the Green nozzle is much larger than that from the Lilac nozzle, a better coverage is expected with the presumption of lesser sensitivity to environmental and operating conditions. However, data from the spray cards indicated a poor relationship between the spray volume and coverage under this configuration as well (Fig. 3). For example, both 200 and 350 gpa had a similar spray coverage. Multiple linear regression analysis, using strawberry canopy characteristics (plant height and width, dry weight, and canopy coverage), operating and weather conditions as explanatory variables, showed a significant linear correlation (Adjusted R2=0.45; F=199.5; P < 0.001) between observed and predicted spray coverages (Fig. 4). A prediction model under this configuration showed nearly 20% decline in spray coverage when the tractor speed increased from 1 to 2 mph (Table 2). Wind speed appeared to have a minimal impact, probably due to the droplet size.
This study demonstrates the importance of weather and operating conditions on spray coverage. Additional data will be collected in 2018 to expand our understanding of the factors that influence spray coverage. These studies will be useful to determine appropriate operating conditions such as the spray volume, tractor speed, and types of nozzles and identify weather conditions that are ideal to achieve good coverage. A free smartphone application is under development for the growers and PCAs to input weather and operating conditions to predict the spray coverage. This information will ultimately improve the pest control efficacy and contribute to sustainable pest management practices.
Acknowledgments: We thank the financial support of the California Strawberry Commission and the collaboration of several growers. We also thank the technical assistance of Daniel Olivier, Marianna Castiaux, and Ariel Zajdband, California Strawberry Commission and Robert Starnes, Jessie Liu, Laurie Casebier, Haleh Khodaverdi, and Isaac Corral, UC Davis.
CDPR. 2017. Summary of pesticide use report data 2016: California Department of Pesticide Regulation, p. 909.
Nansen C, Ferguson JC, Moore J, Groves L, Emery R, Garel N and Hewitt A. 2015. Optimizing pesticide spray coverage using a novel web and smartphone tool, SnapCard. Agronomy for Sustainable Development: 1-11. DOI: 10.1007/s13593-015-0309-y.
Nansen C & Ridsdill-Smith TJ (2013) The performance of insecticides – a critical review: Insecticides (ed. by S Trdan) InTech Europe, Croatia, pp. 195-232.
Nansen C, Vaughn K, Xue Y, Rush C, Workneh F, Goolsby J, Troxclair N, Anciso J, Gregory A, Holman D, Hammond A, Mirkov E, Tantravahi P and Martini X (2011) A decision-support tool to predict spray deposition of insecticides in commercial potato fields and its implications for their performance. Journal of Economic Entomology 104: 1138-1145. DOI: 10.1603/EC10452.
Shi M, Collins PJ, Ridsdill-Smith TJ, Emery RN and Renton M. 2013. Dosage consistency is the key factor in avoiding evolution of resistance to phosphine and population increase in stored-grain pests. Pest Management Science 69: 1049–1060. DOI: 10.1002/ps.3457.
USDA_NASS. 2016. Quick stats.
- Author: Surendra K. Dara
Adult and nymphs of the green peach aphid, Myzus persicae (Photo by Jack Kelly Clark, UC IPM)
Different species of aphids infest celery and celeriac crops in California. The black bean aphid, Aphis fabae, the foxglove aphid, Aulacorthum solani, the green peach aphid, Myzus persicae, the hawthorn or parsley aphid, Dysaphis apiifolia, and the cotton/melon aphid, Aphis gossypii are among the aphids that could cause damage. Damage includes distorted or stunted plant growth at high numbers, vectoring viral diseases, and contamination of the produce with honeydew secretion and debris.
A study was conducted at Babe Farms, Santa Maria to evaluate the efficacy of various chemical pesticides against aphids. Field was planted in celeriac variety Brilliant on 15 June, 2016. Treatments included i) untreated control, ii) Actara 4 oz/ac, Beleaf 50 SG 2.8 oz/ac, iii) Sequoia 4.5 fl oz/ac, v) Sivanto 200 SL 14 fl oz/ac, and vi) Actara 4 oz + Beleaf 2.8 oz + Radiant SC 8 fl oz/ac as the grower standard. Induce was used as a surfactant at 0.25% vol/vol rate. Treatments were administered on 14 and 25 July and 6 August in 80 gallons/acre of spray volume using a standard spray equipment. Each treatment had eight 38” wide and 100' long beds that were replicated four times and arranged in a randomized complete block design.
Experimental design - six treatments replicated four times
Pre-treatment aphid counts were taken on 13 July and post-treatment counts were taken on 22 and 29 July and 9 August, 2016. On each observation date, 20 random plants from the middle two rows of each plot were gently beaten with the lid of a plastic container and aphids dislodged into the container were recorded.
Data were analyzed using Analysis of Variance model in Statistix software and significant means were separated using Tukey's HSD test.
Only green peach aphids were seen on celeriac during the study. Their numbers were very low and uniform (P = 0.15) before the treatments were initiated (Table 1). After the first spray, there were no aphids in plots treated with Beleaf and it was significantly lower (P =0.0009) than untreated control and Actara treatment. Sequoia was the next best treatment, but it had significantly lower aphids than Actara treatment. Due to a sampling error, data collected after the second spray were excluded from the study. After the third spray, aphid numbers declined only in plots treated with Beleaf and Sequoia and increased at varying degrees in other treatments. Significantly lower (P < 0.00001) number of aphids were present in Beleaf and Sequoia than Actara, Sivanto, and Actara+Beleaf+Radiant treatments. Combination of different chemicals appeared to perform worse than some of the chemicals that were applied independently.
Mean number of aphids per plant (above) or 20 sampled plants (below) before and after pesticide treatments
When percent change in aphid numbers from pre-treatment counts to the counts after the third spray were compared, Beleaf was the only treatment that caused a 33% reduction. Sequoia treatment limited the population build up to a minimum level compared to the rest of the treatments.
Percent change in aphid numbers from pre-treatment counts to post-third spray application
This study demonstrated the efficacy of different chemical pesticides against green peach aphid in celeriac. It was not clear why the combination of some chemicals failed to bring down aphid populations, but results warrant caution while choosing compounds for tank mixes. It is important to avoid repeated use of the best chemical compounds to reduce the risk of resistance development. Select some of the effective chemicals and use them in combination or rotation with botanical and microbial pesticides. Regular monitoring, adopting cultural practices that might reduce pest populations, conservation of biological control agents, and timely application of botanical, microbial, and chemical pesticides, and other appropriate measures are critical components of a sound integrated pest management program.
This study was originally designed for evaluating the efficacy of chemical pesticides against the western tarnished plant bug (lygus bug), Lygus hesperus, which is becoming a problem in vegetable crops such as lettuce, celery, and celeriac. Random sampling in some areas of the field, prior to the initiation of the study, showed a few western tarnished bugs, but due to their negligible numbers thereafter, meaningful results could not be obtained from the study.
Acknowledgements: Thanks to Jason Gamble, Babe Farms, Santa Maria for his collaboration, Bayer CropSciences, Dow AgroSciences, FMC, and Syngenta for the support of the study, and Tamas Zold and Danielle Cadena for the technical assistance.