We found them. Referring back to the previous post, as our readers know we've been looking for spotted wing drosophila pupae under fruit in raspberries, and now on the second read have confirmed that they are indeed pupating within a centimeter of the fallen fruit. In the meantime, the pupae collected on the first read have eclosed and the adults are SWD.
Pictures below. Really nice work on the part of Staff Research Associate Monise Sheehan on figuring this out.
Looking to do a bigger run of the same late this summer and then get a nice paper written about it.
Mark here. I'm including below really nice overview of the current ag labor issue in California by colleague Laura Tourte. The intensity of work and dependence of our agriculture on labor here on the Central Coast make this topic really relevant and, given the looming changes in cost and availability, pretty important to understand well.
Growers often report – and researchers generally agree – that labor shortages exist in agriculture along the Central Coast and elsewhere in California, and that labor costs are rising. The reasons are for this situation are complex and multifaceted. Here are some considerations:
- The fresh market crops that dominate agricultural production along the Central Coast are labor intensive. Weeding, pruning and training, irrigation and harvest are examples of practices that are especially labor intensive.
- Labor represents between almost 30 and 60 percent of total production and harvest costs, depending upon the crop and crop cycle. It may be even higher for some crops grown elsewhere in California.
- Labor costs are rising, in part because of changing regulations associated with minimum wage, overtime, health care, paid sick leave and non-productive time, but also because there is a shortage of agricultural labor along with an increased demand for workers.
- Increased labor and production costs can strain and negatively impact the already thin profit margins associated with some crops.
- Immigration constraints and tightened border enforcement have reduced the number of agricultural workers from Mexico—the primary source of labor—that are seeking work in the area and state. The expanding agricultural industry in Mexico has also reduced the number of workers seeking employment here.
- The agricultural labor force is aging and more settled, and have families and other connections to local communities. Because of this, experienced workers do not migrate with the crop production and harvest cycles as often as in the past.
- Most harvest and other labor intensive practices for fresh market crops have not yet been highly mechanized or automated because of important “sensory attributes”—particularly sight and touch—that humans bring to agricultural work. Some commercially available technology already exists, and public and private research efforts are underway to mechanize or automate other labor intensive practices. Mechanical aids are also being used if available, or are being developed, with the goal of improving labor efficiency.
- Some of the area's farmers now supplement their labor forces with foreign guest workers using the federal H-2A program. The program has expanded rapidly in California in recent years increasing from roughly 3,000 certified farm jobs in fiscal year 2012 to 15,000 in fiscal year 2017. However, the program's recruitment process, requirements and associated costs limit it as a viable option for some growers.
- Affordable housing for farm workers is often lacking or constrained. Efforts to address housing issues are in discussion and in progress in the area.
The full impact of labor shortages and rising labor costs is not yet known. The Race in the Fields: Imports, Machines and Migrants, a California Agriculture article by Philip Martin, Professor Emeritus of Agricultural and Resource Economics at UC Davis considers whether current conditions will result in rising imported produce, mechanization, or more foreign guest workers in agriculture. It is also one of the sources of information for this blog article, along with other articles from California Agriculture. http://calag.ucanr.edu/. Cost information is from various cost and return studies, which can be found at https://coststudies.ucdavis.edu.
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.
One of the unsolved mysteries of our work in berries has been what of the pupae of spotted wing drosophila? As anyone who has worked with this fly in the lab knows, many larvae exit the fruit and pupate outside, either on the surface of the fruit or on the floor and walls of the container in which they are being held.
In the field however, it's been very rare to find the pupae. We don't see them on the leaves or fruit hanging on the plant, and one generally doesn't find them on the surface of the soil.
Following the lead of a group of scientists out of Maine on blueberry, my research assistant Monise and I are going to attempt to solve this issue once and for all. We first confirm that a fallen fruit has at least one larvae in it, and then covering each of these with a centrifuge tube with airholes punched in the sides, taking care to push the tube about an inch into the ground (see picture below). Since we are engaged in science and not a quest to confirm our own bias, we accompany these tubes with an equal number of tubes without fruit in them. After about a week, Monise will recover these tubes, separate the fruit from soil and look in both for the pupae.
Here's a first for me, maybe for a lot of you as well. By way of colleague Laura Tourte, we have an example of Chobani Yogurt being marketed as a having a taste of a specific strawberry variety in it - in this case the UC variety Monterey. Really intriguing to see this and something to think about.
Photo courtesy Laura Tourte, UCCE.