Crop Protection Research Institute The Benefits of Insecticide Use: Spinach Aphids on Spinach Parasitized Aphids Leafminer Damage Plowing Spinach Under Due to Aphid Presence March 2009 Leonard Gianessi CropLife Foundation 1156 15th Street, NW #400 Washington, DC 20005 Phone 202-296-1585 www.croplifefoundation.org Fax 202-463-0474
Key Points Because of consumer complaints about insects in spinach, the FDA will seize spinach shipments that contain excessive numbers of aphids. In the 1940s it was common for growers to plow under about 20% of the spinach acres in Arkansas/Oklahoma/Texas because aphid populations were so high. Leafminer tunneling make spinach unmarketable. Although a fungus has proven effective in tests to kill the aphid, its use has not been adopted since the dead aphids adhere to the spinach which results in processor rejection. Technical Summary California growers produce 647 million pounds of spinach with a value of $176 million on 42000 acres. In the three states of Arkansas, Oklahoma, and Texas approximately 8,000 acres of spinach are grown with two-thirds of the acres going to processed production and one-third to the fresh market. Texas accounts for about all the fresh market spinach in the region and 75% of the processed. The processed harvest is approximately 100 million pounds/year with a value of $4 million while 25 million pounds of spinach with a value of $11 million are harvested for the fresh market. The three state region accounts for 5% of fresh market spinach grown in the U.S. and 40% of the total for the processed market. Three crops (fall, overwintered, and spring) are produced for processing in the Arkansas River Valley each year. Crystal City, Texas calls itself the spinach capital of the world and a statue of Popeye stands in front of City Hall. Approximately 86% of the processing spinach acres are treated with insecticides [11]. Approximate cost of insecticides are $94/A for processing spinach [12]. Green Peach Aphid Because of processing industry requirements, savoyed (i.e. crinkled leaf) cultivars are grown preferentially. Compared with flat leaf spinach, savoyed leaves offer advantages that include color and firmness [1]. However, the savoy attribute represents disadvantages for the spinach grower and processor. The broad, deeply crinkled leaves provide shelter for the green peach aphid, the major insect pest of spinach in the southcentral states [1]. The green peach aphid feeds by sucking juice from the spinach plant. Aphid populations seldom reach sufficient levels to reduce spinach yield [2][3]. The principal concern surfaces when aphids are detected in the processed spinach product in the can. The broad and crinkled leaves of spinach make removal of aphids by washing at processing plants extremely difficult [3]. Although flat leaf spinach is widely-planted in Texas and aphids are more easily washed off, large aphid populations in harvested spinach can require multiple costly washings in the processing plant. In the 1930s the FDA was made aware of consumer complaints regarding the presence of aphids in canned spinach and adopted a standard of 500 aphids per pound of spinach. In
1972 the FDA adopted the current standard which is set at 250 aphids per pound of spinach [4]. Canned or frozen spinach that exceed this standard are subject to seizure due to adulteration of a food product. It is believed that processor standards are more stringent than the FDA s and that processors strive for no aphids in the can. As a result, entire spinach fields may be rejected by the processor if aphids are detected at harvest [3]. In the 1940s surveys indicated that approximately 20% of the spinach acres in the Arkansas/Oklahoma region were not harvested due to aphid infestations at harvest time [8].The spinach pack in Arkansas in 1950 was reduced from an estimated 3 million to 100,000 cases due to the presence of insects [9]. Insecticide spraying is initiated when numbers reach 1-2 aphids per leaf. As harvest nears, the threshold for spraying is reduced. In Texas approximately 80% of the spinach acreage develops aphid problems one in every four years requiring treatment [5]. These fields receive 2-3 insecticide applications. Research with the insecticide most widelyused for green peach aphid control (imidacloprid) showed a reduction from 98 aphids/3 plants untreated to 9 aphids/three plants with the treatment [6]. In the 1980s, significant variation in levels of aphid infestation was observed on spinach breeding lines. A study was undertaken to explore the potential for using host plant resistance as an aphid management tool [7]. Research demonstrated that aphids on certain spinach lines required a longer period to reach reproductive age and produced fewer young than aphids held on other commercial varieties [7]. However, the spinach resistance work was dropped because the green peach aphid has such a broad a host range that the population can develop on other crops before moving into the spinach crop. Diseased aphids had been noticed for many years in the Arkansas River Valley and a study was initiated to determine to what extent fungi could be used as a management option [3]. Nine of ten fields that were sampled had aphids infected with the fungus Erynia neoaphidis. In fields with high numbers of aphids, the population decline due to fungal infections occurred at or after the normal spinach harvest. Aphids killed by the fungus were held tightly to spinach foliage and the spinach was rejected by the processor due to difficulty in washing the aphid cadavers from the product [3]. Beneficial insects can have a limited effect on aphid population development during the fall and spring. Beneficial activity, however, is more limited during much of the cool season in which spinach is grown [10]. Leafminers Leafminers are the most important insect pests of spinach grown in California. Three species predominate: serpentine leafminer, vegetable leafminer, and pea leafminer [14]. Leafminers exist in all spinach producing areas of California, and with the exception of December and January, leafminers are present throughout the year. Leafminer populations are highest and cause the greatest harm during the late summer and fall [13].
Adult leafminers puncture leaves to feed on sap- creating bumpy, unsightly holes called stings [16]. Females puncture leaves to feed and lay eggs within the tissues. After 2 to 4 days, eggs hatch. Larvae feed between the upper and lower surface of the leaves, making distinctive, whitish tunnels or mines. Larvae emerge from the mines. Many generations occur each year and the entire life cycle can be completed in less than 3 weeks when the weather is warm. Excessive mining renders leaves unmarketable, reduces photosynthetic capacity, and provides easy access for disease organisms [15]. Fields of spinach are abandoned due to excessive leafminer damage. Because leafminers feed within the leaf, they are protected from most predators. Sprays of azadirachtin are acceptable on organically-grown spinach [15].Insecticide cost for conventional spinach growers are about $31/A [17]. Recently, USDA researchers have produced two parent spinach lines with resistance to leafminers [16].Although the plants are not resistant to the stings of the adult leafminers, they have many fewer mines than other lines of spinach. The new spinach plants are not market ready; germplasm has been made available to researchers and breeders for further work [16]. References 1. McLeod, Paul and Alfredo Gonzalez, A Rotary Leaf Washer for Sampling Myzus persicae (Homoptera: Aphididae) on Spinach, Journal of Economic Entomology, 81(2):741-742, 1988. 2. McLeod, Paul, Aphid Dynamics on Overwintering Spinach, Arkansas State Horticultural Society, Proceedings of the 106 th Annual Meeting, 1985. 3. McLeod, Paul, et al., Prevalence of Erynia neoaphidis (Entomophthorales: Entomophthoraceae) Infections of Green Peach Aphid (Homoptera: Aphididae) on Spinach in the Arkansas River Valley, Environmental Entomology, 27(3): 796-800, 1998. 4. Revision of Defect Action Levels for Spinach, Department of Health, Education, and Welfare, Food and Drug Administration, 1972. 5. Holloway, Rodney L., Kent D. Hall, and Dudley T. Smith, Crop Profile for Spinach in Texas, revised 2003, Available at http://www.pestdata.ncsu.edu/cropprofiles/docs/txspinach.html. 6. Edelson, J.V., Spinach: Comparison of Soil Applications of Insecticides to Control Aphids, 2003, Arthropod Management Tests, 2003. 7. McLeod, Paul, T.E. Morelock, and M.J. Goode, Preference, Developmental Time, Adult Longevity and Fecundity of Green Peach Aphid (Homoptera: Aphididae) on Spinach, Journal of Entomological Science, 26(1):95-98, January 1991.
8. Harding, J. A., Tests Comparing Insecticides for the Control of Thrips on Spinach, Journal of Economic Entomology, Vol. 52, No. 3, June 1959. 9. Austin, H. L., Canned Spinach, Worms, and Politics, in Association of Food and Drug Officials of the United States, Quarterly Bulletin, Volume XVI, Number 1, January 1952. 10. Sweeden, M.B. and P.J. McLeod, Aphicide Persistence on Spinach and Mustard Greens, Journal of Economic Entomology, 90 (1): 195-198, February 1997. 11. USDA, Agricultural Chemical Usage, 2000 Vegetable Summary, NASS, July 2001. 12. Table 30A. Estimated Costs and Returns per Acre, Processed Spinach, Irrigated, 2006 Projected Costs and Returns per Acre, Texas Extension Service. 13. Crop Profile for Spinach in California, United States Department of Agriculture, Office of Pest Management Policy & Pesticide Impact Assessment Program, Prepared September 28, 1999, http://pestdata.ncsu.edu/cropprofiles/detail.cfm?factsheets_recordid=198 14. LeStrange, Michelle, Steve Koike, Jesus Valencia, and William Chaney, Spinach Production in California, University of California: Division of Agriculture and Natural Resources, Publication 7212, 1996. 15. How to Manage Pests: UC Pest Management Guidelines, Spinach Leafminers, UC IPM Online: Statewide Integrated Pest Management Program, http://www.ipm.ucdavis.edu/pmg/r732300311.html, Updated November 2005. 16. Spinach: Protecting and Enhancing this Nutrition Superstar, Agricultural Research, United States Department of Agriculture: Agricultural Research Service, October 2007. 17. Takele, Etaferahu, Spinach Production: Sample Costs and Profitability Analysis, University of California: Agriculture and Natural Resources, 2001, Publication 8032.