Crop Protection 62 (2014) 72e78 Contents lists available at ScienceDirect Crop Protection journal homepage: www.elsevier.com/locate/cropro Incidence of cabbage maggot (Diptera: Anthomyiidae) infestation and plant damage in seeded Brassica fields in California’s central coast Shimat V. Joseph a,*, Jesus Martinez a,b a University of California Cooperative Extension, 1432 Abbott Street, Salinas, CA 93901, USA b Hartnell College, 411 Central Ave., Salinas, CA 93901, USA article info abstract Article history: The temporal incidence of cabbage maggot, Delia radicum L. was investigated using three exclusion cage Received 21 February 2014 experiments, one each during spring, summer and fall, in broccoli fields as well as two surveys, one each Received in revised form in three broccoli fields, and sixteen turnip plantings in central coast of California. In the cage experi- 10 April 2014 ments, sets of broccoli plants were exposed to natural populations of D. radicum flies for w14-d periods Accepted 11 April 2014 after plant emergence throughout the growing season. For the surveys, soil, root samples, and yellow Available online sticky traps were collected every week from broccoli fields to determine number of eggs, maggots, feeding-injury and adults. Only roots were sampled from turnip plantings to determine feeding-injury. In Keywords: fi Delia radicum all three cage experiments, feeding injury from D. radicum maggot was less during the rst 14-d than w e Brassicaceae 15 28 d after plant emergence (DAE). In the summer and fall, feeding injury by D. radicum was less Root maggot during 29e42 and 43e56 DAE than it was 15e28 DAE. In the survey of broccoli fields, a greater number Broccoli of D. radicum eggs were detected starting the fourth week after planting (WAP). Similarly, an increase in Salinas Valley number of D. radicum maggots and feeding injury was observed at fifth and sixth WAP, respectively. Reduced-risk insecticide However, adults were abundant throughout the growing period. In the turnip survey, increase in injury from D. radicum feeding did not appear until the fifth WAP. Overall, these studies indicate that increased incidence of D. radicum was delayed by about two to three weeks after plant emergence. The implications of these results for timing of insecticide application for D. radicum in the central coast of California are discussed. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction L.), broccoli raab (Brassica rapa L. subspecies rapa), and Brussels sprouts (Brassica oleracea L. var. gemmifera). Because cruciferous Cabbage maggot, Delia radicum (L.) (Diptera: Anthomyiidae) is crops are produced year round in the California central coast, one of the most destructive pests of cruciferous crops in North cabbage maggot could persist in the agricultural crops. They could America and Europe (Coaker and Finch, 1971) and has become the persist in weeds even when there are no crops under favorable major persistent pest of cruciferous crops in the central coast of conditions (Johnsen and Gutierrez, 1997). California. D. radicum causes severe yield losses to cruciferous crops Cabbage maggot flies lay eggs in the soil around the base of the in the central coast of California. The value of cruciferous crops is plant. A single female can lay about 300 eggs under laboratory estimated at w1 billion USD in California (U.S. Department of conditions (Finch, 1974). Legless, 8-mm long white-maggots feed Agriculture, NASS, 2013). In the Salinas Valley of California, crucif- on the taproot and affect normal plant development. After about 3 erous crops are grown in more than 34,398 ha and are valued at weeks of feeding, the maggot pupates in the surrounding soil and >$485.5 million USD (Monterey County Crop Report, 2012). The remains at this stage for 2e4 weeks before emerging into an adult majority of this acreage has been affected by cabbage maggot. fly(Harris and Svec, 1966). The most common above-ground Important crops that are at-risk from cabbage maggot include feeding symptoms of cabbage maggot are yellowing, stunting and broccoli (Brassica oleracea var. italica Plenck), cauliflower slow growth (Natwick, 2009). (B. oleracea L. var. botrytis), cabbage (Brassica oleracea L. var. capitata In other Brassica growing regions where cabbage maggot is known to cause economic injury to roots, pupae undergo diapause during the winter, which enabled several studies to accurately fl * Corresponding author. Tel.: þ1 831 759 7359; fax: þ1 831 758 3018. determine emergence of overwintering adult ies in the spring and E-mail address: [email protected] (S.V. Joseph). precise timing of subsequent generations (Baok et al., 2012; Broatch http://dx.doi.org/10.1016/j.cropro.2014.04.016 0261-2194/Ó 2014 Elsevier Ltd. All rights reserved. S.V. Joseph, J. Martinez / Crop Protection 62 (2014) 72e78 73 et al., 2006; Coaker and Wright,1963; Collier et al.,1988; Collier and through them and a transverse cut was made to each cup to facil- Finch, 1985; Dreves et al., 2006; Eckenrode and Keith, 1972; Finch itate placement and removal of cups (Fig. 1b and c). The fabric was et al., 1986; Finch and Collier, 1983, 1985; Jyoti et al., 2003; glued length-wise around the cup from end to end of the transverse Walgenbach et al., 1993). However, unlike other regions where cut and the rest of the fabric was wrapped around the cup. The cabbage maggot is a serious pest, the winter weather in California’s fabric roll formed on the top of the cage was tied using a twist-tie. central coast is mild and rarely goes below freezing point, thereby Within w7-d after planting, seeds germinated and emerged out failing to trigger diapause in most of the cabbage maggot popula- of the soil surface. At the cotyledon stage (Fig. 1a), cages were tion (Johnsen and Gutierrez, 1997). It is proposed that this unique deployed over individual broccoli plants (Fig. 1b). As the plant grew environment enables cabbage maggot flies to remain active even in in size, the rolled fabric on the top of the sleeve cage was untied and winter months, producing multiple overlapping generations carefully re-tied to the base of the stem, leaving the growing point throughout the year. In order to determine and implement appro- outside the cage (Fig. 1c) but preventing cabbage maggot fly priate integrated pest management (IPM) tactics for cabbage oviposition at the base of the plant. The cages were secured by maggot, it is critical to understand the biology of the cabbage pushing the bottom edges into the soil. Treatments included plants maggot on cruciferous crops in California’s central coast. (n ¼ 50/treatment) that were never exposed (i.e. always caged), Current management practices for cabbage maggot in Brassica always exposed (i.e. never caged), or exposed to natural cabbage crops mainly involved the use of soil-applied organophosphate maggot populations by selective cage removal in w14-d intervals insecticides, such as chlorpyrifos and diazinon (Natwick, 2009), starting from plant emergence. All treatments were blocked along which rarely provides100% control. This persistent use of organo- the beds. The number of beds used was 12 with 57.3 m between phosphate insecticides has resulted in higher concentrations of blocks and 8.1 m between cages for spring; 5 with 29.3 m between insecticide residues in the water bodies of California’s central coast blocks and 4.2 m between cages for summer; and 5 with 22.3 m (Hunt et al., 2003), which pose risks to non-target organisms and between blocks and 3.2 m between cages for fall experiments. public health through contaminated water. It is likely that this Seeds were planted on 27 February, 14 May and 28 August and the widespread use potentially provided the opportunity for cabbage plants were caged on 7 March, 23 May, and 28 August 2013 for maggot to develop resistance to broad-spectrum insecticides. Since spring, summer, and fall experiments, respectively. Exposure pe- 2008, regulatory agencies in the state have enforced stringent re- riods began on 25 March, and 15 and 24 April for spring; 1 May, 7 strictions to curb the use of organophosphate insecticides in com- and 21 June, and 5 and 19 July for summer; and 20 September, 4 and mercial Brassica crop production, leaving growers with limited 18 October, and 1 and 14 November for fall experiments. All the options to combat cabbage maggot infestation (CEPA, 2013). exposure periods lasted 14 days except for those deployed on 15 Because of the fewer effective IPM options, widespread crop losses and 24 April, which exposed plants for 19 and 13 days, respectively. to cabbage maggot have been reported from 2008 to the present. Following each treatment (exposure period), plants were re-caged In this post organophosphate era with reduced-risk, less and remained in the field for another 14-days until harvested; persistent insecticides being available for cabbage maggot man- however, the set of plants in the last exposure treatment in all three agement, knowledge of field-level incidence of cabbage maggot experiments was harvested once the exposure period was infestation is critical to determine precise timing for insecticide completed along with harvest of never and always exposed applications in Brassicas. The major objective of the study is to treatments. determine the temporal incidence of cabbage maggot relative to seeded broccoli and turnip in California’s central coast. Our hy- 2.2. Survey of commercial broccoli pothesis is that seasonal periods in the field crop cycle can be identified that represent greater susceptibility to cabbage maggot A survey was conducted in three commercial broccoli fields in damage which will help to temporally target insecticide the Salinas Valley (one field in Chualar [cultivar ‘Durapak’] and two treatments. fields [cultivars ‘Durapak’, and ‘Imperial’] in Gonzales CA) during May, June, and July 2013.