Economic Threshold for Three Lepidopterous Larval Pests of Fresh-Market Cabbage in Southeastern New Brunswick

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1 HORTICULTURAL ENTOMOLOGY Economic Threshold for Three Lepidopterous Larval Pests of Fresh-Market Cabbage in Southeastern New Brunswick P. M. MALTAIS, 1 J. R. NUCKLE, 1 AND P. V. LEBLANC 2 J. Econ. Entomol. 91(3): 699Ð707 (1998) ABSTRACT Economic thresholds for the management of imported cabbageworm, Pieris rapae (L.), diamondback moth, Plutella xylostella (L.), larvae, and cabbage looper, Tricoplusia ni (Hübner), on cabbage, Brassica oleracea L., were evaluated at Bouctouche, New Brunswick, Canada, in 1992, 1993, and Six treatments were tested in 1992: an untreated control; a weekly application of insecticide after insects appeared; a weekly application of insecticide after heading; and an insecticide application when thresholds of 0.25, 0.50, or 1.0 cabbage looper equivalent per plant per week were reached. Eight treatments were tested in 1993 and 1995: an untreated control; a biweekly application of insecticide when insects appeared; a biweekly application of insecticide after heading; and an insecticide application when thresholds of 0.10, 0.15, 0.20, 0.25, or 0.50 cabbage looper equivalent per plant per week were reached. Generally, on average, for similar marketable yields, plots using the 0.10 cabbage looper equivalent threshold needed 3 fewer insecticide applications compared with plots treated biweekly after insects appeared. In 1995, revenues for the 0.10 cabbage looper equivalent threshold treatment were $9.49 per hectare greater than those for the biweekly treatments beginning after insects appeared. KEY WORDS Pieris rapae, Plutella xylostella, Tricoplusia ni, cabbage, economic threshold 1 Current address: Department of Biology, Université de Moncton, Moncton, NB, E1A 3E9 Canada. 2 Current address: Agriculture and Agri-Food Canada, Senator Hervé J. Michaud Research Farm, Box 667, Bouctouche, NB, E0A 1G0 Canada. FRESH-MARKET CABBAGE, Brassica oleracea L., represents 27% of the total annual commercial cole crop production of New Brunswick, Canada (Anonymous 1996). However, because cole crop acreage in this province is relatively small (460 ha) compared with the potato, Solanum tuberosum L., acreage (20,400 ha), pest management strategies have been developed for potato and not for cole crops (Maltais et al. 1994). The principal lepidopterous larval pests of cabbage in eastern Canada are the imported cabbageworm, Pieris rapae (L.), the diamondback moth, Plutella xylostella (L.), and the cabbage looper, Tricoplusia ni (Hübner). No thresholds for cabbage are used in New Brunswick. Growers generally rely on insecticide applications on a regular basis without regard to larval densities on the crop. This technique often results in poorly timed or unnecessary applications of pesticide. Several management strategies based on action thresholds have been suggested for cabbage. Because these strategies are economically and environmentally desirable, they offer the possibility of reducing insecticide use compared with standard Þxed-schedule spray programs (Morisak et al. 1984). Thresholds for cabbage vary from region to region and according to the proportion of each larval species on the crop (Stewart and Sears 1988). Thus, various researchers have tested thresholds based on damage, insect density, or the proportion of plants infested with larvae. By using insect counts, Greene (1972) concluded that a threshold of 0.10 cabbage looper per plant resulted in damage-free marketable cabbage. Similarly, Shelton et al. (1982), working with diamondback moth, cabbage looper, and imported cabbageworm larvae, suggested that a threshold of 0.50 cabbage looper equivalent per plant during head formation results in 95% marketable yields. Kirby and Slosser (1984) suggested a composite threshold of 0.30 larvae per plant produced 80% marketability. Cartwright et al. (1987) found the level of 0.30 larvae per plant to be useful in commercial cabbage Þeld and small-plot tests that included the cabbage looper, the diamondback moth, and the beet armyworm, Spodoptera exigua (Hübner). Chalfant et al. (1979) and Workman et al. (1980) suggested thresholds based on visual ratings of leaf damage. This technique resulted in savings in sampling time and reductions in insecticide sprays and was as effective as larval counts with no loss of marketability. Morisak et al. (1984) reported that a management program that uses thresholds based on the proportion of infested plants is effective. Sears et al. (1985) concluded that thresholds based on feedingdamage evaluations, proportion of infested plants, or larval counts resulted in marketable yields similar to treatments that used a fortnightly schedule while requiring fewer insecticide applications. Eastman et al. (1995) advocated the use of variable percentagesplants-infested at different growth stages of cabbage as threshold treatments for the caterpillar complex on crops in the midwestern United States /98/0699Ð0707$02.00/ Entomological Society of America

2 700 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 91, no. 3 Fig. 1. Mean populations of lepidopterous larvae on cabbage, expressed as cabbage looper equivalents per plant per week, managed with (a) control, (b) weekly sprays after insects appeared, (c) weekly sprays after heading, and thresholds of (d) 0.25, (e) 0.50, or (f) 1.0 cabbage looper equivalent per plant per week for the 1992 planting, Bouctouche, NB. Dashed lines indicate threshold; arrowheads indicate insecticide application. All the previous studies were conducted in locations where population levels of lepidopterous larvae tend to be higher than in our province. We concur with Shelton et al. (1982), who developed action thresholds for lepidopterous pests of fresh-market and processing cabbage in upstate New York, that thresholds developed elsewhere, mainly in the southern states, may be unrealistic for our northern areas. The objectives of our study were to establish an economic threshold based on visual counts for cabbage loopers, diamondback moth larvae, and imported cabbageworms on fresh-market cabbage in southeastern New Brunswick, and to compare costs and revenues of programs using economic thresholds with programs using weekly or biweekly insecticide treatments.

3 June 1998 MALTAIS ET AL.: THRESHOLD FOR LEPIDOPTERA ON CABBAGE 701 Table 1. Mean number of cabbage looper equivalents per plant per week ( SD) for cabbage managed with different spray schedules, Bouctouche, NB Treatment C W BW WH BWH 0.10 CLE 0.15 CLE 0.20 CLE 0.25 CLE 0.50 CLE 1.0 CLE Planting a b Ñ ab Ñ Ñ Ñ Ñ ab ab a a Ñ d Ñ b cd bcd bc b b Ñ a Ñ c Ñ bc bc bc bc b bc Ñ C, control; W and BW, weekly and biweekly sprays after insects appeared; WH and BWH, weekly and biweekly sprays after heading; 1 CLE 1 cabbage looper 1.5 imported cabbageworms 5 diamondback moth larvae. Means within a row followed by the same letter are not signiþcantly different (P 0.05; LSD, Steel and Torrie [1980]). Materials and Methods Experiments were conducted at the Agriculture and Agri-Food Canada Senator Hervé J. Michaud Research Farm in Bouctouche, NB, Canada, in 1992, 1993, and Four- to 6-wk-old cabbage seedlings were transplanted on 29 June 1992 (ÔBartoloÕ), 16 June 1993 (Bartolo), and 1 June 1995 (ÔMinicoleÕ). Plants were spaced 35 cm apart in 8-row plots each with 16 plants per row and with 100 cm between rows in 1992 and 1993 and in 6-row plots with 15 plants per row with the same spacing in The 4 center rows of each plot were used for the test, and the outer rows were untreated buffer rows. The 1st and last 2 plants of each row were not evaluated. All plots were treated with fensulfothion (Dasanit 720 SC [soluble concentrate]; Chemagro, Mississauga, Ontario) at a rate of 1.8 kg (AI)/ha at planting to prevent damage by root maggots (Diptera). Plots were replicated 3 times in 1992 and 4 times in 1993 and 1995 in a randomized complete block design. In 1992, the 6 treatments were as follows: an untreated control, a weekly application of insecticide from heading to harvest, a weekly application of insecticide after insects appeared, and insecticide applied when thresholds of either 0.25, 0.50, or 1.0 cabbage looper equivalent per plant per week were reached. One cabbage looper equivalent equals 1 cabbage looper, 1.5 imported cabbageworms, or 5 diamondback moth larvae as determined by Harcourt et al. (1955) and modiþed by Stewart and Thompson (1988). Eight treatments were used in 1993 and 1995: an untreated control, a biweekly application of insecticide from heading to harvest, a biweekly application of insecticide after insects appeared, and insecticide applied when thresholds of either 0.10, 0.15, 0.20, 0.25, or 0.50 cabbage looper equivalent per plant per week were reached. For all plantings, the insecticide used was permethrin (Ambush 500 EC [emulsiþable concentrate], Chipman Chemical, Stoney Creek, Ontario) (70 g [AI]/ha) applied with a 10-nozzle side boom tractor-mounted sprayer calibrated to deliver 1,050 liter/ha at 700 kpa. Lepidopterous pests were monitored on a weekly basis during the growing season (6 JulyÐ4 October 1992, 24 JuneÐ30 September 1993, and 6 JuneÐ14 August 1995) by using a nondestructive 10-plant sample from the middle 4 rows from each plot. Cabbage yield data and insect damage estimates were collected by harvesting 30 heads per plot in 1992 and 1993, and 10 heads per plot in Heads were considered unmarketable if any insect damage was incurred to any portion of the head, wrapper leaves excluded. Data were subjected to analysis of variance (ANOVA) (Sokal and Rohlf 1981), and the means were separated using Fisher (protected) least significant difference (LSD) test (Steel and Torrie 1980). Marketability (%) was converted to arcsine x before analysis. The economics associated with managing lepidopterous larvae on cabbage were estimated in U.S. dollars for the 8 treatments tested in Field monitoring and insecticide application costs were estimated according to Maltais et al. (1994). On

4 702 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 91, no. 3 Table 2. Mean yield of cabbage ( SD) managed with different spray schedules, 1992, Bouctouche, NB Treatment No. of sprays Head Wt, g Diam, cm Marketability, % a Control 0 1, c Weekly sprays 13 1, a Weekly after heading 7 1, a 0.25 CLE 3 1, a 0.50 CLE 1 1, b 1.0 CLE 0 1, c Means followed by the same letter are not signiþcantly different (P 0.05; LSD, Steel and Torrie [1980]). a Arcsine % transformation. the basis of visiting 15 plants per Þeld of up to 3 ha weekly from transplantation to harvest, total scouting costs were estimated at $ per hectare per season for 13 visits of 67.5 min each. Permethrin application costs were estimated at $38.74 per application per hectare. For each treatment, crop yield (CY) was determined by using the following formula: CY M/100 E Wt, where M is percentage of marketable heads per treatment, E is the estimated number of marketable heads per hectare assuming no insect damage, and Wt is the average weight of a head of cabbage (Stewart and Sears 1988). At spacings of 1 m between rows and 0.35 m within rows, E was estimated at 24,285 heads per hectare, 85% of the total number of cabbage heads per hectare. Crop value was estimated by multiplying the crop yield by the unit price for cabbage in 1996, $0.22 per kilogram (Anonymous 1996). Results and Discussion In 1993 and 1995, the proportions of diamondback moth larvae and imported cabbageworms found on cabbage in the Bouctouche area were the opposite of those reported by Stewart and Sears (1988) on caulißower for southern Ontario, but similar to those reported by Maltais et al. (1994) on broccoli for southeastern New Brunswick. Cabbage looper population proportions, however, were similar to those reported by Stewart and Sears (1988). During this study, population proportions for diamondback moth, imported cabbageworm, and cabbage looper were 77.6, 21.4, and 1.0%, respectively, in 1993 and 87.5, 11.2, and 1.3%, respectively, in In 1992, the weekly application of insecticide after insects appeared treatment, with 13 sprays (Fig. 1b), had a signiþcantly lower (P 0.05) mean cabbage looper equivalent per plant per week than the 1.0 cabbage looper equivalent treatment or the control (Table 1). This result, however, was not signiþcantly different (P 0.05) from that of the weekly application of insecticide from heading to harvest, 0.25, and 0.50 cabbage looper equivalent treatments (Table 1), all of which received less insecticide (Table 2; Fig. 1 cðe). The mean cabbage looper equivalent per plant per week was not signiþcantly different (P 0.05) for the control and the 1.0 cabbage looper equivalent threshold treatment because both did not receive any insecticide (Fig. 1 a and f). Even though insect populations were lower for that treatment, the weekly application of insecticide from heading to harvest treatment, with 7 insecticide applications (Fig. 1c), did not result in a signiþcantly lower cabbage looper equivalent per plant per week than that of the 0.25 or 0.50 cabbage looper equivalent threshold treatment (Table 1), which received fewer sprays (Table 2; Fig. 1 d and e). All treatments of the 1993 planting had signiþcantly lower (P 0.05) mean cabbage looper equivalents per plant per week than the control (Table 1), and except for the biweekly application of insecticide after insects appeared and 0.10 cabbage looper equivalent threshold treatments, were not signiþcantly different (P 0.05) from one another (Table 1). With 6 sprays (Fig. 2b), the biweekly application of insecticide after insects appeared treatment recorded lower insect populations but this did not result in a cabbage looper equivalent threshold signiþcantly lower (P 0.05) than that of the 0.10 and 0.15 threshold treatments, both of which received fewer sprays (Table 3; Fig. 2 d and e) than the biweekly application of insecticide after insects appeared treatment. All treatments of the 1995 planting had signiþcantly lower (P 0.05) mean cabbage looper equivalents per plant per week than the control (Table 1). As in 1993, the biweekly application of insecticide after insects appeared treatment of 1995 recorded the greatest number of sprays (Table 4; Fig. 3b), but the mean cabbage looper equivalent per plant for this treatment was signiþcantly lower only from that of the 0.25 cabbage looper equivalent treatment (Table 1). Low insect populations during that growing season required minimal insecticide applications (Table 4). No signiþcant differences (P 0.05) in head weight or head diameter of plants were observed among treatments of either the 1992 (Table 2), 1993 (Table 3), or 1995 (Table 4) plantings. Head weight and head diameter of plants managed with thresholds were similar to those of plants treated weekly or biweekly. There were signiþcant differences (P 0.05) in the percentage of marketable heads among treatments of every planting (Tables 2Ð4). The untreated controls always had the lowest values for marketability, ranging from 9 to 56.7%. The biweekly application of insecticide after insects appeared treatments of 1993 (Table 3) and 1995 (Table 4) resulted in the highest market-

5 June 1998 MALTAIS ET AL.: THRESHOLD FOR LEPIDOPTERA ON CABBAGE 703 Fig. 2. Mean populations of lepidopterous larvae on cabbage, expressed as cabbage looper equivalents per plant per week, managed with (a) control, (b) biweekly sprays after insects appeared, (c) biweekly sprays after heading, and thresholds of (d) 0.10, (e) 0.15, (f) 0.20, (g) 0.25, or (h) 0.50 cabbage looper equivalent per plant per week for the 1993 planting, Bouctouche, NB. Dashed lines indicate threshold; arrowheads indicate insecticide application.

6 704 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 91, no. 3 Table 3. Mean yield of cabbage ( SD) managed with different spray schedules, 1993, Bouctouche, NB Treatment No. of sprays Head Wt, g Diam, cm Marketability, % a Control 0 1, e Biweekly sprays 6 1, a Biweekly after heading 3 1, c 0.10 CLE 3 1, ab 0.15 CLE 2 1, bc 0.20 CLE 2 1, bc 0.25 CLE 1 1, bc 0.50 CLE 1 1, d Means followed by the same letter are not signiþcantly different (P 0.05; LSD, Steel and Torrie [1980]). a Arcsine % transformation. able yields, ranging from 98 to 100%. Among the threshold treatments, the 0.10 cabbage looper equivalent treatment of 1993 (Table 3) and 1995 (Table 4) resulted in the highest marketable yields whereas the 0.50 cabbage looper equivalent treatment, the lowest. Because maximum marketability (100%) was obtained with biweekly sprays, we concur with Greene (1972) that weekly applications of insecticide (after insects appeared or from heading to harvest) on cabbage are less efþcient than biweekly applications. Even though cabbage received the same number of sprays (Table 3; Fig. 2 c and d), the biweekly application of insecticide from heading to harvest treatment in 1993 was less effective in the control of lepidopterous pests than the 0.10 cabbage looper equivalent treatment. Timing of insecticide applications is critical if pest populations are to be properly managed. Because there was no scouting in this treatment, populations had already peaked and damage had occurred before the insecticide was Þrst applied (Fig. 2c). Maximum marketable yields were obtained from the biweekly application of insecticide from heading to harvest treatment in 1995 (Table 4) because, of the 4 insecticide applications, 2 were applied during population peaks (Fig. 3c). The omission of preheading sprays in plantings where no scouting is done may reduce the number of insecticide applications on cabbage but will fail to produce consistently as high-quality yields as biweekly sprays after insects appear (Workman et al. 1980). Preheading sprays kill larvae before damage occurs. These data do not agree with Shelton et al. (1982) who suggested that larval populations can build before head formation without loss of marketability. Sears et al. (1985) reported that larvae can rapidly move into the head when it starts to form, or larvae develop on wrapper leaves Þrst, then invade the head, making it more difþcult to manage these pests. The economics associated with managing insect pests on cabbage in 1995 are presented in Table 5. Because there were no signiþcant differences among treatments (P 0.05) (Table 4), head weight of plants from all treatments except the control were averaged to calculate crop yield. Total pest control costs were greater for the biweekly application of insecticide after insects appeared treatment than for any other treatment because it received the most sprays (Table 5). Scouting costs were the same for all the threshold treatments. The 0.10 and 0.15 cabbage looper equivalent threshold treatments had greater total pest control costs because they received more sprays than the other scouted treatments. Crop yield was proportional to marketability. Because plants managed with biweekly treatments (after insects appeared or from heading to harvest) or with the 0.10 cabbage looper equivalent threshold (Table 4) had the highest percentage of marketable heads, crop yield and crop value were also greatest for those treatments (Table 5). The biweekly application of insecticide from heading to harvest treatment, with $6,256.28, had the highest revenues, $29.25 more than the 0.10 cabbage looper equivalent threshold treatment. For the scouted treatments, revenues decreased with increasing thresholds. Table 4. Mean yield of cabbage ( SD) managed with different spray schedules, 1995, Bouctouche, NB Treatment No. of sprays Head Wt, g Diam, cm Marketability, % a Control d Biweekly sprays 5 1, a Biweekly after heading 4 1, a 0.10 CLE b 2 1, a 0.15 CLE 2 1, a 0.20 CLE 1 1, b 0.25 CLE 1 1, bc 0.50 CLE 1 1, c Means followed by the same letter are not signiþcantly different (P 0.05; LSD, Steel and Torrie [1980]). a Arcsine % transformation. b 1 CLE 1 cabbage looper 1.5 imported cabbageworms 5 diamondback moth larvae.

7 June 1998 MALTAIS ET AL.: THRESHOLD FOR LEPIDOPTERA ON CABBAGE 705 Fig. 3. Mean populations of lepidopterous larvae on cabbage, expressed as cabbage looper equivalents per plant per week, managed with (a) control, (b) biweekly sprays after insects appeared, (c) biweekly sprays after heading, and thresholds of (d) 0.10, (e) 0.15, (f) 0.20, (g) 0.25, or (h) 0.50 cabbage looper equivalent per plant per week for the 1995 planting, Bouctouche, NB. Dashed lines indicate threshold; arrowheads indicate insecticide application.

8 706 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 91, no. 3 Table 5. Costs and revenues (U.S. dollars) associated with managing lepidopterous larvae on cabbage with different spray schedules, Bouctouche, NB, 1995 Biweekly sprays Thresholds a Costs and revenues Control After insects appear After heading Insecticide costs b Scouting costs c Total pest control costs d Crop yield e 8,391 29,142 29,142 29,142 28,413 24,800 23,314 20,458 Crop value f 1, , , , , , , , Revenues g 1, , , , , , , , a Expressed as cabbage looper equivalents per plant per week. One CLE 1.0 cabbage looper 1.5 imported cabbageworms 5.0 diamondback moth larvae. b Permethrin applied at 140 ml/ha. Figures include product and application costs ($/ha). c Wages, beneþts, and traveling expenses of one scout and one-fourth supervisor for Þelds averaging 3 ha ($/ha). d Total pest control costs insecticide costs scouting costs ($/ha). e Crop yield M/100 E Wt (kg/ha). f Crop value crop yield US $0.22/kg ($/ha). g Revenues crop value total pest control costs ($/ha). Thus, the 0.50 cabbage looper equivalent threshold treatment, with 70% marketable yields, had revenues $1, per hectare less than the 0.10 cabbage looper equivalent threshold treatment, which had 100% marketable yields. Even though the biweekly application of insecticide from heading to harvest treatment had greatest revenues, it did not consistently produce high yields from year to year (78% in 1993, 100% in 1995). These data indicate that the use of economic thresholds for the management of lepidopterous pests on cabbage is as effective as biweekly sprays applied beginning when insects appear, and that if populations are kept below a threshold of 0.10 cabbage looper equivalent per plant per week from when insects appear until harvest, revenues are more than those of biweekly sprays for cabbage grown in southeastern New Brunswick (Table 5). It is important that scouting be maintained according to a rigorous schedule and that sprays be applied as soon as the designated threshold is reached if management of insect pests on cabbage is to produce maximum marketable yields. Acknowledgments We thank M. Caissie, N. Caissie, A. Rossignol, J. Landry, A. Noël, and C. Ouellette for their technical assistance. We express our deep gratitude to G. R. Thébeau (New Brunswick Agriculture and Rural Development, Bouctouche, New Brunswick) for his able assistance in this study. Support for this research was provided by the Canada-New Brunswick Cooperation Agreement on Agri-Food Development project No. B6001-R1. Extensive support also was given by Agriculture and Agri-Food Canada, the New Brunswick Department of Agriculture and Rural Development, and the Faculté des études supérieures et de la recherche, Université de Moncton, Moncton, New Brunswick. References Cited Anonymous Agricultural Statistics. Province of New Brunswick, Fredericton, NB. Cartwright, B., J. V. Edelson, and C. Chambers Composite action thresholds for the control of lepidopterous pests on fresh-market cabbage in the Lower Rio Grande Valley of Texas. J. Econ. Entomol. 80: 175Ð181. Chalfant, R. B., W. H. Denton, D. J. Schuster, and R. B. Workman Management of cabbage caterpillars in Florida and Georgia by using visual damage thresholds. J. Econ. Entomol. 72: 411Ð413. Eastman, C., S. Mahr, J. Wyman, C. Hoy, and H. Oloumi- Sadeghi Cabbage, broccoli, and caulißower, pp. 99Ð110. In R. Foster and B. Flood [eds.], Vegetable insect management with emphasis on the Midwest. Meister, Willoughby, OH. Greene, G. L Economic damage threshold and spray interval for cabbage looper control on cabbage. J. Econ. Entomol. 65: 205Ð208. Harcourt, D. G., R. H. Backs, and L. M. Cass Abundance and relative importance of caterpillars attacking cabbage in eastern Ontario. Can. Entomol. 87: 400Ð406. Kirby, R. D., and J. E. Slosser Composite economic threshold for three lepidopterous pests on cabbage. J. Econ. Entomol. 77: 725Ð733. Maltais, P. M., J. R. Nuckle, and P. V. LeBlanc Economic threshold for management of lepidopterous larvae on broccoli in southeastern New Brunswick. J. Econ. Entomol. 87: 766Ð774. Morisak, D. J., D. E. Simonet, and R. D. Lindquist Use of action thresholds for management of lepidopterous larval pests of fresh-market cabbage. J. Econ. Entomol. 77: 476Ð482. Sears, M. K., A. M. Shelton, T. C. Quick, J. A. Wyman, and S. E. Webb Evaluation of partial plant sampling procedures and corresponding action thresholds for management of Lepidoptera on cabbage. J. Econ. Entomol. 78: 913Ð916. Shelton, A. M., J. T. Andaloro, and J. Barnard Effects of cabbage looper, imported cabbageworm, and diamondback moth on fresh market cabbage and processing cabbage. J. Econ. Entomol. 75: 742Ð745. Sokal, R. R., and F. J. Rohlf Biometry, 2nd ed. Freeman, New York. Steel, R.G.D., and J. H. Torrie Principles and procedures of statistics, a biometrical approach, 2nd ed. McGraw-Hill, New York.

9 June 1998 MALTAIS ET AL.: THRESHOLD FOR LEPIDOPTERA ON CABBAGE 707 Stewart, J.G.G., and M. K. Sears Economic threshold for three species of lepidoptera larvae attacking caulißower grown in southern Ontario. J. Econ. Entomol. 81: 1726Ð1731. Stewart, J. G., and L. S. Thompson Action thresholds for control of leaf-feeding insects on broccoli. Pest Management Research Report 68. Agriculture and Agri-Food Canada, Ottawa, Ontario. Workman, R. B., R. B. Chalfant, and D. J. Schuster Management of the cabbage looper and diamondback moth on cabbage by using two damage thresholds and Þve insecticide treatments. J. Econ. Entomol. 73: 757Ð758. Received for publication 14 May 1996; accepted 13 February 1998.