Aluminum-Coated Plastic for Repulsion of Cucumber Beetles

Commercial Horticulture Newsletter, January - February 1998

John S. Caldwell
Department of Horticulture
Virginia Tech (0327)
Blacksburg, VA 24061

Paul Clarke
Albemarle County

Introduction.

Striped, Acalymma vittata (Fabricius), and spotted, Diabrotica undecimpunctata howardi Barber, cucumber beetles (Coleoptera: Chrysomelidae) are major pests of cucurbits in Virginia, especially for biological farmers who do not use insecticides (Caldwell et al., 1995). Feeding damage on young cucurbit seedlings can be serious in May and June. Bacterial wilt is transmitted by these beetles and can cause serious problems when insecticides are not used. Incidence of virus in squash is especially high in August in Virginia. In the Northern Neck of Virginia, average losses due to viruses were 70-80% of marketable yield of sample farms in 1997, and up to 100% in the worst case (Sam Johnson, Extension Agent, personal communication, 1998). Virus diseases on cucurbits include Cucumber mosaic virus (CMV), Squash mosaic virus (SqMV), Zucchini yellow mosaic virus (ZYMV), and Watermelon mosaic virus 2 (WMV2). CMV, WMV2, and ZYMV are transmitted by aphids, but SqMV is transmitted by cucumber beetles (Matthews, 1991).

Aluminum-coated plastic has been known for many years to repel aphids, reduce and delay the incidence of aphid-transmitted virus diseases, and increase total and marketable yield (Brown et al., 1993; Brown et al., 1996; Chalfant et al., 1977; Conway et al., 1989; Lancaster et al., 1987). It has also been shown in one study to reduce the incidence of striped and spotted cucumber beetles (Schalk et al., 1979), but it has not been widely been used for cucumber beetle control. In 1996, there appeared to be few cucumber beetles in an observational plot of squash planted into aluminum-coated plastic (P. Clarke, personal observation). In 1997, we therefore established an experiment to determine the extent to which aluminum-coated plastic repelled cucumber beetles.

Materials and Methods.

Sixteen rows with three types of plastic were laid in May 1997 on a field in Albemarle County, Virginia, that had been planted in cucurbits for the preceding five years. The three types of plastic were: black plastic (1 mil thickness, Tredigard, Richmond, Virginia); aluminum-coated plastic with a solid silver reflective appearance (1.5 mil thickness, Clarke Ag Plastics, silver over clear); and black plastic onto which two aluminum-coated strips each 8 in (20 cm) wide were attached with 1" x 6" x 1/8" size staples, with 1-2 ft (0.30-0.61 m) between the strips. The plastic was laid on rows with 5 ft (1.52 m) centers and 150 ft (45.72 m) length, in sets of four rows wide with a 10 ft (3.05 m) space between each set. Each four-row set was divided into three 50 ft (15.24 m) long sections, and one type of plastic was randomly assigned to each section, for four replications of the three plastic treatments. In each replication, two rows were planted in squash cv. General Patton (Asgrow Seed) and two rows were planted in cucumber cv. Meteor (Asgrow Seed). Both crops were direct-seeded into the three types of plastic on May 8 (initial seeding) and 24 (spot reseeding), 1997.

From June 5 to July 24, yellow sticky-card traps (Olsen Products, through Great Lakes IPM, Vestaburg, Michigan) were attached weekly with 1/4 in (6 mm) staples on 4 ft (1.22 m) tomato stakes at a height 2 ft (0.61 m) above the soil line. Each trap had dimensions of 6 in x 6 in (15 cm x 15 cm). One week later, numbers of striped and spotted cucumber beetles on both sides of the traps were counted, for a total of 8 sampling dates. Esfenvalerate (>Asana,= produced by DuPont) was applied at the rate of 6 fl oz. 0.66 EC/ac (438 ml ha-1) when counts in a given treatment exceeded 15 beetles total of both species combined. Squash and cucumber fruits were harvested 14 times from July 2 to August 6.

Differences between treatments in numbers of cucumber beetle counts, numbers of squash and cucumber fruits, and numbers of boxes of squash fruit were analyzed by analysis of variance and orthogonal contrasts (black plastic vs. aluminum; solid aluminum vs. aluminum strips) (PROC GLM of the Statistical Analysis System); insect counts were transformed using _ (x + 0.5) prior to analysis. Partial budgeting was used to determine potential economic benefits. The cost of insecticidal application included the cost of rental of a tractor, sprayer, and driver (calculated for the time to apply to 1 ac), in addition to the cost of the insecticide. The cost of aluminum strips included labor time to cut a roll of aluminum plastic and apply the strips, in addition to the cost of both types of plastic and staples for attachment.

Results and discussion.

For cucumbers, there were the highly significant differences in striped cucumber counts on June 19 between the solid aluminum (7 beetles / trap) and strips (15 beetles / trap) compared to black plastic (42 beetles / trap). There were 6 times as many beetles in the black plastic compared to the solid, and nearly 3 times as many as in the strips. A similar trend for spotted cucumber beetles was seen on June 12, 19, 26 and July 2, but the differences were not statistically significant on any of these dates (fig. 1; table 1).

More dramatic differences were seen in squash. Both striped and spotted cucumber beetle counts were significantly higher on black plastic on June 12, 19, and 26 (table 2) than on solid aluminum and aluminum strips. Counts on June 19 and 26 were 4.9 and 5.5 times higher in black plastic (40 and 23 beetles / trap) than in the solid aluminum (8 and 5 beetles / trap), and 2.6 and 2.3 times higher than in the strips (15 and 10 beetles / trap). Smaller but still significant differences were similarly seen for spotted cucumber beetles. The concentration of striped cucumber beetles on black plastic is particularly striking on June 19 and 26. Although counts of cucumber beetles on these two dates were higher on strips than on solid silver, the differences between strips and solid were not statistically significant (fig. 2; table 2).

When combined with our preliminary threshold of 15 beetles / trap (based on a visual threshold of 1 beetle / plant first established in Indiana (Brust et al., 1996; Foster and Flood, 1995), and then derived from trials comparing sticky trap and visual counts in Westmoreland County 1996 (Caldwell and Johnson, unpublished data), these results show that both strips and solid aluminum can reduce high populations of cucumber beetles below threshold levels.

An average of 1.8 insecticidal applications were needed on black plastic, and 0.8 insecticidal applications were needed on aluminum strips. The cost of black plastic and insecticidal applications on it ($186 ac^-1) was $102 less than the cost of aluminum-coated plastic ($288 ac^-1). However, its use permitted fruit to be marketed as pesticide-free, at a price 25% higher ($10 / box for squash) than fruit on which pesticide has been applied ($8 / box). Using an average yield in Virginia 600 boxes per acre of squash, this translates to a $1,200 increase in revenue. This increase compares favorably with the added $102 of expense for using solid aluminum plastic.

Even higher revenue could be obtained with the yields obtained in this trial of 1567 boxes / ac. There were no significant differences among treatments in overall yield, although yield in the first week of harvest was reduced by 38% on aluminum (185 boxes / ac) relative to black plastic (297 boxes / ac) (trend at 0.05 < p < 0.10) (fig. 3). This delay in yield was likely due to the soil warming properties of black plastic.

The use of reflective aluminum-coated plastic mulch could have several benefits for both conventional and organic vegetable growers. For conventional growers, it could give them an alternative to insecticidal application that would enable them to market pesticide-free produce and thereby increase income. For organic growers, repulsion of cucumber beetles could enable them to avoid bacterial wilt transmission. In addition, the repulsive effect of reflective aluminum-coated plastic may also reduce virus transmission by both cucumber beetles and aphids.

In this experiment, cucumber beetles faced a field with a mosaic of appearances. Plots with solid aluminum, solid black, and aluminum strips on black were all adjacent to one another. More research is needed to determine whether beetles would be repelled from a field planted entirely in silver-coated plastic, or whether the repulsion is relative. In the latter case, black plastic might be placed in occasional rows in the field as a trap strategy, to concentrate beetles in those rows, and preferential pesticide application be made on those rows only.

Literature cited

Caldwell, J.S., J-P. Amirault, and A.H. Christian. 1995. Insect pests, beneficial insects, and cover crops of biological farmers. HortScience 30(4):806 (Abstr).

Brown, J. E., J. M. Dangler, F. M. Woods, and K. M. Tilt. 1993. Delay in mosaic virus onset and aphid vector reduction in summer squash grown on reflective mulches. HortScience 28(9):895-896.

Brown, J. E., R. P. Yates, C. Stevens, V. A. Khan, and J. B. Witt. 1996. Reflective mulches increase yields, reduce aphids and delay infection of mosaic viruses in summer squash. J. Veg. Crop Production 2(1):55-60.

Brust, G. E., R. E. Foster, and W. G. Buhler. 1996. Comparison of insecticide use programs for managing the striped cucumber beetle (Coleoptera: Chrysomelidae) in muskmelon. J. Economic Entomol. 89(4):981-986.

Chalfant, R. B., C. A. Jaworski, A. W. Johnson, and D. R. Sumner. 1977. Reflective film mulches, millet barriers, and pesticides: effects on watermelon mosaic virus, insects, nematodes, soil-borne fungi, and yield of yellow summer squash. J. Amer. Soc. Hort. Sci. 102(1):11-15.

K. E. Conway, B. D. McCraw, J. E. Motes, and J. L. Sherwood. 1989. Evaluations of mulches and row covers to delay virus diseases and their effects on yield of yellow squash. Applied Agr. Res. 4(3):201-207.

Foster, R., and B. Flood (eds.). 1995. Vegetable insect management. Meister Publishing Co., Willoughby, Ohio.

Lancaster, D. M., H. K. Whitam, and L. L. Black. 1987. Reflective mulch delays virus spread in summer squash. Louisiana Agr. Exp. Stn. 30(3):16-17.

Matthews, R.E.F. 1991. Plant Virology. 3rd edition. Academic Press, San Diego, CA.

Schalk, J. M., C. S. Creighton, R. L. Fery, W. R. Sitterly, B. W. Davis, T. L. McFadden, and A. Day. 1979. Reflective film mulches influences insect control and yield in vegetables. J. Amer. Soc. Hort. Sci. 104(6):759-762.

Table 1. Effects of black plastic, solid aluminum, and aluminum strips on populations of striped and spotted cucumber beetles on yellow sticky traps in cucumber, Clarke Farm, Albemarle, Virginia, 1997.

Sampling date	Black plastic vs. solid aluminum and strips			Aluminum strips vs. solid aluminum
	Spotted	Striped	Both	Spotted	Striped	Both
12 June 1997	*	NS	*	NS	NS	NS
19 June 1997	NS	**	**	NS	NS	NS
26 June 1997	NS	NS	NS	NS	NS	NS
2 July 1997	NS	NS	NS	NS	+	NS
10 July 1997	NS	**	+	NS	NS	NS
17 July 1997	+	*	*	NS	NS	+
24 July 1997	NS	NS	NS	NS	NS	NS

Statistical significance: probability of differences occurring naturally, not due to treatments
	NS + * **	Not significant 10% (trend) 5% 1%

Return to Results and Discussion.

Table 2. Effects of black plastic, solid aluminum, and aluminum strips on populations of striped and spotted cucumber beetles on yellow sticky traps in squash, Clarke Farm, Albemarle, Virginia, 1997.

Sampling date	Black plastic vs. solid aluminum and strips			Aluminum strips vs. solid aluminum
	Spotted	Striped	Both	Spotted	Striped	Both
12 June 1997	*	*	*	+	NS	NS
19 June 1997	*	**	**	NS	+	NS
26 June 1997	**	*	*	NS	NS	NS
2 July 1997	NS	+	NS	NS	NS	NS
10 July 1997	NS	NS	NS	NS	NS	+
17 July 1997	*	NS	NS	**	+	**
24 July 1997	NS	NS	NS	NS	NS	NS

Statistical significance: probability of differences occurring naturally, not due to treatments
	NS + * **	Not significant 10% (trend) 5% 1%

Return to Results and Discussion.

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