Organic methods for managing cucumber beetles (Acalymma vittatum Fab. and Diabrotica undecimpunctata Barber) were examined in the production of watermelon [Citrullus lanatus (Thunb.)] and muskmelon (Cucumis melo L.) using sticky traps to monitor beetle populations. Organic methods included the use of Al-coated plastic mulch, companion plants, pyrethrin insecticide, and row covers. In 2002, populations of striped and total (striped + spotted ) cucumber beetles were significantly (P < 0.05) reduced by combined use of three companion plants [radish (Raphanus sativus L.), tansy (Tanacetum vulgare L.), and nasturtium (Tropaeolum spp. L.) thought to repel cucmber beetles or by combined use of plants (buckwheat [Fagopyrum esculentum Moench], cowpeas [Vigna unguiculata (L.)], and sweetclover [Melilotus officinalis (L.)] known to attract beneficial insects. The companion plant treatment consisted of the combined use of radish and buckwheat in 2003 and 2004. In 2003, use of Al-plastic and companion plants, significantly (P < 0.05) increased muskmelon yields and vine cover, while significantly (P < 0.05) reducing populations of striped, spotted and total cucumber beetles. Use of pyrethrin insecticide reduced beetle populations to a lesser extent than companion plants and did not affect muskmelon yields or vine cover. In 2004, effects of companion plant and Al-plastic treatments on muskmelon yields and vine cover were also significant (P < 0.05) and similar to those in 2003. However, these treatments only affected early season beetle populations. Yield increases in Al-plastic and companion plant treatments appeared additive when they were combined in a single treatment. Use of row covers significantly (P < 0.05) increased muskmelon yields and vine cover in 2003 and 2004 but did not affect beetle populations after row cover removal. It was concluded that use of companion plants and Al-plastic mulch increased muskmelon yields and vine cover while reducing populations of cucumber beetles. Use of row covers also increased muskmelon yields and vine cover, but it was unclear how row covers affected muskmelon production or if row cover effects were related to cucumber beetles.
1. Compare organic methods for managing cucumber beetles in watermelon, including use of reflective mulches, beneficial insects, trap crops, cover crops, and companion plants.
2. Develop an organic system for managing cucumber beetles with muskmelon including combinations of management methods in a systems-oriented approach.
3. Determine direct and systemic toxic effects of pawpaw extracts on striped cucumber beetles.
4. Determine insecticidal effects of pawpaw extract on cucumber beetles in muskmelon.
To accomplish objectives 1 and 2, field experiments were conducted during the growing season, whereas laboratory experiments were performed during the off-season to address objective 3. There was insufficient time to address objective 4.
Striped (Acalymma vittatum Fab.) and spotted (Diabrotica undecimpunctata Barber) cucumber beetles are the most important insect pests of cucurbits, being especially destructive in the South (Encyclopedia of Organic Gardening, 1978; Hoffman, 1998). These beetles are vectors of the pathogen, Erwinia tracheiphila (Smith), causing bacterial wilt disease in cucurbits, and both adults and larvae can cause damage by feeding on cucurbit roots, shoots, and flowers. Bacterial wilt is the most serious threat to muskmelon production in Kentucky (Rowell et al. 2002).
Inorganic insecticides can be used to control cucumber beetles in conventional vegetable production. However, production of organically grown vegetables is increasing, and they are a high-value crop that may be used to supplement small-farm income lost in Kentucky and neighboring states as a result of decreases in tobacco production (Cramer 1993; Jolly 1998). In an unpublished Kentucky survey conducted by the authors, 120 respondents growing or interested in growing organic vegetables indicated that insect control was the most important production concern (see Sustainable Agriculture Research and Extension Grant No LS99-098 final report). In a second survey, organic management of cucumber beetles was the most mentioned insect problem. Thus, the surveys indicated improved methods of organic cucumber beetle management are needed.
Use of row covers and the botanical insecticide rotenone are current means of organically managing cucumber beetles (Smith and Henderson 1998). However, row covers are only useful until flowering when they must be removed to allow insect pollination. Rotenone is highly toxic to cucumber beetles, but residual effects only persist one to three days because it is not stable in sunlight (Ware 1994). Thus, an intensive and costly spraying program is needed. Also, Rotenone is as toxic to humans as many inorganic insecticides, and most organic growers are health conscious and reluctant to use it (Ware 1994). Thus, new, effective organic management practices for cucumber beetles are needed. Pyrethrin is another organic insecticide that is not as toxic to insects as rotenone, but which may be an effective insecticide for cucumber beetles. Finally, Entrust is a recently registered organic insecticide but spray programs using it could be costly.
Several other organic methods may reduce populations of cucumber beetles. Caldwell and Clark (1998, 1999) reported that cucumber beetle densities on squash were five times less with aluminum-coated plastic (Al-plastic) mulch than with black plastic mulch. No insecticidal treatment was required with Al-plastic, making it cost-effective. Trap crops such as ‘Blue Hubbard’ squash [Cucurbita maxima (Carriere)] are thought to attract cucumber beetles away from cucurbit cash crops (Barbercheck and Warrick, 1996). Beneficial insects including Pennsylvania leatherwings [Chauliognathus pennsylvanicus (Fab.)] and the tachinid flies [Celatoriae diabrocitae (Shimer)], and [Celatoriae setosa (Coquillet)] are believed to prey on cucumber beetles (Platt et al, 1999). Companion plants may be planted near cucurbits to attract beneficial insects. Such plants include buckwheat (Fagopyrum esculentum Moench), cowpeas [Vigna unguiculata (L.)], and sweetclover [Melilotus officinalis (L.)] (Bowman et al. 1998, Platt et al. 1999). Other types of companion plants are thought to repel cucumber beetles, including radish (Raphanus sativus L.) and tansy (Tanacetum vulgare L.).
The overall objective of this research was to examine the use of companion plants, Al-plastic, and pyrethrin as organic methods for managing cucumber beetles in production of watermelon [Citrillus lanatus (Thunb.)] and muskmelon (Cucumis melo L.).
In 2002, a field experiment was conducted at the KSU research farm in Frankfort, KY to examine use of companion plants and plastic mulch in management of cucumber beetles. Although watermelon attracts cucumber beetles, it is not as highly susceptible to problems associated with other cucurbits. It was used in the initial experiment to minimize early crop failure related to cucumber beetles, and hopefully allow monitoring treatment of effects on beetle populations over the entire season. Thus, observation of potential late-season effects of a particular treatment on beetle populations was not eliminated by early crop failure associated with beetles. Two treatments might be combined in subsequent experiments if they reduced beetle populations at different times during the growing season. Based on 2002 results, the most promising treatments were selected and used in 2003 and 2004 with muskmelon, which is susceptible to bacterial wilt. Conventional fertilizer and pesticides were used in 2002 in the initial watermelon experiment, whereas organic cropping methods were used in 2003 and 2004. In all years, trickle irrigation was used and plots were cropped with corn the preceding year. The experiment was rotated between two sites in following years. Dates of experimental activities are presented in Table 1. To view Table 1, please request a print copy from Sue Blum, SARE, at email@example.com .
Four treatments were replicated three times in a randomized block design to examine cucumber beetle management in watermelon grown on black plastic mulch, except when Al-plastic was used as a treatment. Treatments included a control treatment and the use of Al-plastic (Clarke Ag Products, Greenwood, VA), companion plants (radish, nasturtium, and tansy) thought to repel cucmber beetles, and companion plants (buckwheat, cowpea, and sweetclover) thought to attract beneficial insects.
All plots were separated by a minimum of 50 ft (15.2 m) of border area which was drilled with tall fescue grass and mowed. Plots not containing companion plants were 42.7 ft (13 m) wide and contained four 50 ft (15.2 m)rows of watermelon. Between-row spacing was 10 ft (3.1 m), and the in-row melon spacing was 4 ft (1.2 m). In the two treatments including companion plants, plots were enlarged to contain an additional five rows of companion plants. In these treatments, a row of companion plants was planted adjacent and parallel to each watermelon row such that each watermelon row was bordered on each side by a row of companion plants.
In one companion plant treatment, single rows of combined cucumber beetle-repelling plants were 3 ft (0.9 m) wide. Alternating nasturtium seeds and tansy divisions were manually planted down the center of these rows at 2 ft (61 cm) intervals, and ‘Summer Cross No. 3′ Daikon radish plants were seeded 2 in (5.1 cm) apart along both outside borders of each companion plant row.
In the other companion plant treatment, each row of beneficial insect-attracting plants was 9 ft (2.7 m) wide and contained randomized 3 ft (0.9 m) wide sub-rows of buckwheat, cowpea, and annual white sweet clover. Buckwheat and cowpea were drilled at seeding rates of 132 and 119 lb/acre (150 and 135 kg ha-1), respectively, whereas sweet clover seed was broadcast at 74 lb/acre (84 kg ha-1) and manually incorporated. After flowering began, 50% of the buckwheat was manually cut at three-week intervals to a height at which flowers were removed. This promoted flowering over the entire growing season. Buckwheat was cut in the middle 8.5 m segment of each row or in the remaining two 4.3 m end segments of each row.
The plots were plowed to a depth of 20 cm and roto-tilled (Table 1). (To view this table, please request a print copy from Sue Blum, SARE, at email address firstname.lastname@example.org .) All plots received 143 lb/acre (160 kg/ha) of K as K2O and 60 lb/acre (67 kg/ha) of N as NH4NO3. After laying of 5 ft wide (1.5 m) Al- or black plastic mulch, three-week old ‘Stars and Stripes’ watermelon seedlings were planted manually. Chlorothalonil (tetrachloroisophthalonitrile) fungicide(a.i.) 2.5 kg ha-1 (2.2 lb/acre) was applied at seven to ten day intervals for disease control. Weeds were controlled by roto-tilling between the plastic much on June 17 and July 2. Also, ethylfluralin (N-ethyl-N-(2-methyl-2-propenyul)-2,6-dinitro-4-(triflluoromethyl) benzenamine) herbicide was applied to all plots at a rate of (a.i.) 1.6 kg ha-1 (1.43 lb/acre) on July 2, and was activated by overhead irrigation on July 2 and 3. Rows of companion plants were kept relatively weed-free by manual weeding. Melons were side-dressed with 20 lbs/acre (22 kg ha-1) N as dissolved NH4NO3 applied through the irrigation system on July 15.
To monitor populations of cucumber beetles, two 15 x 15 cm double-sided yellow sticky cards were placed in the middle two melon rows of each plot. The tops of the cards were positioned two feet (61 cm) above the soil surface and 14 ft (4.3 m) from the ends of the rows. Beetles on cards were counted and replaced weekly.
Melons were harvested on Aug. 12, 21 and 29 from a 24 x 20 ft (7.3 x 6.1 m) from a centrally located area in each subplot theoretically occupied by 12 watermelon plants in the middle two rows. Total and marketable melons according to USDA standards (USDA, 1997) were counted and weighed individually.
In 2003, muskmelon was grown organically on plastic mulch on a different site at the KSU Research Farm using a 4 x 2 split-plot, factorial, randomized block design with three replications. Four main plot treatments included a control treatment and use of Al- plastic mulch, companion plants (radish + buckwheat), or pyrethrin organic insecticide. Split-plot treatments consisted of the presence or absence of row covers. The 2003 companion plant treatment included the combined use of radish as a beetle-repelling plant and buckwheat as a beneficial insect-attracting plant. These two plants were selected because they grew well and required minimum weed control in 2002.
Except for the companion plant treatment, main plots were 40 ft (12.2 m) x 28 ft (8.5 m) and were divided into two 20 ft ( 6.1 m) x 28 ft (8.5 m) subplots. Main plots were separated by at least 18 m. Soil preparation was similar to that in 2002 (Table 1). However in 2003, organic Nature Safe fertilizer was added to all plots to provide N (155 lbs/acre = 174 kg/ha), P (31 lbs/acre = 35 kg/ha), and K (125 lbs/acre = 157 kg/ha), and the plots were roto-tilled. In each subplot, a total of 48 ‘Eclipse’ muskmelon seedlings were planted into black or Al-coated plastic mulch (4 ft = 1.2 m wide) in four 20 ft (6.1 m) rows (12 plants/row) spaced 2.1 m apart using an in-row spacing of 18 in (46 cm). Planting was delayed until June 24 due to high amounts of precipitation and resulting wet soil.
Each 4 ft wide companion plant row contained a center 3 ft (0.91 m) wide row of buckwheat bordered on each side by 0.5 ft (0.15 m) wide rows of Daikon radish. Plot widths were increased from 28 ft (8.5 m) to 40 ft (12.2 m) to include three companion plant rows. The companion plant rows were parallel to muskmelon rows and were placed between the middle two muskmelon rows and along each of the plot borders adjacent to the two outside watermelon rows. Light-weight 8 ft (2.4 m) wide row covers (Gardens Alive, Lawrenceburg, IN) were installed randomly in one subplot in each main plot soon after planting and removed after three weeks to allow insect pollination. Row covers straddled the plastic mulch and confined vines to the mulch area. Vines from plants not receiving row covers were manually confined to the mulch area to facilitate mechanical weed control between plastic mulch strips.
Two 15 x 15 cm yellow sticky cards were centered in the middle two melon rows of each subplot (four traps/main plot) to weekly monitor populations of striped and spotted cucumber beetles. Before row cover removal, all four traps in each main plot were located in the subplot not containing row covers. Per cent vine cover of subplots was visually rated on August 14 and 27. Marketable muskmelons according to USDA standards were harvested on six dates from Aug. 21 to Sept. 9 (Table 1) from a centrally located 7.8 m2 area located in the middle two rows of each subplot theoretically occupied by 16 plants.
The 2003 experiment was repeated in 2004, except that the 2003 pyrethrin insecticide treatment was replaced with a 2004 treatment which included a combination of Al-mulch and companion plants. Thus, main plot treatments included a control treatment and use of Al-plastic mulch, companion plants (radish + buckwheat), or Al-plastic mulch plus companion plants. Split plot treatments again consisted of the presence or absence of row covers. Muskmelon was planted on June 10 and harvested on Aug. 10, 13, 17, 23, and 27. The methods were the same as those in 2003.
In all years, analysis of variance and the least significant difference (P < 0.05) were used to determine significance of treatment interactions and significance differences among treatment means. Laboratory Research Twigs of different selections of pawpaw trees were collected from the Kentucky State University Research Farm. Three selections, r1t21, r4t5, and r5t12 were chosen for the extraction. The twigs were dried in an oven at 45 C for two days and then ground to a particle size less than 0.4 mm. Two extraction procedures, methods A and B, were performed. In method A, the final fraction contained acetogenins dissolved in methanol. In method B, the final fraction contained acetogenins dissolved in dichloromethane. Method A Extraction In method A, 5 g of dried, ground twigs were placed in a funnel lined with Whatman 42 filter paper. Five, 37 ml volumes of 95% aqueous methanol were poured over the ground twigs. Ethanol was evaporated from the mixture by rotary evaporation to produce a green solid phase residue. The residue was redissolved by decanting eight, 5 ml volumes of 50% aqueous chloroform to the sample. Rinses were combined in a separatory funnel. The bottom chloroform layer was reserved, and the chloroform was removed from the sample by rotary evaporation to produce a green solid phase residue. This residue was then redissolved in four, 5 ml volumes of 1:1 hexane: 90% aqueous methanol. These rinses were combined in a separatory funnel. The bottom methanol layer was reserved, and the methanol was removed by rotary evaporation to produce another green solid phase residue. The methanol solubles were rinsed with 3 ml of methanol to remove them from the flask. The resuspended fraction was poured into a preweighed vial and the methanol was left to evaporate overnight. The vials were reweighed and residue was removed until 20 mg of sample remained in each vial. Two ml of methanol were added to each vial to dissolve the residue. Five, 50, and 500 micro liters of each resuspended extract were transferred to 2 dram vials to obtain 10, 100, and 1,000 mg l-1 concentrations of each extract for the brine shrimp bioassay without solvent interference. Controls were prepared by adding five, 50, and 500 micro liters of methanol to 2 dram vials. The extracts were dried overnight to allow the methanol to evaporate. Twigs of all three pawpaw selections were extracted at the same time on three different days, resulting in a total of three extracts of each pawpaw selection or a total of nine extracts. Three replicates of each extract concentration were prepared for use in the brine shrimp bioassay (Ratnayake et al. 1992). Method B Extraction In method B, 2.5 g of ground twigs were placed into vials with 20 ml of dichloromethane. The vials were capped and left over night. The following day, vial contents were filtered using Whatman 42 filter paper placed in funnels. Pre weighed vials containing filtrates were left in a hood for 24 hours to allow the dichloromethane to evaporate from the samples. The product consisted of a green solid phase residue in each vial. The vials were reweighed and residue was removed until 20 mg of sample remained in each vial. Two ml of dichloromethane were added to each vial to dissolve the residue. Five, 50, and 500 micro liter of each resuspended extract were transferred to 2-dram vials to obtain 10, 100, and 1,000 mg l-1 concentrations of each extract for the brine shrimp bioassay without solvent interference. Controls were prepared by adding five, 50, and 500 micro liter of dichloromethane to 2-dram vials. The extracts were dried overnight to allow the dichloromethane to evaporate. As in method A, twigs of all three pawpaw selections were extracted at the same time on three different days, resulting in a total of three extracts of each pawpaw selection or a total of nine extracts. Three replicates of each extract concentration were prepared for use in the brine shrimp bioassay (Johnson et al. 1996). Brine Shrimp Bioassay Brine shrimp bioassays for both extraction procedures were performed in the same manner. Five ml of 3.8% aqueous sea salt containing 10 to 12, two-day-old brine shrimp were added to each vial. Numbers of live and dead shrimp were counted after 24 hours and recorded (Ratnayake et al. 1992). Means were calculated from these values based on the three subsets of three replicate extracts obtained from each pawpaw selection. An analysis of variance statistical procedure was used to determine if statistical differences occurred among treatments (P = 0.05). The least significant difference mean separation test was then used to determine which treatments were significantly different from one another. Cucumber Beetle Bioassays Striped cucumber beetle bioassays were performed in the same manner for both extraction procedures. No-choice bioassay Pawpaw twig residues were diluted to a target concentration of 0.5% (w/v) or 5,000 ppm in acetone and 0.01%, or 1.0% Tween 20 or Tween 80. “Burgess Buttercup” squash leaves were cut into 2.5 cm disks, dipped into each treatment solution and air dried. Expeimental units consisted of 10.0 cm diam plastic Petri dishes containing a circle of Whatman No. 1 filter paper moistened with 1 ml of double distilled water and 3 treated discs. Five 2 day old striped cucumber beetles were released into each dish and dishes were sealed with parafilm. They were then placed in an environmental growth chamber at 27 C and 14-h photoperiod at > 90% RH. Two replicate dishes were prepared per treatment. Beetle mortality and percent leaf area consumed were quantified.
Contact bioassay # 1
Two week old adult beetles were dropped into glass Petri dishes containing solutions of papaw twig residues prepared as described above. Beetles were submerged for 1-2 seconds and then placed in plastic Petri dishes containing moistened filter paper and fresh zucchini leaves. Nine dishes were prepared with five beetles per dish. Petri dishes were then placed in an environmental growth chamber at 27 C and 14-h photoperiod at > 90% RH. Mortality was quantified 72 h after exposure.
Contact bioassay #2
The contact toxicity bioassay was repeated using freshly prepared solutions. Each was diluted to 0.5% (w/v) extracts in 1% Tween 80. Two samples were prepared from a single pawpaw accession., one using the multiple-solvent extraction and the other the single-solvent procedure. Beetle mortality was quantified 48 h after exposure.
The single solvent extraction method was used to examine consumption of treated leaf tissue. Extract of Accesion R5T12 was diluted to 1% (w/v) and 0.1% and mixed with 1% Tween 80 or not. ‘Burgess buttercup’ leaf disks 3.5 cm in diam were treated as above and air-dried. Three leaf discs were placed in 10 cm diam tissue culture dishes lined with Whatman No. 1 filter paper (9.0 cm diam) and moistened with 1 ml tap water. Three replicate dishes per treatment were used.
Five three day old adult striped cucumber beetles were transferred into each Petri dish. Mortality and leaf area consumed were quantified after 10 days.
An analysis of variance statistical procedure was used to determine if statistical differences occurred among treatments (P = 0.05).
Watermelon Yields. No significant (P < 0.05) differences in watermelon yields were detected among treatments, indicating that use of Al-plastic or companion plant treatments did not adversely affect watermelon production (Figure 1).
(To view this figure, please request a print copy from Sue Blum, SARE, at email address email@example.com .)
As described in Experimental Approach, watermelon was used in this initial experiment to minimize beetle/disease effects on crop production.
Cucumber Beetles. In 2002, numbers of striped cucumber beetles captured on sticky cards were negligible in June (Figure 2A, B, C). (To view this figure, please request a print copy from Sue Blum, SARE, at firstname.lastname@example.org .) In July and August, numbers of captured striped beetles tended to be consistently higher in control and Al-plastic treatments than in the repellent plant or beneficial insect treatments. These differences were significant (P = 0.05) on Aug. 8 and 22 when beetle populations in the two companion plant treatments were only about 50% as large as in the control treatment. This trend may have been caused by companion plants repelling cucumber beetles and attracting beneficial insects. However, on given dates beetle populations did not vary greatly between repellent plant or beneficial insect treatments, suggesting that beetle exclusion may have been related to physical barriers to beetle movement provided by rows of companion plants bordering watermelon rows (Radin and Drummond 1994, Javaid and Joshi 1995). On the other hand, the buckwheat, cowpea and sweetclover plantings in the beneficial insect treatment were much taller and three times wider than the radish, tansy and nasturtium plantings in the repellent plant treatment. Thus, if the companion plants were lowering beetle populations in watermelon merely by their physical presence, the larger plants in the beneficial insect treatment might be expected to have a greater effect.
The fact that the Al-coated plastic did not reduce numbers of captured beetles may have been caused by the late arrival of the beetles in July (Figure 2). (To view this figure, please request a print copy from Sue Blum, SARE, at email address email@example.com .) By this time much of the Al-plastic was covered with vines which reduced the ability of the Al-plastic to reflect light. Although cucurbit crops were grown at the KSU farm in previous years, insecticides were commonly used to control cucumber beetles, which may account for the initial low beetle populations
In 2002, companion plant treatments did not appear to affect populations of spotted cucumber beetles, whose populations were lower than those of striped beetles later in the season (Figure 2A, B). To view this figure, please request a print copy from Sue Blum, SARE, at email address firstname.lastname@example.org .
For combined striped and spotted beetles, companion plant effects were similar to those described for striped beetles and were also significant (P < 0.05) on two dates (Figure 2C).
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Interactions between main plot treatments and row cover treatments on dependent variables were not significant (P > 0.05) in the analysis of variance. Thus, main plot treatments were analyzed for combined row cover treatments and vice versa.
Main Plot Treatment Effects
Muskmelon Yields. Use of Al-plastic and companion plants increased watermelon yields. Total weight and numbers of muskmelon were highest in the Al-plastic treatment, and these yields were significantly (P < 0.05) greater (75% and 66%, respectively) than those in the control treatment (Figure 3A, B). (To view this figure, please request a print copy from Sue Blum, SARE, at firstname.lastname@example.org .) Muskmelon numbers from the companion plant treatment were also significantly (P < 0.05) greater (39%) than in the control. No significant differences were detected between yields from the Al-plastic and companion plant treatments or between yields from the pyrethrin and control treatments. Yields from the pyrethrin treatment were also not significantly less than those in the companion plant treatment, and thus appeared intermediate between yields from control and companion plant treatments. Vine Cover. Responses of vine cover to main plot treatments on both sampling dates were generally similar to responses of muskmelon yields (Figs. 4A, B). (To view this figure, please request a print copy from Sue Blum, SARE, at email address email@example.com .) Vine cover obtained using Al-plastic was highest and significantly (P < 0.05) greater than in the control or pyrethrin treatments. Vine cover in the companion plant treatment was intermediate between cover in Al-plastic and control treatments, and not significantly different from cover in either of those treatments. Other than cucumber beetles, no significant numbers of other insect pests or diseases were observed. Furthermore, The University of Kentucky Plant Diagnostic Laboratory detected only beetle feeding on damaged plants, and no diseases were found. This suggests that treatment effects on melon yields were due to cucumber beetles. For all treatments vine cover was lower on the later sampling date possibly due to increased beetle damage or vine maturation. Cucumber Beetles. Populations of striped and total (striped + spotted) cucumber beetles (determined by sticky traps) were consistently greater in the control than in Al-plastic and companion plant treatments, and differences were significant (P < 0.05) on four dates for both populations (Figure 5A, C). (To view this figure, please request a print copy from Sue Blum, SARE, at firstname.lastname@example.org .) This trend was less evident for spotted beetles in agreement with 2002 results, and differences were only significant (P < 0.05) on two dates (Figure 5B). (To view this figure, please request a print copy from Sue Blum, SARE, at email address email@example.com .) Although no significant differences were detected between beetle populations obtained using Al-plastic and companion plants, populations of striped, spotted, and total beetles obtained with companion plants were always lower than those in the Al-plastic treatment, except for spotted beetles on July 15 when these populations were similar (Figure 5 A, B, C). (To view this figure, please request a print copy from Sue Blum, SARE, at firstname.lastname@example.org .) Effect of Al-plastic on beetle populations appeared to persist over the entire growing season, well after vines covered the plastic. Beetle populations in the pyrethrin treatment were sometimes significantly (P < 0.05) greater than in the control, but they tended to be intermediate between populations in the control and populations in the other two treatments. This trend was most evident when populations were high and was in agreement with yield and vine cover results. Row Cover Subplot Effects: Muskmelon Yields. Use of row covers for 24 days after planting significantly (P < 0.05) increased total melon weight (47%) and melon numbers (49%) (Figure 6A, B). (To view this figure, please request a print copy from Sue Blum, SARE, at email@example.com .) Row covers were included in this study to prevent loss of small muskmelon seedlings to cucumber beetle damage shortly after planting. However, in the absence of row covers, no seedlings were lost and early beetle damage appeared minimal. Thus, these large yield increases were unexpected but similar in nature to observations made by Lopez (1998) in squash and by Santos et. al. (1995) in cantaloupe. Vine Cover. Immediately after row cover removal, previously covered muskmelon vines generally appeared visually larger than those not covered. This difference was at least in part due to increased leaf size of covered vines caused by shading effects of the row covers (Salisbury and Ross 1978, Lopez 1998). Leaves of uncovered vines were probably thicker, but this was not determined. Prior use of row covers increased vine cover on the Aug 14 (18%) and 27 (33%) rating dates, but the effect was only significant (P < 0.05) on the second sampling date (Figure 7A). (To view this figure, please request a print copy from Sue Blum, SARE, at email address firstname.lastname@example.org .) As with main plot treatments, no disease or insect pests other than cucumber beetles were observed, and The University of Kentucky Plant Diagnostic Laboratory detected only beetle feeding and no diseases on damaged plants obtained from subplots not receiving row covers. Cucumber Beetles. After the row covers were removed, beetle populations were similar in row cover treatments (Figure 7B). (To view this figure, please request a print copy from Sue Blum, SARE, at email@example.com .) Thus, row covers did not affect populations of aboveground, adult cucumber beetles after removal. The beneficial effects of row covers on yields and vine cover can be explained by enhanced vine and leaf growth under row covers which in turn may have directly increased yields and vine cover. Interaction between main and subplot treatments on yields and vine cover was not significant, indicating these treatments acted independently. However, both main and subplot treatments may have affected cucumber beetle damage but in different ways. Although beetle populations were similar in row cover treatments, their impact may have been less with row covers because vine cover was greater with row covers immediately after their removal. It is also possible row cover effects may have been caused by root damage by soil larvae of cucumber beetles or some other pest, and that use of row covers may have prevented early season egg laying and reduced or delayed crop damage by emerging larvae later in the season. 2004 Experiment Main Plot Treatment Effects Muskmelon yields. In 2004, mean muskmelon weights in all four treatments were significantly (P < 0.05) different (Figure 8A). (To view this figure, please request a print copy from Sue Blum, SARE, at email address firstname.lastname@example.org .) Weights were greatest in the Al-plastic + companion plant treatment and lowest in the control treatment. Weights in the Al-plastic treatment were greater than in the companion plant treatment. Melon weights were 30.4%, 72%, and 96.3% higher in the companion plant, Al-plastic, and Al-plastic + companion plant plots, respectively, compared to the control. Treatment effects on melon numbers were similar, except that no significant difference was detected between numbers in the Al-plastic and companion plant treatments (Figure 8B). (To view this figure, please request a print copy from Sue Blum, SARE, at email address email@example.com .) Compared to the control, melon numbers were 10.6%, 56.3%, and 72.3% higher in the companion plant, Al-plastic, and Al-plastic + companion plant treatments, respectively. Thus, increases in muskmelon weights and numbers obtained using Al-plastic and companion plants appeared additive. The 2004 results supported results obtained in 2003. Vine Cover. On both assessment dates, responses of vine cover to all main plot treatments were all significantly (P < 0.05) different and almost identical to responses of muskmelon yields (Figure 9). (To view this figure, please request a print copy from Sue Blum, SARE, at email address firstname.lastname@example.org .) Vine cover was significantly (P<0.05) less in the control than in other treatments. Treatment differences appeared related to cucumber beetles since treatment effects on vine damage appeared similar to those obtained in 2003, which were attributed to cucumber beetles as described previously. As in 2003, vine cover was lower for all treatments on the later sampling date. Cucumber beetles. On the first four sampling dates, 2004 beetle populations were generally similar to those obtained in 2003 (Figure 10A, B, C). (To view this figure, please request a print copy from Sue Blum, SARE, at email address email@example.com .) Populations tended to be greater in the control and this difference was significant (P < 0.05) on the first three sampling dates. After July 20, 2004, beetle populations in the control were not greater than in other treatments, nor were there other trends or significant differences among other treatments. The fact that mid to late-season beetle populations in control and other treatments were similar did not support the contention that beneficial treatment effects on yield and vine cover were related to cucumber beetle populations in 2004. Note, in 2003, there were trends and significant (P < 0.05) treatment effects on beetle populations that were consistent with beetles affecting treatment yield differences, especially for the control treatment. In 2004, beetle populations in the control treatment never reached the high levels obtained in 2003. The apparent lack of treatment effects on mid to late-season 2004 beetle populations was unexpected because positive treatment effects on muskmelon yields and vine cover were similar to those obtained in 2003, which appeared related to beetle populations over the entire season. Rainfall was much higher in 2004 than 2003 and may have reduced the efficacy of traps and/or the propensity of beetles to fly and be trapped. However, except for control treatments, there did not appear to be a large difference in beetle numbers trapped in 2003 and 2004, suggesting that rainfall was not a factor. Another explanation may be that beetle movement from the control treatment to other treatments may have increased as vine cover was reduced in control plots by beetle feeding. This would tend to minimize treatment differences later in the season and is supported by the fact that 2004 beetle populations were initially higher in the control treatment than in other treatments. However, vine cover in the 2004 control treatment did not differ greatly from vine cover in the 2003 control, which supported relatively high levels of cucumber beetles. Row Cover Subplot Effects Muskmelon Yields. As in 2003, use of row covers significantly (P < 0.05) increased weights and numbers of muskmelons (Figure 11A, B). (To view this figure, please request a print copy from Sue Blum, SARE, firstname.lastname@example.org .) Use of row covers increased melon weight by 73.1% and melon numbers by 37.2% . Vine cover. As in 2003, vine cover and leaf size appeared greater with than without row covers immediately after row cover removal. Muskmelon vine cover was significantly (P < 0.05) greater with row covers than without row covers on both assessment dates in 2004 (Figure 12). (To view this figure, please request a print copy from Sue Blum, SARE, at email address email@example.com .) As in 2003, cucumber beetles were the only insect pest observed in significant numbers, and no diseases were observed. Cucumber Beetles. As in 2003, after row cover removal, no significant difference in beetle populations was detected between 2004 row cover treatments based on sticky trap counts. It was concluded that use of companion plants and Al-plastic mulch increased muskmelon yields and vine cover while reducing populations of cucumber beetles. Use of row covers also increased muskmelon yields and vine cover. It was not entirely clear how row covers increased muskmelon production, or if such increases were related to cucumber beetles. Laboratory Research Brine Shrimp Bioassays Extracts containing acetogenin compounds were obtained from twigs of different pawpaw selections using single and double solvent extraction methods. In initial experiments, brine shrimp were used to examine the two extraction methods and investigate differences in extract toxicity among different pawpaw selections. Extracts obtained using the double solvent method were more toxic than extracts obtained using the single solvent method. Extracts obtained using the double solvent extraction at concentrations of 1000 mg/l (w/v) were generally completely lethal to shrimp, whereas 20% and 40% of shrimp survived at extract concentrations of 100 and 10 mg/l, respectively. There was little variation in toxicity to shrimp among extracts obtained from different pawpaw selections. Cucumber Beetle Bioassays In all experiments, pawpaw twig extracts at concentrations of 5000 g/l were not toxic to striped cucumber beetles when beetles were fed treated leaves or were directly treated with extract. Also, treatment of leaves with such extracts did not appear to greatly deter beetles from feeding on leaves that were treated with extract.
Educational & Outreach Activities
Cline, G.R. S. K. Parker, A. F. Silvernail, K. Kaul, R.J. Barney, A.M. Hanley, and J.D. Sedlacek. 2002. Organic management of cucumber beetles in watermelon (Citrillus lanatus). Kentucky Academy of Science Annual Meeting. Highland Heights, KY.
Cline, G.R. S.K. Parker, J.S. Sedlacek, and A.F. Silvernail. 2003. Research in organic control of cucumber beetles: year 1 results. Annual Meeting of Kentucky Vegetable Growers Association. Lexington, KY.
Pettaway, V., S.K. Parker, G.R. Cline, and K.W. Pomper. 2003. Organic cucumber beetle control: preliminary experiments examining toxicity of pawpaw extracts to brine shrimp. Association of Research Directors Annual Symposium. Atlanta GA.
Pettaway, V. 2003. Organic cucumber beetle control: toxicity of pawpaw extracts. Senior Student Biology Seminar. Kentucky State University. Frankfort, KY
Pettaway, V., S.K. Parker, G.R. Cline, and K.W. Pomper. 2003. Organic cucumber beetle control: preliminary experiments examining toxicity of pawpaw extracts to brine shrimp. Association of Research Directors Annual Symposium. Atlanta GA.
Cline, G.R., K. Kaul, and A.F. Silvernail. 2003. Organic management of cucumber beetles in muskmelon (Cucumus melo). Kentucky Academy of Science Annual Meeting. Highland Heights, KY.
Hillman, S.L., J.D. Sedlacek and G.R. Cline. 2005. Organic management of cucumber beetles in muskmelon. Annual meeting of the Kentucky Academy of Science. Eastern Kentucky University, Richmond, KY.
Striped and spotted cucumber beetles are important insect pests in the production of cucurbits because they feed on these plants and act as vectors of the pathogen which causes bacterial wilt disease. Current organic insecticides for cucumber beetles (e.g., rotenone, pyrethrins) are highly toxic to humans and/or easily degraded by sunlight. Cucumber beetles were the most important organic vegetable insect pest identified in a national survey and in a survey conducted in Kentucky by the authors in a SARE planning project. Thus, cucumber beetles are an important national and local problem. Organic vegetable production is especially appealing to small farmers. Improvement of organic management methods for cucumber beetles would make organic production of cucurbits more profitable for small farmers and help to preserve small farms. Also, such improvements should reduce use of inorganic insecticides, which are potential environmental pollutants and health hazards. Results from 2004 were similar to those of 2003 indicating that use of row covers, companion plants, and Al-coated plastic significantly increased organic muskmelon yields. Thus, adaptation of these methods by organic growers has potential impact locally and nationally.
Three farmers participated in on-farm research during 2003, which tested organic methods for managing cucumber beetles. One farmer participated in on-farm research during 2004, which tested organic methods for managing cucumber beetles. Experimental plots in the large field experiment at the Kentucky State University Research Farm were visited by participants at monthly “Third Thursday” Sustainable Agriculture Workshops and at the KSU Farm Field Day in 2003 and 2004. On-farm research plots were viewed by other local farmers.
Areas needing additional study
Results of the field research suggests that treatment effects do exist but do not explain the mechanisms by which the treatments are effective. It is believed that additional field research should be performed to explain why the different treatments are effective. Additional laboratory assays should be performed that screen a greater variety and sources of acetogenins and other botanicals for toxicity against striped cucumber beetles.