Final Report for OS11-060

Project Type: On-Farm Research
Funds awarded in 2011: $14,978.00
Projected End Date: 12/31/2013
Region: Southern
State: Florida
Principal Investigator:
Dr. Oscar Liburd
University of Florida
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Project Information

Abstract:

A comparison of different buckwheat intercropping tactics with bareground treatments in an organic squash production system determined that yields in bareground treatments were significantly greater than buckwheat treatments, even in the presence of high pest densities and virus incidence. Plant size and yields were reduced in the intercropping arrangements where buckwheat was planted down the middle of a squash bed and where buckwheat was planted on both sides of the squash compared with buckwheat alternating on either side of the squash, and therefore we would not recommend these intercropping arrangements.

Introduction

Zucchini squash, Cucurbita pepo L., is a high value vegetable crop in Florida (Nyoike and Liburd 2010).  Plant physiological disorders and insect-transmitted diseases are serious problems for many growers around the state.  One of the most damaging plant physiological disorders in squash is squash silverleaf (SSL) disorder, which is associated with the feeding of immature silverleaf whiteflies, Bemisia tabaci B biotype (Frank and Liburd 2005).  SSL is characterized by silvering of the upper leaf surface and blanching of fruit, which can reduce the quality of the fruit produced depending on the severity of the disorder (Frank and Liburd 2005, Liburd and Nyoike 2008).  Cucurbit leaf crumple virus is a whitefly-transmitted virus that has the potential to cause significant squash yield losses (Nyoike et al. 2008). 

The implementation of cultural control techniques in agriculture, such as the use of mixed cropping systems and crops interplanted with non-host cover crops (living mulches), when used in conjunction with other pest suppression methods has the potential to reduce whitefly numbers as well as the impact of SSL disorder and other whitefly-transmitted viruses on cucurbits (Frank and Liburd 2005, Liburd and Nyoike 2008, Manandhar et al. 2009).  Several studies evaluating the efficacy of living mulches for the control of whiteflies have demonstrated successful reductions in whitefly population densities, as well as lower incidences of whitefly-transmitted viruses (Hooks et al. 1998, Summers et al. 2004, Liburd and Nyoike 2008).  Buckwheat mulches have been observed to aid in the suppression of adult whiteflies on zucchini squash plants (Hooks et al. 1998, Frank and Liburd 2005).  In addition, flowering buckwheat attracts beneficial insects to the cucurbit crop (Frank and Liburd 2005).  Attraction of natural enemies of whiteflies may be an important advantage of implementing buckwheat mulches, such that natural enemies can play an important role in pest reduction.

A more sustainable approach is needed to address the limitations of the current management strategy, which heavily relies on insecticides to manage aphids and whiteflies and the diseases they transmit in squash.  The use of buckwheat as a living mulch intercropped with squash has shown promise to reduce pest and disease pressure while increasing the abundance of beneficial insects (Hooks et al. 1998, Nyoike et al. 2008, Nyoike and Liburd 2010).  However, yields can be significantly reduced, most likely due to early season competition for shared resources.

Project Objectives:

The purpose of this study was to evaluate several methods of intercropping buckwheat and squash to find a tactic that reduces pest and disease pressure while increasing marketable yield.  The specific objectives were to 1) to compare several tactics of intercropping buckwheat and squash and their effects on pest and natural enemy densities, disease incidence, and marketable yields in field grown squash, 2) to incorporate a key natural enemy, Delphastus catalinae, into buckwheat and squash crops to determine the effects on pest populations and marketable yields, and 3) to use an on-farm demonstration model to implement the buckwheat-squash intercropping tactic on a grower’s field while incorporating a key natural enemy, Delphastus catalinae, and compare to current organic squash growing practices.

Research

Materials and methods:

The first two objectives were evaluated during the fall of 2011 and 2012 at the University of Florida Plant Science Research and Education Unit (PSREU) in Citra.  In 2011, twenty plots of zucchini squash, measuring 7.6 m x 7.6 m and separated from adjacent plots by 4.5 m of bare soil on all sides, were set up and maintained as described in Nyoike et al. (2008) and Nyoike and Liburd (2010).  Four replicates of five treatments were arranged in a randomized complete block design.  The first treatment (A) involved alternating 1.8-m2 areas of buckwheat and bare ground on either side of each squash bed.  The second treatment (B) was planted identical to the first treatment (A) and D. catalinae was released into the plot.  Therefore, treatments A and B were referred to as buckwheat arrangement A. The third treatment (C) involved planting buckwheat in the center of the squash bed along the length of the bed with squash planted on both sides.  The fourth treatment (D) was identical to the third treatment (C), but D. catalinae was released into the plot.  Treatments C and D were referred to as buckwheat arrangement B. The final treatment (E) served as a control with buckwheat growing on both sides of the squash.  This was the standard treatment that was previously evaluated in Nyoike and Liburd (2010), where yield was lower in squash due to competition from buckwheat.  In 2012, a sixth treatment was added (F) which served as a bareground control with squash planted down the middle of the bed and no buckwheat was present. Treatments with identical arrangements were compared to evaluate the influence of D. catalinae on pest populations and yields. In treatments where D. catalinae was present, 100 adults were released into each plot.

The third objective was evaluated during the fall of 2013 at on-site at Hammock Hollow Farm in Island Grove, Florida.  The field consisted of thirteen plots of Zephyr hybrid summer squash, measuring 4 m x 4 m and separated from adjacent plots by 4.5 m of bare soil on all sides.  Four treatments were compared. The first treatment (A) involved alternating buckwheat and bare ground on either side of each squash bed (i.e., buckwheat arrangement A).  The second treatment (B) involved planting buckwheat in the center of the squash bed along the length of the bed with squash planted on both sides (i.e., buckwheat arrangement B).  The third treatment (C) served as a standard control with squash planted down the center of the bed and otherwise surrounded by bareground (no buckwheat).  The fourth treatment (V) served as the grower’s standard treatment with three different varieties of squash randomly mixed and planted on both sides of the bed and otherwise surrounded by bareground (no buckwheat). The varieties included Sunburst summer squash, Eight Ball zucchini squash, and Floridor zucchini squash. Fifty adult Delphastus catalinae were released in plots where buckwheat was planted (Treatments A and B).

Sampling
Aphids. Alate and apterous aphids, both immatures and adults, were sampled from plants in the outer rows of each plot using the leaf-turn method.  Leaf-turn sampling occurred weekly.  Alate aphids were also monitored using blue pan traps containing detergent solution.  The number of alate aphids were counted and recorded.

Whiteflies. Adult whiteflies were monitored using yellow sticky traps.  They were left in the field for 24 h before the number of adult whiteflies per trap was counted.  Leaves used for sampling apterous aphids were excised and a leaf disc was taken from each leaf using a cork borer.  The number of immature whiteflies were counted using a dissecting microscope and recorded.

Diseases. Visual observations of viral symptoms and incidence were monitored each week by recording the number of plants in each plot showing virus symptoms.  Leaves were collected and assayed for the most commonly occurring aphid-transmitted cucurbit viruses by a double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA).  Leaves were also assayed using polymerase chain reaction (PCR) techniques to confirm the presence of CuLCrV.  Squash silverleaf (SSL) was also monitored each week.  Plants were randomly selected from the inner rows of each plot.  Symptomatic plants were scored with an arbitrary scale adapted from Yokomi et al. (1990) that goes from 0, which indicates a healthy plant, to 5, which indicates a plant with all leaves completely silvered.

Natural enemies. Natural enemies were monitored using in situ counts.  Plants were randomly selected from the outside rows of each plot and examined for natural enemies.  The numbers of predators and parasitoids on each leaf were counted and recorded.  Natural enemies were also monitored using pitfall traps containing a soap solution. 

Plant Measurements and Marketable Yields. Squash plant height and width was measured each week from randomly selected plants in the inner rows of each plot.  Plant height was measured from the ground to the terminal bud with a tape measure.  Plant width was measured along the length between the two widest opposing lateral shoots. Squash was harvested from the inner rows of each plot.  Fruit was examined for any evidence of viral symptoms or physiological disorders, such as irregular fruit ripening.  Marketable fruit was harvested and weighed in the field every other day until the end of the season.

Data Analysis

Aphid, whitefly, virus incidence, yield data, and natural enemy counts were analyzed by repeated measures (PROC GLIMMIX) and LSD procedure was used to test for treatment mean differences.

Research results and discussion:

Aphids. In 2011, aphid densities sampled by in situ counts were observed to be significantly less in the control treatment (E) with buckwheat growing on both sides of the squash compared to both buckwheat arrangement A (treatments A and B) where buckwheat was alternated on either side of the squash plants and buckwheat arrangement B (treatments C and D) where buckwheat was planted down the middle (Fig. 1). Aphid densities observed in pan trap were not significantly different by treatment (Fig. 2). In 2012, aphid densities sampled by in situ counts were observed to be significantly less in the control treatment (E) with buckwheat growing on both sides of the squash compared to both buckwheat arrangement A where buckwheat was alternated on either side of the squash plants, buckwheat arrangement B where buckwheat was planted down the middle, and the bareground control (treatment F) without buckwheat (Fig. 3). Aphid densities observed in pan trap counts were not significantly different by treatment. In 2013, there were significantly more aphids sampled by in situ counts in the bareground control (treatment C) compared to buckwheat arrangement A (treatment A) where buckwheat was alternating on either side of the squash plants, buckwheat arrangement B (treatment B) where buckwheat was planted down the middle, and grower’s standard control (treatment V) with multiple squash varieties planted without buckwheat (Fig. 4). Aphid densities observed in pan trap counts were not significantly different by treatment (Fig. 5). The findings from all three years suggest that buckwheat significantly reduced aphid populations on squash as supported by reduced densities on the buckwheat treatments when compared to bareground treatments. We hypothesize that the buckwheat serves to impair the aphid’s host-finding abilities and deters aphids from landing on the host plant.

Whiteflies. In 2011, immature whitefly densities counted from leaf-disk assays were not significantly different by treatment (Fig. 6).  Adult whitefly densities counted from yellow sticky traps were also not significantly different by treatment (Fig. 7). In 2012, immature whitefly densities counted from leaf-disk assays were significantly less in the bareground control (treatment F) without buckwheat compared to treatments with buckwheat, including buckwheat arrangement A where buckwheat was alternated on either side of the squash plants, buckwheat arrangement B where buckwheat was planted down the middle, and the control treatment (E) with buckwheat growing on both sides of the squash (Fig. 8). Adult whitefly densities counted from yellow sticky traps were not significantly different by treatment (Fig. 9). In 2013, there were significantly fewer immature whiteflies counted from leaf-disk assays from the grower’s standard control (treatment V) with multiple varieties compared to buckwheat arrangement A where buckwheat was alternating on either side of the squash plants, buckwheat arrangement B where buckwheat was planted down the middle, and the bareground control (treatment C) (Fig. 10).  Adult whitefly densities counted from yellow sticky traps were significantly higher in the bareground control (treatment C) compared to buckwheat arrangement A where buckwheat was alternating on either side of the squash plants and the grower’s standard control (treatment V) with multiple varieties (Fig. 11). Whitefly densities were not significantly different by treatment in 2011. However, our findings from 2012 suggest that immature whitefly densities were lower in the bareground treatment compared to the buckwheat treatments. We hypothesize that immature whiteflies were more apparent to natural enemies in the bareground treatment compared to the buckwheat treatments, therefore reducing whitefly densities. In 2013, we observed lower immature whitefly densities in the mixed variety treatment without buckwheat compared to buckwheat treatments, but not in the bareground treatment. This finding suggests that planting multiple varieties together may have had a more significant impact on reducing whitefly densities. Also, in 2013, we observed more adult whiteflies in the bareground treatment compared to buckwheat arrangement A and the mixed varieties treatment without buckwheat. Again, planting multiple varieties may have deterred whitefly populations, while the absence of buckwheat in the bareground treatment may have made the host crop more apparent to whiteflies.

Diseases. Samples obtained from the field and tested for viruses in all three years were predominately found to test positive for Cucurbit leaf crumple virus using PCR techniques. Although not significantly present in the field, several leaf samples tested positive for Zucchini yellow mosaic virus and Papaya ringspot virus Watermelon strain using ELISA techniques in 2011 and 2012, but not in 2013. In 2011, virus counts were significantly higher in treatment A where buckwheat was alternating on either side of the squash and D. catalinae was not present compared to treatment B where buckwheat was alternating on either side of the squash and D. catalinae was present, and both treatments C and D where buckwheat was planted down the middle (Fig. 12). In 2012, virus counts were significantly higher in the bareground control (treatment F) without buckwheat compared to treatments with buckwheat, including buckwheat arrangement A (treatments A and B) where buckwheat was alternated on either side of the squash plants, buckwheat arrangement B (treatments C and D) where buckwheat was planted down the middle, and the control treatment (E) with buckwheat growing on both sides of the squash (Fig. 13). There were also significantly more plants showing virus symptoms in treatments with buckwheat arrangement B compared to treatments with buckwheat arrangement A (Fig. 13). In 2013, virus counts were significantly lower in the grower’s standard control (treatment V) with multiple varieties compared to buckwheat arrangement A where buckwheat was alternating on either side of the squash plants and the bareground control (treatment C) (Fig. 14).  Virus counts were also significantly lower in buckwheat arrangement B where buckwheat was planted down the middle compared to buckwheat arrangement A where buckwheat was alternating on either side of the squash plants and the bareground control (treatment C) (Fig. 14). Overall, virus counts were observed to be higher in the bareground treatment compared to the buckwheat arrangement B in 2013, and both buckwheat treatments in 2012. This finding correlates with greater adult whitefly densities observed in the bareground treatment. Again, virus counts were low in the mixed varieties treatment which correlates with lower whitefly densities. In 2011 and 2013, we observed lower virus counts in buckwheat arrangement B treatments compared to buckwheat arrangement A treatments. However, we observed the opposite trend in 2012 with higher virus counts in buckwheat arrangement B compared to buckwheat arrangement A.

In 2011, SSL ratings were significantly higher in the control treatment (E) where buckwheat was planted on both sides of a row of squash compared to both buckwheat arrangements A (treatments A and B) where buckwheat was alternated on both sides of a row of squash and buckwheat arrangement B (treatments C and D) where buckwheat was planted in the middle of each row (Fig. 15). SSL ratings were also significantly higher in both buckwheat arrangements A where buckwheat was alternated on both sides of a row of squash compared to buckwheat arrangement B where buckwheat was planted in the middle of each row (Fig. 15). In 2012, SSL ratings were significantly lower in the bareground control (treatment F) without buckwheat compared to treatments with buckwheat, including buckwheat arrangement A where buckwheat was alternated on either side of the squash plants, buckwheat arrangement B where buckwheat was planted down the middle, and the control treatment (E) with buckwheat growing on both sides of the squash (Fig. 16). In 2013, SSL ratings were significantly lower in the grower’s standard control (treatment V) with multiple varieties compared to buckwheat arrangement A where buckwheat was alternating on either side of the squash plants, buckwheat arrangement B where buckwheat was planted down the middle, and the bareground control (treatment C) (Fig. 17). SSL ratings were also significantly lower in buckwheat arrangement B where buckwheat was planted down the middle compared to buckwheat arrangement A where buckwheat was alternating on either side of the squash plants and the bareground control (treatment C) (Fig. 17). In 2011 and 2012, we observed higher SSL symptoms rating in the control treatments compared to the buckwheat and bareground treatments, which suggests that the control buckwheat arrangement may promote higher immature whitefly densities (the life-stage responsible for inducing SSL) while making the whiteflies less apparent to natural enemies. In 2012, we observed that SSL symptom ratings were lower in the bareground treatment compared to the buckwheat treatments, supporting the observations of lower immature whitefly densities in the bareground treatment. In 2013, we also observed lower SSL symptom ratings in the mixed squash varieties treatment without buckwheat compared to other treatments, supporting the observations of lower immature whitefly densities in this treatment. In 2011 and 2013, SSL symptom ratings were lower in buckwheat arrangement B compared to buckwheat arrangement A, suggesting that buckwheat arrangement B may reduce the incidence of SSL.

Natural enemies. The natural enemies observed during in situ counts for all three years included green lacewings (Neuroptera: Chrysopidae); lady beetles (Coleoptera: Coccinellidae); ground beetles (Coleoptera: Carabidae); hover flies (Diptera: Syrphidae); big-eyed bugs, Geocoris spp. (Hemiptera: Lygaeidae); minute pirate bugs, Orius spp. (Hemiptera: Anthocoridae); and spiders. In 2011, lacewing densities were significantly greater in treatments planted according to buckwheat arrangement A (treatment A and B) compared to treatments with buckwheat arrangement B (treatments C and D) and the control. Lacewing densities were also significantly greater in treatments where D. catalinae was not released (treatments A and C) compared to treatments where D. catalinae was released (treatments B and D). Orius spp. densities were significantly greater in the control treatment (E) compared to both buckwheat arrangement A and buckwheat arrangement B. In 2012, lacewing densities were significantly less in the bareground control (treatment F) without buckwheat compared to buckwheat arrangement A where buckwheat was alternated on either side of the squash plants and buckwheat arrangement B where buckwheat was planted down the middle. Lacewing densities were also significantly less in the control treatment (E) with buckwheat growing on both sides of the squash compared to buckwheat arrangement B (treatments C and D). Geocoris spp. densities were significantly less in the bareground control (treatment F) without buckwheat compared to buckwheat arrangement B where buckwheat was planted down the middle and the control treatment (E) with buckwheat growing on both sides of the squash. Geocoris spp. densities were also significantly greater in buckwheat arrangement B compared to buckwheat arrangement A. In 2013, there were no significant differences in the mean number of natural enemy taxa observed during in situ counts among treatments.

            Overall, lacewing densities were lower in both the bareground treatment and the control treatment with buckwheat compared to buckwheat arrangements A and B. We hypothesize that lacewings may attracted to the buckwheat, but only in treatments where the host plant of the pest was still apparent, thus utilizing resources from both the buckwheat and the main crop. In 2011, our findings suggest that the lacewing densities were lower in treatments where D. catalinae was released most likely due to competition of resources. In addition, our findings suggest that both Geocoris spp. and Orius spp. were attracted to buckwheat treatments compared to bareground treatments. Geocoris spp. and Orius spp. were also more abundant in the buckwheat arrangement B treatments compared to buckwheat arrangement A treatments, suggesting that the buckwheat arrangement B favored these species.

            The natural enemies collected from the yellow sticky traps include lady beetles (Coleoptera: Coccinellidae); minute pirate bugs, Orius spp. (Hemiptera: Anthocoridae); hover flies (Diptera: Syrphidae); and several parasitoids including Aphelinus spp. (Hymenoptera: Aphelinidae); Encarsia spp. (Hymenoptera: Aphelinidae); Eretmocerus spp. (Hymenoptera: Aphelinidae); and Trichogramma spp. (Hymenoptera: Trichogrammatidae). In 2011, lady beetle densities (not including D. catalinae) were significantly greater in treatments where D. catalinae was not released (treatments A and C) compared to treatments where D. catalinae was released (treatments B and D). There were significantly fewer Encarsia parasitoids recorded in buckwheat arrangement B (treatments C and D) compared to buckwheat arrangement A (treatments A and B) and the control treatment (E). Similar to the Encarsia observation, there were significantly fewer Eretmocerus parasitoids recorded in buckwheat arrangement B compared to buckwheat arrangement A and the control treatment (E). There were significantly more Trichogramma parasitoids recorded in buckwheat arrangement A compared to buckwheat arrangement B and the control. In 2012, there were significantly more Encarsia parasitoids recorded in buckwheat arrangement B compared to the bareground control (treatment F) without buckwheat and the control treatment (E) with buckwheat growing on both sides of the squash. There were significantly more Trichogramma parasitoids recorded in the bareground control (treatment F) without buckwheat compared to buckwheat arrangement A, buckwheat arrangement B, and the control treatment (E) with buckwheat. In 2013, there were no significant differences in the mean number of natural enemy taxa collected from yellow sticky traps among treatments.

            In 2011, our findings suggest that the lady beetle densities (excluding D. catalinae) were lower in treatments where D. catalinae was released most likely due to competition of resources. Both Encarsia and Eretmocerus spp. were observed to be more abundant in buckwheat arrangement A treatments compared to buckwheat arrangement B treatments in 2011; however, the opposite trend is observed in 2012, where these parasitoid species are more abundant in buckwheat arrangement B compared to buckwheat arrangement A. These findings correlate with changes in immature whitefly densities observed in both 2011 and 2012. For Trichogramma spp., our findings demonstrate that densities were greater in treatments with no buckwheat (bareground treatment F) or in buckwheat arrangement A compared to the control and buckwheat arrangement B treatments. In treatments where buckwheat was absent, the pest or the host plant of the pest would have been more apparent to the parasitoid and could have facilitated greater host finding abilities. This hypothesis could also be applied to buckwheat arrangement A treatments.

            The natural enemies collected from pitfall traps include ground beetles (Coleoptera: Carabidae); big-eyed bugs, Geocoris sp. (Hemiptera: Lygaeidae); minute pirate bugs, Orius spp. (Hemiptera: Anthocoridae); and spiders. In 2011, there were no significant differences in the mean number of predator taxa collected from pitfall traps among treatments. In 2012, there were significantly fewer ground beetles in the bareground control (treatment F) without buckwheat compared to buckwheat arrangement A (treatments A and B), buckwheat arrangement B (treatments C and D), and the control treatment (E) with buckwheat. In 2013, the number of predator taxa collected from pitfall traps was not significantly different by treatment. Overall, our findings support the hypothesis that ground cover promotes greater densities of ground beetles.

Plant Measurements and Marketable Yields. In 2011, zucchini plant height (cm) was significantly less in buckwheat arrangement B (treatments C and D) compared to buckwheat arrangement A (treatments A and B) and the control treatment (E) (Fig. 18). Zucchini plant width (cm) was also significantly less in buckwheat arrangement B compared to buckwheat arrangement A and the control (Fig. 19). In 2012, zucchini plant height was significantly greater in the control treatment (E) with buckwheat compared to buckwheat arrangement A, buckwheat arrangement B, and the bareground control (treatment F) without buckwheat (Fig. 20). Additionally, plant height was significantly less in the bareground control (treatment F) without buckwheat compared to buckwheat arrangement A and buckwheat arrangement B (Fig. 20). Zucchini plant width was significantly less in in the control treatment (E) with buckwheat compared to buckwheat arrangement A, buckwheat arrangement B, and the bareground control (treatment F) without buckwheat (Fig. 21). Zucchini plant width was also significantly less in buckwheat arrangement B compared to buckwheat arrangement A  and the bareground control (treatment F) without buckwheat (Fig. 21). In 2013, squash plant height was significantly less in the grower’s standard control (treatment V) with multiple varieties compared to buckwheat arrangement A where buckwheat was alternating on either side of the squash plants, buckwheat arrangement B where buckwheat was planted down the middle, and the bareground control (treatment C) (Fig. 22). Squash plant height was significantly greater in buckwheat arrangement A compared to buckwheat arrangement B and marginally significantly greater compared to the bareground control (treatment C) (Fig. 22). Squash plant width was significantly less in the grower’s standard control (treatment V) with multiple varieties compared to buckwheat arrangement A and the bareground control (treatment C) (Fig. 24). Squash plant width was also significantly less in buckwheat arrangement B compared to buckwheat arrangement A and the bareground control (treatment C) (Fig. 24).

            Our findings suggest that in 2011 and 2012, the plants in control treatment (E) were significantly taller compared with other treatments, and we hypothesize that the presence of buckwheat on both sides of the squash plants forced growth in height as opposed to girth. We also observed that squash plant height was significantly reduced in the bareground control treatment compared with the buckwheat treatments; however plant width was significantly greater in the bareground control treatment compared to buckwheat treatments. We hypothesize that the absence of buckwheat allowed the plant to grow in girth as opposed to height. The zucchini plants in the grower’s standard control (treatment V) in 2013 were significantly smaller than the other treatments planted with Zephyr squash, which is a significantly more rigorous plant that the other varieties planted. In all three years, the squash plants in buckwheat arrangement B were significantly smaller than the squash plants in buckwheat arrangement A. This finding suggests that competition between squash and buckwheat was greater in buckwheat arrangement B treatments compared to buckwheat arrangement A treatments.

In 2011, total zucchini yields (g) were significantly less in buckwheat arrangement B compared to buckwheat arrangement A and the control treatment (Fig 24). In 2012, total zucchini yields were significantly greater in the bareground (treatment F) without buckwheat compared to the control (treatment E) with buckwheat (Fig 25). In 2013, total squash yields were significantly greater in the bareground control (treatment C) compared to buckwheat arrangement A, buckwheat arrangement B, and the grower’s standard control (treatment V) with multiple varieties. Squash yields were significantly lower the grower’s standard control (treatment V) with multiple varieties compared to treatments in the buckwheat arrangement A  and buckwheat arrangement B (Treatment B) (Fig 26).

Overall, yields were observed to be greater in the bareground treatments compared with both the buckwheat treatments and the mixed variety treatment. It is hypothesized that the Zephyr variety is a more rigorous plant compared to the other varieties tested. In 2011, treatments in buckwheat arrangement A where buckwheat was planted on alternating sides of the squash was observed to yield more than treatments in buckwheat arrangement B where buckwheat was planted down the middle. This finding suggests that competition between the squash and buckwheat may be reduced by implementing the buckwheat arrangement A. However, there was no significant difference between yields in the different buckwheat arrangements in 2012 and 2013. Therefore, we could not find a buckwheat intercropping arrangement that rivaled the yields promoted in a bareground treatment.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

The findings from this study will be reported in a PhD dissertation entitled “Investigating IPM tactics in organic squash production to increase natural enemy populations, reduce pest and disease pressure, and increase yield.” A manuscript has been compiled detailing the findings from this study and will be submitted to the Florida Entomologist.

Project Outcomes

Project outcomes:

Our findings suggest that aphid densities were significantly reduced in treatments where buckwheat was present compared with the bareground (control) treatment with one variety. Therefore, intercropping buckwheat with squash could be an effective strategy for suppressing aphid populations. Virus counts were significantly greater in bareground treatments compared to buckwheat treatments, suggesting that buckwheat also aided in reducing virus transmission in squash. However, whitefly densities were not observed to be significantly affected by buckwheat treatments, and in 2012 we actually observed significantly fewer whiteflies in the bareground treatment compared with the buckwheat treatments. Therefore, buckwheat may not be as effective as an intercropping plant to suppress whitefly populations during the fall planting season when whitefly infestations are high. We would not recommend intercropping buckwheat in fall plantings of squash to manage whitefly populations.

Natural enemy abundance varied between treatments, and we hypothesize this was likely due to differences between natural enemy species in host-finding behavior and their dependence on alternative resources. For instance, Trichogramma parasitoids were more abundant in the bareground treatment compared to the buckwheat treatments, whereas Encarsia parasitoids and lacewings were more abundant in buckwheat treatments compared with the bareground treatment. We were unable to demonstrate a significant difference among treatments with similar intercropping tactics when considering the effect of D. catalinae on pest populations and zucchini yield. We hypothesize that there was movement of D. catalinae between plots into areas where it was not released, and future considerations will have to focus on minimizing the movement of D. catalinae between plots through monitoring and weed reduction techniques. Therefore, we recommend that more research should be conducted on the release of D. catalinae in field-grown squash to determine the effectiveness of suppressing whitefly populations.

            In all three years, the squash plants in buckwheat arrangement B where buckwheat was planted down the middle of the bed and squash planted on either side were significantly smaller than the squash plants in buckwheat arrangement A where squash was planted down the middle of the bed and buckwheat was alternating on either side. Yields were also reduced in buckwheat arrangement B in 2011 and the control treatment in 2012 where buckwheat was planted on both sides of the squash compared to the buckwheat arrangement A treatments. However, yields were significantly greater in the bareground treatment with one variety compared to buckwheat treatments and the bareground treatment with mixed squash varieties.

Based on these findings we would not recommend the use of the arrangements utilized in buckwheat arrangement B where buckwheat is planted down the middle of a squash bed or in the control treatment where buckwheat is planted on both sides of the squash.  Our findings suggest that plant size and yields are reduced in these intercropping arrangements compared with  buckwheat  alternating on either side of the squash, and we hypothesize this is due to high competition for resources between buckwheat and zucchini in those intercropping arrangements. Therefore, this study should be useful in providing an example of how intercropping tactics can be utilized to maximize yields in squash and other crop production systems. However, further improvements to the intercropping tactic need to be considered as the yields from bareground treatments were still significantly greater than buckwheat treatments, even in the presence of high pest densities and virus incidence. We could not find a buckwheat intercropping arrangement that rivaled the yields promoted in a bareground treatment. During this study we did explore a mixed variety tactic and observed reduced pest densities and virus incidence, however yields were also compromised in comparison with the bareground treatment with one squash variety. Our findings suggest that this could be an effective strategy if higher yielding varieties are incorporated.

Farmer Adoption

The purpose of this study was to investigate organic squash production during the fall planting season when pest pressure is high. Typically, squash is planted in the spring when pest pressure is significantly reduced and production in the fall is not considered to be a viable option. The grower we collaborated with at Hammock Hollow Farm has not planted cucurbits in the fall for over twelve years because pest pressure was too damaging to yields. Fall 2013 was no exception, and despite the bareground treatment producing the greater yields, the significant pressure of whitefly pests and Cucurbit leaf crumple virus reduced marketable yields across all treatments. The only treatment that was observed to be minimally affected by pest pressure and disease incidence was the bareground treatment with multiple varieties; however the varieties did not produce significant yields. While the farmer was hesitant to consider future fall plantings, it is our understanding that future research investigating the effectiveness of planting mixed varieties in a diversified landscape with the release of Delphastus catalinae as a biological control agent could be of interest to organic cucurbit growers.

Recommendations:

Areas needing additional study

We did not observe a significant difference among treatments where D. catalinae was released compared to treatments where D. catalinae was absent. However, findings of D. catalinae in plots where the predator was not released suggest that dispersal between plots was high. Therefore, more research needs to be conducted to determine the effect that D. catalinae has on pests and marketable yields in a zucchini-buckwheat intercropping system. Future studies should focus on modifications in research design to determine the role of D. catalinae in the system (i.e., separate fields, physical barriers). Furthermore, laboratory studies investigating the effect of D. catalinae on whitefly populations will provide support for D. catalinae being a significant whitefly predator.  Additional intercropping tactics need to be considered in a buckwheat-squash intercropping system to continue to address the issue of competition. The buckwheat arrangement where buckwheat is alternating on either side of the squash on the same bed needs to be further investigated and possibly modified so that the buckwheat is not on the bed with the squash but rather broadcasted between rows. Future studies should also consider the utility of incorporating multiple squash varieties and determine which varieties are both resistant to pests and diseases while producing high yields.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.