Investigating various tactics of intercropping buckwheat with squash to increase natural enemy populations, reduce pest and disease pressure and increase yield

Investigating various tactics of intercropping buckwheat with squash to increase natural enemy populations, reduce pest and disease pressure and increase yield

Summary

Zucchini squash, Cucurbita pepo L., is a high value vegetable crop in Florida. Plant physiological disorders and insect-transmitted diseases associated with the feeding of immature silverleaf whiteflies, Bemisia tabaci B biotype, are serious problems for many growers around the state. The implementation of mixed cropping systems and crops interplanted with alternative host cover crops, when used in conjunction with other pest suppression methods, has the potential to reduce whitefly numbers as well as the impact of whitefly-transmitted viruses on cucurbits. In particular, buckwheat (Fagopyrum esculentum Moench) has been cited as an important living mulch in cucurbit production systems. 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. This study evaluated several methods of intercropping buckwheat and squash, as well as introducing the natural enemy, Delphastus catalinae, to find a tactic that reduces pest and disease pressure while increasing marketable yield. The five treatments evaluated include A) alternating buckwheat on either side of each squash bed; B) arranging buckwheat and squash in the same manner as treatment A, however, releasing D. catalinae into the plot; C) planting buckwheat in the center of the bed with squash planted on both sides; D) arranging buckwheat and squash plants in the same manner as treatment C, however, releasing D. catalinae into the plot; and E) planting buckwheat on both sides of the squash (control). We found aphid densities from in situ counts were significantly greater in treatment C, where buckwheat was planted in the middle of each row without D. catalinae released, compared to treatment E, the control. However, whitefly densities and diseases were not significantly different among treatments. The natural enemies collected include green lacewings (Neuroptera: Chrysopidae); lady beetles (Coleoptera: Coccinellidae); ground beetles (Coleoptera: Carabidae); big-eyed bugs, Geocoris sp. (Hemiptera: Lygaeidae); minute pirate bugs, Orius sp. (Hemiptera: Anthocoridae); spiders; and several parasitoids including Aphelinus sp. (Hymenoptera: Aphelinidae); Encarsia sp. (Hymenoptera: Aphelinidae); Eretmocerus sp. (Hymenoptera: Aphelinidae); and Trichogramma sp. (Hymenoptera: Trichogrammatidae). Plant sizes were significantly lower in treatments C and D compared with the other treatments. Marketable yields were significantly lower in treatments C and D compared with treatments A and E (the control). Based on these findings, we would not recommend the arrangement utilized in treatments C and D (planting buckwheat in the center of the bed with squash planted on both sides, without and with D. catalinae, respectively). The influence of D. catalinae on pest populations and yields did not appear to be significantly different among treatments. It is hypothesized that high D. catalinae dispersal occurred between plots; therefore more research is needed to determine the effect of D. catalinae in this system.

Objectives/Performance Targets

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, and 2) to identify the best intercropping system and incorporate a key natural enemy, Delphastus catalinae, into buckwheat and squash crops to determine the effects on pest populations and marketable yields.

Accomplishments/Milestones

This report summarizes the findings from the first year of a 2-year study. Once the findings from the second year have been compiled, the data from both years will be combined into a complete dataset demonstrating the effects of various intercropping tactics on squash yields for a two year period. One of the greatest accomplishments for the first year field season was demonstrating that there was a difference in squash plant size and marketable yields among the different intercropping tactics, such as in treatments C and D that shared the same intercropping tactic and had higher competition between squash and buckwheat. Therefore those plots experience smaller plants and a decrease in yields compared to other treatments A, B, and E. 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.
There was not a significant difference among treatments that shared the same intercropping strategy, but D. catalinae was either present or 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 influence of D. catalinae on pest densities and marketable yields. We hope to accomplish this the next field season by reducing the number of D. catalinae released in a plot for the purpose of reducing the likelihood of crowding and dispersal.

Impacts and Contributions/Outcomes

Aphid densities were significantly greater in treatment C, where buckwheat was planted in the middle of each row without D. catalinae released, compared to treatment E, our control where buckwheat was planted on both sides of a row of squash, based on in situ counts. This finding could suggest that interplanting tactics implemented in treatment C and E may not be favorable for reducing aphid densities. Whitefly densities were not significantly different among treatments. Whiteflies were abundant in all plots sampled (25+ adults per yellow sticky trap), and there may have been movement between plots, as well as movement into the field from surrounding cucurbit fields.
Virus counts and SSL ratings were not significantly different among treatments, suggesting that both interplanting tactics and the presence of D. catalinae did not have a significant effect on disease incidence. There appear to be a trend of lower whitefly densities and lower disease incidence in treatment C, where buckwheat was planted in the middle of each row without D. catalinae released. This finding could suggest that this intercropping tactic is effective at reducing whitefly densities and disease incidence compared to the other intercropping tactics. A regression analysis showed that there was not a significant correlation between virus counts and pest densities. This finding could suggest that increasing virus counts may not correlate with increasing pest densities because high pest densities are not needed to vector viruses, and only a few individual pests could be responsible for spreading a virus throughout the whole field.
There were no clear differences among treatments for the natural enemy counts recorded. We hypothesize that with the addition of buckwheat in each zucchini plot, natural enemy presence and diversity was enhanced when compared to a plot containing only zucchini. Future considerations will be to add another treatment containing only zucchini squash that will serve as a control. Similarly, there were no significant differences among treatments with similar intercropping tactics when considering the effect of D. catalinae on pest populations and zucchini yield. This finding may suggest that there is movement of D. catalinae between plots into areas where it is not released, and future considerations will have to focus on minimizing the movement of D. catalinae between plots through monitoring and weed reduction techniques.
Zucchini plants were significantly smaller in treatments C and D compared to the other treatments, suggesting that the intercropping tactic used in treatments C and D significantly impaired plant growth rates. Therefore, it is likely that higher competition between buckwheat and zucchini occurred in treatments C and D compared to the other treatments. Similarly, zucchini squash yield was greater in treatment A, where buckwheat was alternated on both sides of a row of squash, and treatment E, the control compared to treatments C and D. This finding supports the hypothesis that there is less competition between buckwheat and zucchini for resources in the intercropping tactic used in treatments A and E compared to the intercropping tactic used in treatments C and D.
Based on these findings we would not recommend the use of the arrangements utilized in treatments C and D where buckwheat is planted down the middle of a squash bed. Our findings suggest that plant size and yields are significantly reduced in this intercropping arrangement compared to other intercropping tactics and we hypothesize this is due to high competition for resources between buckwheat and zucchini. Future studies will focus on the implementation of the other intercropping tactics utilized in this study. Also, the effect that Delphastus cataliane has on pests and marketable yields in a zucchini-buckwheat intercropping system should also be further researched. Due to the, inconsistencies in the results it is too early to determine the effect of D. catalinae on pest populations and yield. Slight modifications in design will help us in the future to determine the role of D. catalinae in the system.