Final Report for LS11-244
A comparison of four systems of vegetable production indicated that cover and companion crops could promote sustainability in vegetable farmscapes by enhancing biotic resistance. The bidens companion plant attracted non virus-vectoring thrips that often displaced viruliferous thrips species. Under some years and combinations with bidens, the cover crop blue lupine had limited positive effect on yield weights when compared with conventional plastic mulch treatments. Although deployment of these types of cover crop / companion crop would require changes in current cropping practices, they can produce comparable crops to those grown with current higher input methods.
Objectives: Evaluation of multi-functional cover crops requires the systems approach to research adopted by SARE. Each component (e.g. type of cover crop, mulching system, etc.) has multiple functionalities. Conversely, each measureable outcome (yield, pest populations, soil fertility) is the result of the interaction of multiple cultural practices. These interrelationships obscure analysis by reductionist techniques and statistics designed to measure independent causes and effects. We will examine four systems of vegetable production based on conventional practices, current cover cropping systems, transitioning from plastic mulch with inclusion of traditional cover crops, and a cover crop system designed to maximize integration of thrips pest suppression with the traditional roles of cover crops. Specifically, we will: 1) Design, implement and demonstrate the following four cropping systems; i) conventional black plastic mulch utilized as a standard control; ii) conservation tillage cover crop, with spring cash crops transplanted into overwinter leguminous cover crops; iii) transitional cover crop, with the cash crops planted on black plastic overlaid in a cover system; iv) beneficial insect cover crop system, designed for spatial/temporal enhancement of beneficial insects and biotic resistance against pest thrips and the spread of TSWV in vegetable crop systems. 2) Determine the effectiveness of these four systems in terms of plant vigor, yield, vegetable quality, the traditional advantages of cover crops (including soil fertility and weed suppression), and pest pressures (thrips abundance, disease incidence, and secondary pest populations) on tomatoes, peppers and cucumbers. 3) Assess the economic value and practicality of cover cropping systems to growers through regional, collaborative on-farm research. 4) Foster adoption of effective practices by providing readily accessible information to growers, commodity groups and other stakeholders.
The western flower thrips (Frankliniella occidentalis) and tobacco thrips (Frankliniella fusca) are key pest of crops such as tomato, peppers, cucurbits, and horticultural crops in the southern USA. Growers have historically responded with intense insecticide use (Bauske 1998) fearing that if left unmanaged, direct feeding damage and Tomato spotted wilt virus (TSWV) transmission by these thrips could result in complete crop failure. However, inappropriate insecticide use can exacerbate damage by increasing pest thrips populations and populations of other secondary pests. Our labs have made considerable progress in management programs for thrips in vegetable crops, which have been widely adopted throughout the southern USA (Funderburk 2009). Although effective, not all of these IPM tactics are inherently sustainable, nor are they amenable to small scale and resource-limited growers because of costs. Further, they tend to rely on a traditional pest management paradigm that addresses pest problems individually rather than as a part of a holistic cropping system. One key sustainable strategy that we have developed to manage pest thrips is to maintain the biotic resistance of agroecosystems by fostering populations of natural enemies (Orius insidiosus) and competitor species of non-pest thrips (e.g., Frankliniella tritici, F. bispinosa) in the farmscape. In part, this can be accomplished by maintaining refuge crops for these species adjacent to cash crop fields. A number of these beneficial companion plants are also useful winter and summer cover crops. Therefore, we propose to integrate pest management into cover crop systems, and develop this strategy in a holistic, sustainable practice by developing an augmented system of cover crops which integrate the traditional uses of cover crops (soil fertility, erosion prevention, weed suppression) with biological control by providing harborages for natural enemies and non-pest competitor thrips over time. The objectives of this proposal are to: 1) evaluate four different cover crop systems for their effects on biotic resistance against pest thrips and the spread of TSWV in vegetable crop systems; 2) determine the effect of cover crops on soil fertility and vegetable crop vigor and yield; 3) assess the economic value and practicality of cover cropping systems to growers through collaborative on-farm research; and 4) foster adoption of effective practices by providing readily accessible information to growers, commodity groups and other stakeholders. We anticipate that this cover crop system will lead to: 1) successful management of two key pest thrips - western flower thrips and tobacco thrips – and TSWV; 2) reduce costly pesticide inputs; 3) reduce secondary pest outbreaks; and 4) improve soil health and increase soil fertility, thus reducing fertilizer and herbicide applications. This proposal integrates the strengths of a multidisciplinary team that includes growers, and researchers and extension personnel from the USDA, University of Florida, University of Georgia and Florida A&M University to better understand the risks and benefits of cover crop integration in vegetable systems and the feasibility of covers crops to manage thrips pests in the Southern USA.
Parallel research trials were conducted at the University of Florida, North Florida Research and Education Center, Quincy, FL, and at the University of Georgia, Tifton Campus Hort Hill Farm, Tifton, GA from 2011-2014. Research plots were located in areas that were bordered by other unrelated research trials. Each of the three target crops (cucumbers, peppers, and tomatoes) was randomly assigned within each of the four cropping systems (plastic mulch, lupine mowed, lupine tilled, and lupine tilled/bidens companion plant). The cropping systems were replicated three times and each plot contained four rows with 20 plants per row. Two rows served as sampling rows throughout the season and the remaining two rows were the harvest rows.
The three cropping systems without plastic mulch were planted in blue lupine (Lupinus augustifolius) in mid-November of the preceding year and allowed to grow until mid-March of the following year. The lupine was mowed in all three systems and was tilled in the ground in two of the three systems. Bidens (Bidens alba), cucumbers (var. Indy), peppers (var. Aristotle), and tomatoes (var. Florida 47) were germinated in the greenhouse in early March. Bidens was transplanted in the field in early April. Bidens were placed 3’ around the outside of one cropping system at one plant per foot spacing. Bidens were planted into beds adjoining the target crop beds and at the ends of rows of each target crop bed. The three target crops were transplanted in mid-April. Fertilization was through the drip system at 25 gallons per acre using 7-0-7 liquid fertilizer on a weekly basis.
Counts of vector thrips, non-vector thrips, natural enemies, and TSWV incidence were recorded from all plots during the respective growing seasons. For the target crops, insect counts were taken beginning two weeks after transplanting and consisted of leaf surveys and destructive flower sampling. For the leaf surveys, one leaf on each of ten plants in each plot was collected weekly. Flowers were collected from 10 plants per plot on a weekly basis when present. Ground cover estimates of weeds were taken weekly. Cucumbers were harvested twice per week, and number of fruit and total weight per plot was recorded. Peppers were harvested once per week and tomatoes were harvested three times during each season. Number of fruit and total weight was also recorded per plot for each of these. Tomatoes were also graded according to their marketability.
The cropping system treatment effects were not significant in 2012 or 2013 when looking at the number of F. fusca, F. occidentalis, F. tritici, and TSWV incidence. In 2014 no significant differences were found in three of the variables; however, there was a significantly higher number of F. tritici collected in the plots with bidens than in either of the other cropping systems.
Conversely, there was a significant difference in each of the variables when looking at the individual crops in all three years. Frankliniella fusca was found in significantly higher numbers on tomatoes than on cucumbers and peppers in 2012. In 2013 and 2014, F. fusca was found in higher numbers on cucumbers than on peppers or tomatoes. In 2012 and 2014, F. occidentalis was found in significantly higher numbers on tomatoes than on peppers or cucumbers and in 2013 it was found on tomatoes and cucumbers more than on peppers. Frankliniella tritici was collected in higher numbers on tomatoes than either of the other two crops in each of the years. Additionally, in 2012 the number of F. tritici was higher on peppers than on cucumbers. The incidence of TSWV was significantly higher on tomatoes than on peppers and cucumbers in all three years.
Comparing only the effect of bidens in the cropping system on the three thrips species and TSWV incidence, there was no significant difference in either the tomatoes or cucumbers grown with or without bidens. In the pepper plots in 2012, there was a significantly higher incidence of TSWV in the plots where bidens was not present as compared to the plots with bidens. On the other hand, in 2014 there were significantly more F. fusca found in the pepper plots with bidens than in the pepper plots without bidens.
More non-vector thrips were found on crop bloom samples than vector thrips in all four cropping systems in 2012 and 2014. However, in 2013 there were more vectors collected on cucumbers than were non-vectors. Non-vectors outnumbered vectors in tomatoes and peppers that year.
Fruit weights and numbers were recorded. The cropping system treatments influenced both fruit numbers as well as weights. Yields numbers and weights of all three crops in 2012 and 2014 were higher under conventional tillage than under conservation tillage, transitional cover crop, and in the presence of the Bidens companion crop. However, in 2013, yield weights in crops with transitional cover crop and Bidens were comparable with conventional plastic mulch. In that year yields associated with conservation tillage was lower than yields associated with crop yields on all three cropping systems. Weed populations in general were very high in other cropping systems than under conventional plastic mulch. Because the conventional black plastic mulch raises soil temperatures, seed germination of cucumber and growth of crops were slightly accelerated in the conventional plastic mulch system compared to non-conventional cropping systems that did not use mulches.
Educational & Outreach Activities
The impact of cover crops and companion plants on thrips vectors and Tomato spotted wilt virus spread in vegetable farmscapes. 2015. Diffie S., S. Reitz, K. Bowers, and R. Srinivasan. Xth International Symposium on Thysanoptera and Tospoviruses. May 16-21, 2015. Pacific Grove, CA.
Results indicate that cover and companion crops could promote sustainability in vegetable farmscapes by enhancing biotic resistance. Although deployment of these types of cover crop / companion crop would require changes in current cropping practices, they can produce comparable crops to those grown with current higher input methods.