Integrated Management of Purple and Yellow Nutsedge in Organic Vegetable Production

Integrated Management of Purple and Yellow Nutsedge in Organic Vegetable Production

Summary

At Gainesville, the effects of summer fallow treatments persisted in spring crops so that purple nutsedge infestations in squash and bell peppers were lower than with the weedy fallow. Improved purple nutsedge suppression and crop yields occurred with infrared transmitting (IRT) film. At Tifton, summer solarization continued to perform well as an alternative method of weed management in organic crop production and IRT film was also effective in suppressing weeds at this location. At Clemson, season-long management is regarded as essential to prevent increases in purple nutsedge tuber production over time, and thus selection of a site free of purple nutsedge was advocated.

Objectives/Performance Targets

Gainesville, Florida

To compare the summer fallow techniques of a summer cover crop, soil solarization, clean fallow with disking, clean fallow with flaming, and a weedy fallow on purple nutsedge population density, tuber number and size distribution, and tuber viability.

To evaluate the persistence of suppression in two subsequent fall cash crops with differing canopy sizes and rates of growth and development.

To compare the effect of clean fallow and an allelopathic winter cover crop on purple nutsedge tuber viability.

To assess the effect of spring crops of differing canopy type and rate of growth and development and weed-suppressive synthetic mulch (IRT – infrared transmitting film).

To identify a combination of treatments applied in sequence that result in the most cost effective and efficacious suppression of purple nutsedge.

Tifton, Georgia

Objectives at Georgia are the same as Florida except for the target weed species, which is yellow nutsedge.

Clemson, South Carolina

To integrate tillage, solarization, an IRT film, a biofumigation/cover crop, mulching, and mowing as multi-facet strategies for suppressing purple nutsedge in organically grown bell pepper.

Economic Analysis

To assess the monetary costs and returns to producers in comparison to conventional (non-organic) production systems, non-market environmental and social benefits associated with reduced consumption of pesticides, and regional economic impacts of expanded local vegetable production.

Accomplishments/Milestones

Gainesville

An on-farm evaluation of serial integrated crop management systems is in progress to manage purple nutsedge (Cyperus rotundus) in organic vegetables in north-central Florida. The multi-pronged approach involves yearlong management during summer fallow and fall and spring cropping periods. The integration of several strategies into a systems approach to vegetable crop management may provide improved nutsedge suppression and crop yields.

Suppression of nutsedge by summer fallow treatments (2005) persisted into spring 2006, so that in summer squash, all treatments had significantly lower nutsedge infestations than the 219 plants/m2 obtained in the weedy control. Nutsedge densities in fallow treatments ranged from 7 to 51 plants/m2, but were not statistically different. In bell peppers, again, nutsedge density was highest with the weedy control. With the fallow treatments, nutsedge densities were lowest with weekly tillage, intermediate with flaming and sunn hemp-mulched, and highest with sunn hemp-incorporated and soil solarization. In both squash and peppers, the use of IRT film significantly reduced nutsedge infestation. The use of IRT also significantly increased numbers of squash by 18% to 43% and weight of squash by 27% to 48%. Only the increase in yield in the sunn hemp-incorporated treatment was not significant. In the bell pepper crop, fruit yields were highest with weekly tillage and lowest with the weedy control. The use of IRT film increased pepper number by 25% and pepper fresh weight by 21%.

Summer fallow treatments and fall crops were repeated in 2006 and those data are currently being analysed and compared with summer and fall 2005 data. The spring 2007 crops of zucchini squash and bell peppers were planted in late March.

Tifton

Trials were initiated in late June 2005 and continued according to the protocol through spring 2007. Currently, the site is being prepared for spring planting of vegetable crops. It was previously reported that this particular site had a history of heavy yellow nutsedge infestation, but the weed was present in 2005 fall-seeded crops at low densities. However, yellow nutsedge was present in spring planted crops in 2006 at very high densities that responded to treatments. All weeds, including yellow nutsedge, were suppressed by IRT thin-film mulch as a seedbed cover. However, yellow nutsedge was present in bareground plots, with previously solarized plots being the only ones with effective yellow nutsedge control. Propane flaming, sunn hemp cover crop, and fallow-tillage the preceding summer did not effectively suppress yellow nutsedge and other weeds. Yields of squash and bell-pepper responded similarly to treatments as yellow nutsedge densities. It was also noted that yellow nutsedge was not present at significant densities in fall-seeded crops both years, regardless of the treatment.

Solarization effectively reduces weed populations in the upper portions of the soil profile. A sunn hemp cover crop suppressed annual weeds, but not yellow nutsedge. Furthermore, direct-seeding turnip green into sunn-hemp biomass was very troublesome due to biomass interfering with vacuum-planter operation.

Clemson

The population dynamics of purple nutsedge was evaluated over two growing seasons in an organic production system where bell pepper was grown as a fall crop. The experimental design was a split plot with four replications. Main plot factors included: 1) green polyethylene film applied immediately following tillage in March, 2) clear polyethylene film applied immediately following tillage in March, 3) tillage in March immediately followed by spring-seeded turnip followed by a green film after mechanically terminating (flail mowing) turnip in mid-June, 4) tillage in March immediately followed by spring-seeded turnip followed by solarization after terminating turnip in mid-June, 5) tillage approximately every 3 weeks beginning in March, and 6) no means of control (fallow) prior to land preparation for bell pepper transplanting. Each tillage operation consisted of rototilling to an approximate depth of 10 cm.

Subplots treatments consisted of no additional weeding, hand-weeding, and wheat straw mulch following bell pepper transplanting. ‘Heritage’ bell pepper was transplanted at the 4- to 6-leaf stage, 16 transplants per each 2-row subplot with 0.3 m spacing between and within bell pepper rows. Plots were 1.8 m wide, and the middle of the row was mowed every other week to minimize purple nutsedge shoot growth and propagation. Hand-weeding and mulching took place in a 0.3-m strip adjacent to either side of the planted row (total of 0.9 m wide). The time needed to hand-weed bell pepper was recorded for each treatment. Purple nutsedge tuber number was determined by removing a known area of soil from each plot to a 15-cm depth and sieving the soil for tubers in March, August, and November each year. Viable tubers were categorized into three sizes: small (0.1 to 0.25 g), medium (0.26 to 0.5 g), and large (>0.50 g). Data were subjected to ANOVA. Initial tuber density was a covariate when analyzing the tuber data. Treatment means were separated using Fisher’s Protected LSD at alpha = 0.05.

The initial viable tuber density averaged 499 small, 298 medium, and 110 large tubers/m2 in mid-March 2005 (907 total tubers/m2). Total tuber density increased to >5,500 tubers/m2 in fallow, nonweeded plots by November 2006. Yearly tuber density remained relatively constant over the two years when the fallow period was followed by hand-weeding in the bell pepper crop. Mulched plots following the fallow period had tuber densities comparable to fallow, nonweeded plots at all sample times, except November 2006 when densities were lower when mulched. Frequent tillage or use of a polyethylene film with or without turnip generally caused tuber density to decline from mid-March through July, but tuber densities then increased to levels higher than the initial density in late summer and fall when subplots were not weeded. A similar but lesser trend occurred in most mulched plots; however, densities were not different from hand-weeded plots.

Density of large and medium tubers in the most intensive management systems remained stable while small tubers were prone to depletion over time. Frequent tillage or use of a polyethylene film with or without turnip resulted in a lower density of large tubers in November 2006 relative to fallow treatments, regardless of management intensity in bell pepper. Large tuber density after two years was generally similar among treatments involving frequent tillage or use of a polyethylene film with or without turnip within hand-weeded, mulched, and nonweeded subplots. A similar response was observed for medium tubers, but not small tubers. All handweeded plots had comparable densities of small tubers, ranging from 25 to 194 viable tubers/m2. With exception of the fallow treatment, small tuber density was comparable in all nonweeded, mulched, and hand-weeded subplots in November 2006, averaging 187 tubers/m2.

Intensive management involving frequent tillage or use of a translucent polyethylene film with or without turnip followed by hand-weeding was not effective in eradicating purple nutsedge over two growing seasons. Purple nutsedge management costs calculated for each main plot treatment revealed that use of a translucent polyethylene film alone was at least 4.5-fold more costly than frequent tillage. Averaged over both years, hours spent hand-weeding bell pepper was comparable among plots involving frequent tillage or use of a polyethylene film with or without turnip, averaging 768 to 879 hr/ha/year. The time spent hand-weeding following the fallow period averaged 1,096 hr/ha/year. Hence, it is not likely that an economic return can be realized at the intensity of management put forth in hand-weeded plots.

This research further documents the difficulty in managing purple nutsedge, especially in an organic production system. Furthermore, it is evident that season-long management is essential to prevent increases in purple nutsedge tuber production over time. Once purple nutsedge becomes established, even at low densities, there is minimal feasibility of economical eradication while still producing a crop. Hence, when selecting a site for organic crop production, an asserted effort should be made to select a site free of purple nutsedge.

Economic Analysis

Costs for vegetable production with organic methods for weed control are being evaluated using information from experimental plots on labor time and materials expenses. Costs will be extrapolated to express on a per acre basis for comparison with conventional (non-organic) production systems. Preliminary results indicate direct pre-harvest costs per acre of $2,888 for broccoli and $3,462 for peppers. This included labor costs of $1,083 and $1,473 per acre, respectively. In addition, costs for summer fallow weed control were evaluated for soil solarization, tillage, a sunn hemp cover crop, and flame weeding. Soil solarization appears to be more economical than flaming ($1,053 vs. $4,672 per acre).

Market prices for organic produce are also being analyzed for comparison with conventional produce. Vegetable products examined include squash, peppers, broccoli and spinach. Terminal market prices are available from the USDA Agricultural Marketing Service-Market News Service, for Miami, Atlanta, and Columbia in the southeast U.S. Shipping point prices (farm gate) are also available for production areas in South Georgia, North, Central and South Florida.

The economic analysis for the project will be completed in the second quarter of 2007.

Impacts and Contributions/Outcomes

The effectiveness of control measures vary with nutsedge species, location, and cropping system. Although at no location will the measures employed eradicate nutsedges, at Gainesville and Tifton combinations of a summer fallow treatment with the use of IRT film appears to have the potential to suppress and manage nutsedge. Information will be forthcoming on the cost of utilizing these measures. Therefore, growers in these areas who already have fields infested with these species will have the information available to decide whether the returns from a particular crop justify the cost of managing nutsedge in those fields.

Presentations

The research resulted in invitations to Dr. Norsworthy and Dr. Chase to give the following presentations at the Symposium “New Innovations for Weed Management in Organically Produced Crops” at the 2007 Southern Weed Science Society Meeting:

• Norsworthy, J.K., S.K. Bangarwa, M. Malik, and P. Jha. 2007. Population Dynamics of Purple Nutsedge in an Organic Production System.

• Chase, C.A., R.L. Koenig, J.E. Pack, and C.L. Brinton. 2007. Effectiveness of cultural and physical measures in suppressing purple nutsedge in organic vegetables.

Organic Workshop and Field Day

A workshop and field day on organic production was held on Wednesday September 20, 2006 at the Plant Science Research and Education Unit in Citra, FL. The event was cosponsored by: the University of Florida, Florida Organic Growers and Consumers, Inc., and Florida A&M University. The 237 attendees included beginning growers, experienced non-organic growers, established organic growers, administrators, faculty, students, and industry representatives. The field day focused on Nutsedge Control in Organic Production Systems and was led by Drs. Chase, Koenig, and Johnson. With samples of plants at different developmental stages and nutsedge tubers, participants were taught how to distinguish between purple and yellow nutsedge. Plots demonstrating the cultural and physical techniques of soil solarization, sunn hemp, flame weeding, and tillage were used to explain how these practices were being used in our studies, which were proving to be most effective, and what short-comings had become apparent with some of the techniques.

An evaluation instrument developed by Dr. Swisher was used to evaluate whether learning had occurred during the field day. A t-test for two independent samples was run to compare pre-test and post-test scores of participants. The t-value was -5.56105 and the p-value was <0.0001. Therefore, it was concluded that overall, based on mean scores only, there was a significant difference between pre- and post-test scores, indicating that our training did in fact work.

Eleven UF-IFAS faculty and 10 certified organic producers provided information during panel discussions and workshops that followed the field day.

Collaborators: