Carlene A. Chase

Greater Interference from Living Mulches than Weeds in Organic Broccoli Production

Twelve winter cover crops were planted in Citra and Live Oak, FL, in 2004, to evaluate their potential for use as living mulches in organic vegetable production: black oat, rye, annual ryegrass, hard fescue, two cultivars of white clover, berseem clover, crimson clover, subterranean clover, arrowleaf clover, barrel medic, and a hybrid disc × strand medic cultivar. The best canopy development and weed suppression occurred with black oat, rye, and annual ryegrass. In 2005, black oat, two rye cultivars, and annual ryegrass were evaluated as living mulches in broccoli at Citra and Live Oak, using organic production methods. ‘Florida 401’ (FL 401) rye was tallest, black oat was intermediate, and ‘Wrens Abruzzi’ (WA) rye and ‘Gulf’ ryegrass were of similar height and were the shortest living mulches. Biomass harvested at 12 and 13 wk after planting at Citra and Live Oak, respectively, was greatest with FL 401 rye. At Live Oak, the three other mulches had similar amounts of biomass; however, at Citra, black oat biomass was greater than that of WA rye, and biomass of ryegrass was lowest. The greatest weed infestation occurred with the weedy control. Weed biomass was highest with the weedy control, intermediate with ryegrass, and lowest with rye and black oat. However, the biomass of the weedy control was lower than that of the living mulches plus any associated weeds. Marketable broccoli yield was highest with the weed-free control. Yields with black oat, WA rye, and ryegrass were similar to that of the weedy control, whereas yield with the FL 401 rye was lower than with the weedy control. Suppression of living mulches by mowing at 3 and 7 wk after planting had no effect on broccoli growth or yield. Nomenclature: Annual ryegrass, Lolium multiflorum Lam.; arrowleaf clover, Trifolium vesiculosum Savi, barrel medic, Medicago truncatula Gaertn., berseem clover Trifolium alexandrinum L., black oat, Avena strigosa Shreb., broccoli, Brassica oleracea L. var. italica Plenck., cereal rye, Secale cereale L., crimson clover Trifolium incarnatum L., disc × strand medic hybrid, Medicago tornata (L.) Mill. × Medicago littoralis Rohde ex Loisel., hard fescue, Festuca longifolia Thuill., subterranean clover, Trifolium subterraneum L., white clover, Trifolium repens L

Competitiveness of Three Leguminous Cover Crops with Yellow Nutsedge (Cyperus esculentus) and Smooth Pigweed (Amaranthus hybridus)

Abstract Greenhouse replacement-series experiments were conducted to evaluate the competitiveness of cowpea, sunn hemp, and velvetbean when grown in combination with yellow nutsedge and smooth pigweed. The effect of the cover crop species on yellow nutsedge tuber production was also evaluated. Cowpea and velvetbean were equally competitive with yellow nutsedge, but sunn hemp was less competitive. Although sunn hemp height was double that of cowpea or velvetbean, photosynthetically active radiation penetrating to the soil surface was twofold to eightfold greater than with the other two species. Leaf area per plant with sunn hemp monocultures were only 63 to 70% of cowpea and 37 to 41% of velvetbean. Increasing the proportion of cover crops in crop : weed mixtures did not significantly affect nutsedge tuber number per plant or tuber weight per plant. Cowpea was more competitive than smooth pigweed, whereas both sunn hemp and velvetbean were less competitive than smooth pigweed. The utility and efficacy of leguminous cover crop species for nutsedge and smooth pigweed suppression do not appear to be due to inherent competitiveness. Until cultivars that are more competitive become available, cultural measures should be employed that enhance cover crop modification of soil environmental conditions to minimize weed seed germination and vegetative propagule sprouting. Nomenclature: Smooth pigweed, Amaranthus hybridus L. AMACH; yellow nutsedge, Cyperus esculentus L. CYPES; cowpea, Vigna unguiculata (L.) Walp; sunn hemp, Crotalaria juncea L; velvetbean, Mucuna pruriens (L.) DC. var. pruriens

Phytotoxic Effects of Glyphosate on Pepper (Capsicum annuum)1

Abstract: Glyphosate was applied to pepper as single or sequential applications to assess the consequences of drift or other accidental exposures. Foliar injury increased and plant vigor declined with increased rates of glyphosate and were exacerbated by a second application. Single applications at flowering (stage 1) were more damaging than single applications after fruit set (stage 2). Decline in marketable yield with increased glyphosate rate was greater with stage 1 applications, except in spring 1987 when marketable yields with single applications of glyphosate at stage 1 or stage 2 were statistically similar. Sequential applications resulted in the lowest marketable yields. Total yields declined with increased glyphosate rate and decline was more pronounced with sequential applications than with single applications. Total yield was affected to a greater extent when glyphosate was applied at stage 1 than at stage 2. Yield was more sensitive to two successive exposures than to single applications. Mean fruit weight was reduced by glyphosate in two of the four experiments. Nomenclature: Glyphosate; pepper, Capsicum annuum L. Additional index words: Simulated drift, herbicide injury. Abbreviations: DAT, days after treatment; WAT, weeks after treatment.

Optimum Densities of Three Leguminous Cover Crops for Suppression of Smooth Pigweed (Amaranthus hybridus)

Abstract Additive experiments were performed to determine optimum densities for nematode-suppressive cover crops to extend the benefit from the cover crops by also using them for weed suppression. In a preliminary experiment in 2002, a range of cover-crop densities was evaluated in mixtures with smooth pigweed at 5 plants m−2. Smooth pigweed biomass accumulation was suppressed by cowpea, sunn hemp, and velvetbean at the lowest cover-crop populations (38, 44, and 15 plants m−2, respectively). Based on these results, experiments were conducted in 2003 at two locations to examine the effects of lower cover-crop densities on a higher smooth pigweed population density of 15 plants m−2. Cowpea and velvetbean densities ranged from 10 to 50 plants m−2 and sunn hemp from 20 to 100 plants m−2. In 2003, cowpea density had no effect on smooth pigweed biomass. However, smooth pigweed biomass declined linearly by 51% as sunn hemp density increased to 100 plants m−2. Similarly, as velvetbean densities increased, smooth pigweed biomass decreased showing a linear response at one location and quadratic response at the second location. Maximum suppression of smooth pigweed biomass by velvetbean occurred at the highest cover-crop density (50 plants m−2). Excellent suppression of smooth pigweed at 5 plants m−2 or fewer will result in densities of 38, 44, and 15 plants m−2 of cowpea, sunn hemp, and velvetbean. However, with smooth pigweed at 15 plants m−2, optimum cover-crop densities were not obtained because no suppression was obtained with cowpea, and the lowest weed biomass with sunn hemp and velvetbean occurred with the highest densities used. Therefore, when high smooth pigweed densities are expected, sunn hemp and velvetbean should be used at densities greater than 100 and 50 plants m−2, respectively, and further study with higher densities will be needed to define optima. Nomenclature: Smooth pigweed, Amaranthus hybridus L. AMACH; cowpea, Vigna unguiculata (L.) Walp. ‘Iron-Clay’; sunn hemp, Crotalaria juncea L. ‘Tropic Sun’; velvetbean, Mucuna deeringiana (Bort.) Merr. and Mucuna pruriens (L.) DC. var. pruriens.

Weed suppression with hydramulch, a biodegradable liquid paper mulch in development

Cost-effective, laborsaving, and environmentally sound weed management practices are needed for sustainable vegetable production. Organic production, in particular, precludes the use of synthetic herbicides and requires that organic farmers utilize practices that reduce harmful environmental impact. Although polyethylene film mulch is used extensively in vegetable production in Florida, its use has a number of drawbacks, among which is the susceptibility of opaque polyethylene mulch to penetration by yellow and purple nutsedge. Appreciable labor and disposal/environmental costs are associated with its removal. A durable mulch material that would effectively control nutsedge and other weeds but with no associated environmental and disposal costs is highly desirable. Hydramulch, a paper-like material applied as a slurry consisting of cotton waste, newsprint, gypsum and a proprietary adhesive, was tested as a biodegradable alternative to polyethylene mulch during the spring of 2003. Experiments were conducted in southeastern and north-central Florida to compare the effects of three hydramulch formulations, polyethylene mulch and a no mulch control on soil temperature, soil moisture and weed infestation. Soil temperature under hydramulch was 1‐4C lower than that under polyethylene. In the absence of rain, the use of hydramulch resulted in soil moisture levels that were 1‐4% lower than with polyethylene mulch. Higher soil moisture with hydramulch than polyethylene was coincident with rainfall. Hydramulch remained intact on most beds and suppressed broadleaf weeds and grasses, particularly at the north-central site where the mulch was applied at a greater thickness. However, purple nutsedge readily penetrated hydramulch. Therefore, hydramulch may be applicable for use for the suppression of broadleaf weeds and grasses at sites with little or no nutsedge pressure in fall or in crops for which cooler soils are desirable or crops that are rainfed or overhead irrigated.

Season-Long Interference of American Black Nightshade with Watermelon

Field trials were conducted over two spring seasons (2005 and 2006) to investigate the interference between American black nightshade and watermelon in polyethylene-mulched and nonmulched (bare ground) trials. Competition studies were performed with watermelon at 1 plant/m in-row and American black nightshade grown at 0, 2, 4, 6, and 8 plants/m2 in-row. Watermelon yield reductions started to plateau at only 2 American black nightshade plants/m2. Yield reduction was 80, 89, 96, and 98% and 54, 67, 81, and 85% at 2, 4, 6, and 8 American black nightshade plants/m2 in mulched watermelon production in 2005 and 2006, respectively. When watermelon was grown on bare ground, yield reduction was 100% at 2 American black nightshade plants/m2 in 2005 and 68, 81, 89, and 93% at 2, 4, 6, and 8 American black nightshade plants/m2 in 2006, respectively. Watermelon fruit numbers were reduced due to American black nightshade interference, but no significant differences in individual fruit weight were observed. Nomenclature: American black nightshade, Solanum americanum Mill., SOLAM, watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai. cv. ‘Mardi Gras’

EFFECTS OF PERENNIAL PEANUT AND COMMON BERMUDAGRASS ON NITROGEN AND WATER UPTAKE OF YOUNG CITRUS TREES

A greenhouse experiment was conducted using a Soil-N Uptake Monitoring (SUM) system to determine nitrogen (N) and water uptake dynamics of citrus (CIT), perennial peanut (PP) (Arachis glabrata Benth), and common bermudagrass (BG) (Cynodon dactylon L.) over time. We also assessed the competition for water and N uptake between citrus and groundcover species and compared citrus N uptake measured using the SUM system with the 15N method. Nitrogen uptake followed cyclic patterns and was greatest for bermudagrass-based systems, while values were similar for PP and citrus systems. Competition for N uptake did occur during the summer months between citrus and BG, while no obvious competition for N uptake occurred between citrus and PP. Water uptake was greatest for the mixed systems and BG monoculture. Citrus, PP, and BG competed for water during the spring and summer seasons. None of the groundcovers significantly affected overall citrus tree growth. Nitrogen use efficiency was greatest for mixed systems and bermudagrass.

Hydramulch for muskmelon and bell pepper crop production systems

Abstract Hydramulch is an experimental biodegradable mulch material comprising cotton by-products, newspaper, gypsum, and a proprietary adhesive. Three formulations of hydramulch were evaluated for potential use as a more sustainable alternative to polyethylene mulch for vegetable production at Loxahatchee in southeastern Florida and at Gainesville in north central Florida. Two crops with differing shoot architecture were selected to evaluate canopy effects on weed suppression and the persistence of hydramulch. Less cracking and wind removal of hydramulch occurred with muskmelon (Cucumis melo L) than with bell pepper (Capsicum annuum L.) and with 4-mm-thick hydramulch compared with 2-mm-thick material. Hydramulch suppressed broadleaf weeds and grasses, but was readily penetrated by purple nutsedge (Cyperus rotundas L.). Muskmelon and bell pepper shoot growth was significantly lower with hydramulch compared with polyethylene mulch. Marketable yield of muskmelon with hydramulch at Loxahatchee and Gainesville was only 56% and 7%, respectively, of the yield obtained with polyethylene mulch. No differences in weed infestation, crop biomass, and crop yield occurred due to hydramulch formulation. Current formulations of hydramulch appear to be applicable to crops with vining plant canopies like cucurbits that can protect hydramulch from cracking, help to anchor the mulch, and aid in suppressing weeds. Locations with nutsedge infestations should be avoided.

Flowering of the Cover Crop Sunn Hemp, Crotalaria juncea L.

Sunn hemp,Crotalaria junceaL., is a warm-season legume that is planted before or after a vegetable cash crop to add nutrients and organic matter to the soil, for weedgrowth prevention, and to suppress nematode populations. Sunn hemp flowers may also provide nectar and pollen for pollinators and enhance biological control by furnishing habitat for natural enemies. Despite these benefits, adoption in the United States has been limited because of restricted availability of seeds, particularly in temperate climates. Experiments were conducted in north-central Florida to compare flowering and seed production of domestic and foreign sunn hemp lines across different seeding rates and planting dates. Our objectives were to test whether a low seeding rate would result in the production of higher numbers of flowers and to test whether planting earlier in the season would also result in higher numbers of flowers. Our results over a 2 year period showed that the domestic cultivar AU Golden is capable of substantial flowering and seed production in the test region, confirming the compatibility of local environmental conditions. Seed costs suggest that ‘AU Golden’ is comparable with sunn hemp lines grown in foreign countries and is much less expensive than the standard cultivar Tropic Sun from Hawaii. The results demonstrate the potential economic viability of early flowering cultivars of sunn hemp as a cover crop alternative in Florida to improve soils in agricultural landscapes. Sunn hemp, Crotalaria juncea L., is a warm-season legume that is planted before or after a vegetable cash crop to add nutrients and organic matter to the soil (Cherr et al., 2006, 2007; Mansoer et al., 1997; Wang et al., 2005). This cover crop provides other benefits to growers such as suppression of weeds (Adler and Chase, 2007; Cho et al., 2015; Collins et al., 2008; Javaid et al., 2015; Morris et al., 2015; Mosjidis and Wehtje, 2011) and suppression of plant-parasitic nematode populations by not providing resources (Bhan et al., 2010; Braz et al., 2016). Sunn hemp is available to growers in northern Florida, where 10,000 ha of vegetables (potatoes, Solanum tuberosum L., and cabbage, Brassica oleracea L. var. capitata) are annually produced (Elwakil and Mossler, 2016; USDA-NASS, 2014). A major advantage of sunn hemp over many cover crops, particularly sorghumsudangrass (SSG) [Sorghum bicolor (L.) Moench], is that it is a poor host for fall armyworm [Spodoptera frugiperda (J. E. Smith)] and other important moth pests (Meagher et al., 2004). Southern Florida is a major overwintering region for fall armyworm populations that annually migrate northward and infest corn acreages along the eastern United States. Sorghumsudangrass is one of the common cover crop and forage grasses in the United States and therefore is a likely source of fall armyworm populations (Meagher et al., 2004; Pair and Westbrook, 1995). Therefore, large scale replacement of SSG with sunn hemp in Florida could mitigate fall armyworm populations before and during these annual migrations on an area-wide scale. Another ecological service that cover crops can provide is flowers that provision pollinators and enhance biological control (Campbell et al., 2016). Studies have shown that early season flowering by cover crops can increase pollinator populations, which promote late-season pollination in cash crops (Riedinger et al., 2014). Flower density and the richness of the cover crop plants have the most direct influence on bee visitation and native bee abundance (Ellis and Barbercheck, 2015; Saunders et al., 2013). The first sunn hemp cultivar commercialized in the United States was ‘Tropic Sun’, which was a direct increase of the original seed purchased in 1958 from the island of Kauai, HI and developed by the USDA Natural Resources Conservation Service (NRCS) and the University of Hawaii College of Tropical Agriculture and Human Resources (CTAHR) as a cooperative release in 1983 (Rotar and Joy, 1983; later identified as developed from PI 468956, Wang et al., 2006). Seed production in the tropics is good; however, because of this cultivar’s flowering response to short days, seed production is generally poor in the continental United States (Mosjidis, 2007; White and Haun, 1965). Therefore, seed availability to growers was limited to importation of ‘Tropic Sun’ from Hawaii or bringing in other germplasm from Brazil, India, South Africa, or other foreign locations. A breeding program to increase flowering and seed production was initiated at Auburn University in 2002. ‘AU Golden’ was developed from accession PI 322377, which was obtained from the National Plant Germplasm System. In a patent application, this germplasm was shown to be able to produce seed in Alabama, with the data extrapolated to indicate flower production, seed production, or both in the region between 40 north and 40 south latitude, and at least 400 lbs seed per acre when grown between 28 north and 28 south latitude (Mosjidis, 2014). These characteristics make it a potentially useful cover crop for much of Florida, which lies between 25 and 31 north latitude. However, it is not clear whether the local environment, including such factors as soil type, disease, herbivores, and appropriate pollinators, is conducive to this line of sunn hemp. To examine the potential and optimize sunn hemp cover crop usage in north-central Florida, multiple sunn hemp lines were tested in field studies to compare flowering and seed production across different seeding rates and planting dates. One objective was to test whether a low seeding rate would result in the production of higher numbers of flowers and seed pods. A second objective was to test whether planting ‘AU Golden’ earlier in the Received for publication 31 Mar. 2017. Accepted for publication 18 May 2017. We thank the staff at the University of Florida Plant Science Research and Education Center in Citra, FL for planting and management of the sunn hemp plots. We recognize the financial support of the National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-67003-30209. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the United States Department of Agriculture or the Agricultural Research Service of any product or service to the exclusion of others that may be suitable. Current address: Entomology and Nematology Department, University of Florida, 1881 Steinmetz Hall, Gainesville, FL 32611 Corresponding author. E-mail: rob.meagher@ars. usda.gov. 986 HORTSCIENCE VOL. 52(7) JULY 2017 season would result in both higher numbers of flowers produced and, because we felt that there was more pollinator activity at this time of year, higher seed production. A final goal was to test whether similar sunn hemp seeding could be obtained but with the potential for higher overall biomass per acre if a mixture of sunn hemp and SSG was used as a cover crop. Materials and Methods Sunn hemp germplasm. Four different sunn hemp lines were used in the experiments. The two lines from the United States were ‘Tropic Sun’, purchased Mar. 2014 from Molokai Seed Co., Kaunakakai, HI, and ‘AU Golden’, purchased Mar. 2014 and Apr. 2015 from Petcher Seeds, Fruitdale, AL. The two foreign lines were Tillage Sunn (purchased Mar. 2014 from Hancock Seed Co., Dade City, FL), a brand of sunn hemp from India which is sold through several seed distributors, and an unknown germplasm (variety not stated) from South Africa (purchased Mar. 2011 from Petcher Seeds). 2014 trial. The experiment in 2014 was designed to compare flowering and seed production of four sunn hemp lines planted at three different seeding rates. Plots were arranged as a randomized complete block with three blocks, yielding 12 plots per block and a total of 36 plots. Sunn hemp plots were planted 23 Apr. 2014 at the University of Florida Plant Science Research and Education Unit, Citra, FL (29 24#42

Effect of sunn hemp (Crotalaria juncea L.) cutting date and planting density on weed suppression in Georgia, USA.

N, 82 06#36