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Charles E. Barrett, Xin Zhao, and Robert McSorley

Organic heirloom tomatoes (Solanum lycopersicum L.) are difficult to grow in Florida as a result of root-knot nematodes (Meloidogyne spp.) (RKN) and hot, humid growing conditions. Although grafting with resistant rootstocks has been shown effective for RKN management in tomato production, little research has been conducted on grafted heirloom tomatoes under Florida conditions. In this 2-year study, two susceptible heirloom tomato scions, ‘Brandywine’ and ‘Flamme’, were grafted onto two hybrid rootstocks, i.e., interspecific tomato hybrid rootstock ‘Multifort’ (S. lycopersicum × S. habrochaites) and tomato hybrid rootstock ‘Survivor’ (S. lycopersicum). Non-grafted and self-grafted scions were used as controls. Three field trials were conducted including the 2010 and 2011 organic field trials as well as a transitional organic field trial in 2011. There was a lack of RKN pressure in the organic field in 2010. In 2011, the RKN population was higher in the transitional field than the organic field, whereas grafting with hybrid rootstocks significantly reduced root galling (P ≤ 0.0001) in both fields. In the organic field, the hybrid rootstocks performed similarly and significantly reduced root galling compared with the non-grafted and self-grafted scions by ≈80.8%. In the transitional field, compared with non-grafted scions, the root galling reduction by ‘Survivor’ (97.1%) was significantly greater than that by ‘Multifort’ (57.6%). In general, tomato plants grafted onto ‘Multifort’ tended to be more vigorous than all other treatments. There was no clear relationship between root galling and tomato yields. Grafting did not significantly affect the total marketable yield for the scion ‘Flamme’ in both years. Total marketable yield was similar among treatments in 2010 but varied in 2011 for the scion ‘Brandywine’. In 2011, the non-grafted ‘Brandywine’ and ‘Brandywine’ grafted to ‘Survivor’ produced significantly higher (P < 0.05) yields than other treatments in the organic field. However, in the transitional field, ‘Brandywine’ grafted to ‘Multifort’ resulted in significantly higher (P < 0.05) yields than the non- and self-grafted ‘Brandywine’ treatments. Grafting with appropriate rootstocks may play an effective role in RKN management during the transition to organic production when high populations of nematodes are present.

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Harsimran K. Gill, Robert McSorley, and Danielle D. Treadwell

Soil solarization is an important practice for small-acreage farmers and home gardeners and is used commercially in areas with high solar radiation and air temperature during the summer. In this technique, clear plastic films are used to increase soil temperature to manage soil-borne plant pests such as insects, diseases, nematodes, fungi, and weeds. Several different kinds of plastic films were evaluated in 2007 and 2008 for durability, weather tolerance, and weed suppression. Treatments were arranged in a randomized complete block design with five replications. In 2007, treatments were four clear plastic films including: ISO, VeriPack, Poly Pak, Bromostop®, and a white plastic control. In 2008, treatments were Polydak®, Poly Pak, Bromostop®, and white plastic. Films were evaluated for weed suppression based on the population density of weeds that emerged through breaks in the plastic, for durability in terms of number and size of breaks in the films, and for the total exposed soil area resulting from breaks. Purple nutsedge (Cyperus rotundus) was the major weed problem throughout both years. In both years, total exposed area was greater with white plastic and Bromostop® (81.5 ft2/bed) compared with other plastic films (<21.5 ft2/bed). Due to their durability, Poly Pak, ISO, and VeriPack suppressed nutsedge more than Bromostop and white plastic. Although a number of very small (<0.75 inch long) breaks were observed in Polydak® plastic film, they never increased in size, and this plastic film remained intact throughout the experiment and provided excellent weed control.

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Jose Linares, Johannes Scholberg, Carlene Chase, Robert McSorley, and James Fergusson

Lack of effective weed control may hamper organic citrus establishment. Cover crop/weed biomass (CCW) indices were used to assess the effectiveness of annual and perennial cover crops (CC) in reducing weed growth. The CCW values for perennial peanut (PP) were 0.06, 0.14, 0.4, and 0.5 during 2002, 2003, 2004, and 2005, respectively (very poor to poor weed control). Initial PP growth was slow and repeated mowing was required, but, over time, PP became more effective in controlling weeds. Weed biomass with sunn hemp was 0.3 Mg/ha in 2002 (CCW = 25, outstanding weed control) compared to 1.4 Mg/ha with use of cowpea (CCW = 1) in 2004. In 2004, the dry weights (Mg/ha) for different summer CC were: hairy indigo = 7.6, pigeon pea = 7.6, sunn hemp = 5.3, cowpea = 5.1, alyce clover = 2.9, velvet bean = 1.3, and lablab bean = 0.8. Corresponding 2005 values were: 9.5, 3.7, 12.6, 1.0, 1.9, and 1.4. Respective CCWI values were: 7, 4, 2, 16, 28, 0.6, and 0.3 (2004) vs. 17, 2, 64, 80, 0.5, 2, and 14. In 2004, winter CC production (Mg/ha) was radish (R) = 3.2, crimson clover (CR) = 1.7, oats (O) + lupine = 1.6, and rye (WR)/vetch (V) mix = 1.1. Results for 2005 were: CR + R + WR = 8.0, WR = 6.0; CR + WR = 5.3, CR = 5.0, CR + O + WR = 5.0, R = 4.3, and O = 3.6 Mg/ha. Corresponding values for CCW-indices were 15, 2, 1, and 3 (2004) and 100, 25, 76, 35, 62, 11, and 16 (2005). Although OMRI-approved herbicides showed up to 84% weed injury for selected species, none of these products provided long-term weed control. Combination of repeated tillage, use of compact/reseeding CC mixes in tree rows, more vigorous annual CC and/or perennial PP in row middle and repeated use of organic herbicides near sprinklers and tree trunks are thus required to ensure effective weed suppression in organic citrus.

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Jose Linares, Johannes Scholberg, Kenneth Boote, Carlene A. Chase, James J. Ferguson, and Robert McSorley

Citrus is one of the most important crops in Florida. During the past decade, increased international competition and urban development, diseases, and more stringent environmental regulations have greatly affected the citrus industry. Citrus growers transitioning to organic production may benefit from premium prices, but they also face many challenges, including development of effective weed management strategies. Cover crops (CC) may constitute an environmentally sound alternative for improved weed management in organic systems. Two field experiments were conducted at Citra in north central Florida from 2002 to 2005, to evaluate the effectiveness of annual and perennial CC to suppress weeds in organic citrus groves. To quantify and compare the effectiveness of CC to suppress weed growth, a new weed suppression assessment tool, the cover crop/weed index (CCWI), was developed using the ratio of biomass accumulation of CC and weeds. Annual summer CC accumulated more biomass in comparison with winter CC. Sunnhemp (Crotalaria juncea L.), hairy indigo (Indigofera hirsuta L.), cowpea (Vigna unguiculata L. Walp.), and alyceclover (Alysicarpus vaginalis L.) all provided excellent weed suppression, which was superior to tillage fallow. Single-species winter CC did not always perform consistently well. Use of winter CC mixtures resulted in more consistent overall CC performance, greater dry matter production, and more effective weed suppression than single species of CC. Initial perennial peanut (PP) growth was slow, and summer planting of PP (Arachis glabrata Benth.) was determined to be the most effective date in terms of weed suppression, which was improved gradually over time, but all planting dates resulted in slow initial growth compared with annual CC. For both PP and annual CC, weed biomass typically was inversely related to CC dry weight accumulation resulting from competition for resources. The CCWI was a suitable tool to quantify CC performance in terms of weed suppression.

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Monica Ozores-Hampton, Philip A. Stansly, Robert McSorley, and Thomas A. Obreza

Many vegetable growers rely on methyl bromide or other soil fumigants to manage soil pathogens, nematodes, and weeds. Nonchemical alternatives such as solarization and organic amendments are as yet largely unproven, but do offer promise of more sustainable solutions. The objective of this study was to evaluate the effects of long-term organic amendments and soil solarization on soil chemical and physical properties and on growth and yield of pepper (Capsicum annuum L.) and watermelon (Citrullus lanatus [Thunb.] Manst.). Main plots consisted of a yearly organic amendment or a nonamendment control. Four subplots of soil sanitation treatments consisted of solarization, methyl bromide, Telone, and nonfumigated. Each subplot was divided into two sub-subplots, one with weed control and one without weed control. Plant biomass was higher in plots with organic amendments than in nonamended plots. There were no differences in marketable pepper and watermelon yields between organic amended and nonamended plots during the 1998-99 and 1999-2000 seasons, respectively. However, higher pepper yields were produced from organic amended plots in the 1999-2000 season. Soil pH and Mehlich 1-extractable P, K, Ca, Mg, Zn, Mn, Fe, and Cu were higher in organic amended plots than in nonamended control plots. Soil organic matter concentration was 3-fold higher in amended soil than in nonamended soil. Effects of soil sanitation and weed management varied with crop and season. The methyl bromide and Telone treatments produced higher yields than soil solarization. In general, weed control did not affect plant biomass and yield for any of the crops and seasons. The results suggest that annual organic amendment applications to sandy soils can increase plant growth and produce higher or comparable yields with less inorganic nutrient input than standard fertilization programs.

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Wenjing Pang, John E. Luc, William T. Crow, Kevin E. Kenworthy, Robert McSorley, and Robin M. Giblin-Davis

Breeding and improvement of new bermudagrass (Cynodon spp.) cultivars with superior nematode tolerance are essential because sting nematode (Belonolaimus longicaudatus Rau) is a major limitation for use of bermudagrass in the sandy coastal soils of the southeastern United States. The screening of both African (Cynodon transvaalensis) and common (C. dactylon) bermudagrass is necessary to develop triploid hybrid cultivars. Five commercial cultivars and 46 germplasm accessions of bermudagrass were tested for nematode responses in two greenhouse trials in 2009. Turfgrass was grown in sand-filled plastic conetainers and inoculated with 50 sting nematodes per conetainer. Nematode and root samples were collected 90 d after nematode inoculation. Fifteen bermudagrass accessions did not have measurable root loss from inoculation with sting nematode. Seven bermudagrass accessions, including ‘Celebration’, produced longer roots in sting nematode-infested soil than the standard ‘Tifway’. Differences in final nematode numbers were identified among the genotypes, and different relative responses were identified in variable ploidy levels and origins. This could aid a turfgrass breeding program by elucidating the genetic diversity available for breeding future bermudagrass cultivars for golf course cultivation.