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Bielinski M. Santos and James P. Gilreath

Purple nutsedge can easily penetrate polyethylene mulch films. However, there are no reports on possible differences among mulch films. Because of this situation, field trials were conducted in Ruskin and Bradenton, Fla., during 2002 and 2003. In Spring 2002, the treatments were a) no mulch, b) black Pliant High Barrier mulch, and c) green Klerk's Virtually Impermeable Film (VIF). In Spring 2002, the films were a) black Pliant High Barrier, b) black IPM Bromostop, c) metallized Pliant, and d) green Klerk's VIF. The number of nutsedge emerged through the films was determined. No fumigants or herbicides were applied. Results indicated that the Klerk's VIF had the lowest nutsedge densities. No nutsedge control differences were found between the IPM Bromostop and the metallized Pliant films. These differences might be due to the physical properties of the films, including stretching and thickness.

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C. A. Sanchez

Approximately 33% of all irrigated lands worldwide are affected by varying degrees of salinity and sodicity. Soils with an electrical conductivity (EC) of, the saturated extract greater than 4 dS/m are considered saline, but some horticultural crops are negatively impacted if salt concentrations in the rooting zone exceed 2 dS/m. Salinity effects on plant growth are generally considered osmotic in nature, but specific ion toxicities and nutritional imbalances are also known to occur. In addition to direct toxic affects from Na salts, Na can negatively impact soil structure. Soils with exchangeable sodium percentages (ESPs) or saturated extract sodium absorption ratios (SARs) exceeding 15 are considered sodic. Sodic soils tend to deflocculate, become impermeable to water and air, and have a strong tendency to puddle. Some soils are both saline and sodic. This workshop presentation will summarize various considerations in the management of saline and sodic soils for the production of horticultural crops.

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Charles A. Sanchez and Jeffrey. C. Silvertooth

About 33% of all irrigated lands worldwide are affected by varying degrees of salinity and sodicity. Soil with an electrical conductivity (EC) of the saturated extract >4 dS·m−1 is considered saline, but some horticultural crops are negatively affected if salt concentrations in the rooting zone exceed 2 dS·m−1. Salinity effects on plant growth are generally osmotic in nature, but specific toxicities and nutritional balances are known to occur. In addition to the direct toxic effects of Na salts, Na can negatively impact soil structure. Soil with exchangeable sodium percentages (ESPs) or saturated extract sodium absorption ratios (SARs) > 15 are considered sodic. Sodic soils tend to deflocculate, become impermeable to water and air, and puddle. Many horticultural crops are sensitive to the deterioration of soil physical properties associated with Na in soil and irrigation water. This review summarizes important considerations in managing saline and sodic soils for producing horticultural crops. Economically viable management practices may simply involve a minor, inexpensive modification of cultural practices under conditions of low to moderate salinity or a more costly reclamation under conditions of high Na.

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Dianne Oakley, Julie Laufmann, James Klett, and Harrison Hughes

Propagation of Winecups [Callirhoe involucrata (Torrey & A. Gray)] for use as a landscape ornamental has been impeded by a lack of understanding of the seed dormancy and a practical method for overcoming it. As with many members of the Malvaceae family, C. involucrata produces hard seed. In the populations tested, it accounted for 90% of an average sample. Impermeability, however, is not the only limiting factor to germination. Three disparate populations of seed, representing two different collection years have been investigated using moist pre-chilling, boiling water, leaching, gibberellic acid, hydrogen peroxide and mechanical and chemical scarification methods. Scarifying in concentrated sulfuric acid stimulates germination of some seed fractions and causes embryonic damage in others, suggesting variation in seed coat thickness. Similar results were obtained using a pressurized air-scarifier; the hard seed coat of some seed fractions were precisely scarified while others were physically damaged using the same psi/time treatment. Placing seed in boiling water increases germination from 4%, 7%, and 18 % to 23%, 25%, and 77% in the three populations, respectively. Leaching for 24/48 h in cold (18 °C) aerated water or for 24 h in warm (40 °C) aerated water showed only a minor increase over the control. Pre-chilling at 5 °C for 30, 60, and 90 days showed no improvement over the control. Gibberellic acid-soaked blotters improved germination at 400 ppm to 20%, 10%, and 41%; at 500 ppm germination was reduced. Soaking seed for 24 h in a 3% concentration of hydrogen peroxide did not effect germination; at a 30% concentration germination was reduced. The considerable variation in seed dormancy expression may be a function of differences in environmental factors during development or seed age.

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Jenjira Chumpookam, Huey-Ling Lin, and Ching-Chang Shiesh

Smoke-water is a chemical extract used to stimulate the germination of many plant species under cultivation. This study evaluated the efficacy of smoke-water on the seed germination and seedling growth of papaya (Carica papaya cv. Tainung No. 2). Smoke-water, prepared from dry rice straw (Oryza sativa) by burning and bubbling the smoke through water, was used for germination experiments, growth experiments, and anatomical structure changes of seeds. In the germination experiments, papaya seeds were soaked with different concentrations of smoke-water (0.1%, 0.2%, 1%, 2%, 3%, 4%, 5%, 7%, or 10%, v/v) for 24 h before planting. Low concentrations of smoke-water (0.1% or 0.2%, v/v) not only promoted the maximum rate of germination, but also shortened the germination time. Analysis of longitudinal sections of seeds treated with smoke-water concentrations of 0.1% or 0.2% v/v suggested that smoke-water could overcome water impermeability barriers, because it stimulated the seedcoat to rupture and allowed the radical to elongate and emerge faster. In the growth experiments, papaya seedlings were transplanted into peatmoss-filled pots that were saturated with different concentrations of smoke-water (0%, 1%, 2%, 3%, 4%, 5%, 7%, or 10%, v/v). Results showed that all growth parameters increased significantly compared with the control. In addition, smoke-water treatments consistently and significantly increased the percentage of nitrogen in roots and shoots and significantly increased the percentage of magnesium in shoots. In these experiments, smoke-water showed potent germination promotion at low concentrations and promoted multiple growth attributes such as chlorophyll content and seedling vigor index at all concentrations in papaya seedling production.

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Bielinski M. Santos, James P. Gilreath, Timothy N. Motis, Marcel von Hulten, and Myriam N. Siham

Field trials were conducted to: 1) determine the effect of mulch types and applied concentrations of 1,3-dichloropropene + chloropicrin (1,3-D + Pic) on fumigant retention; and 2) examine the influence of mulch films and 1,3-D + Pic concentrations on purple nutsedge (Cyperus rotundus) control. 1,3-D + Pic concentrations were 0, 600, 1000, and 1400 ppm, and mulch types were white on black high-density polyethylene mulch (HDPE), white on black virtually impermeable film (VIF-WB), silver on white metalized mulch, and green VIF (VIF-G). Regardless of the initial 1,3-D + Pic concentrations and mulch types, fumigant retention exponentially decreased over time. When 1400 ppm of 1,3-D + Pic were injected into the soil, 1,3-D + Pic dissipation reached 200 ppm at 3.2, 2.9, 2.2, and 1.5 days after treatment (DAT) under VIF-G, VIF-WB, metalized, and HDPE mulches, respectively. At 5 weeks after treatment (WAT), HDPE mulch had the highest purple nutsedge densities among all films. The treatments covered with VIF-G had purple nutsedge densities <5 plants/ft2, regardless of the applied fumigant concentration, while VIF-WB and metalized mulch reached this weed density with 696 ppm of the fumigant. In contrast, 1186 ppm of 1,3-D + Pic were needed to reach this weed density with HDPE mulch. Correlation analysis showed that mulch fumigant retention readings at 3 DAT effectively predict purple nutsedge densities at 5 WAT (r ≤ –0.94). These findings proved that 1,3-D + Pic activity on purple nutsedge can be improved with the use of more retentive films, which cause longer fumigant retention, thus improving efficacy. Growers might elect reducing 1,3-D + Pic rates to compensate for the relatively higher cost of fumigant-retentive mulches, without losing herbicidal activity.

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Bielinski M. Santos, James P. Gilreath, Myriam N. Siham, and Camille E. Esmel

In Florida, nutsedge (Cyperus spp.) is a major weed problem in mulched-vegetable production. As methyl bromide (MBr) is phased out, alternatives are essential for growers. However, because of critical use exemptions, growers will still be able to use restricted amounts of MBr. Therefore, using highly-retentive mulch, such as virtually impermeable film (VIF), can reduce fumigant loss and may allow rate reduction without compromising efficacy. Preliminary studies have shown that metalized mulches can be an alternative to VIF. However, further studies are needed to compare MBr retention properties and nutsedge control of high density polyethylene (HDPE) mulch, VIF, and metalized mulch. Two field studies were conducted in spring 2005, in Ruskin, Florida. Metalized and HDPE mulches, and VIF were combined with the following rates of MBr + chloropicrin (Pic) (67/33, w/w): 175 and 350 lb/acre. Methyl bromide retention was evaluated in soil air samples at 1, 2, 4, and 6 days after treatment (DAT). Nutsedge plants were counted at 2, 4, 7, 9, and 12 weeks after treatment (WAT). Data were examined with regression analysis to establish the relationship between the time and both MBr concentration and nutsedge densities. Concentration of MBr + Pic under either the metalized mulch or VIF was about 6 times higher than under HDPE at 5 DAT, regardless of the MBr + Pic rate. At 12 WAT, nutsedge population was <1 plant/50 ft row with metalized and VIF and 175 lb/acre of MBr + Pic, whereas about 25 plants/50 ft row were present with 350 lb/acre of the fumigant and HPDE. The weed population reached >100 plants/50 ft row with 175 lb/acre of MBr + Pic. These findings demonstrate that metalized and VIF mulches can provide effective control of nutsedge with one-half of the commercially used MBr + Pic rate.

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Bielinski M. Santos, José Manuel López-Aranda, James P. Gilreath, Luis Miranda, Carmen Soria, and Juan J. Medina

Tunnel and open field trials were conducted in two locations in Huelva, Spain, and one in Florida to determine the effect of selected methyl bromide (MBr) alternatives on strawberry yield. In Spain, the tunnel treatments were: a) nontreated control, b) MBr + chloropicrin (Pic) 50:50 at a rate of 400 kg·ha–1; c) dazomet at 400 kg·ha–1, d) 1,3-dichloropropene (1,3-D) + Pic 65:35 at 300 kg·ha–1; e) Pic at 300 kg/ha; f) dimethyl disulfide (DMDS) + Pic 50:50 at 250 + 250 kg·ha–1; and f) propylene oxide at 550 kg·ha–1. All treatments were covered with virtually impermeable film (VIF), except the nontreated control, which was covered with low-density polyethylene (LDPE) mulch. Dazomet was rototilled 10 cm deep, whereas the other fumigants were injected with four chisels per bed. In Florida, the open-field treatments were a) nontreated control, b) MBr + Pic 67:33 at a rate of 400 kg/ha with LDPE; c) MBr + Pic 67:33 at 310 kg·ha–1 with VIF; d) 1,3-D + Pic 65:35 at 300 kg·ha–1 with VIF; e) methyl iodide (MI) + Pic 50:50 at 230 kg·ha–1 with VIF; f) Pic at 300 kg·ha–1 with VIF; g) DMDS + Pic 50:50 at 250 + 250 kg·ha–1 with VIF; and g) propylene oxide at 500 kg·ha–1 with VIF. The fumigants were applied with three chisels per bed. In Spain, the results showed that 1,3-D + Pic, DMDS + Pic, and Pic consistently had similar marketable yields as MBr + Pic. Similar results were found in Florida, with the exception of propylene oxide, which also had equal marketable fruit weight as MBr + Pic.

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Yung-I Lee, Nean Lee, Edward C. Yeung, and Mei-Chu Chung

This investigation documents the key anatomical features in embryo development of Cypripedium formosanum Hayata, in association with the ability of embryos to germinate in vitro, and examines the effects of culture media and seed pretreatments on seed germination. A better understanding of zygotic embryogenesis for the Cypripedium L. species would provide insights into subsequent germination events and aid in the in vitro propagation of these endangered species. In seeds collected at 60 days after pollination (DAP), soon after fertilization, no germination was recorded. The best overall germination was found at 90 DAP (≈70%), at which time early globular to globular embryos with a single-celled suspensors can be observed. After 135 DAP, the seeds germinated poorly. At this time the inner integument shrinks and forms a tight layer, which encloses the embryo, the so-called “carapace.” Using Nile red stain, a cuticular substance was detected in the carapace, which may play a role in the impermeability of the mature seed and may help the seeds survive in the stringent environment. At maturity (after 210 DAP), the embryo proper has an average size of eight cells along its length and six cells across the width. Lipids and proteins are the main storage products within the embryo. To improve seed germination, experiments were conducted to test the suitability of various media and pretreatments of seeds. When different media were used, except for the Harvais medium at 120 DAP, there was no significant difference in seed germination at three different developmental stages tested. Soaking mature seeds in 1% NaOCl or treating them with ultrasound may slightly increase the germination percentage. For seed germination, our results indicate that the timing of seed collection outweighs the composition of medium and the seed pretreatments.

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S.D. Nelson, C. Riegel, L.H. Allen Jr., D.W. Dickson, J. Gan, S.J. Locascio, and D.J. Mitchell

One of the proposed alternative chemicals for methyl bromide is 1,3-D. The most common forms of 1,3-D products are cis- or trans-isomers of 1,3-D with the fungicidal agent, chloropicrin, containing such mixtures as 65% 1,3-D and 35% chloropicrin (C-35). Soil fumigants are commonly applied under a polyethylene film in Florida raised bed vegetable production. Much of the research regarding cropping system effects of alternative fumigants to methyl bromide has focused primarily on plant growth parameters, with little regard to the atmospheric fate of these chemicals. The objective of this research was to determine both the atmospheric emission of 1,3-D under different plastic film treatments and to evaluate effects of application rates of 1,3-D and C-35 on plant pests, growth, and yield of Sunex 9602 summer squash (Cucurbita pepo L.). Results showed that use of a high barrier polyethylene film (or virtually impermeable film - VIF) greatly reduced fumigant emission compared to ground cover with conventional polyethylene films or uncovered soil. Summer squash seedling survival was a severe problem in several of the 1,3-D alone treatments where no fungicidal agent was added, whereas C-35 resulted in excellent disease control at both full and one-half of the recommended application rates for this chemical. Both 1,3-D and C-35 provided good plant stands and higher yields when applied at their recommended application rates. However, all squash yields were lower than typical squash production levels due to late planting and early winter frost kill. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitropropene (chloropicrin).