Chemical control of root rot complex and stem rot of greenhouse cucumber in straw-bale culture

Experiments were conducted in three different commercial greenhouses wherein cucumber (Cucumis sativus L.) cv. Kalunga F₁ (Long English type) were grown in composted straw bales, heavily infested with Fusarium oxysporum Schlechtend.:Fr. f.sp. radicis-cucumerinum Vakalounakis (FORC), the causal agent of Fusarium root and stem rot of cucumber. FORC was isolated from roots and stem bases of symptomatic plants either in single infections or simultaneously with other root infecting pathogens, including species of Phytophthora and Pythium and Rhizoctonia solani Kühn AG-4. Verticillium dahliae Kleb. was obtained from individual cucumber plants showing wilt symptoms. Fungicide applications started at the beginning of fruiting time when the first symptomatic plants occurred and followed at 45-day intervals. Three fungicides, either alone or as tank-mixed combinations of 0.1% Topsin M 70WP (thiophanate-methyl 700 g kg⁻¹) plus 0.15% Previcur 607SL (607 g L⁻¹ propamocarb hydrochloride), or 0.1% Benomyl 50WP (benomyl 50 g kg⁻¹) plus 0.15% Previcur 607SL, were applied to the crown and root area of cucumber plants through drip irrigation systems as drenches at a rate of 0.25 L/plant. Plant mortality was reduced by 11.1%–84.8% and 23.8%–77.7% when plants were drenched with Topsin M 70WP in combination with Previcur 607SL or Benomyl 50WP plus Previcur 607SL, respectively. In comparison, significantly lower levels of disease control were achieved when these fungicides were applied individually. Three fungicide applications during the crop season increased the inhibitory effect of the fungicide regime on the disease incidence compared to one or two treatment.     

Fumigant persistence and emission from soil under multiple field application scenarios

Chemical fumigants are routinely used for soil disinfestation of high value crops. Good agricultural practices (GAPs) are needed to reduce their human health risks, environmental impacts, and improve their cost-effectiveness. This study investigated the effect of fumigant application methods on soil persistence and emission of 1,3-dichloropropene (1,3-D) and chloropicrin (CP). Field experiments were conducted to measure the individual and combined effects of pre-application tillage practices, fumigant application technology, and plastic films on 1,3-D soil concentrations to obtain a numerical index (CT value) to estimate their potential for pest control efficacy and to compare soil persistence, atmospheric flux rate, and cumulative emission of CP and 1,3-D under two diverse application scenarios. Greater 1,3-D soil vapor concentrations were observed by combining a pre-application soil seal with low soil disturbance application technology when compared to pre-application soil tillage and the use of back-swept application shanks. Under high density polyethylene plastic, the low disturbance scenario resulted in time weighted exposure concentration (CT) values ranging from 6.8 to 12.2 μg h cm⁻³ of soil as compared to CT values ranging from 2.9 to 5.4 μg h cm⁻³ under the conventional application scenario. Cumulative atmospheric emission of 1,3-D was decreased by 18% under the low disturbance scenario and atmospheric emission of CP by 21% when compared to a conventional application scenario. This study identified GAPs that can be readily implemented in the field to reduce the human and environmental impacts of soil fumigants and improve their cost-effectiveness under solid-tarp (broadcast) applications.     

Efficacy of 1,3-dichloropropene plus chloropicrin gelatin capsule formulation for the control of soilborne pests

A gelatin capsule (gel cap) formulation of the mixture of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) has been developed to reduce environmental emissions and potential human exposure from the use of 1,3-D/CP as a soil fumigant. The objective of the present study was to evaluate the biological efficacy of 1,3-D/CP gel cap formulations under greenhouse trial conditions. The current results indicate that a 1,3-D/CP gel cap formulation at 30 or 50 g a.i. m⁻² can reduce the soil populations of Fusarium spp., Phytophthora spp., Pythium spp. and Meloidogyne spp.. In all tested crops, the 1,3-D/CP gel cap formulation provided marketable yields that were significantly higher than untreated controls and equal to the methyl bromide and 1,3-D/CP liquid injection treatments. Yields of tomato and a subsequent melon crop in plots treated with 1,3-D/CP gel cap were 93% and 87% greater, respectively, than the control. The yields of grafted cucumber and the subsequent balsam pear crop were increased by 16% and 201% respectively, compared to the control. The present study confirms that the tested 1,3-D/CP gel cap formulation provides a promising method for soil pest and disease control and reducing environmental emissions and potential human exposure in greenhouse vegetable cultivation.     

Integrated management of major diseases of mungbean by seed treatment and foliar application of insecticide,fungicides and bioagent

Field experiments were conducted during the rainy seasons of 2009 and 2010 for the management of the major diseases of mungbean, namely, wet root rot (Rhizoctonia solani), cercospora leaf spots (Cercospora canescens and Pseudocercospora cruenta) and yellow mosaic (Mungbean Yellow Mosaic Virus) by using different combinations of an insecticide, fungicide, and bio-formulation as seed treatment, with or without foliar sprays. A combination of seed treatment with thiamethoxam (Cruiser™) at 4 g kg⁻¹, carboxin (Vitavax™) at 2 g kg⁻¹ and Pusa 5SD (Trichoderma virens) at 4 g kg⁻¹ followed by simultaneous foliar sprays of thiamethoxam (Actara™) 0.02% and carbendazim (Bavistin™) 0.05% at 21 and 35 days after sowing resulted in the highest seed germination and grain yield in mungbean with the lowest intensities of cercospora leaf spots and mungbean yellow mosaic, and moderate incidence of wet root rot. The lowest whitefly population was also observed in this treatment during all stages of the crop. The treatment combinations having Pusa 5SD as seed treatment provided the lowest wet root rot incidence. Two sprays were superior to single spray for all variables recorded, but in combination with seed treatment, single spray was found to be more cost effective as it obtained the highest return per rupee of input. Use of T. virens based bio-formulation Pusa 5SD with insecticide thiamethoxam has been effectively demonstrated for the first time along with fungicides Bavistin and Vitavax for the management of the major diseases of mungbean.     

Effects of 1,3-dichloropropene plus chloropicrin on weed seed germination

Telone C-35, a commercial formulation of 1,3-dichloropropene (1,3-D) and chloropicrin (CP), is one of the potential replacements to methyl bromide (MB) for soil fumigation. A laboratory dose–response study and two field trials in tomato were conducted to evaluate their weed control efficacy and their effect on tomato yield. Laboratory studies found that the seeds of Digitaria chinensis were the most sensitive to soil fumigation with Telone C-35, followed by Eleusina indica, Portulaca oleracea and Stellaria media with the LC₅₀ values between 3.35 and 11.68 mg kg⁻¹ soil. Field trials revealed that Telone C-35 applied to the field at 327, 243 and 164 L ha⁻¹ could suppress the percentage of germination weed seeds while maintaining high tomato marketable yields, with no significant differences between MB + CP and the higher two Telone C-35 rates. The yield data from both seasons indicated that all Telone C-35 treatments had a positive effect on tomato yield; there was a 32%–62% increase the mean marketable tomato yield. Our results indicated that Telone C-35 was an excellent MB alternative and could provide acceptable weed control efficacy. Based on our results, Telone C-35, in combination with other alternatives to MB, is recommended to achieve integrated pest management.     

Using dazomet to reduce broomrape seed banks in soils with low moisture content

Dazomet (Basamid^®) is a dry powder formulation that releases the toxic gas methyl isothiocyanate for the control of soil borne pests and weed seeds when applied to moist soils. We evaluated its efficacy for destroying Phelipanche mutelii (branched broomrape) seed banks. Dazomet is typically used where effectiveness can be improved with the addition of water but we examined its performance in soils with low moisture content in container experiments and field trials. In containers, less than 10% of P. mutelii seed remained viable 30 days after dazomet applications of 112.8–338.4 kg ha⁻¹ at soil moisture content from 0.05 to 0.15 g g⁻¹. Seeds buried at a depth of 5 cm needed to be in contact with the product for longer than one week before viability was affected. An initial field trial did not detect a decline in seed viability 7 days after dazomet application. Viability assessments in a second field trial were made 30 days after dazomet application with an airseeder at a rate of 338.4 kg ha⁻¹. Less than 10% of P. mutelii seeds at a depth of 5 cm survived and dazomet was as effective as two other soil fumigants, methyl bromide and a methyl iodide/chloropicrin mixture. The release of methyl isothiocyanate is reduced in soils in containers with low soil moisture content but occurs over a long time period. Methyl isothiocyanate dissipated more rapidly in soils in containers with higher soil moisture content and at lower dazomet application rates. A higher application rate is required in the field to ensure the dazomet powder is evenly distributed through the soil profile and there is adequate methyl isothiocyanate resident in the top soil layer to achieve seed kill. This has consequences for plant back times in fumigated land following dazomet application.     

Management of herbicide-resistant Phalaris minor in wheat by sequential or tank-mix applications of pre- and post-emergence herbicides in north-western Indo-Gangetic Plains

Development of cross resistance or multiple cross resistance in Phalaris minor in wheat will continue to increase, as the weed develops mechanisms of resistance against new herbicides. This weed is a major threat to wheat productivity in north-western India, and as such needs to be addressed with integrated weed management approaches, including crop and herbicide rotations, herbicide combinations along with cultural and mechanical methods. Three field experiments were conducted during 2008–09 to 2012–13 along with large plot adaptive trials during 2012–13 with the objective to evaluate the efficacy of sequential applications of pendimethalin applied pre-emergent followed by clodinafop, sulfosulfuron, or pinoxaden applied post-emergent and tank-mix applications of metribuzin with these post-emergence herbicides for the management of herbicide-resistant P. minor in wheat. Clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 days after sowing (DAS) and pendimethalin 1000 g ha⁻¹ as pre-emergence did not provide consistently effective control of P. minor in wheat. An increase in the dose of clodinafop from 60 to 75 g ha⁻¹ and of sulfosulfuron from 25 to 30 g ha⁻¹ also did not improve their efficacy to a satisfactory level. However, pinoxaden 50 g ha⁻¹ provided effective control (97–100%) of P. minor but not of broadleaf weeds. The tank-mix application of metribuzin with clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 DAS and the sequential application of pendimethalin 1000 g ha⁻¹ or trifluralin 1000 g ha⁻¹ just after sowing followed by clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 DAS provided 90–100% control of P. minor along with broadleaf weeds in wheat, thus resulting in improved grain yields (4.72–5.75 t ha⁻¹) when compared to clodinafop 60 g ha⁻¹ (3.85–5.60 t ha⁻¹) or sulfosulfuron 25 g ha⁻¹ alone (3.95–5.10 t ha⁻¹). The efficacy of mesosulfuron + iodosulfuron (a commercial mixture) 14.4 g ha⁻¹ against P. minor was not consistent across the experiments and over the years. The ready-mix combination of fenoxaprop + metribuzin (100 + 175 g ha⁻¹) at 35 DAS provided effective control of weeds but its varietal sensitivity needs to be determined before its use in field conditions. The tank-mix or sequential application of herbicides would be a better option than their applications alone to manage the serious problem of herbicide-resistant P. minor in wheat.     

The Effect of Alfalfa Residue Incorporation on Soil Bacterial Communities and the Quantity of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> Microsclerotia in Potato Fields in the Columbia Basin of Washington State,USA

Verticillium wilt, caused by the soil-borne fungus Verticillium dahliae, is one of the most important diseases of potato in North America. Soil incorporation of alfalfa residues prior to planting potato could be a nonchemical Verticillium wilt management tactic by reducing the number of viable microsclerotia in field soil. Verticillium dahliae microsclerotia were quantified in field soils where organic material from alfalfa was incorporated, and numbers of microsclerotia were compared to fields where alfalfa residue was not incorporated. In addition, bacterial metagenomics was utilized to characterize soils where organic material from alfalfa was or was not incorporated to determine if alfalfa residue incorporation facilitates the formation of soils that suppress or kill V. dahliae microsclerotia. The number of V. dahliae microsclerotia in soil was greater (P = 0.0003) in fields where crop residue was incorporated than fields without incorporation when chloropicrin was used as a fumigant. Conversely, the number of V. dahliae microsclerotia observed in potato plants did not differ (P = 0.4020) between fields where residues were or were not incorporated if chloropicrin was used. Alfalfa residue incorporation did not significantly alter the soil bacterial metagenome compared to fields not subject to residue incorporation in both years of study. Despite these conclusions, the method can be employed to analyze the effect of grower practices with the intent of linking a field practice to increasing soil bacterial diversity and decreasing Verticillium wilt severity on potato.     

Effects of combined application of potassium phosphite and fungicide on stem and sheath disease control,yield, and quality of rice

Phosphite has been shown to suppress some diseases in different plant species but disease control in rice has not been investigated. In 2012/13 and 2013/14 potassium phosphite was sprayed at 1775 g ha⁻¹ and 3550 g ha⁻¹ in field plots of rice in Uruguay to determine if phosphite alone or in combination with label rates of a mixed strobilurin and triazole fungicide could be used to effectively control stem rot and aggregate sheath spot in irrigated rice. Six treatments consisting of different combinations of potassium phosphite alone or with a fungicide and an unsprayed control were assayed in one application at late-boot to early-heading. Phosphite alone in single and double rate slightly reduced severity and incidence of stem rot and produced a small yield increase over the unsprayed control. Fungicide at a 50% label rate with phosphite reduced stem rot severity and incidence to a similar level as the fungicide alone applied at the label rate. Disease severity was reduced by approximately 25% and incidence by 17–20% when compared with untreated control. Yield increase was 5% for both treatments over the unsprayed control. Fungicide combined with phosphite at single and double rates reduced stem rot severity by 40–45% and incidence by 34–38% when compared with untreated control, with yield increased by 10% over the unsprayed control and 5% over plots treated with a fungicide. These results indicate that a single application of potassium phosphite combined with fungicide can be used efficiently to manage of rice stem diseases.     

Impact of managing cover crop residues on the floristic composition and species diversity of the weed community of pepper crop (Capsicum annuum L.)

The decline of farmland biodiversity is mainly attributed to the intensive use of chemical inputs in agriculture. Cover crop residues may contribute to improve weed management while maintaining a high level of weed diversity. A 2-year field experiment was carried out in central Italy to study the effect of cover crop species and their residue management on weed community composition and weed species diversity in a winter cover crop – pepper sequence. Hairy vetch (Vicia villosa Roth.), oat (Avena sativa L.) and canola (Brassica napus L.) were sown in September 2009 and 2010 and grew undisturbed during the winter season until spring when they were suppressed one week before pepper transplanting. Cover crop residues were: (i) green manured at 30 cm depth (conventional tillage, CT), (ii) green manured at 10 cm depth (minimum tillage, MT), and (iii) left on the soil surface as mulch strips covering 50% of the ground area in no-tilled soil (NT). A winter weedy fallow and a bare soil without cover crop in NT, MT and CT were also included as controls. Weed plant density data in pepper were used for calculating weed species richness. Compared to weedy fallow, oat, hairy vetch and canola consistently reduced the weed density and weed aboveground biomass by the time of their suppression (on average 3.6, 21.5, and 41.3 plants m⁻² and 11.0, 49.2, and 161.8 g m⁻² of DM, respectively). In pepper, oat residues generally determined a higher reduction of weed density and species richness compared to hairy vetch and canola regardless the residue management treatments. Converting cover crop aboveground biomass into mulch strips greatly reduced weed species density but did not always imply a reduction of weed species diversity in pepper compared to MT and CT. The weed species richness was reduced inside the mulch strips, while a richer and more diverse weed community was found outside the mulch strips in NT. Weed community in pepper was mainly composed of annual dicot weeds such as Amaranthus retroflexus, Chenopodium album, Solanum nigrum, Polygonum aviculare which were mostly associated with MT and CT tillage systems, while in NT an increase of perennial species such as Rumex crispus was observed. These results suggest that it is possible to manage cover crop residues in NT in order to obtain a lower weed density and consequently a higher yield in pepper compared to MT and CT while maintaining a high level of weed diversity.     

Population dynamics of Verticillium species in cauliflower fields: Influence of crop rotation,debris removal and ryegrass incorporation

Verticillium wilt, caused by the soil-borne fungus Verticillium longisporum, leads to economic losses in cauliflower production in Belgium. Development of sustainable control measures of the disease is necessary. Previous studies in our laboratory have shown that incorporation of ryegrass can reduce the viability of V. longisporum microsclerotia in soil. However, field experiments are lacking in Belgian conditions. To gain knowledge about the population dynamics of V. longisporum and its relationship with Verticillium wilt, experiments were conducted from 2006 to 2010 in two cauliflower fields (Oppuurs and Ardooie) with history of Verticillium wilt. Three main crop systems (fallow, cauliflower and cauliflower followed by removal of debris) and two cover crop systems (no cover crop and ryegrass) were tested. The results of this study showed that (i) crop rotation intensity of cauliflower cultivation does not affect the inoculum density of microsclerotia forming Verticillium species in soil, (ii) amendment of lignin-rich ryegrass may reduce the soil inoculum, and (iii) seasonal fluctuations of inoculum densities occur but any soil inoculum variation above a level of one microsclerotium per gram of soil does not affect disease levels. Furthermore, we found that Verticillium wilt of cauliflower in Ardooie was reduced in soil containing Verticillium tricorpus-like organisms. The Verticillium isolate Vt305 obtained from the cauliflower field in Ardooie was morphologically similar to V. tricorpus, but its rDNA ITS region showed 100% identity with the non-pathogenic species Verticillium isaacii, recently described in literature.     

The effect of increasing NaCl in irrigation water on growth,gas exchange and yield of tobacco Burley type

Despite the economic importance of tobacco, there is limited field study on the quantitative response of growth and yield to increasing soil salinity. The effects of irrigation with saline water on yield components of field-grown tobacco (Nicotiana tabacum L.) “Burley” type plants were studied over two growing seasons. Growth, dry matter partitioning and gas exchange were measured either in rainfed or fully irrigated plants growing in a clayey–sandy–loam soil. The four fully irrigated treatments received amounts of saline waters at 0.54, 2.5, 5.0 or 10 dS m⁻¹ electrical conductivity (EC_w) equal to crop evapotranspiration. In both years, the electrical conductivity of the saturation phase (EC_e) across the 0.6 m topsoil profile increased with increasing salinity of the irrigation water. Soil moisture was markedly lower in the rainfed treatment than in fully irrigated treatments. Different saline concentrations of irrigation water had virtually no effect on soil moisture. Carbon assimilation rate, stomatal conductance and water use efficiency of the saline treatments were lower than the fully irrigated plants at 0.54 dS m⁻¹ (NW treatment) in 1996, but not in 1997. Transpiration rates were unaffected by salinity in both years. The highest yield was produced by plants irrigated with good quality water. The number of leaves per unit land area was greater for the NW plants, whereas there were no differences between the other four treatments. Salinity decreased plant dry matter and height at harvest, increased dry matter partitioning into leaves and decreased that into stems in both years. Dry matter partitioning to leaves was also greater for the rainfed plants than for the NW plants. Tobacco plants grown under field conditions showed a maximum reduction of relative yield at the highest salinity level of only 31%. The threshold values (0.56 and 0.96 dS m⁻¹) and the EC_e at which a 10% yield reduction was obtained (3.12 and 2.55 dS m⁻¹) calculated from the linear model of response of relative yield to increasing EC_e were typical of moderately sensitive crops. The EC_e values at which 50% yield was reduced (13.34 and 8.91 dS m⁻¹) were indicative of moderate tolerance to salinity.     

Translocation and distribution of P labelled potassium phosphonate in black pepper (Piper nigrum L)

The aim of this project was to study the translocation of potassium phosphonate within black pepper (Piper nigrum L.) and to elucidate the amount of chemical distributed through out the plant based on a tracer technique. Potassium phosphonate is a potential fungicide used against the pathogen Phytophthora capsici, which causes Phytophthora foot rot (Quick wilt) in the plant. Reports indicate that translocation of phosphonate is ambimobile, but there is no visual evidence for this. Potassium phosphonate labelled with radioactive phosphorus, ³²P, was applied to the black pepper vine and bush pepper and its translocation to different parts of the pepper plant was studied using an autoradiography technique. The chemical which migrated to different parts of the plant was quantitatively estimated by measuring ³²P on a liquid scintillation spectrometer following Cerenkov counting. Only traces of the chemical were lost to the soil through root systems. These results indicate that foliar sprays of potassium phosphonate to pepper could be a viable method of application for soil and foliar pathogens.     

Performance of drip-irrigated dry-seeded rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) in South Asia

Drip irrigation in dry-seeded rice (DSR) is a new water-saving cultivation technology; however, very little is known of its productivity and water-saving capacities. The study was conducted for 2 years (2013 and 2014) in a split-plot design in three replicates with treatment combinations of four irrigation regimes [drip irrigation at 1.5, 2.25, and 3.0× pan evaporation (Epan) and flood irrigation at 3.0× Epan] and three nitrogen (N) levels (120, 150, and 180 kg ha^?1). Drip irrigation in DSR resulted in higher grain yield (7.34–8.01 t ha^?1) than flood irrigation (6.63–7.60 t ha^?1) , with water savings of more than 40 %. Water-use efficiency with drip irrigation was higher (0.81–0.88 kg m^?3) than flood irrigation (0.42–0.52 kg m^?3) , being highest with drip irrigation at 1.5× Epan. Root density at soil depths of 15–30 cm was also higher in drip (0.86–1.05 mg cm^?3) as compared to the flood (0.76–0.80 kg m^?3)-irrigated crop. This study implicated that under water-scarce scenario, drip-irrigated DSR is a profitable, and water- and energy-saving technology. This study also suggested that policy focus in future must be tilted towards the promotion of solar-operated drip irrigation in those regions, where DSR is being promoted in the face of water and energy crisis.     

Efficacy of azoxystrobin for the control of cucumber downy mildew (Pseudoperonospora cubensis) and fungicide residue analysis

During a five-year trial (2007–2011), the efficacy of azoxystrobin (Quadris, 250 g a.i. L⁻¹, Syngenta) in two doses (187.5 g a.i. ha⁻¹ and 250 g a.i. ha⁻¹) and chlorothalonil (Bravo 720-SC, 720 g a.i. L⁻¹, Syngenta) at a rate of 1.44 kg a.i. ha⁻¹ was tested for the control of cucumber downy mildew (CDM). Cultivars that were susceptible or resistant to CDM (Regal and Haros, respectively) were tested for their response to fungicide applications. Differences in both disease severity and yield of the cultivars among resistance levels and fungicide treatments were observed. A highly significant and negative correlation was obtained between AUDPC and yield. Higher yields can be achieved by planting more resistant cultivars in combination with lower doses of fungicides. This is an indication that CDM contributes significantly to yield losses in cucumber production in Serbia. While monitoring the degradation of azoxystrobin residues, a decrease in residue levels to 1.0 mg kg⁻¹ below the maximum residue level (MRL) was observed at the end of the pre-harvest interval (PHI).     

膜下滴灌灌溉制度对土壤水盐空间分布及玉米产量的影响

灌溉制度对土壤水盐分布具有密切的关系,土壤水盐的分布又直接影响着作物产量。为了正确合理配置和利用水资源,改善试验区生态环境,减小肇州地区土壤含盐量对玉米产量造成的危害,选择肇州县水利科学试验站作为试验地点,试验结合膜下滴灌,设置4个水平的灌溉定额(200、300、400和500 m~3/hm~2),灌水次数分别为2次、3次和4次,测定并分析不同土层深度处土壤含水率、土壤可溶性盐浓度和玉米产量的变化。结果表明,灌溉定额为400 m~3/hm~2、灌水次数为4次时,玉米产量达到最大,且根系部位抑盐效果较好,是肇州地区较为经济合理的灌溉制度。     

Slow Growth In Vitro Conservation of Potato Germplasm at Low Temperature

The efficacy of mannitol versus sorbitol for in vitro conservation of potato microplants at low (7 ± 1 °C) temperature was studied. Two concentrations of sucrose (20 and 40 g l⁻¹) in combination with two concentrations (20 and 40 g l⁻¹) of either mannitol or sorbitol in Murashige and Skoog (MS) medium were tested. Microplant survival, microplant condition, and root growth in three potato genotypes belonging to different maturity groups were studied up to 18 months of in vitro storage without sub-culturing. Best results were achieved with MS medium having 20 g l⁻¹ sucrose plus 40 g l⁻¹ sorbitol. After 18 months without sub-culturing, maximum survival (58.0%) coupled with a microplant condition good enough to provide suitable nodes for sub-culturing was observed with the use of this medium. The results showed that the in vitro storage period could be prolonged by reducing the root growth. The success of conservation was unaffected by the maturity group of the genotypes.     

Efficacy of fumigant treatments and inoculum placement on control of Macrophomina phaseolina in strawberry beds

Soil disinfestation is one of the main concerns of strawberry growers. The phased-out of methyl bromide (MeBr) and the lack of equally effective fumigants has increased the difficulty in controlling soilborne pathogens such as Macrophomina phaseolina, causal agent of charcoal rot. Soil fumigant treatments were tested in Dover, Florida during the 2012–13, 2013–14 and 2014–15 seasons. The treatments included MeBr as a standard and common alternatives such as chloropicrin (PIC), 1,3-dichloropropene (1,3D), dimethyl disulfide (DMDS), potassium N-methyldithiocarbamate (Kpam) and sodium methyldithiocarbamate (Vapam). The efficacy of different fumigation rates and application methods was also investigated. Treatment effects were evaluated using sclerotia of M. phaseolina buried in bags 7.6 and 20.3 cm deep in the center of the bed, or 7.6 cm deep on the side of the bed (7.6 s). Additionally, strawberry crowns infected with M. phaseolina were buried 7.6 cm deep in the center of the bed during the 2012–13 and 2013–14 growing seasons. At the end of the 2013–14 and 2014–15 growing seasons, plant mortality and charcoal rot incidence (%) were also determined. Except for 1,3-dichloropropene:chloropicrin 39/60, most treatments were effective in reducing the colony forming units (CFUs) of M. phaseolina in buried bags or crowns buried at the center of the bed and reduced percent of charcoal rot incidence each season. Most treatments applied by shank produced similar reductions in inoculum levels at the center and sides of the bed, whereas drip treatments effectively reduced inoculum in bags buried at both depths in the center of the bed, but not at the side of the bed. Thus, one of the main problems of the current fumigants is poor distribution in the soil beds and strawberry growers should consider application methods that will achieve a more uniform distribution of the fumigants.     

Fungicidal activity of fluopicolide for suppression of Phytophthora capsici on squash

The efficacy of a new fungicide fluopicolide in suppression of Phytophthora blight caused by Phytophthora capsici was evaluated under laboratory and field conditions. Studies with 51 P. capsici isolates from vegetable crops in Georgia, USA, indicated that 5.9% of the isolates were resistant, 19.6% were intermediately sensitive, and 74.5% were sensitive to 100 μg ml⁻¹ of mefenoxam based on in vitro mycelial growth. EC₅₀ values of fluopicolide in inhibiting mycelial growth of 25 isolates, representing resistant, intermediately sensitive, and sensitive to mefenoxam, ranged from 0.05 to 0.35 μg ml⁻¹ with an average of 0.2 μg ml⁻¹ EC₅₀ values of fluopicolide in suppressing zoospore germination and sporangium production of the 25 isolates ranged from 1.1 to 4.5 μg ml⁻¹ and 0.3–9.0 μg ml⁻¹, respectively. Evaluation of a collection of 150 P. capsici isolates from vegetables and irrigation ponds found none of the isolates were resistant to 10 μg ml⁻¹ of fluopicolide. Field experiments were conducted to determine the efficacy and application methods of fluopicolide for control of P. capsici on squash in spring 2007 and 2009. Fluopicolide applied through drip irrigation or as a foliar spray at 86.6 or 115.4 g ha⁻¹ consistently provided significant disease reduction and increased squash yield. Results with fluopicolide were similar or slightly superior to mefenoxam applied at recommended rate. Fluopicolide applied at 57.7 g ha⁻¹ did not provide consistent satisfactory disease suppression. The results indicated that fluopicolide was effective in suppression of different stages of the life cycle of P. capsici and could be a viable alternative to mefenoxam for managing Phytophthora blight in squash production.     

Effects of irrigation system and green manure on yield and nicotine content of Virginia (flue-cured) Organic tobacco (Nicotiana tabaccum), under Mediterranean conditions

Organic tobacco consists of a new industrial crop product. Field experiments were conducted to determine the effects of irrigation system and fertilization on the growth (biomass and roots) of organic tobacco plants (Nicotiana tabaccum cv NC 71). The experiment was designed as a split plot design with four replicates, two main plots (drip and sprinkler irrigation) and three sub-plots (vetch as green manure, red clover as green manure and control; without fertilization). Drip irrigation was characterised by lower amount of water applied to the soil. Furthermore the tobacco yield was not affected by the reduced water application and the crops under drip irrigation were higher than those with sprinkler irrigation. Positive effect of green manure in the nicotine content of tobacco leaves was also observed, and that reported for first time under organic system. Equally the higher amount of nitrogen from green fertilization with vetch led to increase of nicotine concentration (0.91% max concentration). Agronomic water use efficiency (WUE) for drip irrigation was always higher than those for sprinkler irrigation. There were no significant differences between the drip and sprinkler irrigation concerning the root biomass. Moreover, green manures increased roots dry weight. Yield of tobacco crop was significantly increased by the green manures, with the lowest yield (1850 kg ha^?1) to be found in the control plots. Finally, green manures increased the SPAD values and number of leaves, with most significant impact the time when vetch applied to soil.