Effects of a range of fungicides used to control rust (Uromyces viciae-fabae) on spring-sown field beans (Vicia faba) in the UK

In two years a range of fungicides was used to control rust (Uromyces viciae-fabae) on spring-sown field beans (Vicia faba). In 1984 fenpropimorph, maneb, mancozeb, maneb plus mancozeb, propiconazole, thiram, triadimefon and zineb-polyethylene thiuram disulphide plus tridemorph were applied once or twice and compared with no fungicide. In 1985 the experiment was repeated with the addition of benodanil. In 1984 there was very little rust or other foliar disease and the effects of treatments on yield were small. In 1985 rust was first found in late June and became severe on untreated plots in August. All the fungicides reduced the incidence of rust but the amount of control differed with frequency of application and on different dates of disease assessment. In 1985 chocolate spot (Botrytis fabae) also became severe in late August. All the fungicides reduced chocolate spot but maneb plus mancozeb was the most effective. In 1985 yields were increased from 5 · 6 to 7 · 7 t/ha by maneb plus mancozeb applied once. Other fungicides gave smaller yield increases. Yield increases given were attributable mainly to control of rust but partly to control of chocolate spot. Yield increases given by non-systemic fungicides came mainly from increases in the weight of individual grains; those yield increases given by systemic materials came, in addition, from better pod retention.     

An effect of rust (Uromyces viciae-fabae) on the yield of spring-sown field beans (Vicia faba) in the UK

Rust (Uromyces viciae-fabae) has recently been noted with increased frequency and earliness on spring-sown beans (Vicia faba) at Rothamsted. In 1982 an experiment was made to assess the damage and yield loss, if any, being caused by the disease. Plots received benomyl sprays to control chocolate spot (Botrytis fabae) or not, maneb plus mancozeb (protective) or propiconazole (systemic) fungicide applied twice or three times to control rust, or no fungicide at all. Rust was first found on 7 July and sprays were applied from 9 July but by 19 August plants of all treatments were dead. Fungicides controlled disease development during July and at harvest overall yields were 4·51 and 5·43 t/ha in unsprayed and sprayed treatments respectively. The difference was accounted for by the weight of individual grains and not by the number of pods per plant or grains per pod. Previously rust has been considered unimportant in the UK but its potential for damage is considerable.     

Chemical control of faba bean rust (Uromyces viciae-fabae)

The effectiveness of eleven foliar-applied fungicides on faba bean rust (Uromyces viciae-fabae (Pers.) J. Schröt.) and on the seed yield of faba bean (Vicia faba L.) were studied in growth chambers and in the field in Spain. Fungicides were tested at recommended and reduced rates. All the fungicides tested provided very effective preventive control in the growth chamber studies. Triazoles (difenoconazol, epoxiconazol, tebuconazol) and their mixtures with benzimidazoles (carbendazim-flutriafol and carbendazim-flusilazole) provided the most effective curative effect, even at 25% of recommended concentrations. They were followed by dithiocarbamates, copper dithiocarbamate mixture, carboxamide and chlorothalonil. Triazoles, benzimidazole-triazole mixtures and carboxamide maintained their effect until 15 days after fungicide application.Under field conditions, rust infection caused 22-26% yield reduction. All fungicides except mancozeb caused a significant decrease in disease severity under field conditions, but only treatments with triazoles and benzimidazole-triazole mixtures provided significant yield increases (22.7-15.6%) when applied twice. Three applications of oxycarbosin or copper-mancozeb were needed to provide a significant yield increase. Dithiocarbamates (thiram, maneb or mancozeb) or chlorothalonil reduced rust severity but did not provide a significant yield increase.     

Toxicity of different fungicides to adult Cryptolaemus montrouzieri mulsant (Coleoptera: Coccinellidae)

Toxicity and persistence of eight fungicides (carbendazim, tridemorph, mancozeb, captafol, triadimefon, Bordeaux mixture, sulphur w.p. and sulphur dust) to Cryptolaemus montrouzieri Mulsant adults was assessed by calculating the median lethal time (LT) values in days, following probit analysis. While tridemorph 0·05% was the safest, triadimefon 0·05% was most toxic with greater persistence. Hence the spraying of tridemorph 0·05% and the release of the predator could be simultaneous.     

The effect of seed treatment with chlormequat on the control of barley leaf stripe, Drechslera graminea (Rabenh. et Schlecht.) Shoemaker, with fungicides

Seed of winter barley, naturally infected with Drechslera graminea (Rabenh. et Schlecht.) Shoemaker (Helminthosporium gramineum Rabenh.), was treated with chlormequat (chlormequat chloride; CCC) (2·5 g a.i./kg seed) alone or mixed with fungicides (thiram plus carboxin; mancozeb; thiophanate-methyl plus maneb; carbendazim; methfuroxam; tolchlofosmethyl; procymidone; nuarimol) before being sown by hand in a randomized block field trial with four replicates. There was no reduction in the number of plants that emerged. CCC alone did not reduce the incidence of barley leaf stripe. However, all the fungicides, apart from thiram plus carboxin, showed increased activity when mixed with CCC, as shown by a reduction either in the number of plants infected, or in the percentage of empty ears. No lodging was observed in the trials: not only CCC alone, but the fungicides also, both alone and in the presence of CCC, significantly reduced the lengths of the first and second internodes. Treatment of winter barley seed with mixtures of CCC and fungicides appears to be a promising method for control of barley leaf stripe and for reduction of lodging.     

Yield performance and pest resistance among peanut genotypes when grown without fungicides or insecticides

Yield trials without fungicides or insecticides were conducted four consecutive years (2007–10) at the University of Georgia, Coastal Plain Experiment Station, Tifton Campus to evaluate for peanut (Arachis hypogaea L.) pest resistance. The most endemic diseases in the southeast U.S. are tomato spotted wilt (TSW) caused by Tomato spotted wilt virus, white mold (WM) caused by Sclerotium rolfsii Sacc, and both early and late leaf spot caused by Cercospora arachidicola Hori and Cercosporidium personatum (Berk & Curt.) Deighton, respectively. The most endemic insects are tobacco thrips (Frankliniella fusca Hinds) and potato leafhopper (Empoasca fabae Harris). Results from these replicated field tests showed significant differences (P ≤ 0.05) among advanced Georgia breeding lines and cultivars. Three Georgia cultivars ‘Georgia-01R’, ‘Georgia-05E’, and ‘Georgia-10T’ consistently produced among the best yields with high levels of resistance to TSW, white mold, leafhoppers, and leaf spot each year. Georgia-01R is a multiple-pest-resistant, runner-type cultivar with late maturity; whereas, Georgia-05E is a multiple-pest-resistant, virginia-type cultivar with medium-late maturity. Georgia-10T is a new runner-type cultivar with high level of TSWV and white mold resistance and late-maturity, similar to Georgia-01R, one of its parents. However, Georgia-10T does not appear to have the high level of leaf spot and leafhopper resistance as Georgia-01R, but it still had high yields in the absence of fungicides or insecticides.     

Evaluation of fungicides to control circular leaf spot of persimmon caused by Mycosphaerella nawae

The efficacy of ten fungicides against Mycosphaerella nawae, the causal agent of circular leaf spot (CLS) of persimmon, was evaluated in vitro and in field experiments. Field trials were conducted in 2009 and 2010 to investigate the comparative efficacy of the fungicides alone or combined using alternating sequences in spray programmes based on two, three or four applications. Disease incidence was assessed by estimating the percentage of affected leaves, which included leaves showing at least one necrotic spot and defoliation. Fenpropimorph, pyraclostrobin, tebuconazole and thiophanate-methyl were the most effective fungicides in inhibiting mycelial growth of M. nawae isolates (EC₅₀ < 2 ppm). In field experiments, the most effective fungicides using two spray applications were captan, chlorothalonil, mancozeb and pyraclostrobin which significantly reduced disease incidence compared with untreated plots. Regarding the number of spray applications, two applications of captan and mancozeb were less efficient than three to control the disease. However, the percentage of affected leaves provided by three applications of captan and mancozeb alone or combined with pyraclostrobin using alternating sequences in spray programmes, was not significantly different from that provided by four applications. Experimental results demonstrated that spray programmes based on three applications of these fungicides could effectively control CLS of persimmon. The advantages of spray programmes based on alternated use of strobilurins and protective fungicides are discussed.     

Application of fungicides to reduce yield loss in anthracnose-infected lupins

A range of fungicides were evaluated for control of anthracnose (Colletotrichum lupini) in lupin. Glasshouse investigation identified fungicides that reduced disease severity with varying degrees of efficacy. When applied 1 d prior to infection, azoxystrobin, chlorothalonil, mancozeb and copper oxychloride fungicides were highly effective. Systemic fungicides such as tebuconazole, benomyl and carbendazim were less effective. Application timing was important; fungicides such as chlorothalonil and mancozeb were less effective when applied 5 d prior to infection compared with 1 d prior. Application after infection was ineffective for all fungicides. In field experiments application of azoxystrobin, mancozeb or chlorothalonil during flowering and podding reduced incidence of anthracnose infection on pods. Yield responses occurred in moderately susceptible, moderately resistant or resistant cultivars. Seed infection was reduced but not eradicated. Application of foliar fungicides for anthracnose control is potentially a viable management option for lupin production in high anthracnose risk areas of Western Australia.     

Phylogenetic reassessment of Mycosphaerella spp. and their anamorphs occurring on Eucalyptus. II.

Species of Eucalyptus are widely planted as exotics in the tropics and Southern Hemisphere and to some extent in southern Europe, for timber and fibre production. Species of Mycosphaerella are commonly associated with leaves and twigs of Eucalyptus and can result in defoliation, dieback, and even tree death. In the present study, numerous isolates of Mycosphaerella species were collected from leaf litter, living leaves exhibiting leaf spot symptoms or severe Mycosphaerella leaf blotch symptoms. Isolates were compared based on DNA sequence data for the internal transcribed spacer region (ITS1 & ITS2) and the 5.8S gene. These data, together with characteristics of the fungal growth on three different media, morphology of the anamorph and teleomorph structures as well as ascospore germination patterns were used to describe 21 new species.Taxonomic novelties: Colletogloeopsis stellenboschiana Crous sp. nov., Mycosphaerella davisoniellae Crous sp. nov. (anamorph Davisoniella eucalypti H.J. Swart), Mycosphaerella eucalyptorum Crous & M.J. Wingf. sp. nov. Mycosphaerella gamsii Crous sp. nov., Mycosphaerella perpendicularis Crous& M.J. Wingf. sp. nov., Mycosphaerella pluritubularis Crous & J.P. Mansilla sp. nov., Mycosphaerella pseudafricana Crous & T. Coutinho sp. nov., Mycosphaerella pseudocryptica Crous sp. nov. (anamorph Colletogloeopsis sp.), Mycosphaerella pseudoendophytica Crous & G. Hunter sp. nov. (anamorph Pseudocercosporella sp.), Mycosphaerella pseudosuberosa Crous & M.J. Wingf. sp. nov. (anamorph Trimmatostroma sp.), Mycosphaerella quasicercospora Crous & T. Coutinho sp. nov., Mycosphaerella scytalidii Crous & M.J. Wingf. sp. nov. (anamorph Stenella sp., synanamorph, Scytalidium-like.), Mycosphaerella secundaria Crous & A.C. Alfenas sp. nov., Mycosphaerella stramenti Crous & A.C. Alfenas sp. nov., Mycosphaerella stramenticola Crous & A.C. Alfenas sp. nov., Mycosphaerella sumatrensis Crous & M.J. Wingf. sp. nov., Mycosphaerella verrucosiafricana Crous & M.J. Wingf. sp. nov., Septoria eucalyptorum Crous sp. nov., Septoria provencialis Crous sp. nov., Stenella pseudoparkii Crous & M.J. Wingf. sp. nov. (teleomorph Mycosphaerella sp.), Stenella xenoparkii Crous & M.J. Wingf., sp. nov. (teleomorph Mycosphaerella sp.).     

Evaluation of spray programmes for the management of leaf spot incited by Pseudomonas syringae pv. syringae on tomato cv. Cuore di bue

Four experimental trials were carried out in northern Italy under greenhouse conditions against bacterial leaf spot of tomato, incited by Pseudomonas syringae pv. syringae, a disease recently observed in the country. The efficacy of spray programmes, based on the use of several copper-based compounds, acibenzolar-S-methyl, fosetyl Al and two biological control agents, Bacillus subtilis strain QST 713 and Pseudomonas chlororaphis MA 342, was tested. The best results were obtained with the alternation of copper oxychloride, used alone or in mixture with acibenzolar-S-methyl, with acibenzolar-S-methyl, applied for a total of two sprays. Acibenzolar-S-methyl applied alone was also effective. However, due to its possible slight phytotoxic effect, observed in our case in one trial, strategies relying on a limited number of its application are preferred. The efficacy of acibenzolar-S-methyl is higher under lower inoculum conditions. Among the tested copper-based fungicides, copper oxychloride provided the best and most consistent results, with no or limited phytotoxicity. Other copper compounds were much less effective and sometimes caused a reduction in plant height. The disease suppression achieved with B. subtilis strain QST 713 was only partial, while P. chlororaphis was not effective. The advantages of programmes based on rotation of copper compounds and acibenzolar-S-methyl are discussed.     

Potato fungicides interfere with entomopathogenic fungi impacting population dynamics of green peach aphid

Fungicides applied to potato can enhance green peach aphid,Myzus persicae (Sulzer), outbreaks by interference with entomopathogenic fungi. (Order Entomophthorales). Late season aphid numbers were highest in potatoes sprayed with metalaxyl + mancozeb, captafol, or mancozeb, and lowest in potatoes sprayed with benomyl, triphenyltin hydroxide, chlorothalonil, or copper hydroxide. In field-collected aphids,Pandora (= Ernyia) neoaphidis (Remaudière et Hennebert) andEntomophthora planchoniana Cornu (F. Entomophthtoraceae) were the predominant cause of mycoses, 66.7% and 22.3%, respectively.Conidiobolus obscurus (Hall and Dunn) Remaudièe and Keller (F. Ancylistaceae) accounted for 8.5% of mycoses. In the laboratory, fungicides were shown to have direct effects on these entomopathogens. Metalaxyl + mancozeb, mancozeb and captafol were strongly inhibitory of germination of conidia, copper hydroxide was intermediate, and chlorothalonil had little effect. Triphenyltin hydroxide, benomyl, metalaxyl + mancozeb, and mancozeb were strongly inhibitory of growth of mycelia, copper hydroxide was intermediate, and chlorothalonil and copper hydroxide had least effect. Benomyl was highly toxic to green peach aphid, copper hydroxide and chlorothalonil intermediate, and captafol, mancozeb, and metalaxyl + mancozeb least toxic. Possible interference of potato fungicides with aphid pathogens is now an important consideration because of the intensity of spraying required to protect the crop from infection by metalaxyl-resistant strains of the late blight pathogen,Phytophthora infestans (Mont.) de Bary. Minnesota potato growers reported high green peach pressure in both 1995 and 1996, years of intensive fungicide spraying. Concomitantly, there was a marked increased in the incidence of PLRV in seed lots entered for winter testing.     

Comparison of chemical treatments for reducing epiphytic Pseudomonas savastanoi pv. savastanoi populations and for improving subsequent control of olive knot disease

The economic impact of the olive knot disease caused by Pseudomonas savastanoi pv. savastanoi (Psv) has dramatically increased in recent years, especially in high-density plantations. Here we report chemical control trials, performed in an olive grove planted with two susceptible cultivars, Arbequina and Picudo, over a four-year period. The effect of treatments made with copper oxychloride, cuprocalcic sulfate plus mancozeb or acibenzolar-S-methyl on the Psv populations and subsequent appearance of the disease were evaluated. Both copper treatments reduced the proportion of samples where Psv was isolated, and greatly reduced Psv populations in trees of cv. Picudo. The effect of copper on Psv populations was observed after the first application, but the greatest differences between copper-treated and untreated plants were observed in the third year, after five copper applications. No resistance to copper was detected in the remaining epiphytic Psv populations in treated plants. The average number of knots per plant was significantly lower in copper-treated plants than in untreated plants. By contrast, acibenzolar-S-methyl did not reduce either Psv populations or the disease during the study. These results support the usefulness of copper treatments for olive knot management. Results indicate that two copper treatments should be performed regularly under an integrated control program, especially in high-density groves, since their efficiency was demonstrated not only in decreasing olive knot incidence, but also in reducing Psv populations.     

Five years' results from a long-term field experiment on carbendazim resistance of Pseudocercosporella herpotrichoides (Fron) Deighton

In a field monitoring experiment, winter wheat sown in large plots with or without applications of carbendazim was used to determine, during 5 years in succession, the development of carbendazim resistance in field populations of Pseudocercosporella herpotrichoides (Fron) Deighton, (Cercosporella herpotrichoides Fron). At the beginning of the experiment, one spore out of about 2·4 × 10⁹ was resistant. This figure increased at a linear rate that was highly statistically significant. Eventually, the frequency of carbendazim-resistant conidia was of the order of 10^?8. The differences in the frequency of resistant spores in the carbendazim-treated and in the untreated plots were highly significant, ranging from twofold to eightfold, depending on the year in question. In practice, there seems to be little danger from carbendazim resistance in the eyespot fungus if normal plant-protection recommendations are followed.     

Evaluation of fungicides to control Cylindrocarpon liriodendri and Cylindrocarpon macrodidymum in vitro, and their effect during the rooting phase in the grapevine propagation process

The efficacy of 14 selected fungicides against Cylindrocarpon liriodendri and Cylindrocarpon macrodidymum was evaluated in vitro by testing their effect on mycelial growth and conidial germination. Carbendazim, hydroxyquinoline sulphate, imazalil, and prochloraz were the most effective fungicides in reducing mycelial growth in both Cylindrocarpon species. Captan, copper oxicloride, didecyldimethylammonium chloride and thiram were the most effective to inhibit conidial germination of both species. A pot assay was also conducted with captan, carbendazim, copper oxychloride, didecyldimethylammonium chloride, hydroxyquinoline sulphate, imazalil and prochloraz in order to determine their potential to prevent infections caused by C. liriodendri and C. macrodidymum during the rooting phase in the grapevine propagation process. All fungicides significantly decreased the root disease severity values in both species compared with control treatment, with the exception of imazalil in C. macrodidymum. In the case of the percentage of reisolation, all values were lower than those obtained for the control treatment, but only captan, carbendazim and didecyldimethylammonium chloride were significantly different in the case of the cuttings inoculated with C. liriodendri, and prochloraz in the case of those inoculated with C. macrodidymum.     

Response of progeny bred from Bolivian and North American cultivars in integrated management systems for leaf spot of peanut (Arachis hypogaea)

Early and late leaf spot (caused by Cercospora arachidicola and Cercosporidium personatum, respectively) are major yield-reducing diseases of peanut (Arachis hypogaea L.) in the southeastern U.S. Effective suppression of both early and late leaf spot, collectively called ‘leaf spot’, can be reached with integrated disease management (IDM) systems utilizing peanut cultivars with moderate levels of resistance to these pathogens. A Bolivian landrace cultivar, Bayo Grande, and a series of progeny breeding lines were evaluated under two IDM systems consisting of various reduced application fungicide regimes and/or tillage treatments in field experiments over two years. In the absence of fungicides or when averaged across fungicide regimes, Bayo Grande and breeding lines had better leaf spot resistance when compared to cultivars Georgia Green, MDR-98 and C-99R in all experiments across years. The addition of three or four fungicide applications to Bayo Grande and several of the breeding lines suppressed leaf spot to levels similar to those genotypes and Georgia Green under the full regime. Conservation tillage reduced the need for fungicides in most genotypes in both years. Yields were higher for Bayo Grande and the breeding lines compared to Georgia Green in three of the four experiments across years. When compared across genotype, yields were greatest for the full season fungicide regime, except in 2002 when yields were similar for all treatments. Leaf spot severity was reduced in conservation tillage compared to conventional tillage in most varieties in the absence of fungicides. However, yields tended to be lower in conservation tillage treatments than in conventional tillage. Under conservation tillage, yields of Bayo Grande and two of the breeding lines were negatively impacted in one year and were overall lower in the other year. Several of these new Bolivian-derived genotypes show promise for use in a reduced fungicide and/or conservation tillage IDM system with the potential to lessen fungicide use compared to standard production practices while maintaining low leaf spot levels and high yields.     

Sensitivity of Cercospora beticola isolates from Serbia to carbendazim and flutriafol

Cercospora beticola, causal agent of Cercospora leaf spot (CLS) of sugar beet, is primarily controlled by fungicides. Benzimidazole and demethylation inhibiting fungicides, including carbendazim and flutriafol, have been widely used in Serbia. Since these fungicide groups have a site-specific mode of action, there is a high risk for developing resistance in target organisms, which is the most important limiting factor in Cercospora leaf spot chemical control. A rapid identification of flutriafol and carbendazim resistance can help researchers in examining the potential of different fungicide resistance management practices, as well as in selection of fungicides for use in the areas where resistance has occurred. One hundred single-conidia isolates were collected from 70 representative locations of the sugar beet production region in Serbia. Evaluation of the isolates' sensitivity was based on the reduction of mycelial growth on medium amended with 1.25 μg mL⁻¹ flutriafol and 5 μg mL⁻¹ carbendazim. Resistance to flutriafol and carbendazim was detected in 16% and 96% of the tested isolates, respectively. All isolates resistant to flutriafol were resistant to carbendazim as well, which is the first report of a double resistance to fungicides in C. beticola. Detection of the isolates resistant to flutriafol and carbendazim using Cleaved Amplified Polymorphic Sequence (CAPS) markers confirmed the results of the in vitro tests. The efficacy of carbendazim, flutriafol, azoxystrobin, and tetraconazole at commercially recommended doses was evaluated in field trials where sugar beet plants in plots were inoculated with a mixture of isolates either sensitive and/or resistant to flutriafol and carbendazim. Carbendazim and flutriafol efficacy was very low in plots inoculated with isolates resistant to these fungicides. Presented results will contribute to development of a pathogen population sensitivity monitoring strategy that could be used for an effective CLS management in the region.     

Spray deposition assessment and benchmarks for control of Alternaria brown spot on mandarin leaves with copper oxychloride

Inadequate disease control on citrus foliage and fruit is often attributed to insufficient fungicide spray deposition on target surfaces. This study describes a novel spray deposition assessment protocol and determines deposition benchmarks indicative of the biological effectiveness for better interpretation of spray deposition results. Suitability of a yellow fluorescent pigment as tracer for copper oxychloride deposition was demonstrated through its similar particle concentration and size. Spray deposition assessment of spray targets, which were sprayed with a mixture that included the fluorescent pigment, involved photomacrography of whole leaf or fruit surfaces, followed by digital image analyses. This protocol proved to be very accurate in determining the quantity and quality of deposition. To determine deposition benchmarks, detached young ‘Nova’ mandarin leaves were sprayed with copper oxychloride and fluorescent pigment at different concentrations (0.1–2 times the recommended concentration) and spray deposition assessed. Subsequently, leaves were spray inoculated with a spore suspension of Alternaria alternata [causal agent of Alternaria brown spot (ABS) of mandarins], moist-incubated for c. 48 h and symptom expression rated. A very good linear relationship was found between fungicide concentration, leaf area covered by fluorescent pigment particles (%FPC) (r = 0.879) and Cu residue analysis (r = 0.992). A von Bertalanffy growth curve best fitted the relation between ABS control and deposition quantity (%FPC) data (91% of the percentage variance accounted for) with a good correlation between observed and predicted values (r = 0.825). Benchmarks for 50% and 75% disease control were calculated as 2.07 %FPC and 4.14 %FPC, respectively. These corresponded with Cu residue levels of 59.4 and 91.0 mg kg⁻¹, respectively. These FPC benchmarks can be used to evaluate spray technology research, specifically for control of ABS and similar citrus fruit and foliar diseases.     

Evaluation of chlorothalonil and paraffinic oil alone and in combinations with registered fungicides for the control of yellow Sigatoka (Mycosphaerella musicola) of bananas in Northern Queensland,Australia

The efficacy of chlorothalonil and paraffinic oil alone and in combinations with the registered fungicides propiconazole, tebuconazole, difenoconazole, epoxiconazole and pyrimethanil was evaluated in a field experiment over two cropping cycles in 2013 and 2014 in Northern Queensland, Australia, for control of yellow Sigatoka (caused by Mycosphaerella musicola) of banana. The predominantly applied by the banana industry treatment mancozeb with paraffinic oil was included for comparison. The results from the two cropping cycles suggested that all chemicals used with paraffinic oil were as effective or more effective than when applied with chlorothalonil, and chlorothalonil alone. Difenoconazole and epoxiconazole with paraffinic oil followed by propiconazole with paraffinic oil were the most effective treatments. Pyrimethanil and tebuconazole plus chlorothalonil were the least effective treatments. None of the chemical treatments was phytotoxic or reduced yield.     

Organic compounds increase the efficacy of famoxadone + cymoxanil in the control of bacterial leaf spot of lettuce

Bacterial leaf spot of lettuce, induced by Xanthomonas campestris pv. vitians, constitutes a major disease on commercial lettuce (Lactuca sativa) production in south Florida. Under greenhouse conditions, resorcinol, two antioxidants, and various sugar alcohols such as mannitol, were evaluated alone, and in combination with Tanos^® 50DF (25% a.i. of each component cymoxanil and famoxadone, E.I du Pont de Nemours and Company, Wilmington, DE) for control of bacterial leaf spot. Among the compounds evaluated, resorcinol (35–50% disease control) and mannitol (9–45%) were the most effective. In field trials, different mixtures containing propionic acid, mannitol, resorcinol, Tanos and or copper hydroxide (Kocide 3000^®, 46.1%, 30% copper equivalent) were evaluated for the control of bacterial leaf spot of lettuce. Field data support a moderate impact of Tanos in disease reduction. Both greenhouse and field data support a synergistic interaction between Tanos and the compounds including copper, in disease reduction. The mixture Tanos + resorcinol, or copper/resorcinol, Tanos + copper provided better or similar disease control than copper alone. No phytotoxicity was observed in our trials. In an integrated management program for bacterial leaf spot of lettuce, Tanos may be useful in tank mixes with these compounds and copper.     

Genetic resistance to and effect of leaf rust and powdery mildew on yield and its components in 50 soft red winter wheat cultivars

Effects of leaf rust (caused by Puccinia triticina f. sp. tritici Eriks.) and powdery mildew [caused by Blumeria graminis (DC.) E. O. Speer f. sp. tritici Em. Marchal], on performance of 50 soft red winter (SRW) wheat (Triticum aestivum L) cultivars were evaluated under natural field conditions. Widely grown cultivars released from 1919 to 2009 with varying disease resistance were grown in split-plot experiments in 2010 and 2011. Treated replications received seed treatments of triadimenol, captan and imidacloprid and foliar applications of propiconazole and prothioconazole + tebucanazole fungicides. Non-treated replications received only tebucanazole + metalaxyl + imazalil seed treatments. Final mean disease severity, agronomic, yield-related traits, yield components and spike characteristics were analyzed to determine individual and combined effects of leaf rust and powdery mildew on the cultivars. Yield losses as high as 54% were observed in the susceptible cultivar Red May. Average yield losses ranged from 1% to 21%. Yield losses primarily due to powdery mildew were as high as 14%, and losses primarily due to leaf rust were as high as 33%. Powdery mildew had the largest negative correlation with harvest index and seeds/spike. Leaf rust was most negatively correlated with plant biomass and harvest index, with a less consistent negative relationship with kernel weight.