Control of tomato powdery mildew (Leveillula taurica) in the Comarca Lagunera, Coahuila State, Mexico, supported by the spray forecast model Tomato.PM

Tomato powdery mildew [Leveillula taurica (Lev.) Arm.] is a common disease of tomato crops in the Comarca Lagunera region of the state of Coahuila, Mexico. To control the disease, fungicides are commonly sprayed up to 18 times on a weekly basis in this region. Effectiveness of the spray forecast model Tomato.PM, developed for California conditions, to reduce fungicide spraying, was evaluated. Disease dynamics on plants treated with three different fungicides (azoxystrobin, myclobutanil and wettable sulfur), with and without model recommendations, was analyzed in three experiments at three locations. When spraying followed model recommendations, it was possible to eliminate 11-16 fungicide applications with no significant effect on fruit yield. All three fungicides reduced the severity of disease but their effects varied with the cropping cycle. A significant increase in total yield due to fungicide spraying was observed in one out of three experiments.     

Potassium phosphite combined with reduced doses of fungicides provides efficient protection against potato late blight in large-scale field trials

Potato late blight caused by the oomycete Phytophthora infestans is a devastating disease of potato worldwide. Most of the potato cultivars grown in conventional agriculture are susceptible, or at best moderately resistant, and require frequent applications of fungicides to avoid heavy yield losses.In field trials spanning four years, we have investigated the effect of potassium phosphite, an inorganic salt on potato late blight. Potassium phosphite is known to induce defence responses in potato and to also have direct toxic effects on oomycetes, which in turn counteract late blight and tuber blight development. However, the use of this salt is not yet implemented and approved in European potato cultivation. We compared the effect of phosphite alone with fungicides currently used in Swedish potato cultivation. We also investigated the combined use of potassium phosphite and reduced doses of fungicides. Table potato cultivars and starch potato cultivars with different levels of resistance were used.We found that potassium phosphite in combination with reduced doses of fungicides results in the same level of protection as treatments with the recommended full dose of fungicides. These combined treatments reduce the need of traditional fungicides and may also decrease the selection pressure for fungicide resistance development in the pathogen. In relatively resistant starch potato cultivars using phosphite alone gave sufficient protection against late blight. Furthermore, in starch potato a combination of phosphite and fungicides at two-week intervals provided similar protection to weekly applications of fungicide at the recommended dose. Foliar treatment with phosphite also gave protection against tuber blight at similar levels to that of the best-performing fungicide. Our data suggests that potassium phosphite could be used in potato cultivation in temperate regions such as in Sweden, at least in combinations with reduced rates of fungicides. The implementation of the use of phosphite in practical potato crop protection as part of an IPM strategy is discussed. Doses, intervals and combinations could be adjusted to the level of cultivar resistance.     

Potato late blight control and top desiccation when pesticides are applied with a controlled droplet and a conventional sprayer

Disease development was observed in field plots to which two different fungicides, each at two rates, were applied regularly with either a conventional or a controlled droplet sprayer. The type of fungicide did not affect disease severity, but more disease damage occurred in the controlled droplet sprayer plots than in conventional sprayer plots. Reduced rates of fungicide resulted in higher disease incidence ratings than recommended rates of fungicides by end of the spraying season. Lower marketable tuber yields and greater incidences of late blight tuber rot were related to foliar disease levels, the different sprayer types, and rates of applied fungicide. No significant differences in terms of potato top desiccation efficacy between the two sprayer types were obtained. In addition, total tuber yield and level of vascular discoloration were similar for both the controlled droplet and conventional sprayer.     

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.     

Efficacy of paste and liquid fungicide formulations to protect pruning wounds against pathogens associated with grapevine trunk diseases in Chile

Trunk diseases are important on grapevines (Vitis vinifera L.) in most countries where grapevines are grown. In Chile, Diplodia seriata, Inocutis sp. and Phaeomoniella (Pa.) chlamydospora are the most prevalent pathogens associated with this syndrome. It has been demonstrated that fresh pruning wounds are the main infection route for fungal trunk disease pathogens. The objective of this study was to evaluate the efficacy of paste and spray fungicide applications in protecting pruning wounds against D. seriata, Inocutis sp. and Pa. chlamydospora on ‘Cabernet Sauvignon’ grapevines in two important Chilean grapevine production areas. The fungicides used in this study were benomyl, pyraclostrobin, tebuconazole, and thiophanate-methyl, which were applied as paste and liquid fungicide on fresh pruning wounds pre- and post-inoculation with mycelium plugs of the different fungal pathogens used in this study. The efficacy of the fungicides was assessed by measuring the length of the discoloration of the vascular system and percent re-isolation obtained on fresh pruning wounds. The results obtained demonstrate that infections caused by D. seriata, Inocutis sp. and Pa. chlamydospora can be significantly reduced using both paste and spray applications of benomyl, pyraclostrobin, tebuconazole and thiophanate-methyl and that the paste formulations provided a better control than spray applications. Regardless of the fungicide and application method used, the pre-inoculation treatments (performed 24 h before inoculation) resulted in better control than the 24 h post-inoculation treatments. The current study showed that Inocutis sp. can induce vascular discoloration on grapevine spurs. This study supports a broader use of benzimidazole fungicides for the control of the devastating trunk diseases in all grape productions worldwide.     

Deposition and biological efficacy of a fungicide applied in charged and uncharged sprays in cereal crops

Barley and wheat crops were both sprayed at growth stages 30 and 61–75 with boom-mounted conventional hydraulic nozzles (250 ?/ha), experimental hydraulic electrostatic nozzles (66 ?/ha), electrically driven spinning discs (2 ?/ha, oil-based sprays and 5 ?/ha, aqueous spray) and ‘Electrodyn’ nozzles (1 and 2 ?/ha, oil). The ULV spray systems (up to 5 ?/haS) were used with or without air assistance. The distribution of both oil and aqueous sprays within the crops was measured with fluorescent tracers on plant parts and on whole plants. An experimental triazole fungicide (mixed with tracer) was applied to the crops by all the spray systems and the degree of control of leaf blotch (scald) caused by Rhynchosporium secalis (Oudem.) J.J. Davis in barley and mildew (Erysiphe graminis DC) in wheat compared with the deposit data. The two highest-volume spray systems gave similar results for disease control and there was no significant difference between the charged and uncharged sprays at 66 ?/ha. The Micron Ulva spinning disc and ‘Electrodyn’ systems with air assistance also performed well. Unassisted ULV sprays were often unevenly distributed within the crops and gave inferior disease control. The ‘Electrodyn’ system often produced large total deposits relative to other spray systems but unassisted sprays were mainly deposited on the upper plant parts. The results indicate that application at volumes as low as 1 ?/h can be as biologically effective as conventional high-volume spraying, when compared at the same dose rate of fungicide (90 g/ha). Relationships between spray distribution within cereals and the sites for pest and disease attack are discussed with regard to different methods of application.     

Evaluation of sprinkler application of fungicides for control of potato early blight in Colorado

Sprinkler application of four fungicides, Du-Ter 47.5% W.P. (0.70 kg/ha), Difolatan 4F (3.51 1/ha), Bravo W-75 (1.68 kg/ha) and Bravo 500 (1.17 1/ha, 1.761/ha and 2.341/ha) were evaluated in Colorado for control of potato early blight caused byAlternaria solani (Ellis & G. Martin) L.R. Jones and Grout and compared to the conventional method of airplane application. Fungicides applied through center pivot irrigation systems generally achieved disease control equal to airplane application. Application of fungicides through both center pivot sprinklers and by airplane effectively reduced early blight infection. Control of early blight by airplane or sprinkler application of fungicides significantly (P = 0.05) increased potato yields in 1978. In other years (1977, 1979 and 1980) fungicide applications which reduced disease severity generally increased tuber yields but the increases were not significant when compared to the control.     

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.     

Characterization of forty-four potato varieties for resistance to common scab,black scurf and silver scurf

Common scab, black scurf and silver scurf belong to serious diseases of cultivated potato that especially impair tuber quality. Tuber infection in 44 potato (Solanum tuberosum ssp. tuberosum L.) varieties was evaluated using two measures – severity and incidence of infected tubers. Both measures were highly correlated. An important result derived from this study supports fungicide application against potato late blight secondarily acts on reducing tuber infection by all evaluated pathogens. Therefore, the conventional potato growing seems to be more effective compared to ecological growing. The pedigree analysis of 44 varieties indicated the presence of Solanum demissum genotypes in the variety genome may negatively affect variety response to Helminthosporium solani presence.     

Prevalence of isolates of Botrytis cinerea resistant to multiple fungicides in Chilean vineyards

Gray mold (Botrytis cinerea) is an important disease of grapevines (Vitis vinifera) and requires several fungicide treatments to achieve a satisfactory control in Chile. Furthermore, a high resistance risk has developed because of the extensive use of specific fungicides with a single-site mode of action. The aim of this study was to determine the presence of resistance to the multiple fungicides currently used against B. cinerea in Chile. During 2007–2009 and 2011, 214 isolates of B. cinerea from 36 commercial vineyards were examined for sensitivity to anilinopyrimidines (cyprodinil or pyrimethanil), demethylation inhibitors (DMIs) (tebuconazole), hydroxyanilides (fenhexamid) and phenylpyrroles (fludioxonil). Of all of the isolates, 62.7% were resistant to anilinopyrimidines, 7.2% to DMIs, 27.1% to hydoxyanilides and 44.8% to phenylpyrrole derivates. Overall, 16 (12.3%) of the isolates were sensitive; although none was resistant to all four of the fungicide classes, and 50 (38.5%), 51 (39.2%), and 13 (10.0%) isolates were resistant to one, two and three fungicides, respectively. In vitro, resistant isolates were capable of causing fruit rot on wounded apples pretreated with any one of the five fungicides at label concentrations. To the best of our knowledge, this is the first report of isolates having simultaneous resistance to anilinopyrimidines, DMIs, phenylpyrroles and hydroxyanilides in B. cinerea populations from grapevines in Chile. Therefore, fungicide resistance is a serious problem that questions the sustainability of the current gray mold control strategy, which relies almost exclusively on fungicides with single-site modes of action.     

Management of mango malformation disease based on a novel strategy of timing of fungicide applications combined with sanitation

Mango malformation disease (MMD) caused by Fusarium mangiferae severely affects the crop and is widely distributed in almost all mango-growing regions worldwide. Since malformed inflorescences do not bear fruit, MMD is a major constraint to crop production in affected areas. No effective management methods have been reported to date. The airborne nature of dissemination and infection of buds suggest that protection of buds from infection when inoculum prevails may be a plausible method for disease control from season to season. Various fungicides were assessed for their ability to control the pathogen under laboratory, greenhouse and field conditions. Prochloraz was the most effective fungicide in inhibiting F. mangiferae in vitro with a 0.01 μg mL⁻¹ concentration required for 50% fungal growth inhibition. In greenhouse trials, protective and curative activity exceeding 90% was achieved when the fungicide was applied up to 14 days prior or post inoculation. Field experiments conducted over a number of seasons in different regions in Israel indicate that combined sanitation with timely applications of prochloraz resulted in a significant reduction in MMD disease severity and incidence, as well as a significant increase in yield in treated plots. It is assumed that long-term treatment by removal of infected panicles (the main source of inoculum) combined with timely sprays will result in disease reduction annually achieving negligible levels of malformation in treated orchards, in time.     

Control of foliar diseases by the axillary application of systemic fungicides in Brazilian coconut palms

Endemic fungal foliar diseases, such as leaf blight – LB [Lasiodiplodia theobromae (Pat.) Griffon and Maubl] and leaf verrucosis, or “lixa-pequena” – LP [Camarotela torrendiela Batista (Bezerra) and Vitoria], reduce the productivity of the coconut palm in Brazil. Damage arises from extensive necrosis of the leaflets, resulting in early abscission of basal leaves and fruit. In Brazil, fungicide terrestrial sprayings has not been a commonly employed practice for the control of coconut foliar diseases because it is not cost-effective, once requiring high-volume of fungicide spraying. Coverage gaps and extensive drift of chemicals can occur due to technological limitations of terrestrial spraying of the tallest mature trees and is further complicated by the peculiar architecture of the palms. The aim of this study was to evaluate the efficacy of systemic fungicides applied directly to the leaf axil of the coconut palm (variety Brazilian Green Dwarf of Jiqui) for the control of foliar diseases. During 2007–2010 and 2009–2012, two field plot experiments were conducted at distinct locations (farms) in the North Fluminense region. Two to 4-monthly applications of the fungicides to the leaf axil of cyproconazole (alone), cyproconazole plus azoxystrobin, cyproconazole plus trifloxystrobin, and flutriafol (alone) were efficacious in controlling coconut palm leaf diseases, resulting in a significant reduction of the LB severity and the number of necrotic LP lesions. When compared with the control treatment, significant increases in the total number of leaves per plant were observed for the most efficacious treatments after one year (2–4 leaves more) and after the second year (3–6 leaves more) after initiating the axillary applications of fungicides in both experiments. This trend continued even after the third year, when there was an average of 8 leaves more for the most efficacious treatment (27 leaves per plant) compared to control (19 leaves per plant) at the end of second experiment. The control of foliar diseases based on the results could ensure a significant increase in regional coconut production.     

Effect of foliar treatments to durum wheat on flag leaf senescence, grain yield, quality and deoxynivalenol contamination in North Italy

Since the production of durum wheat in the drier areas of the Mediterranean Basin is characterized by high variability in terms of yield and grain quality, there is also considerable interest in developing durum wheat in the northern regions, where the pedo-climatic conditions can offer the possibility of obtaining grain yields with higher technological quality and stability. However, the climatic conditions in the northern regions make durum wheat more prone to fungal foliar disease, particularly to Septoria Tritici Blotch (Septoria tritici Rob.) and to Fusarium Head Blight (Fusarium graminearum Petch and Fusarium culmorum Sacc.), with the consequent occurrence of DON in grains.Field experiments have been conducted over two growing seasons at four sites in North West Italy to evaluate the effect of fungicides and foliar nitrogen fertilizer application on durum wheat yield and grain quality. Five combinations of foliar application were compared at each site and each year (untreated control, azole fungicide application at heading, strobilurin fungicide at the stem elongation stage and/or at heading, the addition of a foliar N fertilizer to a fungicide programme). The following parameters were analysed: Septoria Tritici Blotch (STB) severity, flag leaf greenness using a chlorophyll meter, grain yield, test weight, grain protein content, ash content, vitreousness, Fusarium Head Blight (FHB) incidence and severity and deoxynivalenol (DON) contamination. The collected data underline that the cultivation of durum wheat at the climatic conditions of North Italy is actually risky and needs a direct control of fungal disease, which would be able to reduce the development of both foliar and head attacks. The double treatment, with a strobilurin application during the stem elongation stage and azole at heading, results to be an essential practice and showed advantages in terms of the delay of flag leaf senescence (+27%), STB control (+31), FHB control (+11%), yield (+32%) and DON contamination (−45%), compared to the untreated control. Other foliar treatments at heading, such as strobilurin or foliar N fertilizer applications, do not seem to provide any further advantage, for either grain yield or quality. No significant effect of fungicide or foliar N fertilizer application was recorded on the protein or ash concentration or vitreousness.     

Response of Potatoes to Soil-Applied Insecticides, Fungicides, and Herbicides

Non-target impacts of pesticides are well documented in crops such as soybeans and corn. However, little effort has been made to evaluate these impacts in potatoes. Field trials were conducted at the Parma and Aberdeen Research and Extension Centers during 2005 and 2006 to evaluate the potential for systemic insecticides, fungicides, and herbicides to affect disease development, crop injury, and tuber yield. The first set of trials evaluated six insecticide treatments (aldicarb, oxamyl, phorate, imidacloprid, thiamethoxam, and non-treated) in a factorial combination with in-furrow application of the fungicide azoxystrobin. Azoxystrobin significantly decreased Rhizoctonia stem canker, while aldicarb and phorate tended to increase it compared to the non-treated control. There was a significant insecticide by fungicide interaction due to a bigger reduction in disease index by the fungicide when certain insecticides were used. Despite the association of these insecticides with increased disease incidence, there was no significant impact on yield. In the second set of trials, sulfentrazone herbicide was applied just prior to plant emergence to potatoes treated with the same six insecticides to evaluate the potential for the in-furrow treatments to increase plant injury. Sulfentrazone caused stunting and visible plant injury, but the level of plant injury was influenced by insecticide treatment in only one out of four trials.     

Reduced efficacy of rovral and botran to control Sclerotinia minor in lettuce production in the Salinas Valley may be related to accelerated fungicide degradation in soil

Accelerated soil degradation with repeated application was suggested to be responsible for the lack of efficacy of commercial fungicides to control lettuce drop caused by Sclerotinia minor in the Salinas Valley in California. In 2000, a study was initiated in a field artificially infested with S. minor to evaluate the efficacy and degradation potential of four selected fungicides (i.e., Rovral, Botran, Switch, and Endura). Crisphead lettuce was direct-seeded twice a year (spring and fall season) from 2000 to 2002. Fungicides were applied at recommended label rates twice during each season. Disease incidence was evaluated in fungicide treatments and nontreated control plots weekly starting immediately after thinning until harvest, and areas under the disease progress curves (AUDPC) were compared between treatments from 2000 to 2002. Soil samples (0–15 cm) were collected at regular intervals during the spring and fall 2002 lettuce seasons, and analyzed for residual fungicide concentration. Disease progress and final disease incidence were significantly affected by the fungicide treatment, season, year and interactions among these factors (p < 0.05). At the end of the three year experiment, up to 18 and 50% of the lettuce was infected by S. minor for the spring and fall seasons, respectively. Fungicide efficacy to control lettuce drop was highest for Endura, followed by Switch and Botran, and lowest for Rovral. Relative persistence in soils was lowest for Rovral and Botran, followed by Switch and Endura. In 2002, residual soil fungicide concentrations were 11% for Rovral and Switch, 23% for Botran, and 88% for Endura relative to their initial concentrations. Results of this study provide first evidence suggesting that reduced efficacy of lettuce drop control from Rovral and Botran in the Salinas Valley may be related to an accelerated degradation of these fungicides due to repeated application. However, insufficient fungicide persistence due to inherent properties of this sandy loam soil or the chemical structure of these fungicides can not be excluded. Both hypotheses deserve further investigation.     

Trunk applications of phosphite for the control of foliar and fruit scab on pecan

Pecan scab (Fusicladium effusum) is the major disease of pecan in the southeastern United States. Apart from issues of fungicide resistance and the need to test efficacy of novel fungicides such as phosphites, management of the disease in tall trees is challenging due to the technical difficulties of getting sufficient spray coverage to the upper parts of the canopy. The use of trunk application of phosphite, which is systemically transported within the tree, was investigated in six separate experiments in 2010 and 2011. Spray application of phosphite to the trunks of young 3 to 4 year-old trees provided excellent control of scab on foliage of cultivar Desirable, but slightly less control on the susceptible cultivar Wichita, but neither incidence nor severity of scab was reduced on 11 to 12 year-old trees of cultivar Desirable by trunk-spray application in 2010, although slightly less severe disease was observed in 2011. In two factorial cultivar × fungicide treatment experiments in 2010 and 2011 using 13 to 14 year-old trees there was little effect of trunk applications on scab incidence or severity on foliage or fruit. However foliar application of phosphite and a conventional fungicide both significantly reduced the incidence and severity of scab on most cultivars on both foliage and fruit, confirming previous observations of the efficacy of these foliar sprays. Different methods of trunk application, for example injections of phosphite, might prove more efficacious than surface application in older trees.     

Management of peach rusty spot epidemics with biorational fungicides

A total of nine biorational fungicides were examined during the 2000 and 2001 growing seasons for their ability to manage rusty spot epidemics, caused by Podosphaera leucotricha, on moderately susceptible ‘Jerseyglo’ peach. The biorationals studied were the biological control agents Bacillus subtilis, Ampelomyces quisqualis and Phoma glomerata; the plant extracts neem seed oil, cinnamon oil and extracts from leaves of giant knotweed, Reynoutria sachalinensis; the inorganic compounds potassium bicarbonate and potassium dihydrogen phosphate; and chitosan, a deacetylated form of chitin derived from crustacean shells. Disease assessments, consisting of fruit lesion counts, were made at three- to six-day intervals during the course of the epidemics. Three biorational fungicides, B. subtilis, neem seed oil extract and potassium bicarbonate, significantly reduced areas under the disease incidence and lesion density progression curves in both years of the study. The remaining biorational materials reduced disease in only one year or neither year. When the logistic model was fit to the disease progress curves, the three most effective biorationals also significantly reduced the estimated maximum disease level or carrying capacity parameter K. Although these reductions were statistically significant, the amount of disease control was relatively low, ranging from 24 to 34%, versus 94% control for the myclobutanil standard. Thus, B. subtilis, neem seed oil extract and potassium bicarbonate provide insufficient efficacy for commercial management of rusty spot when applied alone. However, since these biorationals consistently provided some levels of control, they may be candidates for use in integrated programs with conventional fungicides.     

Economics of foliar fungicides for hard red winter wheat in the USA southern Great Plains

Grain yields of winter wheat (Triticum aestivum L.) in the southern Great Plains are often reduced by the presence of foliar diseases. This study was conducted to determine whether the application of foliar fungicides is an economically optimal management strategy. The effects of fungicide treatment on commercially available hard red winter wheat varieties with differing levels of genetic resistance (i.e., resistant, intermediate, and susceptible) to foliar diseases were investigated at two locations, Apache and Lahoma, OK, USA, for the harvest years 2005–2012. Two fungicides were rotated between the two locations and applied at approximately Feekes growth stage 9–10.5. When averaged across years, plots to which fungicide was applied generated greater average net returns than plots that did not receive fungicide for susceptible varieties at Apache, and for resistant, intermediate, and susceptible varieties at Lahoma. However, foliar fungicide application was not economical in every year at either location suggesting fungicide use should be reassessed each year given that profitability depends on year specific yield potential, prices, and foliar disease conditions. At both locations high disease incidence occurred in all but one site-year when the average March through May relative humidity exceeded 65%. Additional research would be required to determine the relationship between weather, including relative humidity, and disease incidence, and to develop an economic threshold for treatment decision aid.     

Sensitivity of Sclerotinia sclerotiorum to fludioxonil: In vitro determination of baseline sensitivity and resistance risk

This work determined the sensitivity of field populations of Sclerotinia sclerotiorum (Lib.) de Bary before exposure to the fungicide fludioxonil (= baseline sensitivity) and assessed the risk of fludioxonil resistance. The mean EC₅₀ (Effective Concentration) and Minimum inhibitory concentration (MIC) values for fludioxonil based on inhibition of mycelial growth of 120 wild-type isolates were 0.015 ± 0.005 μg/ml and <0.05 μg/ml, respectively. Positive cross-resistance was not detected between fludioxonil and benzimidazole fungicides but was detected between fludioxonil and dicarboximide fungicides which are considered as high resistance risk fungicides by FRAC, even though these fungicides have different molecular structures. By growing wild-type isolates on potato dextrose agar (PDA) containing sublethal concentrations of the fungicide, we obtained four fludioxonil-resistant mutants with resistance factors (EC₅₀ resistant/EC₅₀ sensitive phenotypes) >2000. The laboratory fludioxonil mutants were less fitter than their parental isolates in terms of mycelial radial growth, pathogenicity and sclerotial production. Moreover, on PDA amended with NaCl, the laboratory fludioxonil mutants grew more slowly than their fludioxonil-sensitive parents, especially at lower concentrations of NaCl. According to the fitness of mutants and the cross-resistance between fludioxonil and dicarboximide fungicides, phenylpyrroles can be considered to pose a moderate resistance risk. In a field trial, fludioxonil provided greater control (over 90% disease control) of S. sclerotiorum than iprodione.     

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.