不同杀菌剂对花生叶斑病防治效果及产量影响的研究

为筛选出有效防治花生叶斑病的新型药剂,以传统药剂多菌灵为对照,采用三次叶面喷雾法测定了12种新型杀菌剂对叶斑病的防治效果及产量影响,结果表明:12种新型杀菌剂对花生叶斑病的防治效果在18.27%~44.24%之间,其中有效成分为25%吡唑醚菌酯、60%唑醚·代森联、32.5%嘧菌酯·苯醚甲、12%氟环唑、490g/L丙环·咪鲜胺、30%苯甲·丙环唑、46.1%氢氧化铜的防治效果较好,达到30%以上。从产量结果来看,各处理对花生产量增幅在10.53%~25.00%之间,其中增产效果最好的是75%肟菌·戊唑醇、25%吡唑醚菌酯、60%唑醚·代森联,增产效果分别为25%、20.8%和20.3%,显著优于其他药剂。总体来看,12种杀菌剂对花生叶斑病的防治效果与增产效果呈一致趋势。     

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.     

Activities of azoxystrobin and difenoconazole against Alternaria alternata and their control efficacy

Tobacco brown spot caused by Alteraria alternata is a devastating disease of tobacco worldwide. In this study, we reported the effects of a strobilurin fungicide azoxystrobin and a sterol inhibitor difenoconazole on mycelial growth, spore germination, and control of brown spot. Both mycelial growth and spore germination bioassay results showed that sensitivity of A. alternata to difenoconazole was significantly lower than that to azoxystrobin. Azoxystrobin and the compound of azoxystrobin plus difenoconazole provided excellent control efficacy on tobacco brown spot in field. Disease control efficacies for three sprays of azoxystrobin at doses of 0.094, 0.19 and 0.28 Kg a.i./ha, of azoxystrobin plus difenoconazole at 0.15, 0.22 and 0.29 Kg a.i./ha, and of difenoconazole at 0.12 Kg a.i./ha were between 86.00% and 89.67%, between 86.14% and 89.23%, and between 55.14 and 58.41%, respectively. No phytotoxic symptoms were observed for the fungicides in field. These fungicides could potentially be used for brown spot control in tobacco.     

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.     

Pests and diseases contribute to sugar beet yield difference between top and averagely managed farms

Crop yield has to increase to meet the expanding demand for food, feed and bio-energy, caused by world population growth and increasing wealth. Raising sugar yield is also the key to sustaining the profitability of the sugar beet crop. This paper describes the factors that impacted on yield differences between 26 ‘top’ and 26 ‘average’ growers based on four years yield data (2000-2004). In 2006 and 2007, the top growers had 20% higher sugar yields compared to their neighbouring average growers. Heterodera schachtii and Beet necrotic yellow vein virus (BNYVV) were mainly found on clay soils. Top growers on clay soil had significantly lower infestation levels of H. schachtii (4.4x lower, P = 0.008), BNYVV (2.7x lower, P = 0.016) and other foliar symptoms (Pseudomonas, Phoma betae and Verticillium spp. combined) (1.5x lower, P < 0.001), than the average growers, respectively. On sandy soils, infestation levels of Meloidogyne spp. (P = 0.016), Cercospora beticola (P = 0.005) and Erysiphe betae (P = 0.027) were significantly lower (5x, 1.4x and 1.8x, respectively) for the top growers. The top growers on clay or sand sowed 5 and 6 days earlier respectively, and made more fungicide applications and thus used more fungicides than the average growers. Insect pests were not observed at levels damaging for sugar yield: Insecticidal seed treatments provided sufficient control of insect pests. In multiple regression, 35% of the variance in sugar yield on clay soils was explained by H. schachtii and BNYVV infestation levels and by sowing date. On sandy soils, the infestation levels of Heterodera betae and Aphanomyces cochlioides, number of fungicide applications and sowing date explained 71% of the variance in sugar yield. Despite crop protection measures, the calculated yield losses due to pests and diseases for the top growers were 30.2 and 13.1% and for average growers were 37.1 and 16.7% on sandy and clay soils, respectively. Therefore, pest and disease infestation levels partly explained the differences in sugar yield between top and average growers analysed. The skills and knowledge of the grower are important to reducing damage by pests and diseases. Communication of knowledge, obtained by research, towards growers is vital for the long-term raising of yield and increasing of productivity in sugar beet, as well as in other crops.     

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.     

Glyphosate and fungicide effects on Cercospora leaf spot in four glyphosate-resistant sugar beet (Beta vulgaris) varieties

The potential for improved management of Cercospora leaf spot (CLS), caused by Cercospora beticola, using the herbicide glyphosate in glyphosate-resistant sugar beet varieties was investigated. Controlled field experiments were conducted in 2008 and 2009 to determine if glyphosate and glyphosate–fungicide combinations improved the management of CLS in four commercial varieties of glyphosate-resistant sugar beet. Variety and fungicide main effects were significant for CLS development. However, regardless of the herbicide program, glyphosate or a conventional herbicide program, CLS development was not affected. Therefore, results from of this research indicate that glyphosate and glyphosate–fungicide combinations do not significantly contribute to CLS management.     

芝麻棒孢叶斑病的发生规律和高效防治药剂的筛选

芝麻棒孢叶斑病是芝麻常发性病害,严重影响着芝麻的产量和品质。为确定芝麻棒孢叶斑病防治的最佳时期,制定有效的药剂防治措施,2017-2019年对黄淮芝麻主产区平舆县的棒孢叶斑病发生情况进行了监测,并测定了16种杀菌剂的室内毒力和田间防效。结果表明,芝麻棒孢叶斑病的发生初期为现蕾期-初花期,病情发展的转折期为初花期-盛花初期（黄淮产区为7月20日-31日,此时田间发病率小于3%或病情指数小于1）。16种供试杀菌剂中己唑醇、咪鲜胺、氟硅唑、戊唑醇、苯醚甲环唑、腐霉利、噻呋酰胺和咯菌腈对芝麻棒孢叶斑病菌的毒力较强,EC₅₀分别为1.5734×10^-4、0.1248、0.7128、1.3922、2.0014、2.7323、5.4327、6.1285 mg/L;噻呋酰胺、己唑醇、嘧菌酯、戊唑醇和苯醚甲环唑的田间防效和增产效果较好,防效分别为67.19%、65.86%、61.17%、60.87%、61.83%,增产率分别为38.96%、36.86%、39.72%、34.96%、38.56%;苯醚甲环唑、己唑醇、嘧菌酯和戊唑醇施药2次的防效和增产效果最佳。综合研究结果,芝麻棒孢叶斑病防治的最佳时期为初花期-盛花初期（黄淮产区7月20日-31日）,或在田间发病率达到3%或病情指数达到1之前进行防治,建议选择噻呋酰胺、己唑醇、嘧菌酯、戊唑醇和苯醚甲环唑等杀菌剂,同一杀菌剂连续施用次数不超过2次,施药间隔10 d。为减少农药残留和防止病原菌产生抗（耐）药性,不同药剂可交替轮换使用。     

Sensitivity of Cercospora sojina isolates to quinone outside inhibitor fungicides

Frogeye leaf spot, caused by Cercospora sojina, causes yield reductions to soybean (Glycine max) grown worldwide. Quinone outside inhibitor (QoI) fungicides have been effective in managing frogeye leaf spot, but the risk of selecting C. sojina strains with resistance to this class of fungicides is considered high. A QoI fungicide resistance monitoring program was initiated, in which sensitivities to azoxystrobin, pyraclostrobin, and trifloxystrobin were determined in C. sojina isolates collected prior to QoI fungicide use on soybean (baseline group) and C. sojina isolates collected from soybean fields in 2007, 2008 and 2009. For the baseline group, the mean effective fungicide concentration at which 50% of the conidial germination was inhibited (EC₅₀) was determined to be 0.01287, 0.00028 and 0.00116 μg ml⁻¹ for azoxystrobin, pyraclostrobin and trifloxystrobin, respectively. When mean EC₅₀ values of 2007, 2008 and 2009 C. sojina isolates were compared to baseline C. sojina EC₅₀ values, a small but statistically significant (P ≤ 0.05) shift towards less sensitivity was observed for trifloxystrobin in 2009. Although small (<1.5-fold), this shift in sensitivity indicates a risk of selecting for C. sojina strains with reduced sensitivity to QoI fungicides, and fungicide sensitivities should continue to be monitored in the future.     

Penthiopyrad applied in close proximity to Rhizoctonia solani provided effective disease control in sugar beet

Rhizoctonia solani Kühn is an important pathogen of sugar beet (Beta vulgaris L.) that can cause damping-off and crown and root rot. Commercial cultivars which are highly resistant to the pathogen are not as high yielding as susceptible cultivars under low or absent disease pressure. These resistant cultivars often do not have resistance to other common pathogens such as Aphanomyces cochlioides, Cercospora beticola, and Fusarium oxysporum. Fungicides, such as azoxystrobin which belongs to the quinone outside inhibitors (QoI) class, are necessary for controlling Rhizoctonia solani, but there are concerns about the buildup of fungicide-resistant strains in the targeted pathogen population. There is a need to find effective fungicides from different chemical groups so they can be rotated with the current widely-used azoxystrobin to manage R. solani. The objective of this greenhouse study was to evaluate the efficacy of penthiopyrad, a succinate dehydrogenase inhibitor (SDHI), in managing R. solani on sugar beet using three different application methodologies. Penthiopyrad effectively controlled R. solani on sugar beet when applied at 210, 280, 420, or 550 g a.i./ha in-furrow at planting and as a soil drench at the 4-leaf stage. However, foliar application of penthiopyrad failed to provide disease control. These trials indicated that penthiopyrad needs to be in close proximity or direct contact with R. solani in the soil to provide effective control. Penthiopyrad has the potential to be used as an effective alternate partner with azoxystrobin for controlling R. solani and to help in mitigating the development of fungicide resistant isolates of R. solani.     

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.     

Fungicide efficacy of dry bean white mold [Sclerotinia sclerotiorum (Lib.) de Bary,causal organism] and economic analysis at moderate to high disease pressure

White mold [Sclerotinia sclerotiorum (Lib.) de Bary, causal organism] is an economically damaging disease of dry bean (Phaseolus vulgaris L.). Producers often require fungicides to control moderate to high disease levels. Evaluation of fungicide efficacy and cost is critical to make cognisant management decisions. Four field studies were conducted at the Huron Research Station, near Exeter, Ontario in 2012 and 2013. Commercially available synthetic fungicides and a biofungicide seed treatment were evaluated for efficacy in suppressing white mold of dry bean and a subsequent economic analysis was conducted. Area under the disease progress curve (AUDPC) was calculated using disease intensity (incidence × severity) ratings. The untreated control and biofungicide seed treatment had the highest AUDPC values, and in addition to the two applications of the low rate of fluxapyroxad + pyraclostrobin and two applications of penthiopyrad, had the lowest yields. The most efficacious products with regard to disease suppression and yield response were two applications of boscalid, all rates of fluazinam and thiophanate-methyl, and two applications of the high rate of fluopyram + prothioconazole. Two applications of the high rate of fluazinam had the lowest AUDPC, which was nearly 60% lower than the untreated control. Two applications of the high rate of thiophanate-methyl was the highest yielding treatment, recovering 70% of yield lost from untreated plots. Economic impacts varied with planting dates. For the first planting, profit margins for all fungicide treatments, with the exception of two applications of penthiopyrad, two applications of the low rate of fluxapyroxad + pyraclostrobin, and the biofungicide seed treatment, were significantly greater than the untreated control. For the second planting, only profit margins for all fluazinam treatments were significantly greater than the untreated control. This study identifies new economically viable fungicide options for dry bean producers to control white mold.     

Yield loss and management of downy mildew on field pea in Alberta,Canada

Downy mildew of field pea (Pisum sativum) caused by Peronospora viciae f. sp. pisi has become widespread in the main field pea production areas of central Alberta. Field experiments were conducted at naturally-infested field sites over several years to assess the effect of seeding depth, seeding date, seed treatment and foliar fungicides on downy mildew incidence and severity, and to estimate the relationship between severity and yield loss. Downy mildew was shown to cause substantial yield loss on field pea. Even a moderately severe infestation reduced pod numbers by 65% and seed yield by 75%. The loss (pod number or seed yield) was best explained by a linear model (y = −2.3114x + 10.086; R² = 0.9441 and y = −2.5165x + 10.378; R² = 0.9533, respectively). Depth of seeding (range 3–7 cm) did not affect downy mildew. Similarly, seeding date (early, mid and late May) did not have a consistent effect on disease levels. Late seeding occasionally reduced downy mildew, but always resulted in low seed yield. Several seed treatment fungicides reduced downy mildew, and metalaxyl-based products produced the highest yield. Several foliar-applied fungicides, including pyraclostrobin, azoxystrobin and metalaxyl, reduced downy mildew severity, but the results were not consistent across years. We conclude that cultural practices may not be sufficient for effective management of downy mildew, and that metalaxyl-based fungicides applied as seed treatments or foliar sprays could represent the best control option until downy mildew resistant pea cultivars become available.     

Interaction between seed treatments,surfactants and foliar fungicides on controlling dry bean anthracnose (Colletotrichum lindemuthianum)

Anthracnose, caused by fungal pathogen Colletotrichum lindemuthianum (Sacc. & Magnus) Briosi Cav. is one of the main production constraints of the dry bean (Phaseolus vulgaris L.) industry in Ontario. A field study was carried out in 2007 and 2008 to investigate the effect of two seed treatments (DCT (diazinon + captan + thiophanate-methyl) and MFA (metalaxyl-M + fludioxonil + azoxystrobin)) and two foliar fungicides (pyraclostrobin and azoxystrobin) applied with and without a surfactant under low and high disease pressure conditions at Exeter ON. Eighteen treatment combinations were tested in a randomized complete block design with four replicates. The treatment effects were examined by measuring disease development on leaf and pod tissue, pod destruction index, pick (discolored and misshaped seed), yield and return on investment (ROI). The seed treatment MFA performed similarly to DCT, and should be considered a suitable replacement to DCT for dry bean growers. However, utilizing a strobilurin fungicide in both seed and foliar treatments raises concern, as this practice increases the risk of disease resistance. The addition of a surfactant to azoxystrobin increased seed yield and ROI under high disease pressure, but had no effect when added to pyraclostrobin. Pyraclostrobin outperformed azoxystrobin for some disease indices as well as for yield under high disease pressure and for ROI under low and high disease pressure conditions.     

Sensitivity and cross-resistance patterns to demethylation-inhibiting fungicides in California populations of Alternaria alternata pathogenic on pistachio

Alternaria late blight (ALB) caused by Alternaria spp. is an annual production concern for pistachio growers in California. In this study, isolates of Alternaria alternata collected from California pistachio orchards between 1998 and 2003 (population A, n = 46) and in 2010 (population B, n = 38) prior to the registration and use of sterol demethylation-inhibiting (DMI) fungicides for ALB control, were tested for their sensitivity to difenoconazole, propiconazole, and tebuconazole using an in vitro mycelial growth assay. The 50% effective dose (EC₅₀) values for isolates in population A to difenoconazole, propiconazole, and tebuconazole, respectively, ranged from 0.02 to 0.82 μg/mL (mean = 0.17), 0.25–5.73 μg/mL (mean = 1.29), and 0.02–2.76 μg/mL (mean = 0.96), and from 0.02 to 0.93 μg/mL (mean = 0.21), 0.13–5.36 μg/mL (mean = 1.25), and 0.17–5.47 μg/mL (mean = 1.03) for those in population B. Among 65 isolates collected in 2012 from orchards with very limited exposure to difenoconazole, propiconazole or metconazole (population C, n = 65), the EC₅₀ values for tebuconazole ranged from 0.02 to 2.99 μg/mL (mean = 0.51), while EC₅₀ values for difenoconazole of 55 of these isolates varied from 0.01 to 0.44 μg/mL (mean = 0.06). The DMI-exposed population C was found to be on average two to four times less sensitive compared with the populations A and B. Pearson correlation analyses of EC₅₀ values for the three fungicides showed significant positive correlations between the sensitivities of tebuconazole and propiconazole (P < 0.01, r = 0.32), tebuconazole and difenoconazole (P < 0.01, r = 0.26), and difenoconazole and propiconazole (P < 0.01, r = 0.40). Results indicate a clear difference in fungicide intrinsic activity, with difenoconazole being more active than the two other DMIs. Although wide variations in sensitivities for tebuconazole and propiconazole were observed in the non- and DMI-exposed Alternaria populations, efficacy of DMI products has been excellent against ALB. The data collected here will be crucial for the rational use of DMIs in fungicide spray programs for ALB management and serve as a reference to detect any shifts in A. alternata sensitivity to these fungicides in subsequent years as they become more frequently used in California pistachios.     

Impacts of foliar fungicides on infection of soybean by Phomopsis spp. in Iowa, USA

Fungicides pyraclostrobin (strobilurin) and tebuconazole (triazole) were applied to soybean [Glycine max (L.) Merr.] at growth stages R3, R5 or R3 + R5, in 2008 and 2009 at two locations in Iowa. Incidence of infection of stems and seeds by Phomopsis spp. was evaluated, along with yield and seed quality. Stem infection by Phomopsis spp. was reduced in both years by pyraclostrobin applied at R3 + R5, and in 2008 by pyraclostrobin at R5, by approximately three-fold compared to the untreated control. In 2009, treatments including applications of tebuconazole at R3 and pyraclostrobin at R5 significantly reduced infection of seed by Phomopsis spp., by approximately two-fold compared to the untreated control. Only the application of pyraclostrobin at R3 + R5 reduced both stem and seed infection by Phomopsis spp. in 2009. None of the treatments had a significant effect on yield, or seed quality, evaluated by warm and cold germination tests. Seed infection by Phomopsis spp. was negatively correlated with seed quality. Fungicides applied at these growth stages can have an impact on infection by Phomopsis spp., but their effectiveness varies with environment and disease intensity.     

Maize genotype susceptibility to Rhizoctonia solani and its effect on sugar beet crop rotations

Root and crown rot is the major soil-borne fungal disease in sugar beet. In Europe, the disease is mainly caused by the anastomosis group (AG) 2-2IIIB of the basidiomycete Rhizoctonia solani (Kühn). No chemical fungicide to control the disease has been registered in Europe. Therefore, agronomic measures must be optimized to keep the disease severity below an economic damage threshold and to minimize white sugar yield losses. R. solani AG 2-2IIIB infects many other crops besides sugar beet, including maize, where it causes root rot. Sugar beet and maize are frequently grown in the same crop rotation. The proportion of cultivated maize in several European sugar beet growing areas is expected to rise due to a projected increase in demand for renewable resources over the next few years. Although the susceptibility to and tolerance of the disease varies among cultivars in both crops, little is known about the effects of cultivar susceptibility in the pre-crop on a subsequent susceptible crop. The cultivation of R. solani-resistant maize genotypes in rotation with resistant sugar beet might therefore be a useful tool in an integrated control strategy against R. solani, eliminating the need to restrict the desired crop rotation for phytosanitary reasons. A crop rotation experiment with artificially inoculated R. solani was conducted in the field to investigate the pre-crop effects of maize cultivars which differed in their susceptibility to R. solani on a susceptible sugar beet cultivar. We hypothesized that the maize genotype would influence the inoculum potential and performance of a susceptible sugar beet genotype grown after a maize pre-crop, and that this would correlate with the susceptibility of the maize genotype. The results demonstrate that the susceptibility of maize genotypes is consistent over a period of years and that cultivated maize genotypes influenced the inoculum potential measured as disease severity in sugar beet. However, disease severity in sugar beet did not correlate with the disease susceptibility of the genotype of the maize pre-crop. Possible reasons for this missing relationship might be differences in the quality of maize residues for the saprophytic survival of the pathogen or a genotype-specific alteration of the antagonistic microbial community. However, our findings showed that in the presence of maize- and sugar beet-pathogenic R. solani, the most favourable maize cultivar for a crop rotation cannot be determined solely on the basis of its resistance level against Rhizoctonia root rot.     

Assessing fungicide resistance in populations of Alternaria in Idaho potato fields

Early blight, caused by the fungus Alternaria solani and brown leaf spot, caused by Alternaria alternata, are important diseases of potato crops in Idaho. In recent years growers have reported a reduction in efficacy of fungicides traditionally used in the past decade to control early blight. In 2009, a collection of A. solani 39 isolates were screened for resistance to azoxystrobin, pyraclostrobin, boscalid and famoxadone. Fungicide sensitivity testing was done using spiral plate dilution gradients. Results showed that of 39 isolates screened, all were resistant to azoxystrobin and three were resistant to boscalid. None were resistant to pyraclostrobin or famoxadone. In summer 2010, more isolates were collected (9 A. alternata and 26 A. solani) and the survey was expanded to include more fungicides with four different modes of action that targeted succinate dehydrogenase (SDH), methionine biosynthesis, mitochondrial respiration and multi-site contact activity. New isolates of A. solani and A. alternata were also collected from two additional sites. The results showed that 57% of the isolates were resistant to boscalid as well as an average of 63% of the isolates being resistant to the strobilurin fungicides. Seven and 15% of isolates were resistant to penthiopyrad (an SDH inhibitor), and pyrimethanil (a methionine biosynthesis inhibitor), respectively. However, none of the isolates were resistant to fluopyram (an SDH inhibitor) or a mixture of fluopyram and pyrimethanil. Although there appears to be cross resistance developing in Alternaria spp. to some of the new SDH inhibitors like penthiopyrad, others such as fluopyram are still showing limited to no resistance development in Alternaria spp. in Idaho.     

花生疮痂病的药剂防治

采用70%甲基托布津可湿性粉剂、10%苯醚甲环唑可湿性粉剂、50%多菌灵可湿性粉剂、70%代森锰锌可湿性粉剂、30%爱苗乳油、75%百菌清可湿性粉剂、50%速克灵可湿性粉剂和苯醚甲环唑.多菌灵等8种药剂对花生疮痂病进行防治试验,结果表明：几种药剂均有一定的防治效果,其中70%甲基托布津可湿性粉剂和10%苯醚甲环唑可湿性粉剂的防治效果最好,单株结荚数多,果饱、果大,增产幅度最大;70%代森锰锌可湿性粉剂防治效果最差,增产幅度最小。     

Fungitoxicity and synergism of mixtures of fluopicolide and pyraclostrobin against Phytophthora infestans

Fluopicolide and pyraclostrobin were new systemic fungicides with highly inhibitory activity on a broad spectrum of oomycetes, but so far the fungitoxicity of their mixtures on the different developmental stages of Phytophthora infestans and whether synergism exists have not been investigated. The joint-toxicity of the mixtures of fluopicolide with pyraclostrobin was determined against the different developmental stages (mycelial growth, zoospore release, cystospore germination and sporangial germination) of P. infestans and late blight on the leaf discs and the potted plants of potato, and whether the synergistic interaction exists in the mixtures of the two fungicides were evaluated in vitro and in vivo based on the synergistic ratios calculated with the Wadley formulas. The protective activity and curative activity against P. infestans and the efficacy duration in controlling potato late blight of the synergistic mixtures of the two fungicides were examined in this study. The results showed that mixtures of fluopicolide (F) and pyraclostrobin (P) at the ratios of 10:1 and 1:4 (F:P) exhibited synergistic interactions and had excellent inhibitory activity against almost all developmental stages of P. infestans. Synergistic interactions of the mixtures at the ratios of 1:4 and 10:1 (F:P) against the mycelial growth of metalaxyl-resistant isolates were more obvious than against the mycelial growth of metalaxyl-sensitive isolates. Synergistic interactions of the mixtures at the ratio of 1:4 (F:P) against the mycelial growth of the most of the tested isolates were more obvious than those of the mixtures at the ratio of 10:1 (F:P). The highest activity of the mixtures was observed against zoospore release at the ratio of 1:4 (F:P) with EC₅₀ value of 0.0044 μg ml⁻¹. The strongest synergistic interaction of the mixtures was observed against zoospore release at the ratio of 10:1 (F:P) with the synergistic ratio of 5.27. The mixtures of fluopicolide and pyraclostrobin at the ratios of 1:4 and 10:1 (F:P) showed synergistic interactions against P. infestans on the leaf discs and intact plants of potato. The EC₅₀ values for protective activity and curative activity of the mixture at the ratio of 10:1 (F:P) were 0.63 μg ml⁻¹ and 0.87 μg ml⁻¹, and EC₅₀ values of protective activity and curative activity of the mixture at the ratio of 1:4 (F:P) were 0.27 μg ml⁻¹ and 0.44 μg ml⁻¹, respectively. At 14 days after spraying of fungicide solutions, the disease control efficacy of the mixtures at the ratios of 10:1 and 1:4 (F:P) was still over 80% at the dosages of 50 μg ml⁻¹ and 100 μg ml⁻¹, and the disease control efficacy of the two mixtures remained at about 97% at the dosages of 200 μg ml⁻¹, indicating long-lasting effective control efficacy of the two fungicides against potato late blight.