Combination effect of chitosan and methyl jasmonate on controlling Alternaria alternata and enhancing activity of cherry tomato fruit defense mechanisms

The effect of chitosan treatment alone or in combination with methyl jasmonate (MeJA) against Alternaria alternata in vitro and in vivo, and defense related enzyme activities were investigated. 100–500 μl/l MeJA significantly inhibited mycelial growth of A. alternata. The inhibitory activity of MeJA on mycelial growth, spore production, spore germination and germ tube length of A. alternata in vitro could be enhanced by 0.1% chitosan. The combination of 0.1% chitosan and 500 μl/l methyl jasmonate was more effective to reduce the disease incidence and lesion diameter of postharvest decay of cherry tomato than the application of MeJA or chitosan alone. The combined treatments resulted in higher activities of PPO (polyphenol oxidase), POD (peroxidase) and PAL (phenylalanine ammonialyase) than the control. This work indicated that the combination of chitosan and methyl jasmonate is a promising method to control postharvest decays of fruit and vegetables.     

Effects of oxathiapiprolin on Phytophthora nicotianae,the causal agent of black shank of tobacco

Oxathiapiprolin is a new fungicide active against oomycetes. In vitro assays and field studies were conducted to examine the effect of oxathiapiprolin on Phytophthora nicotianae (Pn), the causal agent of black shank. The efficacy of oxathiapiprolin on mycelial growth, sporangia production, zoospore motility, and zoospore germination was assessed with four Pn isolates. EC₅₀ values were low ranging from 0.0039 to 0.0049 μg a.i./mL for mycelial growth, 0.00052–0.00081 μg a.i./mL for sporangia production, 0.0035–0.0051 μg a.i./mL for encysted zoospore germination, and 0.0055–0.0166 μg a.i./mL for zoospore motility. Sixty six Pn isolates, 60 from tobacco and six from ornamental plants were examined for sensitivity to oxathiapiprolin at 1 μg a.i./mL. Mycelial growth at 1 μg a.i./mL was observed in only one isolate from tobacco whereas the six Pn isolates from ornamental plants five of which were resistant to mefenoxam at 100 μg a.i./mL, were found to be sensitive to oxathiapiprolin. The efficacy of oxathiapiprolin against black shank was assessed in three field studies in North Carolina. Treatments of oxathiapiprolin were equal or superior to mefenoxam against black shank in each field study. Our results suggest that oxathiapiprolin is a highly efficacious fungicide against P. nicotianae, and will be a useful tool in controlling black shank of tobacco.     

Effects of azoxystrobin, difenoconazole, polyoxin B (polar) and trifloxystrobin on germination and growth of Alternaria alternata and decay in red delicious apple fruit

Alternaria alternata is the predominant fungal pathogen responsible for moldy-core in red delicious strains of apple. In this study, we report on the effects of the polyoxin B compound Polar, the strobilurin fungicides, azoxystrobin and trifloxystrobin, and the sterol inhibitor difenoconazole on spore germination, mycelial growth and fruit decay on detached fruits caused by A. alternata. Germination was most sensitive to polyoxin B and trifloxystrobin among the tested compounds. The 50% and 95% effective concentration (EC₅₀, and EC₉₅), values for in vitro inhibition of conidial germination of the fungus were lowest for polyoxin B and trifloxystrobin, ranging from <0.01 to 0.15 μg/ml and 180 μg/ml, respectively. Germination was least sensitive to difenoconazole and azoxystrobin (EC₅₀ and EC₉₅ values ranging from 25 to 72 μg/ml and 720 μg/ml, respectively). Mycelial growth in vitro of A. alternata was most sensitive to difenoconazole (EC₅₀ and EC₉₅ values of 0.8 and 12 μg/ml, respectively) and least sensitive to both strobilurin fungicides (EC₉₅>1000 μg/ml). Decay formation by A. alternata on mature detached fruits was most affected by trifloxystrobin and azoxystrobin (EC₅₀ and EC₉₅ values of 0.015–0.087 μg/ml and 8 μg/ml, respectively), intermidiate in sensitivity to Polyoxin B (EC₅₀ and EC₉₅ from 1 to 33 μg/ml, respectively), and difenoconazole was the least effective (EC₅₀ and EC₉₅ from 20 to 490 μg/ml, respectively). Polyoxin B applied at 24 or 48 h post-inoculation inhibited fruit decay development. Difenoconazole and trifloxystrobin were less effective and azoxystrobin was ineffective when applied at 48 h post inoculation. The activity of azoxystrobin, difenoconazole, Polyoxin B and trifloxystrobin on one or more stages of the life cycle of A. alternata and on decay development in fruits suggests that these compounds potentially could provide control of moldy-core disease in apple.     

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.     

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...     

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.     

Effects of in-season crop-protection combined with postharvest applied fungicide on suppression of potato storage diseases caused by oomycete pathogens

The effects of fungicides and biofungicides applied during the growing season in combination with storage applications to control potato storage diseases caused by oomycete pathogens were evaluated. The in-season treatments included in-furrow and foliar application of mefenoxam or phosphorous acid and foliar application of Bacillus subtilis. Storage treatments included phosphorous acid, B. subtilis and a 3-way mixture of azoxystrobin, fludioxonil and difenoconazole. These products were tested for control of tuber late blight, Pythium leak and pink rot at 10 °C (cv. FL1879) or 4 °C (cv. Goldrush). The combination of phosphorous acid in the field and during storage significantly reduced tuber blight development. Field treatment with B. subtilis, mefenoxam or phosphorous acid combined with the storage treatment of phosphorous acid significantly reduced Pythium leak development. Interaction of field treatments, mefenoxam or phosphorous acid, with storage treatments, phosphorous acid or the 3-way mixture of azoxystrobin, fludioxonil and difenoconazole significantly reduced pink rot incidence.     

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.     

Sensitivity of Phytophthora parasitica to mandipropamid: In vitro determination of baseline sensitivity and in vivo fungitoxicity

Tobacco black shank caused by Phytophthora parasitica is a devastating soil-borne disease of tobacco in China. Control of tobacco black shank relies on numerous fungicide applications. A new carboxylic acid amide (CAA) fungicide, mandipropamid, was examined for its effects on various asexual developmental stages of P. parasitica in vitro and in tobacco seedlings. Although mandipropamid did not affect discharge of zoospores from sporangia, it strongly inhibited mycelial growth (mean EC₅₀ value of 0.0112 μg ml⁻¹), sporangia production (mean EC₅₀ value of 0.009 μg ml⁻¹), germination of encysted zoospores (mean EC₅₀ value of 0.014 μg ml⁻¹), and germination of sporangia (mean EC₅₀ value of 0.017 μg ml⁻¹). For protective activity in tobacco seedlings, various applications of mandipropamid were superior in reducing black shank compared to that of metalaxyl and of azoxystrobin; while for curative activity assay, 100 μg ml⁻¹ of mandipropamid exhibited the same efficacy as that of metalaxyl, and presented superior activity than that of azoxystrobin. In 2010 and 2011, 119 isolates of P. parasitica from Guizhou Province of China were characterized for the baseline sensitivity to mandipropamid by measuring mycelial growth. Values of effective concentrations for 50% mycelia growth inhibition varied from 0.0068 to 0.0285 μg ml⁻¹ and averaged 0.013 (±0.0045) μg ml⁻¹, with a unimodal distribution. This information will serve as a baseline for tracking future changes in sensitivities of P. parasitica populations to mandipropamid in China.     

Disease variation and chemical control of Ramularia leaf spot in sugar beet

Data from 1999 to 2009 on Ramularia leaf spot caused by Ramularia beticola in sugar beet showed that it was a serious disease in sugar beet in 5 out of 11 seasons. The severity and significance of the disease was found to vary depending on events with precipitation, particularly in two specific weeks in July and September. Several fungicides were found to give effective control, and positive net yield responses were found in 9 out of 11 seasons. The average sugar yield response varied in individual years between 0.7 and 2.2 t ha⁻¹. High levels of control of Ramularia leaf spot was obtained in field trials, a semi-field trial and an in vitro test using the compounds pyraclostrobin, epoxiconazole, difenoconazole and propiconazole. Dose response trials with epoxiconazole from two seasons showed both reduced efficacy and yield responses from low doses. They also proved that the optimal input of fungicides varies significantly between seasons depending on disease severity. A sensitivity test of R. beticola to different fungicides showed a normal distribution of sensitivity with no sign of resistance development to either strobilurins or triazoles. Results from a semi-field trial showed both good preventive and curative effects with 84–100% disease control from epoxiconazole, difenoconazole and pyraclostrobin. In order to optimize an IPM control strategy better forecasting systems are needed along with cultivars providing higher levels of resistance to the disease.     

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.     

Efficacy of a new glyphosate formulation for weed control in maize in southwest Nigeria

A field trial in 2003 and 2004 assessed the efficacy of a new formulation of glyphosate, Touchdown Forte HiTech (glyphosate-TF) and two older versions, Roundup (glyphosate-RP) and Touchdown (glyphosate-TD) for weed control in Nigeria. Treatments were glyphosate-TF at 0.25–1.25 kg a.i./ha, glyphosate-RP at 1.8 kg a.i./ha, and glyphosate-TD at 1.0 kg a.i./ha. Weeded and unweeded treatments were controls. Visual evaluations of weed control at 4 and 8 weeks after treatment (WAT) in both years indicated that glyphosate-TF at all doses gave moderate to complete control of all major weeds (50–100%). At 4 WAT, control of Ageratum conyzoides L., Commelina benghalensis L., Ipomoea involucrata P. Beauv., Brachiaria comota [Hochst ex A. Rich] stapf, and Acalypha ciliata Forssk was at a level similar to that in the weeded control. In 2003, all herbicide formulations and the weeded control reduced Imperata cylindrica (L.) Beauv. shoot dry biomass to the same level at 8 WAT (91–100%) and at maize harvest (83–88%). In 2004, 0.50–1.25 kg a.i./ha of glyphosate-TF and 1.8 kg a.i./ha of glyphosate-RP gave 95% reduction at 8 WAT and 97% at harvest, similar to the weeded control. Maize grain yield in the weeded control and herbicide treatments was 2.8 times higher than that in the unweeded control in both years. These results indicate that glyphosate-TF is effective for weed control in maize at herbicide doses lower than the older formulations.     

Antifungal activity of some plant extracts on Alternaria alternata, the causal agent of alternaria leaf spot of potato

Pure methanol (m) and methanol water (mw) extracts of 5 plants namely: peppermint, eucalyptus, lavandula, Russian knapweed and datura were screened for their antifungal ability against Alternaria alternata, the causal agent of Alternaria leaf spot of potato at 5, 10 and 15% concentrations in vitro. Fungicide mancozeb 0.2% was also used for better comparison. Poisoned food technique and spore germination assay method were used to evaluate the antifungal efficacy of plant extracts. Present findings showed that methanol extracts of eucalyptus, peppermint and lavandula had impressive antifungal effects in inhibiting the mycelial growth as well as spore germination of the pathogen. It was also found that methanol extracts were quite more effective than methanol water extracts in this regard. Methanol extracts of peppermint (15%), lavandula (15%), peppermint (10%) and eucalyptus (15%) demonstrated promising ability in inhibiting the mycelial growth of A. alternata by 0.13, 0.40, 0.43 and 0.50 cm, mycelial growth respectively, while majority of methanol water extracts had either less or no effects in this connection. Spore germination of A. alternata was prominently reduced by methanol extracts, while those of methanol water extracts had very less effects in this regard. Mancozeb (0.2%), methanol extracts of eucalyptus (15%) and peppermint (10%) by 2, 6 and 7% spore germination were best, while methanol water extracts of datura 10, 15 and 5%, lavandula 15 and 10% and also Russian knapweed 5% represented no effect and by 91, 89, 87, 87, 85 and 85% spore germination were at par with control. Findings from this study confirmed that plant extracts can be used as less hazardous natural fungicides in controlling plant pathogenic fungi, thus reducing the dependence on the synthetic fungicides. Methanol extracts of peppermint, eucalyptus and lavandula might be promising materials for natural formulations in controlling Alternaria leaf spot of potato in the field.     

Response of weeds and soil microorganisms to imazaquin and pendimethalin in cowpea and soybean

Herbicides applied to combat weeds and increase crop yields may also have undesired effects on beneficial soil microorganisms. Field studies were conducted in 2005 and 2006 in Zaria, Nigeria, to evaluate the response of weeds and soil microorganisms to imazaquin applied at 0.05, 0.10, 0.20 and 0.40 kg a.i./ha and pendimethalin applied at 1.0, 2.0, 4.0, and 8.0 kg a.i./ha in cowpea and soybean. Hoe-weeded and unweeded (no herbicide) plots were controls. Both herbicides significantly reduced weed biomass in both crops, when compared to the unweeded control, which had the highest weed biomass at all sampling dates. Treatments with 0.40 kg a.i./ha of imazaquin, 2.0 and 4.0 kg a.i./ha of pendimethalin, and the hoe-weeded control, had the highest cowpea grain yield. The unweeded control had the lowest grain yield which was comparable to that in all other herbicide treatments. All treatments except 4.0 and 8.0 kg a.i./ha of pendimethalin had higher soybean grain yield than the unweeded control. Soybean yield was lowest in the unweeded control, and treatments that received 4.0 and 8.0 kg a.i./ha of pendimethalin. All rates of imazaquin gave similar soybean grain yields that were 29–41% higher than that from pendimethalin. The hoe-weeded control had the highest yield, which was 79% more than that in the unweeded control. Higher rates of imazaquin and pendimethalin reduced nodulation, nitrogen fixation, and vesicular arbuscular mycorrhizal (VAM) fungi colonisation in both crops. VAM fungi species diversity and species richness in cowpea rhizosphere soil and species diversity in soybean rhizosphere soil were reduced relative to the controls due to application of both herbicides with the rates of 0.10, 0.20, and 0.40 kg a.i./ha of imazaquin and 8.0 kg a.i./ha of pendimethalin being significantly effective.     

木薯褐斑病菌的室内药剂筛选

采用孢子萌发法对分离自海南的木薯褐斑病菌进行了10种杀菌剂的室内筛选。结果表明,国光多菌灵(50%多菌灵WP)和咪鲜胺(25%咪鲜胺EC)的EC50值最小,抑菌效果最好;腐霉利(50%WP)的EC50值最大,抑菌效果最差。建议生产上使用多菌灵和咪鲜胺等来防治木薯褐斑病。     

五种杀菌剂对花生褐斑病菌室内毒力的影响和田间药效

为了筛选对花生褐斑病田间防治效果好的杀菌剂,结合室内毒力测定(菌丝生长速率法和载玻片萌发法)和田间小区药效试验对四种杀菌剂与常规使用的杀菌剂多菌灵进行了比较。结果表明,室内毒力测定中,多菌灵对菌丝的抑制效果最强,抑菌率为91.4%;其余四种供试杀菌剂中以咪酰胺效果最好,抑菌率达85.6%;王铜效果最差;多菌灵对分生孢子的抑制率为60.9%,其余四种杀菌剂效果差异不显著。田间药效试验结果显示,咪酰胺2 000mg/kg对花生褐斑病的田间防治效果达60.62%,远远高于对照药剂多菌灵(15.53%)以及其它三种供试杀菌剂(王铜、爱可和戊唑醇)。此外咪酰胺比清水对照增产32.28%,也远远高于其它几种药剂。通过室内毒力试验和田间药效试验表明,田间杀菌剂防治花生褐斑病时,咪酰胺比对照药剂多菌灵具有更好的防治效果,适用于花生褐斑病重病地区。     

Management of Eumusae leaf spot disease of banana caused by Mycosphaerella eumusae with Zimmu (Allium sativum × Allium cepa) leaf extract

Among extracts of 33 plant species screened against Mycosphaerella eumusae, the causal agent of Eumusae leaf spot disease of banana, water extract of Cassia senna, Zimmu (Interspecific hybrid between Allium cepa × Allium sativum) and Rhincanthus nasutus provided 100% inhibition of spore germination and 1.7–2.0 cm zone of inhibition of mycelial growth under in vitro conditions. The maximum efficacy of mycelial inhibition was observed with Zimmu leaf extract. When Zimmu leaf extract was tested at different concentrations (5, 10, 25, 50 and 100% w/v), all tested concentrations provided complete inhibition of mycelial growth of the pathogen. The field evaluation of Zimmu leaf extract at different concentrations in cv. Grand Naine showed that the application of the water extract of Zimmu leaf at 50% concentration (w/v) provided 55% reduction of disease severity compared to the unsprayed control. Besides, the application of Zimmu leaf extract increased the value of youngest leaf spotted-0 (up to 60.5%) as well as increased the yield of banana (up to 46.8%) as compared to control. The effect of Zimmu in increasing the value of YLS-0 and the bunch yield was comparable with the chemical fungicide Propiconazole 25% EC (0.1%). Thin layer chromatography (TLC) analysis showed that among different major compounds, two lipid compounds (LP-B1 and LP-B2) extracted using methanol had the ability to inhibit M. eumusae growth (0.7–1.5 cm zone of inhibition). The gas chromatography–mass spectrometry (GC–MS) analysis of lipid bands revealed the presence of six different lipid compounds, which may be responsible for the growth inhibition of the pathogen. Since the application of water extract of Zimmu was found to be not only effective in controlling the leaf spot disease severity but also increased the number of green leaves and yield of banana fruits, the Zimmu extract can be used effectively in integrated disease management of Eumusae leaf spot disease for enhancing banana production in an ecologically sustainable manner.     

Cyhalofop application timing and adjuvant selection for Echinochloa crus-galli control in rice

Field experiments were conducted in Stuttgart, Arkansas, in 2007 and 2008 to evaluate cyhalofop application timing and adjuvant selection for Echinochloa crus-galli L. Beauv. (barnyardgrass) control in drill-seeded rice. In the application timing experiment, cyhalofop was applied at 1 d prior to flooding (PREFL) and at 7, 14, and 21 d post-flood (POSTFL) as single (314 g a.i./ha) or sequential application (first application at 314 g a.i./ha followed by a second application 14 days later at 213 g a.i./ha). In the adjuvant study, the adjuvants evaluated were non-ionic surfactant (NIS) at 0.25% v/v, crop oil concentrate (COC) at 1% v/v, methylated seed oil (MSO) at 1% v/v, 28% urea ammonium nitrate (UAN) at 2.5% v/v, combination of NIS or COC or MSO with UAN, a proprietary blend of MSO/organosilicone (OSL)/UAN at 2.5% v/v, and MSO/OSL/UAN applied with NIS or COC. All adjuvants applied with cyhalofop (314 g a.i./ha at 14 d after flood establishment) resulted in E. crus-galli control and rice yields comparable to cyhalofop alone. In 2007, a single application of cyhalofop controlled E. crus-galli 98–100% by the end of the season, except in the 14-d POSTFL timing (90%). In 2008, E. crus-galli plants were more robust, and control was inconsistent and less than in 2007 (10–91%). At the PREFL timing, sequential applications were needed to improve end-of-season E. crus-galli control. The 7-d POSTFL timing was one of the best single application timings for increased E. crus-galli control and rice yield. Delaying the cyhalofop application to 21-d POSTFL resulted in unacceptable E. crus-galli control of 10 and 46% with single and sequential programs, respectively. Average rice yield was reduced almost three-fold when the first cyhalofop application was at 21-d POSTFL compared with 7-d POSTFL.     

Effects of fungicides applied at seeding on stripe rust and common bunt of wheat

Control of stripe rust (Puccinia striiformis) and common bunt (Tilletia caries and T. foetida) of wheat (Triticum aestivum), with fungicides applied on or adjacent to seed at sowing, was studied. Etaconazole pellets (2800 g a.i./ha), fenfuram liquid seed treatment (17 · 5 g a.i./ha) and imazalil granules (5000 g a.i./ha) were phytotoxic, reducing the number of heads per plot. All treatments reduced the incidence of common bunt although benomyl granules (2500 g a.i./ha), benomyl pellets (1400 g a.i./ha) and imazalil granules (5000 g a.i./ha) were not as effective as the registered smut fungicides carboxin, fenfuram, fenaminosulf and triadimefon. Triadimefon pellets (7000 g a.i./ha), PP347 pellets (1400 g a.i./ha), triadimefon granules (1500 g a.i./ha), flutriafol pellets (1400 g a.i./ha) and etaconazole pellets (2800 g a.i./ha) reduced stripe rust severity 17 weeks after sowing by 90, 89, 88, 86 and 74%, respectively.