Deposition and redistribution of fungicides applied by air and chemigation for control of late blight in commercial potato fields

The fungicides metiram, mancozeb, metiram + triphenyltin hydroxide, propamocarb hydrochloride + chlorothalonil, dimethomorph + mancozeb, cymoxanil + mancozeb, and chlorothalonil were applied by aircraft and through center-pivot irrigation systems (chemigation) to replicated plots in commercial fields of ‘Russet Burbank’ potato. Fungicide deposition and redistribution were indirectly determined by inoculation of excised leaves withPhytophthora infestans and directly by chlorothalonil residue analysis from upper, middle, and lower crop canopies. The effectiveness of two surfactants added with fungicide and applied by aircraft, an increased water volume rate used by aircraft, and a reduced water volume used with chemigation was also determined. The addition of synthetic latex and siliconepolyether surfactants did not increase efficacy of metiram or mancozeb in controlling late blight when applied by aircraft. The protectant fungicides metiram, mancozeb, and chlorothalonil were not significantly different from dimethomorph + mancozeb, cymoxanil + mancozeb, and propamocarb hydrochloride + chlorothalonil in late blight control when applied by aircraft. However, cymoxanil + mancozeb had limited efficacy when applied by chemigation. Fungicide deposition through the canopy differed when air applications were made before or after canopy closure (row closure). Fungicides applied by aircraft prior to row closure protected the entire canopy; whereas, fungicide application after row closure initially protected the top and middle canopies, and subsequent applications and redistribution of the fungicides were needed for adequate protection throughout the canopy. The fungicides and fungicide mixtures tested were evenly deposited throughout the potato canopy with each chemigation application. Severity of late blight did not differ on leaves treated with mancozeb or chlorothalonil applied by aircraft at water volumes of 47 L/ha and 94 I/ha and then inoculated withP. infestans, nor did severity of late blight differ on inoculated leaves previously treated with chlorothalonil by chemigation at water volumes of 15,145 and 50, 571 L/ha.     

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.     

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.     

Interactive effects of fungicide programs and nitrogen management on potato yield and quality

The use of azoxystrobin (Quadris) for early blight control often results in potato vines remaining greener later in the growing season. This observation has lead to the suggestion that nitrogen (N) fertilizer could be applied at lower rates when azoxystrobin is used in a fungicide program since high N rates are sometimes used to help manage early blight. The objectives of this study were to evaluate the effectiveness of azoxystrobin for control of early blight under various N fertility management regimes and to determine if azoxystrobin affected plant N fertilizer requirements. Plots were established in 1999 and 2000 at Becker, MN, on a Hubbard loamy sand as a complete factorial, split-plot arrangement using a randomized complete block design with four replications. Fungicide treatments were used as the whole plot factor and included an untreated control, chlorothalonil, and azoxystrobin rotated with chlorothalonil. Fertility treatments were used as the sub-plot factor and included N applied at three levels (170, 250, and 340 kg ha^?1) and two timings (all prehilling or pre- and post-hilling). Early blight was problematic in 1999 and both early and late blight were severe in 2000. Significant interactions were observed between fungicide and fertility treatments for disease control. Control of diseases with fungicides was generally more effective at higher N rates regardless of N application timing. When azoxystrobin was used in the fungicide program, N rate was not as critical in managing foliar disease. In 1999, an interaction was not observed between N rate and fungicide treatment for yield. Yields increased with increasing N rate regardless of fungicide program. However, a significant interaction did occur between N rate and fungicide treatment in 2000 where yields decreased linearly in the control with increasing N rate, increased linearly with N rate using chlorothalonil, and did not respond significantly to N rate using azoxystrobin/chlorothalonil. Results of this study indicate that interactions between the incidence of early/late blight disease and N requirement for potato may depend on the rate of vine death and conditions affecting tuber maturity. At equivalent N rates, post-hilling N tended to depress yield regardless of fungicide program, suggesting that under the conditions of this study late season N is not an effective practice for managing foliar diseases such as early or late blight.     

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.     

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

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

Comparison of deposition patterns in two programs for applying protectant fungicides to potato stems and leaves for the control of late blight (Phytophthora infestans)

Fungicides are applied by air, chemigation, and ground in the Columbia Basin of Oregon and Washington. These methods of fungicide application differ in deposition of fungicide to the canopy and cost. This study compared the alternate use of air and chemigation application of fungicides (AIRCHEM) with chemigation alone (CHEM), by either measuring chlorothalonil or manganese (mancozeb) amounts in three canopy levels (upper, middle, lower), both on leaflets and stems, after multiple fungicide applications on a 7-day schedule. Greater amounts of chlorothalonil or mancozeb were usually found on the leaflets in the upper and middle canopy locations from AIRCHEM compared to CHEM, the day of fungicide application and 7 days later. Deposition of fungicides on stems generally follow the same pattern as leaflets, but the amount deposited and maintained on stems was significantly less than leaflets. Mancozeb deposition in the three canopy levels followed the same pattern as was found for chlorothalonil. The greater the amounts of chlorothalonil on leaflets and stems resulted in better disease reduction during inoculation assays. Reduced fungicide amounts on stems compared to leaflets may be the reason for increased stems infections in recent years by more aggressive strains of late blight. This is the first report quantifying chlorothalonil or mancozeb amounts on potato stems and the first to report amounts of mancozeb on potato foliage after fungicide application.     

Efficacy and timing of application of fungicides for plum rust control in Turkey

Little information is available regarding the efficacy and timing of modern fungicides for the control of plum rust. In this study, modern fungicides, including triazoles, strobilurins, and benzimidazoles, and a classic fungicide (chlorothalonil) were tested under both greenhouse and field experiments. Excellent disease control was obtained by the pre-inoculation application of all fungicides in the greenhouse experiments. However, only triazoles (tebuconazole, difenoconazole, flusilazole and hexaconazole) were effective when applied up to 6 or 7 days after inoculation. Unexpectedly, strobilurins (azoxystrobin and trifloxystrobin) and benzimidazoles (thiophanate-methyl and carbendazim) were not effective when applied at any time after inoculation. In field experiments, early-season fungicide applications effectively inhibited primary infections; however, these applications provided no apparent benefit in preventing secondary infections and premature leaf fall later in the season. All fungicides provided better control over the season and significantly reduced premature leaf fall when applied immediately after rust pustules (uredinia) were first observed. It is suggested that all fungicides tested in this study can be used for plum rust control. Disease monitoring data indicated that disease severity remained low throughout May but dramatically increased in early June. Mid-May is evidently the best time to initiate fungicide sprays against rust on plums; the spray should be applied before or when rust pustules are first observed and when rust is present at low severity.     

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

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

Temporal sensitivity ofAlternaria solani to foliar fungicides

Alternaria solani Sorauer (Ellis) is a causal agent of early blight of potato (Solanum tuberosum L.). Sensitivity to chlorothalonil, triphenyl tin hydroxide (TPTH), and mancozeb was determined for field isolatesof A. solani in 1998 and 1999. Specifically, the relative sensitivity ofA. solani to foliar fungicides in field populations collected from several commercial fields was evaluated over the course of two growing seasons. Sensitivity to these foliar fungicides was determined with anin vitro spore-germination assay method. The fungicide concentration that inhibited conidial germination by 50% (EC₅₀) was estimated for each isolate. Sensitivity ofA. solani isolates to TPTH and mancozeb varied little during the growing season, possibly because there were few TPTH and mancozeb applications made to the fields studied. At several locations, however, repeated exposure ofA. solani populations to chlorothalonil resulted in considerable variability in sensitivity, frequently causing isolates to have decreased sensitivity to this fungicide at the end of the growing season. In five of seven fields, isolates of A.solani collected at the end of the season were significantly less sensitive to chlorothalonil than isolates collected at the beginning of the season.     

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.     

Resistance management strategies for dicarboximide fungicides in grapes: results of six years' trial work

In a series of trials over a period of 6 years the effect of various fungicide combinations and the number of treatments on dicarboximide-resistant Botrytis strains was investigated. At the same time the ratio of sensitive to resistant strains under the influence of the different measures was observed throughout the year. Where infection by dicarboximide-resistant Botrytis strains was light to moderate (about 15%), 4–5 applications of vinclozolin by itself achieved an adequate reduction in infection; this could be enhanced by using vinclozolin in combination with other fungicides possessing additional activity against Botrytis. Where Botrytis infection was heavy, then the effect of 4–5 applications of vinclozolin, and that of the combinations of vinclozolin with dichlofluanid, thiram, captan or captan/mancozeb, was unreliable. Under these conditions the only way to achieve adequate reduction in infection was with vinclozolin in combination with chlorothalonil or with a high rate of thiram (3·2 kg/ha). In trials with fewer applications, treatments with combinations of fungicides were sufficiently effective to achieve good control of Botrytis strains resistant to dicarboximides, even when infection was heavy. The correct times of application are shortly before ‘berry touch’ (stage 32/33) and beginning of ripening/softening of the berries (stage 35). By suppressing Botrytis with two treatments it was possible to prevent losses in yield of about 20%. Treatment with vinclozolin alone and in combination induced an increase to a level of 90–100% in the proportion of resistant Botrytis strains up to harvest in October: this increase could be induced by even a single application. In the absence of a selection pressure in the period from October to the initial vinclozolin treatment in the following growing season, the proportion of the resistant strains in a population fell to a base level of 10–20%. The increase and decrease in the resistant population can be attributed to reduced fitness of the resistant strains. These results do not suggest that there is any easily detectable relationship between the proportion of resistant strains in a population before the start of treatment and the success of these control measures. Under certain conditions, however, trends do become apparent: vinclozolin alone and in combination, with five applications and heavy infection pressure, was effective against Botrytis only when the initial proportion of the resistant strains was well below 50% (1980, 1981). This relationship was less clear in years with only a light infection; where only two or three applications were made, a relationship was no longer apparent.     

Effects of cultivar resistance and single fungicide application on rice sheath blight, yield, and quality

The increased number of sheath blight (Rhizoctonia solani)-resistant rice (Oryza sativa) cultivars available will allow producers to use less fungicide and avoid significant reductions in grain and milling yields. Among cultivars currently in cultivation in the southern United States, sheath blight resistance levels range from very susceptible to moderately resistant. A study was conducted to determine the response of cultivars, with different levels of susceptibility, to sheath blight inoculations and fungicide application and to determine the impact of sheath blight disease development on rice yield and quality. Sheath blight epidemics in field plots were initiated by inoculation at the panicle differentiation growth stage in 2006 and 2007. Azoxystrobin at 0.17 kg a.i. ha⁻¹ was applied at mid-boot. Inoculation significantly increased sheath blight severity and incidence and caused yield losses of 8% in moderately resistant cv. Jupiter to 40% in very susceptible cv. Trenasse. Milling yields were affected to a lesser extent. Fungicide treatments reduced sheath blight incidence and severity, regardless of cultivar except in Jupiter. Single azoxystrobin applications were effective in minimizing yield loss due to sheath blight in all cultivars.     

Variability in responses of US-8 and US-11 genotypes of potato and tomato isolates ofPhytophthora infestans to commercial fungicidesin vitro

Isolates ofPhytophthora infestans collected in Canada from potato and tomato plants from 1994 to 1998 were tested for their responsein vitro to equal active ingredient concentrations (1, 2.5, and 5 μg a.i/mL) of six commercial fungicides: Acrobat MZ (dimethomorph and mancozeb), Ridomil Gold (metalaxyl-m), Dithane (mancozeb), Curzate (cymoxanil), Bravo (chlorothalonil), and Tattoo C (propamocarb and chlorothalonil). Relative mycelial growth of isolates estimated on fungicideamended vs fungicide-free media was compared among isolates of the US-8 and US-11 genotypes from the two host plants. The effects of these fungicides on spore germination of isolates from the two genotypes were also estimated. Mycelial growth of US-8 and US-11 isolates was most affected by Bravo and Tattoo C, followed by Acrobat, and then Curzate and Dithane. Ridomil Gold was not effective in inhibitingin vitro growth of US-11 isolates at the concentrations tested. Variations in sensitivity to different fungicides among isolates of the same genotype collected in different years were observed. For example, based on 2.5 and 5 μg a.i./mL, potato/US-11 isolates collected from 1995 to 1997 showed increased sensitivity to Curzate and Ridomil Gold, while decreased sensitivity was recorded with Dithane. For US-8 isolates, responses to the fungicides varied according to fungicide and year. Variations were generally not significant for Acrobat, Curzate, Bravo, and Tattoo C over time. Conversely, potato/US-8 isolates from 1995 and 1998 were less sensitive to Dithane and Ridomil Gold than those from 1994, 1996, and 1997.     

橡胶树棒孢霉落叶病与炭疽病苗圃同防药剂筛选

4种农药对橡胶树棒孢霉落叶病和炭疽病的苗圃防效试验结果：参试农药对棒孢霉落叶病和炭疽病都有不同程度的防效,其中以百菌清最好,防效分别达到80.05%和74.12%,显著高于其它农药处理。     

Field study of the relative susceptibility of eleven potato (Solanum tuberosum L.) varieties and the efficacy of two fungicides against Rhizoctonia solani attack

Rhizoctonia black scurf is an economically important disease of potatoes in Tunisia and around the world. It reduces the quality and yield of potatoes and has become an important impediment for export of potatoes, especially to Europe. The information on comparative susceptibility of potato cultivars will help the growers make informed decisions regarding the management of this disease. The eleven potato cultivars used in this study showed a range of susceptibility reactions to Rhizoctonia solani but none of these was completely resistant to the disease. The Spunta variety showed the least percentage of infection of progeny tubers by R. solani sclerotia at harvest, while the varieties Nicola, Santana, Labadia, Liseta and Tango showed a high percentage of infection of progeny tubers. Seed treatment using fungicides, presently registered in Tunisia, are not effective in controlling the disease to growers’ satisfaction. Field experiments conducted to evaluate the efficacy of two newly introduced fungicides pencycuron (Monceren^®) and azoxystrobin (Amistar^®) showed that they were effective for the control of the disease. Seed potatoes treatment and in-furrow application of azoxystrobin consistently provided superior protection in two years of experimentation.     

Post-harvest development of anthracnose in pepper (Capsicum spp): Etiology and management strategies

Chilli anthracnose, caused by Colletotrichum spp, is one of the main causes for post-harvest decay of chilli. It can develop on the field, during long distant transport, cold storage and shelf-life. In conventional agriculture, the whole plant including the fruits, are sprayed with fungicides as a prerequisite for post-harvest control of chilli anthracnose. Due to consumer concerns regarding the use of synthetic fungicides and the demand for safer storage methods, the use of synthetic fungicides is no longer allowed for the post-harvest control of chilli anthracnose. As a result, studies on alternative methods to control post-harvest decay have been developed over the years along with the demand for safer storage methods. In this review, results published within the last decade have been summarized and alternative approaches to synthetic fungicides for post-harvest control of chilli anthracnose were discussed in detail. Overall, the use of natural antimicrobials, biocontrol agents, resistant cultivars and ozone shows promise as treatments that can be adopted on a commercial scale to control post-harvest chilli anthracnose caused by Colletotrichum species.     

Improved metribuzin tolerance in narrow-leafed lupin (Lupinus angustifolius L.) by induced mutation and field selection

Narrow-leafed lupin (Lupinus angustifolius L.) is a grain legume well adapted to sandy soils of a Mediterranean climate and is the major grain legume in Australia. Improved herbicide tolerance of lupin cultivars is now considered as top priority by the industry for effective weed management. This paper reports induced mutation by seed mutagenesis in metribuzin-sensitive but anthracnose resistant cv. Tanjil, selection for metribuzin tolerant mutants in the field and evaluation of the tolerant mutants to metribuzin and anthracnose resistance. Two highly tolerant mutants Tanjil-AZ-33 and Tanjil-AZ-55 were identified and they were the first reported metribuzin tolerant mutants. The estimated mutation rate was 2.5 × 10⁻⁵. Tanjil-AZ-33 was six times and Tanjil-AZ-55 was four times more tolerant to metribuzin than the original cultivar Tanjil and they were also more tolerant than the tolerant cv. Mandelup. Tanjil-AZ-33 was the most tolerant lupin germplasm. Disease nursery assessment over 2 years revealed that both mutants also retained anthracnose resistance. Seed yield under irrigation was 4.2 t/ha for Tanjil-AZ-33 and 1.9 t/ha for cv. Tanjil when the seedlings were treated with metribuzin at 300 g/ha at the six-leaf stage. Clearly the mutation process has created new tolerance to metribuzin, but did not alter the anthracnose resistance. The mutant Tanjil-AZ-33 has been used as a parent in the lupin breeding program as a source of both metribuzin tolerance and anthracnose resistance. Seed mutagenesis followed by field selection in M₂ proved to be an effective method to develop new tolerance to herbicides.     

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.     

Combined use of Streptomyces sp. A6 and chemical fungicides against fusarium wilt of Cajanus cajan may reduce the dosage of fungicides required in the field

Biological control agents offer one of the best alternatives to reduce the use of pesticides. This investigation studied the tolerance to fungicides and integrated use of the potential biocontrol agent Streptomyces sp. A6 for control of Fusarium wilt of pigeon pea, Cajanus cajan. Streptomyces sp. A6 exhibited strong tolerance towards most of the fungicides used in the study at concentrations higher than those recommended for field applications. The isolate showed enhanced growth and mycolytic enzyme production in the presence of sulphur, mancozeb, carbendazim, fosetyl aluminium and triadimefon. The fungicides mancozeb, sulphur and carbendazim were selected for further studies. Effective concentrations (EC₅₀ values) of the test fungicides that reduced Fusarium spore germination and fungal biomass by 50% were determined. Similarly, the EC₅₀ for inhibiting fungal spore germination and reducing fungal biomass to 50% by Streptomyces sp. A6 and culture filtrate (CF) were also determined. Combining the EC₅₀ dose of the culture and CF with test fungicides was found to be more effective for controlling Fusarium infection in C. cajan compared to the sum of the effects of the individual treatments. Such combined use of biocontrol agent with fungicides can reduce the dosage of toxic fungicides in agricultural fields, thereby reducing environmental risks. Tolerance and synergistic interaction of Streptomyces sp. A6 with frequently used fungicides suggested its potential in integrated pest management. To the best our knowledge, this is the first extensive study on integrated use of Streptomyces species with fungicides.