The ilv2 gene, encoding acetolactate synthase for branched chain amino acid biosynthesis, is required for plant pathogenicity by Leptosphaeria maculans.

BACKGROUND: Control of blackleg disease of canola caused by the fungus Leptosphaeria maculans relies on strategies such as the inhibition of growth with fungicides. However, other chemicals are used during canola cultivation, including fertilizers and herbicides. There is widespread use of herbicides that target the acetolactate synthase (ALS) enzyme involved in branched chain amino acid synthesis and low levels of these amino acids within leaves of Brassica species. In L. maculans the ilv2 gene encodes ALS and thus ALS-inhibiting herbicides may inadvertently impact the fungus. METHODS AND RESULTS: Here, the impact of a commercial herbicide targeting ALS and mutation of the homologous ilv2 gene in L. maculans was explored. Exposure to herbicide had limited impact on growth in vitro but reduced lesion sizes in plant disease experiments. Furthermore, the mutation of the ilv2 gene via CRISPR-Cas9 gene editing rendered the fungus non-pathogenic. CONCLUSION: Herbicide applications can influence disease outcome, but likely to a minor extent.

Influence of Propiconazole and Metconazole Formulations on Bacillus subtilis Vegetative Cell Growth and Disease Control of Fruit Crops.

Biological control agent Bacillus subtilis formulated as Theia is registered for control of fungal and bacterial diseases of fruit crops. Combinations of Theia and strategic concentrations of two demethylation inhibitor (DMI) fungicides were investigated to explore potential synergisms. Bacteria were cultured in nutrient broth and combined with technical grades and two formulations of propiconazole (emulsifiable concentrate [EC] and wettable powder) and metconazole (EC and water-dispersible granule) at 0, 10, 50, 100, and 150 µg/ml of active ingredient. After cocultivation, the optical density (OD600) and colony forming units (CFU/ml) were evaluated. In contrast to EC formulations, the wettable powder or water-dispersible granule formulations at 10 or 50 µg/ml of both DMIs did not affect vegetative cell growth. The mixture of Theia and each formulated DMI at 50 µg/ml of active ingredient resulted in a significant reduction of Monilinia fructicola lesion development on apple, Colletotrichum siamense lesion development on cherry, and Botrytis cinerea lesion development on cherry. The combination of Theia with EC formulations showed weaker disease reduction due to antagonism. Only Theia plus non-EC formulated propiconazole and metconazole significantly reduced brown rot disease incidence of apple compared with the respective solo treatments and anthracnose disease incidence of cherry compared with the untreated control. Our results indicated that at least some DMI fungicides possess bactericidal effects depending on the formulation and concentration. The combination of Theia with a lower-than-label-rate concentration (50 µg/ml) of the DMI fungicides propiconazole and metconazole showed potential for synergistic effects, especially when non-EC formulations were used.

Validation of fungicide spray strategies and selection for fenhexamid resistance in Botrytis cinerea on greenhouse-grown grapevines.

In this study, in planta assays were conducted to assess the effects of fungicide spray tactics, such as the reduction of the labeled fungicide dose and mixture with a multi-site fungicide, on fungicide resistance selection and disease control using Vitis vinifera 'Cabernet Sauvignon' grown in a greenhouse for two years. The entire clusters were inoculated with B. cinerea isolates at varying frequencies of fenhexamid resistance, followed by fungicide sprays, disease and fenhexamid resistance investigations at critical phenological stages. Our findings indicate that the lower dose of the at-risk fungicide, fenhexamid, effectively managed fenhexamid resistance and disease as well as the higher, labeled dose. In addition, mixture with the multi-site fungicide captan generally resulted a net-positive effect on both resistance management and disease control.

Strategic control of the cattle tick Rhipicephlaus microplus applied to rotational and silvopastoral grazing systems in subtropical areas.

This work evaluated if strategic control based on no more than three or four annual treatments is useful to control Rhipicephalus microplus infestations on cattle when it is applied to intensive rotational grazing and silvopastoral systems with high stocking rates in subtropical areas. In the intensive rotational grazing system, three annual treatments with chemical acaricides were applied on cattle in two different schemes: between spring and early summer and from late winter and late spring. Strategic control based on three treatments with chemical acaricides from late winter to late spring plus an additional fourth treatment in summer was tested in the silvopastoral system. In the intensive rotational grazing systems, the control schemes allow to reach a significant reduction in the tick load on cattle considering a time interval from spring to autumn. However, the efficacy levels were not high enough in some specific moments, namely, the tick counts of summer and autumn (there were not significant differences between treated and control groups). The scheme evaluated in the silvopastoral grazing system yielded better results than those tested for the intensive rotational system, because significant differences in tick load between treated and control groups were observed in all post-treatment counts and when the analysis was performed for the whole study period. However, values of efficacy in the count-by-count comparison were disparate, ranging from 64.1 to 99.7. Although the efficacy values obtained in the silvopastoral system were better than those of the rotational grazing systems, the total tick load on treated cattle in autumn was not low enough (mean abundance values 25.14 and 38.14). Ticks were more evenly distributed among hosts in late summer and autumn than in spring or early summer, where few hosts carry most of the ticks. Some management strategies as intensive rotational systems or silvopastoral structures can lead to a more efficient forage use, but they imply greater tick challenge than in extensive grazing systems. In these situations, the schemes of strategic control bases on three or four annual treatments should be complemented with additional tactical treatments in late summer or autumn.

A Comparison of a Standard Radial Airflow and a Double Volute-Generated Focused Airflow Air Blast Sprayer to Control Scab in Tall Pecan Trees.

Pecan (Carya illinoinensis) is a valuable crop in the southern United States. Scab (caused by Venturia effusa) is a major biotic constraint to pecan production in the southeastern region and requires 10 to 15 or more fungicide applications for control. Spray application relies on large standard radial airflow air blast sprayers (SSs). Some SSs have been adapted to include a volute on one side to project spray higher into the canopy because of a decline in coverage with height. A grower-designed and engineered double volute-generated focused airflow air blast sprayer (DVS) was assessed for scab control and spray coverage compared with an SS. Over three seasons, on foliage and fruit, scab control was either equal to or superior using the DVS sprayer. On mature fruit, in 2017, scab severity on the control was 9.07%, on the DVS it was 0.19%, and on the SS it was 0.24%; in 2018 severity was 84.4, 18.4, and 29.1%, respectively; and in 2019 it was 32.7, 7.0, and 11.6%, respectively. There were no discernable gradients in scab severity with tree height with either sprayer in 2017, but in 2018 the difference was significant, with the DVS having a shallower gradient, and in 2019 the DVS slope was numerically less steep compared with the SS. Mature fruit weight was significantly greater on trees treated using the DVS compared with the SS in 2017 and 2018 but was not different in 2019. Spray coverage studies showed that the DVS sprayer had significantly more coverage at heights >13.8 m (up to 19.0 m), ranging from 18.4 to 14.1%, compared with coverage using the SS, which ranged from 7.9 to 2.9%. The slope in decline of spray coverage with height was significantly shallower with the DVS sprayer, and spray profiles reflected these differences. Disease control was improved overall when using the DVS, and the DVS provided greater spray coverage at heights >13.8 m when compared with the SS sprayer. The DVS design may offer economical, superior scab control in pecan orchards where trees are >13.8 m tall.

Bipolaris fujianensis sp. nov., an Emerging Pathogen of Sapling Shoot Blight on Chinese Fir, and Its Sensitivity to Fungicides.

Chinese fir is an extremely important economic tree species in southern China. In recent years, 74.5% of Chinese fir saplings suffered from shoot blight in Shunchang County, Nanping City, Fujian Province, China. Seventeen isolates were collected from rotten shoots, and their pathogenicity was confirmed following Koch's postulates. The five pathogenic isolates were identified as belonging to the genus Bipolaris based on morphological characteristics, including septate and geniculate conidiophores, smooth to slightly verruculose conidiogenous nodes, dematiaceous phragmospore conidia, oblong or fusiform conidia, and slightly protruding or truncate hilum on conidia, but the number of pseudosepta (3 to 11, mostly 5 to 8) and the size of conidia ([22.81 to 116.13] × [9.16 to 26.58] µm) are different from those of the known species of Bipolaris. A phylogenetic analysis based on ITS, GAPDH, and Tef1-α sequences determined that the five strains belong to a new species of Bipolaris, and the name Bipolaris fujianensis sp. nov. is proposed. The fungicide sensitivity of the pathogen strain Cfsb3 was further evaluated using eight fungicides. Flusilazole, difenoconazole, tebuconazole, and propiconazole exhibited high toxicity to Cfsb3, and the effective concentration inhibiting 50% (EC50) of mycelial growth was 0.08, 0.20, 0.34, and 0.36 µg/ml, respectively, for these four fungicides. Flusilazole, difenoconazole, and iprodione inhibited B. fujianensis by 100% on detached Chinese fir shoots at their recommended concentrations, but azoxystrobin and thiram were ineffective. In conclusion, this study reported an emerging pathogen of Chinese fir sapling shoot blight and proposed triazole and dicarboximide fungicides for disease control.

Comparative fitness of Monilinia fructicola isolates with multiple fungicide-resistant phenotypes.

This study characterized 52 isolates of Monilinia fructicola from peach and nectarine orchards for their multi-resistance patterns to thiophanate-methyl (TF), tebuconazole (TEB), and azoxystrobin (AZO) using in vitro sensitivity assays and molecular analysis. The radial growth of M. fructicola isolates was measured on media amended with a single discriminatory dose of 1 µg/ml for TF and AZO and 0.3 µg/ml for TEB. Cyt b, CYP51, and ß-tubulin were tested for point mutations that confer resistance to quinone outside inhibitors (QoIs), demethylation inhibitors (DMIs), and methyl benzimidazole carbamates (MBCs), respectively. Eight phenotypes were identified including isolates with single, double, and triple in vitro resistance to QoI, MBC, and DMI fungicides. All resistant phenotypes to TF and TEB presented the H6Y mutation in ß-tubulin and the G641S mutation in CYP51. None of the point mutations typically linked to QoI resistance were present in the Monilinia isolates examined. Moreover, fitness of the M. fructicola phenotypes was examined in vitro and detached fruit assays. Phenotypes with single-resistance displayed equal fitness in in vitro and fruit assays compared to the wild-type. In contrast, the dual and triple-resistance phenotypes suffered fitness penalties based on osmotic sensitivity and aggressiveness on peach fruit. In this study, multiple resistance to MBC, DMI, and QoI fungicide groups was confirmed in M. fructicola. Results suggest that Monilinia populations with multiple resistance phenotypes are likely to be less competitive in the field than those with single resistance, thereby impeding their establishment over time and facilitating disease management.

Combined treatment with amitraz and thymol to manage Varroa destructor mites (Acari: Varroidae) in Apis mellifera honey bee colonies (Hymenoptera: Apidae).

The parasitic mite Varroa destructor (Anderson and Trueman) is one of the greatest stressors of Apis mellifera (L.) honey bee colonies. When Varroa infestations reach damaging levels during fall, rapid control is necessary to minimize damage to colonies. We performed a field trial in the US Southeast to determine if a combination of registered treatments (Apivar, amitraz-based; and Apiguard, thymol-based) could provide rapid and effective control of Varroa. We compared colonies that received this combination treatment against colonies that received amitraz-based positive control treatments: (i) Apivar alone; or (ii) amitraz emulsifiable concentrate ("amitraz EC"). While not registered, amitraz EC is used by beekeepers in the United States in part because it is thought to control Varroa more rapidly and effectively than registered products. Based on measurements of Varroa infestation rates of colonies after 21 days of treatment, we found that the combination treatment controlled Varroa nearly as rapidly as the amitraz EC treatment: this or other combinations could be useful for Varroa management. At the end of the 42-day trial, colonies in the amitraz EC group had higher bee populations than those in the Apivar group, which suggests that rapid control helps reduce Varroa damage. Colonies in the combination group had lower bee populations than those in the amitraz EC group, which indicates that the combination treatment needs to be optimized to avoid damage to colonies.

Compatibility of pesticides with the predatory mite Neoseiulus barkeri.

Multiple arthropod pests can affect the same crop in agricultural systems, requiring the integration of control methods. In the present study, the effects of residual exposure to four broad-spectrum insecticides/acaricides (azadiractin, abamectin, chlorfenapyr, and fenpyroximate) on immature (development and survival time) and adult females (longevity, fecundity, and fertility life table parameters) of the predatory mite Neoseiulus barkeri were evaluated. Additionally, the insecticides/acaricides were categorized according to their selectivity based on the classification proposed by the International Organization for Biological Control (IOBC) for assessing the susceptibility of arthropods in laboratory experiments. Method 004, proposed by the Insecticide Resistance Action Committee (IRAC), was adopted for the bioassays with predators exposed to insecticide-acaricide residues. Among the insecticides/acaricides studied, azadirachtin had minimal effects on immature and adult N. barkeri (all non-significant) and was considered harmless based on the classification of toxicity according to the standards/categories proposed by the IOBC. All other insecticides/acaricides affected immature and adult N. barkeri and were considered slightly harmful in terms of toxicity, according to the IOBC.

Historical and Contemporary Control Options Against Bed Bugs, Cimex spp.

Bed bugs (Hemiptera: Cimicidae) are an important group of obligate hematophagous urban insect pests. The global resurgence of bed bugs, involving the common bed bug, Cimex lectularius L., and the tropical bed bug, Cimex hemipterus (F.), over the past two decades is believed to be primarily due to the development of insecticide resistance, along with global travel and poor pest management, which have contributed to their spread. This review examines and synthesizes the literature on bed bug origins and their global spread and the literature on historical and contemporary control options. This includes bed bug prevention, detection and monitoring, nonchemical and chemical control methodologies (and their limitations), and potential future control options. Future research needs are highlighted, especially the factors behind the modern resurgence, the necessity of identifying differences between the two bed bug species relevant to control, and the need to improve insecticide test protocols and management strategies.

Key Discoveries in Plant Pathology During the Past Half Century: Impacts on the Life Sciences and on Plant Disease Management.

Plant pathology plays a critical role in safeguarding plant health, food security, and food safety through science-based solutions to protect plants against recurring and emerging diseases. In addition, plant pathology contributed significantly to basic discoveries that have had broad impacts on the life sciences beyond plant pathology. In December 2021, The American Phytopathological Society (APS) conducted a survey among its members and among the readership of its journals to identify and rank key discoveries in plant pathology that have had broad impacts on science and/or practical disease management during the past half century. Based on the responses received, key discoveries that have broadly impacted the life sciences during that period include the Agrobacterium Ti plasmid and its mechanism in T-DNA transfer, bacterial ice nucleation, cloning of resistance genes, discovery of viroids, effectors and their mechanisms, pattern-triggered immunity and effector-triggered immunity, RNA interference and gene silencing, structure and function of R genes, transcription activator-like effectors, and type-III secretion system and hrp/hrc. Major advances that significantly impacted practical disease management include the deployment and management of host resistance genes; the application of disease models and forecasting systems; the introduction of modern systemic fungicides and host resistance inducers, along with a better understanding of fungicide resistance mechanisms and management; and the utilization of biological controls and suppressive soils, including the implementation of methyl-bromide alternatives. In this special issue, experts from the pertinent fields review the discovery process, recent progress, and impacts of some of the highest ranked discoveries in each category while also pointing out future directions for new discoveries in fundamental and applied plant pathology.

Fifty Years of Fungicide Development, Deployment, and Future Use.

Plant disease management has not significantly changed in the past 50 years, even as great strides have been made in the understanding of fungal biology and the etiology of plant disease. Issues of climate change, supply chain failures, war, political instability, and exotic invasives have created even more serious implications for world food and fiber security, and the stability of managed ecosystems, underscoring the urgency for reducing plant disease-related losses. Fungicides serve as the primary example of successful, widespread technology transfer, playing a central role in crop protection, reducing losses to both yield and postharvest spoilage. The crop protection industry has continued to improve upon previous fungicide chemistries, replacing active ingredients lost to resistance and newly understood environmental and human health risks, under an increasingly stricter regulatory environment. Despite decades of advances, plant disease management continues to be a constant challenge that will require an integrated approach, and fungicides will continue to be an essential part of this effort.

Efficacy of Iminoctadine Trialbesilate and Trifloxystrobin in Inhibiting and Controlling Pear Powdery Mildew (Phyllactinia pyri) in Hebei Province, China.

Pear powdery mildew (PPM), caused by Phyllactinia pyri, is one of the most serious diseases affecting production in the Hebei pear-growing region of China. Iminoctadine trialbesilate and trifloxystrobin are known to have broad-spectrum activity against a wide range of plant pathogens, including P. pyri. A total of 105 P. pyri strains were isolated from 11 cities in Hebei Province from 2017 to 2019. Iminoctadine trialbesilate and trifloxystrobin significantly inhibited P. pyri growth. Microscopic observation showed that P. pyri mycelia had different degrees of desiccation and that the conidial cell contents had been released. The sensitivities of 60 P. pyri strains to iminoctadine trialbesilate and trifloxystrobin were determined in vitro, and the average EC50 values were 0.5773 ± 0.0014 and 1.2038 ± 0.0010 µg/ml, respectively. The average EC50 values for 85 and 75% of the strains with continuous single peak frequency distributions were 0.4534 ± 0.0012 and 0.8124 ± 0.0039 µg/ml, respectively. These data could be used as the baseline sensitivities of P. pyri to these two fungicides. The maximum difference multiples of the sensitivities of P. pyri strains from the different cities to iminoctadine trialbesilate and trifloxystrobin were 13.5- and 17.2-fold, respectively. Cluster analysis showed that there was no significant correlation between P. pyri sensitivity and geographical origin. The field efficacies in controlling PPM were higher than 85%. These findings can improve how we monitor iminoctadine trialbesilate and trifloxystrobin resistance and improve application efficiency.

Efficacy and Profitability of Fungicides for Managing Frogeye Leaf Spot on Soybean in the United States: A 10-Year Quantitative Summary.

Frogeye leaf spot (FLS), caused by Cercospora sojina, is an economically important disease of soybean in the United States. Data from 66 uniform fungicide trials (UFTs) conducted from 2012 to 2021 across eight states (Alabama, Arkansas, Illinois, Iowa, Kentucky, Louisiana, Mississippi, and Tennessee) were gathered and analyzed to determine the efficacy and profitability of the following fungicides applied at the beginning pod developmental stage (R3): azoxystrobin + difenoconazole (AZOX + DIFE), difenoconazole + pydiflumetofen (DIFE + PYDI), pyraclostrobin (PYRA), pyraclostrobin + fluxapyroxad + propiconazole (PYRA + FLUX + PROP), tetraconazole (TTRA), thiophanate-methyl (TMET), thiophanate-methyl + tebuconazole (TMET + TEBU), and trifloxystrobin + prothioconazole (TFLX + PROT). A network meta-analytic model was fitted to the log of the means of FLS severity data and to the nontransformed mean yield for each treatment, including the nontreated. The percent reduction in disease severity (%) and the yield response (kg/ha) relative to the nontreated was the lowest for PYRA (11%; 136 kg/ha) and the greatest for DIFE + PYDI (57%; 441 kg/ha). A significant decline in efficacy over time was detected for PYRA (18 percentage points [p.p.]), TTRA (27 p.p.), AZOX + DIFE (18 p.p.), and TMET + TEBU (19 p.p.) by using year as a continuous covariate in the model. Finally, probabilities of breaking even were the greatest (>65%) for the most effective fungicide DIFE + PYDI and the lowest (<55%) for PYRA. Results of this meta-analysis may be useful to support decisions when planning fungicide programs.

Identification and Fungicide Sensitivity of Colletotrichum spp. from Apple Flowers and Fruitlets in Brazil.

Glomerella leaf spot (GLS) and bitter rot (BR), caused by Colletotrichum spp., are major diseases on apple in southern Brazil. Among integrated pest management tools for disease management in commercial orchards, fungicides remain an important component. This study aimed to identify Colletotrichum spp. from cultivar Eva in Paraná state orchards; evaluate their in vitro sensitivity to cyprodinil, tebuconazole, iprodione, and fluazinam; and determine the baseline in vitro sensitivity of these isolates to benzovindiflupyr and natamycin. Most isolates belonged to Colletotrichum melonis and C. nymphaeae of the C. acutatum species complex. The two species varied in sensitivity to fluazinam and tebuconazole, but no variability was found for any other fungicide. The lowest 50% effective concentration (EC50) values of Colletotrichum spp. were observed for cyprodinil (mean EC50 < 0.02) and benzovindiflupyr (mean EC50 < 0.05); EC50 values were intermediate for fluazinam (mean EC50 < 0.33) and tebuconazole (mean EC50 < 0.14), and they were highest for natamycin (mean EC50 < 5.56) and iprodione (mean EC50 > 12). Cyprodinil and fluazinam are registered for use in Brazil for apple disease management but not specifically for GLS and BR. Tebuconazole is one of the few products registered for Colletotrichum spp. control in apples. In conclusion, flowers and fruitlets can serve as sources of inoculum for GLS and BR disease; C. acutatum was the predominant species complex in these tissues; cyprodinil and fluazinam applications may suppress GLS and BR; and benzovindiflupyr and natamycin warrant further investigation for GLS and BR disease control of apple due to comparably high in vitro sensitivity.

Assessment of Fungicide Resistance via Molecular Assay in Populations of Podosphaera leucotricha, Causal Agent of Apple Powdery Mildew, in New York.

Podosphaera leucotricha, causal agent of apple powdery mildew, is a pathogen endemic worldwide where apples are produced. In the absence of durable host resistance, the disease is most effectively managed in conventional orchards with single-site fungicides. In New York State, increasingly erratic precipitation patterns and warmer temperatures due to climate change may create a regional environment more conducive to apple powdery mildew development and spread. In this scenario, outbreaks of apple powdery mildew may supplant the apple diseases of current management concern: apple scab and fire blight. Presently, there have been no reports from producers of fungicide control failures for apple powdery mildew, though increased disease incidence has been reported to and observed by the authors. As such, action was needed to assess the fungicide resistance status of populations of P. leucotricha to ensure key classes of single-site fungicides (FRAC 3, demethylation inhibitors, DMI; FRAC 11, quinone outside inhibitors, QoI; and FRAC 7, succinate dehydrogenase inhibitors, SDHI) remain effective. In a 2-year survey (2021 to 2022), we collected 160 samples of P. leucotricha from 43 orchards, representing conventional, organic, low-input, and unmanaged orchards from New York's primary production regions. Samples were screened for mutations in the target genes (CYP51, cytb, and sdhB) historically known to confer fungicide resistance in other fungal pathogens to the DMI, QoI, and SDHI fungicide classes, respectively. Across all samples, no nucleotide sequence mutations that translated into problematic amino acid substitutions were found in the target genes, suggesting that New York populations of P. leucotricha remain sensitive to the DMI, QoI, and SDHI fungicide classes, provided no other fungicide resistance mechanism is at play in the population.

Identification and characterization of Colletotrichum truncatum and C. destructivum causing stem rot of white clover in China.

White clover (Trifolium repens L.) is an excellent quality forage legume species with superior planting efficiency, which reduces the cost of artificial weeding and nitrogen fertilizer inputs and has feeding and economic value. However, from June to September 2022, severe stem rot affected the yield and quality of white clover crops in Harbin, Heilongjiang Province, China. The aim of this study was to identify the causative agents of the disease. Overall, Colletotrichum truncatum (6 isolates) and C. destructivum (10 isolates) were obtained from rotten white clover stems and identified according to morpho-molecular characteristics and phylogenetic analyses. Pathogenicity tests of the isolates revealed that C. destructivum had a higher pathogenicity to white clover than C. truncatum. In addition, all isolates were highly pathogenic to broad bean, fodder soybean, soybean, pak choi, and chickpea, pathogenic to mint, and did not infect corn, wheat, or cilantro. C. destructivum and C. truncatum isolates were very sensitive to tebuconazole and pyraclostrobin, with EC50 values of 0.54 to 0.70 µg/ml and 0.42 to 0.62 µg/ml, respectively, efficacies ranging between 93.2 to 94.9% and 90.2 to 95.2% at 600 µg/ml and 450 µg/ml, respectively, and EC90 values of 1.88 to 13.36 µg/ml and 1.32 to 23.39 µg/ml, respectively. Therefore, intercropping of host and non-host plants and chemicals can be considered to control stem rot in white clover. These results provide a basis for controlling C. destructivum and C. truncatum in white clover in China.

Field Evaluation of Fungicides for the Management of Neofabraea Leaf Lesion of Olive in California.

Field experiments were conducted during the fall-winter seasons of 2017 to 2018 and 2018 to 2019 to evaluate the efficacy of various fungicides to control Neofabraea leaf lesion of olive. Field trials were conducted in the highly susceptible cultivar Arbosana in a commercial, super-high-density orchard in San Joaquin County, California. Up to eight fungicidal products were applied using an air blast backpack sprayer, and their efficacy was compared with different application strategies. Results showed that most products were effective in reducing infection by the pathogens and limiting disease severity. Overall, best disease control was achieved by thiophanate-methyl, cyprodinil, difenoconazole + cyprodinil, and chlorothalonil, providing up to 75% reduction in disease severity. Copper hydroxide did not control the disease. In 2018 to 2019, the fungicides difenoconazole + cyprodinil and ziram were evaluated in additional field trials using different application strategies (single, dual, and combined applications) suitable for pathogen resistance management. Results showed that both products provided significant reduction in disease severity (∼50%), although no differences in efficacy were found between the two products nor between the different application strategies. Both products performed equally using one or two applications at 2-week intervals following harvest.

Colletotrichum siamense leaf blight/spot: Characterization of a newly identified disease on Cinnamomum tamala.

Cinnamomum tamala (bay leaf) is widely used for culinary and medicinal purposes in South Asia. A leaf blight/spot disease was first discovered on nearly 90% of C. tamala plants with a mean severity of 48% to 74.4% in Gazipur and Bogura, Bangladesh, in 2019. The present study identified and characterized the causal organism and formulated the optimum growth conditions and effective fungicides for the chemical control of the pathogen. The characteristic symptoms on the infected leaves appeared circular to oval reddish-brown spots with raised margins and often developed in tear-stain patterns. Severe infection of C. tamala sapling resulted in dieback symptoms with leaf defoliation. A fungus with floccose, dense, white colonies with well-differentiated acervuli was isolated from the infected leaves. Combined cultural, morphological, and molecular characteristics identified the pathogen as Colletotrichum siamense. Inculcating healthy leaves and 1-year-old saplings of C. tamala with a conidial suspension of the fungus reproduced the same symptoms observed in the bay leaf orchard. The highest mycelial growth was recorded on V-8 Juice Agar media, while the maximum radial mycelial growth and level of sporulation of the fungus were significantly higher in incubation temperature 30°C. Fungicide trials showed that carbendazim 50 WP, azoxystrobin, mancozeb, and trifloxystrobin, either singly or in combination, successfully reduced fungal mycelial growth in vitro. Therefore, disease management strategies should be opted to halt the further spread of this issue. To our knowledge, this is the first study to document the incidence of Colletotrichum leaf blight on C. tamala in Bangladesh and even in the world.

Contact and Gastric Effect of Peppermint Oil on Selected Pests and Aphid Predator Harmonia axyridis Pallas.

Peppermint essential oil (EO) has been extensively tested to date in reducing stored-product insects and insects of public health concern with very promising results, while only a few studies target important crop pests. There is also very little information on the effects of peppermint EO on non-target organisms, especially concerning contact and gastric effects at the same time. The goal of the investigation was the determination of the effect of peppermint EO on the mortality of Aphis fabae Scop.; the feeding intensity and weight gain of Leptinotarsa decemlineata Say. larvae; and the mortality and voracity of non-target organism Harmonia axyridis Pallas larvae. Our research indicates promising use for the M. piperita EO against aphids and young larvae (second instars) of the Colorado potato beetle. M. piperita EO showed good insecticidal efficacy against A. fabae with LC50 = 0.5442% for nymphs and 0.3768% for wingless females after 6 h. Over time, the LC50 value decreased. For the second instar larvae of L. decemlineata, the LC50 values were 0.6278%, 0.3449%, and 0.2020% after 1, 2, and 3 days of the experiment, respectively. On the other hand, older larvae (fourth instar) were characterized by significant resistance to the tested oil concentrations with LC50 value = 0.7289% after 96 h. M. piperita oil (contact and gastric effects) at a concentration of 0.5% was found to be toxic to young larvae (2 and 5 days old) of H. axyridis, while EO at a concentration of 1% was toxic to 8-day-old larvae. Thus, for the sake of ladybug safety, it would be advisable to use EO from M. piperita against aphids at concentrations lower than 0.5%.