Fungicide Spray Programs Research Articles

Optimizing fungicide programs for peanut leaf spot management in Southeast Alabama: A case for reducing chlorothalonil use

Early leaf spot (caused by Passalora arachidicola) and late leaf spot (Nothopassalora personata) are the most damaging fungal diseases of peanuts (Arachis hypogaea L.) in the southeastern United States. Producers rely heavily on single-site fungicides, which pose a moderate to high risk for resistance development. To mitigate this risk, chlorothalonil, the predominate multi-site fungicide used to manage leaf spot diseases in peanuts, is the backbone of leaf spot spray programs. However, the future availability of chlorothalonil in agriculture is at risk due to regulatory decisions and toxicity issues. Thus, this study was undertaken to evaluate the efficacy of copper sulfate, dodine, and sulfur alone or in combination with other single-site fungicides against leaf spot diseases as chlorothalonil alternatives as well as their influence on yield. Under low disease pressure, all the alternative fungicide programs provided statistically similar leaf spot control when compared to chlorothalonil alone. In contrast, under high disease pressure in 2022, dodine alone and dodine + penthiopyrad did not significantly decrease leaf spot severity when compared to the nontreated control. Additionally, dodine alone and the 2022 premium fungicide program had significantly higher leaf spot severity when compared to chlorothalonil alone under favorable weather patterns for rapid disease development. Sulfur + copper sulfate significantly reduced leaf spot severity as compared to chlorothalonil alone only in 2022. All other remaining fungicide programs provided statistically similar control as chlorothalonil alone. Overall, dodine, sulfur, and copper sulfate have potential to serve as alternatives to chlorothalonil in leaf spot fungicide spray programs in peanuts.

Response of selected peanut commercial cultivars to leaf spot diseases as influenced by fungicide inputs

Early leaf spot (caused by Passalora arachidicola) and late leaf spot (caused by Nothopassalora personata) are the most widespread, damaging foliar diseases of peanuts in the southeastern United States. When left nontreated, both diseases can prematurely defoliate peanuts and reduce peanut yields by up to 70%. Leaf spot diseases are primarily managed through a combination of fungicide applications and cultivar selection. In this study, six field experiments were conducted from 2021 to 2022 in Brewton, Headland, and Tallassee, Alabama, to evaluate the response of ten selected commercial peanut cultivars to various levels of leaf spot pressure as influenced by low- and high-input fungicide programs when compared to nontreated controls. The low input fungicide program included seven applications of chlorothalonil, whereas the high input fungicide program comprised of fluxapyroxad, pyraclostrobin, mefentrifluconazole, flutolanil, bixafen, flutriafol, tebuconazole, and/or chlorothalonil. Effects on leaf spot and pod yields were assessed. Leaf spot severity was higher for TUFRunner™ ‘297’, Georgia-16HO, and FloRun ‘331’, but was lower for AU-NPL 17, Georgia-06G, Georgia-12Y, and Georgia-14N. In terms of yield, leaf spot tolerant varieties showcased superior performance in high disease pressure, whereas susceptible varieties excelled in low disease pressure. Fungicides significantly enhanced the performance of susceptible cultivars under high leaf spot pressure, with marginal impact in low leaf spot pressure. These results highlight the importance of selecting cultivars and fungicide spray programs based on disease pressure to maximize profits.

Genetic Diversity, Mycotoxin Profiles, and Population Structure of Fusarium spp. Associated with Fusarium Head Blight in Georgia, United States.

Fusarium head blight (FHB) has become a limiting factor in soft red winter wheat production in the southeast United States. Recent epidemics have occurred in Georgia, but genetic information on the Fusarium species responsible for FHB is unknown. This study aimed to assess pathogen population structure and genetic diversity, trichothecene profiles, and representative pathogenicity of 196 Fusarium isolates collected from 44 wheat (n = 85) and 53 corn (n = 111) fields in Georgia. Phylogenetic analysis using the translation elongation factor 1-alpha (635 bp) and RNA polymerase second largest subunit (930 bp) sequence data resolved isolates into 185 haplotypes, which represented 12 Fusarium species grouped under five species complexes. F. graminearum with 15-acetyl-deoxynivalenol (15ADON) chemotype (75.6%) and F. incarnatum (57.7%) predominated in wheat and corn, respectively, with a surprisingly higher frequency of nivalenol (NIV) F. graminearum (21.8%). Using nine variable numbers of tandem repeat markers, 82 multilocus genotypes out of 86 F. graminearum isolates were identified and grouped into two genetic clusters, pop1fg (n = 29) and pop2fg (n = 32), as part of the North American populations (NA1 and NA2) but with no chemotype differentiation. F. graminearum populations in Georgia are mostly clonal and might have evolved through at least two introductions from the northeast United States and Canada and local adaptation to maintain high genetic diversity. Pathogenicity of F. graminearum isolates from wheat and corn had high FHB severity (>60%) in wheat, which depicted the risk they can pose towards future FHB outbreaks. Overall, this baseline study provided important information on Fusarium species diversity including F. graminearum associated with FHB in Georgia that will be useful to formulate integrated disease management incorporating improved host resistance and fungicide spray programs.

First report of anthracnose caused by Colletotrichum grevilleae on apple in Korea.

In October 2022, typical symptoms of anthracnose were observed on apple (Malus ⅹ domestica cv. Fuji) fruits collected from Pocheon in Gyeonggi province, South Korea (N37.98074°, E127.33995°). In the surveyed orchard, the incidence rate of apple anthracnose was less than 1%. The initial symptoms were brown-to-dark brown lesions, and with disease progression, they enlarged and the pulp became soft, forming a brown band. In total 29 apple fruits were collected, and the causal agent was isolated by removing the peel, and the diseased tissues were directly transferred onto potato dextrose agar (PDA), followed by incubation for 7 days at 25°C. As the results, two isolates (GgPc22-1-11 and GgPc22-1-13) were obtained. For describing morphological and cultural characteristics, isolate GgPc22-1-11 was cultured on PDA and synthetic nutrient-poor agar (SNA) at 25°C under near-UV light with a 12-h photoperiod for 10 days. The colonies of GgPc22-1-11 on PDA were initially white and subsequently appeared light gray to olivaceous with white margins. The reverse side of the plates were dark brown and slate blue (Supplementary Fig. S1). Colonies on SNA were flat with an entire margin and short sparse white aerial mycelium. No setae were observed. Conidia on PDA were hyaline, straight, aseptate with a rounded apex, clavate to cylindrical, and measured 16.4 ± 2.4 (10.8-23.8) × 5.5 ± 0.7 (3.6-7.7) μm (n = 200). Appressoria were medium-to-dark brown, aseptate, solitary or in groups with irregular outlines, and lobate or having undulate margins (Supplementary Fig. S1). These morphological and cultural characteristics of GgPc22-1-11 were consistent with those of Colletotrichum grevilleae F. Liu, Damm, L. Cai & Crous, pathogens of Proteaceae and Punica granatum (Liu et al. 2013; Huang et al. 2023). DNA was extracted from GgPc22-1-11, PCR was performed and Phylogenetic analysis of concatenated partial sequences of the internal transcribed spacer (ITS) of rDNA, β-tubulin (TUB2), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), chitin synthase 1 (CHS-1), and actin (ACT) genes was conducted (Weir et al. 2012). The resulting sequences were deposited in GenBank under the accession numbers LC773710-LC773714. A nucleotide BLAST search revealed that the ITS sequences of the isolates were 98.95% identical to those of C. grossum CAUG7 (KP890165.1). The TUB2, GAPDH, CHS-1, and ACT sequences of the isolates were 99.79%, 99.24%, 100%, and 100%, respectively, identical to those of C. grevilleae WP4. GgPc22-1-11 was clustered with C. grevilleae WP4 using neighbor joining analysis conducted with MEGA X software (Kumar et al. 2018) (Supplementary Fig. S2). Pathogenicity tests were conducted using GgPc22-1-11 and repeated three times. A total of 12 symptomless apples of each variety were selected, including Fuji, Hongro, Tsugaru, and RubyS. The apples were surface-sterilized with 70% ethanol and wounded using a sterile needle. Both wounded and unwounded apples were inoculated with mycelium plugs and paper disks containing a conidial suspension (1 × 106 conidia/ml) and placed in a plastic box with moist paper towels (>90% relative humidity) at 25°C in dark. At 5 days after inoculation, all artificially wounded fruits exhibited symptoms and 30% (4 out of 12) of unwounded inoculated fruits showed symptoms in each apple variety while control fruits were asymptomatic both the unwounded and wounded inoculations (Supplementary Fig. S1). To fulfill Koch's postulates, the fungi were reisolated from symptomatic tissues and were identical to GgPc22-1-11 confirmed by morphological and molecular analysis. To the best of our knowledge, C. grevilleae has been reported in Protea sp. and pomegranate (Liu et al. 2013; Huang et al. 2023) but not in apples to date, and this is the first report of C. grevilleae causing anthracnose in apple fruits. This research of the newly emerged unreported Colletotrichum species can offer valuable information for development of an effective fungicide spray program to control apple anthracnose.

Reevaluation of Sensitivity of Monilinia fructicola Isolates to the DMI Fungicide Propiconazole in the Southeastern United States and Investigation of the Genetic Element Mona.

Sterol demethylation inhibitor (DMI) fungicides continue to be essential components for the control of brown rot of peach caused by Monilinia fructicola in the United States and worldwide. In the southeastern United States, resistance to DMIs had been associated with overexpression of the cytochrome P450 14α-demethylase gene MfCYP51 as well as the genetic element Mona, a 65 bp in length nucleotide sequence located upstream of MfCYP51 in resistant isolates. About 20 years after the first survey, we reevaluated sensitivity of M. fructicola from South Carolina and Georgia to propiconazole and also evaluated isolates from Alabama for the first time. A total of 238 M. fructicola isolates were collected from various commercial and two experimental orchards, and sensitivity to propiconazole was determined based on a discriminatory dose of 0.3 μg/ml. Results indicated 16.2, 89.2, and 72.4% of isolates from Alabama, Georgia, and South Carolina, respectively, were resistant to propiconazole. The detection of resistance in Alabama is the first report for the state. All resistant isolates contained Mona, but it was absent from most sensitive isolates. It was unclear if the resistance frequency had increased in South Carolina and Georgia. However, the resistance levels (as assessed by the isolate frequency in discriminatory dose-based relative growth categories) did not change notably, and no evidence of other resistance genotypes was found. Analysis of the upstream MfCYP51 gene region in the resistant isolate CF010 revealed an insertion sequence described for the first time in this report. Our study suggests that current fungicide spray programs have been effective against increasing resistance levels in populations of M. fructicola and suppressing development of new resistant genotypes of the pathogen.

Grapevine Leaf Epiphytic Fungal and Bacterial Communities Are Influenced More by Spatial and Temporal Factors than by Powdery Mildew Fungicide Spray Programs

Synthetic fungicide treatments for managing grapevine powdery mildew have been widely applied in vineyards for decades, yet their ecological impacts on microorganisms in the phyllosphere have not been sufficiently studied. To investigate the impact of fungicide sprays on the grapevine leaf microbiota, grapevine leaf epiphytes were collected throughout the growing season from two California vineyards, each treated with identical spray programs. Each spray program was designed to control grapevine powdery mildew and contained five rotating synthetic fungicides. Leaf samples were collected before the first spray and between subsequent spray applications. Amplicon sequencing of ITS2 and 16S rRNA V4 regions was used to compare leaf epiphytic fungal and bacterial/archaeal diversities, taxonomic compositions, and differential abundances of taxa among treatments, locations, and sampling time points. Location (vineyard) and time significantly affected bacterial and fungal community compositions, whereas spray treatment did not. Plant-pathogenic fungi were the dominant fungal guild in both locations, and, in one location, their dominance increased significantly as the season progressed. Botrytis, an important postharvest pathogen in grapes, was significantly higher in relative abundance in one of the locations in the late season and acted as a hub genus in a co-occurrence network. In summary, the overall impact of the different spray programs on microbial community compositions was not significant, suggesting that the shifts of grapevine foliar microbial communities may be driven mainly by spatial and temporal factors rather than specific fungicide applications. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Leaf shredding as an alternative strategy for managing apple scab resistance to demethylation inhibitor fungicides

Within integrated apple scab control there is a strong focus on reduction of Venturia inaequalis primary inoculum. The hypothesis that leaf shredding as an orchard sanitation practice would reduce the effective population size of the fungus (resulting in lower genetic variation due to reduction in sexual offspring) was tested. Assuming the allele causing fungicide resistance is already present in the population, it will be widely distributed at the end of the season, since selection occurs when the demethylation inhibitor (DMI) fungicide was applied. For short-term disease management a reduction of inoculum size, (i.e. potential ascospore dose) is most important. In the long-term resistant isolates/genotypes would be less likely to survive the winter and/or to infect in the spring, if that inoculum (i.e. in fallen leaves) has been removed. To sustain the use of highly effective synthetic fungicides, such as the DMIs, fungicide resistance management practices have to be evaluated. Fungicide resistance, which negatively affects pathogen fitness, is hypothetically reversible, if the selection pressure by the fungicide is removed. This study quantified the effect of leaf shredding on changes in the pathogen’s flusilazole sensitivity and population genetic structure using SSR markers. Venturia inaequalis populations in orchard trials, where sanitation practices had been applied, were tested for flusilazole sensitivity in planta and in vitro. Significant shifts towards flusilazole resistance were identified in orchards with a history of DMI application without sanitation treatment, with a mean sensitivity of EC50= 0.208 ug/ml (n=49) compared to an unexposed V. inaequalis population (EC50= 0.104 ug/ml, n=55). However, the isolates from the same sanitation trial orchards, from leaf shredding treatment in combination with a fungicide spray programme, had a mean EC50 of 0.110 ug/ml (n=41), similar to an unexposed V. inaequalis population. Furthermore, V. inaequalis offspring after sanitation treatment, showed shifts in microsatellite allele frequency distribution patterns used as an indicator of sexual reproduction. This study concludes that sanitation treatments, i.e. leaf shredding, impact on fungicide sensitivity and therefore effectively contributes to fungicide resistance management.

Sensitivity of Clarireedia spp. to benzimidazoles and dimethyl inhibitors fungicides and efficacy of biofungicides on dollar spot of warm season turfgrass.

Dollar spot caused by Clarireedia spp. (formerly Sclerotinia homoeocarpa) is an economically destructive fungal disease of turfgrass that can significantly compromise turf quality, playability, and aesthetic value. Fungicides are frequently used to manage the disease but are costly and potentially unfavorable to the environment. Repeated use of some active ingredients has resulted in reduced efficacy on C. jacksonii causing dollar spot in cool-season turfgrasses in the US. Experiments were conducted to study fungicide sensitivity of Clarireedia spp. as well as to develop alternatives to fungicides against dollar spot on warm-season turfgrass in Georgia. First, 79 isolates of Clarireedia spp. collected across the state were tested on fungicide-amended agar plates for their sensitivity to thiophanate-methyl (benzimidazole) and propiconazole (dimethyl inhibitor). Seventy-seven isolates (97.5%) were sensitive (0.001 to 0.654 μg/mL) and two isolates (2.5%) were found resistant (>1000 μg/mL) to thiophanate-methyl. However, in the case of propiconazole, 27 isolates (34.2%) were sensitive (0.005 to 0.098 μg/mL) while 52 isolates (65.8%) were resistant (0.101 to 3.820 μg/mL). Next, the efficacy of three bio- and six synthetic fungicides and ten different combinations were tested in vitro against C. monteithiana. Seven bio- and synthetic fungicide spray programs comprising Bacillus subtilis QST713 and propiconazole were further tested, either alone or in a tank mix in a reduced rate, on dollar spot infected bermudagrass 'TifTuf' in growth chamber and field environments. These fungicides were selected as they were found to significantly reduce pathogen growth up to 100% on in vitro assays. The most effective spray program in growth chamber assays was 100% B. subtilis QST713 in rotation with 75% B. subtilis QST713 + 25% propiconazole tank mix applied every 14 days. However, the stand-alone application of the biofungicide B. subtilis QST713 every seven days was an effective alternative and equally efficacious as propiconazole, suppressing dollar spot severity and AUDPC up to 75%, while resulting in acceptable turf quality (>7.0) in field experiments. Our study suggests that increased resistance of Clarireedia spp. to benzimidazoles and dimethyl inhibitors warrants continuous surveillance and that biofungicides hold promise to complement synthetic fungicides in an efficacious and environmentally friendly disease management program.

Duration of fungicide spray program for the control of citrus black spot in sweet orange based on cultivar maturation and orchard age

Citrus black spot (CBS) damage and Phyllosticta citricarpa inoculum tend to increase in old orchards and in late-maturing cultivars of sweet orange. However, CBS control in São Paulo citrus belt is based on standard fungicide program of 180–220 days of fruit protection, regardless of cultivar and orchard age. This study aimed to investigate whether the protection period may be adjusted based on the cultivar maturation and age of orchards intended for juice processing. The efficacy of protection periods of 60, 100, 140, 180, 220 and 260 days was determined by assessing CBS incidence and severity and CBS-related fruit drop in 12 orchards over two seasons. The standard protection period, with 180 days targeted for mid-age and 220 days for old orchards, was the most cost effective for mid-season and late-maturing cultivars. These protection periods resulted in a significant reduction in CBS severity and fruit drop by up to ∼95% and ∼50%, respectively. For early-maturing cultivars, the duration of CBS spray program may be drastically reduced to 60 days for mid-age orchards and to 100 days for old orchards. These protection periods significantly reduced CBS severity and fruit drop by up to ∼92% and ∼50%, respectively. These adjustments in CBS fungicide protection period based on cultivar and orchard age may save up to US$14.3 million per season if adopted throughout the main Brazilian citrus belt. The results of this study allow citrus growers to save inputs, reduce costs, improve the operational efficiency within the farm and contribute to a more sustainable citrus industry.

Using Inpyrfluxam to Control Peanut (Arachis hypogaea L.) Foliar and Soil-Borne Diseases

Aims: To determine peanut disease control and yield response to inpyrfluxam applied at various timings during the growing season.
 Study Design: Randomized complete block design with 4 reps.
 Place and Duration of Study: Field studies were conducted from 2016 through 2020 in the south Texas peanut growing region near Yoakum (29.276o N, 97.123o W).
 Methodology: Fungicides were applied with a CO2-propellant sprayer. The spray boom was equipped with three D2-23 hollow-cone spray nozzles per row with the middle nozzle centered over each plant in the row and another nozzle located as such to spray on each side of the plant to provide thorough coverage with a spray volume was 187 L ha-1. Some studies included a non-treated control while other studies included chlorothalonil only at 1.26 kg ha-1 as the comparison treatment. Each plot consisted of four rows spaced 97 cm apart and 7.9 m long.
 Results: Inpyrfluxam applied twice in a 4 to 5 fungicide spray program in combination with chlorothalonil provided early leaf spot control as good as or better than the standards of chlorothalonil plus either azoxystrobin alone or azoxystrobin plus benzovindiflupyr applied 2 times. Control of Rhizoctonia pod rot, caused by Rhizoctonia solani Kuhn, with inpyrfluxam at 0.04, 0.05. 0.075, or 0.1 kg ai ha-1 applied 2 times during the growing season was comparable to two applications of azoxystrobin at 0.22 kg ai ha-1. Control of southern blight, caused by Sclerotium rolfsii Sacc., with one to two applications of inpyrfluxam at 0.05 to 0.1 kg ha-1 was comparable to azoxystrobin plus benzovindiflupyr. Peanut yield response was influenced by the level of soilborne and foliar disease control exhibited with each fungicide program, as those programs which provided the best control also produced the highest yield.
 Conclusion: These studies show the ability of inpyrfluxam to provide control of multiple diseases found in southwest peanut production.

The Influence of Chitin- and Chitosan-Based Soil Amendments on Pathogen Severity of Apple and Pear Scab

Apple and pear scab are foliar pathogens of apple and pear trees. Unmanaged, yield and aesthetic losses can be severe. The risk of resistance associated with over-reliance on fungicides means novel pathogen management methods and products are increasingly required. Chitin and chitosan are widely recognised as induced resistance (IR) agents that trigger plant defence responses that in turn enhance plant resilience to pathogen ingress. A container and field trial was conducted using apple (Malus sylvestris) and pear (Pyrus communis ‘Conference’) respectively to assess the efficacy of a range of liquid and granular chitin/chitosan-based IR agents and fertilisers against apple and pear scab. A synthetic fungicide (penconazole) spray program used within the UK for apple and pear scab control was included for comparison. Application of chitin/chitosan IR agents at concentrations above 1% caused phytotoxicity. Limited efficacy as scab protectants was also demonstrated when chitin/chitosan IR agents were applied at concentrations of 0.25%. However, chitin IR agents when applied at 0.5% and 1% and chitosan IR agents at 1% demonstrated efficacy as scab protectants and resulted in an increased leaf chlorophyll content, increased fruit yield, and reduced leaf scab severity when compared against the watered control. Only one of three chitin/chitosan fertilisers evaluated demonstrated efficacy as scab protectants (liquid chitosan). A synthetic fungicide penconazole spray program provided the greatest protection against apple and pear scab in the container trials. However, under field conditions the degree of scab control following application of chitin and chitosan at 1% and the chitosan containing fertiliser liquid chitosan was statistically comparable to fungicide treated trees. Results suggest application of an appropriate chitin/chitosan IR agent(s) and fertiliser offers a useful addition to existing methods of apple and pear scab management under field and container conditions.

The Blueberry Fruit Mycobiome Varies by Tissue Type and Fungicide Treatment

The microbial ecology of agricultural products may provide crucial insights into the management of postharvest fruit rots. To investigate postharvest microbial communities of highbush blueberry ( Vaccinium corymbosum), five fungicide spray programs were evaluated for their influence on the mycobiome of fruit skin and within the fruit pulp. The mycobiome was characterized by sequencing amplicons of the internal transcribed spacer 1 (ITS1) region with primers ITS1f and ITS4 with the Illumina MiSeq 300bp v3 system. Two of the five programs utilized commercial biological fungicides, two utilized azoxystrobin, and one utilized a series of treatments to simulate a realistic disease management program. Fungicide applications reduced diversity of the fruit skin mycobiome ( R2 = 0.409, P = 0.0001) and had a moderate impact on the pulp mycobiome ( R2 = 0.233, P = 0.0001). The mycobiome of the fruit pulp was also more variable than the skin mycobiome. In comparison with the untreated controls, each fungicide treatment program had a strongly significant effect on the β diversity of the blueberry fruit skin mycobiome ( R2 = 0.53 to 0.73, P = 0.0001). In the pulp, three of the five treatments had moderate but significant effects on β diversity in comparison with the control ( R2 = 0.10 to 0.18, P = 0.0005 to 0.017). Most samples indicated that fungi belonging to genera Epicoccum, Papiliotrema, and Sporobolomyces were widely prevalent and abundant across treatments and tissues. Fruit pathogen Botrytis cinerea was particularly abundant in the pulp of three of the fungicide treatments. Results from this study provide a baseline for future exploration of postharvest rot pathology and provide a community context on how fungicides may alter fungal communities in agricultural systems.

Efficacy of cuprous oxide for control of dothistroma needle blight in Pinus radiata plantations in Australia

ABSTRACT Dothistroma needle blight (DNB, Dothistroma septosporum) is a significant disease in Pinus radiata plantations on the Northern Tablelands of New South Wales and in the Murray Valley region of Victoria/New South Wales, Australia. Aerial application of copper oxychloride has been used to control DNB in these regions since soon after it was established. Research in New Zealand, however, has identified cuprous oxide as a more efficient and cheaper fungicide for controlling DNB. In this study, we test the efficacy of a single (applied in late October–early November) and double (October and February) application of cuprous oxide for controlling severe (50%) DNB in P. radiata plantations on the Northern Tablelands. We established replicated blocks 5–10 ha in size to ensure the results were operationally valid. Disease severity and defoliation were assessed on individual trees pre- and post-treatment, and aerial surveys were conducted to gauge the effect of treatments on the subsequent operational fungicide spray program. Cuprous oxide application significantly (P 0.01) reduced disease severity compared with no application, with a second application reducing severity even further. Ten months post-treatment, tree-level disease severity was 39% in unsprayed plots, 31% in single-sprayed plots and 8.5% in double-sprayed plots. The double application effectively reduced disease to negligible levels, while the single application provided adequate control for up to three months. At an operational level, even the single fungicide application reduced disease severity at the block scale when mapped during aerial surveys. Based on aerial assessments that trigger control action, all unsprayed plots required fungicide application in the season after the study (2013), while only two of seven single-sprayed blocks and none of the double-sprayed blocks required additional control. Extrapolating from this, a single fungicide application meant that 70% of the area did not require a fungicide application in the subsequent year. Based on these results and evidence from New Zealand, we recommend that cuprous oxide replace copper oxychloride for DNB control in Australia and that a double application is used in areas with severe (50%) levels of the disease.

Coffee Leaf Rust (Hemileia vastatrix) in Kenya—A Review

Coffee is one of the most important cash crops and beverages in the world. Production of coffee is limited by many factors, which include insect pests and diseases, among others. One of the most devastating coffee diseases in many coffee-producing countries is Coffee Leaf Rust caused by the fungus Hemileia vastatrix. Kenya is a coffee-producing country and has conducted studies to understand and manage the disease. Management strategies for the disease include the development and use of fungicide spray programs, cultural control practices, breeding resistant coffee varieties, and biological control agents. This paper reviews the status of the disease and management options applied in Kenya.

Factors affecting boxwood blight spread under landscape conditions

Abstract We investigated the spread of boxwood blight in a simulated landscape under conducive natural conditions from 2017 to 2019. We used strict sanitation to greatly reduce or eliminate spread by contact. Movement of the pathogen from an infected source plant was limited to one plant, likely spread by means of water splash. Plants were mulched with composted hardwood chips and mulching likely was primarily responsible for limiting spread to only the adjacent plant. Boxwood (Buxus spp.) cultivar susceptibility and fungicide spray programs influenced the incidence of spread and severity of disease; in 2018 and 2019 the more susceptible cultivar had higher disease incidence and severity, respectively, than less susceptible cultivars. Fungicide application only caused a small reduction in disease incidence in 2018. We also demonstrated that spores in clumps could survive extended dry conditions, indicating the importance of sanitation procedures on reducing spread. This experiment demonstrates that boxwood blight can be controlled in a landscape by following best management practices including cultural, sanitation, host susceptibility and fungicide application tactics. Index words: epidemiology, fungicide management, Buxus, chemical disease management, mulch, resistance. Chemicals used in this study: chlorothalonil (Daconil WeatherStik 54.0% F), fludioxonil plus cyprodinil (Palladium 25% and 37.5% WDG), mancozeb (Manzate 80% WP), metconazole (Tourney 50% WDG), propiconazole (ProCon-Z 14.3 L), pyraclostrobin (Insignia 20 WG), pyraclostrobin plus fluxapyroxad (Orkestra Intrinsic 21.26 SC), tebuconazole (Torque 38.7 SC), thiophanate-methyl (Spectro90 50% WP). Species used in this study: boxwood (Buxus L.), boxwood blight (Calonectria pseudonaviculata (Crous, J.Z. Groenew. & C.F. Hill) L. Lombard, M. J. Wingf. & Crous.

Use of Ultraviolet Light to Suppress Powdery Mildew in Strawberry Fruit Production Fields.

We designed and deployed an apparatus to apply UV light for suppression of powdery mildew in open field production of strawberry. The unit was evaluated in a commercial production field for one season, and for two additional seasons in open field research plots at the University of Florida Gulf Coast Research and Education Center. The apparatus contained two 180-cm-long hemicylindrical arrays of twenty 55-W low-pressure discharge UV-C lamps (operated at 30 W; peak wavelength = 254 nm) backed by polished aluminum reflectors covering two adjacent beds of the strawberry planting. The lamp arrays were suspended within a steel carriage that was tractor-drawn through the planting at 2.3, 4.6, and 5.6 km h-1. Nighttime applications of UV-C at doses ranging from 65 to 170 J⋅m-2 either once or twice weekly provided suppression of foliar and fruit disease that was consistently equal to or better than that provided by a commercial calendar-based fungicide spray program.

Evaluation of Electrolysed Oxidizing Water for European Pear Rust Management on Pear (Pyrus cv. Conference)

Pear rust is a foliar pathogen of ornamental and fruiting pear trees. Unmanaged, yield and aesthetic losses can be severe. Over-reliance on synthetic fungicides means novel means of pathogen management are required. Field trials were conducted using pear (Pyrus cv. Conference) to assess the efficacy of electrolysed oxidizing water (EO water) as a rust protective compound. A synthetic fungicide (boscalid + pyraclostrobin) spray program used for pear rust management was included for comparison. Each treatment was applied 4 times prior to the visible appearance of rust (April through June, i.e., preventatively). Studies were conducted in 2017 and repeated in 2018. Efficacy of EO water as a rust protectant compound was confirmed (increased leaf chlorophyll content, reduced leaf rust incidence and severity). The degree of leaf rust severity protection conferred was not statistically different from a boscalid + pyraclostrobin spray program. Results suggest 4 spray applications of EO water provides a useful addition to existing methods of pear rust management under field conditions that may have applicability against other foliar pathogens.

Reducing Chlorothalonil Use in Fungicide Spray Programs for Powdery Mildew, Anthracnose, and Gummy Stem Blight in Melons.

Fungicides are applied to nearly 80% of U.S. melon acreage to manage the numerous foliar and fruit diseases that threaten yield. Chlorothalonil is the most widely used fungicide but has been associated with negative effects on human and bee health. We designed alternative fungicide programs to examine the impact of reducing chlorothalonil use (Bravo Weather Stik) on watermelon, cantaloupe, and honeydew melon in 2016, 2017, and 2018 in Maryland. Chlorothalonil was replaced in the tank mix of weekly sprays of targeted fungicides with either polyoxin D zinc salt (Oso) or an extract of Reynoutria sachalinensis (Regalia). Powdery mildew (PM; Podosphaera xanthii), gummy stem blight (GSB; Stagonosporopsis spp.), and anthracnose (Colletotrichum orbiculare) were the most prevalent diseases to occur in the 3 years. Replacing chlorothalonil with the biopesticides as the tank-mix component of the fungicide spray program was successful in reducing GSB and PM severity in cantaloupe, honeydew melon, and watermelon compared with the untreated control, with the exception of GSB in 2017 in cantaloupe, and similar to the program including chlorothalonil in all cases, except anthracnose in watermelon. Anthracnose disease severity was not significantly reduced compared with the untreated control when chlorothalonil was replaced with the biopesticides and yields were not improved over the chlorothalonil-alone treatment in any of the trials. Therefore, replacement of chlorothalonil may not fully address its loss as a fungicide resistance management tool but efficacy can be maintained when polyoxin D is alternated with R. sachalinensis as a tank mix with targeted fungicides to manage PM and GSB.

The Influence of Inducing Agents Applied by Soil Drenches on Disease Severity of Apple and Pear Scab

Apple and pear scab are foliar diseases of ornamental and fruiting apple and pear trees. Unmanaged, yield and aesthetic losses can be severe. Overreliance on synthetic fungicides means novel means of disease management are required. Field trials were conducted using apple (Malus cv. Crown Gold) and pear (Pyrus communis ‘Williams Bon Chrétien’) to assess the efficacy of a range of commercially available inducing resistance (IR) agents (harpin protein, potassium phosphite, salicylic acid derivative, and chitosan) as root drenches against both scab diseases. A synthetic fungicide (penconazole) spray program used within the UK for apple and pear scab control was included for comparison. Each IR agent was applied four times, (i) before the visible appearance of scab (April through June, i.e., preventatively) or (ii) after symptoms of scab were visibly observed (June through August, i.e., curatively). Limited efficacy as scab protectants was demonstrated when IR agents were applied curatively. Likewise, limited efficacy was recorded when IR agents were applied once or twice as a preventative measure. However, when IR agents were applied as root drenches greater or equal to three times, efficacy as scab protectants was confirmed (increased leaf chlorophyll content, increased fruit yield, reduced leaf and fruit scab severity). A synthetic fungicide penconazole spray program provided the greatest protection against apple and pear scab in all trials when sprayed preventatively rather than curatively. Results suggest application of at least three root drenches from April through June with an appropriate IR agent provides a useful addition to existing methods of apple and pear scab management under field conditions.

A Decision Support System Based on Degree-Days to Initiate Fungicide Spray Programs for Peach Powdery Mildew in Catalonia, Spain.

The incidence of peach powdery mildew (PPM) on fruit was monitored in commercial peach orchards to i) describe the disease progress in relation to several environmental parameters and ii) establish an operating threshold to initiate a fungicide spray program based on accumulated degree-day (ADD) data. A beta-regression model for disease incidence showed a substantial contribution of the random effects orchard and year, whereas relevant fixed effects corresponded to ADD, wetness duration, and ADD considering vapor pressure deficit and rain. When beta-regression models were fitted for each orchard and year considering only ADD, disease onset was observed at 242 ± 13 ADD and symptoms did not develop further after 484 ± 42 ADD. An operating threshold to initiate fungicide applications was established at 220 ADD, coinciding with a PPM incidence in fruit around 0.05. A validation was further conducted by comparing PPM incidence in i) a standard, calendar-based program, ii) a program with applications initiated at 220 ADD, and iii) a nontreated control. A statistically relevant reduction in disease incidence in fruit was obtained with both fungicide programs, from 0.244 recorded in the control to 0.073 with the 220-ADD alert program, and 0.049 with the standard program. The 220-ADD alert program resulted in 33% reduction in fungicide applications.