Fungicide Programs Research Articles

Efficacy of Natamycin Against Gray Mold of Stored Mandarin Fruit Caused by Isolates of Botrytis cinerea With Multiple Fungicide Resistance.

Gray mold caused by Botrytis cinerea is an emerging postharvest disease of mandarin fruit in California. Management of postharvest diseases of mandarins relies on postharvest fungicides; however, multiple resistance to fungicides of different modes of action is common in B. cinerea populations from mandarin, leading to their failure to control decay. Natamycin is commonly used in the food industry as an additive, and it has been registered as a biofungicide for postharvest use on citrus and some other fruits. Sensitivity to natamycin of 64 isolates of B. cinerea from decayed mandarin fruit with known resistance phenotypes to other citrus postharvest fungicides (azoxystrobin, fludioxonil, pyrimethanil, and thiabendazole) was tested. Effective concentrations of natamycin to cause a 50% reduction relative to the control for conidial germination were from 0.324 to 0.567 µg/ml (mean of 0.444 µg/ml), and those for mycelial growth were 1.021 to 2.007 µg/ml (mean of 1.578 µg/ml). Minimum inhibitory concentrations where no fungal growth was present were 0.7 to 1.0 µg/ml for conidial germination and 5.0 to 10.0 µg/ml for mycelial growth. No cross-resistance between natamycin and other citrus postharvest fungicides was detected. Decay control efficacy tests with natamycin were conducted on mandarin fruit inoculated with B. cinerea isolates exhibiting five different fungicide resistance phenotypes, and natamycin significantly reduced incidence and lesion size of gray mold on fruit, regardless of fungicide resistance phenotypes. Natamycin has the potential to be an effective tool for integration into postharvest fungicide programs to control gray mold and manage B. cinerea isolates resistant to fungicides with other modes of action.

Corroboration That Highly Resistant Impatiens Cultivars Are Not Immune to Downy Mildew Disease: A Report of Crop Losses from Two California Producers

Two new series of Impatiens walleriana (impatiens) cultivars, Beacon and Imara XDR, were released to commercial growers in the United States in 2019 to 2020. Field trials show these new cultivar series are highly resistant to impatiens downy mildew (IDM). However, neither of these two impatiens series are completely immune to the disease, and preventive fungicide programs are still recommended for use throughout production to maintain plant health. Here we report two destructive outbreaks of IDM from Imara XDR in two commercial production facilities in California, one in 2019 and one in 2020. The disease outbreaks were caused by a known rDNA genotype of Plasmopara destructor (synonym = P. obducens). Modified Koch’s postulates showed that the pathogen could infect and cause disease in both Beacon and Imara XDR plants. Mefenoxam applied by both growers may have been ineffective due to resistance in P. destructor populations, which has been demonstrated on several previous occasions. Given these findings, fungicide programs intended to supplement genetic resistance should not be overly reliant upon application of mefenoxam and should utilize effective materials from different mode of action groups, in rotation. Fungicides to supplement genetic resistance are particularly appropriate in frost-free areas or in any circumstances that provide a potential inoculum source.

Evaluation of Improved Valencia Peanut Varieties for Production in Haiti

ABSTRACT Late leaf spot (Cercosporidium personatum) and peanut rust (Puccinia arachidis) are the most important diseases of peanut (Arachis hypogaea L.) in Haiti. Traditional Haitian peanut varieties are not only susceptible to these diseases but are also typically grown without benefit of a fungicide program. Five trials were conducted from 2015 to 2017 to evaluate the performance of six Valencia varieties in Quartier-Morin, Haiti (with an additional trial in 2017 at the Central Plateau) with respect to yield, resistance to rust and leaf spot diseases, and response to a fungicide program. A split-plot design with four or six replications was used in these studies. In each, “variety” was the whole plot and presence or absence of a fungicide program was the subplot. Valencia market types 309 Red, 309 Tan, M2, M3, SGV0801 and a local landrace were compared with and without Muscle ADV (tebuconazole + chlorothalonil, Sipcam) (2.3 L/ha) applied at 45, 60 and 75 days after planting (DAP). Final disease ratings (late leaf spot and peanut rust) were assessed approximately 94 DAP and plots were harvested the day following. In all trials, 309 Tan variety had the least amount of leaf spot and rust, but resulted in the lowest yield in four out of five trials, averaging 1727 kg/ha across fungicide treatments. M3, M2 and 309 Red were generally the numerically highest-yielding varieties, averaging 2906, 2864 and 2541 kg/ha across fungicide treatments, respectively, but were not statistically higher than the local Haitian Valencia, averaging 2374 kg/ha. Three fungicide applications during the season significantly increased yields in most trials for all varieties except 309 Tan. The highest and lowest average increase in yield from fungicide was for 309 Red (1126 kg/ha) and 309 Tan (103 kg/ha), respectively. The results from this study conducted over 2 years and 4 seasons document that while resistance to late leaf spot and rust is available in Valencia varieties, yield potential is not directly associated with that resistance. Also, use of fungicide improves yield potential in more susceptible varieties.

Efficacy of Biological and Conventional Fungicide Programs for Foliar Disease Management on Pomegranate (Punica granatum) in Florida

Pomegranate (Punica granatum L.) is an emerging alternative perennial crop in the southeastern United States. However, foliar diseases are present across this production area, causing almost 100% premature defoliation. A series of fungicide efficacy trials were conducted to evaluate biological, systemic, and contact fungicides at two locations in Florida, Plant City (cv. Angel Red) and Parrish (cvs. Christina, Azadi, Vikusnyi, Alsirinnar, Sakerdze, and Wonderful), for foliar disease management. Based on AUDPC, the fungicides Captan 80 WDG (captan, 78.2%), Penncozeb 75DF (mancozeb, 75%), Merivon (pyraclostrobin, 21.3% + fluxapyroxad, 21.3%), and Topsin 4.5 FL (thiophanate methyl, 45%) significantly reduced the percentage of foliar disease severity compared with biologicals consisting of Serenade OPTI and Tenet WP (Plant City) and the nontreated control (Plant City and Parrish cv. Wonderful). All treatments applied in a rotational program three times at bloom significantly reduced disease severity compared with the nontreated control in both locations. Rotational programs applied throughout the season also reduced disease severity compared with nontreated controls and repeated applications of neem oil. Foliar disease management is critical for long-term establishment of pomegranate as a viable economic crop in the southeastern United States.

Multiyear Regional Evaluation of Foliar Fungicide Applications for Cotton Target Spot Management in the Southeastern United States.

Fungicide programs for managing target spot of cotton caused by Corynespora cassiicola were evaluated over 15 site-years in the southeastern United States between 2014 and 2016. Two cultivars, hypothesized to vary in target spot susceptibility, PhytoGen 499WRF (PHY499) and Deltapine 1137B2RF (DPL1137), and four fungicides (azoxystrobin, flutriafol, pyraclostrobin, pyraclostrobin + fluxapyroxad) plus nontreated control, were compared. Fungicide programs consisted of 1) a single application at first flower or disease onset and 2) the first application followed by a second 14 days later. Treatments were applied in a factorial, randomized complete block design. Target spot onset and severity varied among site-years. Except when severity was low, target spot-associated defoliation was greater on PHY499 than on DP1137. Fungicides delayed disease development and defoliation, but application number had little impact. Based on a meta-analysis of 15 site-years, pyraclostrobin-based applications resulted in a 4 to 6% yield preservation, and yield preservation was greater at site-years with early disease onset and >40% target spot associated defoliation. Results suggest a single well-timed application of a pyraclostrobin-based fungicide reduces defoliation and protects cotton yield at locations with high target spot severity. Additional research is needed to identify risk factors for target spot-associated yield losses in cotton production systems.

Discontinuance of tebuconazole in the field restores sensitivity of Monilinia fructicola in stone fruit orchards

Demethylation inhibitor (DMI) fungicides are used to control brown rot in stone fruit worldwide. However, their specific mode of action can select resistant isolates of Monilinia fructicola. Monilinia fructicola resistant to DMI fungicides are associated with a fitness cost in the absence of selective pressure, indicating that the sensitive population can be re‐established when discontinuing the fungicide in the field. This work aimed to build up the sensitive population of M. fructicola after discontinuing the use of tebuconazole for successive crop seasons. The sensitivity of M. fructicola to tebuconazole was assessed in four commercial peach orchards in Paraná and São Paulo States from 2012/13 to 2015/16. Different fungicide programmes were used and DMI fungicides were discontinued from 2013/14. The sensitivity of M. fructicola to tebuconazole was assessed by a mycelial growth assay in vitro and by determining the frequency of the G461S mutation in the MfCYP51 gene. The isolates from Paraná had high sensitivity to the fungicide across all seasons and the frequency of the G461S mutation remained below 5%. The isolates from São Paulo were highly resistant in the 2012/13 season; however, there was a gradual decline until 2015/16. In addition, the G461S mutation frequency in Sao Paulo State was about 80% in the 2012/13 season, but reduced until it was completely undetectable in 2015/16. These results provide evidence that resistance can be managed in orchards with high selective pressure to tebuconazole after discontinuing the use of the fungicide for at least 3 years.

Relating Peanut Rx Risk Factors to Epidemics of Early and Late Leaf Spot of Peanut.

Previous research has demonstrated the efficacy of prescription fungicide programs, based upon Peanut Rx, to reduce combined effects of early leaf spot (ELS), caused by Passalora arachidicola (Cercospora arachidicola), and late leaf spot (LLS), caused by Nothopassalora personata (syn. Cercosporidium personatum), but the potential of Peanut Rx to predict each disease has never been formally evaluated. From 2010 to 2016, non-fungicide-treated peanut plots in Georgia and Florida were sampled to monitor the development of ELS and LLS. This resulted in 168 cases (unique combinations of Peanut Rx risk factors) with associated total leaf spot risk points ranging from 40 to 100. Defoliation ranged from 13.9 to 100%, and increased significantly with increasing total risk points (conditional R2 = 0.56; P < 0.001). Leaf spot onset (time in days after planting [DAP] when either leaf spot reached 1% lesion incidence), ELS onset, and LLS onset ranged from 29 to 140, 29 to 142, and 50 to 143 DAP, respectively, and decreased significantly with increasing risk points. Standardized AUDPC of ELS was significantly affected by risk points (conditional R2 = 0.53, P < 0.001), but not for LLS. After removing redundant Peanut Rx factors, planting date, rotation, historical leaf spot prevalence, cultivar, and field history were used as fixed effects in mixed effect regression models to evaluate their contribution to leaf spot, ELS or LLS prediction. Results from mixed effects regression confirmed that the selected Peanut Rx risk factors contributed to the variability of at least one measurement of development of combined or separate epidemics of ELS and LLS, but not all factors affected ELS and LLS equally. Historical leaf spot prevalence, a new potential preplant risk factor, was a consistent predictor of the dominant disease(s) observed in the field. Results presented here demonstrate that Peanut Rx is a very effective tool for predicting leaf spot onset regardless of which leaf spot is predominant, but also suggest that associated risk does not reflect the same development for each disease. These data will be useful for refining thresholds for differentiating high, moderate, and low risk fields, and reevaluating the timing of fungicide applications in reduced input programs with respect to disease onset.

Quantifying Control Efficacy of Fungicides Commonly Applied for Potato Early Blight Management

Early blight is an economically important foliar disease of potato in the United States. Because of the lack of resistant potato cultivars, fungicides are applied extensively to obtain adequate control. To manage early blight, standard protectant fungicides and single-site mode-of-action "specialty" fungicides are applied either alone or incorporated into a fungicide rotation program. Control efficacy at two crop growth stages (tuber initiation/early bulking and late bulking/tuber maturation) and the overall tuber yield response to standard and specialty fungicides were assessed using network metaanalytic models. Control efficacy of fungicides ranged from moderate to very high (>30 to 75%) compared with the nontreated control. For both potato growth stages, specialty fungicides performed better than standard protectant fungicides. Furthermore, control efficacy of both fungicides was higher (3 to 9%) at late bulking and tuber maturation when compared with early bulking crop growth stage. Specialty fungicide programs increased overall tuber yields by 4 and 9% over standard fungicides and nontreated control, respectively. Based on the results, more precise fungicide use recommendations and fungicide programs can be developed for early blight management.

Disease and Yield Response of a Stem-rot-resistant and -Susceptible Peanut Cultivar under Varying Fungicide Inputs.

Peanut (Arachis hypogaea L.) producers rely on costly fungicide programs to manage stem rot, caused by Sclerotium rolfsii. Planting disease-resistant cultivars could increase profits by allowing for the deployment of less-expensive, lower-input fungicide programs. Field experiments were conducted to characterize stem rot and early and late leaf spot (caused by Passalora arachidicola and Nothopassalora personata, respectively), yield, and overall profitability of cultivars Georgia-06G (stem-rot-susceptible) and Georgia-12Y (stem-rot-resistant) as influenced by seven commercial fungicide programs. Stem rot incidence was consistently lower on Georgia-12Y for all fungicides when compared with Georgia-06G and was lowest for both cultivars in plots treated with prothioconazole plus a tank mixture of penthiopyrad and tebuconazole. Leaf spot severity was similar for both the resistant and susceptible cultivars, and the greatest reduction occurred in plots treated with prothioconazole plus a tank mixture of penthiopyrad and tebuconazole. Fungicide programs gave similar yield and net return on Georgia-12Y; however, plots of Georgia-06G treated with prothioconazole plus a tank mixture of penthiopyrad and tebuconazole had the greatest yield and net return. Yields and economic return from the highest level of fungicide inputs on Georgia-06G were numerically less than those of Georgia-12Y treated with only chlorothalonil. These results show the value of fungicides in peanut disease management with susceptible cultivars, as well as the benefits of planting stem-rot-resistant cultivars in high-risk situations.

Within-season changes in Alternaria solani populations in potato in response to fungicide application strategies

Early blight, caused by the fungus Alternaria solani, is a common foliar disease in potato. Quinone outside inhibitor (QoIs) fungicides have commonly been used against A. solani. To avoid or delay development of fungicide resistance it is recommended to alternate or combine fungicides with different modes of action. Therefore, we compared two different fungicide programs against early blight in field trials and studied within season changes in the pathogen population. An untreated control was compared with treatments using azoxystrobin alone and with a program involving difenoconazole followed by boscalid and pyraclostrobin combined. Isolates of A. solani were collected during the growing season and changes in the population structure was investigated. We also screened for the amino acid substitution in the cytochrome b gene and investigated changes in sensitivity to azoxystrobin. Treatment with azoxystrobin alone did not improve disease control in 2014 when the disease pressure was high. However, lower severity of the disease was observed after combined use of difenoconazole, boscalid and pyraclostrobin. The efficacy of both fungicide treatments were similar during the field trial in 2017. Two mitochondrial genotypes (GI and GII) were found among isolates, where all isolates, except two, were GII. All GII isolates had the F129 L substitution while the two GI isolates were wild type. Population structure analysis and principal component analysis (PCA) of amplified fragment length polymorphisms (AFLP) data revealed within season changes in the A. solani populations in response to fungicide application. Isolates with the F129 L substitution had reduced sensitivity to azoxystrobin in vitro and their sensitivity tended to decrease with time.

First report of leaf spot on Cucurbita pepo caused by Fusarium incarnatum‐equiseti species complex in Jamaica

Cucurbita pepo is the most economically important species in the genus Cucurbita (Cucurbitaceae) and is grown worldwide. Yellow-orange-fleshed varieties, known as curry pumpkin, are produced in Jamaica, and in particular the variety Bodles Globe is grown for export. Since 2012, chlorotic or necrotic leaf spot symptoms (Fig. 1) have been observed on about 60% of farms in the major production areas (Clarendon, Portland, St. Ann, St. Catherine, St. Elizabeth and St. Mary). To determine the causal agent, 70 leaves of diseased pumpkin (cv. Bodles Globe) were collected from fields across the six major production areas. Leaves were surface-sterilised with sodium hypochlorite solution (0.5%), rinsed in sterile water and 1-cm segments cultured on potato dextrose agar (PDA) at 25°C for one week. A fungus with pink mycelium was consistently isolated and hyphal tips were transferred to fresh PDA plates to obtain pure cultures. The resulting cultures had dense, pink mycelium with elongate, crescent shaped macroconidia measuring 32 times 12 μm. Total genomic DNA was subsequently extracted from seven-day-old cultures (Cenis, 2) and ITS1/ITS4 primers (White et al., 5) were used in PCR amplification and sequencing of the rDNA internal transcribed spacer (ITS) region. The resulting sequences of two representative isolates (GenBank Accession Nos. KM580656 and KM580657) were identical to Fusarium incarnatum-equiseti species complex (FIESC) sequences (NRRL43297 and NRRL13379) present in the FUSARIUM-ID database (Gieger et al., 3). The pathogen was therefore identified as FIESC based on the culture morphology and DNA sequence analysis. To confirm pathogenicity, ten three-week-old C. pepo (cv. Bodles Globe) plants were inoculated through either a foliar spray (12.5 ml) or root-dip with spore suspensions (15 ml) that were harvested from 21-day-old cultures at concentrations of 10 conidia/ml and 105 conidia/ml respectively. Ten surface-sterilised fruits were also inoculated by wounding with a scalpel and applying 1012 conidia/ml (2 ml). Control plants and fruits were mock inoculated with sterile distilled water. All plants were covered with polyethylene bags for five days. Fruit was placed in a humidity chamber for 27 days at 22°C at 95% relative humidity. After 14 days, 13 to 33% of the root-dip inoculated plants exhibited veinal chlorosis and chlorotic leaf spots. After 14 days, lesions were observed on 30% of the inoculated fruit and by 21 days, 80-100% of fruit showed fungal growth originating from the area of inoculation which also appeared water-soaked. FIESC was consistently isolated from symptomatic leaves and fruit. Disease symptoms were not observed on spray-inoculated test plants nor the control plants and fruits and FIESC could not be isolated from this material. The experiments were repeated twice with consistent results each time. To our knowledge, this is the first confirmed report of a member of the FIESC on C. pepo in Jamaica. Recent reports describe FIESC infecting cucurbits in Asia, such as Cucumis trigonus in India (Mali et al., 4) and muskmelon (Cao et al., 1) in China. While appropriate fungicide programmes can give adequate control, disease management should rely on preventative methods, such as avoiding infested fields and applying seed treatments.

The Effect of Different Forms of Sulphur on Incidence of Apple Scab on Apple Tree (Malus x domestica Borkh) Gloster CV.

Abstract From 2014 to 2015 the influence of foliar application of sulphur on apple trees (Gloster cv.)was investigated in the apple orchard at the Research and Breeding Institute of Pomology in Holovousy (North-East Bohemia, Czech Republic). The experiment was based on foliar applications of fertilizers containing different forms of sulphur: elemental S0, sulphate SO4 2− and thiosulphate S2O3 2− (in combination with other macro- and microelements) and fungicides with or without sulphur: Kumulus (S0 + F) and the conventional fungicide programme (F), in the respective treatments. Apple scab incidence on leaves and fruits was investigated in each experimental year according to the relevant methodology of the OEPP/EPPO standard PP1/5(3) Venturia inaequalis. Data on the incidence of apple scab correlate with the process of pathogen life cycle and risk of infection on the given dates. The incidence of apple scab was the lowest in 2014 in treatment S0 + F (10.8 % on leaves, 2.8 % on fruits) and F (15.8 % on leaves, 6 % on fruits) where conventional fungicides were used. When compared with the other treatments these treatments were the most effective even if the incidence of scab in the individual treatments in 2015 increased by 28 to 60 % due to high infection pressure. The results confirmed the efficiency of the conventional fungicide programme (S0 + F and F) against apple scab incidence on fruits. What is more, the results were slightly better in the treatment, where the conventional fungicide programme was combined with fertilizer containing elemental S (S0 + F) in comparison with fungicides applied alone (F). The effect of the other forms of sulphur (SO4 and S2O3) on apple scab control has not been confirmed. According to the results, the application of the conventional fungicide programme (S0 + F and F) is more effective against scab incidence than the inorganic forms of sulphur alone.

Effect of inoculum density of Stromatinia cepivora on the amount of white rot reduced by Trichoderma species in garlic

BackgroundWhite rot, a garlic disease caused by the soil-borne fungus Stromatinia cepivora (Berk.) Whetzel, is a serious problem of garlic productions in Egypt. This study examines the potential of controlling the disease biologically by using three Trichoderma species, i.e., Trichoderma harzianum, Trichoderma koningii, and Trichoderma virens employed either alone or in combination.ResultsIn in vitro assays, three Trichoderma species, i.e., Trichoderma harzianum, Trichoderma koningii, and Trichoderma virens and tebuconazole, were compared for their ability to suppress S. cepivora isolate (Sc8). In greenhouse experiments, the chemical treatment was the most effective, with the lowest incidence of garlic white rot compared with the control. The antagonistic fungi tested either individually or in combination significantly reduced the incidence of white rot on garlic. In general, dual and triple combinations of the fungal isolates were more effective than these isolates used individually. The combination of the three Trichoderma species was the most effective treatment, decreasing disease incidence by 50.0% in 2016/2017 season and 40.0% in 2017/2018 season, respectively. The three Trichoderma species employed alone or in combinations and tebuconazole were evaluated under low and high disease pressures in field trials to determine which situation (s) provided the best control of garlic white rot. Under low (40 sclerotia/kg of soil) and high (600 sclerotia/kg of soil) inoculum density, the standard fungicide programme (dipping of garlic cloves in tebuconazole (1 ml of Folicur 25% l−1 of water) plus spraying garlic stem bases with the same concentration of tebuconazole) gave statistically significant disease control, decreasing disease incidence by 67.7 and 29.4% in 2016/2017 season and 72.6 and 31.1% in 2017/2018 season, respectively. Under low disease pressure, significant control, equal to the fungicide treatment, was achieved with the trip combination of three Trichoderma species. However, Trichoderma species employed alone gave insignificant control of garlic white rot under high disease pressure. The triple combination of three Trichoderma species decreasing disease incidence by 65.6 and 15.5% in 2016/2017 season and 74.2 and 18.6% during 2017/2018 season, under low and high inoculum density, respectively. The activities of defense enzymes, i.e., peroxidase, polyphenoloxidase, and chitinase due to application of Trichoderma species, were enhanced in garlic plants either grown under low or high disease pressures. Reduction of white rot disease incidence was accompanied by increased growth parameters and bulbs yield of garlic plants grown under field conditions.ConclusionsThese results indicated that the performance of three Trichoderma species may be influenced as much by the absolute disease pressure. It was concluded that, at the low disease pressure site, the low level of inoculum and disease incidence enabled three Trichoderma species to bring about disease control.

Meta-Analysis of the Effects of QoI and DMI Fungicide Combinations on Fusarium Head Blight and Deoxynivalenol in Wheat.

Field trials were conducted in 17 U.S. states to evaluate the effects of quinone outside inhibitor (QoI) and demethylation inhibitor (DMI) fungicide programs on Fusarium head blight index (IND) and deoxynivalenol (DON) toxin in wheat. Four DMI-only treatments applied at Feekes 10.5.1, five QoI-only treatments applied between Feekes 9 or Feekes 10.5, three QoI+DMI mixtures applied at Feekes 10.5, and three treatments consisting of a QoI at Feekes 9 followed by a DMI at Feekes 10.5.1 were evaluated. Network meta-analytical models were fitted to log-transformed mean IND and DON data and estimated contrasts of log means were used to obtain estimates of mean percent controls relative to the nontreated check as measures of efficacy. Results from the meta-analyses were also used to assess the risk of DON increase in future trials. DMI at Feekes 10.5.1 were the most effective programs against IND and DON and the least likely to increase DON in future trials. QoI-only programs increased mean DON over the nontreated checks and were the most likely to do so in future trials, particularly when applied at Feekes 10.5. The effects of QoI+DMI combinations depended on the active ingredients and whether the two were applied as a mixture at heading or sequentially. Following a Feekes 9 QoI application with a Feekes 10.5.1 application of a DMI reduced the negative effect of the QoI on DON but was not sufficient to achieve the efficacy of the Feekes 10.5.1 DMI-only treatments. Our results suggest that one must be prudent when using QoI treatments under moderate to high risk of FHB, particularly where the QoI is used without an effective DMI applied in combination or in sequence.

Adjusting Product Timing during the Powdery Mildew Critical Window to Improve Disease Management

Summary Goals: This project was designed to answer questions about the timing of different cultural (leaf removal) and chemical (fungicide rotation) disease management practices and how they influence the overall efficacy of a powdery mildew management program. Key Findings: The timing of specific chemical modes of action plays an important role in the overall efficacy of powdery mildew fungicide programs. In this study, programs in which the evaluated products were applied once during the critical window performed as well as programs in which the same products were applied twice (during the critical window and at bunch closure). This finding indicates that disease control depends on application of sprays during the critical window rather than later in the season. As expected, leaf removal significantly improved spray coverage in the fruit zone; however, this improved coverage did not last the entire season. Canopy refill, which occurred as summer laterals developed, reduced fruit-zone coverage later in the season. Leaf removal also did not result in any positive additive effects on overall disease control. Impact and Significance: These findings can be used to aid growers in the selection and rotation of products used for powdery mildew management programs to maximize the efficacy of disease control and minimize the risk of fungicide resistance. While early fruit zone leaf removal did not improve overall disease control in this high-pressure scenario, leaf removal resulted in improved spray coverage, which may enhance disease control when low-volume spray applications or contact-active chemistries are emphasized in a commercial program.

Evaluating the Profitability of Foliar Fungicide Programs in Mid-Atlantic Soft-Red Winter Wheat Production.

In mid-Atlantic soft-red winter wheat (SRWW) production, the standard timing for a fungicide application is between flag leaf emergence (Feekes growth stage [FGS] 8) and heading (FGS 10.5). However, two-pass and anthesis (FGS 10.5.1) applications are becoming common, although these programs have not been thoroughly evaluated for disease control, yield, and profitability. Experiments were conducted in the mid-Atlantic in 2015 and 2016 to evaluate fungicide programs with applications at FGS 8, FGS 10.5.1, and two-pass programs with an early application at green-up (FGS 5) followed by (FB) applications at either FGS 8 or FGS 10.5.1. Fungicide programs that included an application at FGS 10.5.1 resulted in the highest probability of no disease on the flag leaf (0.29 to 0.40). The estimated mean yield increases ( ) relative to the nontreated check ranged from 253.65 to 634.16 kg ha-1. Using a grain price of $0.18 kg-1 ($5 bushel-1), probabilities were similar between applications at FGS 8 (0.49 to 0.56) and FGS 10.5.1 (0.53). The probability of profitability ranged from 0.48 to 0.57 for FGS 5 FB FGS 8 applications and 0.52 to 0.59 for FGS 5 FB FGS 10.5.1 applications, indicating limited benefit to two-pass programs.

Resistance to Fluopicolide and Propamocarb and Baseline Sensitivity to Ethaboxam Among Isolates of Pseudoperonospora cubensis From the Eastern United States.

Chemical control is currently the most effective method for controlling cucurbit downy mildew (CDM) caused by Pseudoperonospora cubensis. Most commercial cucurbit cultivars, with the exception of a few new cucumber cultivars, lack adequate disease resistance. Fluopicolide and propamocarb were among the most effective fungicides against CDM in the United States between 2006 and 2009. Since then, reduced efficacy of these two fungicides under field conditions was reported starting around 2013 but occurrence of resistance to fluopicolide and propamocarb in field isolates of P. cubensis had not been established. Thirty-one isolates collected from cucurbits in the eastern United States were tested for their sensitivity to fluopicolide and propamocarb using a leaf disc assay. This same set of isolates and four additional isolates (i.e., 35 isolates) were also used to establish the baseline sensitivity of P. cubensis to ethaboxam, an ethylamino-thiazole-carboxamide fungicide, which was recently granted registration to control CDM in the United States. About 65% of the isolates tested were resistant to fluopicolide with at least one resistant isolate being present in samples collected from 12 of the 13 states in the eastern United States. About 74% of the isolates tested were sensitive to propamocarb with at least one resistant isolate being among samples collected from 8 of the 12 states in the study. The frequency of resistance to fluopicolide and propamocarb was high among isolates collected from cucumber, while the frequency was low among isolates collected from other cucurbit host types. All isolates tested were found to be sensitive to ethaboxam and EC50 values ranged from 0.18 to 3.08 mg a.i./liter with a median of 1.55 mg a.i./liter. The ratio of EC50 values for the least sensitive and the most sensitive isolate was 17.1, indicating that P. cubensis isolates were highly sensitive to ethaboxam. The most sensitive isolates to ethaboxam were collected from New York, North Carolina, and Ohio, while the least sensitive isolates were collected from Georgia, Michigan, and New Jersey. These results show that ethaboxam could be a viable addition to fungicide programs used to control CDM in the United States.

In-field assessment of an arabinoxylan polymer on disease control in spring barley

With the threat of certain plant protection products becoming ineffective due to reduced pathogen sensitivity to fungicides or through the removal of products due to changes in legislation, alternative compounds are sought for use in disease management programmes. The effects of an arabinoxylan film-forming polymer derived from maize cell walls to control crop diseases of spring barley was assessed in field experiments. Control of powdery mildew, Rhynchosporium scald, and Ramularia leaf spot on barley was achieved with the polymer but control was inconsistent between trials. However, good levels of disease control were observed when the polymer was applied with a reduced fungicide programme. No yield penalties were associated with use of the polymer in any trial irrespective of the level of disease control. Alternative plant protection products such as this arabinoxylan polymer may be useful components in future integrated disease management strategies aimed at reducing fungicide inputs without any cost to disease control.

Temporal dynamics and management of downy mildew on the table grape ‘BRS Vitória’ in northern Paraná

Downy mildew caused by Plasmopara viticola is a major disease of grapes in Paraná State, Brazil and other wine-producing regions. The seedless table grape ‘BRS Vitória’ stands out for its tolerance to this disease and is a viable alternative to reduce fungicide applications. The objectives of this study were to analyze the influence of weather-related factors, such as temperature and rainfall on disease progress and to evaluate the efficacy of fungicide spray programs for controlling downy mildew of grapes during the summer-fall and winter-spring crop seasons in northern Paraná, Brazil. Field trials were conducted in Marialva, Paraná, during the winter-spring crop seasons (August to December) in 2013 and 2014 and the summer-fall crop seasons (January to May) in 2014 and 2015. The experimental design used was completely randomized with repeated measurements over the phenological periods, with five treatments and 10 replicates. The following treatments were compared: (1) conventional, in which fungicides were applied according to conventional standards; (2) preventive fungicide sprays every seven days; (3) preventive fungicide sprays every 14 days; (4) fungicide sprays after observing the first downy mildew symptoms; and (5) no fungicide sprays. In the conventional fungicide program, sprays were performed two or three times per week. Treatments 2 and 3 received sprayings between the start of branch budding and fruit ripening. In treatment 4, sprays started from the first occurrence of oil spot symptoms, and then, the applications were spaced every seven days until fruit ripening. The severity of disease was evaluated weekly. The disease was severe only in the 2014 and 2015 summer-fall crop seasons, reaching a maximum severity of 17.3% and 21.3% of the leaf area, respectively. The highest disease severity in the summer-fall crop seasons was associated with higher frequencies of rainy days and higher temperatures. Disease severity in conventional treatments did not differ from severity in treatments with sprayings made every seven and 14 days during the summer-fall crops in both years. Severity index on bunches were not observed for the evaluated trials. The seedless grape ‘BRS Vitória’ is less dependent on the use of fungicides to control downy mildew in northern Paraná.

First Report of Rust Caused by Puccinia arachidis on Peanut in South Carolina

Puccinia arachidis Speg. (phylum Basidiomycota, class Pucciniomycetes) causes rust on peanut (Arachis hypogaea L.) and is a biotroph. In September 2016, several plants exhibiting numerous rust-colored pustules characteristic to peanut rust (Subrahmanyam 1997) on abaxial leaf sides were observed in two plots (12.19 × 12.67 m) at approximately 5% incidence of total leaflets (≈3% severity) in a localized area of approximately 2 × 2 m in a peanut field in Blackville, SC (Barnwell County) on the commercial variety ‘Georgia 12Y’. Also in September, identical symptoms were observed in a localized area of approximately 3 × 3 m (80% leaflet incidence, 40% severity) in a commercial field (≈40 hectares) of ‘Georgia 06G’ (industry-standard runner variety) in Orangeburg County, SC. Both locations were managed under reduced fungicide programs. The Barnwell County location received four applications of chlorothalonil alone as part of a separate disease study, whereas the Orangeburg County field received five chlorothalo...