Hop Powdery Mildew Research Articles

Identification and distribution of mating‐type idiomorphs in populations of Podosphaera macularis and development of chasmothecia of the fungus

Podosphaera macularis, the causal agent of hop powdery mildew, is known to produce chasmothecia (formerly cleistothecia) in eastern North America and Europe. Ascocarps have not yet been reported from the Pacific Northwestern region of North America. Reasons for the apparent absence of chasmothecia in the Pacific Northwest were unknown. This study established that P. macularis is heterothallic and ascocarp ontogeny, maturation, dehiscence and ascospore infection proceed similarly to other powdery mildew fungi. Genome sequencing of a MAT1‐1 isolate revealed the structure of the MAT1 locus and presence of MAT1‐1‐3, demonstrating further similarities to other powdery mildew fungi. PCR assays with primers designed from conserved domains of the MAT1 idiomorphs were developed to characterize the frequency of idiomorphs in populations of P. macularis. Amongst 317 samples of P. macularis collected during 2012 and 2013 from the Pacific Northwest only the MAT1‐1 idiomorph was found. In contrast, among 56 samples from the eastern United States and Europe, MAT1‐1 and MAT1‐2 idiomorphs were detected at equivalent frequencies. At temperatures representative of late season conditions in the Pacific Northwest, chasmothecia formed readily when a Pacific Northwest MAT1‐1 isolate was paired with a MAT1‐2 isolate collected from outside the region. Although these findings do not encompass all climatic, geographic or temporal barriers that could inhibit the formation of chasmothecia, the current absence of the ascigerious stage of P. macularis in the Pacific Northwest could be explained by the absence of the MAT1‐2 mating type idiomorph.

Characterization of Resistance to Powdery Mildew in the Hop Cultivars Newport and Comet

Hop powdery mildew, caused by Podosphaera macularis, is an important disease in the Pacific Northwest. Resistant cultivars of hop have been developed and have provided field immunity to the disease until virulent strains of P. macularis emerged. Due to the increase of powdery mildew on formerly resistant cultivars, studies were conducted to characterize potential sources of host resistance. Accepted for publication 5 February 2014. Published 27 March 2014.

Decision Aids for Multiple-Decision Disease Management as Affected by Weather Input Errors

Many disease management decision support systems (DSSs) rely, exclusively or in part, on weather inputs to calculate an indicator for disease hazard. Error in the weather inputs, typically due to forecasting, interpolation, or estimation from off-site sources, may affect model calculations and management decision recommendations. The extent to which errors in weather inputs affect the quality of the final management outcome depends on a number of aspects of the disease management context, including whether management consists of a single dichotomous decision, or of a multi-decision process extending over the cropping season(s). Decision aids for multi-decision disease management typically are based on simple or complex algorithms of weather data which may be accumulated over several days or weeks. It is difficult to quantify accuracy of multi-decision DSSs due to temporally overlapping disease events, existence of more than one solution to optimizing the outcome, opportunities to take later recourse to modify earlier decisions, and the ongoing, complex decision process in which the DSS is only one component. One approach to assessing importance of weather input errors is to conduct an error analysis in which the DSS outcome from high-quality weather data is compared with that from weather data with various levels of bias and/or variance from the original data. We illustrate this analytical approach for two types of DSS, an infection risk index for hop powdery mildew and a simulation model for grass stem rust. Further exploration of analysis methods is needed to address problems associated with assessing uncertainty in multi-decision DSSs.

QTL mapping of powdery mildew susceptibility in hop (Humulus lupulus L.)

Hop powdery mildew (Podosphaera mac- ularis (Wallr.) U. Braun & S. Takam.) is best controlled via the production of resistant varieties. Recent evidence supports selection against plant susceptibility genes to fungal pathogens as a more durable resistance mechanism than selection for resistance genes. The objective of this study was to identify molecular-based QTLs, their genetic effects and epistasis among QTLs associated with suscepti- bility to powdery mildew. Parents and offspring from the cross, 'Perle' 9 'USDA 19058M', were clonally replicated and inoculated in a greenhouse using a CRD experimental design in Corvallis, OR. DNA was extracted, purified and analyzed via three different marker systems. Analysis of the resulting markers was based upon the ''two-way pseudo- testcross'' procedure. QTL mapping using multiple interval mapping and Bayesian interval mapping analyses were performed using WinQTL Cartogra- pher 2.5_003. Comparison amongst mapping analy- ses identified three persistent QTLs on three linkage groups without significant epistatic effect upon expression. The persistent QTL on linkage group C7 had both additive and dominant effects control- ling phenotype expression. The presence or absence of the two AFLP markers bordering the QTL on C7 defined susceptibility in offspring. This is the first report in hop identifying molecular markers linked to QTLs associated with disease susceptibility.

Effect of Temperature on Sporulation and Infectivity of Podosphaera macularis on Humulus lupulus

Hop powdery mildew, caused by Podosphaera macularis, can result in complete crop loss and requires numerous fungicide applications for effective management. To assess the impact of temperature on the production of infective conidia, 10-day-old sporulating colonies were exposed to 18, 30, 33, 36, 39, and 42°C for 6 h, and then incubated at 18°C for 18 h. Conidia were harvested, inoculated onto hop plants, incubated at 18°C for 10 days, and then lesions/cm2 of leaf area was determined. Disease was significantly reduced at temperatures ≥30°C with a nonlinear response in the production of infective conidia (P < 0.0001). Temperature effects on sporulation of P. macularis were examined using a custom impaction conidia sampler in growth chambers programmed at constant temperatures of 5, 10, 15, 20, 25, 30, and 35°C, or 18°C before and after ramping to 18, 22, 26, 30, 34, and 38°C for 6 h. The effect of constant temperature on sporulation was best described by a nonlinear thermodynamic model (P = 0.0001) with maximal production near 25°C. Exposure to fluctuating temperatures produced a curvilinear response in sporulation (P = 0.0122) with maximum production near 25°C. These data indicate that inoculum availability is reduced when ambient temperature exceeds 30°C and that modeling inoculum availability could help further refine current disease forecasting models.

Effects of Powdery Mildew Fungicide Programs on Twospotted Spider Mite (Acari: Tetranychidae), Hop Aphid (Hemiptera: Aphididae), and Their Natural Enemies in Hop Yards

Twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and hop aphid, Phorodon humuli (Schrank) (Hemiptera: Aphididae), are the most important arthropod pests of hop (Humulus lupulus L.) in the Northern Hemisphere. A potential barrier for greater adoption of conservation biological control strategies for spider mites and hop aphid is the extensive use of fungicides for management of hop powdery mildew, Podosphaera macularis (Wallr.:Fr.) U. Braun & S. Takamatsu. Field studies conducted in experimental plots in Oregon and Washington in 2005 and 2006 quantified the effects of powdery mildew fungicide programs (i.e., sulfur, paraffinic oil, and synthetic fungicides) on arthropod pests and natural enemies on hop. Fungicide treatment significantly affected spider mite populations in all four studies. Multiple applications of sulfur fungicides applied before burr development resulted in 1.4-3.3-fold greater spider mite populations during summer. Near the cessation of the sulfur applications, or after a lag of 20-30 d, spider mite populations increased significantly faster on sulfur treated plants compared with water-treated plants in three of four experiments. The effect of paraffinic oil on spider mites was varied, leading to exacerbation of spider mites in Oregon and Washington in 2005, suppression of mites in Oregon in 2006, and no significant effect compared with water in Washington in 2006. Significant relative treatment effects for cone damage due to spider mite feeding were detected in Oregon in 2005 in plots treated with sulfur and paraffinic oil compared with water and synthetic fungicides. Mean populations of hop aphids were similar among treatments in Oregon, although sulfur treatment suppressed hop aphid populations in Washington in 2005 and 2006. Populations of individual predacious insect species and cumulative abundance of macropredators were not consistently suppressed or stimulated by treatments in all trials. However, predatory mite abundance in Washington was affected by fungicide treatments, with plots treated with sulfur consistently having 10-fold fewer phytoseiids per leaf compared with the other treatments. Based on the results of these studies, powdery mildew fungicide programs that minimize or eliminate applications of sulfur and paraffinic oil would tend to conserve predatory mites and minimize the severity of spider mite outbreaks. However, mechanisms other than direct or indirect toxicity to phytoseiid mites likely are associated with exacerbation of spider mite outbreaks on hop.

Spatial and Temporal Stability of the Estimated Parameters of the Binary Power Law

The incidence of hop powdery mildew on leaves, caused by Podosphaera macularis, collected from 1,606 transects in 77 commercial hop yards in Oregon and Washington over 9 years was used to assess variability in heterogeneity of disease and the estimated binary power law parameters. Spatial analyses of data sets were conducted at the level of individual rows (row level) and multiple rows within a yard (yard level). The binary power law provided a good fit to all data sets, with R(2) values ranging from 0.933 to 0.993. At the row level, the intercept parameter ln(A(x)) was >0 for 8 years, but was not significantly greater than 0 in 2006. The parameter b was greater than 1 for all row-level data sets collected from 1999 to 2005, but was <1 in 2006 and not significantly different from 1 in 2007. Covariance analysis indicated the factor 'region' affected ln(A(x)) in 3 years, and b in 2 years. 'Cultivar' had an effect on ln(A(x)) in 3 years and b in year. At the yard level, ln(A(x)) was greater than 0 for 6 years, but in 2006 and 2007, ln(A(x)) was not significantly different from 0. The slope parameter b was greater than 1 in 6 years, but was not significantly different from 1 in 2006 and 2007. Differences in b among years were large enough to have practical implications for sample sizes and precision of fixed and sequential sampling. Although the binary power law parameter tended to be relatively stable, variability of the estimated parameters may have practical consequences for sampling precision and costs.

A Decade of Hop Powdery Mildew in the Pacific Northwest

Hop powdery mildew, caused by the fungus Podosphaera macularis, was confirmed for the first time in hop yards in the United States Pacific Northwest in 1997. The US hop industry experienced significantly crop loss and damage from the disease, but new knowledge, grower experience, and management approaches have allowed the industry to survive the introduction of this damaging pathogen. This review provides an overview of research on and progress towards economically sustainable management of hop powdery mildew in the US, and future directions for research and further innovation. Accepted for publication 2 January 2008. Published 14 March 2008.

Sequential Sampling for Estimation and Classification of the Incidence of Hop Powdery Mildew I: Leaf Sampling.

Hop powdery mildew (caused by Podosphaera macularis) is an important disease of hops (Humulus lupulus) in the Pacific Northwest. Sequential sampling models for estimation and classification of the incidence of powdery mildew on leaves of hop were developed based on the beta-binomial distribution, using parameter estimates of the binary power law determined in previous studies. Stop lines, models that indicate that enough information has been collected to estimate disease incidence and cease sampling, for sequential estimation were validated by bootstrap simulations of a select group of 18 data sets (out of a total of 198 data sets) from the model-construction data, and through simulated sampling of 104 data sets collected independently (i.e., validation data sets). The achieved coefficient of variation (C) approached prespecified C values as the achieved disease incidence ( ) increased. Achieving a C of 0.1 was not possible for data sets in which < 0.10. The 95% confidence interval of the median difference between the true p and included zero for 16 of 18 data sets evaluated at C = 0.2 and all data sets when C = 0.1. For sequential classification, Monte-Carlo simulations were used to determine the probability of classifying mean disease incidence as less than a threshold incidence, pt (operating characteristic [OC]), and average sample number (ASN) curves for 16 combinations of candidate stop lines and error levels (α and β). Four pairs of stop lines were selected for further evaluation based on the results of the Monte-Carlo simulations. Bootstrap simulations of the 18 selected data sets indicated that the OC and ASN curves of the sequential sampling plans for each of the four sets of stop lines were similar to OC and ASN values determined by Monte Carlo simulation. Correct classification of disease incidence as being above or below preselected thresholds was 2.0 to 7.7% higher when stop lines were determined by the beta-binomial approximation than when stop lines were calculated using the binomial distribution. Correct decision rates differed depending on the location where sampling was initiated in the hop yard; however, in all instances were greater than 86% when stop lines were determined using the beta-binomial approximation. The sequential sampling plans evaluated in this study should allow for rapid and accurate estimation and classification of the incidence of hop leaves with powdery mildew, and aid in sampling for pest management decision making.

Sequential Sampling for Estimation and Classification of the Incidence of Hop Powdery Mildew II: Cone Sampling.

Sequential sampling models for estimation and classification of the incidence of powdery mildew (caused by Podosphaera macularis) on hop (Humulus lupulus) cones were developed using parameter estimates of the binary power law derived from the analysis of 221 transect data sets (model construction data set) collected from 41 hop yards sampled in Oregon and Washington from 2000 to 2005. Stop lines, models that determine when sufficient information has been collected to estimate mean disease incidence and stop sampling, for sequential estimation were validated by bootstrap simulation using a subset of 21 model construction data sets and simulated sampling of an additional 13 model construction data sets. Achieved coefficient of variation (C) approached the prespecified C as the estimated disease incidence, , increased, although achieving a C of 0.1 was not possible for data sets in which < 0.03 with the number of sampling units evaluated in this study. The 95% confidence interval of the median difference between of each yard (achieved by sequential sampling) and the true p of the original data set included 0 for all 21 data sets evaluated at levels of C of 0.1 and 0.2. For sequential classification, operating characteristic (OC) and average sample number (ASN) curves of the sequential sampling plans obtained by bootstrap analysis and simulated sampling were similar to the OC and ASN values determined by Monte Carlo simulation. Correct decisions of whether disease incidence was above or below prespecified thresholds (pt) were made for 84.6 or 100% of the data sets during simulated sampling when stop lines were determined assuming a binomial or beta-binomial distribution of disease incidence, respectively. However, the higher proportion of correct decisions obtained by assuming a beta-binomial distribution of disease incidence required, on average, sampling 3.9 more plants per sampling round to classify disease incidence compared with the binomial distribution. Use of these sequential sampling plans may aid growers in deciding the order in which to harvest hop yards to minimize the risk of a condition called "cone early maturity" caused by late-season infection of cones by P. macularis. Also, sequential sampling could aid in research efforts, such as efficacy trials, where many hop cones are assessed to determine disease incidence.

PCR detection of Pseudoperonospora humuli and Podosphaera macularis in Humulus lupulus

Hop downy mildew (&lt;I&gt;Pseudoperonospora humuli&lt;/I&gt;) and hop powdery mildew (&lt;I&gt;Podosphaera macularis&lt;/I&gt;) are the most important pathogens of hop (&lt;I&gt;Humulus lupulus&lt;/I&gt;). The early detection and identification of these pathogens are often made difficult by symptomless or combined infection with another pathogens. Molecular analysis of internal transcribed spacer (ITS) regions of rDNA is a novel and very effective method of species determination. Therefore, specific PCR assays were developed to detect the pathogens &lt;I&gt;Pseudoperonospora humuli&lt;/I&gt; and &lt;I&gt;Podosphaera&lt;/I&gt; &lt;I&gt;macularis&lt;/I&gt; in naturally infected hop plants. The specific PCR primer combinations P1 + P2 and S1&amp;nbsp;+&amp;nbsp;S2 amplified specific fragments from &lt;I&gt;Pseudoperonospora humuli&lt;/I&gt; and &lt;I&gt;Podosphaera macularis&lt;/I&gt;, respectively, and did not cross-react with hop DNA nor with DNA from other fungi. PCR primer combinations R1 + R2 and R3&amp;nbsp;+&amp;nbsp;R4 could be used in multiplex PCR detection of &lt;I&gt;Pseudoperonospora humuli&lt;/I&gt;, &lt;I&gt;Podosphaera macularis&lt;/I&gt;, &lt;I&gt;Verticillium albo-atrum&lt;/I&gt; and &lt;I&gt;Fusarium sambucinum&lt;/I&gt;. Phylogenetic relationships were inferred for 42 species of the &lt;I&gt;Erysiphales&lt;/I&gt; from nuclear rDNA (ITS1, 5.8S, ITS2). The molecular characterisation and phylogenetic analyses confirmed the species identification of hop powdery mildew. The PCR assays used in this study proved to be accurate and sensitive for detection, identification, classification and disease-monitoring of the major hop pathogens.

(397) Atypical Disease Response to Hop Powdery Mildew

Open-pollinated hop seeds (Humulus lupulus var. lupuloides E. Small, H. l. var. pubescensE. Small, H.l. var. neomexicanusNelson and Cockerell, and H.l. var. lupulusL.) were collected from the United States, Canada, and Kazakhstan and screened for resistance to hop powdery mildew (Podosphaeramacularis Braun &amp; Takamatus). A total of 2108 seedlings were repeatedly inoculated with high levels of P. macularis. Under greenhouse conditions, most seedlings exhibited a compatible disease response typical of susceptible hosts with sporulating colonies covering both leaf surfaces. Three genotypes from hop seed native to Emba, Kazakhstan, remained uninfected in greenhouse assays. Further experimentation of those genotypes in growth chambers at 18 °C revealed that they demonstrated an atypical disease response. Six days after inoculation, necrotic lesions on the adaxial leaf surfaces were visually apparent. Microscopic examination showed areas of collapsed epidermal cells, collapsed hyphae, and golden-brown discolorations extending out from the center of the infection. These symptoms contrasted those of a hypersensitive response in which fungal growth is restricted by the collapse of epidermal cells in advance of the fungus. The infection frequency of Kazakhstani genotypes was intermediate compared to H.l. cultivars Symphony (susceptible) and Nugget (resistant) after exposure to three preinoculation temperature regimes. These genotypes could represent a new source of polygenic resistance to hop powdery mildew, and could broaden hop germplasm available to global breeding programs.

Spatial Pattern Analysis of Hop Powdery Mildew in the Pacific Northwest: Implications for Sampling

ABSTRACT The spatial pattern of hop powdery mildew was characterized using 3 years of disease incidence data collected in commercial hop yards in the Pacific Northwest. Yards were selected randomly from yards with a history of powdery mildew, and two to five rows were selected for sampling within each yard. The proportion of symptomatic leaves out of 10 was determined from each of N sampling units in a row. The binomial and the beta-binomial frequency distributions were fit to the N sampling units observed in each row and to SigmaN sampling units observed in each yard. Distributional analyses indicated that disease incidence was better characterized by the beta-binomial than the binomial distribution in 25 and 47% of the data sets at the row and yard scales, respectively, according to a log-likelihood ratio test. Median values of the beta-binomial parameter theta, a measure of small-scale aggregation, were near 0 at both sampling scales, indicating that disease incidence was close to being randomly distributed. The variability in disease incidence among rows sampled in the same yard generally increased with mean incidence at the yard scale. Spatial autocorrelation analysis, used to measure large-scale patterns of aggregation, indicated that disease incidence was not correlated between sampling units over several lag distances. Results of a covariance analysis showed that heterogeneity of disease incidence was not dependent upon cultivar, region, or time of year when sampling was conducted. A hierarchical analysis showed that disease incidence at the sampling unit scale (proportion of sampling units with one or more diseased leaves) increased as a saturation-type curve with respect to incidence at the leaf level and could be described by a binomial function modified to account for the effects of heterogeneity through an effective sample size. Use of these models permits sampling at the sampling unit scale while allowing inferences to be made at the leaf scale. Taken together, hop powdery mildew was nearly randomly distributed with no discernable foci, suggesting epidemics are initiated from a well-distributed or readily dispersible overwintering population. Implications for sampling are discussed.

Effect of Variable Temperature on Infection Severity of Podosphaera macularis on Hops

ABSTRACT The effect of variable temperature on the infection severity of Podosphaera macularis was investigated. Potted 'Symphony' hop plants were inoculated and exposed to different temperature regimes that included supraconducive temperatures (30 to 42 degrees C) for varying periods of time (2 to 9 h). Infection severity (lesions per cm(2) of leaf area) was calculated 7 to 10 days after inoculation. Immediately exposing inoculated plants to 30 degrees C for as little as 2 h significantly (P </= 0.05) reduced infection severity compared with exposure at a constant 18 degrees C. However, exposure of inoculated plants to optimal conditions for 24 or 48 h prior to exposure to supraconducive conditions reduced this effect for plants exposed to 30, 33, or 36 degrees C. Exposure to 39 or 42 degrees C for 2 or more hours resulted in infection frequencies not significantly different from that of the uninoculated control regardless of prior exposure to favorable conditions. Exposure to simulated field temperatures programmed into growth chambers indicated that inoculation at 1700 or 2100 h resulted in significantly more disease than did inoculation at 0900 or 1300 h. Plants exposed to supraconducive or simulated field temperatures for 7 days prior to inoculation developed significantly lower disease severity than did plants maintained at 18 degrees C for 7 days. The magnitude, length, and time of exposure to supraconducive temperatures in relation to time of inoculation plays an important role in the development of hop powdery mildew, and rules addressing these variables could be a useful addition to disease risk assessment models.

Responding to an Introduced Pathogen: Podosphaera macularis (Hop Powdery Mildew) in the Pacific Northwest

Powdery mildew of hop (Humulus lupus L.), which is caused by Podosphaera macularis (formerly Sphaerotheca macularis) was found in the Yakima Valley, WA in 1996 and subsequently spread to the growing regions in Oregon and northern and southern Idaho. To rapidly assist growers in reducing the cost associated with the preventive fungicide program, the Gubler/Thomas grape powdery mildew risk infection model was adapted for hops. In addition, field surveys were utilized to identify other management practices that impacted disease development. Weather networks were established and utilized to deliver daily regional maps indicating the risk index. These maps were posted to the web for daily access. Lessons learned from this experience will be useful in addressing future pathogen introductions. Accepted for publication 28 March 2003. Published 13 November 2003.

Development of Management Strategies for Hop Powdery Mildew in the Pacific Northwest

Hop powdery mildew, caused by Sphaerotheca macularis, was first discovered in the Yakima Valley of Washington in 1997 and has since become the most serious disease of hop (Humulus lupus) in the Pacific Northwest. Lack of understanding of the epidemiology of S. macularis has made it difficult to develop sound management practices. Results from our field and laboratory studies suggest that control measures applied early in the growing season are probably the most important in shaping the epidemic in a particular field and that late season control measures may not need to be applied at the same intensity as in early to mid-season. Accepted for publication 9 March 2001. Published 13 March 2001.

First Report of Hop Powdery Mildew in the Pacific Northwest.

Hop powdery mildew (HPM) was first observed in commercial hop (Humulus lupulus L.) fields in Washington State on 10 June 1997 near Toppenish in the Yakima Valley. The disease appeared throughout the valley in 1997; by mid-July, scattered fields throughout the Yakima growing area reported HPM. Approximately 2,000 of 30,000 acres in production were not harvested in 1997 due to HPM. The pathogen apparently perennated in buds, and flagshoots originating from infected buds were observed during March and April 1998 at various locations throughout the Yakima Valley. During the 1999 growing season, the majority of hop acreage in Washington State was affected, and most fields planted to susceptible cultivars contained at least one infected plant. HPM was initially discovered in southern Idaho during early July 1998, in two adjacent fields of hops in Canyon County. HPM was found ≈644 km (400 miles) north in another hop-growing region of Idaho, Boundary County, during mid-July 1998. HPM eventually was observed in more than 20 Idaho hop fields. The initial discovery of HPM in Oregon's Willamette Valley was made during late-July 1998, in two neighboring hop fields. By the end of the growing season, HPM was observed in nine commercial fields representing 3.7% of the hop production acreage in Oregon. Affected cultivars include Brewer's Gold, Chinook, Cluster, Columbus/Tomahawk, Eroica, Fuggle, Galena, Golding, Liberty, Olympic, Perle, Symphony, Tettnanger, Willamette, and Zeus. Infected basal leaves of bines had small whitish circular spots on adaxial surfaces. In some cases, blisters preceded direct observation of the fungus. Cones also were infected, appearing stunted and malformed. The pathogen usually was visible on infected cones but sometimes was found only under overlapping bracts. Cleistothecia have not been observed in the field to date. Conidia were transferred to leaf disks (12 mm diameter) excised from greenhouse-grown cv. Galena hop plants. Inoculated leaf disks were incubated on moistened filter paper in glass petri dishes at 20°C with illumination provided for a 12 h day by two cool-white fluorescent bulbs. HPM lesions with chains of unicellular, barrel-shaped conidia (30 to 36 × 15 to 18 μm) were visible within 7 days. The causal agent was identified as Sphaerotheca macularis (Wallr.:Fr.) Lind (synonym S. humuli (DC.) Burrill) on the basis of conidial shape and size as well as host range (1). Reference: (1) D. J. Royle. 1978. Powdery mildew of the hop. Pages 381-409 in: The Powdery Mildews. D. M. Spencer, ed. Academic Press, New York.

The fungicidal properties of certain spray-fluids, X. Glyceride oils. (With two text-figures.)

Summary1. The fungicidal action of vegetable oils on the conidial stage of the hop powdery mildew, Sphaerotheca Humuli (DC), Burr., is a property common to glyceride oils. When applied with 0·25 per cent. Agral I, the various samples of vegetable and animal oils examined, with the exception of castor oil, proved fungicidal at a concentration of 0·5–1·0 per cent.2. The fungicidal action of glyceride oils is associated with the glyceride structure and, in the presence of Agral I, is unaffected by the presence of those impurities of the oil which are removed by refinement.3. Glycerol, at 4 per cent., is not completely fungicidal and, under the conditions of the experiments, causes leaf injury; oleic acid, at 1 per cent. is phytocidal; triolein, prepared by synthesis from glycerol and oleic acid, is fungicidal at 0·5 per cent. and causes no injury to the leaves.4. The fungicidal properties of glyceride oils are affected by the type of emulsification used and the stable emulsions produced by the twosolution oleic acid method are less effective than the unstable emulsions obtained by agitation with dilute Agral I solutions.

The Fungicidal Properties of Certain Spray-Fluids, IX. The Fungicidal Properties of the Products of Hydrolysis of Sulphur

1. The action of the following sulphur compounds on the conidial stage of the hop powdery mildew (Sphaerotheca Humuli) has been examined:Sodium sulphite, prepared by direct solution or by the neutralisation of solutions of sodium metabisulphite and applied with either 0·5 per cent, gelatine or 0·5 per cent. Agral I as the spreader, proved fungicidal at a content of 0·25 per cent, sulphur, and non-fungicidal at a content of 0·16 per cent, sulphur. The solutions, at these concentrations, caused injury to the leaves, which is not prevented by the neutralisation of solutions of sodium metabisulphite by calcium hydroxide instead of sodium hydroxide.

POLYSULPHIDE SULPHUR IN RELATION TO THE FUNGICIDAL EFFICIENCY OF CERTAIN SPRAY MATERIALS

SummaryThe results of a prolonged investigation of the fungicidal properties of solutions containing sulphur in polysulphide form upon the hop powdery mildew (S. Humuli) have been classified and summarised. During the course of this work the fungicidal efficiency of various lime sulphurs, liver of sulphurs, and solutions containing sodium, potassium, ammonium, calcium and barium polysulphides have been compared and it has been shown that, in all cases, the effect upon the fungus, when growing under similar biological and external conditions and provided that the sprays are applied under standardised conditions, is determined solely by the content of polysulphide sulphur of the spray fluid. The estimation of the amount of polysulphide sulphur present provides, therefore, a measure of the efficiency of these materials against S. Humuli.