Commercial Fungicide Formulations Research Articles

Evaluation of fungicides for management of Botryosphaeriaceae associated with dieback in Australian walnut orchards

Dieback of fruiting spurs, stems and branches of walnut trees (Juglans regia L.), caused by Botryosphaeriaceae, is widespread in walnut orchards in Australia. Five species of Botryosphaeriaceae (Diplodia seriata, Dothiorella omnivora, Neofusicoccum macroclavatum, N. parvum, and Spencermartinsia viticola) were recovered from the Australian walnut orchards in a previous study, with D. seriata and N. parvum being the most prevalent. The present study evaluated inhibitory effects of ten fungicides on mycelium growth of those five species and on conidium germination of D. seriata and N. parvum. It investigated the preventative and curative efficacy of selected fungicides on disease incidence in glasshouse and field trials. In vitro experiments showed that nine of the fungicides reduced mycelium growth, and all ten inhibited conidium germination, but to varying extents. Tebuconazole, prochloraz manganese chloride, fluazinam, fludioxonil and pyraclostrobin were the most effective for inhibiting mycelium growth (EC50 < 0.14 µg a.i. mL-1), whereas pyraclostrobin, fluxapyroxad, fluopyram, penthiopyrad and tebuconazole were the most effective for inhibiting conidium germination (EC50 < 2.2 µg a.i. mL-1). In planta experiments with five fungicides confirmed that preventative treatments had greater efficacy than curative treatments. A field trial with four commercial fungicide formulations demonstrated that tebuconazole and tebuconazole + fluopyram provided protection of walnut trees for the longest period. The field trial also confirmed the efficacy of pyraclostrobin and the inhibitory effect of fluazinam. This study is the first in Australia to evaluate fungicides in different classes and with different modes of action for efficacy against Botryosphaeriaceae recovered from walnut orchards in Australia, and provides a wider selection of active ingredients for a fungicide rotation programme than that which is currently available to the Australian walnut industry.

Visualizing active fungicide formulation mobility in tomato leaves with desorption electrospray ionisation mass spectrometry imaging.

Newer and safer agrochemicals are always in demand to meet the increasing needs of a growing population for affordable food. Spatial chemical monitoring of the active mobility of an agrochemical is essential to this agrochemical development process and mass spectrometry imaging (MSI) is proposed as a safer, easier alternative to the existing standard of autoradiography for the same. With desorption electrospray ionisation mass spectrometry imaging (DESI MSI) using leaf imprints, we were able to visualize the active agrochemical mobility of a commercial fungicide formulation with the active ingredient Azoxystrobin in whole tomato leaves. The leaf-imprinting method was optimized with precise control over the pressure conditions and time of imprinting to yield highly consistent samples for imaging. The reproducibility of this method was tested with the Azoxystrobin formulation applied to tomato leaves and was compared to the mobility of the unformulated Azoxystrobin standard in similar application conditions. The xylem mobility and the lateral-leaf lamina spreading of the fungicide were visualized with mass spectrometry imaging and validated using complementary LC-MS studies. The necessity and importance of the agrochemical application as a formulation were re-iterated by the limited mobility observed in Azoxystrobin standard studies compared to the Azoxystrobin formulation. This mass spectrometry imprint-imaging method could be translated for the visualization of any xenobiotic in further foliar systems particularly with soft leaves.

Abatement of some commercial fungicide content from model dispersions by a new thiourea-graft-polyethyleneimine derivative

A new derivative of polyethyleneimine (PEI) with 9% degree of substitution of its primary and secondary amino groups with thiourea moieties (TU9-PEI) has been synthesized and investigated as flocculant in model suspensions of commercial fungicide formulations Dithane M45, Melody Compact 49 WG, Cabrio®Top, and their mixtures. The structure of TU9-PEI, obtained by an aqueous one-pot strategy involving formaldehyde mediated coupling of PEI and TU, was confirmed by FTIR and 1H NMR spectroscopy as well as the streaming potential measurements. The settling time, polymer dose, and fungicide type and concentration were the parameters used for assessing the flocculation ability of the new polycation sample. The UV-Vis spectroscopy measurements revealed a good removal efficiency of TU9-PEI for all of the fungicides investigated, between 88 and 94%. Slightly higher removal percent was found for greater fungicide concentrations. The charge neutralization was indicated by zeta potential measurements (values close to zero recorded at the optimum polymer dose) as the main mechanism which contributed to the Dithane and Cabrio®Top particle removal and a combined effect of the TU9-PEI/fungicide particle electrostatic attractions and hydrogen bonds between both the amine and thiourea groups of the polycation chains and the hydroxyl ones on the copper oxychloride particles (negative values) in case of the Melody Compact 49 WG particle separation. Particle size and surface morphology analysis data gave supplementary evidences regarding the TU9-PEI ability to separate the fungicides investigated from simulated wastewater.

Evaluation of disease alert systems for postbloom fruit drop of citrus in Florida and economic impact of adopting the Citrus Advisory System

Gama, A. B., Peres, N. A., Singerman, A., and Dewdney, M. M. 2021. Evaluation of disease alert systems for postbloom fruit drop of citrus in Florida and economic impact of adopting the Citrus Advisory System. Crop Protec. XX: xx-xx.Postbloom fruit drop of citrus (PFD) is caused by Colletotrichum abscissum in the Colletotrichum acutatum species complex. PFD does not occur annually but some growers tend to apply fungicides during flowering every year, wasting resources and negatively impacting the environment. Due to its sporadicity, the Fungicide Application Decision system (PFD-FAD) and the Citrus Advisory System (CAS) were developed in Florida and Brazil in 2001 and 2017, respectively, to aid in PFD management. Our objectives were to compare the recommendations from CAS and PFD-FAD, a weekly fungicide treatment schedule, and a nontreated control. We also aimed to assess the economic impact of adopting CAS over the other fungicide schedule treatments with low- and high-risk aversion profile scenarios. Weather conditions were not favorable to PFD in seven field trials. We performed one fungicide application based on CAS over four seasons. An average of approximately 2 and 3 fungicide applications per trial was performed based on PFD-FAD and the weekly treatments, respectively. Average cost to manage PFD following CAS, PFD-FAD, and the weekly treatments were, respectively, $17.52, $186.87, and $272.35. The reduction in management costs related to CAS also translates to reduced use of commercial fungicide formulations in small properties by 382 and 573 L compared to PFD-FAD and the weekly treatments, respectively. CAS recommendations greatly reduced production costs and fungicide usage without compromising disease control and citrus yield in years of low weather favorability for PFD in Florida.

Association of hydrogen peroxide with commercial fungicide formulations in the control of Asian soybean rust

ABSTRACT: In recent years, there have been reductions in the efficacy of the fungicidal control of Phakopsora pachyrhizi, thereby hindering the management of soybean rust and compromising crop yield. This study evaluated the effects of incorporating hydrogen peroxide (H2O2) in commercial fungicide formulations on the control of soybean rust. We conducted two experiments, one of which was performed in a greenhouse environment and the other under field conditions. In both environments, we examined the following four control programs using commercial fungicide formulations: (I) azoxystrobin + cyproconazole (quinone outside inhibitor [QoI] + demethylation inhibitor [DMI]); (II) picoxystrobin + cyproconazole (QoI + DMI); (III) pyraclostrobin + epoxiconazole + fluxapyroxad (QoI + DMI + succinate dehydrogenase inhibitor); and (IV) water (H2O) (program without fungicide application), combined with the incorporation of (i) H2O2; (ii) mancozeb (positive control I); (iii) chlorothalonil (positive control II); or (iv) water (H2O) alone. Analyses of infected leaf area and grain yield revealed that the addition of H2O2 to the formulations of DMI and QoI fungicides led to a reduction in disease severity of between 33% and 44% relative to the effects of these products used alone, as well as an increase in yield and SPAD values. The use of H2O2 and multi-site fungicides alone failed to provide effective control of soybean rust. In addition to enhancing the efficacy of disease control, the use of H2O2 associated with commercial fungicide mixtures was shown to be a potential tool for the management of fungicide resistance and reduction in losses from Asian soybean rust.

Comparison Between Prothioconazole and Prothioconazole-Desthio in Poison-Plate Mycelial Growth Assays of Fusarium graminearum

The active ingredient prothioconazole is a demethylase inhibitor (DMI) widely used in numerous commercial fungicide formulations for crop protection. However, prothioconazole converts in planta to prothioconazole-desthio, which was found to be the primary active form inhibiting CYP51 activity in fungi. Here, experiments were performed on Fusarium graminearum to compare the use of technical-grade prothioconazole-desthio, technical-grade prothioconazole, and formulated product Proline in poison-plate mycelial growth assays to investigate the relevancy of using prothioconazole for sensitivity testing. Prothioconazole-desthio was significantly more efficacious at mycelial growth inhibition than prothioconazole but mycelial growth and effective concentration to reduce growth by 50% (EC50) values between the two correlated significantly. Although care should be taken in interpreting EC50 values of prothioconazole, the compound is still suitable for monitoring sensitivity rather than purchasing the more expensive prothioconazole-desthio.

From laboratory to the field: Validating molecular markers of effect in Folsomia candida exposed to a fungicide-based formulation

Under controlled laboratory conditions, toxicity data tend to be less variable than in more realistic in-field studies and responses may thus differ from those in the natural environment, creating uncertainty. The validation of data under environmental conditions is therefore a major asset in environmental risk assessment of chemicals. The present study aimed to validate the mode of action of a commercial fungicide formulation in the soil invertebrate F. candida, under more realistic exposure scenarios (in-field bioassay), by targeting specific molecular biomarkers retrieved from laboratory experiments. Organisms were exposed in soil cores under minimally controlled field conditions for 4 days to a chlorothalonil fungicide dosage causing 75% reduction of reproduction in a previous laboratory experiment (127 mg a.i. kg−1) and half this concentration (60 mg a.i. kg−1). After exposure, organisms were retrieved and RNA was extracted from each pool of organisms. According to previous laboratorial omics results with the same formulation, ten genes were selected for gene expression analysis by qRT-PCR, corresponding to key genes of affected biological pathways including glutathione metabolism, oxidation-reduction, body morphogenesis, and reproduction. Six of these genes presented a dose-response trend with higher up- or down-regulation with increasing pesticide concentrations. Highly significant correlations between their expression patterns in laboratory and in-field experiments were observed. This work shows that effects of toxicants can be clearly demonstrated in more realistic conditions using validated biomarkers. Our work outlines a set of genes that can be used to assess the early effects of pesticides in a realistic agricultural scenario.

Comparing plant–insect trophic transfer of Cu from lab-synthesised nano-Cu(OH)2 with a commercial nano-Cu(OH)2 fungicide formulation

Environmental contextNanomaterials are being extensively researched for use as agrochemicals, and some commercial formulations containing nanomaterials are already on the market. Information on environmental fate and effects of nanomaterials, however, are largely based on laboratory-synthesised materials. This study questions whether data on trophic transfer of Cu from pure, laboratory-synthesised Cu(OH)2 nanomaterials can be used to predict trophic transfer of Cu from a complex commercial fungicide formulation containing Cu(OH)2 nanomaterials. AbstractTo examine whether studies conducted with highly purified, laboratory-synthesised nanomaterials are predictive of behaviour of commercial nanopesticide formulations, we studied the trophic transfer of Cu(OH)2 manufactured nanomaterials (MNMs) by tobacco hornworms (Manduca sexta) feeding on surface-treated tomato leaves (Solanum lycopersicum). We compared laboratory-synthesised copper(II) hydroxide (Cu(OH)2) nanowire with the widely used fungicide Kocide® 3000, whose active ingredient is nano-needles of copper(II) hydroxide (nCu(OH)2). All leaves were treated at rates in accordance with the product label (1.5kgha−1 or 150mgm−2). As a control, we used highly soluble CuSO4. Over the course of the study (exposure up to 7 days followed by up to 20 days of elimination), hornworms accumulated Cu from all three treatments far exceeding controls (ranging from ~55 to 105 times greater for nCu(OH)2 and CuSO4 respectively). There were also significant differences in accumulation of Cu among treatments, with the greatest accumulation in the CuSO4 treatment (up to 105±18μg Cu per g dry mass) and the least in the nCu(OH)2 treatment (up to 55±12μg Cu per g dry mass. The difference in their toxicity and accumulation and elimination dynamics was found to be correlated with the solubility of the materials in the exposure suspensions (r2=0.99). We also found that first-instar larvae are more susceptible to toxicity from all forms of Cu than second-instar larvae. Our results provide valuable knowledge on whether the ecotoxicity of commercial MNM products such as Kocide can be compared with laboratory-synthesised counterparts and suggests that predictions can be made based on functional assays such as measurement of solubility.

Differences in sensitivity between earthworms and enchytraeids exposed to two commercial fungicides

The use of pesticides in crop fields may have negative effects on soil Oligochaeta Annelida, i.e., earthworms and enchytraeids, and thus affect soil quality. The aim of this study was to assess the effects of two commercial fungicide formulations on the earthworm Aporrectodea caliginosa and the enchytraeid Enchytraeus albidus in a natural soil. The fungicides were Cuprafor micro® (copper oxychloride), commonly used in organic farming, and Swing Gold® (epoxiconazole and dimoxystrobin), a synthetic fungicide widely used in conventional farming to protect cereal crops. Laboratory experiments were used to assess the survival, biomass loss and avoidance behaviour. No lethal effect was observed following exposure to the copper fungicide for 14 days, even at 5000mgkg−1 of copper, i.e. 650 times the recommended dose (RD). However, a significant decrease in biomass was observed from 50mgkg−1 of copper (6.5 times the RD) for A. caliginosa and at 5000mgkg−1 of copper (650 times the RD) for E. albidus. These sublethal effects suggest that a longer period of exposure would probably have led to lethal effects. The EC50 avoidance for the copper fungicide was estimated to be 51.2mgkg−1 of copper (6.7 times the RD) for A. caliginosa, and 393mgkg−1 of copper (51 times the RD) for E. albidus. For the Swing Gold® fungicide, the estimated LC50 was 7.0 10−3mLkg−1 (6.3 times the RD) for A. caliginosa and 12.7 10−3mLkg−1 (11.0 times the RD) for E. albidus. No effect on biomass or avoidance was observed at sublethal concentrations of this synthetic fungicide. It was concluded that enchytraeids were less sensitive than earthworms to the two commercial fungicides in terms of mortality, biomass loss and avoidance behaviour. Therefore we discuss the different strategies possibly used by the two Oligochaeta species to cope with the presence of the pesticides were discussed, along with the potential consequences on the soil functions.

Degradation and sorption of the fungicide tebuconazole in soils from golf greens

The fungicide tebuconazole (TBZ) is used to repress fungal growth in golf greens and ensure their playability. This study determined the degradation and sorption of TBZ applied as an analytical grade compound, a commercial fungicide formulation or in combination with a surfactant product in thatch and soils below two types of greens (USGA and push-up greens) in 12-cm vertical profiles covered by three different types of turf grass. Only minor TBZ degradation was observed and it was most pronounced in treatments with the commercial fungicide product or in combination with the surfactant compared to the analytical grade compound alone. A tendency for higher TBZ sorption when applied as the formulated product and lowest sorption when applied as a formulated product in combination with the surfactant was observed, with this effect being most distinct on USGA greens. No correlation between occurrence of degradation and soil depth, green type or grass type was observed. Sorption seemed to be the main process governing the leaching risk of TBZ from the greens and a positive correlation to the organic matter content was shown. In light of these findings, organic matter content should be taken into consideration during the construction of golf courses, especially when following USGA guidelines.

Determination of Thiophanate-methyl (TM): A Well Known Fungicide by Potentiometric and Spectrophotometric Methods

The instantaneous formation of green colour obtained on mixing methanolic solutions of thiophanate-methyl (TM) and iron(III) has led to the development of spectrophotometric and potentiometric titration procedures for the determination of thiophanate-methyl—a well known commercial fungicide. Spectrophotometric measurements have been made at λmax = 365 nm. Green colour results from the formation of a complex between disulphide derivative of TM i.e. TMDS (an oxidized product of TM) and iron(II)—a reduced form of iron(III). Potentiometric titrations are marked by an increase in potential with equivalence point at TM to iron(III) ratio of 4:1 (molar ratio). The methods have been successfully adapted to the analysis of commercial fungicide formulations. The proposed methods for the determination of TM are simple, rapid and reliable.

Fungicide Management of Brown Patch of Tall Turf-type Fescue in the Residential Landscape in Oklahoma

In the transition zone of the USA, cool-season grasses such as tall fescue are often planted in shaded areas, where warm-season grasses are less adapted. The most damaging disease of tall fescue is brown patch, caused by Rhizoctonia solani. Fungicide applications and cultural practices are often used to manage brown patch in this region. A three-year study was implemented in Oklahoma to evaluate ready-to-use fungicides available to residential lawn owners and compare these to several common commercial fungicide formulations used by professional lawn care applicators. A selection of fungicides representing products commonly available to the residential market and commercial standards were applied to small plots of tall fescue or tall fescue/Kentucky bluegrass mixtures from 2008 to 2010. All products tested, with the exception of azoxystrobin, provided limited or inconsistent control of brown patch and resulted in lower turfgrass quality in all years. Further examination of carrier type (granular vs. liquid) and timing (preventive vs. curative) did not result in strong differences in the level of brown patch control or overall quality. These studies suggest that control of brown patch in tall fescue in the transition zone should focus on integrated disease management principals and not only on applications of fungicides directed at the residential market. Accepted for publication 5 August 2013. Published 22 October 2013.

Behaviour of metalaxyl as copper oxychloride–metalaxyl commercial formulation vs. technical grade-metalaxyl in vineyards-devoted soils

The objective of this work is to asses the sorption of metalaxyl applied as a copper oxychloride (CO)-metalaxyl formulation, for a set of selected soils devoted to vineyards. The method involved batch incubation of soils suspended with a commercial copper oxychloride–metalaxyl-based fungicide in 0.01 M CaCl 2. Afterwards, the metalaxyl concentration remaining in solution was determined by high-performance liquid chromatography (HPLC). The amount of dissolved metalaxyl in the fungicide suspension depends mainly on the soil pH, its potential acidity, and the cation exchange capacity. Of the approx. 20% metalaxyl retained by the solid colloids, the effect of organic matter colloids in soils (15–20 mg kg −1) had a poor contribution (six times lower) than the copper oxychloride colloids (40%, w/w) in the commercial fungicide formulation (100–130 mg kg −1). When comparing these retention data with the behaviour of metalaxyl used as a technical grade fungicide of about 100% purity (10–15 mg kg −1 in solids), it is clear that the commercial formulation increases a 30% retention of metalaxyl by soil (15–20 mg kg −1 in solids). The overall effect of the metalaxyl formulation plus soil show values of 10 times higher retention than technical grade-metalaxyl plus soil. Commercial formulation can decrease the mobility of soluble metalaxyl in agricultural soils with regard to the expected values obtained from batch studies using analytical grade-metalaxyl. Therefore, the effect of surfactants should be considered in the assessment of water contamination by the pesticides used in agriculture.

Detachment of sprayed colloidal copper oxychloride–metalaxyl fungicides by a shallow water flow

Flow shear stress induced by rainfall promotes the loss of the pesticides sprayed on crops. Some of the factors influencing the losses of colloidal-size particulate fungicides are quantified by using a rotating shear system model. With this device it was possible to analyse the flow shear influencing washoff of a commercial fungicide formulation based on a copper oxychloride-metalaxyl mixture that was sprayed on a polypropylene surface. A factor plan with four variables, i.e. water speed and volume (both variables determining flow boundary stress in the shear device), formulation dosage and drying temperature, was set up to monitor colloid detachment. This experimental design, together with sorption experiments of metalaxyl on copper oxychloride, and the study of the dynamics of metalaxyl and copper oxychloride washoff, made it possible to prove that metalaxyl washoff from a polypropylene surface is controlled by transport in solution, whereas that of copper oxychloride occurs by particle detachment and transport of particles. Average losses for metalaxyl and copper oxychloride were, respectively, 29 and 50% of the quantity applied at the usual recommended dosage for crops. The key factors affecting losses were flow shear and the applied dosage. Empirical models using these factors provided good estimates of the percentage of fungicide loss. From the factor analysis, the main mechanism for metalaxyl loss induced by a shallow water flow is solubilisation, whereas copper loss is controlled by erosion of copper oxychloride particles.

Mixing calcium chloride with commercial fungicide formulations results in very slow penetration of calcium into apple fruits

AbstractFoliar applications of calcium salts are usually combined with fungicides. In the years 2002 and 2003, it was tested if this practice assures high rates of penetration of calcium. Amounts that penetrated in 24 h were measured at 20 °C using 45CaCl2. To ensure maximum penetration rates, humidity was maintained at 100 %. Sample size was 40 to 50 fruits, and data were presented as box plots because distribution of data was not normal. Median rates of penetration of CaCl2, measured with mixtures of fungicides and CaCl2 at 5 or 10 g l–1, respectively, were very slow, and amounted to only a few percent of the dose applied. Rates were a little higher with very young fruits (55 days after full bloom, DAFB). Adding alkyl polyglycoside surfactants at 0.2 g l–1 significantly decreased surface tensions, and increased rates of penetration by up to 15‐fold. Still, total penetration of CaCl2 rarely exceeded 20 % of the dose applied (median penetration), even in the presence of an additional surfactant. In all treatments, outliers with 60 to 100 % penetration in 24 h occurred, and this was attributed to penetration into lenticels. This is expected to result in unequal concentrations of calcium in fruits, especially in the sub‐epidermal layers. Addition of a suitable surfactant to mixtures of fungicides with CaCl2 is strongly recommended as it enhances wetting and greatly increases penetration rates of CaCl2.

Fungicide application and phosphorus uptake by hyphae of arbuscular mycorrhizal fungi into field-grown peas

The effect of two commercial fungicide formulations on phosphorus (P) uptake into peas via hyphae of a native arbuscular mycorrhizal (AM) fungal community was examined in the field. The fungicides contained carbendazim or a mixture of propiconazole and fenpropimorph as their active ingredients and were applied at 1× and 100× the rate recommended for field use. Hyphal compartments (HCs; soil cylinders completely surrounded by nylon mesh of 25 μm mesh size) were buried between two rows of peas. The soil inside these HCs was labelled with 32P to distinguish hyphal P uptake from inside the HCs from overall P uptake. Fungicides were added to the soil inside the HCs at concentrations assumed to reflect their concentration in the surrounding soil. At two harvests, plant growth, total P and 32P uptake as well as root length density and AM root colonisation were measured. Length of hyphae inside the HCs was measured at the final harvest. Both carbendazim and the propiconazole/fenpropimorph-mixture stimulated hyphal P uptake from inside HCs when applied at rates recommended for normal field use. This increase in hyphal P uptake was significant only in the case of carbendazim. A negative effect of the fungicides on other components of the soil microbial community with which AM fungi interact is considered the most likely explanation for the observed stimulation in hyphal P uptake. Hyphal P uptake was completely inhibited by application of carbendazim at 100× the recommended rate. Plant growth and overall P uptake were not affected by fungicide applications apart from application of the propiconazole/fenpropimorph mixture at 100× the recommended rate. This rate completely inhibited plant growth. AM root colonisation was reduced by the high rate of carbendazim application only. This reduction had no effect on plant growth which may be due to the fertile soil conditions at the field site. It is concluded that the testing for side effects of pesticides on non-target organisms should include functional parameters such as P uptake by AM fungi. Such measures may be more sensitive to harmful effects than measures of plant growth or biomass.

Commercial Fungicide Formulations Induce In Vitro Oospore Formation and Phenotypic Change in Mating Type in Phytophthora infestans

ABSTRACT A wide range of commercially formulated fungicides cause in vitro effects on mating behavior in specific isolates of Phytophthora infestans, the causal agent of late blight of potato and tomato. Four isolates of P. infestans representing each of the four common US genotypes, US-1, US-6, US-7, and US-8 and varying in their sensitivity to metalaxyl, were exposed to a variety of fungicides used to control late blight in petri dish assays at concentrations ranging from 1 to 100 mug a.i./ml. Exposure of each of these normally heterothallic single mating type isolates of P. infestans to 9 of the 11 commercial fungicide formulations tested resulted in the formation of oospores after 2 to 4 weeks. The highest numbers of oospores were formed on media amended with Ridomil 2E (metalaxyl) and Ridomil Gold EC (mefenoxam) at 0.1 to 10 mug a.i./ml, averaging as many as 471 and 450 oospores per petri dish, respectively. Several other fungicides including Maneb, Manzate (Mancozeb), Curzate (cymoxanil + mancozeb), and Acrobat MZ (dimethomorph + mancozeb) also induced oospore formation, producing from 0 to 200 oospores per plate at fungicide concentrations from 0.1 to 10 mug a.i./ml. The metalaxyl resistant isolates formed oospores in response to the fungicides more often than the metalaxyl sensitive isolates. No oospores were formed on media amended with Bravo (chlorothalonil) or Tattoo C (chlorothalonil + propamocarb HCl) and these compounds completely suppressed growth of the isolates at 0.1 and 1 mug a.i./ml. Three metalaxyl resistant A2 isolates mated with both A1 and A2 isolates after exposure to the fungicides Ridomil 2E and Ridomil Gold EC. Alterations in mating type expression were also observed in a metalaxyl sensitive A1 isolate after exposure to Benlate (benomyl). Copious amounts of chemicals are applied annually to potato and tomato production areas to control late blight. Our results indicate that a wide range of chemically diverse fungicides can induce normally heterothallic metalaxyl resistant isolates of P. infestans to form oospores in vitro after short exposures to the fungicides.

Fungicides for Dutch Elm Disease: Comparative Evaluation of Commercial Products

The commercial fungicide formulations, Arbotect 20-S, Phyton-27, Fungi-Sol, and biological product, Binab-T, were injected into juvenile (ave. 17.5 cm diameter) American elms prior to (prophylactic) or after (therapeutic) the trees were inoculated with the Dutch elm disease (DED)-causing fungus, Ceratocystis ulmi. Samples of all trees were cultured to verify establishment of C. ulmi and DED symptom development was monitored for two growing seasons. At the end of the second growing season none of 20 Arbotect-injected trees (prophylactic and therapeutic) displayed DED symptoms. Fungi-Sol and Binab prophylactic groups (5 and 10 trees, respectively) contained significantly fewer diseased trees than the control group, but no treatment, other than Arbotect, showed significant therapeutic effect. Sapwood damage associated with each of the treatments was greater than that associated with injection of water. Discolored sapwood was localized around injection sites in Fungi-Sol and Binab-treated trees, but extended a maximum of 2 m and 6 m, respectively, above the points of injection of Arbotect and Phyton. Injection holes were overgrown and closed for all water, Fungi-Sol, and Binab treatments while one Arbotect and five Phyton-treated elms had injection holes that remained open and were weeping with bacterial slime flux. Two trees treated with a high dosage of Phyton had an aggregate of five open lesions associated with injection holes.

RESIDUES OF ETHYLENEBISDITHIOCARBAMATES (EBDC) AND DINOCAP IN GREENHOUSE CUCUMBER FRUITS

By the third day following the application of the last of three sprays of the fungicides dinocap and mancozeb to greenhouse cucumber fruits, residues, on a whole-fruit basis, did not exceed the levels permitted in Canada of 0.1 μg/g and 7 μg/g, respectively. The permitted level of zineb equivalent EBDC was never exceeded following the application of a dinocap-mancozeb commercial fungicide formulation. The results support an Ontario recommendation for a 3-day waiting period between fungicide application and harvest in the case of EBDC, and argue for a reduction in the 30-day period for dinocap.Key words: Residue, dissipation, mancozeb, dinocap, cucumber, greenhouse