Application Of Triadimefon Research Articles

Fungicide evaluation against head smudge (Curvularia spp.) and its impact on yield and germination of tef (Eragrostis tef Zucc.)

Head smudge, caused by Curvularia spp., is the major disease of tef in the humid tef-growing areas of Ethiopia. Despite this, farmers continue producing tef without any disease management strategies, which is leading to substantial quantitative and qualitative losses. Hence, the field and laboratory experiments were conducted to assess the efficacy of seven fungicides for the management of head smudge and simultaneously to assess the possible effects of the disease on seed quality of tef. The field experiment was conducted at Dangila and North Achefer districts and the treatments were arranged in a randomized complete block design with three replications. Tef seeds harvested from field experiments were subsequently used for laboratory studies using the blotter method and arranged in a completely randomized design. The effect of fungicides on reducing disease incidence and severity and increasing yield was significant (p < 0.001). The highest overall mean disease control (88.9%) was obtained from propiconazole sprayed plots followed by trifloxystrobin + tebuconazole and tebuconazole, both of which had a similar 85.5% disease reduction. The applications of triadimefon resulted in intermediate disease reduction (69.9%). However, the application of mancozeb + cymoxanil, cymoxanil + copper oxychloride, and thiamethoxam + metalaxyl + difenoconazole doesn’t bring a significant improvement from the untreated plot. According to our findings, head smudge can reduce tef yield by up to 62% and germination by 18.7 to 45.4%. Therefore, the application of propiconazole, trifloxystrobin + tebuconazole, and tebuconazole can be considered as effective head smudge management practice until other management options are developed.

Absorption, translocation, and accumulation of the fungicide triadimefon in Pak choi (Brassica rapa var chinensis), pepper (Capsicum annuum), and cucumber (Cucumis sativus).

Triadimefon is a typical systemic fungicide that is widely used in the management of powdery mildew, rust disease, and southern blight. In this study, we measured fungicide residue to profile its absorption, translocation, and accumulation in three representative vegetable crops (Pak choi, cucumber, and pepper) after over-application. The fungicides were applied through entire-plant spraying (EPS), root-irrigation (RI), and middle-leaf-daubing (MLD). The half-life of triadimefon depends on the application method and plant species. In EPS, the half-life was 5.42 days (Pak choi), 6.86 days (cucumber), and 6.73 days (pepper), while in RI it was 4.39 days (Pak choi), 6.30 days (cucumber), and 5.98 days (pepper). In the EPS treatment, triadimefon is translocated both upward/outside and downward/inner-side from the daubed leaves in all the three vegetable crops. The transfer amount to each organ reached a peak on the 2nd day after fungicide application. The mesophyll of Pak choi exhibited a higher fungicide deposition compared to the petiole. In cucumber and pepper, the leaves demonstrated the highest accumulation of triadimefon (approximately 0.3-0.5 mg·kg-1), followed by stems. Roots and fruits displayed the lowest levels of triadimefon accumulation. Furthermore, triadimefon was found to have an impact on chlorophyll content, root activity, as well as the activity of superoxide dismutase and catalase in Pak choi, indicating its potential as a plant growth regulator. These aforementioned studies provide novel insights for the safe and efficient application of triadimefon in the production of Pak choi, cucumber, and pepper.

Beneficial effects of triadimefon in overcoming drought stress in soybean at fluorescence stage

Soybean (Glycine max [L.] Merr.) at fluorescence stage frequently experiences drought stress. Although triadimefon has been observed to improve drought tolerance of plants, reports on its role in drought resistance on leaf photosynthesis and assimilate transport are limited. This study examined the effects of triadimefon on leaf photosynthesis and assimilate transport at fluorescence stage of soybean experiencing drought stress. Results showed that triadimefon application relieved the inhibitory effects of drought stress on photosynthesis and increased RuBPCase activity. Drought increased soluble sugar contents, yet reduced starch content in the leaves by heightening the activities of sucrose phosphate synthase (SPS), fructose-1,6-bisphosphatase (FBP), invertase (INV), and amylolytic enzyme, impeding the translocation of carbon assimilates to roots and reducing plant biomass. Nevertheless, triadimefon elevated starch content and minimized sucrose degradation by augmenting sucrose synthase (SS) activity and restraining the activities of SPS, FBP, INV, and amylolytic enzyme compared with drought alone, regulating the carbohydrate balance of drought-stressed plants. Therefore, triadimefon application could reduce the photosynthesis inhibition and regulate the carbohydrate balance of drought-stressed soybean plants to lessen the impacts of drought on soybean biomass.

Peanut (Arachis hypogaea) response to weed and disease management in northern Ghana

ABSTRACTWeeds and diseases can reduce peanut (Arachis hypogaea L.) yield or increase cost of production to maintain acceptable yield. While herbicides and fungicides have limited availability in many areas of Ghana and currently are too expensive for resource-poor farmers, control by these pesticides can have a major positive impact on peanut yield. Field experiments were conducted during the rainy seasons of 2009 and 2010 in northern Ghana to determine the effects of herbicide and hand weeding in combination with fungicides on pest management and peanut yield. Peanut pod yield was often more highly correlated with disease severity and canopy defoliation resulting from early leaf spot (caused by Cercospora arachidicola Hori) and late leaf spot (caused by Cercosporidium personatum (Berk. & M.A. Curtis) Deighton) than weed biomass. In some instances, less disease and canopy defoliation were observed when weeds were not controlled effectively compared with increased weed management through hand weeding or herbicide. Two hand weedings or applying pendimethalin preemergence with one hand weeding in combination with 4 applications of triadimefon and chlorothalonil resulted in the lowest weed density and canopy defoliation and often resulted in the highest peanut yield.

Responses of physiochemical attributes of kinnow budded on Jatti Khatti to triazole treatment under salinity

The response given by the photosynthetic pigments, antioxidant enzyme activity and nutrient accumulation of kinnow (Citrus nobilis×C. deliciosa) budded onCitrus jambhiriLush rootstocks (var. Jatti Khatti) to triazole compounds was studied under NaCl stress. Eighteen-month-old budded kinnow plants were irrigated with 0 or 50 mM NaCl with or without triazole compounds. Paclobutrazol (PBZ) at 100 mg 1−1and triazole (TRZ), triadimefon (TDM) and hexaconazole (HEX) at 20 mg l−1were applied by drenching the soil one week prior to NaCl application. PBZ, TRZ and TDM were equally effective in preventing chlorophyll degradation under NaCl stress. The improvement in catalase (CAT) activity was greater in TRZ- and TDM-treated plants under stress, while for superoxide dismutase (SOD) activity, TRZ, PBZ and TDM were found to be equally effective. The peroxidase (POX) activity increased more in TDM-treated plants. The application of TDM and HEX had a more pronounced effect on the upregulation of proline content under stress. Furthermore, triazole compounds increased the accumulation of K+and Ca2+ions and inhibited that of Na+and Cl−, resulting in an improvement in the K+/Na+and K+/Cl−ratios. For PBZ-treated plants, the K+/Na+and K+/Cl−ratios in leaf tissues increased 2.4- and 2.1-fold compared to plants treated with NaCl alone, while HEX had a more striking effect on Ca2+upregulation and significantly (1.5-fold) increased leaf Ca2+under stress.

Evaluation of Preventive Fungicide Applications for Fairy Ring Control in Golf Putting Greens and In Vitro Sensitivity of Fairy Ring Species to Fungicides.

Fairy ring species induce symptoms on putting greens mostly indirectly, by modifying the soil physical or chemical properties. Therefore, preventive rather than curative fungicide applications may be more effective in managing fairy ring. Two field experiments were conducted on a creeping bentgrass research green to evaluate fairy ring control from preventive fungicide applications. A 3-year study investigated the optimal rate and soil temperature-based timing of a preventive application of triadimefon and tebuconazole. A 2-year study evaluated the impact of irrigation timing and fungicide + surfactant tank mixtures on the efficacy of preventive applications of triadimefon and triticonazole. Fungicide-treated plots in both studies exhibited less fairy ring severity than untreated plots. Data suggest that a 5-day average soil temperature range of 13 to 16°C may be suitable for initiating preventive applications. Symptoms occurred earlier in plots treated with a surfactant tank mix than in those treated with fungicide alone. Irrigation timing had no effect on fungicide performance. The sensitivity of 16 isolates representing major fairy ring species to flutolanil, propiconazole, tebuconazole, triadimefon, and triticonazole was determined with a mycelial growth assay. No significant differences in fungicide sensitivity were detected among species. Isolates had significantly higher 50% effective concentration values for triadimefon than for the other fungicides tested.

Persistence of repeated triadimefon application and its impact on soil microbial functional diversity

The effects of repeated applications of the fungicide triadimefon in agricultural soil on the microbial functional diversity of the soil and on the persistence of the fungicide in the soil were investigated under laboratory conditions. The degradation half-lives of triadimefon at the recommended dosage, simulated by a first-order kinetic model, were 23.90, 22.95, and 21.52 days for the first, second, and third applications, respectively. Throughout this study, no significant inhibition of the Shannon-Wiener index (H′) was observed. However, the Simpson index (1/D) and the McIntosh index (U) were obviously reduced (p ≤ 0.05) during the initial 3 days after the first triadimefon application and thereafter, gradually recovered to or exceeded the level of the control soil. A similar trend in variation but with a faster recovery in the 1/D and U was observed after the second and third triadimefon applications, respectively. Taken together, the above results indicate that the repeated application of triadimefon enhanced the degradation rate of the fungicide and the recovery rate of the soil microbial functional diversity. It is concluded that repeated triadimefon applications in soil have a transient or temporary inhibitory effect on soil microbial communities.

Evaluation of endophytic bacterial strains as antagonists of take-all in wheat caused by Gaeumannomyces graminis var. tritici in greenhouse and field

Six endophytic bacterial strains from wheat roots, selected from extensive screening tests, were studied in greenhouse pot experiments against take-all disease of wheat, caused by Gaeumannomyces graminis var. tritici (Ggt). For comparison, the fungicide triadimefon was included. All six bacterial strains and triadimefon significantly reduced take-all in wheat plants between 39.4 and 57.3% compared to the inoculated control. Treatment with the bacterial strains also significantly increased growth parameters of roots (e.g., average length, fresh, and dry weight) in comparison with the inoculated control. One of the endophytic bacterial strains, designated EDR4, which proved to be most consistent in further greenhouse tests, was also examined in field trials against take-all in wheat. In the field experiment 2006/2007, height of wheat plants in Ggt inoculated plots was significantly reduced compared to the non-inoculated treatments. Yield parameters such as kernels per head and thousand kernel weight (TKW) in the inoculated control were lower compared to other treatments. In the inoculated plots, individual treatments with the strain EDR4 increased yield compared to the inoculated control. In the field trial 2007/2008 treatments with strain EDR4 as well as the fungicide triadimefon reduced take-all by 49.6 and 61.9%, respectively, compared to the inoculated control. At harvest, in the inoculated control plant height, seeds per head and TKW were significantly lower compared to the other treatments. Treatments with EDR4 eliminated the detrimental effects of take-all on grain yield to a similar degree as triadimefon application. The strain EDR4 distinctly inhibited growth of Ggt in vitro and was identified as Bacillus subtilis on the basis of its morphology and 16S rRNA sequence analysis as well as physiological and biochemical characteristics. These results indicate that the strain EDR4 has potential in directly controlling take-all disease of wheat.

Biological control of take-all in wheat by endophytic Bacillus subtilis E1R-j and potential mode of action

The bacterial strain E1R-j, isolated as an endophyte from wheat roots, exhibited high antifungal activity to Gaeumannomyces graminis var. tritici ( Ggt). Strain E1R-j was identified as Bacillus subtilis based on morphological, physiological and biochemical methods as well as on 16S rDNA analysis. This strain inhibited mycelium growth in vitro of numerous plant pathogenic fungi, especially of Ggt, Coniothyrium diplodiella, Phomopsis sp . and Sclerotinia sclerotiorum. In greenhouse experiments, soil drenches with cell densities of 10 6, 10 9 and 10 12 CFU ml −1 E1R-j reduced significantly take-all disease, caused by Ggt, in wheat seedling by 62.6%, 68.6% and 70.7%, respectively, compared to the inoculated control, 4 weeks after sowing. Growth parameters such as lengths and fresh weights of roots and shoots of Ggt-inoculated control plants were significantly lower compared to Ggt-inoculated and E1R-j treated plants. Field experiments in the season 2006/2007, heights of wheat plants in the Ggt inoculated plots were significantly reduced compared to the non inoculated treatments. Yield parameters such as kernels per head and thousand kernel weight (TKW) in inoculated control plants were lower compared to the other treatments. In the experimental year 2007/2008, independent treatments with the bacterial strain E1R-j and the fungicide Triadimefon reduced take-all disease in wheat roots by 55.3% and 61.9%, compared to the inoculated control plants. In this season plant height in inoculated control was significantly lower and also the yield parameters seeds per head and especially TKW were drastically reduced compared to the other treatments. E1R-j treatment alleviated the detrimental effects of take-all on grain yield parameters to a similar extent as Triadimefon application. SEM studies revealed that in the presence of E1R-j, hyphae of Ggt showed leakage, appeared ruptured, swollen and shriveled. Following root drench, strain E1R-j was able to colonize endophytically roots and leaves of wheat seedlings. While the population of the bacterial strain in wheat roots steadily increased from the second to the fourth leaf stage, in the leaf tissue the population of the strain rapidly declined. TEM studies also showed that cells of E1R-j were present in roots of wheat seedlings and effectively retarded infection and colonization of Ggt in root tissue; suppression of Ggt by E1R-j was accompanied by disintegration of hyphal cytoplasm. In addition, in the presence of E1R-j cells in Ggt-infected root tissue morphological defense reactions were triggered such as formation of wall appositions and papillae. The results presented indicate that the endophytic strain E1R-j of B. subtilis meets demands required for biocontrol of take-all.

Endogenous hormonal and enzymatic responses of Catharanthus roseus with triadimefon application under water deficits

The effect of triadimefon was investigated in a medicinal plant, Catharanthus roseus subjected to water deficit stress. The abscisic acid (ABA) level, DNA and RNA contents and activities of ATPase and protease were found varying in different parts of the plants under treatment. Drought treatment increased the ABA level more than twofold in all parts of the plants. TDM treatment to the drought stressed plants showed highest contents. In roots, stem and leaves, drought stress caused a decrease in the DNA and RNA contents when compared with control and other treatments. TDM treatment with drought increased the nucleic acid contents to the level of the control roots. The activity of ATPase and protease were increased under drought treatment and lowered due to TDM applications. This information could be useful in the field of soil water deficits reclamation efforts by using plant growth regulators. To cite this article: C.A. Jaleel et al., C. R. Biologies 331 (2008).

Osmoregulation and antioxidant metabolism in drought-stressed Helianthus annuus under triadimefon drenching

A pot-culture experiment was conducted to estimate the ameliorating effect of triadimefon (TDM) on drought stress in sunflower ( Helianthus annuus L.) plants. The plants were subjected to 3-, 6-, and 9-day-interval drought (DID) stress and drought stress with TDM @ 15 mg l −1 and 15 mg l −1 TDM alone from the 30th day after sowing (DAS). One-day-interval irrigation was kept as control. The plant samples were collected on and separated into root, stem and leaf for estimating the amino acid (AA), proline (PRO) and glycine betaine (GB) contents and the activities of antioxidant enzymes. Individual and combined drought stress and TDM treatments increased AA, PRO and GB contents, superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and polyphenol oxidase (PPO) activities when compared to control. From the results of this investigation, it can be concluded that the application of TDM caused a partial amelioration of the adverse effects of drought stress by its influence on quaternary ammonium compounds and antioxidant potentials in H. annuus plants. To cite this article: P. Manivannan et al., C. R. Biologies 331 (2008).

Host resistance and fungicide control of leaf rust ( Puccinia hordei) in barley ( Hordeum vulgare) and effects on grain yield and yield components

The effectiveness of varying levels of host resistance in five barley ( Hordeum vulgare L.) genotypes and three fungicide application protocols on the control of leaf rust (caused by Puccinia hordei G. Otth) and losses in grain yield, test weight, and 1000-kernel weight was evaluated in field experiments at two locations over four crop years. Fungicide treatments applied to all barley entries at each location and each year included a non-treated control, a single threshold-based application of triadimefon (140 g a.i. ha −1), and a complete control treatment comprised of multiple applications of triadimefon to emulate a disease-free environment. Leaf rust severity was assessed using the James [1971. A Manual of Assessment Keys for Plant Diseases. Canada Dep. Agric. Publ. 1458. The American Phytopathological Society, St. Paul, MN.] scale (0–25%) at three to four plant growth stages and data were used to calculate mean rust severity (MRS) and area under the disease progress curve (AUDPC). Leaf rust epidemics were severe in 1 (1995) of the 4 years of the study, and the treatment effect on grain yield was significant at one location (Warsaw). The susceptible cv. Wysor had a grain yield loss of 33% and MRS was 9.25% (34.23% in modified Cobb scale) at this location. In 2 (1995 and 1997) of 4 years of study, significant ( P ⩽ 0.05 ) negative correlations were obtained between MRS and grain yield, test weight, and 1000-kernel weight of cv. Wysor at both locations. In the other 2 years (1994 and 1996) when leaf rust epidemics were mild, these correlations were mostly non-significant. In general, fungicide treatment significantly ( P ⩽ 0.05 ) reduced MRS and AUDPC and reduced losses in grain yield, test weight, and 1000-kernel weight for the susceptible and moderately susceptible cultivars compared with the non-treated control. The cv. Starling, possessing adult-plant resistance, did not consistently benefit from fungicide application. There was no benefit from fungicide application for control of leaf rust in the resistant line VA92-42-46. In general, the complete-control fungicide treatment did not result in further significant reduction in leaf rust or losses in grain yield compared to threshold-level fungicide applications.

Triadimefon induced changes in the antioxidant metabolism and ajmalicine production in Catharanthus roseus (L.) G. Don.

The effects of triadimefon, a triazole compound on the antioxidant potentials and root alkaloid ajmalicine content were studied in two varieties, rosea and alba of Catharanthus roseus (L.) G. Don., an important medicinal plant. The plants of both the varieties were subjected to 15 mg l −1 triadimefon treatment by soil drenching on 53, 68 and 83 days after planting (DAP). The plants were harvested on 60, 75 and 90 days after planting and the antioxidant potentials and ajmalicine content were estimated. The antioxidant potentials viz., ascorbic acid (AA), α-tocopherol and reduced glutathione (GSH) were found increased under triadimefon treatment. The antioxidant enzymes like superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) activities showed slight changes in both the varieties under triadimefon treatment when compared to control plants. Indole alkaloid ajmalicine content increased significantly under triadimefon treatment. The increase in ajmalicine content was more in rosea variety than in alba variety. These preliminary results suggest that, the application of triadimefon may be a useful tool to increase the alkaloid production in medicinal plants.

The role of leaf chemistry inMelampsora medusaeinfection of hybrid poplar: effects of leaf development and fungicide treatment

Immature leaves of poplars are immune to Melampsora leaf rust infection, regardless of the level of resistance or susceptibility of older leaves. Leaf phenolic and protein concentrations were quantified in leaves of varying maturity (measured by leaf plastochron index, LPI) from a rust-susceptible, interspecific hybrid poplar clone, 47-174 (Populus trichocarpa Torr. &amp; Gray × Populus deltoides Bartr. ex Marsh.). Using leaf water extracts and apoplastic solutions, concentrations of phenolics and proteins decreased as LPI increased. Urediniospore germination increased 3-fold, and hyphae elongation increased 3.5-fold as LPI increased from 1 to 11. Inoculation significantly increased concentrations from 9% (LPI 5) to over 120% (LPI 11). Application of triadimefon (Bayleton®) significantly increased the apoplastic concentrations of phenolics and proteins by 43% and 25%, respectively. In vitro urediniospore germination and hyphae elongation decreased over 7-fold and 3-fold, respectively, in these leaves, to levels comparable to immature leaves. This study has shown that defense compounds are present in immature poplar leaves that likely contribute to Melampsora medusae rust immunity, and that triadimefon application created a similar immunity in susceptible leaves. Identification of specific compounds associated with this immunity could assist in the development of resistant poplar clones through traditional breeding or gene modification.

Improvement of Biomass Partitioning, Flowering and Yield by Triadimefon in UV-B Stressed Vigna radiata (L.) Wilczek

Elevated UV-B radiation (12.2 kJ m-2 d-1) as against the ambient level of 10 kJ m-2 d-1 affected flowering, productivity and biomass partitioning of green gram [Vigna radiata (L.) Wilczek cv. KM-2]. UV-B stress delayed flowering initiation and achievement of 50 % flowering, reduced flower retention by 25 %, potential yield by 18 % and all yield attributes such as pod number (25 %), pod mass (41 %), seed number (32 %) and seed mass (45 %). Harvest index and shelling percentage were also reduced by 31 and 7 %, respectively. Application of triadimefon (20 mg dm-3) to unstressed plants accelerated flowering and enhanced flower retention (21 %), potential yield (15 %) and yield attributes (7 to 44 %). The partitioning of biomass between plant parts also showed improvement over the control plants. In UV-B-stressed plants, triadimefon treatment compensated the inhibitions to varying extents.

Resistance to Triadimefon and Benomyl: Dynamics and Impact on Managing Cucurbit Powdery Mildew.

Frequency of fungicide-resistant strains of Podosphaera xanthii on pumpkins in New York before treatment varied from 3 to 80% for the demethylation inhibiting (DMI) fungicide triadimefon and from 0 to 48% for the benzimidazole fungicide benomyl between 1993 and 1996. When the initial frequency of triadimefon-resistant strains was less than 55%, one application of triadimefon plus chlorothalonil was effective. This application was made after reaching the action threshold of one leaf with powdery mildew symptoms per 50 old leaves (defined as the oldest third of the foliage). The frequency of triadimefon-resistant strains increased from 3 to 71% by 20 days after the first fungicide application in 1993. Triadimefon in the second application did not contribute to control. Loss of efficacy was due to resistance because, compared with triadimefon-treated pumpkins, pumpkins treated with other systemic fungicides were less severely infected by powdery mildew on abaxial leaf surfaces where the companion multi-site contact fungicide contributes little to control. Triadimefon was not effective in 1995 when 80% of the pathogen population was resistant before treatment. Benomyl was effective in 1995, but not in 1996 when 48% of the isolates tested were resistant to both benomyl and triadimefon before treatment. An in-field seedling assay was developed to determine local occurrence of resistant strains before the first treatment was needed. Although sensitivity of the pathogen population to the DMI fungicides myclobutanil and propiconazole also decreased after they were applied, these fungicides were more effective than triadimefon.

Chemical Manipulation of Reproductive Efficiency of Chickpea (Cicer arietinnum L.) by Triadimefon in Relation to Changes in Ethylene

Reproductive efficiency was successfully manipulated by the application of different concentrations of triadimefon at pre-flowering, flowering and post-flowering stages in chickpea (Cicer arietinum L.). Triadimefon improved the parameters determining reproductive efficiency. Yield was significantly improved due to reductions in flower and pod abscission by the application of triadimefon, which also lowered the ethylene levels in leaves, flowers and pods and delayed senescence. These findings suggest a relationship between ethylene level and reproductive efficiency in chickpea. Further, they indicate that triadimefon can be used for chemical manipulation of the reproductive efficiency of chickpea under field conditions.

Investigation on fungicide residues in greenhouse-grown strawberries.

Maximum residue limits (MRL's) for different agricultural food products in Norway are harmonized with EU standards. In field-grown strawberries in Norway, tolylfluanid has a 7 day quarantine from last application to harvest, while other approved fungicides have 14 days quarantine. Greenhouse production of strawberries is newly introduced to the country. Residue levels in strawberries of the cultivar Korona grown in a commercial greenhouse were investigated 4, 7, and 14 days after application of eight different fungicides at rates recommended by the manufacturers and at half rates. Iprodione, tolylfluanid, and vinclozolin were tested in two experiments, while chinomethionat, chlorothalonil, imazalil, penconazole, and triadimefon were tested once. For chinomethionat, imazalil, iprodione, penconazole, and vinclozolin, the residue levels were below MRL 2 weeks after application. Application of triadimefon in normal rate gave residues below MRL 14 days after application. However, its metabolite, triadimenol, was above MRL at the same time. Tolylfluanid gave very high residue levels, and except from half concentration in the second experiment, all other residue levels were above MRL. Seven days after application, residues in both experiments were approximately 3 times higher than MRL when normal rate of tolylfluanid was applied. For chlorothalonil at the recommended rate, the residue level was above MRL at any sampling time, while half rate gave residues below MRL 14 days after treatment. In view of the present results, tolylfluanid, chlorothalonil, and triadimefon will need longer time from last application to harvest and/or reduced application rates in greenhouse-grown compared to field-grown strawberries. In addition or as an alternative, recommended rates could be lowered.

Control of loose smut (Ustilago nuda and U. tritici) infections in barley and wheat plants by foliar application of triadimefon

Foliar application of the broad‐spectrum systemic fungicide triadimefon to loose smut‐infected plants of wheat and barley produced a marked curative effect. Triadimefon was particularly effective when applied at the beginning of and during stem extension. In addition to reducing percentage plant infection, foliar application of this fungicide (particularly prior to flag leaf emergence) resulted in an increased proportion of infected ears which were only partially smutted. The curative effect of these early fungicide applications resulted in significant yield increases, as a consequence of increased grain number per m2. Application of triadimefon to crops at ear emergence had no significant effect on percentage plant infection but resulted in lower levels of re‐infection following artificial or natural inoculation of healthy ears, apparently as a result of a protectant effect of fungicide residues on or in the ovaries.

Long-term Effect of Temperature and Triadimefon on Proliferation of Uncinula necator: Implications for Fungicide Resistance and Disease Risk Assessment.

Triadimefon has been used in California to control Uncinula necator, causal agent of grape powdery mildew, since 1982. Instances of unsatisfactory control have occurred mainly in the cooler coastal areas of California. The effect of temperature and application of triadimefon was investigated over a 53-day-period on two U. necator isolates, sensitive and resistant to triadimefon. At 15°C, 25°C, or temperatures fluctuating between 15 and 25°C, in absence of triadimefon, the isolates continued to produce high numbers of conidia for the entire duration of the experiment. Sporulation declined at daily maximum temperatures of 32°C for 6 h, 36°C for 3 h, and 40°C for 1 h, but was detectable when the experiment was terminated. At these temperature regimes, sporulation of the triadimefon-treated sensitive isolate ceased after 23 days. When treated with triadimefon, sporulation of the resistant isolate was comparable to that of the water-treated control. At daily maximum temperatures of 32°C for 11 h, 36°C for 6 h, and 40°C for 3 h, sporulation of both isolates generally ceased after 23 days, regardless of triadimefon application. Triadimefon resistance is most likely to manifest itself under high disease pressure, which is in part a function of temperature. The duration of daily maximum temperatures may be a valuable addition to disease risk assessment models.