Suppression Of Powdery Mildew Research Articles

Evaluation of Germicidal UV-C Light for Suppression of Grape Powdery Mildew and Botrytis Bunch Rot in Western Oregon.

Germicidal UV light (UV-C) has been shown to effectively suppress several plant pathogens as well as some arthropod pests. Recent reports describe the efficacy of nighttime applications of UV-C at doses from 100 to 200 J/m2 in vineyards to reduce grape powdery mildew (Erysiphe necator). Our in vitro studies confirmed the efficacy of UV-C to inhibit germination of E. necator and Botrytis cinerea conidia, demonstrated a range of tolerances to UV-C within a collection of E. necator isolates, and showed growth stage-specific effects of UV-C on B. cinerea. Nighttime use of UV-C was evaluated at 48 to 96 J/m2 in small plot trials (<1,000 vines) from 2020 to 2023. Once- or twice-weekly UV-C applications significantly reduced the incidence of foliar powdery mildew compared with non-UV-C-treated controls (P < 0.02). Suppression of powdery mildew on fruit was less consistent, where once or twice weekly UV-C exposure reduced powdery mildew disease severity in 2020 (P = 0.04), 2021 (P = 0.02), and 2023 (P = 0.003) but less so in 2022 (P = 0.07). Bunch rot severity was not significantly reduced with UV-C treatment in any year of the study. Application of UV-C until the onset of fruit color change (veraison) also had a minimal effect on the fruit-soluble solids, pH, anthocyanins, or phenolics in harvested fruit at any UV-C dose or frequency (P > 0.10). Suppression of powdery mildew by nighttime application of UV-C at lower doses in small plots suggests that such treatments merit further evaluation in larger-scale studies in Western Oregon.

Suppression of Powdery Mildew and Two-Spotted Spider Mite by UV-B Radiation and Mulching Type of Strawberry Cultivation in the Greenhouse

Powdery mildew and two-spotted spider mite are detrimental to strawberry plants and are controlled with traditional pesticides. To accommodate consumer demand, eco-friendly methods of pest control are required. Strawberries were cultivated (in soil and in a hydroponic system) for two years, and ultraviolet B (UV-B) irradiation was used as an alternative pest control during the harvesting season. Three varieties were grown (Seolhyang, Kingsberry, and Durihyang), and four UV-B lamp/mulch (black, green, and light reflection sheet [LRS]) combinations were used during harvesting: UV-B+black or green mulch, UV-B+black or green+LRS, no UV-B+black or green, and no UV-B+black or green+LRS. In all varieties, powdery mildew was 65% more controlled when UV-B irradiation was used. The adult two-spotted spider mite density was lowest in the UV-B lamp+black or green+LRS treatments. Therefore, UV-B irradiation during the strawberry harvesting season could effectively control powdery mildew and two-spotted spider mite with little side effect on the plants.

Design, Construction, and Evaluation of Equipment for Nighttime Applications of UV-C for Management of Strawberry Powdery Mildew in Florida and California

We designed and constructed two tractor-drawn ultraviolet-C (UV-C) lamp arrays housed in hemicylindrical hulls adapted to two widths of raised bed planting systems for strawberry. Onboard UV dosimeters were fitted to the arrays to monitor UV-C output in field studies to suppress strawberry powdery mildew. Nighttime applications of UV-C were evaluated in replicated-plot field plantings in Florida and in California. Suppression of powdery mildew by nighttime applications of UV-C at 200 J m−2 was equivalent to that provided by weekly fungicide applications in California and superior to that provided by fungicide treatments in Florida. Costs of construction and operation of the UV-C apparatus were estimated to allow comparisons to conventional fungicide-based suppression of disease. UV-C applications had no negative effects on yield nor any visual phytotoxic effect on plants or fruit throughout the season. The results confirm and expand upon previously published studies involving UV-C applications in different environments.

Suppression of Powdery Mildew in Okra and Sunflower Plants under Natural Infection through Peroxyacetic Acid Foliar Application

Suppression of Powdery Mildew in Okra and Sunflower Plants under Natural Infection through Peroxyacetic Acid Foliar Application

Interaction of Basal Foliage Removal and Late-Season Fungicide Applications in Management of Hop Powdery Mildew.

Canopy management is an important aspect of control of powdery mildew diseases and may influence the intensity of fungicide applications required to suppress disease. In hop, powdery mildew (caused by Podosphaera macularis) is most damaging to cones when infection occurs during bloom and the juvenile stages of cone development. Experiments were conducted over 3 years to evaluate whether fungicide applications could be ceased after the most susceptible stages of cone development (late July) without unduly affecting crop yield and quality when disease pressure was moderated with varying levels of basal foliage removal. In experimental plots of 'Galena' hop, the incidence of leaves with powdery mildew was similar whether fungicides were ceased in late July or made in late August. Disease levels on leaves were unaffected by the intensity of basal foliage removal, whereas the intensity of basal foliage removal interacted with the duration of fungicide applications to affect disease levels on cones. Similar experiments conducted in large plots of 'Tomahawk' hop in a commercial hop yard similarly found no significant impact on disease levels on leaves from either the duration of fungicide applications or intensity of basal foliage removal. In contrast, on cones, application of fungicides into August had a modest, suppressive effect on powdery mildew. There was also some evidence that the level of powdery mildew on cones associated with fungicide treatment was influenced by the intensity of basal foliage removal. When fungicide applications ceased in late July, there was a progressive decrease in the incidence of cones with powdery mildew with increasing intensity of basal foliage removal. Removing basal foliage two to three times allowed fungicide applications to be terminated in late July rather than late August without diminishing disease control on cones, yield, or cone quality factors. Thus, this study further establishes that fungicide applications made during the early stages of hop cone development have the strongest effect on suppression of powdery mildew on cones. The additive effect of fungicide applications targeted to the periods of greatest cone susceptibility and canopy management to reduce disease favorability may obviate the need for fungicide applications later in the season. This appears to be a viable strategy in mature hop yards of certain cultivars when disease pressure is not excessively high.

Foliar application of microbial-enriched compost tea enhances growth, yield and quality of muskmelon (Cucumis melo L.) cultivated under fertigation system

Microbial-enriched compost tea (CT) is a water extract of compost that is amended with nutrient supplements during brewing to enhance their microbial diversity. The potential use of fertigation nutrients via drip irrigation system followed by weekly foliar application of microbial-enriched CT on growth of muskmelon (Cucumis melo L.) and suppression of powdery mildew caused by Golovinomyces cichoracearum DC. was studied under rain shelter conditions. Full and half strength fertigation nutrients in combination with weekly foliar application of microbial-enriched CT, fungicide (Daconil®@2gL−1) or water as a control were utilised in this study. The study showed that there was no added advantage in using full strength fertigation nutrients in terms of chlorophyll content, mean flower formation, mean fruit set, disease severity, and disease progress (AUDPC) or epidemic rate. A repeat trial was also conducted using half strength fertigation nutrients (twice a day) in combination with weekly foliar application of microbial-enriched CT or Daconil®, as a result there was reductions in the disease severity by 38 and 21%, respectively. In addition, a delay in disease onset for two weeks was observed in the plants treated with either microbial-enriched CT or Daconil®. The experimental results revealed significant variations in the yield and fruit qualities amongst the treatments. There were 18.3, 16.21, 8.81, 7.11 and 7.50% increases in mean fruit fresh weight (kg), total soluble solids concentration (°Brix), firmness (N), linear increment in the diameter (cm) and mesocarp size (cm) of muskmelon fruits, respectively after the application of half strength fertigation nutrients in combination with the weekly foliar application of microbial-enriched CT as compared with the control. Thus, it is rational to conclude that a reduced strength of the nutrients in the fertigation systems in combination with weekly foliar application of microbial-enriched CT could be used successfully as a biofertiliser and a bioprotectant on muskmelon crop without compromising their fruit quality.

Suppression of Powdery Mildew on Flax by Foliar Application of Essential Oils

AbstractSix essential oils were evaluated as to their efficiency in controlling powdery mildew (PM) of flax when they were applied as foliar sprays in an outdoor pot experiment. Onion, flax and fenugreek oils did not affect PM severity ratings – that is, they were ineffective in controlling the disease. On the other hand, black cumin, jojoba and coriander oil showed variable levels of efficiency in controlling the disease. Black cumin was moderately effective in controlling the disease because it reduced disease severity by 32.87%, while jojoba and coriander oils were highly effective as they reduced disease severity by 66.24 and 68.64%, respectively. Essential oils did not affect seed weight; however, coriander oil was a notable exception as it reduced seed weight by 55%. Straw weight was not affected by any oil. Foliar application of essential oils resulted in significant changes in the levels of protein, phenols, ascorbic acid and malondialdehyde and in activities of peroxidase and polyphenol oxidase. The lack of significant correlation between levels and activities of these biochemical components and PM severity demonstrate that these components are not involved in the suppression of PM by essential oils. Therefore, direct toxicity of essential oils to the causal pathogen Oidium lini is the most likely explanation for the disease suppression.

Suppression of Powdery Mildew on Cucumber Using Silicate Fertilizer

Suppression of Powdery Mildew on Cucumber Using Silicate Fertilizer

규산질 비료의 참외 흰가루병 발생 억제 효과

Silicon is known to accumulate in plants and results in greater resistance to diseases and insect pests. In this study, we investigated the effect of silicate fertilizer applied in soil on the development of powdery mildew of oriental melon. Oriental melon seedlings of four-leaf stage were transplanted and grown in a plastic film house. Silicate fertilizer was applied to maintain soil available level of 200 mg/kg one week before transplanting. Fungicide triflumizol was sprayed three times; one, two, and three weeks after transplanting. Sphaerotheca fuliginea was inoculated 2 weeks after transplanting. The number of infected leaf and the number of fungal colony in leaves were measured one, two, and three weeks after the inoculation. Three weeks after the fungal inoculation, in the treatment of fungicide triflumizol. infected leaf numbers and number of colony per leaf were reduced by 10 and 58%, respectively. In the silicate fertilizer treatment, infected leaf numbers and numbers of colony per infected leaf were suppressed only by 6 and 16%, respectively, and the efficacy was lower than that of the fungicide triflumizol. The combined treatment of silicate fertilizer and the fungicide suppressed powdery mildew more effectively, and infected leaf numbers and numbers of colony per leaf were reduced by 31 and 80%, respectively. These results indicate that although silicate fertilizer itself is not much effective in the suppression of powdery mildew, it can significantly enhance the efficacy of the fungicide.

Suppression of Powdery Mildew on Greenhouse-Grown Cucumber by Addition of Silicon to Hydroponic Nutrient Solution Is Inhibited at High Temperature.

Silicon amendments to hydroponic nutrient solutions have been used successfully in Canada to suppress powdery mildew (PM) caused by Sphaerotheca fuliginea on cucumber (Cucumis sativus). In contrast, preliminary trials in Florida greenhouses failed to achieve the level of disease suppression reported in the literature for Canadian studies. A series of greenhouse experiments were conducted in Florida to determine the factors involved in reducing the effectiveness of silicon amendments for PM suppression on cucumber. Three horticultural practices (cultivar, nutrient solution formula, and rooting medium) and two environmental factors (light intensity and temperature) were tested in combination with silicon amendments for their effects on the suppression of PM on cucumber. When plants were irrigated with a standard nutrient solution amended with potassium silicate at 0 mg/liter, the cucumber cv. Vetomil was found to be resistant and cvs. Corona, Cilla, Farbio, and Toska were found to be susceptible to PM. Susceptible cultivars irrigated with potassium silicate at 100, 150, or 200 mg/liter exhibited a slight but statistically significant reduction in PM over the course of a 49-day trial. Although PM in the cultivar trial was slightly lower in treatments with added silicon, disease suppression with silicon was not commercially useful because it failed to increase fruit yields. Nutrient solution formula, rooting medium, and light intensity had no effects on the levels of PM suppression, regardless of whether plants were irrigated with potassium silicate at 0 or 100 mg/liter. Temperature was found to act in a synergistic manner with silicon. The greatest effect of temperature on PM suppression was observed at 20°C in which cucumber plants, irrigated with silicon at 100 mg/liter, exhibited significant reductions in the numbers of PM colonies per leaf. Disease suppression by silicon was observed at 25 and 30°C, but the magnitude of the disease suppression was significantly lower than when plants were maintained at 20°C. The effect of temperature on PM suppression by silicon may explain the difference in results between previous experiments in Canada, where greenhouse temperatures averaged 20 to 25°C, and the current study in Florida, where greenhouse temperatures averaged 24 to 32°C.

Suppression of powdery mildew (Sphaerotheca fuliginea) in cucumber by the detergent Zohar LQ-215

The effect of the detergent Zohar LQ-215 alone or combined with the fungicide fenarimol (Rubigan) on cucumber powdery mildew (caused bySphaerotheca fuliginea) was examined under controlled environmental conditions and in the field. In laboratory tests conducted on leaf disks, the efficacy of fenarimol was 30 times greater than that of Zohar LQ-215 as indicated by the ED50 values of the compounds (0.012% and 0.356%, respectively). Zohar LQ-215 did not reduce spore germination or germ-tube elongation, but inhibited the later stages of the disease cycle (i.e., mycelial growth and sporulation). Although the detergent was degraded relatively quickly, its effect on the polycyclic development of the disease lasted for up to 24 days after spraying. Low disease severity (2.4% compared with 27% in the control) was maintained following three applications of the detergent at 5 days intervals. In a greenhouse trial, a mixture of Zohar LQ-215 and fenarimol at half rate did not improve disease suppression beyond the effect of fenarimol applied alone at half rate. However, the effects of the two compounds were additive when applied in the field as a mixture.

Suppression of powdery mildew in squash by applications of whitewash, clay and antitranspirant materials

The incidence of powdery mildew, caused bySphaerotheca fuliginea (Schlecht. Fr.) Polacci, in squash plants, was suppressed in the field to 50–60% of that in untreated control plants by weekly sprays with whitewash (Loven or Yalbin) or clay. Loven or Yalbin sprays resulted in significant reductions in disease level, more on the adaxial (59–65%) than on the abaxial (38–52%) surface of leaves, and more on young (53–59%) than on old (12–18%) leaves. The addition of 0.1% Dabak (a commercial sticker) to the whitewashes significantly increased their efficiency (22% above that of the controls), the degree of protection being associated with whitewash concentration. Squash leaves were protected from powdery mildew also by weekly sprays of the antitranspirant Vapor Gard, to a level comparable with that achieved by a whitewash plus sticker. However, the protection levels achieved with whitewashes, clays and antitranspirant were lower than with a fungicide (propiconazole). Experiments conducted under controlled conditions resulted in higher rates of escape from infection and a lower rate of hyphal and conidial development on plants and tissues following whitewash, clay and antitranspirant treatments.