Control of Cucurbit Powdery Mildew with JMS Stylet-Oil

Fungicide Physical Mode of Action: Impacts on Suppression of Hop Powdery Mildew

Understanding of the physical mode of action of fungicides allows more efficient and effective application and can increase disease control. Greenhouse and field studies were conducted to explore the preinfection and postinfection duration and translocative properties of fungicides commonly used to control hop powdery mildew, caused by Podosphaera macularis. In greenhouse studies, applications made 24 h before inoculation were almost 100% effective at suppressing powdery mildew, regardless of the fungicide evaluated. However, percentage control of powdery mildew based on the number of pathogen colonies per leaf varied significantly between fungicides with increasing time from inoculation to application, ranging from 50 to 100% disease control depending on the fungicide. Fluopyram or fluopyram + trifloxystrobin was particularly efficacious, suppressing nearly all powdery mildew development independent of application timing. In translocation studies, fluopyram and flutriafol were the most effective treatments in each of two separate experiments, resulting in zones of inhibition of 1,036 and 246.3 mm², respectively, on adaxial leaf surfaces when a single droplet of each fungicide was applied to the abaxial surface of leaves. In field experiments, all fungicide treatments provided nearly complete control of powdery mildew infection when applied before inoculation. Levels of disease control decreased with time depending on treatment, showing trends similar to those observed in greenhouse studies. In the 2017 field experiments, high levels of disease control (>75%) were observed at postinoculation time points for all treatments tested, whereas the same fungicides were more sensitive to application timing in a different year. Findings from this research indicate that differences in efficacy between fungicides are small when applications are made preventively, but postinfection activity and translaminar movement of certain fungicides may render some more effective depending on application coverage and preexisting infection.

Evaluation of a Disease Warning System for Phomopsis Cane and Leaf Spot of Grape: A Field Study

A field evaluation of a warning system for Phomopsis cane and leaf spot of grape (Vitis spp.), caused by Phomopsis viticola, was conducted in Ohio over 3 years (2002 to 2004) by applying fungicides and fungicide-adjuvant combinations based on predicted infection events. Three different criteria for risk-light, moderate, and high-were evaluated with the warning system. The warning system is based on measured weather conditions (temperature and wetness duration following rain) and a model for risk of leaf and internode infection. Vines were sprayed with fungicides based on either the warning system or a calendar-based 7-day protectant program, from 2.5-cm shoot growth (Eichhorn-Lorenz [E-L] stage 7) to the end of the broom (E-L stage 27). Fungicides were tested with or without an adjuvant (JMS Stylet-Oil or Regulaid). In the controls, the mean percentage of leaves and internodes with infections ranged from 36 to 100%, the number of lesions per leaf ranged from 1 to 28, and percentage of internodes covered by lesions ranged from 1 to 12%. Both the calendar-based protectant treatment (based on use of mancozeb) and the warning system treatment based on spraying in response to light or moderate predicted infection events (especially with mancozeb + Regulaid) resulted in significantly less disease incidence and severity compared with the controls. The mean percent control (relative difference in disease between a treatment and the control) was higher for the protectant schedule (˜55% and ˜80% for incidence and severity, respectively, based on application of mancozeb) than for the warning system (˜36% and ˜60% for incidence and severity, respectively, based on application of mancozeb + Regulaid), but there were two to three times more fungicide applications with the protectant schedule than with the warning system.