Environmental Influences on the Evaporation Rate of Horticultural Disinfestants

Authors: Copes, Warren; Smith, Barbara

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2023
Publication Date: 2/1/2024
Citation: Copes, W.E., Smith, B.J. 2024. Environmental Influences on the Evaporation Rate of Horticultural Disinfestants. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-09-23-0125-R.
DOI: https://doi.org/10.1094/PHYTOFR-09-23-0125-R

Interpretive Summary: Instructions on disinfestant products labeled for use in horticultural plant production typically specify contact times of 5 to 10 minutes for optimum efficacy. The problem is contact times are hard to control when disinfestants are spray applied on horticultural production surfaces. The difficulty occurs because the evaporation rate, thus contact time, varies depending on weather conditions, with more rapid drying under hot and sunny versus cool and cloudy conditions. This study is an initial investigation into understanding evaporation of commercial disinfestants that contain alcohol, hypochlorite, quaternary ammonium compounds or peroxygen compounds. Evaporation rates were measured from open jars containing water or six commercial disinfestants under eight weather condition categories. Alcohol always evaporated faster than the other five disinfestants and water, while the other solutions evaporated at the same rate. However, the evaporation rate of all disinfestant solutions incrementally changed with weather conditions, from hot and sunny, to warm and partly cloudy, to cool and cloudy. To better understand these changes, the evaporation rate of water was measured from a dielectric leaf wetness sensor while air temperature, relative humidity, solar radiation, vapor pressure deficit and wind speed were monitored. The weather model showed the amount of sun intensity, air temperature and wind speed were the most influential factors affecting evaporation. The next step will be to evaluate how fast different types of horticultural plant production surfaces dry when disinfestants are applied under different weather conditions. The goal is to more consistently eliminate pathogens that cause plant diseases.

Technical Abstract: The evaporation rate of disinfestants when sprayed on production surfaces is expected to vary under different weather conditions but it is unknown how that affects efficacy. This study is an initial investigation into how the evaporation rates of water and six commercial disinfestants that contain alcohol, hypochlorite, quaternary ammonium compounds or peroxygen compounds vary under eight weather condition categories. Additionally, an empirical model was developed on the evaporation rate of water from a dielectric leafwetness sensor in response to air temperature, relative humidity, solar radiation, vapor pressure deficit and wind speed under the same weather conidtions. Isopropyl alcohol (IPA) lost more weight due to evaporation over 4 hours (P < 0.0001) than all other disinfestant solutions and no differences (P = 0.0500) existed between the other five disinfestant solutions and water. IPA had a mean percent weight loss of 70% under hot and sunny conditions, 43% under cool and cloudy conditions, and 6% under laboratory conditions. Hypochlorite, quaternary ammonium and peroxy disinfestant solutions evaporated at a similar rate over four hours, with an approximate mean percent weight loss of 18% under hot and sunny conditions, 6% under cool and cloudy conditions, and 1% under laboratory conditions. The regression model that best explained the influence of weather on evaporation included the variables solar radiation, temperature and wind speed (P < 0.0001, R2 = 0.5603). This information will be used further to model the complex interactions between the evaporative rate of disinfestants under the same range of weather conditions when applied to multiple types of substrate materials that represent common horticultural plant production surfaces.