Environmental Influences on the Drying Rate of Spray Applied Disinfestants from Horticultural Production Surfaces

Authors: Copes, Warren; Read, Quentin; Smith, Barbara

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2024
Publication Date: 5/9/2024
Citation: Copes, W.E., Read, Q.D., Smith, B.J. 2024. Environmental Influences on the Drying Rate of Spray Applied Disinfestants from Horticultural Production Surfaces. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-03-24-0019-R.
DOI: https://doi.org/10.1094/PHYTOFR-03-24-0019-R

Interpretive Summary: Instructions for disinfestants typically specify a dose and a contact time to kill plant pathogens on production surfaces. A problem occurs when disinfestants are applied to large production areas where the evaporation rate is affected by weather conditions. The common contact time recommendation of 10 min may not be achieved under hot, sunny conditions that promote fast drying. This study is an investigation into how the evaporation rates of six commercial disinfestants [isopropyl alcohol, two quaternary ammonium compounds, two peroxygen compounds, and sodium hypochlorite (bleach)] vary when applied to six types of substrate materials (concrete, galvanized metal, polypropylene ground fabric, polypropylene plastic sheet, pressure-treated pine, and twin-wall clear polycarbonate) under cool to hot and cloudy to sunny weather conditions. Initially, disinfestants with low surface tension spread out to provide 100% coverage and disinfestants with high surface tension beaded up to provide about 60% coverage when applied to hard smooth surfaces. Disinfestants applied to porous materials were quickly absorbed into the body of the material, such as wood and concrete. Even though disinfestants evaporated faster under hot sunny conditions than under cool cloudy conditions, coverage was reduced considerably in the first 2.5 min under most weather conditions and reduced to less than or equal to 50% coverage by 5 min. It is unknow how different evaporation rates affect efficacy of disinfestants, so that will be tested in subsequent research.

Technical Abstract: Drying rates of disinfestants commonly applied to horticultural plant production surfaces were evaluated under cool to hot weather and under laboratory conditions to characterize the range of drying times and how this relates to contact times specified on product labels. Drying rates of six disinfestants [isopropyl alcohol (IPA), two quaternary ammonium compounds (QACs), two peroxygen compounds (PXs), sodium hypochlorite (bleach)] and water were evaluated when applied to six substrate materials (concrete, galvanized metal, polypropylene ground fabric, polypropylene plastic sheet, pressure-treated pine, and twin-wall clear polycarbonate) based on the weather variables of solar radiation, temperature, and relative humidity. Differences were evident at the point of application. Disinfestants with low (IPA, both QACs and one PX) and high (bleach, one PX and water) surface tension provided approximately 100% and 60% coverage, respectively, when applied to horizontal, non-porous solid materials. Disinfestants applied to horizontal porous materials (concrete, fabric and wood) persisted on the surface for a mean of only 9 to 113 sec because solutions were actively drawn into the substrates internal structure. Disinfestants applied to vertical twin-wall greenhouse material flowed off, while retaining only a maximum beaded wetness coverage of 14%. A Bayesian analysis procedure was used to model drying effects of disinfestants correlated with substrate and weather variables based on posterior marginal and prediction trends. Generally, the fastest drying rate occurred in the first 2.5 min and approximately 50% of coverage was retained by 5 min. The evaporative process was variable with distinct interactions occurring between the experimental variables.