Gordon Johnson, Extension Vegetable & Fruit Specialist;gcjohn@udel.edu
Particle films are reflective mineral based materials that are sprayed on crops. Available particle films are Kaolin based (a type of clay) and include products such as Surround and Screen Duo. Particle films reflect both infrared (IR) and ultraviolet (UV) light. From a horticultural perspective, they have the potential to reduce heat stress and water stress on the plant and to reduce sunburn on fruit. Particle films have been shown to improve fruit quality and color in some crops. In tree fruits, they have been shown to increase photosynthesis. Particle films also have been shown to reduce damage by certain insects and diseases on tree fruits.
While particle films have gained use in tree fruits, their usefulness in vegetables is still unclear. Research in a number of states has shown reduced fruit disorders such as sunburn in peppers and white tissue in tomatoes when applied over those crops. Watermelon growers have used clay products for many years to reduce sunburn in that crop in southern states. However, there are some drawbacks to their use. If used for sunburn protection on fruits, there is added cost to wash the material off at harvest. Where overhead irrigation is used, or during rainy weather, the material can be partially washed off of plants, reducing effectiveness and requiring additional applications.
Research on the use of these products is ongoing at the University of Delaware and the University of Maryland. In Delaware trials, focus has been on reducing stress in watermelons and lima beans and results have been mixed so far. In 2012 (a hot year), there was some increase in early yield in watermelons; in 2013 (a cool year) there was a decrease in overall yield of watermelons (3 weekly applications were made starting at mid fruit set). In lima beans, there was an increase in yield in 2012 when combined with other stress reducing products but not alone; in 2013 there was no effect (one application was made at first flowering). Maryland trials have shown improvements in tomato and pepper fruit quality with the use of particle films.
More research is needed to determine the benefits of particle films for vegetable crops in our region and the best way to use them (timing, rates, and application number).