Research Terms
This colored clay protects crops by effectively changing the reflectance of the foliage, camouflaging it to prevent insect attacks. Huanglongbing disease, or citrus greening, is the biggest threat to the $9.3 billion Florida citrus industry. The disease is present throughout Florida’s citrus growing regions but is also found in Texas, California, and Arizona. Diaphorina citri (D. citr) is the insect responsible for the transmission of Huanglongbing disease. These insects are strongly responsive to visual host plant cues. Recent laboratory studies have discovered that D. citri are most attracted to reflected yellow and green light. Available technologies to manage pests and diseases in agricultural crops mainly consist of chemical pesticides, which may be harmful to the environment and non-target species. Researchers at the University of Florida have developed colored kaolin clays that alter the spectral reflectance of coated citrus leaves, preventing D. citri from identifying citrus leaves as a food source. In general, colored clays offer an environmentally friendly option for pest control. Colored clay also can be used in the paper, paint, and cosmetic industries.
Crop protection through optical deterrence of insects
The purpose of the colored clays is to interfere with the visual cues of citrus plants, preventing D. citri from identifying and attacking them. Colored clay coatings change the reflectance of the foliage depending on the spectral profile of the dye used. Dyes having absorbance/reflectance in UV – visible – near infrared range are particularly useful for this application. Combining kaolin clay particles with surfactants and dyes produces the colored clays. The kaolin clay particles are negatively charged on their surface and positively charged on the edges. Positively charged surfactants and polymers added to the kaolin clay particles change the surface charge. After removing excess surfactant, researchers add negatively charged dyes, which are absorbed into the clay. As a result, the dye is non-covalently attached to the surface of the clay particles. The leaching of dye from the clay is minimized by adjusting the dye to surfactant ratio. Researchers investigated the effect of color by examining the number of D. citri found on plants coated with different color kaolin clays, as compared to an untreated citrus plant. Additionally, polymer adjuvants coated on top of the colored clay increase the longevity of the clay when exposed to rainfall.
These colored particle films coat citrus plants to repel insect pests and improve water-use efficiency, protecting crops from citrus greening and increasing growth in dry conditions. Huanglongbing disease, commonly known as citrus greening, threatens Florida’s $9.3 billion citrus industry, as well as those in California, Texas, and Arizona. Citrus greening spreads through the Asian citrus psyllid, an insect that feeds on citrus leaves and identifies them by their reflected yellow and green light. Using insecticides to reduce the population of these pests can be harmful to the environment and non-target species. Researchers at the University of Florida have developed colored particle films that alter the visual appearance of citrus foliage, preventing Asian citrus psyllids from targeting them for food. The red-dyed kaolin coatings more effectively reduce insect populations than available white kaolin coatings and greatly increase water-use efficiency of the crop to improve growth during dry seasons.
Citrus crop particle film that protects against citrus greening and improves growth in dry conditions and may have similar effects in other crop systems
These colored kaolin films physically and optically repel insects like the Asian citrus psyllid. The red-dyed films alter the reflectance of citrus leaves, which inhibits insect populations’ ability to target the crop as food. Together with physically impairing feeding, movement, and egg placement, this reduces the spread of the citrus greening disease. To prepare the colored kaolin, researchers dissolve dye into a solution of water and cetylpyridinium chloride, and then incorporate it into a kaolin mixture for approximately two hours. Adjusting the dye-to-surfactant ratio reduces any potential leaching of the dye.