How To Keep Kaolin on Your Trees Through the Rain

By Gregory Vincent and Rashmi Kumari

Florida summers come with intense sunlight, high temperatures and frequent rain. Just as people use sunscreen to protect exposed skin from intense sunlight, plants can benefit from a protective coating on exposed leaf and fruit surfaces. One way to provide this protection is by spraying a kaolin clay particle film on the tree. Although rain can wash off kaolin if applied by itself, wax-based products can make your application stick through months of rainfall.

IMPROVE TREE HEALTH

Kaolin can improve the health of HLB-affected trees. Kaolin is a naturally occurring white clay that forms a thin coating on leaf and fruit surfaces when mixed with water and sprayed on the canopy. The white coating reflects some of the incoming sunlight, helping reduce heat load on the tree. In citrus, kaolin can keep leaves about 7-10°F cooler during hot conditions, reduce water loss and help protect exposed fruit from sunburn.

HLB-infected trees have fewer functional roots, which makes it harder for the tree to keep up with water demand. Keeping the canopy cooler with kaolin can help trees cope with these stressful summer conditions. The white coating can also make it difficult for psyllids to recognize and settle on the tree.

However, just like sunscreen needs to remain on our skin to provide protection, kaolin also needs to remain on the leaf surface to provide its benefits. Two to three inches of rain can wash kaolin from the canopy and, in Florida, the hottest months are also some of the rainiest. A few heavy rain events can reduce the kaolin coverage.

STICK TO LEAVES

One way to overcome this problem is to use products that help kaolin stick to the leaves. Our  research has found that mixing kaolin with Raynox, a carnauba wax-based product, dramatically improves its rainfastness. The wax helps the kaolin particles adhere to the leaf surface. Once the mixture has dried on the leaf surface, there is very little rain wash-off, allowing the protective film to last longer.

Because of this effect, to avoid having too much kaolin on the leaves, we recommend monitoring for new growth on citrus trees if using a mixture with Raynox. Only reapply when there are new leaves. Spraying kaolin after each flush has become fully expanded helps bring the new leaves under the same protective coating as the rest of the canopy.

Ongoing research on Hamlin sweet orange has shown that applying 12 pounds of Kaolin + 12 pounds of Raynox in 100 gallons of water per acre after the expansion of each major flush resulted in higher yield and Brix and lower fruit drop. That research was conducted at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center (CREC) in Lake Alfred.

Good coverage that stays on the tree can help growers get the most out of kaolin applications. Click here for more detailed information; see the UF/IFAS particle film page. 

Christoper Vincent is an associate professor of horticultural sciences at the UF/IFAS CREC in Lake Alfred. Rashmi Kumari is a PhD student at CREC.