Tips of the leaves turn brown, which may indicate problems occurring in the root zone. Fertilizer salts, nematodes, excessive water or lack of nutrients may cause these symptoms. Root rot fungi may also cause similar symptoms. Insects Thrips are the most common insect affecting avocados. Thrips affect the fruits and leaves by turning them silvery-brown in color.
Mites have similar effects, except they turn leaves and fruits rusty-brown.
Other insects which attack avocados are scales, beetles, fruit flies, and, occasionally, wood boring beetles, such as the black twig borer. Most of these insects can be controlled through the use of malathion. When using pesticides, always read the label and follow directions carefully. Flower Behavior Almost all of the avocado varieties are classified in two groups with reference to the normal time and sequence of the flowers opening and closing. The same flowers open the next day in the P.M. and shed pollen while stigmas are no longer receptive.