Managing Leaf Health for Better Avocado Production

Healthy green avocado leaves are critical for getting the best yields from avocado trees, and at flowering, because the leaves convert sunlight into sugars that support the production of fruit on the trees. Avocado leaves should be green, of good size, well distributed around the tree (in order to best “capture” the sunlight) and layered so as to shade the avocado fruit and branches from the damaging effects of the sun.

While it is likely that avocado leaves can tolerate some damage before their ability to produce sugars is harmed, the key to high avocado yields is having undamaged avocado leaves. In California, avocado leaves are often damaged by pests like Persea mites, or by toxic elements such as chlorides.

Monitoring avocado leaf health

Fortunately, it is easy for an avocado grower to assess the health and quality of the avocado leaves. An obvious sign of trouble is leaves that are yellow or yellow-green. The human eye is very good at picking up slight changes in the color green and with practice a grower can tell when leaves begin to turn from a dark green color to a more yellow-green color.

The yellowing of leaves is due to the breakdown of chlorophyll pigment. If detected early enough, the yellowing can be reversed with carefully calculated applications of fertilizer. Fertilizer applications at the right time and amount can supply leaves with minerals that may be lacking and can also be used to reduce the yellowing that may occur during winter and in spring when the trees are in bloom.

Avocado leaf damage from pests

More difficult to manage is avocado leaf damage caused by pests. This damage generally cannot be reversed because the pests destroy leaf cells and can cause leaves to fall. While it is not known for certain how much pest damage is needed before leaf function is reduced, it is reasonable to assume the greater the damage to the leaf, the lower the amount of sugars the leaf will produce.

To minimize avocado leaf damage, pests must be minimized. Monitoring pest populations should be a routine part of California avocado grove cultural management. This ensures that changes in pest levels are detected early and timely control measures can be applied. In particular, a build-up of brown mite and Persea mite populations can quickly result in badly damaged leaves.

Signs of a stressed avocado tree

Small leaves and too few leaves on an avocado tree indicates the avocado tree is under stress.

Small leaves:

• suggest poor root health and low nutrient availability
• can result in smaller crops and smaller fruit
• may be an indication of root disease and trunk or branch cankers that need to be treated
• may indicate a reduced root system and poor nutrient uptake caused by poor drainage and/or soil that is too wet

If the limbs of neighboring trees can easily be seen through where the canopy is thickest, corrective action may be needed to increase the number of leaves on the tree. Too few leaves can lead to sunburn of the avocado fruit and branches that can, in turn, lead to branch cankers and reduces avocado production of fruit from the tree.