My Avocado Has Lost Its Leaves

Excess Nitrogen

• An excessive application of nitrogen to an avocado tree can cause the tree to lose leaves. A high level of nitrogen is also likely to cause leaf burn and root damage with potential death of the tree. Though nitrogen is regularly required by the tree, the recommended rate is only a small amount in relation to the tree size, once a year in spring. A young avocado tree needs only a few ounces per year, advises Dennis R. Pittenger in "California Master Gardener Handbook."

Armillaria Root Rot

• Armillaria root rot disease is caused by the soil-borne Armillaria mellea fungus that infects avocado trees through the roots. Also commonly referred to as shoestring fungus, honey mushroom and oak root fungus, the infection causes gradual decline in overall tree health, yellow foliage and defoliation from either certain parts of or the entire tree. Severely infected trees often wilt and die within a short period of time. Among the disease symptoms is the presence of black, threadlike growth resembling feeder roots growing in the soil around the tree base.

Avocado Thrips

• Avocado thrips are extremely small, 1/20-inch long, slender flying pests with fringed wings, three red spots on the head and light yellow abdomen. The thrips larvae is light yellow in color. The insects feed inside the curled leaves and buds of infested trees. This leads to gradual distortion and discoloration of foliage followed by leaf drop. Cases of severe infestation also cause stunted growth and scarred fruit surface.

Avocado Brown Mites

• Avocado brown mites are 0.01 to 0.3 inch long, eight legged, dark brown anthropods. The pests are more common in avocado trees growing along the coast between July and September. The mites feed on the upper foliage surfaces, causing discoloration of leaves and eventual defoliation. The insects are intolerant of high temperatures of 90 to 95 degrees Fahrenheit and the cold fall and winter weather.