Avocado trees flourish in warm locations that include Florida, southern Texas, California and Hawaii. Certain diseases crop up in these areas that can cause the avocado's leaves to drop. Mites and root rot both contribute to fallen leaves. Knowing what causes these diseases to occur and figuring out how to prevent them ensures a healthy, fruit-bearing avocado tree.
Persea mites attack avocado trees mainly in California. These mites have eight legs and an oval shape. Certain mites, such as the avocado brown mite and six-spotted mite, can cause occasional damage to avocado trees. Mites are most active during the spring and summer months. These tiny insects grow to only 0.01 inches and their colouration is a mixture of green and yellow. Oftentimes, they have up to six dark spots on their abdomen.
Phytophthora root rot is a large contributing factor to most of the problems that avocado trees face. Rehabilitating an avocado with root rot is difficult once the tree is diseased. Root rot forms in locations where there is a lack of soil moisture and inadequate drainage for the dirt.
Avocado trees displaying signs of root rot will have shrunken foliage and dropped leaves. Tiny roots affected by root rot appear weak, breakable and black in colour. Affected avocado leaves curl into each other even when soil moisture levels are adequate. When mites feed on avocado trees, the leaves change over to a brown colour before dropping off. Webbed veins can show up on damaged leaves before they drop.
Natural methods often control the spider mite population because other mites and insects are predators.The lady beetle (Stethorus picipes) is a mite enemy along with six-spotted thripes (Scolothrips sexmaculatus) that live on some avocado trees. These predators help reduce the population of spider mites that are harmful to avocado trees.
Other methods of eliminating problematic spider mites include spraying the affected areas on the avocado tree with miticide. Removing as much dirt road dust around the trees as possible will help reduce the amount of mites on the avocado. This is achieved by oiling or paving the roads leading to, and those in between, the orchards. Another way to tame road dust entails watering the dirt down with a water truck. Misting home-grown avocado trees reduces your chances of having issues with mites.
Start at the nursery to reduce the chances of the avocado tree becoming infected by root rot. Root rot tends to spread in plant and tree nursery stores. Select disease-resistant avocados. Use nitrogen in moderation to help prevent root rot. However, do not over-spray with fertiliser. Animal manure is not good for avocado trees because it contains ammonia and salt. The avocado roots are sensitive to ammonia and salt.