Guacamole lovers are in luck! The avocado industry is booming, and most consumers can find this oily fruit in grocery stores throughout the year.
In California, locally-grown avocados are available during a smaller window. Southern areas like San Diego typically start harvesting as early as January or February, while regions like the Central Valley begin their harvest during the spring. No matter where these California avocados are grown, the crop is subject to a number of diseases that impact as many as 30% of all avocado trees.
If you’re looking to maintain a healthy crop, it’s important to know the diseases that might halt your progress. Below, we’ll take a look at some of the most common issues facing avocado trees, as well as the steps you can take to protect your crops during the upcoming season.
Anthracnose
Anthracnose is a fungal disease characterized by brown and black spots on the leaves and fruit. In California, Anthracnose spores cause the most damage during periods of high humidity, heavy rain, and mild winter temperatures. Once the fruit is infected and begins to ripen, temperatures above 75°F can speed up the development of anthracnose. Once temperatures dip below 59°F, the development of the disease slows down.
Signs of infection include fruit dropping off too early without properly ripening, yellowed leaves, lesions, stunted growth, and dieback of branches or leaves. Anthracnose can cause tree death within two years if left untreated, so it’s important to take the following steps:
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- Follow sanitation practices such as removing diseased fruit immediately and pruning all dead limbs and twigs.
- Remove fallen leaves from soil and plants, so they can’t rot where insects like thrips can breed.
- In serious cases, using copper or other fungicide applications to help prevent spread and infection.
Armillaria Root Rot
Armillaria is a fungus that rots the avocado roots, essentially killing the plant from the bottom up. By the time symptoms are noticeable above ground, the disease is often already well-established beneath the soil. The first visible signs of infection included yellowing leaves, wilting foliage, and leaf drop. Infected trees often have sunken cankers in the trunk, which may be white or brown and cracked.
Spacing is important! This fungus is most commonly found in avocado trees that have been planted too closely together. It spreads quickly through avocado roots that are near one another, creating a dense mat of fungus. Although there is no cure, it can be treated with pesticides like methyl bromide if caught early enough. Some other preventative measures include:
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- Planting avocados in groups of ten or fewer trees, so they have plenty of room. Avoid overcrowding, which will cause root competition for nutrients. This also helps prevent spreading the disease via close proximity to nearby trees.
- Pruning avocado tree roots after planting or during the first year.
- Fungal root washes using a water-based fungicide, which will help prevent avocado tree issues like infections before they start.
- Cultivating in a well-drained site with plenty of organic material, which will help reduce the competition for nutrients and ease soil compaction.
Avocado Black Streak
Avocado Black Streak Disease, or BSD, is a bacterial disease that causes black streaks to appear on the trunks and limbs of avocado trees. Bacterial diseases like BSD are most severe when the weather is hot and humid with little air movement, which provides an environment for bacteria to grow at an uncontrolled rate.
Symptoms of this disease typically appear in late summer or early fall. Once BSD occurs, the avocado tree will grow a tuft of brown, felt-like fuzz on the black streaks or cavities in its woody outer layer. The best way to prevent this disease is by planting new trees away from old ones, to ensure the trees will have plenty of space and airflow. Treatment involves removing the diseased parts of a tree and keeping it well-watered during dry periods.
Verticillium Wilt
Once an avocado tree becomes infected with Verticillium Wilt, its vascular system becomes clogged up with fungal cells, which begin to grow and spread throughout the tree, causing it to die slowly. Signs of this disease include yellowing leaves, drooping branches, and scorched leaf tips. Verticillium Wilt is most often spread by pruning tools that have been used on infected plant material, or by soil to which the fungus is clinging.
The best way to avoid this avocado tree issue is to sterilize those tools after use. It can also be prevented by planting new avocado trees at least 75 feet away from trees that may have been exposed. There are no known preventative measures for Verticillium Wilt, the disease can be treated with fungicides like benomyl, azoxystrobin, captan, thiram, carbendazim, and trifloxystrobin.
Phytophthora Canker
One of the most common avocado diseases, Phytophthora Canker attacks avocado trees by infecting shoots and leaves. It is spread by spores from infected plants that land on healthy ones. Symptoms include dark lesions on leaf edges, browning, and the dying of leaf tips. Infested leaves eventually fall off the tree in a manner similar to wilting. To get rid of Phytophthora Canker, try the following:
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- Remove infected plants or plant parts, so spores cannot spread further.
- Cut back avocado trees and remove dying or dead branches.
- Burn infected plant material in a fire.
- Spray copper-based fungicides on the avocado tree’s leaves.
Dothiorella Canker
The Dothiorella Canker is an avocado disease that can be caused by many different factors, including bacterial infection, insect infestation, and invasion of an infectious plant fungus from soil and water contamination. This avocado tree problem starts as a small discoloration on the bark or branches, and it’s most notable during wet periods.
Symptoms start with small spots on the bark, which take on a darker color and spread until they cover most of the tree’s surface. The leaves may start to wilt or fall off before other symptoms are noticeable. There are no known cures for this condition, but there are ways to prevent its spread. A fungicide can be used to help control the infection, and you should also make sure that your tree’s roots are not in contact with any contaminated soil.
Get Help From Fruit Growers Supply
At Fruit Growers Supply, we know avocados. If you’re having trouble with your avocado trees or need to bulk up on supplies, take the time to contact us here. We’re here to help you increase those yields and get your trees into healthy shape.