It takes years to grow a healthy fruiting avocado tree. Longer if things go wrong. Finding the solutions to possible problems is best done before leaves start shedding at astonishing rates.
The more leaves drop, the more foliage grows. The longer the leaf drop cycle continues, the less energy the plant puts into fruiting.
One common problem with Avocado trees is brown spots on their leaves.
These brown spots are a clear sign that something is wrong with your Avocado plant.
That said, let’s find out what that is and what you can do about it!
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What Causes Brown Spots on Avocado Leaves?
Brown spots on avocado leaves almost always indicate a pest infestation or fungus infection. The shape, size and texture can tell you a lot. Lighter tan-brown spots can be caused by one of two mite species – The Persea Mite, or the Six-Spotted Mite. The avocado lacy bug causes mottled browning. Lighter yellow-to-brown spots scattered across the leaf indicate a fungus infection of either anthracnose, algal leaf drop, or scabbing.
The Two Mites that Leave Brown Spots on the Leaves of Avocados
1. Persea Mite
The Persea mite may as well be called the Mite of California. It’s rare to find it anywhere else.
Like most mites, these feed on the underside of leaves. But they leave behind a giveaway silvery webbing that’s denser than any other mites webbing.
The brown spots on avocado leaves caused by the Persea mite are darker on the underside, eventually becoming so darkened that they’re visible on the topside of the leaf.
The spots are always small circles (as opposed to larger blotching) and are mostly concentrated on the veins of the leaf.
A high-pressure spray of water that’s forceful enough to blast the mites off and disturb their webbing is the simplest pest control method. The webbing is the most important part because that’s what protects them from natural predators.
Remove their protective webbing and let nature run its course.
2. The Six-Spotted Mite
The six-spotted mite feeds similar to the Persea mite. On the underside of leaves. But rather than small brown dots along the veins of the leaf, the six-spotted mite leaves larger brown blotches in its wake.
The blotching is usually dark brown but it can take a purplish color. However, the most peculiar change to the damage is the irregular size and shape of the brown patches.
The feeding pattern is the same. Along the veins on the underside of leaves. The brown spots caused by six-spotted mites are bigger and less circular.
Brown mites are attracted to avocados too, but they don’t leave brown spots. They cause bronzing on the entire leaf.
The Avocado Lace Bug
The avocado lace bug gets its common name from its lacy appearance. In small numbers, they don’t do much harm, but they do feed on the juices in the leaves.
In high enough numbers, lace bugs can create a mottled yellow-to-brown spotting effect on the leaves they’re feeding on.
Not just because they’re sucking juices out the leaves, but also the dark, brown-to-black fecal droppings they leave across the underside of leaves.
Similar to mite infestations, the safest method to get rid of them is to blast them with water at high pressure.
It should be noted that the Avocado lace bug lays eggs in the leaves so repeated treatments will be needed.
Fungal Diseases that Cause Brown Spots on Avocado Leaves
Algal Leaf Spot
The most susceptible parts to algal leaf spot on avocado trees are the leaves on low hanging branches. Particularly, the bottom 2-feet.
The spots are raised, look like spots of rust and can be orange to light brown. Scrape the surface, it’ll be dark gray underneath.
The leaf spot it leaves just looks terrible. It doesn’t harm the plant, and pruning them off won’t harm it either.
Avocado Scabbing
Avocado scabbing is rare, unless you’re growing them outdoors in Florida. The Lula cultivar is the most susceptible. Pollock, Fuchs, and Waldin cultivars are the least susceptible to scabbing.
Like algal leaf spot though, scabbing doesn’t harm the plant. It just looks unsightly, presenting as small brown spots on the foliage, and bigger dark patches if it’s on the fruit.
Anthracnose
An early sign of an anthracnose infection is yellow to brown spots on avocado leaves and it is a foliage killer. Given time, the brown spots will be accompanied with brown leaf tips, the leaves die and then fall off.
If you’re experiencing higher than usual leaf drop, look at the leaves on the ground to see if there’s brown spots and brown leaf tips. The spots appear first, then spread and the leaf eventually falls off, if it doesn’t die before that.
Pruning back the lower hanging branches and twigs to at least 2-feet above ground level increases air circulation, lowering the humidity levels.
Rincon, Fuerte and Wartz cultivars are more prone to anthracnose. The Hass avocado is more susceptible.
Brown spots on Avacado FAQ’s
How do I prevent brown spots on avocado leaves?
The most effective method is to keep avocado trees pruned to 2-feet above ground level. Certain fungal infections such as algal leaf spot can be treated with a copper fungicide, but that’s only going to prevent new spots from developing.
Existing spots caused by most fungal infections are better pruned. Fungicides only prevent new spots developing. They won’t make existing spots vanish.
Can Pesticides or Insecticides be Used to Control Mites on Avocados?
Yes, but you’ll also kill beneficial insects. Insecticidal soaps and other pesticides are best left to use as a last resort.
If you can’t get the insect population under control with water alone, you could try spraying the leaves with a pesticide. However, be careful not to overdo it.
Too much pesticides, even natural insecticidal soaps, can weaken a plant, leaving it more susceptible to other types of infections, be it fungus infections, bacterial infections, or pest infestations.
It is recommended to spray with water alone, at a high pressure, to blast mites off the leaves, and get rid of the webbing.
With the webbing gone, beneficial insects such as ladybugs can take care of a mite infestation naturally, without feeding on your plant’s foliage.
Daniel has been a plant enthusiast for over 20 years. He owns hundreds of houseplants and prepares for the chili growing seasons yearly with great anticipation. His favorite plants are plant species in the Araceae family, such as Monstera, Philodendron, and Anthurium. He also loves gardening and is growing hot peppers, tomatoes, and many more vegetables.