15 Common Avocado Tree Diseases and Problems (With Proven Fixes)

An avocado tree is a long-term investment. It can take years to bear a good crop. So it hurts when a tree starts to yellow, drop leaves or lose its fruit.

I have met many growers who only noticed a problem when half the canopy was already thin. By then, treatment is harder. Early recognition makes the difference between a quick fix and a lost tree.

This guide explains 15 common avocado tree diseases and problems. For each one, you will learn the symptoms, the cause and the practical steps to take. 

Many avocado problems share one root cause: stress from water, soil or pests. Healthy trees resist most threats. Weak trees invite them.

Soil-Borne and Vascular Diseases

1. Phytophthora Root Rot

Phytophthora root rot is the most serious avocado disease. University of California researchers describe it as the most serious and important disease of avocado worldwide. It is caused by Phytophthora cinnamomi, a water mold that lives in soil.

Look for small, pale or yellowing leaves with brown tips. The canopy turns thin and new growth is weak. Feeder roots turn dark, brittle and black. Eventually, limbs die back and the whole tree may collapse.

The pathogen is hard to remove once it settles in. It has over 1,000 hosts, and it thrives where soil stays wet and drains poorly. Moving contaminated soil, shoes, tools or nursery plants spreads it.

Water management is the first defense. UC IPM calls careful irrigation the single most critical practice for prevention and recovery. Plant on mounds or slopes, use certified disease-free trees and apply mulch. UC specialists also note that phosphonate treatments help trees tolerate infection but cannot eradicate it, so ongoing care is needed.

2. Phytophthora Trunk Canker and Crown Rot

This disease attacks higher up the tree. Another Phytophthora species infects the root crown and lower trunk. UC researchers rank it second only to root rot in severity.

The most obvious sign is a dark, weeping patch on the lower trunk. A reddish-brown liquid may seep out and dry into white powder. Under the bark, the tissue looks brown and dead.

Symptoms above ground resemble root rot. The leaves yellow and the canopy thins. In California, both diseases are increasingly found together, so a tree can suffer a double attack.

Prevention is about protecting the trunk. Do not wound the bark with mowers or string trimmers. Keep irrigation water off the trunk base. Where disease has been common, plant more than one rootstock type, since tolerance differs between them.

3. Laurel Wilt

Laurel wilt is a deadly vascular disease. It is carried by the redbay ambrosia beetle, which bores into the wood and brings a fungus with it. The fungus blocks the tree’s water channels.

The beetle arrived in the United States in 2002, hidden in wood packing material from Asia. University of Florida scientists link the disease to the death of over 120,000 commercial avocado trees in Florida. It has now been found in all of Florida’s 67 counties.

Symptoms are sudden. Leaves wilt, turn brown and stay attached to the dying branches. Tiny sawdust “toothpicks” may stick out of the bark. Death can come fast, with four to eight weeks from infection to tree death.

There is no easy cure. Do not move firewood or infested wood from one area to another. Remove and chip or burn dead trees quickly. Commercial growers can use prophylactic fungicide injections and beetle monitoring. Home growers should contact their local extension office for advice.

4. Avocado Sunblotch

Sunblotch is caused by a viroid, a tiny piece of genetic material that infects plant cells. It is often called the silent disease. Infected trees may look normal for years.

UF/IFAS experts warn that the viroid can cut yields by as much as 80%. It was first reported in Florida in 1941. Fruit may show yellow, red or white sunken streaks and an odd shape. Twigs may show yellow or red streaking.

The disease spreads mainly through infected budwood and seed. It can also pass on pruning and grafting tools. There is no treatment once a tree is infected.

Prevention is therefore everything. Use tested, certified budwood and never take seed or cuttings from a tree with sunblotch symptoms. UF/IFAS advises sanitizing pruning and grafting tools between cuts. Infected home trees should be tested and, if positive, removed.

ALSO READ: 10 Cold Hardy Avocado Trees (Identification, With Growing Details)

Leaf, Fruit and Skin Diseases

5. Anthracnose

Anthracnose is the best-known fruit disease of avocado. It is caused by Colletotrichum gloeosporioides. The fungus waits quietly in young fruit and shows itself as the fruit ripens.

You will see dark, sunken, circular spots on the skin. Inside, the flesh turns brown and bitter. Infected fruit may rot quickly after harvest.

Anthracnose is a weak pathogen. University of Florida sources explain that it needs entry points, which may be created by scab or Cercospora spot. Bruises and cuts from handling help it, too.

So the best control is to manage the other diseases first. Handle fruit gently, harvest carefully and discard any fruit that shows spots. Preventive copper-based sprays are often used, timed before infection. Always follow your local extension advice and the label.

6. Cercospora Spot

Cercospora spot is caused by the fungus Cercospora purpurea. It marks both leaves and fruit. The spots are small, angular and dark brown, and they often have a yellow halo.

On fruit, the spots can join into rough patches. This hurts the fruit’s appearance and opens a door for anthracnose. In wet, warm climates, the disease is a regular visitor.

University of Florida resources suggest starting a preventive spray program around May 1 and continuing until harvest where Cercospora is a problem. The exact timing depends on your climate, so check locally.

Cultural practices matter too. Prune the canopy for airflow and clear fallen leaves. Avoid overhead irrigation that keeps the foliage wet. I always advise growers to scout in early summer, since catching the first spots saves a lot of work.

7. Avocado Scab

Avocado scab is caused by Sphaceloma perseae. It attacks young, soft tissue. You will see rough, raised, corky brown scabs on leaves, twigs and fruit.

Severe scab can distort fruit and leave ugly scars. The fruit is still edible, but it may not sell well. Heavy early infection can also cause small fruit to fall.

Some varieties suffer more than others. University of Florida extension notes that the ‘Lula’ variety is very susceptible and is not recommended for home landscapes where scab is common. Choosing a resistant variety is the cheapest fix.

Treatment works best if applied before infection, when new growth is just emerging. The fungus likes cool, wet weather. Thorough spray coverage of all young tissue is needed. Remove infected twigs and leaves where possible.

8. Algal Leaf Spot

Algal spot sounds odd, but the culprit really is an alga. It is called Cephaleuros virescens. It forms raised, rusty-orange or green velvety patches on leaves, twigs and sometimes fruit.

University of Hawaii and University of Florida sources list algal spot as a common avocado problem in humid areas. On a healthy tree, it causes little harm. But heavy infection can weaken a stressed tree and mark the fruit.

The alga loves shade, humidity and wet leaves. Dense canopies and poor airflow make it worse. Weak trees suffer the most.

Pruning is the best remedy. Thin the canopy so the sun can dry the leaves. Keep the tree well fed and watered. Copper sprays can help in severe cases, but better care usually solves the problem.

9. Stem-End Rot

Stem-end rot is a post-harvest disease. A dark, soft area starts at the stem end of the fruit and spreads inward. The flesh turns brown and mushy, often with an off smell.

University of Florida sources link it to fungi such as Diplodia. These fungi live on dead twigs and bark. They enter the fruit through the cut stem, then wait until the fruit ripens.

Orchard hygiene prevents most of it. Remove dead wood, keep the canopy open and harvest with clean tools. Do not pull fruit off roughly. Leave a short stem button if possible.

After harvest, keep fruit cool and avoid bruising. Do not store damaged fruit with good fruit. Check ripening avocados every day. One rotting fruit can quickly spoil the rest.

ALSO READ: 25 Types of Avocado Trees (Identification, With Pictures)

Insect and Mite Pests

10. Persea Mite

The persea mite is a tiny sap-feeding mite. It lives on the underside of leaves. It is native to Mexico and later reached other regions, including California in 1990.

Look for round brown or yellow spots on the leaf’s underside, covered with fine webbing. A hand lens helps. Heavy attacks cause leaf drop and sunburn on exposed fruit.

University researchers have studied biological control, using predatory mites that eat the pest. In California, a common practice is applying abamectin with horticultural oil in summer. Check what is legal in your area before using any product.

You can help natural enemies by avoiding broad-spectrum sprays. Keep trees well watered, because dusty, stressed trees often have worse mite outbreaks. Scout regularly from late spring.

11. Avocado Thrips

Avocado thrips are slender insects, so small you need a lens to see them. They feed on young leaves and on the skin of small fruit. Their feeding leaves scarring and bronzing.

On leaves, thrips cause irregular brown marks. This damage is mostly cosmetic. On fruit, it leaves brown, corky scars that downgrade fruit for market. Heavy damage can also reduce fruit size.

UC IPM notes that thrips and persea mite were carelessly introduced into California in the 1990s. Before that, insects only occasionally damaged avocado fruit and leaves. Exotic pests are a real risk, which is why plant imports are regulated.

Monitor young fruit during the early fruit set stage. That is when thrips damage matters most. Predatory insects help control them. If sprays are needed, time them early and follow the label to protect pollinators.

12. Avocado Lace Bug

The avocado lace bug is a small sap-sucking insect. It lives in groups on the underside of leaves. The top side shows pale, stippled or bleached spots, as if mites were feeding.

The giveaway is the black, tar-like excrement on the leaf underside. Heavy infestations can cause the tree to lose its leaves. A thin tree then suffers sunburn and poor yields.

UC pest guidelines report that numbers increase during summer. In California, severe damage occurs on some untreated trees. Low populations are harmless, so do not rush to spray.

Check the underside of leaves before acting. Identify the pest correctly, since mites, thrips and salt burn can look similar. Natural enemies such as lacewings and lady beetles help. If numbers climb, soil-applied or contact insecticides may be needed, as local guidance advises.

13. Scale Insects, Mealybugs and Whiteflies

These sap-feeding insects hide on leaves, twigs and fruit. Scales look like tiny bumps. Mealybugs look like small cotton tufts. Whiteflies fly up in a cloud when you shake a branch.

They weaken trees and leave sticky honeydew. A black sooty mold often grows on the honeydew. UC IPM adds a useful point: infestations of these insects indicate that biological control has been disrupted.

In other words, the pest outbreak is often a symptom. Broad-spectrum insecticides, dust and ants can kill the natural enemies that normally keep these insects down. Fix the cause, not just the symptom.

Control the ants that protect them, using trunk barriers. Reduce dust on roads near the trees. Use horticultural oils or soaps for light infestations. Protect parasitic wasps and predators wherever possible.

Environmental and Cultural Problems

14. Salt Burn and Leaf Tip Burn

Not every leaf problem is a disease. Avocados are very sensitive to salt. Salty irrigation water or too much fertilizer can burn the leaf tips and margins.

The damage starts as brown, dry tips on older leaves. It then creeps along the leaf edges. UC IPM explains that salt damage occurs mainly at the tips and margins of leaves. Lace bug damage, by contrast, shows up between the veins.

Salt stress also makes root rot worse. UC IPM notes that avocado roots are sensitive to ammonia and salts. Heavy animal manure is therefore risky.

Test your irrigation water and soil. Leach salts by giving a deep, occasional watering, if drainage is good. Mulch helps reduce salt buildup near the surface. Use moderate amounts of nitrogen fertilizer, not heavy doses.

15. Sunburn, Heat and Frost Damage

Avocado fruit and bark are thin-skinned and sensitive. Strong sun can scorch exposed fruit and branches. Frost can kill young shoots and even whole young trees.

Sunburn causes brown, sunken patches on the sun-facing side of fruit. On trunks and limbs, bark can crack. Trees that have lost leaves to pests or disease suffer the most, since the canopy no longer shades the fruit.

Cold damage turns young leaves black and shoots limp. Young trees are most vulnerable in their first winters. A mature, healthy canopy offers the best protection.

Protect trunks of young trees with white tree paint or wraps. Mulch the base but keep it away from the trunk. Plant in a sheltered spot, away from cold air pockets. Keep the canopy healthy, because a leafy tree shields its own fruit.

ALSO READ: 25 Fruit Trees That Grow in Shade (With Details Explained)

How to Prevent Avocado Tree Problems

Most avocado problems can be avoided with a few steady habits. Prevention costs far less than rescue.

• Buy certified trees. Choose disease-free, tested nursery stock on a suitable rootstock.
• Get drainage right. Plant on mounds if your soil is heavy. Never let water pool around the trunk.
• Water carefully. Deep, infrequent watering works better than daily sprinkles.
• Mulch, but not against the trunk. Mulch supports helpful soil life.
• Sanitize tools. Clean pruners and grafting knives between trees.
• Scout weekly. Check leaf undersides, fruit and bark during the growing season.
• Avoid moving wood. Firewood and prunings can carry laurel wilt beetles and pathogens.

Final Thoughts

Avocado trees are rewarding but sensitive. The 15 problems above explain most of the damage that growers see. Root rot, laurel wilt and sunblotch are the most serious, because they can kill a tree or cripple a crop.

The good news is that careful management works. Healthy soil, good drainage and clean practices protect trees from most threats. I find that the growers with the best crops are simply the ones who look at their trees most often.

If you are unsure what you are seeing, contact your local extension office. A quick diagnosis can save a season. With patience and attention, your avocado trees can stay productive for many years.

References

1. University of California Statewide IPM Program (UC ANR). Avocado Pest Management Guidelines: Phytophthora Root Rot: https://ipm.ucanr.edu/agriculture/avocado/phytophthora-root-rot/
2. University of California Statewide IPM Program (UC ANR). Avocado Pest Management Guidelines: Phytophthora Trunk Canker and Crown Rot: https://ipm.ucanr.edu/PMG/r8100511.html
3. University of California Statewide IPM Program (UC ANR). Avocado Root Rot, or Phytophthora Root Rot (home and landscape): https://ipm.ucanr.edu/PMG/GARDEN/FRUIT/DISEASE/avocadortrot.html
4. University of Florida IFAS Extension. Recommendations for Control and Mitigation of Laurel Wilt and Ambrosia Beetle Vectors in Commercial Avocado Groves in Florida (HS1360): https://edis.ifas.ufl.edu/publication/HS1360/pdf
5. University of Florida IFAS Tropical Research and Education Center. Avocado Sunblotch Viroid: https://trec.ifas.ufl.edu/people/romina-gazis/avocado-sunblotch-viroid/
6. University of California Statewide IPM Program (UC ANR). Avocado Lace Bug (Pest Notes): https://ipm.ucanr.edu/home-and-landscape/avocado-lace-bug/
7. USDA National Institute of Food and Agriculture. Biological Control and Invasion Ecology of Arthropod Pests Attacking Avocado: https://portal.nifa.usda.gov/web/crisprojectpages/0178688-biological-control-and-invasion-ecology-of-arthropod-pests-attacking-avocado.html