Why Are My Avocado Leaves Turning Brown?

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Although avocado leaves turning brown is often an indication that something is wrong with your tree, it isn’t always a cause for alarm. Sometimes, brown avocado leaves can be quite benign.

How do you know when to worry?

Seeing a few brown avocado leaves on your tree is normal and shouldn’t trouble you. This could be due to high ambient temperatures or other processes that will resolve on their own.

The problem is often the number and pattern of leaf browning you see on your tree. A few avocado leaves turning brown won’t affect your fruit yield or harm your avocado tree, but having more than ten percent of brown leaves might. 

If many of your avocado leaves are turning brown or show similar leaf browning patterns, it’s a sign that your tree is experiencing high levels of stress. There are several reasons this could happen, and you’ll learn all about them in this article.

8 Reasons for Avocado Leaves Turning Brown

Avocados on tree with leaf starting to get brown spots
Avocados on tree with leaf starting to get brown spots

More often than not, brown avocado leaves are caused by lack of water or chloride salt buildup. However, other factors can also cause your leaves to turn brown.

1. There is Too Much Chloride Salt in Your Soil or Water

One of the most common reasons avocado leaves turn brown is that there is too much chloride salt in the soil. Chloride salt refers to sodium chloride (table salt), and it often gets into your soil from the water you use.

Chloride salt is naturally present in water, even in freshwater. If you live in places with naturally high chloride salt levels in the soil or get your irrigation water from rivers with fairly high salt content, this problem is even more pronounced.

You can check the water quality report applicable to where you live to see how high the chloride level in your water is. A salt content of more than 75 parts per million is often enough to stress your avocado tree and cause brown leaves.

But even if your salt content is much lower than 75 ppm, it can still cause salt to build up in your soil and turn your avocado leaves brown.

Why avocado leaves turn brown when chloride salt levels are high

When you water your avocado tree, the water goes into the soil and is absorbed by your tree’s roots. This water then travels up the tree trunk and branches to the leaves.

Avocado leaves naturally lose water when in the sun through a process called evapotranspiration. This process is similar to how humans sweat.

If this water has high levels of chloride salts, the salt stays behind while the water evaporates from the leaves. Repeated cycles of watering and evapotranspiration causes the chloride salt to accumulate in the leaves.

When the amount of chloride salt in the leaves reaches toxic levels, leaf tissues start dying. This process turns the leaves brown and usually begins at the tip of the leaves, where the salt buildup is highest.

This process can also happen if your salt level in your water isn’t high. The small chloride content in your water can build up in the soil around your roots overtime if you practice shallow watering.

What to do about chloride salt buildup 

The easiest way to solve this problem is to leach the soil. You can leach your soil by practicing deep watering, which involves watering your soil with more water than your plant needs every time.

The purpose of deep watering is to flush most of the salt buildup around your tree roots further down so the roots can’t absorb them. Using around 20 percent more water than normal and concentrating the water on the soil around your roots works well.

There’s one caveat to pay attention to.

Your solid must have good drainage for deep watering to work. If your soil isn’t well-drained, all that extra water will only accumulate around the root and cause root rot.

2. Your Avocado Tree isn’t Getting Enough Water

Avocado trees need plenty of water to grow well, but their sensitivity to water accumulation around their roots can make it difficult to know just how much to water these trees.

If you water your avocado tree infrequently or rely on rain to water trees planted outdoors, you’ll soon notice many of your avocado leaves turning brown and dying. The reason for this is simple.

We’ve talked about avocado trees losing water from their leaves by evapotranspiration. This is done to cool themselves, and the water they lose needs to be replenished by watering.

All living cells and tissues require water to function. If the water your avocado tree loses isn’t replaced on time, the leaves will start to turn brown as their cells and tissues die.

Leaf browning in response to lack of water begins around the margins of the leaves. This lack of water can also worsen the effects of chloride salt buildup on your tree’s leaves.

When the brown leaves on your avocado tree are caused by lack of water, the leaves often dry up and curl as they turn brown.

How to address this problem

You want to water your avocado tree, but you don’t want to do it too much. To strike the perfect balance, only water your tree when the top two to three inches of soil are dry.

You can check this by sticking your finger in the soil and feeling for moisture or pushing a wooden stick into the first few inches of soil.

If soil remains attached to the stick after pulling it out, it’s still moist and may not need watering. However, if the soil falls off the stick after removing it, it’s dry and needs watering.

When watering your soil, make sure to deeply water it so that the water reaches far below the soil surface. Stop once the soil surface seems fairly saturated or feels like a squeezed-out sponge in your hands.

Make sure to check your tree frequently so that it doesn’t go too long without water. During dry seasons, you can slow how fast water evaporates from the soil by covering the soil with mulch.

3. Nutrient Deficiency

Your avocado leaves turning brown may be due to a lack of essential nutrients. These range from major elements like nitrogen, phosphorus, and potassium to trace nutrients like zinc, iron, boron, and manganese.

If your tree is deficient in any of these minerals, your leaves may develop brown dead spots that often appear with leaf yellowing (chlorosis). The extent of these brown spots depend on the severity of the nutrient deficiency.

The most common solution to nutrient deficiency is to apply fertilizer to your soil. This often works, but it isn’t always the best solution.

Citrus fertilizers work well in treating most general nutrient deficiency in avocado trees. However, if your tree is only deficient in one nutrient but not others, applying general fertilizers might cause some trace nutrients to become too high.

The best thing to do is to test your soil to see what nutrients it lacks and supply it with fertilizer rich in that nutrient. Your leaves should start to clear up once this deficiency is addressed unless the problem was wrongly diagnosed.

4. High Temperatures (Sun Scorch)

Sometimes prolonged exposure to sunlight can turn tree leaves brown. This phenomenon is known as sun scorch.

Avocado trees are tropical and used to full sunlight exposure, so they don’t suffer as much as other trees from sun scorch. However, intense sunlight with temperatures exceeding 100 °F may still cause sun scorch in some avocado trees during the summer.

Young avocado trees grown indoors are more susceptible to sun scorch and may benefit from partial shade until they are nature enough to handle full sun.

If you’re trying to figure out whether the brown leaves on your tree are due to sun scorch, look around the tree and see there are more brown leaves on one side. Depending on where you live, the side that receives the just sunlight will have more brown leaves.

There’s no magic cure for sun scorch. The condition will resolve with the turn of the season, but you can water your tree to reduce the effect of the sun’s heat.

5. Low Temperatures (Frost Burn)

During colder months, avocado trees experience what sounds like the opposite of sun scorch: frost burn. Though frost burn and sun scorch are quite different, both result in avocado leaves turning brown.

Avocado trees, being tropical, thrive in warmer climates and often struggle in cold months, especially in mid-winter. This is true even for cultivars built to tolerate cold climates.

When temperatures get very low, young avocado leaves may curl up and turn brown as they develop frost burn, while more mature leaves develop a mottled brown pattern. The brown mottles may cover all or part of the leaf.

When temperatures drop below 20 °F, brown avocado leaves may remain attached to the tree but dry up completely as the cold damages them. This damage is pronounced in the outer leaves since those are in more direct contact with the cold environment.

The best defense against frost burn is to move your trees indoors during winter if they are potted. If your tree is planted in the ground, you can cover your tree with burlaps or frost blankets for a short time period.

There’s no cure for frost burn. You’ll have to wait until the spring when they’re replaced by new leaves.

6. Check Your Avocado Tree for Pests

Brown leaves on avocado trees can also be caused by pests. Pests that live on your avocado leaves might damage parts of the leaves when feeding, causing these parts of the leaves to turn brown.

Common pests that cause brown avocado leaves include mites, lace bugs, and aphids. The pattern of browning caused by these pests are all slightly different from each other, but seeing holes on your leaves is often a sure sign of pests.

Mites on your avocado tree

Close up of a spider mite
Close up of a spider mite

Mites can cause brown streaks or spots to appear on your avocado leaves, resembling frost burn. This pattern may be spread out across the leaves or concentrated along the leaf veins.

Flip over affected leaves to see if there are mites chewing away under the leaves. Spider mites also spin silvery webs on your leaves or avocado tree branches, which you can use to confirm their presence.

Check your tree for lace bugs

Lace bug on a leaf
Lace bug on a leaf

Lace bugs cause brown dead spots roughly the size of your thumbnail on avocado leaves. Like mites, you may find lace bugs under your avocado leaves by flipping them over.

If you don’t find live lace bugs but find black spots under the leaves, you may be looking at lace bug eggs or lace bug excrement.

Aphids and caterpillars

Close up of a lot of Aphids on a leaf
Close up of a lot of Aphids on a leaf

Aphids and caterpillars can cause browning at the tip of your leaves. Usually, this tip curls over itself to protect the aphid or caterpillar using it for shelter.

Unfurl the leaves to confirm if your avocado leaves turning brown is caused by aphids or caterpillars.

You can use pesticides to take care of pests if your tree is overrun with them. However, if you only have a few brown leaves caused by pests, flushing them off with water might be better because pesticides will also kill insects beneficial to your tree.

7. Humidity Problems

Humidity refers to how much water vapor is in the atmosphere. The more humid the air is, the wetter it feels. On the other hand, dry air has low humidity.

Avocado trees do well in places where the humidity is above 50 percent and may struggle when humidity is low. The effect is similar to underwatering because cells that don’t get enough water from the atmosphere might die and turn the leaves brown.

You can treat low humidity issues by making sure your avocado tree gets watered enough so it doesn’t depend too much on atmospheric water. You can also use humidifiers for indoor trees.

Avocado trees can also turn brown if the humidity is too high. This happens because the leaves are absorbing water faster than they can release it, saturating cells and damaging their function.

To avoid this problem, make sure you only water your tree when the top soil is dry. This prevents you from overloading the tree with water.

8. Fungal Diseases that Cause Brown Avocado Leaves

Brown leaves on avocado trees may occur due to a wide range of diseases, mostly of fungal origin.

Phytophthora Root Rot

Root rot is often caused by the fungus Phytophthora cinnamomi, which thrives in wet, warm environments. Factors that predispose your tree to root rot include overwatering and poor soil drainage.

Avocado trees are highly susceptible to root rot. If you overwater your avocado tree or plant it in clay or other types of soil with poor drainage, the roots will absorb too much water and allow this fungus to colonize it.

Once root rot has set it in, it interferes with your tree’s ability to absorb and use water in the soil. Symptoms of this problem include browning at the tips of your avocado leaves, which may be mistaken for underwatering or chloride salt buildup.

Unfortunately, there is almost nothing you can do once your tree has developed root rot. You can try fungicides, but the fungus is notoriously hard to deal with and will most likely cause your tree to die.

The best way to prevent this problem is to ensure you only water your tree when needed and plant it in well-drained soil. Sandy soil rich in humus is great for avocado trees.

Anthracnose 

Anthracnose is a fungal disease that affects avocado trees and can turn leaves brown. It begins as yellow leaf spots that slowly turn brown and merge into larger spots as the leaf dies.

You’ll often notice this problem along the leaf veins, margins, and tips where. As the disease worsens, the leaves on your avocado tree will die and drop.

Anthracnose doesn’t just affect your leaves. It affects your tree’s flowers, twigs, and fruits, but symptoms on fruits usually only become obvious after harvest.

Anthracnose is caused by the fungus Colletotrichum gloeosporioides. Although this fungus is quite common, the disease is uncommon because high numbers of spores and humid conditions are required to produce serious infections.

If this disease is common in your state, you can spray your avocado with copper or other fungicides to prevent an infection.

Powdery Mildew

This disease is often caused by the fungus Oidium perseae and is most common in dry months. It appears as dark green powdery spots on young avocado leaves, but the spots turn brown on older leaves.

Powdery mildew is usually not a cause for alarm since it only directly affects avocado leaves and not the fruits. However, untreated infections can become widespread and severely weaken your tree.

Powdery mildew may disappear on its own, but you can use herbicide to ensure the infection doesn’t spread.

Scab Disease

If you notice small, circular lesions with raised edges all over your avocado leaves, you may be dealing with scab disease. This disease is caused by the fungus Sphaceloma perseae and can severely impact your tree’s health and fruit production.

You can treat scab disease by pruning infected branches and applying fungicides like copper oxychloride and mancozeb.

Laurel Wilt

Laurel wilt is a severe fungal infection caused by the fungus Raffaelea lauricola and transmitted ambrosia beetles. It can cause most of your avocado tree’s leaves to turn brown and dry without dropping for up to a year.

Signs that your tree is suffering from laurel wilt include the presence of small holes on your tree trunk where ambrosia beetles have drilled into the tree. Tube-like projections with sawdust often extend out of the holes.

There’s still a lot we don’t know about laurel wilt. For now, the recommended course of action if you notice laurel wilt in your garden is to remove the tree and destroy any dead wood around that ambrosia beetles may use as shelter.

It’s best to take samples of your tree’s sapwood for laboratory analysis before destroying it if you suspect your tree has laurel wilt but the symptoms aren’t pronounced yet.

Frequently Asked Questions

Here are some of the most asked questions about avocado leaves turning brown.

Is avocado leaves turning brown a bad sign?

Not all the time, but it can be. Brown leaves on avocado trees are always worth examining so you can decide if the problem is insignificant or threatening to your tree’s health.

What to do when avocado leaves turn brown?

It depends on the cause. Brown leaves following a barrage of cold or hot temperatures can be left alone as the tree will recover once the weather stabilizes.

Other types of leaf browning should be treated on a case by case basis as described in this guide. General practices that can help prevent avocado leaves from turning brown include deep watering, planting in well-drained soil, and fertilizer application.

Should I remove brown avocado leaves?

Yes, you can prune dead brown avocado leaves from your tree. Once the brown leaves on your tree are dead, there’s no way your tree can revive them. It can only replace them with new ones.

Conclusion

There are several reasons for avocado leaves turning brown. Some of these reasons, you can’t do very much about. Others, you can prevent or fix with good gardening practices.

Watering your tree deeply when the soil starts to get dry, pruning brown leaves, applying fertilizer, and controlling pests are practices that can help you prevent or manage brown leaves on avocado trees.

The soil you plant your avocado tree in is critical. It’s important that the soil has good drainage; otherwise, you might kill your tree while trying to save it from other problems by watering.

Most avocado trees that develop brown leaves do so due to a buildup of chloride salt in the leaves or due to underwatering. Other reasons, while probable, are less common.

If you have questions about avocado leaves turning brown or have tips to share, please drop them in the comment.

More plant guides

Sources

UF/IFAS Communications (no date) Laurel Wilt – a Disease Impacting Avocados – UF/IFAS Extension. Available at: https://sfyl.ifas.ufl.edu/miami-dade/agriculture/laurel-wilt—a-disease-impacting-avocados/ (Accessed: 13 July 2023).

University of California Agriculture and Natural Resources (no date) Anthracnose / Avocado / Agriculture: Pest Management Guidelines / UC Statewide IPM Program (UC IPM). Available at: https://ipm.ucanr.edu/agriculture/avocado/anthracnose/ (Accessed: 12 July 2023).

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