Ask The Expert: Why Are My Avocado Leaves Turning Brown?
Ask the Expert: Avocado tree question.
Hi all, I have a well established (~10-20 yrs old) which has produced avocados the last 6 years. This year, no fruit and the top 1/3 of the trees canopy has turned brown. I have no idea what is happening. I water the tree every other day for ten minutes. I have also noted splits in the bark at the base of the trunk. Does anyone have any ideas or suggestions? Attached is a photo of the leaves. This problem began after our gardener removed the ground cover around the tree earlier this spring. The tree initially looked stressed but began to rebound after a few months. Now the current situation appears to be worsening again. – Art G
Flower Shop Network‘s Plant Expert’s Reply:
Art, there are several reasons that could cause your avocado tree’s leaves to turn brown. This is a hard diagnosis without knowing the previous conditions of your tree’s environment.
1. Overexposure to the Elements – Harsh conditions could be the reason your avocado tree is turning brown. Overexposure to the following could be the problem:
- Drying Winds
- Salt (carried in the air)
2. Changes in Soil – You mentioned your gardener removed the ground cover around the tree. This loss of mulch could have quite an impact. The ground cover helps retain water for the roots by keeping it from evaporating. When watering, it’s best to water thoroughly then wait until the ground is dry before watering again. A good rule is about 5 gallons twice a week. The best way to do this is by using a 5 gallon bucket with a 1/4″ hole in the center of the bottom. Fill up your bucket and set it a couple of feet away from the trunk of your tree, so that the water oozes across the feeder roots.
3. Root diseases – Root diseases kill or weaken the roots of trees. There is no cure for these, although improved conditions may help the tree to bounce back to normal and outgrow the disorder.
4. Insect Damage – Take a close look at the branches and trunk of your tree. If you notice insect damage or see ants crawling over your tree, this could be a sign of borers. If so, you will need an insecticide to kill the borers in time to heal the tree.
So what to do?
Well, it depends on how far the dieback has progressed. If the brown is just on your leaves then your tree will probably be fine. Keep it well-watered and it should bounce back. It is a good idea to get your soil tested to see if it needs any additional nutrients.
If your branches and trunk are browning, you’re going to have to do some rescuing. Find out exactly how far your tree’s dieback has progressed. Cut into the wood just a bit to see where your tree’s brown turns into fresh green. You’re going to need to cut everything dead off at this point. It’s tough love, but someone’s got to do it!
Before you go hacking off half of your tree, visit your local garden center or contact your extension service for a true diagnosis of your tree. We do the best we can with a description and a photo, but you need to be sure before taking any drastic measures.
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Phytophthora Root Rot: Treating Avocados With Root Rot
If you are fortunate enough to live in a tropical or subtropical region, zone 8 or above, then you may already be growing your own avocado trees. Once associated only with guacamole, avocados are all the rage these days, with their high nutrition content and versatility in many recipes.
Growing your own avocado trees can provide you with a seemingly endless supply of these delicious fruits. However, no plant is without its problems. If you were expecting an avocado tree laden with fruit, but instead have a sickly tree that rarely bears avocado fruits, this article may be for you.
About Phytophthora Root Rot
Phytophthora root rot is a fungal disease caused by the pathogen Phytophthora cinnamomi. This fungal disease affects avocado trees and thousands of other plants. It can be a particularly devastating disease in avocados and is estimated to result in about $50 million in crop loss in California each year.
Avocado root rot can affect trees of all sizes and ages. It mostly affects the feeder roots of avocado trees, causing them to become black, brittle and unable to take up valuable nutrients and life sustaining water. Because these roots lie beneath the soil surface, this disease can severely infect a plant while going mostly unnoticed.
The first visible symptoms of root rot in avocado trees is light green to yellow, undersized foliage on infected plants. Leaves may also have brown, necrotic tips or margins. As the disease progresses, foliage will wilt and drop, exposing the fruit to sunscald. The upper branches of infected avocado trees will also die back.
Fruit production also declines in infected trees. They may bear small or sparse fruit at first, but eventually fruit production will stop altogether. This disease does usually result in the death of infected trees.
Treating Avocados with Root Rot
Excessive soil moisture and poor drainage are contributing factors of phytophthora root rot. It is most prevalent in sites that periodically floor or puddle up from bad drainage, low grade, or improper irrigation. Fungal spores can be spread by wind, but most often trees are infected from water runoff or infected scion or rootstock in grafting practices. The disease can also be spread by dirty gardening tools. Proper sanitation of gardening equipment and garden debris is always essential in controlling the spread of disease.
Prevention is the most important step in controlling avocado root rot. Before planting an avocado tree, ensure that it is in a site with good drainage and no runoff from other potentially infected avocado trees. Berming up the site or adding garden gypsum and organic matter can be excellent ways to provide proper drainage.
Planting avocado trees from certified stock is also recommended. A few avocado cultivars that have shown resistance to phytophthora root rot are Dusa, Latas, Uzi, and Zentmyer.
While fungicides will not cure root rot in avocados, they can help control the disease. Research has shown that fungicides containing potassium phosphonate can help avocado trees become more resilient to avocado root rot. Fungicides should be used in combination with proper soil conditions, irrigation and fertilizing practices to treat this condition.
Fertilizers that contain ammonium nitrogen and calcium carbonate, calcium nitrate or calcium sulfate can help avocado trees survive phytophthora root rot.