Bougainvillea are pest and disease resistant but sometimes they can be affected by bacteria or fungus that can cause spots and dots on their leaves turning them brown. Leaves can also turn brown if the plant has been overwatered, underwatered or is attacked by pests.
This article will explore the top causes of brown leaves on bougainvillea and simple ways to fix each problem.
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Brown spots on bougainvillea leaves
Bacteria and fungal infections can cause brown spots to appear to appear on the leaves. New growth is more susceptible to this browning but if it is not controlled it can spread to the whole plant.
This can cause the whole leaf to go brown eventually and drop off. Fungal leaf spot can be treated with copper based fungicides or natural options.
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Bacterial leaf spot is more difficult to treat. It best treated by removing and binning the affected areas so it doesn’t spread further. Trim the leaves affected so it doesn’t spread to other parts of the plant or nearby shrubs. Water the plant well at the roots and feed it with a well balanced fertilizer to help it to recover.
To prevent bacterial and fungal leaf spot appearing on bougainvillea leaves it is important to avoid watering the plant directly on the leaves. This will reduce the chance of bacteria spreading and growing in the leaves.
It is also important to trim the lower branches and any leaves that are close to touching the ground. Bacteria or fungus can splash onto the leaves from the soil if they are too close. Surround the tree with 3 inches of bark mulch around the root zone to stop the soil splashing.
It is also important to trim back old stems to allow good air flow during humid summers.
Brown leaf edges on bougainvillea
Brown leaf edges on bougainvillea are usually a sign of pest attack or the plant drying out. Check out these top causes of brown leaf edges on bougainvillea plants.
Aphids
Tiny green or brown aphids can cause problems for your bougainvillea plants. They are more likely to attack in spring and fall when the weather is mild but still warm. These green or brown bugs will sit on the leaf veins sucking the sap from the plant. This can cause the leaf to develop brown marks and edges.
Treat aphids with neem oil by spraying it on the top and underside of the leaves. Repeat this again if the bugs are still there a few days later. This natural extract from the neem plant will not hurt pets, people or other beneficial insects like bees.
Chewing bugs – caterpillars, slugs and snails
Chewing bugs can cause leaves on bougainvillea to develop brown edges or holes. These bugs will take bite marks on the edges of leaves. Look out for silver lines on the leaves to see if slugs and snails have been. They will visit your plant during the night or early hours of the morning.
Caterpillars and slugs can be flicked off and squished with gloved hands or knocked into a bucket filled with soapy water. Set snail traps by filling low dishes with a small amount of beer. The yeast will attract the slugs and snails which will crawl in and die.
Scale insects
Scale insects are common in spring. Scale insects can look brown and will create a tough outer coating over the top of their bodies sealing themselves to the leaf stems. They will suck the sap from the tree and cause the leaves eventually to turn brown and drop off.
Scale is best treated with neem oil. They usually need 2-3 applications of neem oil if they have sealed themselves over. The neem oil needs to penetrate the scale cover which can take a few applications. Squirt them off with a strong hose to try to remove them manually to help the process.
Leafminers (moths, flies)
They mine the leaves of nutrients causing a brown line through the leaves. These insects will chew through the surface of the leaves. This will eventually cause the whole leaf to turn brown and fall off.
Neem oil will work well for any insect that is chewing or ‘mining’ the leaf for nutrients and sap. You can spray the leaf thoroughly with neem oil and this will treat the problem.
Whole brown leaves on bougainvillea
If the whole leaf of the bougainvillea has turned brown it could be because of underwatering, damage to the root system or transplant shock.
Underwatering
Bougainvillea plants that are not getting enough water can turn brown. The leaves can turn yellow first and then turn brown. These are drought hardy plants but if they dry out too much they can become damaged.
Deep water the bougainvillea with your hose to help it recover. Mix seaweed solution with water and add it to the plant to help it to recover.
Damaged roots
Bougainvillea plants that have root damage may not get enough nutrients or water causing their leaves to brown. Raking or digging near the surface of the plant around the roots can damage the top feeder roots that sit near the surface of the soil.
Transplanting bougainvillea from the ground to a new location or repotting them can also cause root damage and transplant shock. Their growth can slow and the leaves can turn brown.
Take care not to add any fertilizer if the plant has roto damage. Allow 2-3 months for it to recover, keeping it well watered and trim back any damaged stems.
Not enough nitrogen
Bougainvillea plants that are not getting enough nitrogen can develop yellow and then brown leaves. Nitrogen is needed for the development of chlorophyll in the plant leaves which gives them their green color.
While bougainvillea only need small amounts of fertilizer, poor soils or potted plants can still lack nitrogen. Feed them yearly with pelleted chicken manure and they will be happy. You can also top dress the plant with a mix of cow manure and compost.
This will slowly add extra organic matter, soil bacteria and worms will break down the matter slowly releasing nutrients to the plant.
Bougainvillea Leaves Turning Brown | Summary
Bougainvillea are beautiful, hardy plants with deep green leaves and colorful leaf adaption that look bright over the spring, summer and fall. They form a great screen and are easy to care for. While most of the time bougainvillea will not have any problems to deal with, brown leaves can happen if they are missing out on nutrients or water.
Check the leaves for pests and fungus and spray with copper fungicide or neem oil to treat the problem.
Happy growing.
I am an accredited practicing dietitian, experienced gardener and a dedicated cook. I love writing and sharing my experience so you can learn from my successes and mistakes.