Identifying and Treating Bougainvillea Diseases

A bougainvillea plant in a walkway.
What You'll Need
Scraping tools
Horticultural oil
Insecticidal soap
Fungicides containing triadimefon or propiconazole
Dry wood mulch
Pyrethrin-based pesticides.

Few bougainvillea diseases are deemed harmful enough to destroy a bougainvillea garden spread. Bougainvillea plants are naturally immune to bacterial diseases and common garden pests. Grown usually for landscaping purposes, bougainvilleas are woody, ornamental shrubs that need minimal care. However, an improper gardening regimen and the failure to spot early signs of fungal infections can cause widespread harm to bougainvilleas.

Bougainvillea Disease 1: Mildew

Powdery mildew is a fungal infection common to most ornamental shrubs. Mildew infections are often caused due to excessive watering of plants and poor soil drainage. Mildew infestations cannot be eradicated for a lifetime. You will have to ensure basic garden hygiene and take some precautions to guard against mildew disease.

Symptoms: The most identifiable feature of mildew infection is the presence of white, powder-like, dusted appearance of the foliage. The infection is more apparent among the leaves than the branches. Crowded branches and dense foliage help in mildew spreading quickly throughout the garden-spread. Root rot is commonly caused by waterlogging in the soil bed but bougainvilleas rarely suffer from it. However, bougainvilleas suffering from mildew infection often develop root rot due to decreased plant vigor.

Treating Mildew: The diseased foliage should be pruned off. You should not use this foliage in the garden compost or for any gardening activity. The best way to reduce chances of a mildew infection is to use a fungicide when transplanting the plants. This also helps to prevent root rot infection. Ensure proper drainage in the soil bed. You can increase the soil’s draining capability by adding some dry mulch prepared from wood bits. During damp weather conditions, regularly check for mildew development. You should water the plant minimally during this period. If signs of fungal growth are present, chemical control can be considered. You can use mild fungicides that contain triadimefon or propiconazole as ingredients. During the growing season, regularly check for decaying foliage and clip it with garden scissors but don’t prune. You should prune bougainvilleas before and after the growing season. Ensure that the basal and mid-level foliage is sufficiently pruned to allow greater air circulation within clustered parts of the foliage.

Bougainvillea Disease 2: Scale Disease

Scale insects or mealybugs are plant parasites, commonly found in household gardens. Mealybugs are attracted to bougainvilleas. They feed intensively on the sap of plants.

Symptoms: The smaller, unhatched scale insects can be observed on the underside of some leaves, covered in a waxy coating. The more mature scales have a sooty, black appearance. Scale infection can be easily detected with extensive canker development on branches and overall, stunted plant growth. Some cankers might develop a bigger, sore-like appearance. Scale-damaged bougainvilleas might have some sap oozing out of these sores.

Treating Scale Disease: You should regularly check for scale insect development. The insect’s eggs are commonly found around the leaf joints. If the number of scale insects is small, you can remove them with a scraping tool. After scarping them off the plant’s surface, wipe the infected site with a cloth dipped in horticultural oil. This seals any underlying canker sores. You can develop a spraying regimen to prevent scale disease. Prepare a mixture of water, insecticidal soap, and horticultural oil. Spray this all over the bougainvillea shrub every two weeks. To control mealybugs, use any of the branded chemical sprays available at garden supply stores. If the scale disease is becoming unmanageable, trying spraying the entire shrub with pyrethrin-based pesticides.