Pest & Disease Leaf gall

Leaf gall

Exobasidium spp.

What are Leaf and flower gall (Exobasidium vaccinii)?

Leaf and flower gall, caused by Exobasidium vaccinii, is a fungal disease affecting plants in the family Ericaceae. It is commonly known as azalea gall, camellia gall, or leaf gall. The disease is distributed in various regions and can impact susceptible plants such as azalea, camellia, huckleberry, manzanita, madrone (strawberry tree), and rhododendron. Infected plants develop distorted, thickened, and initially, pale green foliage, which may turn pink. Leaf and flower gall caused by fungus results in distorted, thickened foliage with a pale green or pinkish color. Severity varies based on cultural practices and weather conditions.

How do Leaf and flower gall (Exobasidium vaccinii) occur?

Exobasidium vaccinii reproduces through spores. The fungus overwinters in infected plant tissue. In spring, as buds open, high humidity and moisture facilitate spore release. Spores can be dispersed by air movement or splashing rain and can infect healthy tissue during prolonged wet conditions. The fungus stimulates rapid cell division, leading to gall formation. Infected tissue develops microscopic, white, spore-forming structures that aid in further spread.

Symptoms

1 - Impacts on Plants

• Leaf and flower gall cases thickening, and discoloration of foliage, leading to reduced photosynthesis and plant vigor. • Severe infections can reduce flower production, result in smaller flowers, and decrease fruit set. Infected branches are more prone to dieback.

Solutions

1 - Prevention

• Select resistant cultivars when planting susceptible plants. • Provide proper spacing between plants to improve air circulation. • Avoid overhead watering and irrigate at the soil level to minimize moisture on foliage. • Practice good plant hygiene by removing and disposing of galled tissue promptly. • Monitor plants regularly for early signs of infection.

2 - Cultural Management

• Prune affected tissue during dry conditions to minimize disease spread. • Improve soil drainage to prevent excessive moisture. • Apply a layer of organic mulch around plants to maintain soil moisture balance and reduce stress.

3 - Chemical Control

• Fungicides may be used as a preventive measure in severe cases. • Copper-based fungicides or other preventive fungicides like the Bordeaux mixture can be applied before wet conditions. • Follow the instructions on the fungicide label and consider potential impacts on the environment.