Lasallia pustulata

Important note: From an agronomic perspective, Lasallia pustulata is not a plant disease in the pathogenic sense. It is a foliose lichen that grows as an epiphyte, meaning it utilizes the tree bark purely as a substrate for attachment without directly feeding on plant nutrients.

The organism is a symbiotic association between a fungus and an alga. While it does not cause necrotic lesions like bacteria or fungi, its presence is a biological indicator suggesting that a tree may be under stress, growing too slowly, or suffering from lack of sunlight and airflow.

It typically colonizes older trees with rough, deeply fissured bark. The development of this lichen is highly favored by high ambient humidity, poorly maintained orchards with dense, unpruned canopies, and locations with low solar exposure, which prevents the bark from drying out quickly.

Symptoms appear as distinct, large, leaf-like thalli that are generally gray to brown in color, featuring characteristic pustules or blisters on their upper surface. These structures expand and soften when wet, and contract when conditions become dry, showing a strong reaction to moisture.

The potential harm is indirect: the thick lichen cover can provide a habitat for overwintering pests, such as scales or beetles, and may harbor harmful fungal spores. Preventative measures include regular tree hygiene, such as mechanical cleaning of trunks, thinning of the canopy to improve ventilation, and application of lime wash on trunks.

• Mechanical removal of lichen
• Proper crown thinning
• Application of copper-based fungicides
• Improving overall tree vitality