Armillaria fungi have the ability to cause diseases in which part of woody plants?

Armillaria fungi, commonly known as honey fungi, are primarily associated with root diseases in woody plants. They infect the roots and lower stem tissues, which can lead to significant structural damage and ultimately the decline or death of the plant. The fungi can systematically affect the plant by attacking the root system, where they can thrive in the moist, nutrient-rich environment around the roots.

The diseases caused by Armillaria often manifest in the lower parts of the plant, including the root crown and the base of the stem. Symptoms may include wilting, yellowing of leaves, and overall declining health, but their initial point of entry and impact is at the roots. This is essential to understanding their role in plant pathology and integrated pest management strategies.

Other options, such as leaves, flowers, or upper branches, are typically not affected in the same manner by Armillaria fungi. These parts of the plant may experience other types of diseases or infestations, but the unique pathogenic behavior of Armillaria is specifically targeted towards the roots and lower stem, making this the correct answer.