On apples the disease is most frequently observed on Golden Delicious. Most Washington irrigation water is contaminated with the fungus that causes sprinkler rot. The disease is most severe in orchards with overtree irrigation, but can occur in orchards with undertree sprinklers if the angle of the sprinklers is sufficiently high to wet the fruit. Sprinkler rot sometimes occurs after trees are sprayed using contaminated water, especially under slow drying conditions. In Washington the disease is most common during July and August.
Infected fruit can have a slight phenolic odor.
The white growth is a mass of fungal threads known as hyphae. Collectively, the threads are called mycelium. Early symptoms on Golden Delicious apple fruit infected with Phytophthora cactorum. At this stage, infected fruit may or may not have a pungent phenolic odor. Advanced symptoms on pear fruit infected with Phytophthora cactorum.