Qualified Applicator License (QAL) Plant Agriculture Practice Test 2025 - Free QAL Practice Questions and Study Guide

The pathogen responsible for avocado root rot is Phytophthora cinnamomi. This organism is a water mold that thrives in poorly drained soils and is particularly aggressive in tropical and subtropical climates where avocados are grown. It infects the roots of the avocado tree, leading to symptoms such as wilting, yellowing of leaves, and eventual tree decline, as it disrupts the plant's ability to take up water and nutrients.

The pathogenicity of Phytophthora cinnamomi is due to its ability to produce hardy oospores, which can survive in the soil for long periods, and its capacity to spread through water movement. This makes management of the disease challenging, and practices such as improving soil drainage, planting resistant rootstocks, and employing fungicides may be necessary to control the pathogen's impact.

In contrast, the other options represent different pests or pathogens. Oligonychus perseae is a mite known to infest avocado leaves, causing damage but not root rot. Scirtothrips perseae, a thrip species, primarily feeds on the foliage and can cause cosmetic damage to the fruit but does not cause root diseases. Colletotrichum gloeosporioides is a fungal pathogen associated with anth