Annual Bluegrass (Poa annua): How to Identify & Treat Fast

Potyviruses (family Potyviridae, genus Potyvirus) are plant viruses transmitted primarily by aphids during feeding and mechanically through sap. They cause mosaic patterns (light and dark patches) on leaves, leaf curling and distortion, vein clearing, leaf blistering, stunting, and in vegetables and fruits, streaks and discoloration. In potatoes (Potato virus Y), necrotic spots on leaves and ringspots on tubers may occur; in cucurbits (e.g., Zucchini yellow mosaic virus), distinct mosaic and deformations of leaves and fruit; in peppers, streaks and spots on fruit; in brassicas (Turnip mosaic virus), mosaic and stunted growth; and in plums, Sharka (plum pox) causing spots and fruit distortion. Infection can also be introduced via seeds, seedlings, tubers, scions, and host weeds. Unfortunately, infected plants cannot be cured.

The Phytophthora genus consists of soil-borne oomycetes (water molds) that act as plant pathogens, primarily affecting trees and woody plants. It typically spreads through the root system, leading to systemic decline and eventual plant collapse.

Pseudoperonospora is a genus of pathogens causing what is known as downy mildew. These are moisture-loving 'molds' from the kingdom Chromista that primarily attack leaves. Angular yellow spots appear between the veins on the upper side of the leaves, while a grayish-purple coating forms on the underside in humid conditions. The leaves turn brown, dry out, and the plant weakens. It most commonly affects cucumbers and other cucurbits (zucchini, pumpkins, melons) and, in our region, hops. It spreads via wind and rain and thrives during prolonged humidity, dew, cooler nights, and in stuffy greenhouses.

These are fungus-like organisms, sometimes referred to as water molds. They are primarily water- or soil-borne and cause many plant diseases (such as downy mildew and late blight).