Bacterial Blight of Geranium: Symptoms, Spread, and Control Measures

V-shaped yellowing that ends on the vein. Pathogen and Importance Bacterial blight, caused by Xanthomonas campestris pv. pelargonii (specific to geraniums), is the single most important geranium disease. If suspected

Aster Diseases: Symptoms, Causes, and Management Options

Disease Reference Table DiseaseSymptomsPathogen/CauseManagement Aster Yellows Leaves yellow; abnormal branching; yellowed leaf-like tissue replaces flower parts. Phytoplasma Destroy infected plants. Maintain good le

Common African Violet Diseases: Identification and Management

Disease Reference Table DiseaseSymptomsPathogen/CauseManagement Bacterial Blight Dark reddish-brown to black rotting on roots and crown; infected petioles appear greasy. Erwinia chrysanthemi Pot and propagate in pas

Plant Virus Diseases: Symptoms, Transmission, and Control Strategies

Virus Basics Viruses are submicroscopic infectious agents: nucleic acid (genetic material) surrounded by a protein coat. Inside the plant cell, the nucleic acid hijacks cellular machinery to replicate virus components, d

Hazardous Tree Diseases: Recognizing Structural Risks from Fungal Decay

The Hazard Potential Most plant diseases reduce yield or aesthetics, but certain tree diseases weaken structure, creating hazards where falling limbs or toppling trees can cause property damage or serious injury. Arboris

Tobacco Mosaic Virus (TMV): Symptoms, Transmission, and Management

Virus Structure and Survival Tobacco mosaic virus (TMV), named for its discovery in tobacco in the 1800s, infects over 350 plant species. It consists of RNA surrounded by a protein coat, forming a rigid, rod-shaped parti

Key Sources of Plant Diseases in Nursery Production

Infested Soil Pathogens in soil include Cylindrocladium, Pythium, Phytophthora, Fusarium, Rhizoctonia, Thielaviopsis, crown gall bacteria, and nematodes. Pythium also occurs in sand and peat. Use only pathogen-free mixes

Common Sources of Plant Diseases in Greenhouse Operations

Infested Soil Many pathogens—Pythium, Phytophthora, Fusarium, Rhizoctonia, Thielaviopsis, crown gall bacteria (Agrobacterium), and nematodes—reside in soil. Pythium also occurs in sand and peat. When crops are potted in

Rhizoctonia Root and Stem Rot: Symptoms, Conditions, and Control

Cross-wall near base of branch Pathogen Biology Rhizoctonia is a soil-borne fungus causing root rots, stem rots, damping-off, and occasional leaf blight. It thrives in warm (70–90°F), moderately moist soils. The fun

Essential References for Diagnosing Floricultural Crop Diseases

Penn State Publications Penn State Publication Distribution Office112 Ag. Admin. Bldg., University Park, PA 16802 Disease and Arthropod Management in Greenhouses – Covers pest/disease biology and specific chemical/nonch

Pythium Root Rot: Identification, Prevention, and Management in Greenhouse Crops

Understanding Pythium Root Rot Pythium root rot is a pervasive disease in greenhouse production caused by several species of this fungus-like organism. In the northeastern United States, the most commonly encountered spe

Pseudomonas syringae: A Common Bacterial Pathogen on Woody Plants

The bacterium Pseudomonas syringae is an opportunistic pathogen that attacks a wide variety of woody plants, especially when they are damaged by frost or mechanical injury. Among its many pathovars, P. syringae pv. syrin

Powdery Mildew: Identification, Conditions, and Management

Powdery mildew affects a wide range of flowers, woody ornamentals, and trees—including roses, snapdragons, African violets, kalanchoe, English ivy, zinnias, photinia, oak, lilac, and begonias. Powdery mildew on Poinse

Phytotoxicity in Plants: Causes, Symptoms, and Prevention

Phytotoxicity—plant injury caused by chemicals—can occur during pest control, fertilization, growth regulation, or other treatments. Understanding why it happens helps you avoid costly damage. When Phytotoxicity Occurs

Over-Fertilization in Container Plants: Symptoms, Causes, and Solutions

Over-fertilizing potted or container-grown crops leads to a buildup of soluble salts in the growing medium. These excess salts hinder water uptake by roots and make plants more vulnerable to root diseases and damping-off

Key Landscape Plants and Their Common Diseases: A Monitoring Guide

Selecting the right plants for your landscape and keeping them healthy becomes much simpler when you know which species are prone to disease and what those diseases look like. By identifying key plants—those that frequen

Key Plants and Key Diseases Indoors

Managing diseases in interior landscapes becomes more efficient when you know which plants are prone to specific pathogens. This guide identifies key indoor plants—those that frequently develop diseases—and their key dis

Impatiens Necrotic Spot Virus (INSV) & Western Flower Thrips: A Greenhouse Crisis

INSV and its relative Tomato Spotted Wilt Virus (TSWV) have devastated greenhouse crops. But growers who aggressively control thrips, inspect incoming plants, and maintain crop health can avoid losses. INSV: The Virus S

Foliar Nematodes (Aphelenchoides): Leaf-Dwelling Roundworms on Ornamentals

Unlike soil-dwelling nematodes, foliar nematodes (Aphelenchoides spp.) live on above-ground plant parts, often asymptomatically. Three key species on ornamentals: A. besseyi, A. fragariae, A. ritzemabosi. Size: 0.5–1.2 m

Downy Mildew: Cool-Weather Obligate Parasites of Ornamentals

Downy mildews are highly specialized obligate parasites of vascular plants—distinct from powdery mildews. Though historically grouped with fungi, they belong to the Oomycota (with Phytophthora and Pythium), requiring dif