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What is Killing My Trees?
Diagnosing plant problems can be a difficult task. To diagnose plant problems, you
need to know how a healthy plant grows and have some knowledge of the stresses that
affect plant health. We need an understanding of the plant’s normal appearance before
we can begin to monitor for signs and symptoms of a problem.
Plant problems can be grouped into four major categories:
Cultural - problems that arise from the car of the landscape, such as fertilizing,
use of herbicides and pesticides, improper pruning, inadequate or over watering,
improper planting, over mulching, etc.
Environmental - problems often out of our control, caused by nature, such as droughts,
hail, lightning, high or low temperatures, floods, etc.
Diseases - plant problems that are brought about by infectious agents such as bacteria,
fungi, nematodes and viruses. Common diseases include leaf spots, vascular wilts,
cankers, and root rots
- Insects - plant problems caused when insects chew leaves, suck sap (plant food)
from leaves and twigs, or borer into the stems. The vast majority of insects in
our landscapes are not harmful to our plants and some are beneficial because they
prey on harmful insects.
When we first see a plant problem (e.g. chewed or distorted leaf), often our first
impulse is to apply a pesticide without even knowing what caused the injury. We
are usually wasting time and money, and sometimes causing more harm than actually
solving the problem. Proper diagnosis of the problem is critical and takes knowledge
of the plant and the pest. Often you might need some help from a landscape professional
or have to bring a plant sample into your local Penn State Cooperative Extension
The following websites will help you gain knowledge about diagnosing plant problems
in your landscape.
Penn State University Disease Fact Sheets
Penn State Entomology Fact Sheets
Penn State University Woody Ornamental Insect, Mite and Disease Management Guide
DCNR Forest Pest Fact Sheets
USDA Forest Service Pest Alert Sheets
USDA Forest Service Tree & Forest Health
USDA Forest Service Forest Health Pubs
"Preserving Trees During Development" - a very good Penn State Publication
PSU Integrated Pest Management Program
Pesticide Education - Penn State Fact Sheets for Home and Garden
“Environmental Stresses and Tree Health,” University of NE publication to help tree owners identify tree health problems caused by environmental stresses
Pest Problem Solver, Forest & Shade Trees – a great website with many links to PSU Fact Sheets and publications as well as USDA Forest Service Pest Alert Fact Sheets
USDA Forest Service Forest Insect & Disease Leaflets
A Practitioner’s Guide to Stem Girdling Roots - Impacts on Trees, Symptomology, and Prevention”
Managing Insects and Diseases of Trees - PSU