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LANDSCAPING | GARDENING | PROBLEM SOLVING

Plant Disease Detective

Diagnosing lawn and landscape diseases is not easy. Many diseases have similar symptoms and symptoms vary as the disease progresses.

Most symptoms become apparent in a plant's leaves. They either turn yellow, curl up, develop gray or black spots, turn brown and drop off. It is extremely difficult to identify specific diseases without actually looking at the plant. To improve the odds of making a diagnosis here are some questions to answer before visiting a local nursery:

  • What appears to be wrong with the plant? Exactly what are the symptoms?

  • What is the condition of the surrounding vegetation? Are other plants displaying similar conditions?

  • How long has the problem been there? Contrary to some common misconceptions, plants do not become sick overnight. Usually, diseases take a considerable amount of time to develop, sometimes years.

After speaking with the nursery, you might want to ask the following:

  • Of the possible remedies, which are practical? This is a crucial step! Remember, doing nothing and merely tolerating the situation may be the "most practical" thing to do.

  • Of the practical remedies, when would be the best time of year to apply them? Will any follow-up activity such as reapplication of a spray be needed?

The following are some general clues that can help you make the call.

Plant Symptoms
Cause

Fungal growth on the blade

Long black streaks of powdery spores

Stripe smut

Powdery white dust

Powdery mildew

Red / Orange powder

Rust

Gray fungus that is easily rubbed off

Slime mold

Spots on leaves but no fungus visible

Reddish brown to blue-black, circular or oval

Leaf spot

Straw-colored bands with a reddish brown border

Dollar spot
Brown or scorched leaves; progressive dieback of branches

Poor root health from poor drainage, excessive soil dryness, excessive fertilizer, compaction and poor water penetration into soils, or girdling roots.

Mechanical injury

Excessive heat or light reflected onto leaves from driveways or buildings.

Root rot or crown rot caused by fungi.
Leaves of only one branch dying

Fungal canker
Mechanical injury
Insect or winter damage
Chemical over-spray damage
Early leaf drop
Poor root health from poor drainage, excessive dryness, excessive fertilizer, compacted soil, or girdling roots.
Mechanical injury, heat stress, insect damage, herbicide injury, or fungal infestations
Wilting or drooping leaves
Poor root health from poor drainage, excessive dryness, excessive fertilizer, compacted soil, over watering, or planting too deep
Mechanical injury or harmful chemicals drained into the soil
Fungal or bacterial infection. Fungal cankers. Root or crown rot by fungi or root-feeding nematodes.
Insect infestation
Leaves with tiny yellow speckling or yellow banding of needles
Mite or other insect infestation
Fungal or bacterial infections
Air pollution
Deformed leaves
Herbicide or late frost injury
Insect infestation
Anthracnose, virus infection
Over-spray injury
Lawn Symptoms
Cause
Circular diseases areas

Observed in late winter or early spring

 Snow mold
Present in summer, spring or fall (1" — 4' or more in diameter)

With mushrooms

 Fairy ring

No mushrooms

 Brown patch
Present in summer, spring or fall (1" — 8" in diameter)

Throughout the lawn

 Dollar spot

Only in full sun, show green center

 Fusarium blight

In low areas and often in streaks

 Pythium blight
Irregularly shaped diseased areas

New lawn seedlings wilt and die

 Damping-off

Mature lawn affected, spots on leaves

 Leaf spot

If diseases do strike your lawn, you can deal with them individually once you are able to recognize their signs. It is important to first know the disease before beginning to make arbitrary treatments.