HGIC Landscape Problem Solver Web Site logo Thursday, October 21, 2021
Maryland Cooperative Extension logo University of Maryland logo

Site Directions

  • From the menu on the left, select a category or type of plant and the part of the plant that is having problems.
  • A new page will be displayed with symptoms and possible causes with photos.
  • Browse the causes for each symptom and click on go to select that cause.
  • From there simply read the information, on the problem and solution, that appears.
  • You can go to another plant part by selecting from the menu at the top of the page.


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Developing Diagnostic and Decision Making Skills

The ability to accurately diagnose a wide range of plant problems can be developed over time by patient observation and consulting on reliable reference materials. Timely diagnosis of plant problems can help you keep your landscape and gardens beautiful and productive. It can also prevent expensive removal and replacement of damaged plants.


  • Keep an open mind. Do not jump to conclusions.
  • Avoid assigning "guilt by association". The insect, animal or disease observed may not be the cause of the problem or the symptoms.
  • A "history-taking" of the problem plant is very useful. Extreme weather, site alteration, grade changes, fertilizer, pesticide and herbicide use, cultural practices, etc. all influence a plant’s relative health over time. Once mature trees begin to decline, there is often no way to reverse the process. White pines and oaks are common examples of plants which are difficult to rejuvenate after decline symptoms begin.
  • Consider all the factors that influence the plant’s growth and health. Take the time to look under leaves, and when possible at the roots, for potential causal factors.
  • Know what your plant should look like. Knowledge of general growth rates, leaf size and coloration may help alert you to early signs of trouble.
  • At least one half of all observed landscape problems are not caused by insects or diseases. Try to eliminate other causal factors first.
  • A particular problem may be caused by several factors: soil drainage, extreme weather from previous years, air pollution, pests, diseases, herbicide drift, etc.
  • The symptom may indicate a problem in a different part of the plant. For example, leaf yellowing and scorching may be caused by root damage.
  • There is a great variation in the expected life-span of landscape plants. All plants go through periods of growth, maturity and decline. Plants grown in urban conditions generally have shorter lives.
  • Many pests and diseases are plant-specific. Symptoms affecting more than one plant species may indicate cultural and environmental problems.
  • There is no substitute for "hands on" training, particularly with an experienced individual.

Examining the Plant

  • Look at the area surrounding the problem plant. Consider factors such as: exposure to elements, proximity to roads or buildings, lighting conditions, drainage, etc.
  • Look for physical evidence of a problem: injury, changes in site conditions, soil compaction, construction injury, lawnmower injury, insects, diseases, etc.
  • Examine all parts of the plant closely and carefully, including roots, shoots, trunk and leaf undersides (use a hand lens if necessary). Look for a pattern to the injury.
  • Physical evidence of a pest includes: the pest itself, shed skins, droppings or frass, webbing, honeydew, sooty mold, pitch, gummosis, galls, slime trails, etc. Evidence of diseases includes: mushrooms, fungal growths, galls, white, orange or black powdery substances, leaf spots, water-soaked areas, cankers, discolored stem and root tissue.
  • Identify the pest, disease or problem. This is critical to making a control decision. Identification of the plant is also critical to control decisions. Some plants can tolerate more damage than others.



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Non-Chemical Control Strategies for Pests and Diseases

Learn to tolerate some damage: Most healthy herbaceous and woody plants can tolerate 20-30% leaf defoliation without suffering long-term damage or yield reduction.

Wait for the "good guys": Aphid feeding in the spring alarms many gardeners. Natural predators and parasites usually clean up local infestations in a month or so.

Remove plant or plant parts: Simply removing and disposing of badly damaged plants may minimize the problem on adjacent plants and prevent recurrence.

Timing of seeding and planting: Some pests can be circumvented by growing vulnerable plants when damage is least likely. For example, late summer squash crops are less troubled by squash vine borer. This requires knowledge of pest life cycles.

Late fall or early spring tillage: Many pests over-winter in the crop debris of host plants or in the soil around host plants. Tilling can disrupt pest habitats.

Water stream: A strong hose spray may temporarily dislodge mites, aphids and other pests. Be careful not to damage plants.

Hand picking: Pick off adult and immature insects and egg masses. Pests can be squashed or dropped into a jar of soapy water.

Grow pest resistant or tolerant plants: Check with the nursery or gardening catalogs when selecting plants for those with resistance or tolerance to pests and diseases. Many native plants are good choices.

Do not overfertilize: Aphids and spider mites will produce more young on overfertilized plants.

Barriers: A floating row cover is an excellent material for excluding insect pests. Other examples are paper collars for cut-worms and diatomaceous earth for slugs.

Rotation: Rotate crops that are prone to pests and diseases. However, it is often very difficult to rotate away from disease problems in small gardens that over-winter in soil or garden debris.



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How to Decide When to Take Action Against a Pest, Disease, or Environmental Problem

  1. In general you have less time to make a control decision on seedlings, transplants, and newly planted trees and shrubs. Many pests and diseases do not need to be controlled on older or mature plants. For environmental problems, the site and/or cultural conditions may need to be modified to correct the problem.
  2. Judgments may be based on aesthetics, or economic (yield) loss. Realistic thresholds should be set for insects and diseases. Pest or disease progression should be monitored carefully. It is very important to identify the pest or disease and become familiar with its life cycle. Some pests and diseases may not require control, while others may. For example, gypsy moth should be controlled, because oaks suffer from early defoliation, and use up energy reserves to refoliate. Eastern tent caterpillar occurs early enough in the season for cherry trees to refoliate without causing harm to the tree. Often by the time disease or insect damage is observed, it is too late to do anything about the problem until next season.
  3. Treatment decisions depend on the type of plant that has a problem. If a plant is easy to replace such as an annual, just pull the problem plant and replace it. Plants that continue to grow throughout the season will often outgrow the pest or disease damage. Examples include locust leafminer on locust, and anthracnose on sycamore.
  4. Once you have identified the problem and determine that it requires corrective action, select a control strategy. Always select the least toxic solutions first such as physical (hand removal, change watering practices, pruning out damage, etc.) and biological (encourage beneficials, release predatory mites, etc.). Pesticides should be used selectively (spot treatments) with the least toxic materials ( B.t., insecticidal soaps, horticultural oils, etc.) used first.
  5. Continue to monitor the plant’s health after treating a problem to determine if further action is needed.

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