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Updated: October 6, 2021

Key points

  • Now more than ever as Maryland’s climate gravitates towards warmer conditions, extreme weather events, and variable, changing seasons, take proper measures to prevent plant problems as part of the landscape planning process. Learn more about the issue, Adapting your Garden to the Impacts of Climate Change
  • For example, select plants that can handle hotter, drier, or wetter summer conditions, plant more native plants (aim for 50% natives), know your site conditions (amount of sun, soil conditions, drainage), research disease and insect resistant cultivars, properly plant and take care of plants after installation. Focusing your time, attention, and efforts selecting and growing “the right plant, in the right place, in the right way” will pay off in the long run.  
  • Diagnosing and managing problems with your plants is a skill set that takes time, research, finding reputable resources (there is a lot of bad information on the internet), and knowing when to turn to an expert for help such as our Ask Extension service.

What is the best way to manage yard and garden problems?

Integrated Pest Management (IPM)

  • IPM is a research-based holistic approach to pest and disease management utilized by farmers, the Extension service, and the landscape/gardening industry for decades. Many principles work well on a smaller scale for home properties and gardens. 
  • IPM principles can be applied to any type of garden including vegetable gardens.
  • IPM emphasizes biological (e.g., attracting beneficial insects), cultural (e.g., knowing the proper care of your plant), and physical (e.g., hand removal of insect pests and weeds) approaches to prevent problems and control pests and diseases at acceptable levels. Learn more about Predatory Insects, Predatory Spiders, and Parasitoids.
  • Monitoring (inspecting plants) before problems become too advanced and accepting some level of plant damage are parts of IPM.  
  • And lastly, using organic or other low-risk pesticides only when pest or disease levels are unacceptable or will seriously impact the health of the plant.

Prevent plant problems

Create a healthy planting environment

Soil building and fertility

  • Incorporate organic matter or compost into flower, ornamental, and vegetable beds on a regular basis. 
  • Take a soil test every three years and adjust the pH if needed. 
  • Do not fertilize on a routine basis but only as needed and according to soil test results. Avoid overfertilizing plants as it can lead to pest problems.
  • Don’t work with plants when foliage or soil is wet.
  • Learn more about soil, compost, and plant fertility.   Choose the right plant for the right place
  • Select well-adapted varieties for the site conditions. Climate change has negatively impacted longtime landscape favorites like Colorado blue spruce, white pines, and sugar maple trees, look for alternatives. Check local gardening references and reputable local nurseries for ideas.
  • Cherry laurels, boxwood, Japanese barberry (invasive species), and burning bush, Euonymus alatus, (invasive species), are just a few examples of problematic and overplanted shrubs. Some ornamental native options are Virginia sweetspire (Itea virginica), dwarf fothergilla (Fothergilla gardenii), highbush blueberry (Vaccinium corymbosum), fragrant sumac (Rhus aromatica), sweet pepperbush (Clethra alnifolia), and Northern bayberry (Myrica pensylvanica).
  • Buy disease or insect-resistant varieties. For example, plant powdery mildew-resistant dogwoods
  • Purchase healthy, certified, disease-free seeds, transplants, and nursery stock. 
  • Choose native plants when appropriate.
  • Replace grass in areas where it does not grow well such as shady sites. Instead plant a shade-loving groundcover. Install a rain garden in a wet area of your yard. Consider lawn alternatives.
  • Plant an assortment of trees, shrubs, and perennial plants. Plant diversity reduces plant problems. A common mistake is planting one tree species when creating a natural barrier or screen. Learn more about Plants for Mixed Privacy Screens and Landscape Planning. 

Proper planting and care

  • Plant at the right time. Spring and fall are the best times for planting in Maryland.   
  • Select suitable plants for the selected site. 
  • Group together plants that require similar cultural care, such as the same requirements for water and soil type. Allow for proper spacing between plants based on the mature height and width. 
  • Learn more about planting trees and shrubs
  • Water trees and shrubs slowly and deeply. Remember that the root zone can extend out 2 to 3 times the height of the tree beyond the dripline. 
  • Check the depth of soil moisture after irrigation by digging a small hole or inserting a stick. 
  • Water early in the day so foliage dries quickly. 
  • Avoid overhead watering and splashing soil onto plants. 
  • Prune trees and shrubs to increase air circulation, allowing foliage to dry faster. This helps to prevent diseases like volutella on boxwood.

Weeds

  • Weeds rob plants of moisture and nutrients and are alternate hosts for pests and diseases. 
  • Select plants that develop an overlapping canopy to shade out weeds.
  • Eliminate any established weeds before planting, especially perennial species like Canada thistle
  • Hand-pull or hoe weeds while they are seedlings but minimize any disturbance to the soil. Soil disturbance prompts weed seed germination because the seeds are now exposed to sunlight. Weeds are easier to manage when the soil is moist. 
  • Avoid accidental root damage when hoeing or tilling.
  • Correctly maintain mulch. 
  • As a last resort, use a preemergent herbicide or spot applications of a contact herbicide where appropriate.

Learn more about weeds and weed management

Identify and diagnose plant problems (monitor)

Identify plant problems

  • Before you can recognize or prevent a problem, become familiar with your plants, their growth habits, and the necessary conditions for good growth. Know what your plants should look like at certain times of the year. Are they growing normally? For example, Pine trees have fall color and interior needles turn yellow and fall off leading folks to assume that the tree has a disease or other problem.
  • Monitor Plants - Regular inspections of your garden and plants will catch most problems before they get out of hand. Examine all plants carefully including leaf undersides where pests or disease symptoms are often observed. Most problems are noticed when symptoms are advanced (making pest or disease management more difficult), often the case with bagworms that cause extensive damage on evergreens. 
  • The vast majority of plant issues are not caused by diseases or insects. Problems and death of a plant may be caused by one or several factors known as abiotic problems. Some examples are poor soil drainage, changes in climate, too much or too little water, extreme weather from recent or previous years, air pollution, herbicide drift, planted too deeply, or too much mulch piled up on the trunk. 
  • Trees and shrubs that decline or die within about 2 years or so after being planted most likely are suffering from abiotic problems. But they can also succumb after a longer period of time. 

Steps to diagnosing a plant problem 

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. 

How to begin

  • 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. Sometimes they will take advantage of the damage or declining plant. 
  • A “history-taking” of the problem plant is very useful. Extreme weather (drought, unusually hot or cold temperatures, excess rain amounts etc…) , 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. Leyland cypress 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, including how the plant is being taken care of. 
  • 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. Take the time to look under leaves, and when possible at the roots, for potential causal factors.
  • 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 than those grown in natural areas. One example is ornamental cherry trees, they have an average lifespan of only 20-25 years in Maryland. 
  • Many pests and diseases are plant or host-specific. Symptoms affecting more than one plant species may indicate cultural and environmental problems (abiotic-not related to insects or diseases). 

Know where to go for help. You can send questions and digital photos to our Ask Extension Service.  Or during the growing season have your questions answered by a Maryland Master Gardener at an Ask a Master Gardener Clinic. Plant clinic locations and times are typically noted on your local county MG website. 

Manage problems

When to take action against a pest, disease, or abiotic (not caused by a disease or insect problem

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

  • 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 (or abiotic, not caused by a disease or insect), the site and/or the plant care may need to be modified to correct the problem. 
  • 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.
  • But, often by the time disease or insect damage is observed, it is too late to do anything about the problem until the next season.
  • After identifying the insect pest, learn the life cycle, habits, characteristics, damage potential, and best time to take action before doing anything else. Look to see if there are beneficial insects already present, reducing pest numbers. 
  • Some insect pests may not require action. For example, bagworms on evergreens should be controlled because the pest can cause serious irreversible damage. On the other hand, Eastern tent caterpillar activity occurs early enough in the season for cherry trees to refoliate without causing harm to trees. 
  • 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 aphids and anthracnose on sycamore.
  • 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 ( Bt., insecticidal soaps, horticultural oils, etc.) used first. 
  • Continue to monitor the plant’s health after treating a problem to determine if further action is needed.

And the most important point is to get outside to enjoy your yard and garden!

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