Insects and diseases can be threatening to trees unless a reasonable diagnosis of the problem is made and the proper treatment is selected.
Plant diseases require three things to develop: the presence of a disease agent called a pathogen, plant susceptibility to that pathogen and environmental factors favoring the activity of the pathogen. These factors are subject to variation, depending on the particular plant and pathogen involved. Infectious disease pathogens include fungi, viruses and bacteria.
Non-infectious plant problems, which account for 70 to 90 percent of all plant problems in urban areas, can be caused by improper watering, improper siting of the plant in too little or too much sun, improper planting techniques, nutrient deficiencies, and temperature extremes, to name a few. Correct diagnosis of problem, caused by either an infectious pathogen or non-infectious condition is essential to effective control and requires careful examination and systematic elimination of possibilities by following these important steps:
- Accurately identify the plant. Infectious pathogens are mostly plant-specific, so this information can quickly limit the number of suspected diseases.
- Look for a pattern of abnormality. Is there a pattern of injury within a plant, or plant grouping? Is more than one plant affected? For example, several plants may show injury all on the south side.
- Examine the roots. Brown or black roots may reflect overly wet soil or the presence of root-rotting organisms.
- Examine the trunk thoroughly for wounds. Weather, fire, lawnmowers, rodents and a variety of other environmental or mechanical factors may cause such wounds..
- Think about current and past management practices. Sometimes a plant's current problem is actually a result of something that happened much earlier. Changes in grade, the use of pesticides or nearby construction work may all contribute to tree problems.
Insects can also cause considerable damage to trees and shrubs. Chewing insects, such as beetles and webworms, eat plant tissue such as leaves, flowers, buds and twigs. Sucking insects, such as aphids and mealy bugs, insert their beak into plant tissues and suck out the liquid cell contents causing leaf discoloration or dieback. Boring insects make tunnels in the wood as they eat through it. The treatment method used for a particular insect problem will depend on the insect species involved.
Your local Extension office is available to help diagnose plant problems, however, most plant problems cannot be diagnosed over the phone. Instead, take in a sample that is representative of the damage you are seeing on the plant, along with a sample of healthy growth if any is available. Extension Educators will diagnose the problem and outline a treatment plan. Sometimes a visit to the site is necessary to adequately observe the damage symptoms and diagnose the problem. Homevisits are available in Dodge & Saunders counties for a small fee- $20.00 per half hour, or $30.00 per hour. To schedule a homevisit, contact the Dodge County Extension office at 727-2775.
Sarah Browning is a Horticulture Extension Educator with the University of Nebraska Cooperative Extension in Dodge and Saunders Counties. She can be contacted by phone at 727-2775: by mail at 1206 W. 23rd Street, Fremont, NE 68025: or by e-mail at sbrowning2@unl.edu
