SAN DIEGO COUNTY – As fall approaches, homeowners and green industry professionals take steps to prepare landscapes for the winter. Leaves are swept away for composting or disposal, perennials and shrubs are pruned, hedges are trimmed, and pesticides are applied in anticipation of next year’s growing season.

For professional arborists and landscapers, fall and early winter is an effective time to use pesticides, a broad term that includes products that kill insect pests and all also kill weeds (herbicides).

Leaf diseases

"Many people don’t have to use pesticides at all," says Tchukki Andersen, staff arborist for the Tree Care Industry Association. "Professionals may be able to solve landscape problems without pesticides by choosing non-chemical alternatives, such as sanitation procedures and selecting shrubs and ornamental trees that are less susceptible to diseases and insects.

"For example, an infestation last year may only require all the old plant material be cut out," notes Andersen. "Often, cultural practices (pruning, raking leaves, etc.) will go a long way toward solving pest problems."

For homeowners who decide to use pesticides, the Tree Care Industry Association offers these suggestions:

• Identify the pest first. There is no use in applying a pesticide that won’t address your pest problem.

• Don’t be tempted to use agricultural chemicals. They aren’t designed for use by homeowners. A small miscalculation in the mixing of a small batch could result in drastic overdosing.

• Buy the least toxic chemical. Most chemicals available to homeowners use the signal words "caution," "warning," or "danger" on their labels. Try to avoid those with the "warning" and "danger" labels, as they are more hazardous.

• Never mix herbicides with other kinds of pesticides, and never use the same equipment to spray herbicides and other pesticides. You could unintentionally kill Advertisement

[ Chatton and Associates ] the plants you are trying to protect.

• Don’t mix or store pesticides in food containers, and don’t measure pesticides with the measuring cups and spoons you use in the kitchen. Always store pesticides in the original container with the label intact.

The best choice may be to consult a professional who can diagnose pest problems and recommend chemical or non-chemical alternatives. A beautiful lawn, shrub or tree isn’t worth the trade-off if pesticides are not being used properly.

Herbicides

Fall is a good time to inspect walkways, driveways and patios for those annoying trapped seeds. Despite drought and frequent sweeping, some seeds from weeds, grasses and trees will have germinated, lining joints with unsightly green. Other seeds simply lie in wait until the spring. This new growth must be stopped before the growing season arrives and those small cracks become gaping holes filled with vegetation. Herbicides are the most cost-effective way of eliminating unwanted weeds, but homeowners need to be careful when using herbicides! When they are used improperly, they can just as easily kill your valuable mature trees and shrubs as sprouting weeds. Users should read the product label to ensure proper application methods.

"Herbicides should not be applied on or near desirable trees," cautions Andersen, "or on areas where their roots may extend or in locations where the herbicide may be washed or move into contact with their roots. Even properly applied chemical applications may be affected by rainfall. Some herbicides can be washed off paved surfaces or soak into the ground through the cracked joints – the very place with the greatest concentration of fine tree roots."

If one is contemplating using herbicides, it may be advisable to consult with a professional arborist.