Insects, diseases, and weeds are collectively the major causes of injury to plants. However, there are other causes of injury, some biological and others nonbiological (see Table 6-1). Many home gardeners have spent time pondering the cause of chewed leaves and stems on their plants when no insects were to be found. Had they made their inspection at night, or checked under nearby rocks or leaf litter during the day, they would have found the culprits. Slugs and snails are nocturnal (active at night), preferring a cool, moist resting area during the daytime. Of the two, slugs do the most damage, finding their way into residential landscapes, production fields, and even greenhouse benches. They leave behind a trail of slimy exudates as they move, so their presence is easily detected.
Still other biotic causes of plant injury or destruction can be traced to birds, rabbits, rodents, deer, and other animals that feed on plants above and below ground. Rabbits can decimate a bulb display, feeding on the tender foliage or buds as they emerge through the soil in the early spring. Rodents can destroy the vascular system of young trees and shrubs by chewing off the bark at the plants’ base, a condition termed girdling. Deer can wipe out an entire block of nursery plants or devastate a landscape planting by winter grazing.
Abiotic injuries may be environmental such as nutrient deficiencies or excesses, or unfavorable climate. They may also be cultural such as lawnmower or snowplow injury, or vandalism.
With the exception of a greenhouse environment, there are few options available to avoid these types of injuries to plants. Compared to the insects, pathogens, and weeds, their economic impact is small, but if yours is the nursery crop ruined by grazing deer, or the spring floral display destroyed by hungry rabbits, or the manicured lawn or fairway rutted by a thoughtless motorcyclist, the damage is real and just as costly.