Introduction:

Spray drift:

Very few experiments have studied the potential impacts of herbicide spray drift on non-target plants present near field margins, or in semi-natural and natural areas (Marrs et al. 1991). In many parts of the United States, drift related problems have occurred for many years and have developed into complex social as well as biological issues (Al-Khatib et al. 1993). These problems are even more prominent in areas where agricultural lands are transforming into urban and residential settlements (Al-Khatib et al. 1993). In the Midwest United States, growers of vegetable crops and home gardeners, often find their gardens surrounded by corn and soybean fields (Romanowski 1980) increasing the risk for spray drift injury.
Spray drift can be defined as the physical movement of particles from the sprayer nozzle. These particles can move from their target area to non-target sites where they can damage susceptible vegetation. Herbicide, its formulation, wind speed, spray droplet size, and boom height all contribute to the amount of drift and its potential for injury. Herbicides when applied at recommended rates can selectively affect the growth and species composition of semi-natural vegetation (Marshall 1988; Willis 1988), but knowledge on the impact of sub-lethal herbicide concentrations is scarce (Marrs et al. 1991). Herbicides, such as 2,4-D, acetochlor, atrazine, dicamba, dimethenamid, glyphosate and metolachlor, are commonly used herbicides in corn and soybean fields in the midwestern United States. Our study evaluates the effect of sub-lethal doses of these herbicides on white and red oak seedlings.

White and Red Oak:

The white oak group, especially white oak, Quercus alba and bur oak, Q. macrocarpa are valuable landscape, lumber, and forest species native to eastern North America (Dirr 1990; Elias 1987). White oak is highly sought after for its splendor in landscapes and for its utility for lumber. Bur oak is widely recommended in the Midwest for use in urban areas because of its tolerance to compacted soils, poor drainage, droughty conditions, and air pollution (Dirr 1990). The red oak is native to eastern North America from Nova Scotia to Minnesota , Kansas and Georgia (Flint 1983). The red oak is a fast growing tree and considered one of the best oaks for city planning. It is valuable for street plantings, lawns, parks, golf courses and commercial areas (Dirr 1990).

White oak (L) and red oak (R) are valuable forest species native to eastern North America