Air Pollution and Chemical Injuries

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Air-Pollution Injury

Sycamore trees are sensitive to ozone, sulfur dioxide, and fluorides, which are released from point-source industrial plants. Consequently, injuries from airborne pollutants often occur near these plants. Airborne pollutants may also cause damage to trees for some distance downwind of the source. Pollutants damage plant foliage by oxidative processes that interrupt normal physiology. Symptoms include stippling, interveinal and marginal chlorosis, and general bleaching of leaves (fig. 39a). Reducing point-source emissions is the only known control. Drought stress (fig. 39b) and some pathogens, can cause leaf symptoms that may be mistaken for air-pollution injury.

Figure 39a. - Tan flecking caused by onzone injury.

Figure 39b. - Interveinal necrosis from drought stress.

Chemical Injury

Sycamore trees are sensitive to several agricultural pesticides, including herbicides and fungicides that are commonly used to control pests in field crops. Clomazone and phenoxy compounds like 2,4-D, are examples of herbicides that can cause chemical injuries when they drift during aerial applications. At higher concentrations, these materials produce symptoms of leaf distortion, curling, and chlorosis (fig. 39c, d). Solvent carriers in fungicide sprays can damage sycamores. Damage from pesticide spray drift can be avoided by carefully planning applications and spraying during periods of low wind.

Figure 39c. - Bleaching of leaves caused by the herbicide clomazone.

Figure 39d. - Cupping, curling, and necrosis of leaves caused by the herbicide 2,4-D.

References

Leininger, T.D; Solomon, J.D.; Wilson, A. Dan; Schiff, N.M. 1999. A Guide to Major Insects, Diseases, Air Pollution Injury, and Chemical Injury of Sycamore. Gen. Tech. Rep. SRS-28. Asheville, NC: USDA Forest Service, Southern Research Station. 44 p.