EFFECTS OF SPRAYING PLANTS WITH SUSPENSIONS OF INERT DUSTS

In an examination of possible harmful effects to plants caused by spraying leaves with inert dust suspensions it was shown that Stockalite (kaolin), talc, silica or Tiona W.D. (titanium oxide), suspended in water and sprayed on excised leaves of three species, significantly (P≯ 0·05) increased water loss and penetration of gaseous ammonia; these increases were not caused by soluble chemicals in the sprays, but depended on intimate contact of the dust particles with the epidermis. With a given dust, epidermal permeability increased with increasing concentration and with decreasing size of particles. The increased permeability persisted for at least 4 weeks and was unaltered by partial removal of deposits; deposits on bean leaves caused more visible damage in dry than in humid air. Water losses from sprayed adaxial and abaxial leaf surfaces were similar, but more was lost when deposits dried on turgid leaves than when they dried on flaccid ones. Spraying potted Coleus plants with a Stockalite suspension increased transpiration and, in one test, decreased the fresh weight of the Coleus shoots. Copyright © 1969, Wiley Blackwell. All rights reserved