TOMATO LEAF MOLD 



25 



coatings were removed and added to water to make a 10 percent extract. The 

 extracts were tested for pH values and atomized on foliage of tomato and lettuce 

 for an index of their toxicity (Table 14). The results confirm the fact that zinc 

 oxide in paint on interior greenhouse surfaces can be a major cause of drip injury 

 following fumigation with burning sulfur. 



Table 15. — Amount of Water Soluble Zinc in Residues Resulting from 

 Exposure of Zinc White Paints to Fumigation with Burning Sulfur 

 AND THE Action of Extracts of the Residues on Lettuce and 

 Tomato Foliage 



♦Asbestine =Magnesium silicate, calcium carbonate not more than 4<; 

 Leaded Zinc=Zinc oxide 65%, lead sulfate 35%. 

 tl cc. sample. 



A further comparative test was made of several prepared paints'^ containing 

 different ratios of zinc oxide. The paints were applied to panels of wood, allowed 

 to air dry, and then exposed to fumigation of burning sulfur in a glass chamber. 

 The residues were removed and treated with distilled water to make a 50 percent 

 mixture. All of the extracts were toxic to tomato foliage (Table 15). Quantitative 

 analysis of 5 c. c. samples of the extracts yielded zinc, and the paint residue yielding 

 the smallest amount of zinc sulfate caused the least injury. None of the extracts 

 contained more than a trace of sulfides or sulfites, from which it may be inferred 

 that sulfurous acid is not involved in the problem of injury. The injury to toma- 

 toes in commercial houses proceeds gradually and continuously for a long time 

 and often extends into the second and later plantings after fumigation. This 



■•Paints were supplied by the Sherwin-Williams Company, Chicago, Illinois, and by the Norfolk 

 Paint and Varnish Company, North Quincy, Massachusetts. 



