TOMATO LEAF-MOLD 



THE USE OF FUNGICIDES FOR ITS CONTROL IN GREENHOUSES i 2. 

 By E. F. Guba, Assistant Research Professor of Botany 



INTRODUCTION 



Tomato leaf-mold caused by the fungus Chtdosporium fulvum Cke. is the 

 most serious disease of greenhouse tomatoes in Massachusetts. Relatively 

 little experimental work has been done to determine the effect of fungicides 

 on the disease, yet there is recommended in the literature a variety of 

 materials the efficacy of which is unsupported by published evidence. Com- 

 mercial growers have tried most of the materials suggested without success. 

 Experimental work with fungicides in greenhouses has not received much 

 recognition largely because successful control of this disease has been con- 

 sidered a matter of proper management of ventilation and heating. In 

 establishments where management might successfully be practiced it usually 

 fails. 



REVIEW OF LITERATURE 



An effective fungicide for this fungus has been a much discussed subject 

 among pathologists. The earlier literature on the subject has been reviewed 

 by Makemson (22). Previous to his study of the fungus some authorities 

 recommended copper mixtures and others sulfur, while others were unable 

 to obtain results with either group of fungicides. Makemson found from 

 spore toxicity tests that Bordeaux mixtures, ammoniacal copper carbonate 

 and potassium sulfide were entirely ineffective and that formaldehyde at the 

 rate of 1 ounce of a 40 per cent solution to 21/0 gallons of water (.12 per cent) 

 and self-boiled liquid lime-sulfur were toxic while commercial liquid lime- 

 sulfur 2. .5 per cent showed promise. His control work on tomato plants 

 substantiated the results of his spore toxicity tests with Bordeaux mixtures, 

 likewise showed lack of value of sulfur dust and formaldehyde and the slight 

 superiority of commercial and self-boiled lime-sulfur. Makemson's work left 

 the Impression that Cladosporium is not as susceptible to copper as to sulfur. 

 This is unfortunate, for his results from self-boiled and concentrated lime- 

 sulfur solutions were too meagre and conflicting to afford an accurate esti- 

 mate of their value, and dusting sulfur proved of no value at all. Williams 

 (38) reported that sulfur susjiensions, colloidal sulfur, sodium polysulfide 

 2.5 per cent, potassium sulfide .5 per cent, ammonium polysulfide .5 per cent, 

 Cheshunt Compound .5 to 2 per cent, copper silico-fluoride .2 to .5 per cent, 

 nickel silico-fluoride .5 per cent, and barium silico-fluoride (sat. sol.) pre- 

 vented germination while sodium polysulfide .5 to 1 per cent and lime-sulfur 

 .5 to 2 per cent permitted germination. Of the materials which prevented 

 germination, only potassium sulfide, ammonium polysulfide and Cheshunt 

 Compound .5 to 1 per cent proved safe to tomato foliage, but when applied 

 to infected leaves none affected the viability of the spores. Neither Makem- 



1 The writer is indebted to Professor A. Vincent Osmun, Head of the Department 

 of Botany for valuable suggestions and criticisms in the preparation of the manu- 

 script of this Bulletin. 



2 The information in this bulletin is based on the results of experiments conducted 

 by the writer at the Market Garden Field Station, Waltham, and in commercial 

 greenhouses in eastern Massachusetts. 



