241 MASS. EXPERIMENT STATION BULLETIN 271 



fore, must occur the same night or the same morning as tliat in which sporula- 

 tion has brought the infecting conidia into existence. 



Greenhouse cucumbers were injured by dusting with sulfur but not by 

 spraying with Bordeaux mixture 1-1-50, 1-5-50, 2-2-50, 2-10-50, 4-4-50, 3-10-50, 

 or 4-0.8-50, nor by copper acetate, Pickering spray, or milk of lime. 



Cucumbers which had been sprayed, the day before, with Bordeaux mix- 

 ture 1-1-50, 2-2-50, 2-10-50, 3-3-50, and 3-10-50 were inoculated with a suspen- 

 sion of the conidia of P. cubensis in water. There was no infection of any of 

 tlie plants so treated, although every leaf of check (unsprayed) plants became 

 infected. In the greenhouse, Bordeaux niixtui-e, 1-1-50 is 2:»robab]y adequate 

 in presenting infection of cuciuubers by this fungus. 



Strawberry Gold Disease 1930. (E. F. Guba, Waltham)- Experiments 

 are under way to determine the nature and manner of spread of the 

 disease. The possible relation of insects to infection is being determined 

 by W. D. Whitcomb. The value of roguing and the selection of healthy 

 plants for the succeeding planting are being considered as means of con- 

 trol. Data from the exi:)eriments undertaken will be available in 1931. 



Tomato Leaf-Mold. (E. F. Guba, Waltham)- Work on this project 

 during the year has been confined to demonstrations of the control of the 

 disease through air management based on knowledge of the temperature 

 and humidity relations of the fungus. Adequate air circulation to prevent 

 excessive temperatures and to insure rapid removal of water of transpira- 

 tion from the leaf surfaces is essential to the control of the disease. From 

 June to September, inclusive, when heating is not practiced, inside condi- 

 tions should parallel outside conditions as nearly as possible; likewise 

 during warm intervals in May and October, and when the outside tem- 

 perature does not drop below 50° F. With a daily minimum of less than 

 50° F. outside, heat to provide an inside temperature of 60°-65° F. witTi a 

 little ventilation is important. After the middle of November ventilation is 

 not necessary so long as the inside temperature is less than 80° F. 



Old-type greenhouses often lack adequate means of ventilation. Ex- 

 periments have shown that for these houses especially, and for modern 

 types where hand control is not efficient, automatic control of humidity 

 will remove the disease as a factor so far as it influences the yield. The 

 system involves a series of exhaust fans and pipe heat, the movement of 

 the former and the flow of the latter called for independently or in unison 

 by a hygrostat, set (for tomato leaf-mold) to demand heat and exhaust 

 air when a maximum relative humidity of 80 per cent is reached. A low 

 thermostat set at 60° F. guarantees the minimum growing temperature, and 

 a high thermostat set at 70° F. determines the range of temperature with- 

 in which heat may be expected to operate the hygrostat for its control 

 of the humidity. Above this range the humidity is controlled by the ex- 

 haustion of air only. Ventilation was necessary only as the inside tem- 

 perature rose above 70° F. In the fall and winter of 1929-30, automatic 

 humidity control gave 17 per cent less infected foliage than automatic 

 temperature control, and in the fall and winter of 1930-31 (up to Decem- 

 ber 1) 10 per cent less than automatic temperature control. Since the 

 comparison was made with conditions which were subjected to careful 

 hand control except for temperature which was automatically regulated, 

 and in a greenhouse with ample ventilating area, the small difference in 

 favor of automatic humidity control is significant. 



