14 MASS. EXPERIMENT STATION BULLETIN 361 



bility of closer cooperation between plant pathologists and greenhouse construc- 

 tion companies. There would seem to be no justification in these times for con- 

 struction with inadequate ventilating area, particularly for tomato culture. 



Proper elevation and exposure contribute to successful ventilation. Situations 

 sheltered by trees and shrubs and buildings, or by surrounding elevations of land 

 are objectionable. The planting of trees and shrubs close to the greenhouse for 

 landscape effect is also objectionable. These conditions obstruct light and air 

 and tend to offset the advantages which desirable greenhouse design can contribute 

 toward efforts to control disease (Fig. 7 B, C). 



PROTECTION WITH FUNGICIDES 



Ordinary preparations of sulfur and copper are of little if any value in con- 

 trolling tomato leaf mold in the greenhouse (17). The vaporization of sulfur 

 combined with sound cultural and management practices is considered the best 

 method of control (8, 17). The merit of vaporized sulfur has been substantiated 

 by scientific reports and growers' experiences. Temperatures around 70° F. 

 combined with bright sun contribute to the volatilization and toxicity of vaporized 

 sulfur. The treatments should begin in April before the disease appears and be 

 continued at about 10-day intervals until the latter part of June. For the fall 

 planting the treatments should be given before the plants are set out and be 

 repeated at 7 to 10 day intervals until early November. The rate of application 

 cannot be computed in any definite ratio but must be judged by the density of 

 the vapors in the greenhouse air. Excessive charges are not injurious except that 

 they are apt to produce a perceptible residue on the fruit which is difficult to 

 remove. 



In practice there has been an evolution of devices for generating and applying 

 vaporized sulfur from a simple assemblage of stove and dish to apparatus of more 

 practical and safer operation attached to the exhaust of an automobile engine 

 and capable of charging large greenhouses in a short space of time. 



The sulfuring of the hot steam pipes is not comparable in substance or effect 

 to the superheating and vaporization of suffur over a heating unit. Sulfur is 

 not vaporized until it reaches its melting point and this requires a steam boiler 

 pressure of around 20 pounds. The usual steam-pipe temperatures merely warm 

 the sulfur and cause it to fume, this being identical with the fuming of the sulfur 

 deposit on the leaf surface under conditions of sunlight and warm house tem- 

 peratures. Even with a pipe temperature high enough to melt the sulfur, only a 

 small amount is vaporized and most of it runs off and is lost. The practice re- 

 quires considerable nightly confinement of the greenhouse air and this encourages 

 the progress of the disease. Moreover, protection is most necessary during the 

 off-heating season when ideal conditions for the disease exist. It is much more 

 desirable to use a special portable apparatus for vaporizing sulfur which can be 

 operated independently of the heating system. 



Bewley and Orchard (9, 10) successfully controlled tomato leaf mold with a 

 spray consisting of 1/8 ounce of salicylanilide paste (Shirlan H. B.^) and J^ 

 ounce of sulfonated oil spreader (Agral 1^) or 1/8 ounce Agral N^ (36) in one 

 gallon of water. The merit of the spray for this purpose has been generally con- 

 firmed (6, 11, 17, 22, 47). The spray does not leave a residue but it cannot safely 

 be used when oil emulsion is used for red spider mite unless 10 days elapse between 

 the two applications. Copper oxychloride suspension (17 percent copper) has 

 also been reported as being effective, but marks the fruit badly. Petroleum oil 



'Manufactured by the Imperial Chemical Industries, Ltd.. Millbank, London, England. 



