C66 STATE BOARD OF AGRICULTURE. 



gardens, rotation is strongly urged. While there is no experimental 

 evidence to demonstrate the value of rotation as a means of control, 

 numerous instances have been noted in which rotation has been success- 

 ful in controlling the disease. 



After transplanting to the field, spray with 4-4-50 Bordeaux mixture 

 every 10 days. As has been shown, the period from time of inoculation 

 to spore exudation is at least 13 days. Allowing this leeway for differ- 

 ences in period of infection, it would seem that a spray so applied would 

 give the necessary protection. 



The greatest part of and the strongest infection results from inocula- 

 tion on the lower surface of the leaf. Therefore, all these precautions 

 are less effective if the plants are allowed to run at will over the ground. 

 The spraying of the under side of the leaf is not accomplished unless the 

 application is thorough. Failures to control the disease by spraying are 

 doubtless due to lack of thoroughness and timeliness. 



Moisture acts as a mechanical factor in disseminating the disease in 

 two ways. (1). The dew carries the spores from the mucilaginous mass 

 to all parts of the leaflet to form secondary infection. (2). The rain 

 by splashing, carries the spores from the ground below to the leaves 

 above and in a similar manner carries the spores from the diseased 

 leaves on the ground to the healthy leaves above. 



The mucilaginous matrix holds the spores until they are released by 

 contact with some object. When tl?e plants are dry, the spores do not 

 float in the air or fall from the leaf but stay embedded in this matrix, 

 which becomes hard and strongly cohesive. 



Accordingly the plants should not be "worked" when wet. Growers 

 have reported cases where cultivation began at a small infected patch 

 and the disease was carried over the entire field, and that in less than 

 three weeks the entire field was spotted. This is now readily explained. 

 In greenhouse practice, irrigation should ^replace the ordinary use of 

 the hose. 



Spraying with 4-4-50 Bordeaux mixture in the fields where tomatoes 

 are staked should be extremely successful. In this state spraying will 

 not pay unless the spray reaches the lower surface of the leaves. A 

 sprayer such as is used for potatoes, with two side nozzles set to shoot 

 upward and if practical, with one central nozzle to spray downward 

 for each row will, under high pressure, be most efficient in Michigan fields. 



