nVENTIimi JNNi'AI. MEETING. 69 



On the other hand, in an orchard that has heen cuhivat- 

 ed and sprayed (of course not plowed in the fall, hut plowed 

 in the spring) and sprayed systematically for twelve years, 

 our results showed 98 per cent of scab on the uns])ra\ed ; so 

 you must not depend upon burying- the foliage. When you 

 are considering that proposition you must not forget fence 

 corners where leaves are stacked up ; those must also be raked 

 out and burned. I don't know whether it would be profitable 

 to do that or not, to rake and burn them. You see this 

 whole question of what practice you shall follow hinges on 

 whether it is profitable or not. There are many ways of 

 controlling diseases which are not practical, but yet w^hich 

 will control diseases if properly carried out, so that probably 

 the most practical way of handling the proposition is a mat- 

 ter of spraying, and then plowing or burning if you think 

 that will be profitable in addition. 



Mr. Newton: You said we should spray just before 

 the rain falls rather than after it ; what is the theory about 

 that ? 



Professor Whetzel: Take the case of apple scab, the 

 spores of the fungus which cause the early infection are in 

 the old leaves on the ground. They are discharged into the 

 air only when the leaf is wxt, when it rains on the leaf, then 

 the spores are shot into the air; they are discharged only 

 during rainy, muggy weather. They are carried by the 

 breezes at that time to the leaves, or to the pedicles, and the 

 pedicles get the infection. More than that, spores cannot 

 germinate and infect a leaf in a few minutes. In the case 

 of apple scab it takes twenty- four to forty-eight hours for 

 the spore to germinate and establish itself, so it is the rainy 

 period, not a showier, which brings about infection. If you 

 wait until that is over to spray so as not to have the fungi- 

 cide washed off, the fungus will already be established, and 

 will develop under your spray. Take the case of black rot 

 in grapes, it will develop under the Bordeaux mixture applied 

 after the rains. So the point is, you want to have the surface 



