VEGETABLE INSECTS 



187 



some, but last year it was recommended not to use it, and i 

 tried it with very good results without the sticker. 



Professor Herrick: I should use only the soap, which 

 helps the tobacco to spread and stick. The objection to these 

 tobacco extracts is that when you spray them on in fine 

 drops, the little drop stays right there — it does not spread 

 like oil. Otherwise, they are the best contact insecticides I 

 have ever seen because you do not have to prepare them. 



Question: Is the black leaf injurious to the cabbages? 



Professor Herrick: The black leaf and the black leaf 

 40 are not in any way injurious to the cabbage. The cab- 

 bage aphis is subject to the attacks of five or six parasites. 

 If you can check the cabbage aphis a little with one or two 

 sprayings, those parasites will get the upper hand and con- 

 trol them later. 



Question : How do you reduce the soap ? 



Professor Herrick: I should just shave it in hot water 

 and heat till it is dissolved. 



Question: When you use black leaf 40, no matter what 

 you spray for, it is advisable to use soap, is it not? 



Professor Herrick: I think it is. 



Question: Can you combine it with lime-sulphur? 



Professor Herrick: You can combine it with lime-sul- 

 phur in spraying apple trees. 



Mr. Russell: You should start to spray as soon as pos- 

 sible after you see them on the plants. 



Professor Herrick: I have watched this cabbage aphis 

 year after year. It will begin in a certain part of the field 

 and gradually spread like the waves on water as you throw 

 in a stone, till fi.nally it covers the whole field. If you would 

 watch that field closely and when you found these little in- 

 fected areas, if you would spray those few thoroughly, you 

 would do a great deal in checking the spread of that insect 

 later in the season. 



