INSECTS AND DISEASES IOI 



survive in the dead tissues of the onion leaves and 

 stalks, the necessity for destroying all such refuse needs 

 hardly to be pointed out. The common practice of 

 plowing in stalk and field refuse generally cannot be 

 too strongly condemned, and in the present instance 

 renders the infection of onions grown on the same 

 land another year almost certain. The stalks should 

 __ invariably be burned in a manner to render their 

 destruction as complete as possible. The repeated use, 

 for the same crop, of land on which the disease has 

 appeared, should be avoided ; and in localities where 

 the disease is known to exist, the use of low sheltered 

 land should be avoided for this crop. 



The Onion Macrosporium (Macrosporium sarci- 

 nula Berk; variety parasiticum Thum) In a majority 

 of cases, the mildew just described was followed by a 

 black appearance, resulting from the growth of a fun- 

 gus wholly different from the Peronospora, namely, the 

 onion Macrosporium (M. sarcinula var parasiticum). 

 Although more common and conspicuous among seed 

 onions which have suffered from the mildew, this 

 fungus appears to be almost universal among onions 

 in the state, occurring on market as well as seed onions 

 and sets. Jt is much more conspicuous on the seed 

 stalks than elsewhere, forming a deep black, velvety 

 coating, which sometimes involves the whole stalk. 

 On the leaves it is less conspicuous, often brownish 

 or not so evenly black, and when the mildew has not 

 preceded it, it is less evenly diffused, occurring here 

 and there in patches. 



In regard to remedies in the case of this disease, 

 it is not probable that any direct treatment would be 

 advisable; but it should be kept in check by the sys- 

 tematic destruction of all stalks and field refuse gener- 

 ally, which can only be done effectually by burning. 



