CONTROL OF MYCELIAL NECK ROT OF ONION BY ARTI¬ 
FICIAL CURING 1 
By J. C. Walker 
Pathologist, Office of Cotton, Truck, and Forage Crop Disease Investigations, Bureau 
of Plant Industry, United States Department of Agriculture 2 
INTRODUCTION 
Neck, rot of onion, though wide¬ 
spread in its occurrence and at times 
very destructive, is very sporadic in 
its appearance. It has long been 
attributed to one or another species of 
Botrytis, but not until the work of 
Munn 3 upon Botrytis allii was a 
distinct species unquestionably estab¬ 
lished as a cause. Further study by 
the writer has shown that two other 
species of the genus are capable of 
invading the neck tissues of the onion 
and causing symptoms sufficiently 
similar to those caused by B. allii to 
create confusion with the latter. Since 
the comparative morphology of the 
three species and the symptomatology 
of the respective diseases are to be de¬ 
scribed in a separate paper, those phases 
will not be taken up in detail here. For 
convenience the three types of decay 
are designated as gray mold neck rot 
(.Botrytis allii Munn), mycelial neck 
rot ( Botrytis sp. 110), and small 
sclerotial neck rot ( Botrytis sp. 108a). 
During the past nine years the 
mycelial neck rot has been by far the 
most destructive in the Racine, Wis., 
and Chicago, Ill., onion-growing sec¬ 
tions. Botrytis allii sometimes occurs, 
but is not generally common; Botrytis 
sp. 108a is sometimes common on 
white varieties, but the nature of its 
attack does not make it as important 
as Botrytis sp. 110. Since the control 
experiments to be reported herewith 
were conducted in the Racine district, 
the results pertain entirely to the 
mycelial neck rot. 
The severity of mycelial neck rot 
varies widely from year to year. In¬ 
fection occurs presumably about har¬ 
vest time. It has been supposed that 
the common practice of cutting the 
tops at this time exposes succulent 
wounds to the wind-borne Botrytis 
spores and thus favors infection. Con¬ 
trolled experiments to be described 
later show, however, that under certain 
conditions as much infection may occur 
with the white varieties in “untopped” 
as in “topped” bulbs. There is little 
doubt that climatic variation from year 
to year is a very potent factor in de¬ 
termining the amount of infection 
which occurs. Moist weather at the 
proper time to promote sporulation of 
the causal organism on dead refuse 
and to facilitate infection of the bulbs 
at the harvest period is apparently 
necessary to cause an epiphytotic. 
The signs of the disease appear one to 
three weeks later, first, as softening of 
the neck tissue, followed by the ap¬ 
pearance of gray mycelial felt upon 
the decayed parts. From this time the 
fungus advances quite rapidly, causing 
collapse of the tissue, and in addition 
to superficial closely wefted gray 
mycelium there develop numerous 
black kernel-like sclerotia, while under 
sufficiently high humidity a gray to 
dark-brown layer of conidia is pro¬ 
duced. 
It has long been generally known 
among onion growers that white vari¬ 
eties of onion are more subject to 
neck rot than are the red or yellow 
types. Munn 3 has pointed out this 
difference in susceptibility to Botrytis 
allii. It is equally true for the mycelial 
neck rot and the small sclerotial neck 
rot. A discussion of the nature of 
resistance to onion neck rot has been 
given in a previous paper. 4 The 
serious losses are therefore usually in 
the white varieties, and it is with these 
that the problem of control becomes 
acute. In the two sections mentioned, 
the White Globe is the most common 
white variety grown for large bulbs, 
while the White Portugal is grown 
extensively for “bottom sets.” 
1 Received for publication May 29, 1924; issued April, 1925. 
2 Investigations conducted in cooperation with the Department of Plant Pathology, University of 
Wisconsin. 
3 Munn, M. T. neck rot disease of onions. N. Y. State Agr. Exp. Sta. Bui. 437, p. 361-455, illus. 
1917. 
4 Walker, J. C., and Lindegren, C. C. further studies on the relation of onion scale pig¬ 
mentation to disease resistance. Jour. Agr. Research 29: 507-514. 1924. 
Journal of Agricultural Research, Vol. XXX, No. 4 
Washington, D. C. Feb. 15, 1925 
Key No. G-454 
13952—25t-6 
(365) 
