A METHOD OF TREATING MAIZE SEED TO DESTROY 
ADHERENT SPORES OF DOWNY MILDEW* 
By William H. Weston, Jr, 
Formerly Pathologist in Charge of Downy Mildew Investigations, Oflce of Cereal Inves¬ 
tigations, Bureau of Plant Industry, United States Department of Agriculture 
POSSIBLE INTRODUCTION OF ORIENTAL DOWNY MILDEWS 
Introduction into the United States of the Sclerospora downy mildews, 
which attack maize and related crops in the Orient, would be especially 
disastrous. These diseases are by nature essentially destructive and 
cause tremendous losses in the Orient. According to all available infor¬ 
mation they would prove equally destructive in the southern portion of 
our own corn belt. 
Despite the dangerous possibility of thus introducing such diseases, 
there is a fundamental need of importing maize, not in commercial 
quantities, but in small quantities for experimental purposes. As the 
extensive maize breeding of Mr. G. N. Collins, of the Office of Crop 
Acclimatization and Adaptation Investigations, has shown, there may be 
obtained from the peculiar types of maize growing in remote countries 
valuable characters which can be combined most advantageously with 
those of our own varieties. 
Under the Federal Horticultural Board regulations (including Quar¬ 
antines 21, 24, and amendments), which thus far have prevented the 
importation of these mildews, the procedure of introducing foreign 
varieties of maize and related Gramineae from infested countries is 
necessarily difficult. As is requisite, such seed is inspected, given such 
treatment as any insect pest or disease found on it may demand, and 
grown under constant observation in an isolated quarantine greenhouse. 
Seed from healthy plants thus grown may then be planted without 
restriction by the experimenters to whom the original shipment was 
consigned. This procedure, although reasonable and necessary, is time- 
consuming and laborious. 
A method of treating maize seed which will eliminate with absolute 
certainty any possibility of introducing maize mildews on such seed 
would be highly desirable. It is the purpose of this paper to present a 
method which the writer, after considerable experiment, has found to 
meet these requirements. 
The oriental downy mildews of maize and related Gramineae all belong 
to the genus Sclerospora of the phycomycetous order Peronosporales. 
Several species are involved, but in the main features of structure and 
reproduction they agree. Through the work of Raciborski (9),^ Rutgers 
(ji), and Palm { 8 ) on the Javan maize mildew; ot Butler (2) on the maize 
mildew of India; of Lyon (5, 6), Miyake (7), and Lee (4) on the maize 
^ Accepted for publication Nov. 24, 1922. 
^Reference is made by numbers (italic) to “Literature cited,” p. 859-860. 
Journal of Agricultural Research, 
Washington, D. C. 
aet 
(853) 
Vol. XXIV, No. 10 
June 9, 1923 
Key No. G-309 
