G-Men of Plant Diseases

by PAUL R. MILLER

FOOD CROPS are attacked by many enemies even in ordinary times. They are especially vulnerable in time of total war. An epidemic in a mainstay crop in wartime could have disastrous results. There are virulent kinds of deadly organisms that could quickly destroy whole crops if distributed when weather conditions are right.

The freedom with which persons move about in this country and the possibility in wartime of distributing disease-causing material by aircraft favored deliberate attempts at such distribution. Strains on transportation facilities enhanced the opportunity for introduction, by friend or foe, of new pathogens. Imports, which normally come to a few ports, were coming to various points along the east coast and made the job of the Plant Quarantine Service that much harder. Also, the activities of submarines were a constant source of danger, because torpedoed cargoes were washed ashore, with an attendant possibility of escape of disease-producing organisms.

On that reasoning, the Plant Disease Survey established the emergency plant disease prevention project in 1943, with the approval of the Secretary of War and support from the President's emergency funds. Broadly stated, the purpose was to help protect the country's supplies of food, feed, fiber, and oil by insuring immediate detection of enemy attempts at crop destruction through the use of plant diseases, and informing production specialists and extension workers promptly regarding outbreaks of plant diseases, whether introduced inadvertently or by design.

The field work was conducted by 24 pathologists, assigned to territories all over the United States. Special attention was given areas of concentrated food production. The field workers were already familiar With the geography and cropping practice of the region in which they worked, and had the help of experiment station officials, county agents, State workers, and others. Laboratories were established at Beltsville and at Stillwater, Okla., with consulting diagnosticians in charge, to whom puzzling cases of plant diseases were sent for verification.

Attention was focused primarily on important food crops, but an effort was made not to overlook disease developments among other plants. The G-men of plant diseases, who were well versed in field diagnosis, spent most of their time in the field, gathering and recording information. They made weekly reports to officials of the State where the observations were made and to Beltsville for publication and action.

For reasons of national security, it was not prudent during the war to discuss malicious activity, and even now certain important phases of this work must remain untold : The residual effect of the Japanese balloon missions is still to be determined, and biological warfare, although less spectacular, may have a tremendous potentiality for devastation of life, both plant and animal.

Our more obvious findings concern the geographic distribution of disease. During the survey, many diseases affecting various crops were observed that were either new to science, had not been known in this country before, had not been known to attack the particular crop before, or were found for the first time in a particular area.

Of the 150-odd diseases on about 60 crops reported as having been found for the first time in States where they had not previously been known to occur, I mention a few examples.

Phloem necrosis, a destructive virus disease, has killed tens of thousands of elm trees in the Ohio River Valley from West Virginia and Ohio to Illinois and Kentucky during the past few years, but west of the Mississippi River it had been observed only in southeastern Missouri. During the survey, the disease was found for the first time in localities in Kansas, Arkansas, Oklahoma, and the southern two-thirds of Missouri, from the Mississippi River to the Kansas border.

On corn, the fungus Cercospora zeae-maydis was found to be the predominant cause of leaf spotting in Kentucky and Tennessee. Previously it had been known only in Illinois.

The yellow-spot disease (Helminthosporium-tritici-vulgaris) of wheat was found in Virginia, West Virginia, Kansas, and Nebraska. The first known occurrences in this country had been reported from New York and Maryland a few years before. The disease is considered serious in Japan, but has not seemed to be bad in the United States.

Another wheat malady, the virus disease mosaic, was observed for the first time in Missouri, where it was found to be rather prevalent.