An example of the importance of correlating information from State to State, which was one of our functions, is the epidemic of the potato late blight in Southern States during the winter and spring of 1943-44, of which the Texas outbreak was a part. An epidemic of late blight depends on a combination of two factors, the presence of inoculum, that is, a source of infection, and weather that favors its spread—in this case, a great deal of rain and rather low temperatures. Several circumstances combined to produce a considerable amount of late blight in seed planted in the South. The 1943 crop in northern seed potato areas had suffered a widespread late blight attack with heavy tuber infection, and shortage of seed stocks resulted in the use of a great deal of inferior seed. Ordinarily, southern potato areas are too warm for late blight development regardless of seed infection, but the combination of infected seed and weather—plus, in many sections, lack of control equipment and experience with the disease—was bound to result in an outbreak. The observations on the prevalence and importance of late blight in Florida and Texas served as an indication as to what might be expected to develop in other southern areas, given favorable weather, and put pathologists and growers on their guard.

The disease was epidemic in every Gulf State from Texas to Florida, and north to South Carolina, causing losses ranging from a quarter to half or more of the expected yield. In some of the areas it had rarely occurred before.

Disease-producing organisms carried on the seed are responsible annually for great losses in small grain crops through seedling diseases and root rots. A new approach to the control of these diseases was instituted by the emergency work in Minnesota and the Dakotas. Seed of barley, oats, wheat, and flax, originating in widely separated regions of those States, were cultured to determine which organisms were present and to what extent, so that extension workers could know whether to advise farmers to treat the seed. The basis of their advice was whether the particular organisms present could be controlled and whether they were present in such concentration as to call for seed treatment. This project is one of more than merely immediate benefits: It can save the expense of seed treatment to farmers in regions where it is not likely to be beneficial, it can prevent controllable losses in regions where seed treatment is advisable, and it is likely to result in a progressive eradication of some of the sources of loss.

Virus diseases were shown to be more widely distributed and more common in Utah stone fruit orchards than had been realized, and a reliable method was established for diagnosing infection by rusty mottle of sweet cherry in the absence of the typical symptoms.

Much progress was made toward determining the cause and the factors associated with the spread of decline in citrus and avocado groves in California.

Results of the nematode survey in Florida and other Southern States showed that besides the root knot nematode (Heterodera marioni) many other plant parasitic forms about which very little is known are widespread and probably of considerable importance.

A survey in Virginia showed that the meadow nematode (Pratylenchus pratensis) was very widely distributed and that it was constantly associated with winter browning of boxwood, and probably was involved in much of the so-called winter injury of many plants.

Bad infestations of both the root knot and the meadow nematodes were found on celery in Oregon.

Surveys of diseases of peanuts in the Carolinas, Georgia, and Alabama added a great deal to the available information on distribution of the diseases, the reaction of different varieties to them, the fungi associated with peg rot and with nut rot in the field and in storage, and methods of harvesting and storing to reduce losses from nut deterioration.

The aster yellows virus disease was found in almost all parts of the country except the southeastern area. Some of the important hosts affected most frequently and severely were potato (on this host the disease is called purple-top wilt), carrots, lettuce, celery, spinach, and onion. In the Winter Garden vegetable growing region of Texas, a severe epidemic affected carrots, an important crop there. A careful watch was kept on the course of its development, including the age when plants became infected, effect on the roots, amount of loss from specific degrees of infection, and abundance of the insect carrier.

In Idaho, on potatoes in field and storage, either a new disease or a new serious aspect of a disease was found. The term "water rot" was applied to the condition, and repeated isolations from typical samples yield a fungus identified at the Stillwater laboratory as Phytophthora erythroseptica. In some fields at digging time as many as 50 percent of the tubers showed the trouble, and the rot increased in storage.

I believe the few examples given show the importance of this type of plant disease reconnaissance, whether during time of war or peace. The work provided probably the most comprehensive and constructive picture of plant diseases any country has ever obtained. It seems doubtful that any important plant enemy could have invaded our country during this time without early detection, apprehension, and control. In the past, unfortunately, this has not always been true. As W. A. McCubbin says, the introduction of plant diseases is not a mere theoretical possibility, but a tragic reality. Think of the chestnut-blight fungus that came in, probably from Japan, about 1900, and has since killed practically all of the American chestnut trees; the Dutch elm disease fungus, which arrived about 1930 from Europe, and is still taking its toll of American elm trees; the potato bacterial ring rot organism that came from Europe and has spread throughout the United States; the golden nematode parasite, which has long been a serious pest of potatoes in northern Europe and was found in the United States in 1941.

Of course, plant disease, surveys and quarantines cannot absolutely prevent new pests from entering the country and establishing themselves. Furthermore, the ultimate result of the introduction of a new parasite cannot be predicted accurately, where such complex factors as environment, crop resistance and susceptibility, and presence or absence of a carrier of the disease organism, are concerned.

But consider the amount of damage to American crops caused by new diseases from abroad, and the billions of dollars spent on their eradication once they are established; does it not seem to be good insurance to take all possible steps, first to prevent their introduction, and second to discover their presence before eradication has become too difficult? Truly, an ounce of prevention is worth a pound of control.

THE AUTHOR

Paul R. Miller, a pathologist in charge of the Plant Disease Survey, Bureau of Plant Industry, Soils, and Agricultural Engineering, has spent 15 years developing survey techniques and conducting field studies of diseases that occur on major economic crops, including peanuts, tobacco, cotton, and truck crops. Dr. Miller shared with Dr. H. A. Edson (now retired) the administrative responsibility of the War Emergency Project discussed in this article and in this capacity traveled throughout the 48 States consulting with agricultural experiment station officials and supervising the work of the field staff.