FIGURE 15—Typical view of a hop field in Oregon at harvest time.
DOWNY Mildew of Hops Causing Serious Damage; Control Studies Under Way
Hops have been grown in many States, but the crop has for years been localized in sections of Oregon, California, and Washington (fig. 15). In 1890 approximately one-half of the 40,000,000 pounds produced in the United States came from New York. Thereafter the production in that State declined steadily, and since 1920 it has been commercially unimportant. About 32,000 acres of hops were grown in the Pacific Coast States in 1934, the production amounting to approximately 35,000,000 pounds with an estimated value of about $10,000,000.
Growers have many problems in connection with the growing and marketing of this crop. At present the most important of these concern (1) the quality of hops produced and their comparison with those of foreign production, and (2) the control of the very serious disease known as downy mildew, which often causes heavy losses.
Hops impart to beer a characteristic flavor and bitterness, depending largely on the quantity of certain constituents present in the hops, of which the resins are of special importance. The soft resins impart the desired flavor to beer, the hard resins having practically no brewing value. It is important, therefore, that all commercial practices be conducted, so far as possible, with a view toward maintaining the quantity and quality of the soft resins. Any progress made in this direction by the flowers and those who subsequently handle and store the hops should permit the industry to meet more effectively the competition of foreign hops.
To encourage concerted efforts and to provide the necessary background of information the Bureau of Plant Industry, through its Division of Drug and Related Plants and in cooperation with growers and dealers, has undertaken an investigation of the various practices involved, to determine the relationship of prevailing methods to the quality of hops and to recommend practicable modifications likely to result in a more uniform and better quality. Attention is given to the influence of fertilizers, stage of picking, methods of drying and baling, and conditions of storage, as determined by chemical analysis of the hops produced under various controlled conditions.
Downy mildew is a fungus disease that has been prevalent in European hop fields since 1920. In this country it-was observed on wild hops in Wisconsin as early as 1909. In 1928 it appeared on cultivated hops in New York and in British Columbia, where a severe outbreak occurred. It was not recognized in Washington until the following year, but in 1930 it appeared in many of the fields in both Washington and Oregon and since then has been the most serious problem of the growers in both States. In the spring of 1934 the first outbreak occurred in California, where it appeared in the coast counties. The spread of the disease and its virulence depend on climatic conditions; cool, humid weather favoring its development. In the Sacramento Valley in California and in the Yakima district in Washington, where hot, dry weather generally prevails during the growing season, the disease may not become established or do serious damage, but in the other hop-growing districts vigorous control measures must be adopted to avoid excessive losses.
The disease attacks all the aboveground parts of the hop plant. It is characterized by two types of spores: (1) Conidia or summer spores, which are capable of spreading the disease at an alarming rate during the growing season if conditions are favorable for the disease, and (2) oospores or winter spores, which are thought to be the chief means of carrying the disease over from year to year. Most of the damage is caused by the effects of the disease on the young vines that develop from the crowns in the spring. These are stunted, causing the so-called “spikes”, which prevent the vines from producing a crop (fig. 16). Under favorable conditions the disease also attacks the hop cones in the late summer and causes a direct loss by lowering the quality of the product. Entire fields are in some cases destroyed, while in others the damage is frequently sufficient to deprive the grower of all profit from his crop.
In 1930 the Bureau of Plant Industry in cooperation with the Oregon Agricultural College undertook an investigation of the disease to assist growers in combating its effects. The problem was approached in two ways: (1) To provide practical control measures in the hop fields, and (2) to develop new varieties resistant to the disease. The first includes studies of the behavior of the disease, its propagation, and the conditions that determine its spread and virulence, also the formulation of methods of control by means of sprays and dusts and of practical cultural methods that minimize its spread. Information of this kind is constantly being brought to the attention of growers in order to provide immediate assistance. The second line of investigation cannot give immediate practical results but seeks rather to provide new commercially useful varieties partly or fully resistant to the disease to replace in the future those now grown and which are especially subject to attack.