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(hop), a genus of perennial and annual dioecious lianas of the family Moraceae. There are four species, distributed in the temperate zone. The European hop (H. lupulus) occurs in the USSR in moist deciduous forests and along rivers; the Japanese hop (H. japonicum) grows in the Soviet Far East.
The European hop is the most commonly cultivated species. It is a perennial with twining ribbed stems that die off for the winter and grow back in the spring from buds of the rhizome. The stems often are greater than 10 m in length. The opposite petioled leaves have small stipules; they are digitipartite or cordate and pubescent beneath. The root system consists of a thickened main rhizome that measures as much as 12 cm across; eight to ten thick principal roots depart from the main rhizome and extend as far as 5 m into the soil. The roots branch into more slender roots and into a dense network of tiny rootlets. The pistillate flowers are gathered in groups of 30 to 50 into cone-like inflorescences, known as hops, located in the leaf axils. At the base of the bracts of the ovary are shiny golden yellow glandules filled with lupulin. The staminate flowers are in panicled inflorescences. The fruit is an achene. The plants grow well and bear fruit readily in regions having a long, not very hot, moderately moist summer. The best soils are chernozems, and slightly acid turf-podzols.
The hops are used in beer brewing. They contain 8–10 percent bitter, tanning, and aromatic substances. The hops are also used with mint and trefoil leaves and valerian roots to prepare a sedative mixture (tea); they are also used as a diuretic and analgesic to treat cystitis. The cosmetics industry also uses the hops. A coarse fiber may be obtained from the stems.
Hop cultivation is concentrated in the Federal Republic of Germany, Great Britain, Czechoslovakia, the German Democratic Republic, Yugoslavia, Belgium, Poland, the USSR, Japan, (where the Japanese hop is also cultivated as an ornamental), the USA, and Australia. In 1975 total world plantings of hops were about 20,000 hectares (ha).
In Russia hops were first cultivated in the tenth century. Plantations are now concentrated in the Ukraine (Zhitomir, Rovno, L’vov, and Khmel’nitskii oblasts) and in the RSFSR (Chuvash ASSR; Mari ASSR; Kirov, Belgorod, and Voronezh oblasts; and Altai Krai). In 1976 hops plantings occupied about 6,000 ha in the USSR; the hops yield was 12–13 quintals/ha (on specialized farms up to 20–22 quintals/ha). Among the best varieties are Klon 30–6, Klon 29–38, Klon 18, Zhitomir 5, and Zhitomir 8.
Cuttings from the rhizomes of three- to eight-year-old plants are set out in the spring in well-fertilized cultivated soil. They are planted in humus-filled depressions spaced at 1-m intervals in rows 2.5 m apart. On older hop plantations manure (40 tons/ha) and inorganic fertilizers (up to 120 kg/ha of NPK) are applied in the fall and are plowed into the interrow areas. In the spring the main rhizome is trimmed: underground parts of the stems and diseased and injured roots are removed. When the plants are 1–1.5 m tall, they are attached to wire supports. During the summer the soil is loosened, the plants are dressed, the shoot apexes are pinched off, and laterals are removed. The hops are gathered in late August and early September. They are dried, cured with sulfur dioxide gas, and compressed in sacks. The life of a hop plantation is 20 to 30 years. Pests include the spider mite, the hop aphid, and wireworms; the most common disease of hops is downy mildew.
REFERENCESKhmelevodstvo. Moscow, 1964.
Slastennikov, V. V. Biologiia i agrotekhnika khmelia. Moscow, 1971.
Uchebnaia kniga khmelevoda. Cheboksary, 1975.
V. P. PROCHAEV