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Alternative Field Crops Manual


P.R. Carter1, E.A. Oelke2, A.R. Kaminski1, C.V. Hanson2, S.M. Combs1, J.D. Doll1, G.L. Worf1, and E.S. Oplinger1

1Departments of Agronomy, Soil Science, and Plant Pathology, College of Agricultural and Life Sciences and Cooperative Extension Service, University of Wisconsin-Madison, WI 53706.
2Department of Agronomy and Plant Genetics, and Center for Alternative Plant and Animal Products, University of Minnesota, St. Paul, MN 55108. September, 1990.

I. History:

German beermakers have been using wild hop (Humulus lupulus L.) to flavor their brew for hundreds of years. Hop was introduced to the United States from England in 1629. The first commercial hop yard in the United States was established in New York in 1808. Cultivation of the crop rapidly spread south and west. Wisconsin became a major producer of hop for a brief period late in the nineteenth century, but New York remained the leader until the crop was virtually wiped out in both states by downy mildew in the 1920s.

Today, the Yakima Valley in Washington produces about 75% of the hop grown in the United States. The combined total production of Washington, Oregon and Idaho (the major producing states) exceeds 50 million pounds annually. Hop is produced on a limited scale in the Upper Midwest for local markets.

Improved varieties have been selected for resistance to downy mildew, adaptation to mechanical harvesting, and brewing characteristics.

II. Uses:

The manufacture of beer utilizes 98% of the world's production of hop. Before the days of pasteurization, brewers used hop for its antibiotic properties as well as its flavor. In some countries the young shoots are eaten as a boiled vegetable.

The female "cone," which contains the small flowers and later the fruits, has resin glands which produce lupulin. Lupulin contains the essential oils and resins that give the hop its aroma and beer its bitter flavor. The alpha acids in the resin contribute to the bitter components and constitute 4.5 to 7% of the weight of the dried hop in most domestic varieties and 8 to 12% in some English varieties. Eight to 13 oz of hop are used for each barrel of beer.

III. Growth Habits:

The hop plant is a vine that produces annual stems from a perennial crown and rootstock. The shoots, or 'bines', grow rapidly to a length of 18 to 25 ft. As the bines grow, they wind around their support in a clockwise direction, clinging with strong, hooked hairs. The leaves are dark green, hairy, heart- shaped, deeply lobed and serrate. The perennial crown becomes woody with age and produces an extensive root system. The roots may penetrate the soil to a depth of 15 ft or more.

The female flowers are borne in clusters on lateral branches. The hop plant is dioecious (male and female flowers are on separate plants). Female flowers form pale green conelike structures that are 1 to 4 in. long and papery. Seedless hop, which is considered more desirable by brewers, is produced by preventing pollination. Seedless hop weighs about 30% less than seeded hop and is more shatter-resistant at harvest.

IV. Environment Requirements:

A. Climate:

Hop is adapted to a wide range of climatic conditions; ample moisture early followed by warm, dry weather is ideal. In areas where rainfall is lacking and the water table is more than 5 ft deep, irrigation may be required.

B. Soil:

A deep sandy loam is best. Poorly drained, strongly alkaline or saline soils should be avoided.

C. Propagation:

Hop plants are propagated from runners that arise from the crown just below the soil surface. The runners are cut into pieces 6 to 8 in. long, each bearing at least two sets of buds. Cuttings should be planted immediately or if not, stored in a cool, moist, well ventilated place. Cuttings that are poorly developed, misshapen, damaged or diseased should not be planted.

Many hop growers establish a nursery block where cuttings are planted and grown for one season. One-year-old sets are transplanted from the nursery in the spring or fall.

V. Cultural Practices:

A. Seedbed Preparation:

The soil should be tilled to create a weed-free field prior to planting. Cuttings are planted in hills with a spacing of approximately 8 × 8 ft at a planting density of 800 hills/acre. Hop is grown on an overhead trellis system that may be designed to facilitate mechanical harvest.

B. Planting Date:

Plant in early May or as soon as the soil can be worked into a fine, mellow condition. Plant 2 to 4 cuttings/hill with the buds pointed up and covered by 1/4 to 1 in. of loose soil.

C. Pruning:

When the young vines are about 2 ft long, two to six vigorously growing vines are selected for each hill and the rest are removed. One to three vines may be trained up each of two strings staked to the hill and extending up to the stringing wires of the trellis overhead. When the vines reach the stringing wires, the lowest 4 ft of foliage and lateral branches are removed to aid in prevention of disease, especially downy mildew, and insect pests, particularly spider mites. The removal of lower leaves (stripping) must be done carefully to avoid damaging the stem. Shoots arising from the crown are continually removed early in the season in order to promote the growth of the selected vines. Allowing the suckers to remain later in the season seems to promote hardiness of the crown.

D. Fertility and Lime Requirements:

Hop can produce good yields in the Upper Midwest if soil has adequate fertility, although little information specific for Wisconsin or Minnesota soil conditions is available. Approximately 100 lb/acre of nitrogen is removed by the harvested portion of a good yielding hop crop. This amount of nitrogen should be applied on soils with organic matter levels between 2 and 5%. Slightly less N (about 70 lb/acre) is needed if soil organic matter levels are greater than 5%. About 130 lb/acre of N is needed if soil is coarse-textured, organic matter level is less than 2% and the field is irrigated. Split applications are recommended on these coarse-textured soils. Organic matter may be added by returning the spent vines to the field, applying manure or plowing under a winter cover crop such as vetch or small grain.

Levels of phosphorus and potassium adequate for good yields are similar to that required by field corn. If soils have optimum levels of extractable P (11 to 20 ppm for silt loams, 23 to 32 ppm for sands) approximately 30 lb/acre of P2O5 should be applied to replace that P removed by the harvested portion of the crop. About 100 lb/acre of K2O are required for soils testing in the medium K range (81 to 110 ppm for silt loams, 61 to 80 ppm for sands). Lesser amounts can be applied if soil test levels are above medium, but additional applications of about 10 to 30 lb/acre P2O5 and/or 20 to 40 lb/acre of K2O are needed for best growth if soil test levels of phosphorus and/or potassium are less than medium. Fertilizer should be applied and incorporated prior to planting.

E. Variety Selection:

Three types of hop are grown in the United States: the Old World (aroma) varieties; the American varieties; and the new High Alpha (extract) varieties.

Old World (aroma) varieties include the traditional aroma cultivars of Europe and hybrids derived from them that share their aroma and brewing characteristics. These varieties are considered to be of moderate brewing value, with 4 to 8% alpha acid and weak to mild aroma. They are usually early maturing varieties and are adapted to production in a cool climate. Some aroma type hop varieties include Fuggle, Willamette, Columbia, Cascade, and the German cultivars Tettnanger, Hallertauer and Hersbrucker.

Fuggle has been grown commercially in England for more than a century. It became popular in Oregon in the 1930s because of its resistance to downy mildew. Fuggle is also resistant to hop mosaic virus, but susceptible to hop nettlehead disease and to Verticillium wilt diseases. Fuggle has an essential oil content of approximately 1.0 ml/gram of dry matter (1%), an alpha acid content of 4 to 6% and a pronounced aroma.

Fuggle is not trained up the strings the first season and does not produce its first full crop until the third season. Fuggle is an early maturing variety with a low yield potential (1,100 to 1,400 lb/acre). Because Fuggle is not naturally high-yielding, growers generally grow male hop plants with Fuggle to pollinate the female plants, resulting in larger cones.

Willamette was released by the Oregon Agricultural Experimentation Station in 1976. This variety produces seedless hop in the presence of male flowers. Pollinated cones are larger than unpollinated cones, but the seed content is low in this triploid cultivar. The pale green cones are easy to see against the dark green foliage. Willamette matures later than its parent, Fuggle, and is picked in late August or early September in Oregon. This variety has an oil content of 1%, alpha acid content of 6 to 7% and a pleasant aroma. Willamette is resistant to downy mildew, but susceptible to the potato strain of Verticillium dahliae. Willamette produces up to 2,000 lb/acre of dried hop.

Cascade, released in 1972, matures later than Fuggle. It is resistant to downy mildew, but very susceptible to Verticillium wilt and to Prunus necrotic ringspot virus (PNRSV). Willamette has an oil content of 1 to 2%, alpha acid content of 5 to 7% and a distinct fragrance. The orange-yellow lupulin of this variety is plentiful, and the cone feels buttery when rubbed. Cascade produces up to 2,000 lb/acre.

Columbia was released in 1976 by the USDA and the Oregon Agricultural Experiment Station. This nearly sterile triploid cultivar is well-suited to a mechanical harvest. Oil, alpha acid and aroma are similar to its parent Fuggle.

Columbia is medium to late maturing with a yield potential of 1,900 lb/acre.

Tettnanger and Hallertauer are continental aroma cultivars from Germany. These cultivars are fairly tolerant to crown infection by downy mildew, though susceptible to mite infestations. Because yield potential is only 50 to 70% that of cultivars released in the United States, production is based on brewery demand. These varieties are grown organically in Wisconsin and produce up to 800 lb/acre.

The American varieties include Early Cluster and Late Cluster, which are the most widely grown hop varieties in the United States. Both varieties are vigorous, high yielding, and well adapted to mechanical harvesting. The Clusters have similar brewing characteristics, with 5 to 7% alpha acid at maturity.

Early Cluster matures approximately 10 to 14 days earlier than Late Cluster. Early Cluster is resistant to Verticillium wilt, but somewhat susceptible to downy mildew via crown and root infection.

Late Cluster produces up to 2,000 lb/acre. Downy mildew can become a problem late in the season, and the several strains of Late Cluster are also somewhat more susceptible to viruses than Early Cluster.

Talisman, released by the Idaho Agricultural Experiment Station in 1965, is the highest yielding variety in Idaho, with a yield potential of up to 3,200 lb/acre. It matures a week later than the Late Cluster. Talisman has an oil content of 1.5% and alpha acid content of 8 to 10%. Although Talisman is resistant to the crown rot phase of downy mildew, it is vulnerable to the cone phase of the disease. Phytophthora root rot is a problem in waterlogged soils.

The Extract or High-Alpha varieties include Brewer's Gold and Bullion and the new high-alpha varieties.

Brewer's Gold and Bullion were developed in England and introduced into the United States in the 1930s. They are medium to late maturing, with Bullion maturing 10 days earlier than Brewer's Gold. Both are vigorous and well-adapted to mechanical harvesting, with a yield potential of 2,500 lb/acre when grown seeded. They are less susceptible to downy mildew than the Cluster varieties. Brewer's Gold and Bullion are high in essential oils and have an alpha acid content of 8%.

Galena, derived from Brewer's Gold, was released by the Idaho Agricultural Experiment Station in 1978. Galena is generally strung and harvested later than Early Cluster (delayed training postpones the onset of maturity and enhances yield.) Galena is moderately resistant to the crown phase of downy mildew. It also shows tolerance to Verticillium wilt, although if planted in potato ground, some of the young plants may show symptoms of the disease. Galena is susceptible to frost damage and may be difficult to establish. Alpha acid levels average 12% (up to 300 lb/acre of alpha acids).

Eroica is a late maturing sibling of Galena released in 1980. In the Willamette Valley, Eroica is ready to be harvested in mid- September. Alpha acid levels are 10 to 13%, with the potential of yielding more than 300 lb/acre of alpha acids. Eroica is not as stable in storage as Galena or the Clusters. This variety has a moderately high degree of resistance to hop downy mildew and the potato strain of Verticillium dahliae.

Nugget, released by the Oregon Agricultural Experiment Station and the USDA in 1983, matures later than Galena but earlier than Eroica. Alpha acid content is similar to Galena and cone weight yield is similar to Eroica. Nugget has about 2% essential oils and appears to have good storage qualities. Nugget has good resistance to hop downy mildew, but appears to be susceptible to Verticillium wilt.

Olympic is a high alpha acid hop released in 1983 by the Washington Agricultural Experiment Station and the USDA. Olympic tends to produce an excessive amount of male flowers, reducing cone cluster density and yield. Olympic is easily trained and frost tolerant, but it does require meticulous pest control management. It has no resistance to the hop-damson aphid or the two-spotted mite. Olympic has moderate resistance to downy mildew, but shows some susceptibility to Verticillium.

Chinook was released by the Washington Agricultural Experiment Station in 1985. It is considered medium-early in maturity, although in Oregon it appears to be late in maturity. Chinook has 11 to 13% alpha acid and 0.5% oil. This variety has moderate resistance to downy mildew, as well as to the hop-damson aphid and the two-spotted spider mite. It appears to be free of PNRSV and apple mosaic virus.

F. Weed Control:

Mechanical cultivation should begin early and continue until the lateral branches are well developed. Deep cultivation (6 to 10 in.) early is recommended to incorporate surface organic matter, followed by shallow cultivation (2 to 4 in.) later in the season to avoid damaging the shallow feeder root system. Avoid late season cultivation if not required for weed control, as it may inhibit growth and lead to early ripening.

Chemical weed control in hop is usually unnecessary. Only one herbicide is registered for use in this crop in Minnesota and Wisconsin. A preplant incorporated application of Treflan (trifluralin) will kill many annual grasses and broadleaves. Apply and incorporate to 2 in. deep while hop is dormant. Weed control normally lasts 4 to 6 weeks or more. When weeds appear, cultivate as necessary.

G. Diseases and Their Control:

Disease problems can be minimized by selection of resistant varieties and removal of diseased plant tissues. Removing lower leaves on the bines at training time will help prevent the spread of disease and insect pests. Pruning should be performed with clean tools. Caution is advised to avoid damaging crowns during pruning and cultivation.

Downy mildew is most severe in areas of heavy spring rainfall, when the combination of moisture and temperature (60 to 70oF) are favorable for infection and disease development. The varieties that show greatest resistance to downy mildew are Willamette, Cascade, Nugget and Fuggle.

The first symptoms of the disease appear in early spring when a part or all of the new shoots arising from a hill may be infected. Badly infected shoots are unable to climb and are stunted, brittle and lighter in color than healthy shoots. These "spikes" are infected internally by the fungus and may carry millions of spores. The spores can be carried by wind or water to other shoots and can infect the tips of healthy shoots.

Flowers often become infected when blooming occurs during wet weather. Young cones that are infected stop growing and turn brown. When older cones are attacked, part or all of the petals turn brown and cones fail to develop properly.

The hop downy mildew fungus survives the winter as winter spores in infected roots or crowns. The Cluster varieties are particularly susceptible to root and crown infection.

Control of downy mildew requires a combination of sanitation practices and strategically timed applications of fungicides, in addition to the use of resistant cultivars. Roots for planting should be clean and disease-free. Spiked shoots should be removed promptly from the field and burned. Individual plants with infected crowns should be dug and removed from the field. Late pruning (end of April) shortens the time that new growth is exposed to favorable mildew conditions in the spring. It is advisable to treat yards that have spikes or those located near yards with spikes with fungicides before warm, wet weather to prevent new infections.

Sooty mold is caused by the fungi Cladosporium and Fumago spp., which grow on the honeydew excreted by aphids. Moldy cones are considered inferior in quality and may be difficult to sell. Sooty mold can be controlled by controlling the aphid.

Root rots are characterized by a brown or black discoloration and rot of the infected parts. To prevent this problem, growers should select only healthy cuttings for propagation. Well- drained sites usually have fewer problems.

Verticillium wilt can best be avoided by starting with planting stock that is certified free of Verticillium. New hop yards should not be planted on sites known to be infested with Verticillium from previous cropping in potatoes, tomatoes, strawberries or peppermint. Only Galena, Eroica and the Cluster varieties show any degree of resistance to Verticillium wilt.

Viral disease symptoms include leaf and tip distortion, tip die-back, yellow spotting of the leaves, stunted growth, failure to climb and flower blasting. To avoid problems with viral diseases, use virus-free planting stock. Distinctly abnormal plants should be removed promptly, and cuttings should not be taken from such plants.

H. Insects and Other Predators and Their Control:

Hop plants are subject to attack by a large number of insects and other pests. Hop aphids and spider mites are the most important of these pests, but wire-worms, root weevils, omnivorous leaf tiers, western spotted cucumber beetles, corn earworms, and several species of cutworm may also require control measures in some years. Though hop growers in northern Wisconsin have produced good yields using little or no pesticides, applications of chemicals may occasionally be necessary.

Hop aphid infestations develop more rapidly during cool weather. Heavy populations of 8 to 10 aphids/leaf will weaken plants and reduce yields, and the application of an insecticide is recommended. Aphids should be controlled before or during the flowering stage to keep them from entering the young cones. Aphid predators, including lady beetles, green lacewings, and syrphid or hover fly larvae, can be used to help control aphids.

Spider mites feed by puncturing the lower leaf surfaces and withdrawing sap. Each puncture produces a small, light-colored spot. Eventually the leaves become bronzed, shrivel and die. Heavy mite infestation results in weak plants and reduced yield. Unlike aphids, spider mites are more likely to become a problem during periods of warm, dry weather. Mite predators useful in hop yards include the western predator mite and the small black lady beetle. During June, a miticide application is recommended if mite populations reach an average of 10/leaf. Good coverage, especially on the undersides of the foliage, is required to obtain good control.

Cutworms overwinter as larvae or pupae in the soil. The adult moths emerge in late spring and lay eggs. The larvae that emerge from the eggs feed on plant stems at night. Cutworms can generally be found just beneath the soil surface during the day.

Omnivorous leaf tier larvae feed on the growing tips of vines. They destroy the tips, thus stimulating growth of lateral shoots. This injury has minimal effect on yield, but when it occurs new shoots have to be trained.

I. Harvesting:

Hop harvest in the Northwest usually runs from mid-August to mid-September. In northern Wisconsin the aroma varieties Hallertauer and Tettnanger approach maturity in late August. Hop is in prime condition for picking for only 5 to 10 days. Premature harvest results in loss to the grower from dry-down (weight loss during drying). After the crop has reached full ripeness, shattering loss increases and cones rapidly become discolored. Because harvesting can be a lengthy process, growing varieties of differing maturities allows for a longer season of harvest.

Hop cones can be picked by hand or mechanically. Most hop growers who harvest the crop mechanically use stationary picking machines. The vines are cut loose from the hill and the trellis wires about 4 ft from the ground. The cut vines are laced into "combs" mounted on a flatbed truck and transported to the picking machine, which strips the hop and most of the leaves from the vines. The hop then passes through a forced air stream to remove debris.

J. Drying and Storage:

Moisture content of the hop cone must be reduced from 65 to 80% to 8 to 10% for storage. Continuous flow dryers blow 140 to 150°F air through layers of hop on a moving belt. Most hop are bleached and conditioned by sulfur dioxide fumes blown through the hop during the drying process (1 to 4 oz of sulfur/100 lb of green hop). After drying, the hop is moved to a cooling room for a week to allow the temperature and moisture content of the cones to level out (even up). As the cones even up, they also toughen up and acquire a finer aroma and better appearance. It may be necessary to humidify the air in the cooling room. The cured hop is then baled or pelletized. Cold storage and transport at temperatures below 40°F is the best protection against deterioration of hop.

VI. Yield Potential and Performance Results:

The yield and performance of hop in the Upper Midwest is competitive with that of the Northwest. In addition to the total yield in cones, it is important to consider the yield of alpha acids. The cultivars Galena, Eroica and Nugget produce the highest yield of alpha acid (300 lb/acre). Other quality characteristics brewers may value are color, oil content and aroma.

VII. Economics of Production and Markets:

The total cost for establishment and the first year operation of a hop yard (based on a 220 acre hop ranch in the Yakima Valley, Washington) is approximately $4,800/acre. Fixed costs, such as the cost of equipment, building and land ownership, amount to approximately 18% of the total cost. Variable costs make up the remaining 82% of total cost and include machinery operation, labor and the services and materials that are required. The total cost of operation of an established hop yard based on similar budget assumptions is $2,800/acre. Labor costs typically amount to close to 50% of the total cost of operation.

Gross receipts from production are difficult to estimate due to the variability in yield and of the commodities contract price. Most hop sales are contracted at a specific price for as long as 7 years in advance. In 1989 breweries paid $1.35 to $1.85/lb for standard domestic hop. Certain imported hops sold for as much as $6.00/lb.

There is an increasing market of small, local breweries producing specialty beers, which are increasing in popularity. These brewers tend to use a high hopping ratio and pay more for their hops. Other markets are home brewer supply stores, independent hop suppliers and organic herb shops.

Contracting a market and a careful cost analysis of establishment and production costs are important first steps in becoming a successful hop farmer.

VIII. Information Sources:

References to seed dealers and pesticide products in this publication are for your convenience and are not an endorsement of one product over other similar products. You are responsible for using pesticides according to the manufacturer's current label directions. Follow directions exactly to protect people and the environment from pesticide exposure. Failure to do so violates the law.