Hop

Description

Hop, Humulus lupulus, is a climbing perennial plant in the family Cannabaceae that is grown for its flowers which are used extensively in the brewing industry. The hop plant is a climbing plant with grasping hooks that help it grasp the substrate. The plant climbs upwards in a clockwise direction and has opposing pairs of leaves which are covered in hairs. The plant produces flowers called 'burrs' which develop into scaly cones, or 'hops'. The hop plant vine can grow 6–9 m (20–30 ft) in length and can be harvested for many years. Hop may also be referred to as common hop and likely originated from Central Asia but now grows native in many areas in the Northern Hemisphere.


Uses

Hop cones are usually dried and used in the brewing of beer to impart bitterness and aroma.


Propagation


Basic requirements
Hop plants can grow in a wide variety of soils as long as there is adequate drainage, but a loose loam or sandy loam with a high organic content and a pH between 6.0 and 7.5 will produce optimal growth. Hop plants are perennial and can be harvested for many years, they should be provided with adequate vertical space to allow the vines to spread. Hop plants should be grown in full sun and require a tall trellis or fence which is large enough to support 6 to 9 m (20-30 ft) of vine growth. The plants require a period of approximately 8 weeks at low temperature in order to break dormancy.

Propagation
Hop plants are vegetatively propagated from the pieces of rhizome which should be obtained from a reputable breeder. Only female rhizomes should be planted as it is the female flower that is harvested. Plants grown from seed exhibit highly variable characteristics and are not suitable for commercial production.

Planting
Hops should be planted as soon as the soil can be worked in the Spring. The plants can survive a frost but will not tolerate the ground freezing over. Rhizomes should be kept refrigerated until the soil is ready for planting. Rhizomes should be planted horizontally in trenches approximately 30 cm (12 in) deep, leaving 1.5–2.5 m (5–8.2 ft) between plants. Hop plant require a trellis system in order to train the long vines. The support system usually consists of a supporting pole and wire with strings for the plant to grow on. There may be up to four strings per plant which are fixed from the ground to the wire.

General care and maintenance
After the first year of growth, the plants will produce an excessive amount of shoots which need to be cut back once several shoots have been selected and trained to grow on the supporting structure. Unwanted shoots can also be defoliated using chemicals. Mounding earth around the base of the plants will help to reduce the amount of unwanted shoots. The soil around the hop vines should be amended with compost every spring and the vines will also benefit from a side dressing of nitrogen fertilizer later in the growing season.

Harvesting
Hop cones should be harvested before the first frost. Generally, cones are harvested in mid-August to mid-September. The cones will have a papery texture when they are ready and will produce a fine yellow powder and strong aroma when crushed. The lower bracts of the cone may also be beginning to turn brown. The vines should be lowered to the ground and the cones removed from the plant. the cones should be dried prior to storage by threading them out thinly on a screen and allowing to air dry. The cones are fully dry when the inner stem becomes brittle.



References

CABI Crop Protection Compendium. (2008). Humulus lupulus datasheet. Available at: http://www.cabi.org/cpc/datasheet/27956. [Accessed 18 November 14]. Paid subscription required.

Drost, D. (20100. Hops in the Garden. Utah State Cooperative Extension. Available at: http://extension.usu.edu/files/public.... [Accessed 18 December 14]. Free to access.

Mahaffee, W., Pethybridge, S & Gent, D. H. (2009). Compendium of Hop Diseases and Pests. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap....Available for purchase from APS Press.


Common Pests and Diseases

Sooty mold
Cladosporium spp.
Fumago spp.

Symptoms
Flat layer of black mold on the leaves (including bracts), and cones; reduced cone quality; wilting of the climbing vines; rapid death of leaves
Cause
Fungal complex
Comments
Mold can develop on sticky residue left behind by aphids

Fusarium canker (Cone tip blight)
Fusarium spp.

Symptoms
Cankers on the base of the climbing stem (bine); sudden wilting of bines at flowering or in high temperatures; leaves at the tips of the cone turning brown; inner supporting portion of the hop cone is brown and dead
Cause
Fungi
Comments

Powdery mildew
Podosphaera macularis

Symptoms
Pale green to yellow spots on top side of leaves; white lesions developing from spots on the leaves, stems, or cones; lesions developing white, powdery fungal masses; slow growth of shoots; shoots covered with white fungal powder
Cause
Fungi
Comments
May cause the hops to dry early; disease favors high wind and little sunlight

Downy mildew
Pseudoperonospora humuli

Symptoms
Stunted, brittle, and light colored shoots; flowers turning brown; curled and/or cup shaped leaves; brown lesions with yellow halos on underside of leaves
Cause
Fungus
Comments
Symptoms resemble damage caused by early frost

Gray mold
Botrytis cinerea

Symptoms
Lesions on the tips of leaves associated with the cones (bracts) turning tan to dark brown; discoloration may spread from the bracts to the entire cone; gray fuzzy growth on the tip of the cones
Cause
Fungus
Comments
Disease favors high moisture and high temperature; symptoms are not evident in dry weather

Red crown rot
Phomopsis tuberivora

Symptoms
Red to orange discoloration of the inner tissue of the plant; uneven root growth; yellow lower leaves; climbing stems developing little side branching
Cause
Fungus
Comments

Verticillium wilt
Verticillium albo-atrum.
Verticillium dahliae

Symptoms
Yellowing of leaf tissue between the veins; swollen climbing vines with brown discoloration of the inner tissue
Cause
Fungus
Comments
Disease favors nitrogen rich soil

White mold. (Sclerotinia wilt)
Sclerotinia slcerotiorum

Symptoms
Water-soaked lesions on the stem just below the soil line; tan to gray lesions develop out of the water-soaked region; white fluffy fungus and hard black specks on diseased tissue; yellowing leaves
Cause
Fungus
Comments
Disease favors poor air circulation and wet, cool environments

Hop aphid
Phorodon humuli

Symptoms
Curling and/or wilting leaves; brown wilting cones
Cause
Insect
Comments
Aphids feed on the underside of hop leaves; aphids transmit a variety of viruses; sugary residue that they excrete promotes sooty fungal growth

California prionus beetle
Prionus californicus

Symptoms
Wilting and yellowing of the climbing vines
Cause
Insect
Comments

Japanese beetle
Popillia japonica

Symptoms
Leaves stripped down to skeleton of veins
Cause
Insect
Comments

Potato leafhopper
Empoasca fabae

Symptoms
Parts of leaves withering and turning brown in a V-shape; reduced plant growth
Cause
Insect
Comments

Two-spotted spider mite
Tetranychus urticae

Symptoms
Small light colored spots on leaves; brown leaves that shrivel and die
Cause
Mite
Comments

Black root rot
Phytophthora citricola

Symptoms
Blackened and water-soaked areas on the roots; yellowing leaves; wilting stems; blackened leaves which remain attached to the stem
Cause
Oomycete
Comments
Disease favors poorly drained soils which are regularly wet; easily mistaken for Verticillium wilt or Fusarium canker

Mosaic virus
Hop mosaic virus (HpMV)
Hop latent virus (HpLV)
American hop latent virus (AHLV)

Symptoms
Yellow and green mottling between the leaf veins; reduced plant growth
Cause
Virus
Comments
Hop mosaic virus causes the most damage; yield losses between 15-62%; transmitted by hop aphid