Insect and Disease
Damage Symptoms
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HOPS | |
Nutrient
Deficiencies, Insect and Disease Damage Symptoms |
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Deficiency N-Nitrogen P-Phosphorus K-Potassium Insects Aphids Spider Mites Diseases Powdery Mildew Downy mildew Virus |
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Introduction This information is intended to help identify common problems associated with growing hops. If detection is made in the early stages of growth there is a better chance of developing a solution and reducing the effects of the problem on your harvest and increasing yield. Please note that most of the pests and diseases have humuli in the Latin name. This means that they are specific problems on hops and do not infect or inhabit other plants. Therefore if hops do not have a history of growing near your location, these problems will hopefully not exist in your area. Don't let the potential problems of growing hops stop you anymore than the potential of brewing a bad batch of beer. Mainly because of the higher heat used in drying commercial hops, the full aromatic potential may be somewhat diminished. Therefore by using lower drying temperatures and hopefully organic growing conditions, homegrown hops are the best. Good luck in your growing efforts. |
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Growth dwarfed and thin: overall plant is light green in color and turning yellow in the late season. Petioles may become light red in color. Defoloiation early. |
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Leaves are smaller' dark olive green and have a dull appearance. They can fade to a dull orange. There is a tendency for the leaves to curl downward and the leaf petioles to become darker red. Brown spots develop interveinally on the under surface of the leaves. |
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The first symptoms are downward curling of the leaf, associated with a bronzing of the interveinal tissue. The interveinal tissue becomes a paler green and eventually dies, giving rise to interveinal scorch. In the final stages the leaves wither to an ashy-gray color and fall. There may be a marginal scorch on the older leaves. |
Insects can generate large numbers very quickly. Your best defense is to check your plants daily or even twice daily, morning and evening, especially in the early stages of growth. Problems can be corrected and damage reduced if caught early.
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Hop Aphid (Phorodon humuli) A frequent pest on hops. It passes the winter as an egg on woody hosts of the genus prunus(cherry, peach, plum). Winged aphids move to the top of the plant late in the spring. Aphid populations may build very rapidly and if left uncontrolled may result in defoliation. |
| Twospotted Spider Mite (Tetranychus urticae) Mobile Adult(#1) A serious pest of hops grown in the warm interior valleys of the northwestern United States. |
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Mite Webs(#2) Part of the reason mites are difficult to control is due to the webbing. Mite webs protect eggs and mobile mites from contact by sprays. Webbing is usually confined to the main interveinal areas of the underside of the leaf. |
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Mite damage (#3) Mites damage hop leaves by inserting needle-like mouthparts into plant cells and pumping out the contents. Injury appears as light colored spotting. Such feeding injury is an early clue in detecting an infestation of mites. |
| Control Options vary with the intensity of the infestation. Removal by hand, pulling the leaves off and destroying them, or using a hose to knock them off with water. Or you can use deterents like pepper sprays or garlic sprays. Planting borders of flowers such as African marigold, nasturiums and garlic plants will help deter the numbers in the early stages of growth. Organic insecticides such as Pyrethrum, insecticidal soap, nicotine and diatomatious earth work well if effectively applied. Some success can be derived via the introduction of ladybugs and lacewing predator insects as long as the predators decide to stay on the hops. But if the infestation has gone unchecked, when discovered, using commercial insecticides such as diazinon or malathion sprays maybe your only option to try and save the crop. |
An ounce of Prevention is worth a pound of hops.
| Powdery Mildew (sphaerotheca macularis) The fungus first appears as small, circular, powdery colonies on the leaves of hops (photo). Young and rapidly growing tissue is very susceptible to infection by HPM. As the disease progresses, the colony size increases from about a sixteenth of an inch, to a half an inch or larger. More colonies appear on the leaf surface and may eventually turn the leaf and occasionally the entire vine white. Infection of the female flower (or burr) is the most serious form of the disease. If the burr is infected early in its growth, the female flower or cone may not develop at all, or may become deformed and brittle. For susceptible varieties under severe disease pressure, yields can drop by 80% or more, even with the application of fungicides. For a more detailed description of Hop Powdery Mildew see |
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 Small white colonies of HPM on the commercial variety galena mark the beginning of infection (inside the three circles). These colonies will enlarge and produce more spores that can spread to other young leaves and cones and eventually turn entire leaves white with their powdery mass. |
| Downy Mildew (pseudoperonspora
humuli) Under favorable weather conditions the mildew spreads from these shoots and infects leaves and other shoots. In the summer the leaves of infected vines often turn yellow and the vine may die. Other vines may be dark green and leaves cupped and arms stunted. Cone blight often occurs if favorable moisture conditions are present. |
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Infects
both above ground and below ground portions of the hop plant. Control options for the mildews. The use of Cocide, a copper based fungicide, and sulfer are two possible solutions to controlling both downy and powdery mildews. |
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Infected tissue will often develop a black rot. |
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The leaves appear yellowish green, stunted and are cupped downward. |
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VIRUS Symptoms become particularly common during cool periods following a period that has been favorable for hop growth. Yellow ringspots and line patterns develop on the leaves. As the disease progresses the yellow areas die and may evolve the whole leaf. |
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On some varieties the leaves roll upward with considerable interveinal necrosis. |
The side arms are shunted and vine growth is poor. Quite often the growing tip of the vines curves downward and becomes brittle and dies. As the new shoots grow this also happens to them. The leaves are dark green and curled downward. The cones may also turn brown and fail to develop.
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Text and Photos
courtesy of:
J.R. Simplot Company
Pocatello, Idaho 83201
updated 09/25/2003
