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The damson-hop aphid is the commonest and most damaging pest. It moves onto hops in late spring, breeds explosively in warm settled weather, and colonises the undersides of leaves and then the developing cones. A heavy infestation coats the plant in sticky honeydew, which then grows sooty mold, and aphids inside a cone are impossible to remove and ruin it.
Look at the undersides of leaves in the middle of the canopy every few days from late spring. The early sign is a handful of small pale green aphids on the underside of a young leaf, sometimes with a little curling. That is the moment to act. Once the cones have formed and aphids are inside them, there is very little you can do.
Strong jets of water knock colonies off effectively and can be repeated every few days. Insecticidal soap works on direct contact and needs to reach leaf undersides. Ladybirds, lacewings and hoverflies do a great deal of the work if you have not sprayed broadly, so avoid anything that wipes out the predators along with the aphids. Stripping the bottom three feet of the bine and keeping the base weed-free both slow the movement of aphids up the plant.
Aphid pressure varies enormously by season. Note the date you first see them each year; after two or three seasons you will know the fortnight to start checking rather than discovering a heavy colony by accident.
Two-spotted spider mite
Spider mite is the hot-and-dry counterpart to the aphid, and it is worst in a dry summer, on plants against a warm wall, and on anything under cover. The mites are barely visible; what you see first is fine pale stippling on the upper surface of the leaves, as if someone had dusted them with pinpricks. Turn the leaf over and you will find the mites, and in a bad case fine webbing at the leaf joints.
Badly affected leaves go bronze, then dry and drop, and mites will move into the cones and turn them a reddish brown from the inside. That damage is permanent for the season.
Mites hate humidity and moving water, so hosing the undersides of the foliage regularly through a dry spell is a genuinely effective control. Keep the plant well watered, since drought-stressed plants are far more susceptible. Remove and bin the worst leaves. Broad-spectrum insecticide makes spider mite worse, because it kills the predatory mites that keep it in check while the pest itself rebounds quickly.
| Problem | First sign | Where to look | First response |
|---|---|---|---|
| Hop aphid | Small pale green colonies, sticky leaves | Undersides of young leaves, mid-canopy | Water jet or insecticidal soap; repeat every few days |
| Spider mite | Fine pale stippling on the upper leaf | Warm sheltered side of the plant | Hose the leaf undersides; water the plant well |
| Downy mildew | Stunted spike-like shoots, yellow angular leaf blotches | New shoots in cool wet spring weather | Cut out affected shoots and bin them |
| Powdery mildew | White powdery patches on leaves and cones | Crowded shaded parts of the canopy | Thin the canopy; remove affected leaves |
| Wilt | Sudden yellowing and collapse of a whole bine | One bine or one crown, mid to late summer | Remove the bine; do not replant hops there |
| Japanese beetle and similar chewers | Leaves skeletonised to the veins | Upper sunlit foliage in midsummer | Pick off by hand into soapy water |
Downy and powdery mildew
These are two different diseases that need different responses, and telling them apart matters. Downy mildew appears in cool wet spring weather. Its signature is a stunted, brittle, pale shoot with the leaves bunched close together, sometimes called a spike, together with yellow angular blotches on leaves that have gray furry growth on the underside. Infected cones turn brown and hard.
Powdery mildew is a warm-weather problem and shows as white powdery patches on the upper leaf surfaces, on stems and eventually on the cones, which then dry out and discolor. It thrives in crowded, still, shaded canopies rather than in wet ones.
Both respond to the same cultural discipline, which is worth more than any spray in a garden: thin the bines to the number you actually train, strip the lower stems, keep plants far enough apart that air moves between them, water at the base rather than over the leaves, and clear fallen leaves away from the crown in autumn so spores do not overwinter there. Cut out and bin, never compost, any shoot showing downy mildew as soon as you see it. Sulfur-based or potassium bicarbonate treatments help against powdery mildew if applied early, but not once the cones are affected.
Wilt, crown rot and knowing when to give up on a plant
Verticillium wilt lives in the soil and enters through the roots. The sign is a whole bine yellowing from the bottom up and collapsing over a week or two in mid to late summer while its neighbors look fine; cut the stem across and you may see brown staining in the tissue. There is no cure. Cut the affected bine out, take it off site rather than composting it, and do not plant hops or other susceptible plants in that spot again.
Crown rot is the other structural failure and is nearly always a drainage problem. A crown that sat wet all winter either fails to shoot in spring or throws a few weak shoots that die back. Dig into it and it will be soft and dark rather than firm and pale. If part of the crown is still sound you can cut away the rot and replant the healthy piece on a raised mound; if the whole crown is soft, start again elsewhere with better drainage.
Be willing to write off a plant. A hop crown that has cropped poorly for two consecutive seasons despite good light, spacing and feeding is usually either diseased or exhausted, and the fastest route back to a crop is a fresh rhizome from a healthy female in a different part of the garden. Keep a note each year of which crown had which problem and on what date; that record is what turns a repeated annoyance into a pattern you can plan around.
Bin or burn diseased hop material rather than composting it. Downy mildew, powdery mildew and wilt all persist in plant debris, and a home compost pile rarely gets hot enough to kill them.