Lupin Aphid and Other Lupine Problems: Spotting Them Early and What Works

Know what you are looking at

Lupines have a short list of problems, but two of them move fast enough to ruin a season in under a week, so identifying them quickly matters more than knowing the whole list. Learn the difference between a plant covered in aphids, a plant grazed by slugs, a plant with mildew and a plant whose root has rotted, because each is treated completely differently and three of them are unrecoverable if left.

The table below covers what you are actually likely to meet. Work through it from the top: the first two account for the great majority of complaints, and the last is the one people misdiagnose as everything else.

Check weekly from the moment the leaves are up, and twice weekly once the buds show. A single walk down the bed with the leaves parted takes a minute and is the whole of lupine pest management done properly.

Lupin aphid: the one that takes a week

This is not an ordinary greenfly. Lupin aphid is a large insect, up to about an eighth of an inch (4 mm), pale gray-white with a mealy waxy coating, and a colony reads at a glance as a gray crust rather than as individual insects. It arrives on the soft growing tips and on the flower spike, and it breeds fast enough to smother a spike within four or five days.

The damage is severe out of proportion to the size of the insect. Spikes become distorted and fail to open, buds abort, foliage wilts, and a heavily infested plant sheds so much sticky honeydew that black sooty mold follows on the leaves below. On a plant already carrying a full set of spikes, a bad attack can cost the entire display and set the plant back going into the following year.

Water is the most effective single tool. A firm jet from a hose knocks the colony off, and because these aphids are large and poor at climbing back onto a plant they do not recover quickly. Repeat every day or two for a week and check the growing tips each time; missing one small cluster restarts the whole thing.

Soft growth is what attracts them, which is the practical reason not to feed lupines. Ladybirds, hoverfly larvae and small birds all take lupin aphid readily and will clear a moderate colony given a few days, so hold off on anything that harms them until you have seen whether the predators arrive. If you do resort to a spray, treat the spikes and growing tips specifically, in the evening, rather than drenching a plant in flower.

1. Look at the tips twice a week From the point where flower buds are visible, check the top three inches (8 cm) of every stem and the undersides of the youngest leaves. A colony is easiest to remove on the day it appears.
2. Hose the colony off at once A firm jet directed up under the spike removes most of the colony. Support the stem with your free hand so you do not snap it, and repeat every day or two until nothing returns.
3. Wipe what the hose misses Squash the clusters tucked into leaf joints and behind the spike between finger and thumb, or wipe them off with a damp cloth. These leftovers are what restart the infestation.
4. Sacrifice a spike if you have to A spike already distorted and encrusted will not recover. Cut it off, bag it and remove it, and put the effort into keeping the remaining spikes clean.
5. Stop feeding Soft nitrogen-rich growth is what a colony builds on. Cutting out feed and rich mulch makes the same plant markedly less attractive by the following season.

Do not spray a lupine in full flower with anything broad spectrum in the middle of the day. Lupines are heavily worked by bumblebees, and hosing plus hand-wiping deals with the majority of aphid attacks without touching them.

Slugs on the spring shoots, and mildew in high summer

Slugs and snails take the fat new shoots as they push through in early spring, and because those shoots are the whole of the plant at that stage, a night of grazing can set a lupine back a month or kill a young one outright. This is the single biggest cause of lupines that never establish after planting.

Protect from the moment the first shoots break the surface until the leaves are open and leathery, three or four inches (8-10 cm) across. Clear the litter, old leaves and hiding places from around the crown in late winter, use whatever slug control you normally use, and go out after dark with a torch on damp evenings during the fortnight when the shoots are most vulnerable. That fortnight is the whole battle.

Powdery mildew turns up later, as white floury patches on the upper surface of the leaves, usually in still air and after the plant has been dry at the root. It rarely kills a lupine but it makes the foliage ugly for the rest of the season. Strip badly affected leaves as you see them, and once flowering is done cut the whole plant to two or three inches (5-8 cm) so it regrows clean.

Downy mildew is a different thing and looks it: yellow blotches on the upper surface with gray or purplish furry growth on the underside, in wet weather rather than dry. Remove affected leaves, stop watering overhead, and space plants at least eighteen inches (45 cm) apart so air moves through the group. In autumn take every leaf away from the crown, because both mildews overwinter in the debris and reinfect next year's shoots from below.

The problems with no cure, and when to give up

A lupine that fails to reappear in spring, or that wilts entirely and collapses in a few days during the season, has almost certainly lost its taproot to rot. This follows waterlogged ground, usually over winter, and there is nothing to treat. The only response is to change the site: replant on a ridge or a raised bed, work grit through a wide area rather than a narrow hole, or move to containers.

Anthracnose is worth recognizing because it is spread by seed and by splashing rain. Stems bend sharply at a sunken, dark lesion and collapse, leaves develop brown spots, and in wet weather the lesions carry pink spore masses. Remove and destroy affected plants, never save seed from them, and do not replant lupines in the same spot immediately.

There is also decline that is nobody's fault. A crown in its fifth or sixth year comes up thin, flowers poorly and picks up every problem going. Nursing it is wasted effort, and it acts as a reservoir of mildew and aphids for the healthy plants around it. Take it out.

Keep a short record of what appeared where and when: the date aphids were first seen, which plants got them worst, when mildew showed up, which crowns failed to come up in spring. After two seasons that record tells you which corner of the bed is too still, which plants are consistently more susceptible, and roughly what week each year to start looking rather than reacting.