Lupine Pests

Lupines are brilliant for adding dramatic height and color to the late spring garden. The colorful flower spikes are host to a wide range of beneficial pollinators and predatory helpers in the garden. The flowers are also highly susceptible to infestations of aphids when the first flush of spring growth is dense. Slugs and snails can’t resist the juicy shoots as soon as they emerge from the ground. 

Aphids

Lupine Aphids (Macrosiphum albifrons) seem to be a fact of life when growing Lupines in a home garden. Typically they will begin to show up in mid-spring as the new growth is quickly developing. Thankfully Lupine Aphids are a species-specific pest that will not travel to neighboring plants, although they can cause the life span of a plant to be greatly reduced. Plants that are growing in fully shaded locations or have been overfertilized and producing great amounts of foliage are the first to attract the pale green and white sap-suckers.

Photo by Peter Abrahamsen, unedited, Flickr, copyright CC BY-SA 2.0 DEED

As the Aphids suck the sap from the foliage and tender stems growth will begin to appear twisted and distorted. Over time sticky honeydew will be more noticeable as it is excreted by the insects, quickly coating lower leaves and plants that are close nearby. Lupines are not typically long-lived perennials, only really growing well for 3-5 years before repeated outbreaks of aphids weaken the plant.  

Treating Aphids on Lupine

A sharp stream of water from a hose helps to knock Aphids off of plants while also clearing any honeydew or sooty mold that has begun to thrive on the honeydew. Horticultural soap or oil sprays are useful early in the season to protect new growth, although they will need to be reapplied every few weeks or after heavy rain episodes. Removing heavily infested plant material is a great way to spur more growth by the plant and physically remove any adults and possible unhatched eggs. Complete removal of the plant may be necessary with a heavy infestation. 

Preventing Aphids on Lupine

Air circulation and the amount of sun the plant receives are key to controlling the amount of Aphid activity on Lupines. At least 6 hours of sun exposure ensures not only prolific flowering but strong growth that is better able to defend against attacking pests. Lupines rarely need supplemental fertilization. They are in the Legume family of plants and are able to harvest nitrogen from the atmosphere, developing nodules of the macronutrient at their root ends.

Over-fertilizing Lupines promotes heavy foliage growth that is weak and very likely to attract Lupine Aphids from seemingly nowhere. Remove all affected leaves and stems and dispose of them in the trash, not your garden compost bin. Aphids overwinter easily on spent plant material, especially in areas with mild winters. Cutting the whole plant back as part of your fall clean-up will help to reduce future populations. 

Slugs and Snails

Mollusks (mainly slugs and snails in a home garden) are most active at night or on overcast and damp days when they can easily move from place to place leaving their telltale sticky trails behind them. The damage to Lupines occurs mainly just as the new season's growth appears. The ends of developing stems will be ragged. More mature leaves will have ragged edges where the snails and slugs have fed.

Also, look for clusters of opaque or white eggs on the undersides of pots, old wood, or in the corners of raised beds. These are laid in the late fall and will hatch in early spring or summer. Climates that have mild winters will see damage earlier in the spring as the adult mollusks stay active when temperatures remain above freezing. 

Treating Slugs and Snails on Lupine

Protecting plants with biologically friendly slug baits (Sluggo or a similar brand with a main ingredient of iron phosphate) will dramatically reduce the damage to new shoots in the spring. Gardeners in areas with heavy spring rains will need to reapply the baits a necessary as rain will dissolve the pellets. Hand-picking and setting traps of beer or orange halves also work well as long as they are emptied or replaced on a regular basis which could be daily in gardens with high slug or snail populations.

Damage to more mature parts of the plant will need to be pruned out to prevent any diseases or other pests from taking advantage of a weakened plant. Native songbirds, chickens, ducks, snakes, or toads love to make a meal out of slugs and snails and are easy to encourage into your outdoor spaces. 

Preventing Slugs and Snails on Lupine

Slugs and snails prefer very dark and damp locations, often spending daytime hours resting under heavy mulches, sections of the garden with deep ground covers, and under pots and other garden debris in shaded locations. Removing non-plant material from the garden where slugs can hide will reduce populations or at least move them away from your plants.

Water during daytime hours so that garden beds are mostly dried before nightfall. Sharp gravel for paths or mulching in areas with heavy populations will reduce damage. Only grow shady plants that slugs do not like and make sure to grow sun-loving plants in a location with at least 6 hours of full sun exposure. 

Common Lupine Pests Chart

Sources: “Common Problems - Insects and Mites”, Washington State University Hortsense. www.hortsense.cahnrs.wsu.edu