Lupine Diseases

Lupines in the garden are a wonderful mix of early spring color and vertical interest. The flower spikes can be upwards of three feet tall and do a great job of attracting a host of beneficial pollinators and other insects to your garden. Lupines are not without their disease problems though. Just like they seem to attract Aphids from out of the blue, Lupines are regularly struck by some of the most common fungal and bacterial diseases: Powdery Mildew, Leaf Rust, Gray Mold, Downy Mildew, and Fusarium Wilt. These fungal infections remain dormant in the soil until just the right conditions are present.

Mosaic virus is often the result of secondary infection by sap-sucking pests that transmit the disease when they feed on the foliage and stems. The virus is also easily transferred between plants by using contaminated knives or pruners to take basal root cuttings.

Powdery Mildew 

Powdery Mildew is a fungal disease that unexpectedly is prevalent during periods of cool and dry weather. The fungal spores spread easily by the wind on dry foliage which is the opposite of the requirements most Mildew diseases need to be active. The most common symptom is spotting or complete coverage on both sides of the leaves with white or grayish spores and fruiting bodies. New growth can become so damaged that it dies back causing early leaf drop or dieback of whole stems. Older growth is not often harmed enough to slow the growth of the plant. 

Identifying Powdery Mildew

White or grayish spots appear on the top and bottom of leaves when days are warm and dry and nighttime temperatures are cool. Look for infection in the early spring or late in the summer as the weather turns cooler. The spores spread on the wind and between plants when their foliage is disturbed. Eventually, the leaves and stems will be completely covered i spores and have a powdery appearance. 

Treating Powdery Mildew

Removing all affected plant material early is key to preventing the spread of the fungal spores. Because Powdery Mildew is active in dry weather, wetting down the plants before pruning helps reduce the amount of spore transmission between plants. Proper watering during dry periods also reduces the chances that Powdery Mildew occurs. Good air circulation between plants and amongst the stems and foliage is crucial. Resist the urge to over-fertilize Lupines since these Legume family members are self-sustaining even in soils with low nutrition. Look for Lupine varieties that have good or excellent mildew resistance.

Plant Rust

Rust diseases are spread by fungal spores and appear as small orange or rusty-colored spots on the stems and leaves of Lupine. Rust diseases are host-specific but generally require an alternate host such as common weeds to develop and transmit the fungi. The small spots eventually develop into streaks that can run the whole length of affected stems. Rust can reappear year after year overwintering on plant debris left in the garden. Fungal Rust can turn into a seasonal issue occurring when temperatures are cooler or wetter than normal in the spring. 

Identifying Rust

Small red, brown, or blackish dots on one side of the foliage, typically the underside. The spots are collections of spores that multiply quickly. Eventually, the spots turn into streaks of fruiting bodies giving the foliage or stems a rusty or yellowed appearance. Affected portions will turn brown and die back when left untreated. 

Treating Rust

Remove affected foliage and stems as soon as possible. Avoid overhead watering which washes the spores across plants and into the soil where they can easily overwinter. Copper-based fungicides work as a protectant for healthy plants and will need to be reapplied after periods of heavy rain.  Remove weeds from around and in the garden which may act as an alternate host for Rust Fungi.

Gray Mold

Gray Mold is scientifically known as Botrytis. It is a naturally occurring fungus in the soil that takes advantage of physical damage to plants, settling into broken or smashed stems and foliage. Particularly active during the cool nights and warm days of spring, just as Lupine begins to put on heavy growth. Gray mold affects the newest growth first and is quite deadly when it occurs on seedlings. 

Identifying Gray Mold

Damaged stems that are left on plants will begin to turn brown and have a water-soaked look to them initially. Quickly the fruiting bodies grow into a fuzzy covering of grey or black. The fungus will spread steadily killing off the plant eventually. Seedlings can be particularly susceptible if grown in a seed-starting mix that has been used repeatedly.

Treating Gray Mold

The best prevention is removing any damaged parts of the plant as soon as possible. Cut stems all the way to the ground to make sure all of the spores are removed. Avoid overhead watering and only water new plants when necessary. Space plants so that there is good air circulation on all sides and prune away any stems or leaves that are resting on the soil or mulch. 

Downy Mildew

Downy Mildew occurs on most ornamental plants and is more active during warm and humid weather. The fungus can easily move between foliage on a plant through overhead watering or watering late in the evening during humid weather. The most tender leaves and stems are affected and will eventually wither, turn brown, and drop prematurely. 

Identifying Downy Mildew

Purplish or darker spots appear on the top of the leaves when Downy Mildew is just starting to grow. Eventually, the fruiting bodies poke through the leaf and begin to grow as gray mats on the underside of the leaf. The infected leaf or stems will die although established herbaceous perennials are able to survive to regrow the following season. 

Treating Downy Mildew

Remove affected foliage as soon as possible. Clean spent foliage or other plant parts at the end of the growing season to prevent reinfection. Infected plant debris needs to be put in the trash or burned if allowed in your community. Do not dispose of it in your home composting system.  

Mosaic Virus

Viruses in plants are spread through the use of a vector such as certain host plants (often considered weeds in the home garden) or a sap-sucking pest like Aphids or Scale insects. Mosaic virus can be spread by mechanical means as well. Pruning or taking cuttings from infected plants and then not sterilizing your cutting tools will quickly spread the virus from plant to plant. The best way to ensure that Mosaic Virus is not a bother for you is to only buy plants that are not affected by the pathogen or varieties and cultivars of the plants that are highly resistant.  

Identifying Mosaic Virus

Mosaic or mottled patterns on the leaves. Flower spikes that are stunted or distorted in some way. Leaves may become more narrow than usual, eventually drooping and looking like the plant needs water when it is not dry. Infected plants may also have dark ring spots on affected leaves or around stems.

Treating Mosaic Virus

Infestation by Lupine Aphids can make your plants more likely to be exposed to Mosaic virus. Treat insect problems quickly to reduce the amount of damage to plants. Remove potential host weeds from the garden. Always sterilize pruning tools between plants when taking cuttings or deadheading. Look for and buy plants that are labeled as being free of and resistant to Mosaic Virus.

Fusarium Wilt

Fusarium Wilt strikes plants that seemingly are healthy and well taken care of. The symptoms are similar to over or under-watered plants leading many gardeners to try to increase or decrease their dewatering schedules which leads to further damage to the plants. The pathogens that cause Fusarium in Lupine block the normal pathways plants use to circulate nutrients and moisture eventually starving portions of the plant which results in dieback of that section and eventually the whole plant. 

Identifying Fusarium Wilt

Portions of the plant are wilted or drooping even though the plant is well watered and has good soil drainage. Foliage will turn yellow as it dies The roots may not be affected until the disease progresses.

Treating Fusarium Wilt

Fusarium wilt does not respond to chemical sprays and is always fatal. Plants need to be removed as soon as possible. Do not replant Lupines in the same area to avoid transferring the pathogen to new plants. Fusarium Wilt can remain in the soil for years. Buy plants that are certified free of disease as well as resistant.  

Lupine Disease Chart 

Sources: “Hortsense pest and diseases of ornamental plants”, Washington State University. www.hortsense.cahnrs.wsu.edu