As a community of plants, we lupines (Lupinus spp.) are known for our striking flower spires and ability to enrich the soil. However, our growth and beauty can be compromised by a variety of pests and diseases that are common across the United States. Understanding these threats is key to ensuring our health and longevity in your gardens and landscapes.
From our perspective, the most immediate and visible pest is the aphid. These small, soft-bodied insects, particularly the Lupin Aphid (Macrosiphum albifrons), congregate in dense colonies on our succulent new growth, flower spikes, and the undersides of our leaves. They pierce our vascular systems to feed on our sap, which directly weakens us by diverting essential nutrients. More critically, their feeding distorts new growth and their excreted honeydew promotes the growth of sooty mold, which can further inhibit our photosynthesis by coating our leaves.
We are highly susceptible to powdery mildew, caused by various fungi in the Erysiphaceae family. This disease appears as a white or gray powdery coating on our leaves, stems, and sometimes flowers. The fungal hyphae penetrate our leaf surfaces to extract nutrients, causing yellowing and potentially premature leaf drop. This severely reduces our leaf surface area and cripples our ability to produce the energy we need for growth and flowering, especially in periods of high humidity and poor air circulation.
Below the soil line, our root systems are vulnerable to rot, primarily caused by the soil-borne fungi Phytophthora and Pythium, as well as the bacterium Rhizoctonia solani. These pathogens thrive in waterlogged, poorly draining soil. They attack our root hairs and larger roots, causing them to become soft, brown, and mushy. This decay prevents us from uptaking water and nutrients, leading to a rapid decline where our upper parts wilt, yellow, and collapse despite adequate soil moisture—a clear sign our foundational structures are failing.
In moist, cool conditions, snails and slugs are significant predators. They use their rasping mouthparts to create irregular holes in our tender young leaves and can even sever seedlings at the stem. This type of damage is not only unsightly but can set our growth back considerably, depleting the energy reserves we need to establish ourselves and produce our characteristic flower stalks.
Beyond aphids, we are host to the larvae of several Lepidopteran species. The caterpillars of the Genista Broom Moth (Uresiphita reversalis) are particularly voracious. They can skeletonize our leaves, consuming all the green tissue between the veins. This defoliation directly robs us of our photosynthetic factories, forcing us to expend energy to produce new leaves at the expense of flowering and overall vigor.
