If you're looking for forgiving plants, you may find your heart's desire in alstroemeria lilies (Alstroemeria spp.), sometimes called Peruvian lilies or lilies of the Incas. Reliably hardy in U.S. Department of Agriculture plant hardiness zones 8 through 11 and easy-care annuals elsewhere, alstroemerias bloom in a host of colors. Many varieties have contrasting, dot-and-dash Morse-code patterns. The 1- to 5-foot ornamentals appreciate full sun along the coast and partial shade in hot-summer climates. A handful of fungal and viral diseases occasionally bother these sturdy, showy performers.
Gray mold, also known as Botrytis blight, invades alstroemerias on warm, damp days when temperatures hover between 70 and 77 degrees Fahrenheit. The fungal spores attack and spread from aged or damaged to healthy tissue once they strike. Decayed areas covered in fluffy, gray or brown spores indicate Botrytis cinerea infection. If you're gardening in a Mediterranean climate, watch for gray mold during rainy fall or winter weather because the spores germinate only on wet plants. Spacing your alstroemerias for good air circulation, watering them from beneath to keep water off their stems, flowers and leaves and promptly removing old or damaged plant parts and debris all discourage gray mold.
Rhizoctonia Root Rot
One of two root-rot fungi to target alstroemerias, Rhizoctonia solani attacks in midsummer, entering at the soil line and moving through the stems. If you have wilted alstroemerias with dry, wiry basal stems and watering them makes no difference, suspect Rhizoctonia. Stopping this disease requires proper bed preparation done the fall before planting. Deprive the fungus of the wet soil it loves by working drainage-improving organic compost into the upper 10 inches of soil. If it persists, remove and destroy the infected plants and water remaining ones only to keep them vigorous.
Pythium Root Rot
While most gardens harbor various Pythium (Pythium spp.) root-rot fungi, alstroemerias in heavy, consistently moist soils are especially vulnerable to infection. The fungal spores penetrate and spread through the roots, dissolving their outer cortical layer and blackening and decaying their interiors. Stunted growth, wilted foliage and collapsing stems all point to Pythium. When the soil dries quickly enough, alstroemerias replace damaged roots and recover before symptoms appear. Improving your soil before planting with composted pine bark at the rate of 4 parts soil to 1 part bark may prevent the disease. If that fails, dispose of the affected plants.
Aphid and thrips insects that occasionally feed on alstroemerias may transmit viruses. Tiny, black winged thrips carry tomato spotted wilt virus, while immobile, pear-shaped aphids sometimes transmit Hippeastrum (Amaryllis) mosaic virus. Foliage marked with irregular lines and spots of white, yellow or dark green indicate tomato spotted wilt virus. Hippeastrum virus causes pale and dark green mosaic patterns on the leaves and stems. Neither is treatable. Destroy your sick alstroemerias and disinfect any tools they might have contaminated in a solution of 1 part household bleach to 5 parts water. After soaking them for five minutes, rinse them in clean water so bleach residue won't damage your other plants.
- North Carolina State University Extension: Alstroemeria
- Fine Gardening: Genus Alstroemeria
- Sunset New Western Garden Book; David E. Clark
- University of California Marin Master Gardeners: Amazing Alstroemerias
- University of California Statewide Integrated Pest Management Program: Floriculture and Ornamental Nurseries -- Gray Mold
- University of California Statewide Integrated Pest Management Program: Botrytis Cinerea
- University of California Statewide Integrated Pest Management Program: Alstroemeria
- Roskam Horticultura: Alstroemeria Cultivation Guide
- University of Illinois Extension: Rhizoctonia Root Rot of Annuals and Perennials
- University of California Statewide Integrated Pest Management Program: Floriculture and Ornamental Nurseries -- Pythium Root Rot
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