Rust on Stargazer Lillies

Asked August 1, 2020, 7:33 PM EDT

My Stargazer Lillies have what looks like large rust spots on a lot of the petals. What is causing this? They are watered from the bottom so no moisture other than dew remains on them. Earlier in the spring, some of the stalks wither away from the top down, killing all the expected blooms. I don’t see any insects on the plants. I do fertilize with Miracle Grow so I’m perplexed at what this could be?

Clark County Washington

1 Response

Hi--Please read to the end, because I see a couple problems.
From your history, I would say that your lilies have been experiencing a botrytis (gray mold) infection each spring. This fungus favors our cool, wet springs, and may cause the symptoms that you are seeing. Growing conditions can help to control the disease:
Remove and burn infected leaves.

Increase spacing between plants.
Water at base of plants and/or with drip irrigation, do not wet foliage
http://hortsense.cahnrs.wsu.edu/Public/FactsheetWeb.aspx?ProblemId=547

A fungicide containing chlorothalonil may also be used during the early growing season. When it's cool and rainy, you may use the fungicide every 7 days. Always follow label directions for application. These are some of the products that are registered in WA for home use:
BONIDE FUNG-ONIL MULTI-PURPOSE FUNGICIDE
FERTI-LOME BROAD SPECTRUM LANDSCAPE&GARDEN FUNGICIDE
GARDENTECH DACONIL FUNGICIDE
HI-YIELD VEGETABLE, FLOWER, FRUIT & ORNAMENTAL FUNGICIDE

This could also be fertilizer burn. You should only be fertilizing your lily in spring as it starts growing. Use a granular fertilizer formulation such as one with 5-10-10. Do not fertilize again until next spring.
https://www.ndsu.edu/pubweb/chiwonlee/plsc211/student%20papers/articles05/sletto,%20amanda/asletto/asletto.htm