My beautiful goldfinch Leucanthemum superbum was blooming beautifully in a sunny spot (full sun) and then some of the stems and blooms turned brown and died. Any idea what might be the cause? And how to fix it and prevent from spreading. The plant next to it is doing week and sending out new buds. Too much rain?
Thank you for contacting Toronto Master Gardeners to inquire about your Leucanthemum x superbum. Leucanthemum x superbum ‘Goldfinch’ is a beautiful cultivar, with the yellowest flowers of the Shasta daisy family. They thrive in dry to medium, well-drained soil in full sun. Good soil drainage is critical. Leucanthemums are susceptible to fungal diseases, including verticillium wilt, leaf spots and stem rots. Common pests include aphids, leaf miners and mites. Check your plant for signs of these 3 pests. If you don’t see any pests, then it’s likely your Shasta daisy plant has a fungal disease.
Fungal infections thrive when there’s high moisture and poor air circulation. As you mentioned, too much rain could be the cause. Ensure your plant is in an area where the soil is well-draining. Remove and destroy any infected plant tissue. Cut right down to the soil level. Water only when the top 3 or 4 inches of soil are dry to the touch during the plant’s early flowering stage to minimize risk of infection. Depending on the type of fungus, organic sulfur or copper octanate can be used to treat the infection. Note that some fungal diseases do not respond well to fungicides. Your nursery should be able to recommend a suitable organic product.
Other cultural practices to reduce the threat of diseases include:
- Remove any plant debris as it falls or accumulates to prevent it from providing a source of disease inoculum or a place for pests to breed and overwinter
- Remove any infected parts of the plant as they appear
- Sanitize any tools you use to remove diseased plants or plant parts. Cleaning with Lysol wipes is an easy method.
- Don’t put any diseased plant tissue into your compost
- Irrigate in early to mid-morning and water at the base of the plants to keep leaves dry
- Increase air circulation by pruning and thinning. Improving air flow helps reduce disease. Prune out over thick growth for better air circulation and better penetration of sunlight.
- Organic matter may stimulate soil microbial activity, which may inhibit development of pathogens. Amending with compost and organic mulches may provide a source of beneficial soil microbes.
- Choose plants that are resistant to fungal diseases
Good luck with your Leucanthemum x superbum ‘Goldfinch’!