Over the Garden Gate: Zinnias, cannas, and Oh, my! What happened to the marigolds?
If you’ve driven by the intersection of Route 18 and Brodhead Road in Center Township near the Beaver Valley Mall this summer you will have noticed a colorful sight.
Once again, the Beaver County Master Gardeners have planted almost 2,000 annuals, which include five colors of zinnias, yellow marigolds and lantana, magenta verbena and red coleus and begonias.
As a centerpiece on one of the islands, we also plant several hundred red cannas, which are dug out each fall and stored over the winter for the next year. In 2021, we added a native perennial and pollinator garden on the opposite island to enhance the garden’s contribution to the health of our ecosystem. We researched 200 native plants that would provide three seasons of bloom, including coreopsis (Coreopsis lanceolata) for the early season, purple coneflower (Echinacea purpura) for mid-season, and brown-eyed Susan (Rudbeckia triloba) for the late season. The seed heads of these flowers become food for the birds and the hollow stems will provide winter shelter for pollinators and beneficial insects.
Before one planting season is over we are already working on plans for the next. We strive to pick the right plant for the right place, which means plants that tolerate full sun and provide excellent summer growth. Like most gardeners, we review the plants that thrived and those that did not perform as well as we hoped.
Several weeks ago, our beautiful yellow marigolds had magnificent healthy blooms. However, in just a few weeks they began to die quickly. Inspection of the plants and soil for insects revealed none, but upon closer examination of the leaves, we discovered purplish spots, which we assessed as a symptom of Alternaria leaf spot disease. Long periods of warm and humid weather as we have experienced are perfect conditions for diseases to spread. Samples of these plants were sent to Penn State’s Plant Disease Clinic for confirmation of our diagnosis.
Alternaria leaf spot is one of several fungal diseases that can affect many different ornamental and crop plants. Irregular tan to brown spots with purplish margins develop on leaves, usually starting on lower leaves and progressing upward. Have you noticed similar symptoms in your garden? Cultural controls include removing affected leaves if there are only a few or the whole infected plants if necessary. Research and rotate to non-susceptible varieties. To reduce disease spread, give careful attention to the timing of watering (avoid late afternoon or evening) and properly space plants to reduce the amount of time during which the plants remain wet. Fertilizing your plants will give them more vigor to resist disease.
You can learn more about the Penn State Plant Disease Clinic at http://plantpath.psu.edu. Check out our Facebook page at Penn State Master Gardeners of Beaver County for photos of the gardens we maintain and for helpful gardening tips. If you have questions about fungal diseases or any other gardening questions, contact the Garden Hotline at beavermg@psu.edu. Be sure to include a few photos to help us more accurately respond to your query.
Fran Lopinsky is a Master Gardener with Penn State Extension, Beaver County.
This article originally appeared on Beaver County Times: Over the Garden Gate: Route 18 marigolds hit with fungal disease
