Canna Mosaic Virus: Dealing With Mosaic On Canna Plants
By: Liz Baessler
Cannas are beautiful, showy flowering plants that have a well-earned spot in plenty of gardeners’ backyards and homes. Suited to both garden beds and containers and requiring very little maintenance, cannas are bred to have both spectacular flowers and foliage. Because they’re such all-around winners in the garden, it can be especially devastating to discover your cannas are infected with disease. Keep reading to learn more about recognizing mosaic virus in cannas, and how to manage mosaic on canna plants.
What is Canna Mosaic Virus?
There are several mosaic viruses out there. The one that infects cannas and is frequently referred to as Canna Mosaic Virus is also known as Bean Yellow Mosaic Virus. When it infects cannas, this virus causes yellow mottling or chlorosis of the plant’s leaves between the veins. Eventually, this can lead to plant stunting and death.
What Causes Mosaic on Canna Plants?
Mosaic virus in cannas is usually spread by aphids. It can also be spread by the propagation of already infected plant material. If one plant is both infected with mosaic virus and infested with aphids, the chances of the disease spreading to nearby plants is very high.
How to Treat a Canna with Mosaic Virus
Unfortunately, there is no biological or chemical treatment for a canna plant infected with mosaic virus. Carefully examine cannas before buying them to make sure you don’t start with an infected plant.
The best thing to do if your plant is infected is to remove the affected parts of it. This may involve destroying the entire plant.
If the plant is also infested with aphids, immediately separate all nearby plants and kill any aphids you find on them.
If you’re propagating cannas by cuttings, study the leaves carefully for signs of mosaic virus first to ensure you don’t accidentally spread the disease yourself.
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Storing and Planting Canna Rhizomes and Seeds
The best-looking canna rhizomes for retail production are starchy white and should have two or three buds. It is important to keep rhizomes in cool moist storage if not planted immediately. For example, production greenhouses will likely purchase rhizomes from wholesalers in the autumn or winter months, then store them in moist peat or horticultural sand and at cool temperatures (50 F). Dormant rhizomes are fleshy and can be subject to rot if they are too moist in storage, or can dry out from too low humidity, which affects their ability to grow. Highly moist environments attract fungal gnats or fungal gnat larvae to rhizomes. Fungal gnats are short-lived flies that deposit larvae in plant roots and rhizomes. The larvae are known to transmit fungi causing rot. Sclerotium rolfsii and Fusarium spp. are reported to infect canna rhizomes (Kessler, 2007). Storing canna rhizomes or planting them in pots with a thin layer of horticulture sand is sometimes recommended to protect rhizomes from fungal gnats (Cloyd, 2010). If the rhizomes are healthy, and grown in a greenhouse with adequate water, foliage emerges fairly quickly. Dwarf varieties produce flowers within two months and taller varieties may take up to three months to produce flowers.
Cannas grown from germinating seeds produce foliage slower than cannas grown from rhizomes. The brown or black seeds, commonly called “Indian shot” because they look like gunshot, measure 2 mm to 8 mm in diameter and have an extremely hard seed coat. The seed coat must be scarified using a nail clipper or knife to expose the white interior and help the embryo imbibe water. While seeds germinate well at room temperature, added warmth by placing germinating trays on heat mats, or transferring pots with seeds to the warmer temperature of the greenhouse are known to speed germination. The root and cotyledonary sheath are the first to appear at germination and the first leaves appear within two weeks of planting.
A bacterium known as Xanthomonas cannae creates large spots on young leaves. The spots may begin as whitish blemishes, but soon become black. Flower buds blacken and never open. Older leaves may be affected as well, showing yellow spots. No chemical solution is available for the disease. Infected plants should be dug up and destroyed.
- Canna leaf rollers curl the large foliage around themselves and feed inside.
- A bacterium known as Xanthomonas cannae creates large spots on young leaves.
Canna - Virus
Cannas are relatively free of disease, however virus problems have been exacerbated in recent years by growers ignoring disease and shipping virus-infected rhizomes. Symptoms of virus infection range from mild to severe resulting in streaks or spots in the former case and stunted growth as well as twisted and distorted foliage and blooms in the latter.
Cannas are susceptible to Canna Yellow Mottle Virus, Bean Yellow Mosaic Virus, and Tomato Aspermy Virus. Over years, affected cannas will lose vigor, become unsightly, and flower before plants are mature. These viruses are spread by aphids and other sap-sucking insects. There is no treatment for viruses. Destroy (burn) affected plants and start again with healthy rhizomes. Keep any new introductions separate until their health can be established.