Aphids
There is an aphid for every plant, it seems, and chrysanthemums are no exception. The key is to catch them early before they start to multiply. Squash the little brownish bugs that are feeding on the leaves, and consider using a biological control like encarsia wasps if you are growing them in the greenhouse.
Spider mite
This is likely to be a pest in a hot dry greenhouse, and these microscopic spiders are hard to spot until they start to build up. Occasionally you will spot silvery webbing under the leaves, so the natural predator phytoseiulus persimilis will then need to be brought into help.
Chrysanthemum rust disease
There are two types of fungal rust disease that affect chrysanths: white and brown. The white rust is more serious and you need to remove and destroy any leaves that are developing dimples of pale dust on the top surface. Humidity and warmth is a common cause, so ensure your greenhouse is well ventilated and avoid overhead watering.
Chrysanthemum leaf spot
Chrysanthemum leaf spot is caused by bacteria rather than fungus, with leaves turning blotched and brown. The preventative methods are however the same, ventilation being the key.
Chrysanthemum stem necrosis virus
In case fungus and bacteria are not enough, we can add virus spread by thrips to the list of ailments, but thankfully this is a rare one, and has indeed been eradicated in the UK!
Chrysanthemum powdery mildew
Another fungal disease which creates a white dust over the whole leaf. Remove and destroy affected leaves and increase ventilation in the greenhouse.
Chrysanthemum nematodes
Microscopic worms that burrow through the surface of the leaves, leaving yellow brown spots in their wake as they move up the plant from the soil where they overwinter. Mulching the plants will help prevent their emergence, and changing the soil might well be necessary.
Why are my chrysanthemums not flowering?
Chrysanths are a late flowering species, so you will need to be patient. Don’t give them too much nitrogen rich food, a well-balanced potash feed such as liquid seaweed is what they need.
Why is my chrysanthemum dying?
Depending on the time of year, this could just be the plant’s natural cycle of losing its leaves in readiness for winter dormancy. If this happens in spring or summer then it could well be suffering from drought or even over watering. Take a look at the leaves and check them out for any of the symptoms listed above.
Why are my chrysanthemums turning brown?
If the whole leaf is turning brown, this is likely to be a sign of stress caused by drought or over-watering. If it is a brown spot or pustule this is more likely to be a fungal or bacterial attack, so remove the affected leaves and destroy.
Why are my chrysanthemums not flowering?
If it is in a pot, check that the compost is not too dry or wet. If that is not the problem, turn out the plant and look for little white grubs in the soil – vine weevils are particularly partial to chrysanthemum roots, and wilt will be the first sign of root damage.
There is also a disease known as Fusarium wilt which could be present, but very unlikely in certified stock.
