Chrysanthemums: Popular for Thanksgiving

Although only those that have been brought indoors may remain, their colors in many shades of yellow and bronze are symbolic of the fall season. While a season of chrysanthemums in the garden is still fresh in mind, it may be well to check over any problems that may have attacked the plants this fall in order to be better prepared for next season. While a few insects attack mums, most people find more problems arise from some of the common diseases. Leaf spots are sometimes a problem, particularly in wet weather or where watering keeps foliage wet.

In the first stages, small dark brown spots develop which gradually increase in size until they unite to form an irregular pattern. These spots normally are more severe on the lower leaves and gradually move up the plant. In septoria leaf spot the affected leaves drop prematurely. In other leaf spots, the general appearance may be similar, but dead leaves cling to the stem after they die rather than drop off. Most leaf spots can be controlled by spraying the plants with a fungicide several times during the growing season.

Materials such as captan, ferbam, or zineb are possibilities. Also, pick off and destroy diseased foliage as soon as noticed and avoid splashing water on the plants. One of the most destructive diseases of chrysanthemums is verticillium wilt. It may be carried on the cuttings, or plants may be attacked by the fungus in the soil. The leaves first become pale green. They then turn brown and die but remain attached to the stem. Plants often wilt and finally die. The degree of infection from this disease may vary. In some cases only lower leaves may die while in others the entire plant is killed.

Wilting may sometimes occur during the day with recovery at night. Infected plants are normally stunted and flowers are small. This is a disease for which the gardener has no good controls. If the disease is suspected, remove and burn infected plants and do not replant susceptible chrysanthemums in the infected area for at least 7 to 10 years.

Yellowing of the lower leaves in mums does not necessarily mean that they have a fatal disease. Mums are quick to yellow and lose their lower leaves whenever growing conditions are not to their liking. Overcrowding, drought, and low fertility, especially low nitrogen, lead to yellowing and browning of lower leaves. Compared to the above diseases, however, there will be no definite spots as evidenced by leaf spots, and the plants will not wilt when moisture is adequate as in the case of verticillium wilt. Aphids are probably the most common insect pests of mums, particularly in early spring and late fall.

Both green and black types seem most common. Any good garden insecticide will clean them up, but several applications may be needed. Thrips, mites, leaf miners, tarnished plant bugs, and cucumber beetles may attack either the leaves or flowers of chrysanthemums. Common garden insecticides such as malathion or diazinon help control them if applied according to directions as the pests return each season.

http://en.wikipedia.org/wiki/Chrysanthemum