|Can you tell me why each year a few of my African daisies bolt (like a head of lettuce)? The newly formed plant has different leaves, grows straight up, and does not bloom. Is there a way to prevent this? plants are in full sun.|
|It sounds as though your plants have a bacterial disease called Aster Yellows. Aster yellows is a disease caused by a mycoplasma-like organism which attacks a wide range of plants. Plants may be stunted or with numerous secondary shoots. Foliage is yellow and seeds are usually sterile. Plants have an upright habit of growth. In many plants the veins of immature leaves are clear. Affected leaves are somewhat narrower than healthy leaves. Old leaves may develop a slightly reddish, brownish, or purplish tinge in the late stages. The main branches will be shortened. Flower parts may develop into leafy structures. The mycoplasma overwinters in leafhoppers on perennial host plants. Leafhoppers can spread the mycoplasma 9 to 21 days after feeding on diseased plants. The mycoplasma multiplies in the insects and leafhoppers can spread the disease for 100 days or more after becoming infective. The ability of leafhoppers to transmit the organism is reduced when temperature is over 90 ? F. Overwintering of the mycoplasma occurs more often in some plants than in others because leafhoppers prefer to feed on those host plants. Symptoms show in plants in 10 to 40 days after insect feeding. The disease can be serious when dry weather forces leafhoppers to migrate from wild weeds to susceptible plants. At least twelve different species of leafhoppers may transmit the organism to healthy plants.
The best control measure is to rogue out all infected plants. Before going to such extremes, however, you might want to take a sample of the problem to your local Extension office for positive identification of the problem. Contact University of Florida, 1303 17th. St. W, Palmetto 34221-2998. (813) 722-4524.