Answer: It sounds like aster yellows disease, says Danny Gay, plant pathologist at the University of Georgia in Tipton. This mycoplasma (virus like organism) causes young inner leaves of carrots to yellow and later form dwarf leaf clusters. The outer leaves may turn reddish purple, and the roots of infected plants usually bulge at the crown, are stunted and have many hairy, secondary roots. Aster yellow is spread with the help of leafhoppers. The six spotted leafhopper is the most likely culprit, but aster yellows can be spread by a dozen other species of leafhoppers, says Gay. As leafhoppers feed they transmit aster yellows to a wide range of garden plants are perennial weeds, such as lettuce, potatoes, sweet peas, thistle, wild aster and plantain, hesays. The simplest control is to cover the carrots with a floating row cover as soon as leafhoppers are spotted. Check periodically under the row cover for any leafhoppers and control them with Sevin or pyrethrum sprays. Certain varieties, such as Scarlet Nantes and Royal Chantenay, tolerate asters yellows and produce a crop when low numbers of leafhoppers are present.
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