Growth of infected carrots is patchy and uneven and severely infected carrots exhibit forking, galls, hairiness, and stubby roots. Root knot nematode forms galls or root thickenings of various sizes and shapes. Infected umbels can be completely blighted and seed infection can occur-use treated seed to prevent introducing this disease. Symptoms can extend into petioles, produce a yellow-brown, gummy exudate, and occur on flower stalks. Leaflets may become distorted and curled. Symptoms of bacterial leaf blight appear primarily on leaf margins as small, yellow, angular leaf spots which expand, turn brown to black with a yellow halo, and become dry and brittle. Langston Bacterial Leaf Blight ( Xanthomonas campestris pv. radicina causes similar foliar symptoms but can also produce a dry, mealy, black decay known as black rot on carrot roots held in storage. Petiole lesions are common, elongate, and can quickly kill entire leaves. When about 40% of the leaf is infected, the leaf yellows, collapses, and dies. Older leaves are more susceptible to infection. Symptoms of Alternaria leaf blight first appear along leaflet margins as greenish-brown, water-soaked lesions which enlarge, turn brown to black, and often develop a yellow halo. Alternaria Leaf Blight ( Alternaria dauci and A. See the UMass Diagnostic Lab website for their sample submission instructions. If you are noticing foliar or root symptoms like those described, send a sample to your state diagnostic lab to confirm, and take steps to protect current and future crops. Some of the major carrot disease symptoms are described below. Proper disease identification will help you to prevent future outbreaks by adjusting crop rotations accordingly, and prevent moving infested soil from field to field. Root diseases are caused by soil dwelling organisms and therefore their incidence may vary considerably from farm to farm. Root diseases can lower yields of fresh eating carrots and can spread in storage, drastically reducing yields brought to later markets. ![]() Foliar diseases may cause lower yields due to loss of photosynthetic area, difficulty in harvest if the tops are weakened, and lower marketability if the carrots cannot be sold in bunches. Carrots can be affected by many bacteria, fungi and nematodes in the field and in storage. Photo: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.Carrot acreage is on the rise in New England, as more growers target expanding, year-round markets. Covering the seeds with compost or Sphagnum Moss (instead of sowing mix) may also help. Sulfur powder, or a tea of Seaweed, Garlic or Chamomile has been used to treat small areas of infection and prevent it spreading. Damping Off fungi need high humidity, so thin your seedlings promptly to prevent overcrowding, avoid overwatering (especially on cool sunless days when water doesn’t evaporate quickly) and make sure there is good ventilation and air circulation. However, if your climate dictates that you start your seedlings inside then you have a potential problem. Growing your seedlings in a well ventilated, cool greenhouse will produce far fewer problems with Damping Off. Damping Off is mostly a disease of indoor seed raising. ![]() You may lose a few plants occasionally, but so what. It shouldn’t be a big problem if you take the precautions outlined below. The best defense against Damping Off is to avoid giving it the growing conditions it needs. Fortunately such techniques aren’t really necessary for the home grower. ![]() Almost all soil contains the spores of Damping Off so commercial growers often avoid soil in their mixes, or sterilize it with heat or chemicals. Other kinds of Damping Off kill the seed before it germinates, or rot the roots, causing the tops to turn yellow and die. This type of Damping Off mainly affects very small seedlings and becomes is less of a problem as they get older and their stems get tougher. These develop shrunken black stems and eventually fall over and die, though the stem may remain upright for a while afterward. The best known type of Damping Off first manifests itself as a fuzzy whitish mold on the surface of the soil and then goes on to girdle the succulent stems of newly germinated plants. This fungus disease can be the bane of the inexperienced seed starter and comes in several guises.
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