Carrots are a cool-tolerant root crop direct-sown in succession for a long, continuous supply. They want deep, loose, stone-free soil — heavy clay or rocks cause the roots to fork and stunt, so broad-shouldered types push through difficult ground best. Sow every three weeks from spring into midsummer; germination is slow (10–20 days), so keep the seed bed constantly moist or cover with burlap until the sprouts appear. Fall carrots harvested after frost are notably sweeter — cold converts stored starches to sugar.
Alternaria blight
Brown circular spots with yellow halos on leaves; spreads rapidly in wet weather.
Remove affected leaves immediately. Water at the base only. A copper-based fungicide can help if caught early.
Aster Yellows
Deformed, greenish flowers, stunted growth, and yellowed foliage. Flower centers may produce tufts of leafy growth instead of normal petals.
No cure. Remove and destroy infected plants immediately to stop spread. Control leafhoppers, which transmit the disease, and remove nearby weed hosts.
Cavity Spot
Sunken, gray-brown elliptical lesions across the root surface, sometimes cracking. Caused by Pythium in wet soils.
Improve drainage and avoid overwatering. Maintain pH near 6.5 and avoid excess potassium. Rotate away from carrots for 3–4 years in affected beds.
Aphids
Aphididae →Clusters of small soft insects on new growth and flower buds.
Knock off with a strong jet of water. Ladybirds and lacewings are natural predators. Insecticidal soap as last resort.
Carrot Rust Fly
Psila rosae →Rust-colored tunnels and brown scarring through the outer root. Foliage may yellow or wilt. Larvae are small white maggots in the root surface.
Cover beds with insect netting at sowing. Delay sowing past the first generation and avoid leaving thinnings in the bed, since their scent attracts flies. Rotate crops yearly.