Roots forked and misshapen. Cause: Lumpy or compacted soil. Prevent problems by working soil deeply and adding lots of compost. Plant shorter-rooted cultivars in rocky or clay soil.
Roots misshapen and covered with numerous hairlike roots. Causes: Root knot nematodes: aster yellows. Root knot nematodes cause tiny round swellings on side roots. Prevent future root knot nematode problems by applying chitin or parasitic nematodes to the soil before planting.
Roots infected with the disease aster yellows are small, woody, hairy, and taste bitter. See "Young leaves yellow and dwarfed; growth bushy" above for controls.
Roots with green shoulders. Cause: Light exposure. Keep carrots covered with 2" of soil to prevent problems.
Roots with dark tunnels. Causes: Carrot weevils: carrot rust flies; carrot beetles.
Carrot weevils usually attack the upper and outer parts of the root. Tunnels are often in a zigzag pattern. Larvae are creamy white, '/>" long grubs with brown heads. Adults are coppery brown, '/&" long snout beetles. Destroy infested roots; don't put them in the compost. Control larvae by applying parasitic nematodes to the soil. Control adults, which emerge early in the spring to lay eggs, by covering the seedbed with row cover or by spraying or dusting plants with pyrethrin as soon as you see adult weevils.
Carrot rust fly maggots feed throughout the root, leaving randomly patterned tunnels filled with a rust-colored, sawdustlike material. Larvae are'/»" long, white maggots. Adults are small flies with yellow heads. Apply parasitic nematodes to soil to control larvae. Prevent problems by planting after June 1st to avoid the first hatching of the season. Cover seedbed with row cover to prevent adults from laying eggs on soil.
Carrot beetle larvae are 1", bluish white grubs that feed on the roots. Adults are '/:", reddish brown or black beetles. Fall cultivation reduces overwintering populations; crop rotation will also help.
Roots with small, irregular holes; plant may be stunted and yellow. Cause: Wireworms. Damage usually occurs later in the season and is worse in dry years. Larvae are up to l'/i" long, yellow to reddish brown, slender, tough-bodied, segmented grubs with brown heads. Adults are i/j"-7«" long, dark-colored, elongated click beetles. Control wireworms by applying parasitic nematodes to the soil.
Roots or crowns rotted. Cause: Various fungal or bacterial diseases. Root rot is often brought on by soggy, poorly drained soil or previous insect damage to the roots. Plant carrots in loose, well-drained soil and keep soil moist, but not soggy. Use raised beds to improve drainage.
Roots with internal cavities; may split open. Cause: Cavity spot. This condition is caused by a combination of factors: calcium deficiency, high levels of potassium, and possibly various diseases. To prevent problems, keep soil moist, but not soggy. Add gypsum, or high-calcium lime if pH is below 6.2, to raise calcium level, and withhold high-potassium fertilizer.
Roots with jagged cracks. Causes: Freezing injury: uneven soil moisture; cavity spot. Temperatures below 30°F cause cracked roots with a water-soaked appearance. Protect roots with mulch before temperatures fall.
Roots can also crack if soil is wetted after being dry. Prevent problems by keeping soil evenly moist.
Severe cases of cavity spot can cause open cracks. See "Roots with internal cavities; may split open" on page 61 for causes and controls.
Roots poorly formed or pale. Causes: Nutrient deficiency; extreme temperatures. Spindly, short roots can be caused by potassium deficiency or excessive heat. Poor color and taste are caused by magnesium deficiency, phosphorus deficiency, and low or high temperatures. Copper deficiency can also cause poor root development. Spray foliage with seaweed extract to prevent deficiencies. Do a soil test and amend soil as needed.
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