Carrot Problems: Pests, Nematodes and Split Roots

Different problems at different stages

Carrot problems divide neatly by growth stage. Just after germination it is drought and damping off rather than insects. While the tops are filling out it is leaf damage and leaf disease. Once the roots are swelling it is nematodes in the soil and splitting. Looking for the right thing at the right time finds it sooner than watching for everything all year.

For a summer sowing, the weeks from sowing until the tops are full are the peak for insects. Once the weather cools, feeding damage more or less stops, so getting through those weeks is effectively the whole pest control plan.

Caterpillars you can deal with by eye

The large caterpillars that strip carrot foliage are conspicuous and there are never many of them, so picking them off by hand is genuinely sufficient. The trouble is that they eat fast: a plant can be reduced to bare stalks in a day or two.

Netting the bed from the day you sow is the reliable prevention. Put it on later and you simply trap what is already inside. Once a week, look under the leaves for eggs and small larvae and you will deal with almost all of it by hand.

1. Net from the day you sow Put a tunnel of insect netting up as you sow and weight the edges into the soil. Anything added after the pests arrive works against you.
2. Look under the leaves weekly Eggs and young larvae are on the undersides. Turning a few leaves once a week catches them while hand removal is enough.
3. Do not panic about tops Foliage eaten late in the season matters much less than it looks. If the roots are already filling, remove the caterpillars and leave the plants.

Nematodes are managed by rotation

Root nematodes cause plants to yellow and stay small, and pulling one shows a root with lesions, galls or a mass of fine roots. There is no treatment once they are in the soil, so this is a design problem rather than a spraying problem.

1. Rotate two or three years Do not grow carrots in the same ground repeatedly. This is the control that actually works.
2. Grow a break crop A season of marigolds or a green manure oat lowers the population. The point is to dig the crop in afterwards, not just to look at the flowers.
3. Solarise in high summer Water the bed thoroughly, cover it with clear plastic and leave it three or four weeks in the hottest part of the year. It lowers the population near the surface and kills weed seed.
4. Take damaged roots off the plot Burying damaged roots and fine roots carries the nematodes straight into the next crop. Bag them and take them away.

Leaf disease is controlled by airflow

Leaf blight shows as dark brown spots on the lower leaves that work upwards, and powdery mildew as a white bloom. Both spread when the foliage is crowded and damp, which is why they are rarely a serious problem on a plot where the thinning and earthing up have been done properly.

1. Do not skimp on spacing Keep the final spacing at four to five inches. Under a crowded canopy nothing dries and the plants die back from the bottom. Thinning is disease control.
2. Take the lower leaves off early Remove yellowing and spotted leaves at the base and take them off the plot. Left, they supply spores.
3. Water at the base Watering over the tops keeps them wet longer. Water at the base, and in the morning if you can.
4. Rotate Leaf diseases carry over in soil and debris too, so the same rotation that handles nematodes handles these.

Splitting is about water and time

There are only two causes of a root splitting lengthways: a sudden change in soil moisture, and leaving it too long. A dry spell followed by heavy rain swells the inside faster than the skin can stretch. A root left in the ground past its point has a hardened skin and does the same thing.

A split root will not store and rots from the crack, but it is perfectly edible. Lift them promptly and use them first.

1. Keep the moisture steady After a dry spell, do not soak the bed all at once. Water a moderate amount every few days. Sudden rewetting is the trigger.
2. Mulch the surface Straw or husks on the bed narrow the swing in soil moisture. It also helps with soil temperature early in a summer sowing.
3. Lift on time A shoulder over two inches (5 cm) means you are running late. If heavy rain is forecast, lift the biggest roots first.
4. Stop feeding late on Nitrogen in the last month causes sudden swelling and pushes splitting. Keeping the feeding deadline is prevention.

Telling similar symptoms apart

Above ground, carrot problems look alike, and it is easy to confuse an insect, a disease and a physiological problem. Where on the leaf the damage starts, and whether it reaches the root, separates them.

If you cannot tell, pull one suspect plant and look at the root. Nothing above ground tells you what is happening below it.