Radish Problems: Flea Beetle Holes and Split Roots

Work out the cause from the symptom

Tiny holes in the leaves, curled new growth, split roots, scars on the root surface. Each needs a different response, and some are urgent while others can wait. Sort them by what you see first and you will not waste time.

Keep flea beetles out with netting

Flea beetles are tiny shiny beetles, some with pale stripes, that jump when disturbed and pepper leaves with holes about a sixteenth of an inch (1 mm) across. Their larvae feed on roots in the soil and leave fine scars. Keeping them out from sowing day works better than chasing them with sprays.

Use fine insect netting and bury or weight the edges so there are no gaps. If there is a gap, beetles that get in cannot get out and the damage is worse than with no net. Leave it on until harvest.

1. Cover on sowing day Once the seed is sown and watered, put up hoops and netting the same day. Waiting until germination is too late.
2. Seal the edges with soil Bury the edges of the netting or hold them down with sandbags. In windy spots add extra weight.
3. Open it only to thin Close it as soon as you are done and reseal the edges. Leave it open and beetles get in within minutes.

Sown next to other cabbage family crops, radishes pick up their pests. Keep some distance, or cover them all under one net.

Prevent split roots with steady watering

When soil dries out while roots are swelling and is then soaked, the inside expands suddenly and the skin cracks. It is a growing problem, not a disease, and it does not spread. Keep the soil evenly moist and it does not happen.

Harvesting late also causes splitting. Overgrown radishes have tougher skins that crack at the slightest change in moisture. Pull them in order as they reach three quarters of an inch to an inch and a quarter (2 to 3 cm) across.

1. Water a little before it dries Water before the surface goes pale and dry. A heavy soaking after the soil has dried completely is the main trigger.
2. Do not wait past prime Harvest at three quarters of an inch to an inch and a quarter across. The longer you wait for bigger roots, the more of them split.
3. Eat split ones first Split roots rot from the crack, so pull them as soon as you see them and use them first. Left in contact with soil they spoil in days.

Diseases from crop rotation and wet soil

Where cabbage family crops are grown back to back, clubroot appears: swollen, distorted roots and plants that wilt. Once it is in the soil it lasts for years, so leave two years before growing any cabbage family crop, including turnips, mustard and cabbage, in that spot.

In poorly drained beds, plants can also blacken at the base and collapse. Raise the bed to shed water and do not let thinning slip so the plants stay uncrowded.

1. Check the roots of wilting plants Pull a plant that wilts by day and recovers overnight. Galls on the roots mean clubroot; dispose of it away from the garden.
2. Lime acidic soil Two weeks before sowing, work in garden lime. Clubroot thrives in acidic soil, so raising the pH ahead of time helps.
3. Raise the beds Where drainage is poor, build beds 4 to 6 inches (10 to 15 cm) high. Avoid beds where water stands after rain.

Problems in containers and indoors

Container radishes have different problems from those in the ground. There are fewer pests, but crowded roots, reused soil and lack of light causing stretched leaves are more common. The cause almost always comes down to soil or light.

Reusing the same potting mix leads to small galls and misshapen roots. Radishes need so little mix that replacing it every time is the quicker fix.

1. Replace the mix every time Do not carry over old roots or leftover fertilizer. Spread used mix out in the sun before using it for something else.
2. Move them if leaves stretch Long, floppy leaf stalks mean too little light. Move the container to a sunnier spot outdoors, or choose a brighter one next time.
3. Check the drainage If water does not run out the bottom, the mix is compacted. Repot with fresh mix and clear the drainage holes.

Deciding whether to spray

Radishes take only three to four weeks, which makes it hard to respect the waiting period between spraying and harvest. Netting and handpicking are almost always enough, so plan on growing them without sprays.

If you must use something, choose a product labeled for radishes and check the preharvest interval and the maximum number of applications on the label. Decide how many days remain until harvest before choosing a product.

1. Start by hand Hose aphids off and knock beetles into soapy water early in the morning while they are sluggish. With small numbers that is enough.
2. Check the label and interval Read which crops the product covers and its preharvest interval. If there are not enough days left before harvest, you cannot use it.
3. Start over if damage is heavy If more than half the crop is eaten, clear the bed, net it properly and resow. You will harvest sooner that way.