Gadenin日本語Get the appA long season means a long exposure
Romanesco attracts exactly the same pests as every other brassica, but it stands in the ground for four or five months rather than two or three. That extra time is the whole difference. A calabrese can outrun a moderate caterpillar attack; a romanesco has to survive two full generations of them, plus the aphids that build up in late summer and the pigeons that arrive when the weather turns.
Almost all of it flies in. Cabbage white butterflies, cabbage root fly, aphids, flea beetles and pigeons all land on an unprotected plant. Fine mesh over hoops, put up the day the plants go in and sealed properly at the edges, stops nearly all of them in one job. On this crop the netting stays up until you cut.
What netting does not stop is soil-borne, and clubroot is the one that matters. It cannot be sprayed away and its resting spores last in the soil for the best part of two decades, so it is handled through rotation, pH and drainage rather than by treatment.
| Stage | Main threats | First sign |
|---|---|---|
| First fortnight after planting | Slugs, cutworms, cabbage root fly | Plants cut off at soil level, or wilting for no reason |
| Early leaf building | Flea beetles, cabbage white caterpillars | Fine shot-holes, then ragged holes in the leaves |
| Midsummer, full canopy | Cabbage white and cabbage moth caterpillars | Frass on the lower leaves, eggs on the undersides |
| Late summer | Cabbage aphid, whitefly | Gray mealy colonies deep in the growing point |
| Head expansion in autumn | Slugs, caterpillars in the wrapper leaves | Holes and slime between the leaves and the head |
| Autumn and early winter | Pigeons | Leaves stripped to the midribs overnight |
| Any stage | Clubroot | Wilting in the heat, recovering at night, stunted |
Caterpillars over a long summer
Cabbage white caterpillars are the most visible problem. The yellow-and-black gregarious kind feed in groups on the leaf surface and are easy to spot; the plain green kind sit along the midrib and stay invisible until the leaf is in shreds. Cabbage moth caterpillars are worse, because they bore straight into the head, where nothing can reach them and where a single one ruins the whole thing.
On a garden scale hand picking works, and the thing that makes it work is looking at leaf undersides at least weekly through the summer. You want to find egg clusters and newly hatched larvae, not half-grown caterpillars that eat a leaf a day. Rubbing off an egg cluster takes a second; picking off forty caterpillars takes twenty minutes.
- Net with fine mesh from planting day Insect mesh of about 0.8 mm over hoops, held well clear of the foliage. Butterflies lay through netting that rests on the leaves, so build the hoops tall enough for a three foot plant.
- Seal every edge into the soil Trench the edges in or weight them down along their whole length with boards. A gap the width of a finger is an open door, and once a butterfly is inside the netting protects her from predators.
- Check the undersides weekly all summer Look for clusters of yellow eggs and lines of tiny larvae, particularly on the lower leaves and along the midribs. Weekly is the interval that keeps the job small.
- Search the head once it appears Cabbage moth larvae tunnel into the base of the head. Part the wrapper leaves and look right down into the center every time you check the plant.
- Use a bacterial spray if numbers get away A Bacillus thuringiensis product works on young caterpillars and spares bees and predators. Apply in the evening and repeat after rain.
- Clear the crop debris when you finish Pupae overwinter in old brassica stems. Pulling and composting spent plants cuts next season's starting population noticeably.
Damage to the outer leaves late in the season looks worse than it is. If the canopy is already built and the head is filling, remove the caterpillars and leave the plant alone rather than stripping damaged leaves it is still using.
Aphids in late summer
Cabbage aphid is the one that does real damage on a long-season brassica, and late summer is when it builds. It forms dense mealy gray colonies deep in the growing point and between the wrapper leaves, distorting new growth and, worst of all, contaminating the head. A romanesco head is an intricate set of cones and crevices, and aphids that get into it are practically impossible to wash out.
Because the colonies sit exactly where sprays cannot reach, early detection is worth more than any treatment. Get into the habit of parting the inner leaves and looking straight down into the center once a week from midsummer on. Flea beetles, by comparison, are mostly a seedling problem: they pepper young leaves with round shot-holes, which an established plant simply outgrows.
- Inspect the growing point, not the leaf tops Part the inner leaves and look down into the crown weekly. Aphid colonies are well established there long before the plant looks unwell from a distance.
- Squash small colonies immediately A colony the size of a coin can be wiped out between finger and thumb or blasted off with a jet of water. Caught at that size this is the entire treatment.
- Use insecticidal soap on larger colonies Soap works only on contact, so aim into the crown and under the leaves rather than over the top. Repeat after five days to catch what has hatched since.
- Keep the net on for flea beetles too The same mesh that excludes butterflies keeps flea beetles off newly planted seedlings, which is the only stage at which they cause a real check.
- Encourage the predators Ladybirds, hoverflies and parasitic wasps clear aphids well. Leave a strip of flowering plants near the bed and avoid broad-spectrum sprays that remove them.
Aphids found in the head after cutting can sometimes be removed by soaking the head upside down in cold salted water for half an hour. It is worth trying before you write off a head you waited five months for.
Clubroot: designed around, not treated
Clubroot is a soil-borne organism that swells brassica roots into distorted knobs so the plant cannot take up water. Above ground it looks exactly like drought: wilting in the heat, recovering overnight, stunted, yellowing, and heads that never fill. Pull a plant and look at the roots and it settles the question at once.
On romanesco it is particularly costly, because the plant needs an unbroken four or five months of growth to build the canopy the head comes from, and a clubrooted plant simply cannot supply that. There is no cure, and the spores survive fifteen to twenty years in the soil. Once a plot has it, the aim shifts to keeping it out of the clean beds and making the affected ones tolerable.
It thrives on acid, wet soil. Liming to pH 7.0 and improving drainage will not eliminate it, but on a long-season crop they often make the difference between a head and nothing.
| Measure | What it does | How much it helps |
|---|---|---|
| Rotate brassicas on a four year gap | Denies the organism a host | Slows the build-up; will not clear an infested bed |
| Lime to pH 7.0 | Suppresses spore germination | Substantially reduces damage on acid soil |
| Improve drainage or build raised beds | Removes the wet conditions it needs | Substantial on heavy ground |
| Raise plants in large pots before planting | Gives a big root system before infection starts | Often the difference between a crop and none |
| Grow resistant varieties | Resists infection directly | Effective, but resistance is partial and erodes |
| Clean boots and tools between beds | Stops spread onto clean ground | The most valuable measure if you are still clean |
| Never compost infected roots | Keeps spores out of the compost pile | Essential; bag them and take them off the plot |
Cabbage root fly produces similar wilting but leaves the roots eaten and ragged rather than swollen and knobbly. Pull a suspect plant and look before deciding which you have, because the responses are entirely different.
Slugs, pigeons, wind and rots
The rest of the trouble comes at specific vulnerable moments rather than as constant pressure. Slugs and cutworms take newly planted seedlings in their first fortnight. Wind levers big autumn plants loose at exactly the point they should be filling their heads. Pigeons strip standing plants once other food runs short. Rots take hold where water sits between the leaves in cold wet weather.
Each has a narrow window, and protecting the plant through that window is far cheaper than dealing with what follows. On a crop that occupies a bed for five months, losing a plant in week one wastes the whole season's space.
- Protect new transplants from slugs Check the soil at the base at dusk for the first fortnight and use a barrier or wool pellets around each plant. A transplant eaten at the growing point does not recover.
- Stake and earth up before the autumn gales Draw three or four inches (8 to 10 cm) of soil up the stem and put a cane against exposed plants. A romanesco rocked loose in early autumn stops growing just as its head should be expanding.
- Net or cage against pigeons Hold the netting off the leaves on hoops. Pigeons will strip a row to bare midribs in a single frosty morning once other food is scarce.
- Never tie the leaves over the head Unlike cauliflower, romanesco is not blanched. Water trapped in a tied head rots it from the surface, and the head should be in the light anyway.
- Remove yellowing lower leaves Dying leaves against damp soil start the soft rots that then move into the stem. Snap them off cleanly and take them off the plot.
- Keep the spacing generous At 27 to 30 inches (70 to 75 cm) the canopy dries out after rain. Crowded plants stay wet all day through the autumn, and every fungal problem follows from that.
Record the date you first see each problem and where in the bed it appeared. Pests arrive on much the same schedule every year, and a note of last season's first sighting tells you precisely when the net needs to be on.