Gadenin日本語Get the appSlugs and snails, at the seedling stage only
The three weeks between emergence and the fourth true leaf are the dangerous ones. Nemophila seedlings are soft, low and sown thickly, which is exactly what slugs want, and a patch can be reduced to bare soil in two damp nights with nothing left to show but slime trails and a few chewed stumps. Because the plant cannot be transplanted, there is no tray of spares to fill the gaps: if the seedlings go, the sowing goes.
Check the patch after dark with a torch for the first fortnight rather than waiting to see damage. Clear leaf litter, boards and pots from the edges of the bed, because that is where the slugs spend the day. A ring of sharp grit or wool pellets around a small patch works while the seedlings are tiny, and hand collecting on damp evenings is more effective than anything else for a bed you can reach across. Once the plants are branching and covering the ground, the problem is over.
Aphids on the growing tips
Aphids are the main pest of established nemophila and they colonise the soft new growth at the shoot tips and the undersides of the youngest leaves. The first sign is usually not the insects but distortion: tips that curl, leaves that crinkle, and a sticky shine on the leaves below where honeydew has dripped. Black sooty mold grows on that honeydew afterwards and marks the plants long after the aphids have gone.
Deal with them mechanically while the colonies are small. A firm jet of water aimed up under the leaves knocks most of a colony off, and aphids that fall rarely climb back. Repeat it every two or three days until the ladybirds and hoverfly larvae catch up, which they will if you have not sprayed. Reserve insecticidal soap for a heavy infestation and apply it in the evening, wetting the undersides of the leaves; broad spectrum insecticides remove the predators and the problem comes straight back worse. An overfed, soft grown patch always gets hit harder, which is one more reason not to feed.
| Problem | First sign | Action |
|---|---|---|
| Slugs and snails | Seedlings gone overnight, slime trails | Night patrol, clear hiding places, grit ring |
| Aphids | Curled shoot tips, sticky leaves | Water jet every two or three days, soap if heavy |
| Powdery mildew | Gray dusty film on upper leaves | Thin the patch, water at the base, remove worst growth |
| Stem and root rot | Sudden wilt with wet soil, brown soft stem base | Pull affected plants, stop watering, do not resow there |
| Spider mites | Fine stippling, dry bronze leaves, webbing | Raise humidity, hose the undersides, cut out worst stems |
| Damping off | Seedlings toppling at soil level | Sow thinner, water less, improve airflow |
Powdery mildew and the crowded patch
Powdery mildew appears as a gray white dust on the upper leaf surfaces, usually late in the season when the nights are warm and the plants are dense. It is a disease of still air rather than of wet leaves, so it turns up in the middle of a thick drift before it reaches the edges. It rarely kills a nemophila outright, but it takes the last two or three weeks off the display and it makes the seed you collect less reliable.
Prevention is spacing and watering technique rather than spraying. Thin properly at the seedling stage even though the gaps look wrong, water the soil rather than the foliage, and pull out the worst affected plants in the center of a patch to open it up rather than treating the whole area. Late season mildew on a plant that is about to finish anyway is not worth fighting; simply collect seed from the cleanest plants and pull the rest.
Rot, the one that kills outright
Stem and root rot is the failure that takes a healthy looking patch overnight. A plant wilts, does not recover, and when you touch it the stem is soft and brown at soil level and comes away in your hand. The cause is water sitting around the crown: heavy soil, a container without drainage, a mulch piled against the stems, or simply a wet spell in a patch that was sown too thickly. Cold and wet together is the worst combination, which is why autumn sown patches on heavy ground sometimes vanish in midwinter.
There is no cure for an affected plant. Pull it, take the soil around it out if the patch is small, and stop watering the area until the surface dries. The real fix is at the next sowing: choose a raised or sloping position, add grit to heavy ground, do not mulch right up to the stems, and thin so air moves through at ground level. If a particular corner rots the plants two years running, that corner is wrong for nemophila and no amount of care will change it.
Do not treat rot as underwatering. A wilting nemophila in wet soil is a rotting nemophila, and watering it again finishes it off within a day or two. Push a finger into the soil before you reach for the watering can.
Keeping a record of what turned up
Note the date you first saw each problem, where in the patch it started, and what the weather had been doing that week. Aphids and mildew arrive at close to the same point in the season each year, and knowing that date lets you start looking a week before rather than a fortnight after. Marking the spot where rot appeared matters even more, because it is a property of that piece of ground and will happen again.
Record what you did and whether it worked, including the things that did not. A note that a water jet cleared the aphids in one season and did not in another, alongside what the weather was doing, is worth more than any general recommendation about which product to buy.