Borage Pests and Problems: Blackfly, Mildew and Collapsing Stems

Blackfly go for the growing tips first

Aphids, usually the black bean aphid, colonise the soft growing tips and the undersides of the youngest leaves from late spring. On borage they cluster in the crook where a flowering stem leaves the main stem, which is exactly where you cannot see them from above, so the first sign is normally ants running up and down the stems or a sticky shine on the leaves below.

Borage tolerates a surprising load without checking, and a moderate colony feeds the ladybirds and hoverflies that then clean up the beans and the roses nearby. Intervene only when the growing tips are distorting or the flower buds are being killed before they open. Because the plant flowers for weeks and bees work it hard, no insecticide belongs on borage at all.

1. Look under the flower stem joints weekly Turn a flowering stem over and check the angle where it meets the main stem. That is where the colony starts, days before you see it anywhere else.
2. Squash rather than spray Run a gloved finger and thumb up the affected stem. On a plant that flowers this heavily nothing sprayed is acceptable, including soap sprays that also kill hoverfly larvae.
3. Cut out a badly infested tip Snap off the worst two or three stems at the base and bin them. Borage regrows from the crown quickly and loses nothing by it.
4. Deal with the ants Ants farm and protect the aphids. A band of grease or a barrier around a container leg, or simply disturbing the nest, lets the predators back in.

Borage is often planted deliberately as a nurse plant near beans and squash precisely because it draws blackfly and then feeds the predators. If you are using it that way, do not clean it too thoroughly.

Powdery mildew arrives with the second half of the season

White powdery patches appear on the upper surfaces of the older, lower leaves from midsummer, spreading upwards until the whole lower half of the plant is gray. It is driven by crowding, dry roots and still air, not by rain, and it always starts in the dense middle of a plant that has flopped open and is lying on itself.

It rarely kills borage but it ends the plant's usefulness early, because you cannot pick leaves off mildewed growth and the flowering thins out fast once the lower foliage stops working. The reliable treatment is the same midseason hard cut back that the plant wants anyway: take everything down to eight to ten inches (20 to 25 cm), clear the infected material away from the bed, and the regrowth comes back clean.

Do not compost mildewed borage foliage in a cold heap that you spread on the same bed. Either heap it hot or put it out with the garden waste.

Slugs take seedlings, and nothing much touches the adult

The one genuinely vulnerable stage is the fortnight between emergence and the fourth true leaf. Slugs and snails will clear an entire row of borage seedlings overnight in damp weather, and because the seedlings are large and fleshy the damage is total rather than partial. Once the bristles harden, slugs lose interest completely and the plant is untouchable for the rest of its life.

Protect that fortnight and you are done. Sow into warm soil so the seedlings pass through the vulnerable stage in days rather than weeks, clear slug shelter from around the row, and go out with a torch after rain for the first week. Cut off plastic bottle cloches over individual stations work well and can be lifted once the plant fills them.

1. Sow late enough to grow fast A row that emerges in six days and grows on gets through the risk quickly. A cold sowing sits at the two leaf stage for a fortnight and gets eaten.
2. Clear the ground around the row Move boards, pots and thick mulch back a foot from the seedlings. Mulch right up against a new sowing is a slug refuge.
3. Patrol after rain for one week Go out at dusk with a torch on the first two damp evenings after emergence. That is when the losses actually happen.
4. Sow spares at the end of the row Half a dozen extra seeds give you replacements that can still be moved at the two leaf stage if a gap opens.

Collapse is a growing problem, not a disease

A borage plant that splits open at the base and lies flat after a storm has not caught anything. Hollow stems, top heavy growth and soft feeding are the whole explanation, and it happens on schedule in any bed that was manured that spring. The mistake is treating it as damage to be tidied around rather than a signal to cut.

A collapsed plant will not stand back up and tying it up rarely holds, because the stems have already creased. Cut the whole thing back hard, remove everything that was lying on the soil, and let it rebuild from the crown. Do that once and the plant carries on to frost; leave it lying and the crushed center rots and the plant is finished within a month.

Write down when each problem appeared

The trouble with borage arrives on a fairly fixed schedule, so a record of dates turns most of it into a preventable calendar. Note the date you first saw blackfly, the date the first white mildew patch appeared, and the date the plant flopped. Two seasons of those dates and you can cut back a week before the mildew instead of a month after it.

Record the position of each plant too, along with what was done to that patch of ground the previous autumn. Bed by bed, the pattern is nearly always that the plants in the manured ground flopped and mildewed and the plants in the poor corner did neither, and having it written down is what stops you repeating the sowing plan next spring.