Gadenin日本語Get the appWhy problems cost more on this crop
On a courgette, a fortnight lost to mildew or beetle damage means a fortnight fewer fruit and then the plant carries on. On luffa the same fortnight can be the difference between twenty finished sponges and twenty green gourds hanging in the frost. Every problem on this crop is a problem with time attached to it, which is why the useful response is early and preventive rather than heroic and late.
The plant itself is tough. A big established luffa shrugs off damage that would flatten a cucumber, and much of what alarms gardeners on the lower leaves in late summer is simply the plant abandoning old growth. Learn the difference between damage that is spreading upward into new leaves and damage that is confined to the oldest ones near the ground.
Keep the lowest 18 in (45 cm) of stem clear of leaves and mulch once the vine is climbing. Almost every fungal problem on cucurbits starts on leaves that touch damp soil and works its way up from there.
What shows up, and when
Most of what troubles luffa arrives on a predictable schedule: chewing insects on the young plant, sucking insects as the vine fills out, fungal disease in the humid second half of summer, and rots on the fruit in a wet autumn. Walking the trellis twice a week and turning a few leaves over is worth more than any spray, because everything below is far easier to deal with in its first days.
| Problem | First sign | When | What to do |
|---|---|---|---|
| Cucumber beetles | Ragged holes in young leaves, striped or spotted beetles on flowers | From planting out onward | Cover young plants with row cover until flowering, then hand pick in the morning while they are sluggish |
| Squash vine borer | Sudden wilt of one stem, sawdust-like frass at a hole near the base | Midsummer | Slit the stem lengthwise, remove the grub, then mound soil over the wound so it roots again |
| Squash bugs | Bronze speckling then collapse of leaves, gray brown bugs clustered at the base | Mid to late summer | Crush the neat bronze egg clusters on leaf undersides; hand pick adults from under a board laid on the soil |
| Aphids | Sticky leaves, curled growing tips, ants running the stems | Any time, worst in hot dry spells | Blast off with water, encourage predators, and check that you are not over feeding with nitrogen |
| Powdery mildew | White dusty patches on upper leaf surfaces of older leaves | Late summer, especially warm days and cool nights | Remove the worst leaves, improve airflow, water at the base only. Accept some on old leaves late on |
| Downy mildew | Angular yellow blotches bounded by leaf veins, gray fuzz beneath | Humid spells | Act fast: it defoliates a plant in a fortnight. Strip affected leaves and open the canopy |
| Fruit rot | Soft brown patch, usually where fruit touches a support or lies on soil | Wet autumn weather | Hang every fruit clear of surfaces; cut off and discard anything that has gone soft |
| Blossom drop | Small fruit yellow at the tip and fall at 1 to 2 in (3 to 5 cm) | Early flowering | Not a disease. These were not pollinated. Hand pollinate in the morning |
Telling trouble from normal behavior
Several things that look like disasters on luffa are not. Enormous leaves wilting flat at two in the afternoon in high heat and standing up again by evening is normal transpiration, not drought. A run of male flowers with no females for two or three weeks is normal sequence, not a failure. Yellowing leaves at the very base of a plant in late summer, while the growing tips stay green and strong, is normal senescence.
- Check at dawn, not at noon Any wilt still present first thing in the morning is real and needs water or points to a borer or root problem. Wilt that appears only in the afternoon heat is the plant managing itself and needs nothing.
- Follow a wilt down the stem If one stem wilts while the rest of the plant is fine, run your fingers down it to the base looking for a hole with wet frass. That is vine borer and is fixable. A whole plant wilting from the ground up is more likely a root or crown rot in wet soil.
- Turn leaves over before spraying Gray fuzz on the underside means downy mildew, which spreads fast and needs immediate leaf removal. White dust on the top surface is powdery mildew, which is slower and can often be tolerated on old leaves in the last weeks.
- Judge by the growing tips The condition of the top three feet (1 m) of vine tells you how the plant is doing. Green, thick, actively extending tips mean the plant is winning, whatever the lower leaves look like.
Deciding when a plant is finished
There comes a point in a bad year when a plant is no longer going to add anything. If downy mildew has taken two thirds of the leaf area by late summer, no fruit still on the vine will finish drying, because that job needs a working canopy. In that case cut the remaining fruit, peel them green as best you can, and clear the plant rather than nursing it. Getting sick material out of the garden promptly protects next year.
The same judgement applies as frost approaches. Fruit that are still deep green a fortnight before your first expected frost will not ripen outdoors. Either cut them and peel them green immediately, or cut whole lengths of vine with the fruit attached and hang them somewhere dry, frost free and airy, where a proportion will finish drying off the plant.
Clear all luffa debris at the end of the season and do not compost mildewed foliage in a cool heap. Rotate the position by two or three years if you can, since squash bugs and beetles overwinter in the soil and litter where the crop stood.
Keeping notes that pay off
Record the date you first saw each problem and where on the trellis it started. Pest and disease arrival is remarkably consistent from year to year on a given site, and a note saying that mildew first appeared on the shaded north end in the third week of high summer lets you open that section up or spray preventively before it starts next season.
Note which plants along the row suffered and which did not, along with what you did and whether it worked. On a crop where the whole game is time, knowing that a preventive row cover over the young plants bought you three clean weeks is worth more than any general advice about cucurbit pests.