Gadenin日本語Get the appFruit that rots from the inside
A young fruit that yellows unevenly, softens at one point and falls has almost certainly been stung by a fruit fly. The female lays into the skin of a small developing fruit, leaving a mark like a pinprick surrounded by a slight dimple, and the larvae feed inside. By the time the fruit is soft there is nothing to be done with it, and every fallen fruit left on the ground produces the next generation.
The response is physical, not chemical. Collect every dropped and damaged fruit and remove it from the garden, do not compost it. Where fruit flies are a regular problem, bag young fruit: slip a paper or fine mesh sleeve over each fruit once it is an inch (2.5 cm) long and tie it loosely at the stalk. It is fiddly, but on a plant carrying twenty fruit it takes twenty minutes and saves most of them.
Bagging works only if the fruit is clean when you bag it. Check the skin for pinprick marks before you cover a fruit, or you will simply be protecting the larvae inside.
What to look for and when
Almost every problem on this crop announces itself on the underside of the lower leaves or in the crowded middle of the plant, both of which you never see unless you deliberately look. Crouch at the base of the plant once a week and look up. That one habit catches most of what follows a week before it is visible from outside.
| Problem | First sign | What to do |
|---|---|---|
| Aphids | Clusters on the growing tips and the underside of young leaves, leaves curling | Wash off with a jet of water, repeat every few days; encourage ladybirds rather than spraying broadly |
| Powdery mildew | White dusty patches on the upper surface of the oldest, lowest leaves | Remove affected leaves, thin the middle of the plant for airflow, water at the roots not over the foliage |
| Downy mildew | Angular yellow patches on top bounded by the leaf veins, gray fuzz underneath in humid weather | Strip the worst leaves and take them off the plot; it moves faster than powdery mildew in wet spells |
| Red spider mite | Fine pale stippling on the leaves, fine webbing in the leaf joints in hot dry weather | Raise humidity by spraying the underside of the leaves; mites thrive precisely where the plant is dry and dusty |
| Fruit fly | Pinprick marks with a dimple on small fruit, then uneven yellowing and softening | Remove and dispose of all affected and fallen fruit; bag young fruit |
| Root knot nematode | Whole plant wilts in the afternoon despite wet soil, swollen galls on the roots when lifted | Nothing saves the plant. Do not grow cucurbits on that ground for several seasons |
Flowers but no fruit
This is the most common complaint and it is usually not a disease at all. Bitter melon carries separate male and female flowers on the same plant, and the male flowers open first, often for a week or two before any female appears. A young plant covered in flowers that drop off after a day is behaving normally. Look closely at the base of each flower: a female has a miniature warty fruit already formed behind the petals, a male has a plain thin stalk.
If females are opening and then yellowing off without swelling, the problem is pollination. The flowers open in the morning and are receptive for a single day, and in wet weather or in a garden short of bees nothing visits them. Hand pollinate: pick a male flower, strip the petals back, and dab the pollen directly onto the center of a female flower in the early morning. One male will serve several females.
- Confirm which flowers you have Check for the small warty swelling behind the petals. All male and no female on a large plant usually means too much nitrogen, so stop feeding high nitrogen and pinch the tips to force laterals.
- Hand pollinate in the morning Between sunrise and mid morning, transfer pollen from a freshly opened male to the center of a freshly opened female. Later in the day the female is no longer receptive.
- Rule out heat Above about 95F (35C) pollen loses viability and fruit set drops off regardless of what you do. Set resumes when the weather breaks, so do not chase it.
Keeping mildew out of the crop
Powdery mildew is the disease that eventually finishes the plant, and it always begins on the oldest leaves at the bottom, in the still air near the soil. The single most effective measure is not a spray but the pruning knife: take the lowest leaves off as they age, thin the crowded middle of the plant so daylight shows through, and never leave the vine hanging in a dense curtain down the far side of the support.
Water at the base rather than over the leaves, and water in the morning so any splashed foliage dries by evening. Mulch the soil surface, which stops rain splashing spores from the ground onto the lowest leaves. Once white patches appear, remove the affected leaves entirely rather than leaving them and hoping. A plant that loses its lower leaves to mildew in mid summer will still be carrying fruit, but the fruit will be small and slow.
At the end of the season, lift the vines off the support with the diseased leaves still attached and take the whole lot off the plot. Leaving the residue on the ground over winter is the commonest reason mildew arrives earlier each year.
Recording what went wrong
Write down the date you first saw each problem and where on the plant it was. The date of the first white patch of mildew is the most valuable single record you can keep on this crop, because it is remarkably consistent on a given site, and it tells you exactly when to start thinning the middle of the plant next season rather than reacting after the event.
Note also which plants in the row were hit and which were not, since the ones at the crowded end almost always go first, and note whether the fruit fly damage came early or late in the season. Two seasons of these notes will tell you whether bagging is worth the effort where you garden or whether the flies arrive too late to matter.