Gadenin日本語Get the appPowdery mildew is close to inevitable
Zucchini is among the more susceptible squashes, and in a home garden a season without it is the exception. So the aim is not zero: it is to delay it until you have finished picking.
It spreads in warm, dry conditions. A run of dry days with a crowded crown is more dangerous than rain. Rather than reacting when white bloom appears, act a fortnight before you expect it.
| Stage | Watch for | What to do |
|---|---|---|
| Just after planting | Aphids and beetles | Mulch, and cover with netting |
| Early picking | First powdery mildew | Strip lower leaves and keep air moving |
| Peak picking | Mildew spreading fast | Take affected leaves off the plot weekly |
| Late season | Gray mold and soft rot | Leave no spent flowers or damaged fruit |
Even a variety sold as mildew resistant gets it. Treat resistance as buying about a fortnight, not as a reason to skip the management.
Designing the delay in
Prevention comes down to two things: moving air, and not overfeeding with nitrogen. Both are decided before planting and in the first few weeks, so there is very little you can change once it has appeared.
- Keep the spacing Three feet (90 cm). On a crowded bed the leaves close into a single canopy by midsummer, the crown never dries, and the outbreak comes a fortnight earlier.
- Stake the plants An upright stem lets air through the crown and keeps damp off the leaf undersides. It also means fewer spores splashing up from the soil.
- Do not overfeed Dark, soft leaves are more easily infected. Stick to the stated rate and skip a feed if the color goes very dark.
- Mulch the ground Covering the soil stops splash carrying the organism up from below. The wetter your plot after rain, the more this helps.
- Line the bed up with the wind Running the bed along the prevailing summer wind lets air move between the plants. A bed against a wall gets it one to two weeks earlier on identical management.
What to do once it appears
The point of decision is when you can see white bloom on a few leaves. Remove those leaves then and the plant lasts to the end of the season. Let it cover the plant and photosynthesis stops, and within a fortnight the fruit are visibly slower.
- Remove affected leaves the same day Do not tear them off into the bed. Bag them and carry them off the plot: spores are produced on the fallen leaf and that becomes next week's source.
- Protect the upper leaves Prioritize the young leaves near the growing point. Losing the lower ones is expected, and as long as the top is clean you keep picking.
- Work in the morning Handling wet foliage moves spores on your hands and clothes. Work once the dew has gone, and wash your hands afterwards.
- Know when to stop When the upper leaves are covered and no new female flowers are forming, it will not recover. Pull it, clear up, and move on to the next crop.
If you use a fungicide, choose one approved for zucchini where you live and follow the label on the number of applications and the interval before harvest.
Beetles and aphids
Foliage eaten while the plant is small stops it dead. The first fortnight after planting is when the damage matters most, and physically covering the plants for that period alone changes the outcome.
| Pest | When | How to tell and what to do |
|---|---|---|
| Cucumber beetles | Early season | Beetles chewing round holes. Cover young plants |
| Aphids | Early season | Clusters on shoots and leaf undersides. Silver mulch reduces arrivals |
| Spider mites | Hot dry spells | Pale stippled undersides. Spray water underneath |
| Cutworms and caterpillars | Mid to late season | Large holes overnight. Search the soil at the base in the morning |
Take insect netting off once flowering starts. Left on, no pollinators get in, and without hand pollination you get no fruit at all.
The other diseases
Several problems look alike but need different handling, so separate white bloom from water-soaked patches. Virus is the one you cannot treat: the plant has to come out.
| Problem | How it shows | What to do |
|---|---|---|
| Mosaic virus | New leaves crumpled and mottled | Pull the plant. Control the aphids that spread it |
| Gray mold | Spent flowers and fruit tips rotting gray | Remove dead flowers and damaged fruit |
| Stem and fruit rot | Sudden water-soaked collapse | Improve drainage and stop rain splash |
| Blackened, shriveled fruit tips | Poor pollination or drought | Review pollination and watering |
Soil-borne diseases shared across the squash family build up with repeat cropping. Leave two or three years, and avoid ground that grew pumpkins or cucumbers.
How often to look, and what to record
A note of the date and the position of the plant is more useful than a photograph of the leaf. A week from first sight is the window to act, and the same note tells you how to lay the bed out next year.
- Twice a week, under the leaves Look from above when you pollinate in the morning, and turn leaves over on the day you pick. Both mildew and mites start on undersides and lower leaves.
- Record the date you first see it Note the day you first see white bloom. A fortnight before that date next year is when to start the preventative work.
- Note which plants go first Even in one bed the plants at the sheltered end go first. Knowing which positions are worst lets you space those more widely next year.
- Watch how fast it spreads Look at the same leaf every other day. If the patch is widening, act. If it is the same size, you can leave it for now.