Zucchini diseases and pests
The database lists 5 problems recorded on this crop. 3 of them can cost the whole harvest, and 4 survive in soil or debris into next season — those are the ones that decide your rotation. The largest number are active in June.
Pressure through the year
The number of problems listed as active in each month. Pick a month to see what to sow, plant and harvest then.
Start from what you can see
What actually prevents them
Water at the base of the plant in the morning, never over the leaves. Splashing soil onto foliage is the delivery route for every problem listed here, and morning watering lets anything that does land dry before nightfall.
Applies to: Downy Mildew
Mulch the soil surface. A physical barrier between last season's spores and this season's lowest leaves removes the first infection of the year, which is the one that seeds all the others.
Applies to: Downy Mildew
Give the plants their full spacing 90×120 cm and keep the centre of each one open. Air moving through the planting dries the leaves faster, and leaf wetness duration is what turns a spore landing into an infection.
Applies to: Powdery Mildew
Rotate this bed and everything else in the same family on at least a three-year cycle. 4 of the problems below survive in soil or crop debris between seasons, so returning the same crop to the same ground hands them the host they were waiting for.
Applies to: Bacterial Wilt, Cucumber Mosaic Virus, Downy Mildew, Powdery Mildew
Clear and remove the spent crop at the end of the season rather than digging it in. Debris left on the surface is where the persistent problems overwinter, and next spring they start from your own bed rather than from somewhere else.
Applies to: Bacterial Wilt, Cucumber Mosaic Virus, Downy Mildew, Powdery Mildew
Control sap-sucking insects early, before the population is obvious. Several of the problems here are carried plant to plant by aphids or thrips, and once a virus has arrived there is no treatment — only the vector was ever treatable.
Applies to: Cucumber Mosaic Virus
Work through healthy plants first and disinfect secateurs between plants. These problems travel on tools, stakes and hands, which means a single careless afternoon of pruning can distribute them along the whole row.
Applies to: Bacterial Wilt
Keep affected material out of the compost heap — 3 of these survive a garden heap and come back with the finished compost. Bag it for municipal green waste, which is composted at temperatures a garden heap does not reach.
Applies to: Bacterial Wilt, Cucumber Mosaic Virus, Downy Mildew
Every listed problem
Ordered by how much they can cost you.
Fungal diseases(2)
- Downy MildewSevere
Angular yellow patches on the upper leaf bounded by veins, with grey-purple fuzzy growth on the underside. Leaves brown and die from the inside of the plant outward.
- How it spreads
- Rain and irrigation splash
- Compost
- Keep out of the compost
- Conditions
- 10–23°C · humidity ≥85% · wet leaves / rain
- First move
- Treat, then re-check in 5–7 days
Also at risk: Cucumbers, Lettuce, Onions, Beetroot, Spinach, Peas
- Powdery MildewModerate
White to grey powdery coating on the upper surface of leaves and stems, later yellowing, curling and premature leaf drop. Fruit may be stunted or sun-scorched as the canopy thins.
- How it spreads
- Wind-blown spores
- Compost
- Hot compost only
- Conditions
- 15–28°C · humidity ≥60%
- First move
- Treat, then re-check in 5–7 days
Also at risk: Cucumbers, Peas, Pumpkins, Apple trees, Grapes, Strawberries
Bacterial diseases(1)
- Bacterial WiltCritical
Rapid wilting of individual leaves then whole vines despite moist soil; cut stems ooze sticky white strands; no recovery overnight. A cut stem dipped in water releases milky threads.
- How it spreads
- Tools, hands and cuttings
- Compost
- Keep out of the compost
- Conditions
- 25–37°C · humidity ≥70%
- First move
- Remove affected material now
Viral diseases(1)
- Cucumber Mosaic VirusSevere
Yellow mosaic mottling and puckering of young leaves, which often become narrow and strap-like. Plants are stunted, flowers are streaked or malformed, and cucumber fruits are warty, pale and bitter.
- How it spreads
- Carried by insects
- Compost
- Keep out of the compost
- Conditions
- Spread by handling, insects or soil — not weather-triggered
- First move
- Remove affected material now
Also at risk: Cucumbers
Pests(1)
- Squash BugsModerate
Wilting and yellow speckling of leaves that progress to brown and crisp; bronze egg clusters in leaf-vein angles; grey-brown adults and pale green nymphs clustered at the plant base.
- How it spreads
- Carried by insects
- Compost
- Safe to compost
- Conditions
- 21–35°C
- First move
- Treat, then re-check in 5–7 days
Also at risk: Pumpkins
Why rotation matters here
4 of these overwinter in the soil or in crop debris rather than on the plant. Pulling the sick plant does not remove them: they wait for the same host to come back to the same ground.