How to stop pests wrecking a zucchini crop

A healthy plant is most of the answer

Zucchini are generous to the point of being a nuisance, and they get eaten because they put out big soft leaves faster than almost anything else in the bed. Most of what goes wrong is preventable before a single pest turns up, and it comes down to the same 2 things. Enough space between plants for air to move through, and soil with enough organic matter in it that the plant is never struggling. Full sun helps on top of both. A crowded, hungry zucchini is the one that gets hammered.

What actually attacks them here

This matters more than it sounds, because a lot of what gets written about zucchini pests online is written for a different continent and names insects we simply do not have.

• Aphids. Clusters on the growing tips and the undersides of young leaves, leaving them curled and sticky. The first response is a sharp jet of water, and it works more often than people expect.
• The 28 spotted leaf eating ladybird. Bigger and duller than the helpful ladybirds, and it grazes the leaf surface into a lacework of fine lines. Both the adults and the spiky yellow larvae do it, and hand picking into a bucket of soapy water deals with a small outbreak.
• Pumpkin beetle. Orange with black spots, chews ragged holes straight through leaves and flowers. It flies off when you get close, so early morning is when you catch them.
• Snails and slugs. Only really a problem on seedlings, and they will take a whole plant overnight at that stage. Go out at dusk with a torch, or use pellets around the seedlings only.
• Fruit fly. Worth knowing about and worth trapping if you have got other fruit on the block, because a trap is a cheap early warning even when nothing is stung yet.

Powdery mildew, which gets blamed on pests and is not one

The white dust on the leaves late in the season is a fungus, and it is a growing conditions problem before it is a spray problem. Water the soil rather than the foliage, water in the morning so the leaves are dry overnight, space the plants so air moves through them, and take off the worst leaves rather than leaving them to seed the rest of the plant. A copper based fungicide will slow it down where that is not enough, and no amount of anything reverses a leaf that has already gone.

The order to try things in

1. Water and hand picking, which cost nothing and handle most of it.
2. Mulch, which stops the soil drying out and keeps the plant strong enough to shrug things off.
3. Flowers nearby that bring in the predatory insects, so something else is doing the work.
4. A horticultural oil or a pyrethrum, on the affected plant only, late in the day.

The order matters because every step down it costs more and hits more things than the one above it, and by the time you are spraying you want to be certain what you are spraying for.

Spray without wiping out the bees

A zucchini is entirely dependent on bees, because the male and female flowers are separate and something has to carry pollen between them. Spray a flowering zucchini in the middle of the day and you can end up with a plant that has no pests and no fruit either, which is a poor trade. So spray late in the day once the flowers have closed, and spray the plant with the problem rather than the whole bed. Never spray into an open flower.

Keep picking

A zucchini left on the plant turns into a marrow and tells the plant the season is over, so picking often is both the thing that keeps the crop coming and the thing that makes you look at every plant every couple of days, which is how you catch a problem while it is still small.

And some years you lose them anyway

I am not going to pretend every crop works. Some seasons the mildew gets in early and the plants are finished by the time you would normally be sick of eating them, and there is not much to be done about it beyond pulling them out and putting something else in. That is gardening rather than failure, and anybody who tells you their patch runs perfectly is showing you the good half of it.

Shop related products

• D.T. Brown Zucchini Lebanese Seed. Plant fewer than you think you need, and space them properly.
• Multicrop EcoPest Oil Insect Spray. A horticultural oil for aphids and the other sap suckers.
• Multicrop Pyrethrum Long Life Insect Spray 1L. For a chewing insect that hand picking is not keeping up with.
• Martins Organic Sugar Cane Bale 11kg. Mulch, which does more for pest resistance than any spray does.
• D.T. Brown Marigold Seed. Flowers in the bed, so the predatory insects have a reason to be there.

Did you know we also stock snail pellets, a slug and snail barrier, a snail and slug trap and a Mediterranean fruit fly trap in store. Those are not all on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

The sprays, the seed, the mulch and the soil improvers are all in the garden centre, with the online range in garden products and the sprays in pest control.

Read next

• When a garden pest is worth spraying, and when it is not
• Which garden insects are worth keeping around
• When to pick vegetables, crop by crop

I still go out at night with a torch looking for snails, and I have stopped pretending that looks normal.

Cheers,
Candeece