Squash & Zucchini problems
A squash plant that collapses overnight has almost always been hollowed out by a vine borer at the base, not infected by anything.
Start from what you can see
Each of these has more than one possible cause, and each page separates them.
Everything that commonly affects squash plants
Most serious first. Most of the list is treatable or can be ignored.
Bacterial disease
The string test: cut stem, press the faces together, pull apart. Sticky threads confirm it.
Pest
Yellow-green beetles with black stripes or spots, about a quarter inch.
Fungal disease
Always check the underside. Fuzzy growth beneath a yellow patch is definitive.
Fungal disease
Cut the stem lengthwise: brown staining in the ring just under the skin confirms it.
Virus
Light and dark green mottling with soft, blurred boundaries.
Pest
Fine even stippling rather than discrete spots or holes.
Pest
Sudden, total collapse rather than gradual decline.
Pest
Dense clusters on new shoots and flower buds rather than scattered individuals.
Nutrient problem
Always at the blossom end, never the stem end, and never on the side.
Nutrient problem
Whole leaf yellows evenly, veins included.
Pest
Neat, regularly spaced bronze eggs in the angle between leaf veins. Nothing else lays like this.
Growing conditions
Leaves dry and crisp rather than soft and limp.
Fungal disease
White powder on the top of the leaf that rubs off with a finger.
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.
Diagnose your squash & zucchini
Already filtered to squash plants. Add the symptoms and where the trouble started.
1.What plant is it?
Many problems are specific to one family, so this removes a large share of the list straight away.
2.What does it look like?
optionalPick everything you can see. Any one match keeps a cause on the list, because you rarely see the whole picture at once.
3.Which part is affected?
optionalIf the roots are involved you will have to unpot or dig to find out — and with a declining plant that is usually the most informative thing you can do.
4.Where did it start?
optionalThe most underused question in plant diagnosis. Trouble that begins at the bottom means something very different from trouble that begins at the top.
- Bacterial WiltAct nowBacterial disease
- Cucumber BeetlesAct nowPest
- Downy MildewAct nowFungal disease
- Fusarium WiltAct nowFungal disease
- Mosaic VirusAct nowVirus
- Spider MitesAct nowPest
- Squash Vine BorerAct nowPest
- AphidsTreatablePest
- Blossom End RotTreatableNutrient problem
- Nitrogen DeficiencyTreatableNutrient problem
- Squash BugsTreatablePest
- UnderwateringTreatableGrowing conditions
- Powdery MildewMostly cosmeticFungal disease