The most common reasons for squash leaves turning yellow are nutrient deficiencies (especially nitrogen), overwatering or underwatering, pests (such as squash bugs, aphids, spider mites), diseases (including powdery mildew, bacterial wilt, and fungal infections), and environmental stress like extreme temperatures. Yellowing leaves often indicate the plant is stressed and not getting what it needs to thrive.
Main Causes of Yellow Squash Leaves:
- Nutrient Deficiency: Squash plants require plenty of nitrogen. Older leaves turning yellow can mean nitrogen is lacking.
- Watering Issues: Both too much and too little water can cause yellow leaves. Overwatering can cause root rot, hindering nutrient uptake; underwatering stresses the plant.
- Pests: Insects like squash bugs, aphids, and spider mites suck plant sap, causing yellowing and leaf damage.
- Diseases: Fungal diseases like powdery mildew cause yellow leaves with white spots. Bacterial wilt leads to yellowing followed by wilting and death.
- Environmental Stress: High heat above 90°F or cold below 50°F can stress plants, causing yellowing leaves.
How to Fix:
- Apply a balanced or nitrogen-rich fertilizer to correct nutrient deficiency.
- Check soil moisture regularly and adjust watering to avoid over or under watering.
- Inspect and treat pests using insecticidal soap, neem oil, or physical removal.
- Prevent and treat fungal diseases by improving air circulation and removing infected leaves.
- Protect plants from temperature extremes with shade or row covers.
By identifying and addressing these factors, squash plants can recover and produce healthy fruit.
