The Q&A Archives: White Powdery Substance On My Lemon Tree Leaves.

Question: I have a lemon tree in my yard, and I noticed a white
powdery substance on the underside of the leaves. Could you
let me know what that is,and what I would use to treat it.

Answer: What you describe sounds suspicously like powdery mildew, a fungal disease that often strikes when days are warm and nights are cold. Prevention is difficult - provide your tree with as much sunshine as possible, and prune (if necessary) to increase air circulation around and within the tree canopy. Here's a spray that rosarians use with great success on their roses. Maybe it'll work on your citrus tree. Use 1 Tbsp. Baking Soda; 2 1/2 tbsp. ultrafine horticultural spray oil; 1 gallon water. Mix all this and spray on a cloudy day. Be sure to cover the leaves thoroughly-even the bottoms. Also, rake up and dispose of all fallen leaves. Good luck with your tree!

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