Picture 1: Bacterial Leaf Spot in oakleaf leaves #1 and #2 and macrophylla leaf #3 + a severe case of Iron Chlorosis and bacterial leaf spot on the macrophylla leaf #3 ('severe' because the leaves have started turning white-ish). Iron chlorosis works like this: dark green leaves turn light green, except for the leaf veins which remain dark green. Then the leaves turn yellow, except for the leaf veins which remain dark green. Then the leaves turn white, except for the leaf veins which remain dark green. The leaves then die and drop.
Picture 2-7: Looks like a case of bacterial leaf spot. That is a fungal infection that primarily affects Hydrangea quercifolia (Oakleaf Hydrangea), Hydrangea arborescens (Smooth hydrangea) and Hydrangea macrophylla (Big Leaf Hydrangea). It starts with individual spots that enlarge around veins. Discard in the trash the worst of the leaves. No signs of iron chlorosis although some foliage is a lighter green color than the older leaves underneath.
Picture 8-10: severe case of iron chlorosis and bacterial leaf spot. Some of the simple spots in pictures 9-10 m-a-y be Cercospora leaf spot but in those last two pictures, the spots were too far away to correctly identify so asume more bacterial leaf spot for now instead. A few spots in 8-9 appear to have the start of bacterial leaf spot.
Copper-based fungicides may help control bacterial leaf spot if applied starting in late spring. I am aware that some people also use compost tea spray on infected leaf but I am not seen recommendations in journals. I think the reasoning is that the compost tea spray introduces beneficial bacteria that is good for combating bacterial leaf spot. Removing diseased leaves as soon as they appear helps prevent further spread of the disease but other times that is not practical... meaning, when the plant is covered with infected leaves (they need some green leaves to produce food for the roots after all).
Fungicides containing chlorothalonil and thiophantate-methyl work to control both cercospora leaf spot and anthracnose. I saw a Bonide Spray Bottle at my Lowes that contains chlorothalonil; not sure if it is for sale on all Lowes though. Dilution rates for raw chlorothalonil-containing fungicides range from 1.4 teaspoons to 2 teaspoons per gallon of water but read the product directions as some products are already diluted and ready to be sprayed. For fungicides containing raw thiophanate-methyl, the dilution rates is usually 1 tablespoon per gallon of water. Apply them every 10 to 14 days as needed. For more severe infections, apply at shorter intervals. Follow all directions on the label when using chemical fungicides. Clean sanitation practices and no overhead watering can also help.
Iron chlorosis can be controlled using any one of these amendments per product directions: garden sulfur, iron sulfate, aluminum sulfate or greensand. Regular applications of organic compost can also help keep the soil pH closer to neutral, which hydrangea leaves do not mind. Because the episode is severe, I would use chelated-iron liquid compounds as they help fix the problem slightly faster.
Luis
