Thank you everyone. Here's a closer pic of the leave.luis_pr wrote:It could be the start of a powdery mildew infestation, very common in H. macrophyllas. Spore germination and infection occurs when the leaf surfaces are dry, humidity is high and temperatures are warm.
Good housekeeping practices may help prevent reoccurrences, especially on small outbreaks. Improve air circulation of inside and outside hydrangeas (hydrangeas do better planted outside so plan to do that as soon as you can), reduce humidity, never water the leaves (water the soil early in the mornings instead) and remove plant debris that may accumulate underneath the shrub.
Consider chemical fungicides for heavy infestations that occur early in the growing season. Start fungicide applications (in future times) as soon as you detect problems (remember to check the underside of the leaves).
Examples of fungicides cleared for control of PM: azoxystrobin (Heritage; has the smallest application rate and largest repeat interval); fenarimol (Rubigan); fenarimol (Cleary's 3336). You can also use Sunspray Ultrafine Oil.
Not all PM fungicides have to be chemicals such as those. If you feel adventurous, try using milk. Prepare a solution of water (80%) and milk (10 to 20%). Use a spray bottle to spray the solution weekly (apply to the top/bottom of the leaves and to the stems). It does not matter which type of milk you use. I use this sometimes on my Crape Myrtles.
Some people also use a baking soda and water solution instead (I have not tried this one) with a drop of liquid soap on cool days: 1 gallon of water, 1 tablespoon of baking soda, 1/2 to 1 teaspoon of liquid soad, 1 tablespoon of ultralight horticultural oil. Dispose of this mix after you spray the shrub.
I went ahead and sprayed milk solution instead last night. however I woke up to see some white spots on some leaves this morning. I wiped it off with wet q-tips. I didn't take any picture, I do hope it was dried milk residue! The milk solution couldn't be accelerate the infection right?luis_pr wrote:Yes, that looks like the start of a powdery mildew infection. The affected areas turn white or grayish looking, even other colors if no corrective action is taken. If you are watering the leaves, "aim" for the soil (potting mix) instead.
Here are some other PM Leaf examples in a more advanced stage of infection so you know:
H. macrophyllas tend to suffer from this problem a lot. Named varieties sold in plant nurseries may resist PM better than those sold in grocery stores or florists. The plant label of named varieties should say something about being resistant if the shrub was developed to be resistant to PM. Just don't forget than resistant does not mean that it is immune. The wholesaler who provided the hydrangeas to the grocery stores could have used nice named hydrangeas but they never advertise the variety's name so, when buying the plant you cannot research if PM will eventually be a problem.
Thank you for the reminder.imafan26 wrote:Check the plant for snails or slugs. There are some holes in the leaves that look like that kind of damage and snails like soft growth.
Mildew likes high humidity and poor air circulation. Fungal diseases are easier to prevent than cure.
I followed your instructions to spray the leaves all over and the stems too, they smell so milky I will spray the plant again in a week. how long or how many application usually does it take you to have the plant cleared of the infection?luis_pr wrote:Yes, the solution with milk might leave a whiteish coating. When I used on my Crape Myrtles, I left it "on". The more milk one uses on the solution, the more noticeable it is. I try not to exceed a 20 or 30% milk solution for that reason. And because in larger concentrations, it has attracted the interest of my pets.
The article was not too clear. Regular watering should be done by watering the soil and not the leaves. However, when you spray an antifungal solution like milk & water or baking soda & water on the shrub, you need to spray to the leaves (to-p and bottom). That is what they were referring to. By the way, I like to also spray the stems too since spores can collect there. It is recommended procedure when treating roses with blackspot so, I spray stems too when applying an anti-PM solution on other shrubs.