In the past week, my Dooley hydrangea has developed spots. Can one of you experts tell me what they are and how to treat them ? Thanks !
Help ! What's Wrong ?
It appears to be a severe case of hydrangea leaf spots. They are common at the end of summer but have to be diagnosed properly in order to treat them effectively.
"Regular" leaf spots are simply a nuisance that can be treated by some of the fungicides listed next but there are more severe infestations. Most of the time, you can control them by keeping the area clean and not allowing the fungi to thrive.
Cercospora Leaf Spot is a recurring problem identified by dark brown spots with dots. It starts at the base and spreads up. It can be controlled by fungicides whose active ingredient is chlorothalonil, mancozeb, myclobutanil or thiophanate-methyl such as Daconil, Dithane, Immunox, or Cleary's 3336.
Antrachnose Leaf Spot is somewhat similar to Cercospora but the symptoms appear simultaneously in leaves and blooms. It can be controlled by fungicides whose active ingredient is chlorothalonil or thiophanate-methyl such as Daconil or Cleary's 3336.
I am curious of something. Can you confirm that the color on the picture (red or reddish) is true and correct? I personally have a hard time taking digital pictures of red roses such that the color in the picture really looks like the one I see in real life.
If it is truly as red as I see, I suggest you take some steps listed below but I also ask that you get confirmation from your Agric. Extension Service that this is not anthracnose, a fungal infection characterized by red/reddish/brownish areas that might eventually develop a purplish discoloration along the leaf veins. You can place sample leaves in a sealed transparent plastic bag for analysis.
As I mentioned earlier, Leaf Spot is a fungal problem common in hydrangeas by the end of the summer or at the beginning of the Fall rainy season. Most times, the amount of leaf spots is not large enough to require purchasing fungicides and applying them (because the growing season is basically over, in other words, because the infected leaves should soon dry out & fall when the plant goes dormant). And once the leaves dry out, you can cut them off, put them in a plastic trash bag and throw them in the trash. Deadhead the blooms and dispose similarly.
You do not want to add these infested plant parts into the compost pile because that will just help spread the fungi. Once the problem is under control, you can again add these plant parts into the compost pile or use them as mulch.
Suggestions:
* never water the leaves of hydrangeas; instead water the soil. Overhead watering promotes development of leaf fungal infections.
* water very early in the morning
* replace the mulch if you can afford to do that and if the infestation is bad
* evaluate if the watering regimen is keeping the area too wet and making the fungi thrive. You should water again when a finger inserted to a depth of 4" feels the soil as being dry or almost dry. A newly purchased plant should need about 1g of water per watering; 1.5 gallons if your soil is sandy.
* pick up plant debris found under the hydrangea as often as you can while this problem persists; regularly when the problem is corrected
* allow for good air circulation in between plants. This is done by making sure that plants do not crowd or touch each other. Prune or transplant elsewhere if this happens.
* do not over fertilize hydrangeas. One application (1/2 to 1 cup) of manure, compost, cottonseed meal in June is enough for the whole year if you live in the northern half of the country. Too much fertilizer keeps the plant in growth mode and can make the plant sensitive to anthracnose.
Go here for more information: http://www.aces.edu/pubs/docs/A/ANR-1212/
Note: the colors on the pictures in the website are not very good and do not appear true. Black colors sometimes are closer to purplish/dark red/dark brown or a combination of all of the above so take those colors in the photos with a grain of salt.
luis_pr -
Thank you ! Your answer is very comprehensive ! Yes, the spots are red - true color in the photo.
I sprayed them yesterday. I must admit, I have been watering the hydrangea leaves, as well as at the base. I'll be more careful in the future and hopefully prevent the spots.