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Need A Leafspot Resistant Hydrangea

holmaneva
January 12, 2019

Hi All:

Zone 7b. I was advised to repost this to the Hydrangea board.


Need a replacement for the hydrangea that currently develops leafspot blight mid early summer & then looks sort of bad the rest of the year until the leaves fall off . Then it becomes a nice winter attraction w/ the dried flowers. It is tucked in a corner area of the front border sheltered from the hot afternoon sun, but not the heat. It starts right out with 4-5 large white to med. blue flowers, pauses during the hottest part of summer, then starts putting out lots of smaller flowers on the tips of the new growth until 1st frost. It only flowers on new growth, so it gets cut back to the ground late winter & I like the fact I can do that for easy maintenance. It has medium to large veined velvety-ish spade shaped leaves & regular flowers. Tried spraying this summer, but it was a rainy one, so the effort yielded only slightly better results (or did all the rain just help washing the leaves of spores?). It grows 4ft tall x 4ft to 5 ft wide.

Comments (3)
  • luis_pr

    I did not see a list of resistant varieties when I moved to my current home 20 years ago (and still have not seen that type of list) so, I focused instead of avoiding/minimizing those things that can cause the problem. Not watering the leaves and good sanitation practices have allowed me to keep an existing pair of diseased hydrangea shrubs very close to other hydrangeas without -so far- spreading the fungus when the problems surfaces every Fall. And I replaced my watering/sprinkler system when it broke.

    Maybe the most important change was to replace the sprinkler system with drip irrigation (you can also use a soaker hose). Planting away from the diseased shrub probably helps too but I have not gone overboard with that. I have diseased and healthy hydrangeas near each other, separated by 2 feet from each other. I have had those diseased hydrangeas for almost 20 years now and none of the healthy ones have caught the cercospora leaf spot.

    When I manually water, I do it early in the day, as close to 6-8am as possible, so the only time when the leaves are wet is when it rains. If you water the plant(s) manually too, never water the leaves; instead, water the soil directly. As soon as you notice plant debris (leaves, flowers, etc) under the shrub, pick those and throw them away in the trash.

    For heavy infestations, consider replacing the mulch with new mulch. At the end of the growing season, I throw into the trash the dried out blooms from the diseased hydrangeas; ditto for the dried out leaves in the Fall/Winter. Feel free to prune branches/leaves that touch the soil/mulch, an area where the spores accumulate.You can also cut the petiole of leaves that aesthetically look very bad.

    Because the spots become visible when chlorophyll production tapers off in the Fall, I have not used fungicides on these infected shrubs... Not worth it since the leaves will soon fall. Note that those fungicides control but do not cure the problem. If money is no object, you can use some of the fungicides recommended below. Prices have gone down on some of these lately. A 32-oz Bonide Fung-onil Spray Bottle was for sale for $9 recently at Ace Hardware. You will need several bottles per year though.

    http://www.aces.edu/pubs/docs/A/ANR-1212/index2.tmpl

    https://ugaurbanag.com/cercospora-leaf-spot-on-hydrangea/

    On my diseased ones, I still get some/less leaf spot every year depending on the weather (due lack of or due to too much rainfall in the late Summer/Fall) but, the spots are not as bad as when I first moved into the house with the sprinklers.

  • holmaneva

    Thank you for the detailed information! I used a bottle Daconil RTU that helped only a little last year. This year I plan to try aspirin water (2 aspirin/1 quart water) to save some money. I hope it works as well as touted.

  • luis_pr

    If you plan to try some of the fungicides that you already have, I would start spraying from leaf out time or from the time when you start to notice the leaf lesions (in mid to late summer, I sometimes observe darker green areas where the lesions crop up later on). Reapply per the instructions. And see if you need to reapply early if it rains.

    All that re-spraying on many hydrangeas sounded like a pain to me, which is why I replaced the sprinkler when it broke and used the good sanitation practices. I have not read of aspirin helping with cercospora (some people use aspirin on tomatoes with a different fungal leaf spot disease) so I would try Daconil (since you already have it) starting with leaf out on the next growing season and repeat until the plant goes dormant... Or, cheaper yet and since it is only for one plant, never water the leaves, pick up debris, put new mulch and feel free to prune the petioles of any leaves that get "too" ugly.

    Good luck, Luis.

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