Hydrangea Dying?

Asked September 11, 2018, 12:17 AM EDT

(NOTE: I have more pix that I can send.)

A Limelight Hydrangea paniculata that I planted in 2009 has done beautifully until this year. It has a southern exposure, with a noon-hour respite as the sun passes over an ash tree. I prune it in fall by a third after harvesting blooms for bouquets. Every year or so I give all my perennials a sprinkle of 10-10-10 fertilizer.

I first noticed the Limelight had a wilting-leaf problem after it leafed out in June (pic no. 1). There are two 2-inch-thick major stems. The stems and branches on both became totally bare over summer.

Still, the shrub pumped along by virtue of many new sprouts emanating from its base and growing as tall as seven feet. It has produced blooms and is not horribly disfigured, but it is not the lush well-shaped shrub that it used to be.

Examining it today, I was dismayed to see that even the new growth seems to be doomed. Below, pic no. 2 shows a new-this-year stem that’s been fine until it started going downhill in August. So far, it's the only new stem that's died. A couple other new stems look OK except for rippled leaf edges, which as you know are not what healthy hydrangea leaves look like (pic no. 3).

From my reading online, it would seem that herbicide poisoning and root rot are the commonest causes of hydrangea failure. I did put a Scott's herbicide-fertilizer combo on my lawn this spring, something I’ve done every spring for the 11 years I’ve owned my home, with no ill effect on the Limelight because I take care not to get the spreader too close to my gardens. Root rot? A 6-ft. gutter downspout extension leads to the shrub. My one-story Cape Cod’s roof is small, the gutter in question only 12 ft. long. I’ve always found it to be an inexpensive means of keeping the Limelight watered.

Are the rippled leaf edges a tip-off to some another problem, e.g., a fungus or virus? The leaves have no spots or powdery appearance.

Whatever the cause, I would like to know what my course of action should be. Should I prune the stems that look healthy by a third and saw off the dead wood at ground level or cut the entire shrub to the ground? Does it make sense to dig up the shrub and examine it for root rot? Assuming it's not turned to jelly, can a partially rotted root ball be replanted with any chance of success?

Of all the many perennials I have in my five gardens, the Limelight is my favorite. It has been a splendid shrub, its blooms furnishing dried bouquets every year for friends. I’m loath to give up on it if there’s a chance it can be saved.




Hennepin County Minnesota scale insects plant health hydrangeas limelight hydrangea

5 Responses

Thank you for the question. The problem with your hydrangea seems a bit mysterious. I don't see leaf spots, discoloration, or rings. Have you thoroughly scouted the plant for insect pests? Some clues to possible problems are:
  • Located near a downspout. Hydrangeas like some moisture but not wet feet. We have had quite a bit of rain lately that might be causing a problem with root rot.
  • Viruses can cause leaf distortion like what you see in photo #3. The only treatment for this is to remove the shrub. Herbicide can cause this too. Virus diagnosis can be verified by submitting a sample to the University of Minnesota Plant Disease lab. Here is a link to their website: https://pdc.umn.edu/
  • Even though you don't think chemical injury is possible, could it be that a neighbor has used an herbicide spray that may have drifted on to your plant? This seems possible because most parts of the shrub look great in the photos and the affected areas are so specific and one sided. Is there any similar damage on other plants nearby? Here is a good link to photos of different kinds of herbicide injury: https://cotton.ces.ncsu.edu/wp-content/uploads/2015/07/CRC-Herbicide-Symptoms.pdf?fwd=no Note that herbicide damage cannot be reversed and plant survival depends on its overall health and the amount and kind of herbicide used.
It is OK to prune off the afflicted areas down to the ground. This hydrangea blooms on new wood growth in the spring. Even if you cut off the entire plant to the ground this fall, it will emerge from the base next year. If you have stems 2 inches in diameter, you might want to consider removing this old wood just to promote a nicely shaped shrub next year. Since there is so much nice, healthy growth, I would advise leaving as many leaves and stems as possible now to photosynthesize and store energy for next year. As best I can tell, the majority of the shrub is doing well so I wouldn't dig it up. I think it makes sense to redirect the downspout away from the base of the plant in case that's the problem. Of course, you will have to water occasionally.

Thank you for contacting Extension.

Anita, thank you for a thoughtful and comprehensive response. No neighbors have used herbicides, and if I had overspread as I passed by the Limelight, more shrubs and perennials along the same route would have been damaged. Checking 2018 precipitation, I see that the big rains came in June, after I'd spotted the afflicted stems (which were throughout the bush, not just on one side). That said, I suppose it could be that the large spring snowfalls on March 9 and April 4 made the ground saturated once it melted.

I'm attaching pix that furnish an additional piece of the puzzle. Earlier this week as I clawed my way into the interior of the shrub to determine what kind of saw I'd need to cut the large original stems at the base, I spotted a fresh hell: beige-colored dots that I'd noticed before but thought were normal had turned white and become enlarged and raised before turning black.

Do they tell you anything?

Anita, thank you for a thoughtful and comprehensive response. No neighbors have used herbicides, and if I had overspread as I passed by the Limelight, more shrubs and perennials along the same route would have been damaged. Checking 2018 precipitation, I see that the big rains came in June, after I'd spotted the afflicted stems (which were throughout the bush, not just on one side). That said, I suppose it could be that the large spring snowfalls on March 9 and April 4 made the ground saturated once it melted.

I'm attaching pix that furnish an additional piece of the puzzle. Earlier this week as I clawed my way into the interior of the shrub to determine what kind of saw I'd need to cut the large original stems at the base, I spotted a fresh hell: beige-colored dots that I'd noticed before but thought were normal had turned white and become enlarged and raised before turning black.

Do they tell you anything?

Thank you for the excellent update photos. When I enlarge them, it appears that your limelight has a scale insect problem. I see pale dome-like spots that look like oyster scale. I'm not sure if the dark spots are the same pest or not. To quickly test for scale, use your thumbnail and try to scrape the spots off. If they come off quite easily, they are scale. The following information is taken from a Virginia Tech publication:

"Scale insects are a peculiar group and look quite different from the typical insects we encounter day to day. Small, immobile, with no visible legs or antennae, they resemble individual fish scales pressed tightly against the plant on which they are feeding. There are over l50 different kinds of scales in Virginia. Many are common and serious pests of trees, shrubs, and indoor plants. Damage: Scale insects feed on plant sap. They have long, threadlike mouthparts (stylets) six to eight times longer than the insect itself. Feeding by scales slowly reduces plant vigor. Heavily infested plants grow poorly and may suffer dieback of twigs and branches. Occasionally, an infested host will be so weakened that it dies. Control: Dormant oils are effective for suffocating the overwintering stage of most species. Sprays and systemic products can be used to control the crawler and adult stages. Adult scales are protected from insecticides by waxy coverings. Control measures, therefore, must be aimed at unprotected immatures (crawlers) or the overwintering stage. During the summer, control requires accurate identification of the pest species so that hatching dates of crawlers can be determined. Once the pest is identified and proper timing known, any one of several common insecticides can be used. Types of Scales: Scale insects can be roughly divided into two groups: armored scales and soft scales. Armored scales are so named because they secrete a protective cover over their bodies. Most species overwinter as eggs beneath the female cover. In spring, eggs hatch into tiny mobile crawlers, which migrate to new feeding sites. After a few days, crawlers settle, insert their mouthparts, and begin feeding. Soon they secrete a protective cover and lose their legs. Large populations can build up unnoticed before plants begin to show visible symptoms".

I can't tell for sure which scale is present on your shrub but you might be able to identify it by reading though our publication on scale insects and their control; https://extension.umn.edu/yard-and-garden-insects/scale-insects-minnesota-trees-and-shrubs

Regardless of type of scale, horticultural oil can be used this fall to suffocate the dormant insects and you can plan your spring attack this winter.

I hope this was helpful.

So the little critters were hiding in plain sight all along. There's no honeydew on the leaves, so they definitely are armored. After looking at pix of armored scale online, I can't ID the species--not important as the management is the same for all.

I'm going to cut the shrub back and apply Bonide horticultural oil later this fall.

Thanks again for your help.