Dying evergreen shrubs - Ask Extension
Shrubs are 60 years old and have always been healthy until this spring. The needles are turning brown and falling off soil as well drained.
Knowledgebase
Dying evergreen shrubs #800198
Asked July 09, 2022, 9:41 AM EDT
Shrubs are 60 years old and have always been healthy until this spring. The needles are turning brown and falling off soil as well drained.
Hardin County Ohio
Expert Response
Thank you for asking Extension about your unhealthy-looking shrubs. They appear to be Taxus yew, a common and long-lived foundation planting.
There are several factors that can cause damage such as you are seeing on your shrubs. Since you say they have been there a long time, I think we can rule out improper planting technique and probably inappropriate soil (pH, mineral content, etc). However, if there has been recent digging in the area, roots could have been cut and if you added soil over the roots (especially over 2" deep), you could have decreased the oxygen available to the roots.
Winter damage can cause browning of branches. I don't know what side of the house these plants are on, but desiccating winds and repeated freeze/thaw can cause damage to shrubs. This will usually occur on the west or north side of the bushes. The damage seems to be too high to be related to dog urine issues.
Yews are fairly pest-free, but weevils and scale insects are both known to feed on yews and can cause significant dieback if the tree is stressed. The first link below shows pictures of the insects that cause the damage.
Yews are typically fairly disease free, but they can develop phytophthora root rot, causing dieback of the roots and therefore loss of greenery. This is usually caused by "wet feet", which shouldn't have happened for the first time in 60 years unless the drainage was changed.
Have you used herbicide near the shrubs? Herbicide spray can drift to unwanted foliage and damage branches or get carried to roots and cause dieback making the plant unable to support its canopy.
If the pictures were taken early in the spring, the tips might still come back. Check carefully for new growth before removing them completely. If, however, the entire branch is dead, it will need to be pruned out. If the underlying cause of the problem can be determined, the plant may survive long-term. Yews are pretty hardy.
This is an excellent fact sheet to help diagnose Yew problems.
ID-52: What's Wrong With My Taxus? (uky.edu)
This is a short paper, mostly describing winter damage to Yews, including that caused by deicing salts.
Common Problems on Yews | Horticulture and Home Pest News (iastate.edu)
If you narrow down the cause of the damage and have other specific questions, please feel free to open your question up again.
There are several factors that can cause damage such as you are seeing on your shrubs. Since you say they have been there a long time, I think we can rule out improper planting technique and probably inappropriate soil (pH, mineral content, etc). However, if there has been recent digging in the area, roots could have been cut and if you added soil over the roots (especially over 2" deep), you could have decreased the oxygen available to the roots.
Winter damage can cause browning of branches. I don't know what side of the house these plants are on, but desiccating winds and repeated freeze/thaw can cause damage to shrubs. This will usually occur on the west or north side of the bushes. The damage seems to be too high to be related to dog urine issues.
Yews are fairly pest-free, but weevils and scale insects are both known to feed on yews and can cause significant dieback if the tree is stressed. The first link below shows pictures of the insects that cause the damage.
Yews are typically fairly disease free, but they can develop phytophthora root rot, causing dieback of the roots and therefore loss of greenery. This is usually caused by "wet feet", which shouldn't have happened for the first time in 60 years unless the drainage was changed.
Have you used herbicide near the shrubs? Herbicide spray can drift to unwanted foliage and damage branches or get carried to roots and cause dieback making the plant unable to support its canopy.
If the pictures were taken early in the spring, the tips might still come back. Check carefully for new growth before removing them completely. If, however, the entire branch is dead, it will need to be pruned out. If the underlying cause of the problem can be determined, the plant may survive long-term. Yews are pretty hardy.
This is an excellent fact sheet to help diagnose Yew problems.
ID-52: What's Wrong With My Taxus? (uky.edu)
This is a short paper, mostly describing winter damage to Yews, including that caused by deicing salts.
Common Problems on Yews | Horticulture and Home Pest News (iastate.edu)
If you narrow down the cause of the damage and have other specific questions, please feel free to open your question up again.
Thanks for your response. The shrubs in question are all on the North side except for one on the East. Freezing and thawing could be an issue but never has been in the past. I do not see any instance of insect damage. I will prune. How far back should I prune? Shrubs on North side are adjacent to farmland in which herbicides are used but there is about 30 ft. between which is grass and shows no damage. May be Winter damage. Your input is very helpful. I will spray with Sevin for insects. Is Sevin a good idea or not? Thanks
With the shrubs on the north and east, winter damage could be part of the problem. If you see no sign of buds on the dead branches, I would prune them back as far as possible.
As far as spraying Sevin, I would not recommend doing this without proof of an active insect pest. Yews are not affected by too many pests. Mealy bugs and scale insects should be visible if you look closely, and they should be accompanied by sooty mold, which I do not see in your pictures. Black vine weevil grubs can do damage to yews, but their work is done underground at the roots and you will not see them on the plant. You may see the adults on the leaves of yew or adjacent plants, as they are generalist feeders.
Extension follows the use of Integrated Pest Management (IPM) when recommending pest treatment. This process requires proper identification of the pest, and use of less harmful controls before you get to synthetic insecticides (the class that Sevin is in). Synthetic pesticides are non-selective, killing beneficial as well as pest insects, even when used as directed. If you are not even sure there is a pest, you could be doing more harm than good.
Use of IPM requires the following steps:
1. make sure plant in question is not reacting to something less than the best gardening practices (eg pH, drainage, lack of water)
2. establish thresholds for the problem--a few pests are probably not really hurting the plant
3. inspect and monitor the plant, identifying insects present, knowing when the damage started or ended, or if it is ongoing
4. identify the cause of the problem
5. apply controls for pests in this order:
--cultural/mechanical (eg prune affected branches and discard)
--hand removal of pests
--screens & barriers
--biological controls (predatory/ parasitoidial insects)
--botanical insecticides (eg pyrethrins, neem)
--synthetic insecticides (eg Sevin) These must be used according to label directions.
The use of Sevin without knowing your target pest, or if it's life cycle is susceptible at this point, would be ineffective and possibly harmful to beneficial insects. If the problem is indeed winter damage, and you see no signs of insect infestation when you trim out the dead limbs, I would not use the Sevin.
Good luck; if you do find signs of insect damage or insects, send me a picture and we'll see if we can figure it out.
General IPM strategies:
https://extension.oregonstate.edu/pests-weeds-diseases/ipm/introduction-integrated-pest-management
IPM specific for Black vine weevils, which can cause serious damage to Taxus yew.
http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/blvinwee.html
As far as spraying Sevin, I would not recommend doing this without proof of an active insect pest. Yews are not affected by too many pests. Mealy bugs and scale insects should be visible if you look closely, and they should be accompanied by sooty mold, which I do not see in your pictures. Black vine weevil grubs can do damage to yews, but their work is done underground at the roots and you will not see them on the plant. You may see the adults on the leaves of yew or adjacent plants, as they are generalist feeders.
Extension follows the use of Integrated Pest Management (IPM) when recommending pest treatment. This process requires proper identification of the pest, and use of less harmful controls before you get to synthetic insecticides (the class that Sevin is in). Synthetic pesticides are non-selective, killing beneficial as well as pest insects, even when used as directed. If you are not even sure there is a pest, you could be doing more harm than good.
Use of IPM requires the following steps:
1. make sure plant in question is not reacting to something less than the best gardening practices (eg pH, drainage, lack of water)
2. establish thresholds for the problem--a few pests are probably not really hurting the plant
3. inspect and monitor the plant, identifying insects present, knowing when the damage started or ended, or if it is ongoing
4. identify the cause of the problem
5. apply controls for pests in this order:
--cultural/mechanical (eg prune affected branches and discard)
--hand removal of pests
--screens & barriers
--biological controls (predatory/ parasitoidial insects)
--botanical insecticides (eg pyrethrins, neem)
--synthetic insecticides (eg Sevin) These must be used according to label directions.
The use of Sevin without knowing your target pest, or if it's life cycle is susceptible at this point, would be ineffective and possibly harmful to beneficial insects. If the problem is indeed winter damage, and you see no signs of insect infestation when you trim out the dead limbs, I would not use the Sevin.
Good luck; if you do find signs of insect damage or insects, send me a picture and we'll see if we can figure it out.
General IPM strategies:
https://extension.oregonstate.edu/pests-weeds-diseases/ipm/introduction-integrated-pest-management
IPM specific for Black vine weevils, which can cause serious damage to Taxus yew.
http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/blvinwee.html
Thank you for your care and support.
You're welcome. Good luck with the yews.
