Mugo Pine -- needles turned brown - Ask Extension
Dear Md. Extension: For the second year in a row the needles on one of two mugo pines planted next to each other have turned brown. I think that last...
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Mugo Pine -- needles turned brown #815291
Asked October 26, 2022, 3:40 PM EDT
Dear Md. Extension: For the second year in a row the needles on one of two mugo pines planted next to each other have turned brown. I think that last year they fell off and there were new needles. But why are the needles on one turning brown and the other has no brown needles? I attach a picture. These are on the front of the house and get a good deal of afternoon sun. A few years ago this happened and I sprayed for insects which seemed to work. The pine that has the brown needles was moved away over five years ago to allow some pipe construction and then moved back to the same spot. It seemed to recover well at that time.
(You were extremely helpful to me in deciding whether to take out a river birch that started to die and I was most grateful.) I would appreciate some guidance -- Should I spray with something and, if so, what? Or should I just wait for spring and see if the needles grow back? (That's a fig growing next to the pine and a Japanese maple behind. Both are thriving.) Many thanks ... Peter
District of Columbia County District of Columbia
Expert Response
Hi Peter,
It's hard to tell what the cause is for the browning needles. We suspect root damage, though even this can be hard to diagnose since the original cause may have occurred weeks or months prior to any symptoms appearing. Drought stress or overwatering (or oversaturated soil from any cause) may be a factor, and they can create nearly identical symptoms in foliage.
Mugo pines can be vulnerable to fungal needle infections like Diplodia Tip Blight, but that probably would not impact only a localized area of the plant at one time. You can use the information on the linked page plus the images on Penn State's page for this disease to see if you notice fungal spore production in the dead needles or other indicators of this particular pathogen. If fungicide use is warranted for such a diagnosis, be aware that it cannot cure existing damage or dieback, and only prevents infection on growth that is still healthy. Pines do not replace growth on branches that have gone completely bare since no living leaf buds remain.
We suggest you not use an insecticide unless you've been able to identify a specific pest. What appeared to be a success after using one in years past may have been unrelated to the plant's apparent recovery. Not only is pest identification needed to confirm which pesticide (if any) will be effective in its control, plus when to apply it, but its use could stress a plant if no insect is actually responsible for the damage. Many pesticides can also harm beneficial insects which are needed to help control pests before they reach outbreak or damaging levels. Insect pests of mugo pine are relatively few, but important ones include one or more species of scale insects, redheaded pine sawfly (chews needles, so would not cause browning), and bagworms (same situation).
For now, just trim off any branches that may be dead (no live needles or buds at the branch tips) and monitor the plant. When determining if it needs water, feel the soil around six inches deep and water well only when it's becoming somewhat dry to the touch at that depth. A raised bed like this, particularly when the stone may be reflecting and retaining heat in summer, might be drying faster than in-ground soil nearby, so might need checking more often than plants grown in level ground. Mugo pine is native to cooler climates than we experience, so heat stress is a potential underlying factor in its vulnerability to pests or diseases.
Miri
It's hard to tell what the cause is for the browning needles. We suspect root damage, though even this can be hard to diagnose since the original cause may have occurred weeks or months prior to any symptoms appearing. Drought stress or overwatering (or oversaturated soil from any cause) may be a factor, and they can create nearly identical symptoms in foliage.
Mugo pines can be vulnerable to fungal needle infections like Diplodia Tip Blight, but that probably would not impact only a localized area of the plant at one time. You can use the information on the linked page plus the images on Penn State's page for this disease to see if you notice fungal spore production in the dead needles or other indicators of this particular pathogen. If fungicide use is warranted for such a diagnosis, be aware that it cannot cure existing damage or dieback, and only prevents infection on growth that is still healthy. Pines do not replace growth on branches that have gone completely bare since no living leaf buds remain.
We suggest you not use an insecticide unless you've been able to identify a specific pest. What appeared to be a success after using one in years past may have been unrelated to the plant's apparent recovery. Not only is pest identification needed to confirm which pesticide (if any) will be effective in its control, plus when to apply it, but its use could stress a plant if no insect is actually responsible for the damage. Many pesticides can also harm beneficial insects which are needed to help control pests before they reach outbreak or damaging levels. Insect pests of mugo pine are relatively few, but important ones include one or more species of scale insects, redheaded pine sawfly (chews needles, so would not cause browning), and bagworms (same situation).
For now, just trim off any branches that may be dead (no live needles or buds at the branch tips) and monitor the plant. When determining if it needs water, feel the soil around six inches deep and water well only when it's becoming somewhat dry to the touch at that depth. A raised bed like this, particularly when the stone may be reflecting and retaining heat in summer, might be drying faster than in-ground soil nearby, so might need checking more often than plants grown in level ground. Mugo pine is native to cooler climates than we experience, so heat stress is a potential underlying factor in its vulnerability to pests or diseases.
Miri
Miri,
Many thanks for this most thoughtful and helpful response. I will follow your advice and let you know what happens next summer.
Peter
You're welcome.
