Do I have phytophthora in these hollies? - Ask Extension
These are 4 Burford Hollies in partial shade in front of my house. A fifth one on the far right died last summer. The third from the left is dead, t...
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Do I have phytophthora in these hollies? #865562
Asked April 23, 2024, 10:31 AM EDT
These are 4 Burford Hollies in partial shade in front of my house. A fifth one on the far right died last summer. The third from the left is dead, the fourth from the left is about to die, the second from the left is struggling, and the left-hand holley is perfect. They are about 30 years old and I've never had any problems with them. I see no signs of insects or root rot. Coud this be phytophthora? If so, can I plant new plants in the same place? Do I have to treat the soil first?
Thank you!
Montgomery County Maryland
Expert Response
It's challenging to determine what the cause was based on the symptoms, but unfortunately there won't be any treatment that can salvage the plants that are declining but not quite dead yet. Chinese Holly (the species to which 'Burfordii' belongs, Ilex cornuta) tends to be fairly drought-tolerant, but either cumulative drought stress and/or periods of over-saturated soil might have led to root loss. Root rot will not be diagnosable from above-ground symptoms alone, but when a plant is uprooted for examination, the roots will tend to pull apart fairly easily (the outer sheath pulls off the stringy inner core with little effort). Phytophthora is one of several fungus-like pathogens that can cause root rot, but there is no fungicide that would work or which would be recommended for soil treatment.
Root rot pathogens take advantage of roots that aren't receiving enough oxygen when the soil stays saturated or doesn't drain well (or is too compacted). They can be present in soil (and often are) without causing problems as long as roots remain healthy and vigorous. Even if a fungicide soil drench worked to eradicate any present in that planting bed, new spores could recolonize it at any time, causing new disease when a vulnerable plant is faced with low-oxygen conditions. Soil that isn't acidic enough for acid-loving species (holly included) can also create conditions suitable for these microbes, so having a soil pH test performed to assess the acidity level might help when it comes to determining what to replant. (Planting something suited to the current conditions will be easier than trying to alter the conditions to suit particular plants.) Maybe the concrete is leaching into the soil over time and raising the pH, though the healthy-looking holly isn't showing indications of nutrient deficiency typically associated with soil that isn't acidic enough.
We recommend removal of the ailing plants and replacement, either with more of the same species (if you prefer and if the conditions still seem suitable for them) or a different species (or mix of species).
Miri
Root rot pathogens take advantage of roots that aren't receiving enough oxygen when the soil stays saturated or doesn't drain well (or is too compacted). They can be present in soil (and often are) without causing problems as long as roots remain healthy and vigorous. Even if a fungicide soil drench worked to eradicate any present in that planting bed, new spores could recolonize it at any time, causing new disease when a vulnerable plant is faced with low-oxygen conditions. Soil that isn't acidic enough for acid-loving species (holly included) can also create conditions suitable for these microbes, so having a soil pH test performed to assess the acidity level might help when it comes to determining what to replant. (Planting something suited to the current conditions will be easier than trying to alter the conditions to suit particular plants.) Maybe the concrete is leaching into the soil over time and raising the pH, though the healthy-looking holly isn't showing indications of nutrient deficiency typically associated with soil that isn't acidic enough.
We recommend removal of the ailing plants and replacement, either with more of the same species (if you prefer and if the conditions still seem suitable for them) or a different species (or mix of species).
Miri
Thank you, Miri. That information is very helpful.
You're welcome!
