How do I save my japonica? - Ask Extension
Hello, This spring my japonica bushes have presented with a disease that is killing them. Can you please tell me what it is and what to do to save bot...
Knowledgebase
How do I save my japonica? #792749
Asked May 26, 2022, 10:51 AM EDT
Hello, This spring my japonica bushes have presented with a disease that is killing them. Can you please tell me what it is and what to do to save both the established japonica and the year-old mountain-air japonica?
Thank you,
Carolyn
Montgomery County Maryland
Expert Response
Hello, I see that you did not receive the upload of the mountain air japonica. I attach it with this email.
Thank you,
Carolyn
Hello, again. I attach another image of the back-side of the leaves of the mountain-air/fire japonica. Are these bugs or fungi?
Thank you,
Carolyn
Trying again to upload image of the back side of the leaf.
Trying a smaller file size.
Trying to upload image of brown on back of leaves of mountain japonica
Hello Carolyn,
We apologize for the lengthy delay in replying to you. We did not receive your submission until this morning for some reason, and are investigating this glitch with the system administrators. We received your first three photo attachments, but none of the others, which may also be a system error.
The Aucuba japonica may have a disease caused by the fungus Phomopsis, though we cannot be certain since symptoms sometimes overlap from different causes. You can trim off the browning and dying stem tips and foliage, though use of a fungicide may not resolve the problem since they cannot cure existing disease and not all fungicides are effective on all fungi. Typically, Phomopsis does not kill shrub roots, so the plant should be able to recover and replace lost growth if the root system is otherwise healthy. Aucuba struggles with soggy or poorly-drained soils, so make sure it's not also suffering root injury from soil that is becoming too wet, either from rain (such as a nearby roof downspout outlet emptying nearby) or irrigation.
Increasing air circulation around the plant and through its branches may also help, because this speeds-up drying of the leaf surfaces after rain or dew. (Prolonged wet leaf surfaces create conditions conducive to infection for most plant-infecting fungi and bacteria.) You can do this by removing tall weeds (if present), trimming back neighboring shrubs that are crowding the Aucuba branches, and/or trimming out some of the dense branches on the Aucuba itself to create more space between stems.
We can't tell from the photos how much shade or sun the Aucuba is exposed to, but it should be shaded during the hottest hours of afternoon sun so the plant isn't stressed; it likes woodland conditions like azaleas, rhododendron, pieris, and other shrubs fond of dappled shade. If it is getting several hours of midday/afternoon sun, you can move it to a shadier spot this time of year with no issues if you can monitor it for watering needs as it re-establishes.
The second plant, a Pieris japonica (also called Japanese andromeda; we're guessing you have the cultivar 'Mountain Fire'), appears to have a heavy infestation of lace bug. These insects are common pests of Pieris and its relatives, and they will have multiple generations per year. They reside on the leaf undersides, where they suck plant juices and lay their eggs in specks of dark tar-like goo.
Treatment involves repeatedly applying horticultural oil in order to smother the insects and their eggs. It may be difficult to thoroughly coat the leaf undersides with the spray, which is needed for good efficacy of the treatment. Do not apply the oil during temperatures above 85 degrees or phytotoxicity (plant tissue damage) may result. Even so, the foliage with lace bug feeding injury (the ones with the pale stippling) could still be damaged by an oil treatment due to their injuries, but that's ok -- damaged leaves don't heal, and they would eventually be falling off the plant anyway. The goal of treatments is to protect the new growth from infestation by lace bugs since the older foliage is already a lost cause. The plant will gradually replace those lost leaves, but on younger growth and not in the exact same locations those leaves were originally attached.
If getting thorough coverage of all foliage surfaces with the oil is too challenging or hasn't been working (which you will see via damage appearing on new growth), you could switch to using a systemic type of insecticide instead. However, we usually discourage their use due to the potential for unintended impacts on beneficial insects. This type of treatment requires fewer applications and lasts longer since the plant absorbs the chemical. Few systemic insecticides exist that the general public are allowed to apply; others must be applied by a professional pesticide applicator (usually accessible through a landscaping company or tree-care company).
If you prefer to avoid pesticides, you can try blasting the Pieris leaf undersides with a strong spray of water periodically to try to dislodge the lace bugs, though this won't dislodge their eggs, so you have to look for new generations every few weeks or so to know when to spray again. Although tedious, you could also opt to trim off all of the individual leaves with damage, since some of the eggs will have been laid on them. Lastly, the other solution is to simply replace the plant if intolerable levels of damage exist and you prefer not to try any of the above approaches. Recovery is likely with treatment (any of the above techniques), but since Pieris grow relatively slowly, it could take a while for the plant to look full and lush again.
Miri
We apologize for the lengthy delay in replying to you. We did not receive your submission until this morning for some reason, and are investigating this glitch with the system administrators. We received your first three photo attachments, but none of the others, which may also be a system error.
The Aucuba japonica may have a disease caused by the fungus Phomopsis, though we cannot be certain since symptoms sometimes overlap from different causes. You can trim off the browning and dying stem tips and foliage, though use of a fungicide may not resolve the problem since they cannot cure existing disease and not all fungicides are effective on all fungi. Typically, Phomopsis does not kill shrub roots, so the plant should be able to recover and replace lost growth if the root system is otherwise healthy. Aucuba struggles with soggy or poorly-drained soils, so make sure it's not also suffering root injury from soil that is becoming too wet, either from rain (such as a nearby roof downspout outlet emptying nearby) or irrigation.
Increasing air circulation around the plant and through its branches may also help, because this speeds-up drying of the leaf surfaces after rain or dew. (Prolonged wet leaf surfaces create conditions conducive to infection for most plant-infecting fungi and bacteria.) You can do this by removing tall weeds (if present), trimming back neighboring shrubs that are crowding the Aucuba branches, and/or trimming out some of the dense branches on the Aucuba itself to create more space between stems.
We can't tell from the photos how much shade or sun the Aucuba is exposed to, but it should be shaded during the hottest hours of afternoon sun so the plant isn't stressed; it likes woodland conditions like azaleas, rhododendron, pieris, and other shrubs fond of dappled shade. If it is getting several hours of midday/afternoon sun, you can move it to a shadier spot this time of year with no issues if you can monitor it for watering needs as it re-establishes.
The second plant, a Pieris japonica (also called Japanese andromeda; we're guessing you have the cultivar 'Mountain Fire'), appears to have a heavy infestation of lace bug. These insects are common pests of Pieris and its relatives, and they will have multiple generations per year. They reside on the leaf undersides, where they suck plant juices and lay their eggs in specks of dark tar-like goo.
Treatment involves repeatedly applying horticultural oil in order to smother the insects and their eggs. It may be difficult to thoroughly coat the leaf undersides with the spray, which is needed for good efficacy of the treatment. Do not apply the oil during temperatures above 85 degrees or phytotoxicity (plant tissue damage) may result. Even so, the foliage with lace bug feeding injury (the ones with the pale stippling) could still be damaged by an oil treatment due to their injuries, but that's ok -- damaged leaves don't heal, and they would eventually be falling off the plant anyway. The goal of treatments is to protect the new growth from infestation by lace bugs since the older foliage is already a lost cause. The plant will gradually replace those lost leaves, but on younger growth and not in the exact same locations those leaves were originally attached.
If getting thorough coverage of all foliage surfaces with the oil is too challenging or hasn't been working (which you will see via damage appearing on new growth), you could switch to using a systemic type of insecticide instead. However, we usually discourage their use due to the potential for unintended impacts on beneficial insects. This type of treatment requires fewer applications and lasts longer since the plant absorbs the chemical. Few systemic insecticides exist that the general public are allowed to apply; others must be applied by a professional pesticide applicator (usually accessible through a landscaping company or tree-care company).
If you prefer to avoid pesticides, you can try blasting the Pieris leaf undersides with a strong spray of water periodically to try to dislodge the lace bugs, though this won't dislodge their eggs, so you have to look for new generations every few weeks or so to know when to spray again. Although tedious, you could also opt to trim off all of the individual leaves with damage, since some of the eggs will have been laid on them. Lastly, the other solution is to simply replace the plant if intolerable levels of damage exist and you prefer not to try any of the above approaches. Recovery is likely with treatment (any of the above techniques), but since Pieris grow relatively slowly, it could take a while for the plant to look full and lush again.
Miri
