Identifying disease or cultural problems on hosta in pot - Ask Extension
First year I've grown hostess in pots - these in the photos are from the "mouse" series so are small hosts. Also most of the areas of concer...
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Identifying disease or cultural problems on hosta in pot #839460
Asked July 07, 2023, 12:32 PM EDT
First year I've grown hostess in pots - these in the photos are from the "mouse" series so are small hosts. Also most of the areas of concern are on the larger one but there are a few leaves affected on the small one so we know that it applies to both varieties.
Early in the season when these plants grew leaves the distinct pattern of spotting on the leaf edges showed up. It has since not been spreading to any degree I can detect although I haven't monitored it closely. They seem to be in ideal light situations, flowered beautifully and all signs are that they are otherwise healthy. They did remain outside all Winter in the same location. I might have fertilized early on with our compost drainage which has a dark very reddish brown color. Have no idea of course of the NPK, pH, micronutrients, etc of that. I probably diluted it some.
So...bacterial or under or imbalanced fertilizing or something else? Thank you!
Montgomery County Maryland
Expert Response
There are several leaf-infecting pathogens (fungi or bacteria, mostly) that afflict Hosta, though not all are serious. Their symptoms are sometimes hard to tell apart, though our assessment for now is that this looks more bacterial than fungal, but we can't rule-out a fungus like Anthracnose, which is quite common. Pathogen spores tend to infect foliage whose surfaces are wet (from rain, dew, or irrigation) more easily than dry leaves, but this is not absolutely necessary for successful infection since some can enter the leaf tissue on their own or through natural pores in the leaf.
A fungicide cannot cure existing infection but it might help protect growth which is still healthy, though few fungicide ingredients have any impact on bacterial diseases. (Check product labels for this information. Several bacterial agent names end in -monas, for example, if the label doesn't explicitly list something more overt like "bacterial leaf spot.") We generally discourage the use of fungicides because repeat treatments are often needed and such sprays might risk harm to pollinators if residues land on any open flowers. They also don't always work since sometimes disease pressures are too high, weather interrupts the spray schedule timing, or because what looked like healthy growth upon treatment already was infected but still asymptomatic.
Normally you could just clip off any symptomatic leaves to slow or perhaps stop disease spread, but in this case that might remove too much growth, so you can monitor the progression of the dead zone on the foliage and if it worsens to envelop more of the leaf approaching the stem, then you can cut them off. (Don't just cut the dead portion of the leaf off, as this risks spreading the pathogen more easily and also creates a wound which can be infected by any number of diseases.) Discard any removed leaves; don't compost them.
Container-grown plants do benefit from occasional fertilization since nutrient levels run low over time, but this symptom does not look related to fertilization and we don't see any obvious symptoms of a nutrient deficiency.
At the end of the season after frost kills the leaves, you can remove all of the Hosta foliage and dispose of it to hopefully reduce spore presence for the following year. It's not a foolproof way of preventing re-infection, but it won't hurt. If symptoms worsen notably or change appearance, feel free to send us additional photos.
Miri
A fungicide cannot cure existing infection but it might help protect growth which is still healthy, though few fungicide ingredients have any impact on bacterial diseases. (Check product labels for this information. Several bacterial agent names end in -monas, for example, if the label doesn't explicitly list something more overt like "bacterial leaf spot.") We generally discourage the use of fungicides because repeat treatments are often needed and such sprays might risk harm to pollinators if residues land on any open flowers. They also don't always work since sometimes disease pressures are too high, weather interrupts the spray schedule timing, or because what looked like healthy growth upon treatment already was infected but still asymptomatic.
Normally you could just clip off any symptomatic leaves to slow or perhaps stop disease spread, but in this case that might remove too much growth, so you can monitor the progression of the dead zone on the foliage and if it worsens to envelop more of the leaf approaching the stem, then you can cut them off. (Don't just cut the dead portion of the leaf off, as this risks spreading the pathogen more easily and also creates a wound which can be infected by any number of diseases.) Discard any removed leaves; don't compost them.
Container-grown plants do benefit from occasional fertilization since nutrient levels run low over time, but this symptom does not look related to fertilization and we don't see any obvious symptoms of a nutrient deficiency.
At the end of the season after frost kills the leaves, you can remove all of the Hosta foliage and dispose of it to hopefully reduce spore presence for the following year. It's not a foolproof way of preventing re-infection, but it won't hurt. If symptoms worsen notably or change appearance, feel free to send us additional photos.
Miri
Thank you! Good reply - it does look a lot like Anthracnose. I'm not concerned enough at this point to use any fungicide but I was interested in identifying the problem.
Good idea about sanitation at the end of the season - I wouldn't have thought of that.
I'll monitor it more closely but like I said in the original description, it is not spreading at any pace that I can detect.
Thank you again!
Katherine
PS I remember you from Behnkes and you were always so knowledgable and helpful especially in answering our questions about native plants. And your writings were really great.
Thank you, and you're welcome!
