Fireweed problem - Ask Extension
Some of my fireweed plants have yellow/reddish/brown spots on the leaves. Any idea what this is and what I need to do about it? Thank you for any help...
Knowledgebase
Fireweed problem #874687
Asked June 25, 2024, 5:51 PM EDT
Some of my fireweed plants have yellow/reddish/brown spots on the leaves. Any idea what this is and what I need to do about it? Thank you for any help. I will note that I have sprayed them with deer repellent (I've used both liquid fence and deer out) but the spray was mostly on the plants in front, most of which are still fine other than their missing flowers.
Marion County Oregon
Expert Response
Dear Cheryl,
Thank you for contacting us about your fireweed plants. Can you please verify whether your plant is known botanically as Pucciniastrum epilobii or Chamaenerion angustifolium? The two are similar in appearance but taxonomically quite different.
Thank you for contacting us about your fireweed plants. Can you please verify whether your plant is known botanically as Pucciniastrum epilobii or Chamaenerion angustifolium? The two are similar in appearance but taxonomically quite different.
Not totally sure how to respond. When I checked the internet for varieties, there were only 2 noted and I’m sure mine is augustifolium because it’s definitely not dwarf.
The first latin name in the response is a disease, so I’m guessing that’s the diagnosis.
There was something online about "not treatable" and "thin plants" so I’m guessing I should remove diseased stalks or at least the leaves - which interestingly enough are all in back at this point. Yesterday was the first time this year we had the water on, so I don’t know how that impacts the situation. It’s overhead watering (dang, but that’s what was here when we moved in) so that’s another factor.
If there is anything besides thinning that helps, please let me know. Thank you for your help!!
Cheryl
On Jun 26, 2024, at 4:39 PM, Ask Extension <<personal data hidden>> wrote:
Dear Cheryl, here's the response to your question:
Dear Cheryl,
Thank you for contacting us about your fireweed plants. Can you please verify whether your plant is known botanically as Pucciniastrum epilobii or Chamaenerion angustifolium? The two are similar in appearance but taxonomically quite different.Need to reply to the expert? Click the link below, or simply reply to this email.
Click here to view #0144605
Best Regards,
Lynne Marie S.
OSU Extension Master Gardener
Dear Cheryl,
From your photo, the leaf spots look like they may be rust, a fungal disease. Fungal diseases are common with our weather conditions. Generally, the leaf spots are unsightly but not usually dangerous to your plants.
However, the reason I want to confirm the species is because there are actually several plants commonly known as fireweed. One in particular, Pucciniastrum epilobii, is a host of fir-fireweed rust (Pucciniastrum epilobii G.) which can seriously affect the growth of balsam firs and some other conifers.
Fungal spores are in the air as well as the soil, and can take hold whenever the conditions for them are right. Cool, wet springs followed by warm, dry summers provide the perfect combination for fungal leaf spots. Plants at the back of a bed are more susceptible because they may not get adequate air circulation.
Once a fungal disease arises, it is very difficult to get rid of it. Copper sprays or bordeaux mix may help, but the key to effective management is prevention and containment. A fairly effective preventative measure to use before a fungal infection sets in is to spray plants with a 1:3 mixture of 2% milk and water.
The best course of action is to use the following best practices:
I hope this information is helpful. If you could send some closeup photos of your plants showing the leaf arrangement on the stems and other details, we may be able to better identify the species in your garden.
From your photo, the leaf spots look like they may be rust, a fungal disease. Fungal diseases are common with our weather conditions. Generally, the leaf spots are unsightly but not usually dangerous to your plants.
However, the reason I want to confirm the species is because there are actually several plants commonly known as fireweed. One in particular, Pucciniastrum epilobii, is a host of fir-fireweed rust (Pucciniastrum epilobii G.) which can seriously affect the growth of balsam firs and some other conifers.
Fungal spores are in the air as well as the soil, and can take hold whenever the conditions for them are right. Cool, wet springs followed by warm, dry summers provide the perfect combination for fungal leaf spots. Plants at the back of a bed are more susceptible because they may not get adequate air circulation.
Once a fungal disease arises, it is very difficult to get rid of it. Copper sprays or bordeaux mix may help, but the key to effective management is prevention and containment. A fairly effective preventative measure to use before a fungal infection sets in is to spray plants with a 1:3 mixture of 2% milk and water.
The best course of action is to use the following best practices:
- Choose the right plant for the site based on sun, soil, and soil moisture.
- Choose resistant varieties of plants when available
- Prune and thin plants to allow good airflow through and between them.
- Clean up plant debris regularly and after the leaves drop in the autumn.
- Use 2 to 3 inches of wood chips or another organic mulch at all times to reduce reinfection through rain splash. Mulch will also retain moisture in the soil and help prevent soil compaction.
I hope this information is helpful. If you could send some closeup photos of your plants showing the leaf arrangement on the stems and other details, we may be able to better identify the species in your garden.
