Pest or fungus? - Ask Extension
Hello! I recently purchased several different flowering plants from a local greenhouse about 2 weeks ago. I am having issues with almost all of them i...
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Pest or fungus? #868775
Asked May 16, 2024, 5:09 PM EDT
Hello! I recently purchased several different flowering plants from a local greenhouse about 2 weeks ago. I am having issues with almost all of them including a mandevilla, dahlias, lantana, and bracteantha. I’m not sure if they are all related or not. I will begin with the mandevilla. It has brown spots on the leaves that turn to holes. The leaves are also turning brown (more visible from the back of the leaf). The stems have developed brown spots and are now splitting.
Kalamazoo County Michigan
Expert Response
Thank you, Melany, for your question/s!
Greenhouses are the perfect environment for disease and pests to get out of control. They usually have elevated temperatures, reduced airflow (compared to outside air), and higher humidity. Without precise monitoring of a greenhouse environment, it doesn't take long for an opportunistic element (disease or pest) to spread rapidly throughout.
It was unfortunate that your plants were purchased before there was any indication of a problem. The first article highlights the various sources of disease
Sources Of Plant Disease In Greenhouses (psu.edu)
and the second demonstrates the different forms disease can take on in a greenhouse
Greenhouse pest and disease gallery | Greenhouse Horticulture (cornell.edu)
Not knowing precisely what is going on with your plant/s there are a few things that you can do to move your plant/s to a brighter future! You will need to prune out the affected areas of your mandevilla and dispose of these in the trash. Examine the underside of the leaves and remove any insects or eggs into soapy water or the trash.
Next you will want to transplant your pruned mandevilla into fresh sterile soil that you have purchased. Remove the plant, placing it on newspaper, cardboard or a brown paper bag cut open. Tease out as much of the soil as possible onto the paper. In the meantime, locate a new pot or using a 10% bleach solution, clean the old pot, rinsing well with water.
Fill whatever you are going to use as the new pot with fresh sterile soil and repot your mandevilla into it. Discard the old soil in the trash and disinfect the area with the remainder of your 10% bleach solution (10 oz. bleach mixed with 90 oz. of water).
Water at the base not overhead avoiding getting the leaves wet. Quarantine this plant from others to be safe. If after a while (5-7days) things still don't look right, try applying a horticultural oil.
I've included a care article for your interest:
Mandevilla - University of Florida, Institute of Food and Agricultural Sciences (ufl.edu)
Happy Gardening!
Greenhouses are the perfect environment for disease and pests to get out of control. They usually have elevated temperatures, reduced airflow (compared to outside air), and higher humidity. Without precise monitoring of a greenhouse environment, it doesn't take long for an opportunistic element (disease or pest) to spread rapidly throughout.
It was unfortunate that your plants were purchased before there was any indication of a problem. The first article highlights the various sources of disease
Sources Of Plant Disease In Greenhouses (psu.edu)
and the second demonstrates the different forms disease can take on in a greenhouse
Greenhouse pest and disease gallery | Greenhouse Horticulture (cornell.edu)
Not knowing precisely what is going on with your plant/s there are a few things that you can do to move your plant/s to a brighter future! You will need to prune out the affected areas of your mandevilla and dispose of these in the trash. Examine the underside of the leaves and remove any insects or eggs into soapy water or the trash.
Next you will want to transplant your pruned mandevilla into fresh sterile soil that you have purchased. Remove the plant, placing it on newspaper, cardboard or a brown paper bag cut open. Tease out as much of the soil as possible onto the paper. In the meantime, locate a new pot or using a 10% bleach solution, clean the old pot, rinsing well with water.
Fill whatever you are going to use as the new pot with fresh sterile soil and repot your mandevilla into it. Discard the old soil in the trash and disinfect the area with the remainder of your 10% bleach solution (10 oz. bleach mixed with 90 oz. of water).
Water at the base not overhead avoiding getting the leaves wet. Quarantine this plant from others to be safe. If after a while (5-7days) things still don't look right, try applying a horticultural oil.
I've included a care article for your interest:
Mandevilla - University of Florida, Institute of Food and Agricultural Sciences (ufl.edu)
Happy Gardening!
