Amaranthus disease or bug - Ask Extension
I have amaranthus that are falling over dead..right at soil leaves it is a mushy stem..I tore it open but did not find any bugs or worms...
Knowledgebase
Amaranthus disease or bug #760445
Asked July 07, 2021, 1:49 PM EDT
I have amaranthus that are falling over dead..right at soil leaves it is a mushy stem..I tore it open but did not find any bugs or worms...
Isanti County Minnesota
Expert Response
Hello Joan, happy to help.
This appears to be gray mold. It's a little hard to tell on a stem but I do see the characteristic dark and light rings as it progresses up and down the specimen photos. Gray mold can be controlled by removing affected plant material and burying it or composting it. I recommend cleaning up the surrounding leaves and weeds on the soil because the mold can persist in the ground over winter. Here is more information about gray mold including conditions that allow it to catch hold on plants.
This appears to be gray mold. It's a little hard to tell on a stem but I do see the characteristic dark and light rings as it progresses up and down the specimen photos. Gray mold can be controlled by removing affected plant material and burying it or composting it. I recommend cleaning up the surrounding leaves and weeds on the soil because the mold can persist in the ground over winter. Here is more information about gray mold including conditions that allow it to catch hold on plants.
Good-luck!
Hello Joan,
I came across another potential culprit namely the Pigweed weevil or Amaranthus stem weevil. Slit the stem up the full length of it to see if there is a larva inside. They can also be found in the root.
If you find the larva, there's not much you can do with this other than cut and destroy the plant so that it doesn't become an adult and lay eggs that will do more harm in the future.
Here is a link to information about the Pigweed weevil that shows what to look for.
Good-luck!
I came across another potential culprit namely the Pigweed weevil or Amaranthus stem weevil. Slit the stem up the full length of it to see if there is a larva inside. They can also be found in the root.
If you find the larva, there's not much you can do with this other than cut and destroy the plant so that it doesn't become an adult and lay eggs that will do more harm in the future.
Here is a link to information about the Pigweed weevil that shows what to look for.
Good-luck!
I cut the stems open and did not see larvae...and no black rings..I am sending a fresh picture of the root line and second picture is of upper line on stem
Hello Joan,
Whether it's gray mold or pigweed weevil, I would err on the side of caution and destroy any affected plant. There's dark material in the opened plant that may be the larva frass and it may be that it has already matured and took flight.
Be on the lookout for the adult pigweed weevil. Its photo is shown in the link I provided. And if you see it, try to catch and smash it. The recommended pesticides in the link may not be legal in this state. Know that all pesticides have complete information on their labels that state which pests they're geared for and how to safely apply them. The labels are oftentimes more up to date than those shown online. Pesticide manufacturers are required by law to provide all that information and we as consumers are required by law to follows the label instructions.
I wish I could find information about the lifecycle of the pigweed weevil in our cold region because the link I sent seems to be about how they cycle through their generations in warmer climates. I recommend cleaning up all plant material at the end of the season and burning or burying it to keep the infestation rate down next year.
That's the best information I can provide.
Whether it's gray mold or pigweed weevil, I would err on the side of caution and destroy any affected plant. There's dark material in the opened plant that may be the larva frass and it may be that it has already matured and took flight.
Be on the lookout for the adult pigweed weevil. Its photo is shown in the link I provided. And if you see it, try to catch and smash it. The recommended pesticides in the link may not be legal in this state. Know that all pesticides have complete information on their labels that state which pests they're geared for and how to safely apply them. The labels are oftentimes more up to date than those shown online. Pesticide manufacturers are required by law to provide all that information and we as consumers are required by law to follows the label instructions.
I wish I could find information about the lifecycle of the pigweed weevil in our cold region because the link I sent seems to be about how they cycle through their generations in warmer climates. I recommend cleaning up all plant material at the end of the season and burning or burying it to keep the infestation rate down next year.
That's the best information I can provide.
Thanks so much ...I will destroy bad plants and put some seven down by the stems as they come out of ground...
Thanks again for all your help...I never had this problem before.. usually these plants are tough...
Joan
Thank you so much for your help...I cut along the stem...but did not see any larvae... or worms
Didn't see any black rings for gray mold
Still puzzled
Joan
Sending new pics One of the bottom half...second one top half
As I wrote earlier, whether it's gray mold or bug, I would destroy the plant and make sure there is no chance for a re-infestation by destroying the material. If there was a bug, it has matured and flown out and lay eggs for a new generation. It's very hard to diagnose these things by photos which is why I hesitate to definitely say what an issue is.
If you want a definite diagnosis of whether it's gray mold, you can send a sample to the U of MN Plant Disease Clinic. Here is their link where you'll learn about their services, prices, and how to submit a sample. They may be able to detect frass in the stem and that would indicate that it was a weevil.
Good-luck!
If you want a definite diagnosis of whether it's gray mold, you can send a sample to the U of MN Plant Disease Clinic. Here is their link where you'll learn about their services, prices, and how to submit a sample. They may be able to detect frass in the stem and that would indicate that it was a weevil.
Good-luck!
