What is happening to my amaranth?

Question: I’m growing amaranth, and everything seems fine until the plant suddenly wilts. They’re growing pretty tall, and then all of a sudden…wilted. This is my first year with a high tunnel, and this is where they are growing.

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied August 05, 2024, 12:58 PM EDT
response: This looks like stem rot caused by Sclerotinia (also called White Rot), which can be fairly common. Nothing will cure an existing outbreak, though sanitation (removing all diseased plant parts and debris) can help to reduce the occurrence of new infections. There might be fungicide applications that can be used on the soil as a drench or fumigant, but they might need to be applied by a certified pesticide applicator.  Are you a cut flower or greenhouse business, or just a home hobbyist? We ask because, if you are a business, you may be able to get samples tested (for confirmation of disease) by area plant diagnostic labs while UMD's lab is temporarily closed. Similarly, you can subscribe to the greenhouse/cut flower IPM alerts, and work with Extension Agents that specialize in plant pest, disease, and nutrition issues which work with commercial growers.  Miri

responder: The Question Asker Replied August 05, 2024, 1:47 PM EDT
response: Thank you for this. I am a small scale commercial flower grower and this was my first year with a high tunnel, so I’m experiencing all kinds of new disease/pest issues.   Am I able to plant something in the space where the diseased plants were in the future? I’d rather not bring in a pesticide applicator. I’m currently planning to flip the bed to a different cut flower crop in the fall.   Additionally, I would actually love to send in some dahlia leaves that I think might have a virus. Is that something I can do? I was looking at the UD website, and it mentioned sending to your county’s extension office. Would this still work if I’m not in Delaware?   Thank you,  Alana

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied August 05, 2024, 5:24 PM EDT
response: Hello Alana,  With UMD's plant pathology lab closed until a new lab director can be hired to replace the person that retired, labs in surrounding states are graciously offering to test samples on our behalf, though they may charge a fee comparable to what in-state residents of those areas would be charged. Even if you bring a sample for diagnosis to your local Extension office, the specialists or agents there still might need to send some samples out to a testing lab for confirmation of a diagnosis for certain pathogens, especially when it comes to plant viruses. (There is no testing lab at the field offices; it was only on campus.) Not every lab has test kits for every plant virus (there are many, and tests can be costly), so contact the lab prior to sending samples if you suspect a certain virus, to make sure they would be able to confirm its presence.  That said, viruses on Dahlias can be very common, and from a cut flower business perspective, probably don't need to be confirmed via testing, as symptomatic plants should be removed (especially if the tuber crop is replanted yearly anyway, as is common). Viral infection won't always affect flower production or quality, so in that sense, might not be that serious of a disease to manage.  Another possibility to the Sclerotinia diagnosis is Southern Blight, since the former fungus is more common early in the season and the latter more common this time of year, since it is highly heat-tolerant. Both can have a very wide host plant range, meaning they are capable of infecting many species of plants. For Southern Blight, cultivating the soil of a bed with the infected plants removed can bury the sclerotia (spore structures) deep enough that they are unlikely to re-infect a new crop. An issue with Sclerotinia might need a different resolution, though, so check with Extension plant pathologists that work with businesses and/or the testing lab once they confirm which pathogen is responsible.  Miri