Trying to identify a plant disease

Question: Hello,
Last fall I began to see what I believe is a fungal disease mainly in the tender leafed brassicas (tat soi, arugula, pac Choi, red Russian kale). In some cases there is a yellowing of the leaves veins, followed by a brittling of the leaf and buckling or almost bubble texture. The leaf then twists and new growth is most intensely affected. In certain cases whole sides of the plant will almost melt away. In some cases a black line moves up the stem and leads to decay and further yellowing. This fall it has been spreading a bunch and seems to be affecting the chichories (radicchios) as well. Any thoughts would be appreciated! At what point do you recommend a plant tissue sample? Thank you.

responder: Jacki D., Master Gardener Diagnostician Volunteer (Washington, Multnomah and Clackamas Counties) Oregon State University Extension Service Volunteer Metro Master Gardeners (http://metromastergardeners.org/) Replied October 07, 2024, 8:55 PM EDT
response: It’s challenging to determine virus, bacterial or fungal. Sometimes a homeowner with send a sample to a laboratory.  Before we advise that step, tell us a bit more about the history of your garden. Basic advice is found in Growing Your Own. The section on disease speaks to crop rotation for disease reduction. Have you done that? Does your garden get enough sun for these crops? How many years have you had success before this problem started? If the advice is lab testing, here is the OSU Plant Clinic website.

responder: The Question Asker Replied October 08, 2024, 10:19 AM EDT
response: Thank you for getting back to me.I recognize it is challenging to distinguish virus/ bacteria/ fungal. But do you have any things you look for when trying to decipher them?We follow basic organic standards for our plot of land, crop rotation being a big piece of that. This issue is popping up in brassicas growing where tomatoes were last season and in the chicories where the melons had been. We have full sun and have successfully grown these crops for 2 years before seeing this issue arise for the first time in the fall of the 3rd year.Any thoughts about what it could possibly be would be greatly appreciated, as I’ve been researching possibilities I’ve had a hard time finding the right words to lead to promising articles. Thank you for your time.On Mon, Oct 7, 2024 at 5:55 PM Ask Extension <<personal data hidden>> wrote:

responder: Jacki D., Master Gardener Diagnostician Volunteer (Washington, Multnomah and Clackamas Counties) Oregon State University Extension Service Volunteer Metro Master Gardeners (http://metromastergardeners.org/) Replied October 08, 2024, 11:10 AM EDT
response: I see now that you sell at farmers markets, so I will refer you to OSU staff. Volunteers generally help home gardeners. If you don’t hear back through this online forum, I encourage you to contact OSU directly. The Small Farms program is a good place to start. Teagan and Heather listed on this staff directory are folks I’m familiar with and are a good starting point. A note about research: add the word “extension”, also try adding “Oregon” “PNW” and “Washington”. This is how I focus in on articles, images and videos that are university-based and aimed more at educating producers and the public than being heavy research links. I was searching “brassica disease extension Oregon” and found a variety of hits. I expect someone will respond to you here in a few days.

responder: The Question Asker Replied October 09, 2024, 9:05 AM EDT
response: Wonderful, thank you so much. I appreciate your time and connecting me with these folks at OSU. Thank you. On Tue, Oct 8, 2024 at 8:10 AM Ask Extension <<personal data hidden>> wrote:

responder: An Ask Extension Expert Replied October 11, 2024, 11:58 AM EDT
response: The yellowing of the leaves on the chicory may be due to downy mildew, which is a fungus-like organism that can cause tissue collapse of the leaf portions.  See https://pnwhandbooks.org/plantdisease/host-disease/radicchio-cichorium-intybus-downy-mildew for information on preventative measures.  You would need to examine the underside of the leave and look for the spores characteristic of Bremia lactucae to diagnosis downy mildew with certainty.    The tatsoi appearance is really dramatic.  I suspect that it is a virus problem since the upper plant in the photo, that is larger in size, looks like the younger leaves are affected too, rather than a nutrient issue, but it may be a nutrient deficiency.  Gross changes in leaf morphology, texture, and coloration are suggestive of a virus pathogen in plants.  Virus problems are typically confirmed by laboratory tests, usually done by plant diagnostic clinics.  Tissue analyses are used to confirm nutrient problems in plants.  I see a bit of what looks like Alternaria on the pak choi, and there may be some slug damage on a couple of the petioles as well as other fungal leaf spot diseases present.  Alternaria is a very common fungal pathogen that affects the range of crucifer crops.  It first causes leaf spots with yellow halos, the end result can be death of an entire leaf, and dark brown to black coloration develops on affected leaves where the fungus is sporulating.  You can read more about this pathogen group at https://pnwhandbooks.org/plantdisease/host-disease/mustard-greens-brassica-juncea-alternaria-diseases-black-spot-gray-leaf-spot-pod-spot.  The fungal pathogens that incite foliar pathogens are typically identified by the morphological shape of spores either produced on tissues or fungal colonies isolated from the affected plants.    There is little hope to cure already infected plants.  But knowing what the problem is prepares one to try and prevent the problem from re-occurring during the next cropping cycle.  If a disease is just starting to develop, growers can initiate management strategies to reduce spread, but the approaches for controlling diseases are usually dependent on the pathogens involved.    Here is a link to a brief synopsis on disease diagnosis in plants https://pnwhandbooks.org/plantdisease/diagnosis-testing/disease-diagnosis-management.  You can submit plant samples to the OSU plant clinic when you seek an absolutely certain diagnosis of the pathogens affecting your plants.  Diagnosis of problems based on photographs where the pathogen's body is not readily visible is very difficult in many cases.  Here is a link for information on plant diagnostic clinics in Oregon as well as what tissues to send and how to pack and ship the plant samples https://pnwhandbooks.org/plantdisease/diagnosis-testing/testing-services.    I expect that more than one pathogen is represented by the plants in the photographs that you submitted.