Tomatoville® Gardening Forums


Notices

Information and discussion regarding garden diseases, insects and other unwelcome critters.

Reply
 
Thread Tools Display Modes
Old May 8, 2013   #1
RayR
Tomatovillian™
 
RayR's Avatar
 
Join Date: Jun 2010
Location: Cheektowaga, NY
Posts: 2,372
Default Phosphorous Acid (Excel LG) vs. Sunflower Downy Mildew

Plasmopara halstedii is a oomycete pathogen that causes Downy Mildew on members of the Sunflower family. This pathogen can reproduce sexually and produces thick-walled oospores that can survive in the soil, even in cold climates.
Plasmopara halstedii can infect a plant in two ways. When conditions are right, the oospores germinate into zoospores and can infect a young seedling systemically through the roots. Airborne zoospores can also infect plants non-systemically through the leaves.

Here’s some informational links about this pathogen:

Downy Mildew of Sunflower in Nebraska

Downy Mildew of Sunflower

Last spring I noticed a volunteer sunflower in my garden that showed the unmistakable signs of systemic infection. I have seen this once before and I pulled the plant because an infected plant would be severely stunted and just plain ugly, would never produce a nice flower and would just be a factory for creating lots of new zoospores and oospores. This year was different; I had recently purchased a bottle of Excel LG (now renamed “Plant Doctor”), one reason for my purchase was to combat Downy Mildew on my cucumber and squash, I never even thought about Downy Mildew on Sunflowers but since I now had a plant with the systemic infection as well as secondary leaf infections on other seedlings in progress I would have to see how Mono-di-potassium salts of Phosphorous Acid would act against it. It is well documented that Phosphorous Acid compounds have a direct effect on many oomycete pathogens by inhibiting their metabolism.

I mixed 1 oz. of the concentrate with 1 gallon of water and filled my pump sprayer and liberally covered the leaves top and bottom. Whatever was left in the sprayer I dumped at the base of the systemically infected plant.
4 days later I went to check on the plants and the white powdery growth was all gone on the bottom of the leaves, those areas were now a grayish brown color (third picture).
I applied the spray once more a week later even though there was no sign of any new infections. The sunflowers grew out normally through the summer, even the systemically infected plant had one side branch coming from the base of the main stem that continued to grow normally and produced a normal flower.
Attached Images
File Type: jpg Sunflower_1.jpg (383.8 KB, 19 views)
File Type: jpg Sunflower_2.jpg (447.3 KB, 17 views)
File Type: jpg Sunflower_3.jpg (78.7 KB, 20 views)
File Type: jpg Sunflower_4.jpg (166.7 KB, 17 views)
File Type: jpg Sunflower_5.jpg (206.2 KB, 18 views)
File Type: jpg Sunflower_6.jpg (379.9 KB, 16 views)
File Type: jpg Sunflower_7.jpg (204.1 KB, 14 views)
File Type: jpg Sunflower_8.jpg (193.7 KB, 14 views)
File Type: jpg Sunflower_9.jpg (317.9 KB, 14 views)
RayR is offline   Reply With Quote
Old May 8, 2013   #2
Tonio
Tomatovillian™
 
Join Date: May 2012
Location: San Diego, CA
Posts: 135
Default

woah, zoospores, oospores, and whats a zygoat?

Appears its a mycoparasitism issue by fusarium merimoides.

Ray, Iv've seen the same reactions - to a lesser degree on volunteer sunflowers germinated from black sunflower bird feed. I didn; research it much but wonder if any effects can be absorbed by trees- i.e. poplar-which I has some type of yellow mildew spots in late fall/winter here. considering I use the poplar tree leaves for compost, I hope I am not infecting my compost. I have read somewhere poplars are not good for a compost pile

Last edited by Tonio; May 8, 2013 at 12:29 AM.
Tonio is offline   Reply With Quote
Old May 8, 2013   #3
RayR
Tomatovillian™
 
RayR's Avatar
 
Join Date: Jun 2010
Location: Cheektowaga, NY
Posts: 2,372
Default

Oomycete
Oomycetes are fungus-like but they are not at all a fungus.

Plasmopara halstedii like many pathogens are host specific. Plasmopara halstedii only infects members of the sunflower family so there is no danger in infecting any other plant families.
RayR is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 02:52 AM.


★ Tomatoville® is a registered trademark of Commerce Holdings, LLC ★ All Content ©2017 Commerce Holdings, LLC ★