Tank mix phosphorous acid + JMS Stylet Oil?

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user 36973

owner, winemaker
Jun 13, 2017
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I'm planning out my spray schedule this year and am looking for a 0 PHI solution for PM and DM, so I can control these diseases throughout the harvest season.

Looks individually the 0.5% phosphorous acid (Rampart) sprays are good for DM and 1% JMS stylet oil is good for PM but is there risk of burning the vines when tank mixing these sprays?
Good question.

"Mixing Rampart Fungicide with certain surfactants, foliar fertilizers or other pesticides may cause crop injury. ... Always conduct a test with the intended tank mix on a small area prior to any large scale applications."

Is stylet oil one of those "certain surfactants"?
I checked with Bruce Bordelon, the viticulturalist at Purdue, and he says he is not aware of any phytotoxicity issues with phosphorous acid and the oil as is known with sulfur and oil, but cautions that it would be best to run a trial before broad application. That being said, he recommended other products for PM with short PHI such as Fracture (0-day PHI) or Topsin M and Procure with 7-day PHIs. He also says that PM can be dealt with post-harvest if needed too, though I'd rather not let it get a foothold.

Since PM is a problem on only my Leon Millot block and they are harvested early, I should be able to resolve PM on those vines with a targeted spray.
I occasionally see foot notes on fungicide recommendation charts: "Because of widespread resistance to thiophanate-methyl in powdery mildew and Botrytis strains in mid-Atlantic vineyards, Topsin-M is currently recommended only for protecting pruning wounds from cankering diseases."
Two thoughts:

1) I don't think there would be any phytotoxicity, but maybe a professional chemist can say if the combo might or might not decrease effectiveness of one or the other if mixed.

2) Grapes after veraison and mature leaves are more resistant to both PM and DM than earlier in the season (but local conditions matter the most of course). Despite warm, humid conditions and rain each month here, I don't bother spraying for either three weeks before harvest. The weeks leading up to harvest I am more concerned with Botrytis, which can become a real problem if there is a lot of August rain.

That all being said, I actually do suggest you do a spray as close to harvest for both PM and DM as possible this year as a baseline, so you know what fully disease free plants should look like. Then I would suggest to start to experiment with timing in the coming years so you can optimize your needed application rate to save as much time and money as you can.
I have not seen PM here, even though I didn't do any late season spraying for it, figuring that I could take care of it with oil or potassium bicarbonate if it showed up.

DM did give me some trouble. I trusted a strobilurin alone at the beginning of September, and sprayed it a couple days later than planned. The next week we had a few days of rain/drizzle/mist/fog. I was able to use a phosphorous acid product (Agri-Fos) to keep the outbreak from progressing, but I did loose some leaves, and was still fighting it through late October.

I may test the phosphorous acid and oil combo this fall, just to see what I can learn. I'm no chemist, but I'm pretty sure a phosphorous acid and potassium bicarbonate tank mix would just neutralize each other, so I'd like to verify that the phosphorous acid and oil combo is safe.
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PM, DM et al. are a real problem for me if I do not spray according to the year's weather conditions. Even if I do spray, I use a contact spray, and not everything always gets sufficient 100% coverage. Basically, "stuff happens" (the child friendly version of that saying).

For example, this cluster was buried in the canopy, did not get applied with contact spray, and this resulted in multiple diseases:


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