fungi spray

[berrycrush]

New shoots have grown to a few inches tall and the rain just keeps coming. Mancozeb is not good in rainy weather as I understand, so Capitan 50 is a better choice? What do you do in a wet spring?

 

[user 36973]

Some (maybe most?) formulations of mancozeb are rain-fast. Regardless you will need to apply it more frequently when it rains. Mancozeb is more effective than captan early in the season.

Maybe also tank mix 0.5% (no more) phosphorus acid as a corrective measure if you are concerned.

 

[Masbustelo]

I've read that it is best to apply prior to rain, or in the midst of a sequence of rainy days if possible. Ive also read that you will have some coverage up to one inch of rain. After an accumulation of an inch, you need to reapply, even if it has only been 2-4 days for instance. I would assume that 1/2 inch of rain would limit effectiveness to five days instead of ten.

 

[berrycrush]

What kind of systemic fungicide is available for grapes?

 

[user 36973]

What kind of systemic fungicide is available for grapes?

Rally is systemic for black rot and downy. But most systemics tend to be prone to resistance development.

 

[Dennis Griffith]

Use Mancozeb early in the season as it has a PHI of 66 days. I rely on Captan and Immunox later in the season. I also add Serenade and Neem. Neem says it works as a fungicide, but I have doubts as to it's effectiveness. I include it as an additional hedge against JBs. The jury is still out with Serenade (for me). I intend to keep it up for this season.

 

[Masbustelo]

I sprayed mancozeb yesterday. We just got an inch of rain. Tomorrow no rain, then rain forecast everyday for the next seven days. I suspect many others are experiencing lots of rain too. What should be done spray wise with this much rain?

 

[Dennis Griffith]

I sprayed mancozeb yesterday. We just got an inch of rain. Tomorrow no rain, then rain forecast everyday for the next seven days. I suspect many others are experiencing lots of rain too. What should be done spray wise with this much rain?

You are facing the same issue I have this year. I'm not sure how many inches we have had here in Ohio, but it looks like the same trend is happening in a lot of places. Too much rain. I had to hold off planting part of a row this year because I'd be planting them in mud. So I potted them to get them growing and will plant them early fall. As for spraying, spray when you can. If you have a dry day, do it. Sure the rain may limit the effectiveness, but you have to do something to curb the fungus. You can't let it get a foothold as it will be more difficult managing it in the long term. BTW, I think I've lost a couple of vines to the rain. Evidently grape vines can't swim.

 

[Masbustelo]

I Mancozeb rainfastness and residue thresholds for control of Venturia inaequalis...Our results on the persistence of mancozeb to rain rather agrees with that of Carbas et al. (2001) on vineyard leaves. Carbas et al. (2001) found that mancozeb residue loss was only 20% after 45 mm of torrential rain (60 mm/h). https://pdfs.semanticscholar.org/bb4c/5e1c2025cfc1e8c2ce6cb606266ce3b104c9.pdf

 

[Masbustelo]

Cabras, P., Angioni, A., Garau, V.L., Melis, M., Pirisi, F.M., Cabitza, F., and Pala, M. 2001. The effect of simulated rain on folpet and mancozeb residues on grapes and on vine leaves. Journal of Environmental Science and Health 5: 609–618.https://vdocuments.mx/amp/the-effec...lpet-and-mancozeb-residues-on-grapes-and.html

 

[Dennis Griffith]

I've read many documents on it's effectiveness after rain as well. From what I gather, if you can get it on for day, it will remain more effective for a longer period. Obviously, if you spray and it rains 30 minutes later, it's effectiveness is minimal, to say the least.

 

[Masbustelo]

If I can read between the lines: It looks like even small amounts of rain wash enough off to bring it down to questionable protective levels. Like 1/5 of an inch. Succeeding rains don't seem to wash much more off, up to 1 3/4 inch. If you increase the amount per gallon you'll have more on the plant before and after the rain. The South African report mentioned that particle size of Dithane is smaller than Mancozeb, and that may be beneficial.

 

[Dennis Griffith]

I don't know how much you can increase it safely. How much are you using per gallon currently?

 

[Masbustelo]

I've been using 1 1/2 tablespoons per gallon. I think that could be doubled. One of those theses said the rain removes 38% of the Mancozeb. Doubling the dose would give significantly more protection with all this rain. It would leave you with 80% protection.

 

[Dennis Griffith]

I go by ounces since I mix larger batches. I typically use about .5 oz per gallon (1 tbsp), but will increase to what you are using if conditions dictate. You must be careful as I don't know at what dose the plant will suffer chemical burn. I would try shortening the spray interval vs increasing potency. If you can get a spray in every 3-4 days between rains, that may be a better option during this weird weather pattern. Guess what it's doing outside now? Yeap, heavy storms today. Seems I live on the local weather site these days.

 

[Masbustelo]

Mancozeb has been on the market for 50 years. If burning is a potential problem, it shouldn't be too hard to reference it. I think for commercial growers it is more an issue of economics. 'What would be the lowest application rate under normal growing conditions", type of question. Two blue sky days in a row here.

 

[Dennis Griffith]

Well, to be honest, I did increase the dosage on one spray this spring (2 oz per gallon). 2 days later new growth on 2 vines wilted. The are coming back with new shoots, but I'm not sure what caused that. Keeping that in mind, I am cautious about increasing dosage at this point. It also appears that I've lost a plum tree that was in full leaf. It just wilted suddenly as well. I did not spray it yet. There is a crop duster type plane I see in the air frequently and he makes me nervous. He doesn't spray anywhere near me. but I am in his flight path to the nearby airport. SO the question is, is he spraying some sort of herbicide somewhere and does his plane 'dribble'?

 

[Masbustelo]

He could be emptying his tanks.

 

[Dennis Griffith]

That's what I'm afraid of.

 

[jandrew156]

I sprayed Bionide FTS a few days ago, at the listed dosage- 2.5 tbl spoons per gallon, and I got some significant leaf burn.
Is this an indication of too much chemical, or to many sprays? I've sprayed 5 times this season and alternated between that and Mancozeb. The Mancozeb seems much more effective and hasn't burned the leaves in the 3 applications this year.