Fungicide for Fabraea pear leaf spot

ltiltonJune 24, 2013

Seem to have this on my pears. Can't find recommended fungicide other than Thiophanate-methyl. Anything better than this?

I'm about to spray propiconazole on plums and cots, but label says not to use on bearing pears.

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alan haigh

Mancozeb

    Bookmark   June 24, 2013 at 5:05PM
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ltilton

Wow - I used to have a bottle of that. Haven't seen it in a while.

Thanks Hman.

    Bookmark   June 24, 2013 at 5:11PM
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creekweb(6,7)

I use mancozeb for early season applications on grapes, but switch over to a different class of fungicide later because of mancozeb's long PHI. I don't know the PHI for pears though this Cornell publication says 77+ days:

http://ipmguidelines.org/TreeFruits/Chapters/CH05/default-2.aspx

and if you have a number of varieties ripening over an extended period, I can see how it may present problems. A number of different classes of fungicides show activity against leaf spot, so if you start with mancozeb, you may consider that it makes sense to switch to one with a shorter PHI later in the season. The switch, I would expect, would help with resistance problems as well. Even if you don't see them, there's still a good chance they're there, so I'm convinced treating for psylla as well makes sense.

    Bookmark   June 25, 2013 at 2:35PM
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ltilton

Since I have thiophanate-methyl, I can switch off with that. I also don't know if it makes a difference, but my Seckel pears are bagged.

[sigh]

Used to be, before I paid any attention to them, I got tons of absolutely pristine pears from this Keiffer tree, most of which went into the trash.

Seems like the harder I try to get good fruit, the more problems it gets.

I never used to spray the pears. Now it seems I'll have to spray against codling moth, leaf spot, and who knows what else.

    Bookmark   June 25, 2013 at 4:47PM
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alan haigh

I don't know if you need worry about resistance, unless there are commercial orchards nearby- home growers are much less likely to develop resistance given their scale of production- I don't think I've encountered resistance from over using a chemical in all my years tending orchards and I use materials that are no longer affective in many Hudson Valley orchards.

With pears, fab may be a symptom of psyla, so get out your glass and look for the little buggers. They are what brought it on in my orchard- control the psyla and all may clear up.

Once you've got scab or fab, mancozeb isn't going to give you kick-back anyway- gotta use it preemptively.

    Bookmark   June 25, 2013 at 5:32PM
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ltilton

Good tip, Hman. Thanks.

    Bookmark   June 25, 2013 at 8:50PM
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creekweb(6,7)

The reason that you have not noticed resistance among your pesticides may be that you follow practices that make the development of resistant strains unlikely, e.g. by using a battery of different fungicides.

This plant pathologists claims that after several years of using a solitary fungicide, the surviving fungus will have developed 100% resistance, even in the setting of a home garden.

http://utahpests.usu.edu/htm/utah-pests-news/fall2011/fungicide-resistance/

    Bookmark   June 25, 2013 at 10:21PM
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alan haigh

Creekweb, I used to listen to Cornell info as gospel, but many years of experience has taught me that they offer guidelines and advice that has severe limitations when applied to home orchards. Of course, commercial growers have to figure out their own methods and adjust to their own experience as well.

My experience may not match yours, but it is what I have to offer. I've been using Myclobutanil as my exclusive fungicide for cedar apple rust and scab as almost an exclusive for over two decades. I also put some captan in the mix at many sites but it has no efficacy against CAR and my two weeks between applications would render it useless for much of that time even against scab- captan also has no kickback. Also there's usually a lot of rain going on washing it off early.

If you consider the math involved in fungus multiplying and evolving to break the code of a single lock fungicide, you can imagine that 10X as many trees would mean 10 times as much opportunity to break the code. A commercial grower might have a thousand times as many of any given variety as you or I- maybe more. If a fungus evolves with the ability to resist a fungicide on a single tree in an orchard it will soon be thriving in all of them.

I've been told that the reduced sprays of my schedule is ideal for increasing the chances of developing resistance by gurus who can't believe that it hasn't happened to me. I guess they don't see the math the way I do.

    Bookmark   June 26, 2013 at 5:34AM
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