When to spray lime sulphur and dormant oil?

ruthie5bpeiMarch 14, 2008

I'm thinking of trying this for the first time this spring (I'm in east coast zone 5b and the temperature tonight is supposed to get down to minus 12 Celsius or plus 10F). Do I wait until after I spring prune before spraying? It seems a waste to spray and then prune off a lot of what I have just sprayed. On the other hand, can the material I have sprayed enter the pruning cuts and do damage? Also, do you put down your slow release fertilizer before spraying? I'm somewhat confused as you can see! I doubt I'll be pruning before mid-April but most of my roses have zero snow cover left right now. Thanks for your help.


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Patricia43(z8 AL)

When the temperature is above freezing but not above 70. Safely about 40-70.

    Bookmark   March 15, 2008 at 7:14AM
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Thanks, Patricia.


    Bookmark   March 15, 2008 at 9:27AM
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I do lime sulfur as soon as the temperatures are right, which is usually before I feel it is safe to prune. I've been waiting for it to be warm enough but the lows here keep dropping below freezing, so it looks like I'm waiting at least another week. You'll want to do it when there isn't any rain predicted for a few days too as you don't want it to wash off right away.

    Bookmark   March 15, 2008 at 1:20PM
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Athenainwi, does it have to be above freezing the night after you spray? I can understand that the sprayer would not work if temps. were below freezing when attempting to apply lime sulfur but am unclear if your mentioning lows below freezing merely means you wouldn't be able to spray until it gets above freezing. Thanks for the reminder about checking for rain in the forecast.


    Bookmark   March 15, 2008 at 8:30PM
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mike_rivers(z5 MI)

Ruth, about lime/sulfur and dormant oil entering the pruning cuts: This is not a problem. Your spray has access only to the xylem and this pumps only upward in a stem, clearly no problem for the plant when the chemical is located on the cut end of a stem. Furthermore, the xylem pumping system requires transpiration from the leaves to operate.

Freezing temps are bad because freezing tends to break up the spray emulsion before the water evaporates. This can lead to deposition of the sprayed chemical as droplets on the plant rather than as a thin film. The droplets are more toxic to the plant (not usually a problem in the dormant season) but also droplet formation can mean less effective pesticide action. If your spray dries on the plant before freezing temps occur, everything should be fine.

People in your zone often do spray lime/sulfur and oil just after pruning, but you want to make sure active growth has not begun or you risk burning the new growth. I don't think spraying a dormant oil over time-release fertilizer beads would be a good idea, even if you work the beads into the soil. I would fertilize at a later date. A lot of people wait until the new growth is a couple of inches long.

    Bookmark   March 15, 2008 at 9:03PM
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That's exactly the information I needed, Mike. Thanks very much.


    Bookmark   March 16, 2008 at 4:19PM
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Thank you Mike. How long does it take for the spray to dry? What little I could find said you need 24 hours of above freezing temperatures. It sounds like you're saying that I could do it as long as I had a few hours. I can't do it today anyway though as we're getting rain/snow on Monday and Tuesday.

    Bookmark   March 16, 2008 at 5:34PM
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jont1(Midwest 5b/6a)

I live in northwest Missouri about 50 miles north of Kansas City. I am in zone 5b/6a depending on the map you are looking at.
I am planning on spraying my lime-sulfur this week while the bushes are still dormant, and then prune in about another week or so depending on the weather forecast.

    Bookmark   March 17, 2008 at 12:24AM
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Hi there! Dormant oil can be used safely as soon as the average daytime temperature is about 5 C, or 45 F. A better way to know when to spray is when the robins first return to your yard, because they know which bugs are hatching. This should be before plants start leafing out since the treatment can destroy new growth.

At any rate, do not spray if the temperature is expected to drop below freezing in the next 24 hours.

    Bookmark   April 11, 2008 at 4:40PM
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It's a month after this post and I still haven't been able to spray. I looks like I might not get a chance to this spring either. I could have sprayed last weekend but I was busy. This weekend it is cold and rainy.

    Bookmark   April 11, 2008 at 9:40PM
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artemis_mo(z5b MO)

What mix ratio do you folks use for lime sulphur in the early spring?

    Bookmark   March 15, 2010 at 9:22PM
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