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Copper soap spray saved my late-season crop
Been getting hit with botrytis in the last two weeks of flower every single year up here. Dense colas, morning fog off the river, nothing dries out fast enough. Tried neem, tried sulfur, tried wishful thinking. Copper soap finally broke the cycle.
Spray it on the stems and lower canopy starting around week five of flower. Not the buds themselves. Get the leaf axils where moisture likes to sit. Biweekly works fine for me, weekly if your humidity is actually bad.
The other thing nobody wants to hear is that you need to thin your canopy before it becomes a problem, not after you already see gray. Pull some interior growth around week three. Feels wrong. Do it anyway.
Copper soap is cheap and it's not a systemic. Washes off, doesn't carry into the harvest. I've run Malawi and Acapulco Gold outdoors in the Pacific Northwest and this is the only thing that let me actually finish them without losing a third of the plant.
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2 Comments
Experienced17d ago
The copper soap thing checks out, been using it the same way for a couple seasons. But honestly the part of your post that deserves more attention is the canopy thinning at week three. That's where most people lose the battle before it even starts, they're so protective of every node and every bud site that they won't pull anything until the rot is already in there spreading.
The other thing i'd add, since you're in PNW fog territory, is that the cultivar selection matters as much as the spray program. Running Malawi outdoors up there is already fighting uphill, that thing wants to stretch into November and you're chasing it the whole time. Dense-budding landraces in high-humidity climates are just hard mode no matter what you spray. I've had years where i did everything right chemically and still lost colas just because the genetics wanted to stack tight and wet air found every gap.
Copper soap earns its keep for sure. Just saying the spray is the last line, not the first.
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Experienced17d ago
Copper soap is solid but i'll push back a little on "doesn't carry into harvest." Technically true that it's not systemic, but if you're spraying anything near dense outdoor buds in high humidity you want to be real careful about copper residue on the actual flower. Not a huge deal at the doses people are realistically using, but worth a rinse and knowing your timing.
The thing i don't see mentioned is airflow between plants. Spacing outdoors is the one thing people consistently underestimate. You can thin your canopy perfectly and still get hammered if your plants are shoulder to shoulder. I grow autos so my whole game is small and tight, but even i know that running big outdoor photoperiods close together in PNV fog is basically setting up a humidity trap at canopy level no matter what you spray.
The cultivar point from the last reply is fair but i'd flip it slightly. The problem isn't just dense-budding genetics, it's that people pick what they want to grow and then try to spray their way around a climate mismatch. Sometimes the answer is just a different cut.
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