please help! powder mildew ...

We've got PM bad in our flower room and the traditional goto here is to defoliate but after a contaminated harvest we have tried lowering the humidity and this just slowed it down, but not by much. Yesterday we brought the temperature up to 95+ for 12 hours and the PM is still there, it might be dead but usually if you spray with fungicides it comes off, so not convinced 12 hrs at 95 F works yet.

I am going to try raising the temperature to 100 F for 2 hours but I did see anyone mention how often to do the heat treatment; daily, once a week, once a month?

Thanks in advance.

GuyLeDuche said:

Watch those low temps, PM loves the 60s. Also be careful from here on, IME most sprays will turn white hairs brown PDQ. My go to in veg/early flower was plucking infected leaves then spray with Neem/silicate/ph 7.5 water bi-weekly at lights on, I don't believe light burn from foliar is a real thing, but PM loving a low temp/ high RH (from spraying) lights out environment is...

As you get to week 5-6 of flower if you are still seeing issues be very mindful of the lowest leaves on the bottoms of the lowest buds, I would always see junk trying to creep in from there when I had PM troubles . I got so sick of it I'm growing some PM resistant strains to increase my odds lol ( Dinafem Critical+ 2.0 and Medical Seeds Malakoff). Too soon to tell, but fingers crossed and knock on wood

Click to expand...

I had the critical+ Cheese , it was a freebie. In my room everything got powdery mildew except that plant. Out of 5 strains so far and 4 phenos each, that is the only plant that doesn't have a spec on it. Wish I would have kept it.

jdsaario said:

We've got PM bad in our flower room and the traditional goto here is to defoliate but after a contaminated harvest we have tried lowering the humidity and this just slowed it down, but not by much. Yesterday we brought the temperature up to 95+ for 12 hours and the PM is still there, it might be dead but usually if you spray with fungicides it comes off, so not convinced 12 hrs at 95 F works yet.

I am going to try raising the temperature to 100 F for 2 hours but I did see anyone mention how often to do the heat treatment; daily, once a week, once a month?

Thanks in advance.

Click to expand...

This is a follow up. We have totally solved the PM problem but not sure exactly what worked.

1) We had some begonias which also had PM. Online sources will tell you that begonia PM only affects begonias not cannabis and this is true, but don't let this information mis-guide you, if you check a table on PM varieties there is a type of PM which affects both! So we moved these other plants out of our cannabis area.

2) We moved into mid spring and started opening the doors and the relative humidity got down below 40 most days and we put dehumidifiers on at night set to kick on-and keep relative humidity below 50-60%, I don't think we ever got it down to 50% at night but we had two running and it got the humidity down some.

3) The previously mentioned heat treatments may have had a role in getting rid of the PM.

4) We did some trimming out of worst areas and spot treated, the areas not the buds with copper soap, at the same time as heat treatment.

My feelings are, get any other PM affected plants out of the greenhouse, lower your humidity to below 50%, and try heat treating to 100-105 F for 2 hours. We have even tried up to 120F for 30 minutes to try heat treating mites, plants were not affected badly as long as they had water.

This though created perfect conditions for russet mites, so we're fighting a new battle, as mentioned with the 120F treatment. Cheers!