Below are the temperatures that killed rust dead in its tracks,
but actually it died during the autumn frosts before the winter temps kicked in.
That is when the summer spores changed to winter spores whereby
they cannot reinfect the next spring because they need a separate
plant host to do so. This is what I observed in my garden. In other climates,
rust may react differently. I was surprised by how much a small amount of
hard frost affected rust. Rust does not worry me anymore due to that
experience.
In December we had 16 lows below 32* with the lowest low for 1 night at 18*
In January we had 18 lows below 32* with the lowest low for 1 night at 18*
In February we had 19 lows below 32* with the lowest low for 1 night at15*
In March we had 16 lows below 32* with the lowest low for 1 night at 16*
So a total of 69 nights below 32* definitely killed rust here. Many low temps fell
in the 25 to 31 range.
