- Dropping air temperatures below 90 for even 2 hours / 8 hour cycles markedly increase the leaf color.
- Soil temperatures above 95 deg stopped fine root hair growth- adding to the chlorosis.
- different varieties can tolerate high temperatures better than others
Take away -??- The Western European varieties (German) Spalters, Hallertauers, Tettnangers are more sensitive to high air and soil temps than American varieties like Newport, Galena, Chinook, and Cascade. Spalter Select obviously cannot be grown like Newport.
This does not mean the former group can't be grown successfully - it means they have to be grown DIFFERENTLY. By "differently" I would suggest closer raised row and plant spacing to create cooler temperatures in the lower hopyard canopy, leaving more lower folige to shade the soil (especially in newly established hopyards), using aerial sprinklers to cool the leaves at mid-day, and mulching new plantings to reduce soil temperatures.
I think is is a great example of how "one size does not fit all".