Quintec's role in the hop yard is very specific. It is used in rotation (no more than 2 applications in a row, 3X per season) during stages of burr and cone development to stop powdery mildew infection of the cones. Heavily infected cones turn brown and are not very marketable. The rest of the year it sits in the pesticide cabinet - so don't purchase more than you need. Apply the first spray when bur formation is visible and a second spray within two weeks when the burrs are fully sized, but before cone scales develop.
The idea is to get the chemical in place before the cone closes up. Applications made after cones form are pretty much ineffective - the disease is shielded inside the cone. Timing is everthing when using this product. It is best used along with an IPM weather forecasting program (like M.S.U.'s) Different varieties of hops develop burrs at different times; so in hop yards with multiple varieties a staggered application , variety by variety, is necessary.
Quintec is relatively safe - it only rates a caution on the label. However, it does have a funky restriction about spraying early morning / late evening because of aerial spray mists effects on certain species of bats.
Grower Notes: For me, Quintec is one of the critical, must-have IPM sprays. I would drop a lot of other applications of other chemicals out of my IPM program before I missed this one. (Missing it would be equivalent to no control sprays for apple scab in an apple orchard.) It has a large effect on the final quality of the harvested cones.
I am very careful not to over-use Quintec, though. Some seasons, weather conditions are not right for powdery mildews to start during burr-out and I will not need to apply it during that critical 2-3 week period. Monitoring the hop yard and weather patterns just before, and during, burr formation help me decide whether it is necessary to apply Quintec. There is a temptation to repeatly spray Quintec just because it works so well. Its mode of action and the quick resistance of powdery mildews makes me be stingy with it's use - I want it to be around and effective for a long time.