If your humidity is ok you shouldn't have this problem.
Low humidity causes stress on plants. I recommend 50-60% humidity until the final 2 weeks of flowering. At this point, the humidity should be lowered as much as possible to encourage the plant to seal and protect itself with additional resin.
If you still have this problem there is something called Soil Moist. They are polymer crystals that expand 40 times their size in water and slowly release over time.
You can buy 2lbs of this stuff on ebay for $20 including shipping.
Hope that helps
p.s. this stuff is also really good to ease transplant shock