UGA Extension Vegetable Entomologist Dr. Stormy Sparks writes this:
OVERWINTERING AND COLD TOLERANCE OF BEMISIA-ARGENTIFOLII (HOMOPTERA, ALEYRODIDAE) IN COASTAL SOUTH-CAROLINA By: SIMMONS, AM (SIMMONS, AM); ELSEY, KD (ELSEY, KD), JOURNAL OF ENTOMOLOGICAL SCIENCE, Volume: 30 Issue: 4 Pages: 497-506. DOI: 10.18474/0749-8004-30.4.497, Published: OCT 1995
It takes about 3 hours of 21 degree Fahrenheit to kill 90% of whitefly adults, but would take 57 hours of 21 degree Fahrenheit to kill 90% of whitefly nymphs (even longer for eggs). So, we’re probably not going to kill nymphs with south Georgia temperatures. On the bright side, if you kill the plant, you kill the eggs and nymphs. We’ll need to watch for whitefly emergence in cabbage and collards this spring.
Comments from Dr. Sparks:
“We overwinter whiteflies every year, last year we simply overwintered larger populations over a larger area (in my opinion). While whitefly populations are down and the cold temperatures will keep them from developing, when growers are done with a crop that MIGHT harbor whiteflies, get rid of that crop ASAP. It’s going to have to be done sometime, and if doing it sooner than later might help, take that chance.”