I have been hit and miss here...my 6 mo pregnant daughter and her DH were here on a visit. She ended up spending 4 days in the hospital w/ a kidney infection! They left yesterday, headed for Boston.
Anyway... I should not rely on my memory! In the book Heucheras and Heucherellas they discuss root weevils and say "Dan has applied hot water (100 to 120F) to the roots and crown of infested plants during the winter; the larvae are killed within two seconds, and the plant "shrugs off" this shock treatment. This requires experimentation but is a very safe method of control".
I would think this would work anytime the weevils are in the larval or pupal forms, which I find even in spring. When I did this the water was just to a boil and the plants were not damaged.
