Disclaimer: This post was originally posted by Hero Member, mjb8743. This user is located in Zone 7, South NJ, Garden State. This was originally posted on June 21, 2009.
No need to block the tube (when your plants get big it would be a nightmare to access.) Just go to Lowes or HD in the pesticide dept and get some Mosquito Dunks... a donut shaped disc, 6/pack. Break it into 1/4s and put 1 piece into the tube. It should last around 30 days or until the problem builds up again. They are a form of BTi, totally harmless to everything except mosquito larve... biological control.
Also available are Mosquito Bits, a granular form of the same ingredient.
Mickie