You want to do a dunk (submerging the whole rootmass) with pyrethrin. Evergreen works well, I used Bonide 857 with good results it is the cheaper option. I used about 1.5Tbs/gallon
The below writeup was done by Dr. Who. I can't find the post he made so I copied the text for you out of a grow journal where it was also posted.
ROOT APHIDS are the most difficult pest to COMPLETELY destroy in your garden!
I have dealt with these damn things before and after contact with MSU and a Bayer Pharm Horticulturist (Word has it that Bayer has developed a new insecticide specific to root aphids, but it's not on the market yet. All though another grower I know was sent some [he badgered the hell out of them] for testing out on his problem - it worked). We came up with this 4 part system to break the cycle of root aphid pain.
Why a 4 part system? Because what ever 1 or 2 things you do they come fucking back! If you follow this method,,,,,they will be GONE!
The first 3 parts involve the actual fight to COMPLETELY kill off the infestation. Lets get started. Get ALL the needed insecticides FIRST, before you start this method!
#1: Root drench with Pyrethrin 2 times, 5 days apart! For soil run it through and use alot to be sure you get UNDERNEATH the root ball (something called the umbrella effect comes into play here, so you want to be SURE that all the media gets wet)! For Hydro,,simply remove the net pot and place it into a now container and pour the Pyreth mix through the stone's, ball's or what ever and let the root ball soak for 10 min. ! This will alone effectively kill off 80 -85 % of the problem only!
NOW 7 DAYS LATER DO THE FOLLOWING
#2: Get something called BotaniGuard (ES [liquid] or 22WP [powder]) Amazon sells this for the best price I have found anywhere, at $93 for the ES and $73 for the 22WP.....not cheap I know,,,BUT,,, it's going to be better then tossing every plant you have out and going to step #4 (unless you want to).
For soil, mix as directed and drench again as listed above. Same thing applies for the soil as above and the same for the hydro.. DO NOT "shortcut" and use this stuff in the nutrient solution as it will kill off the fungal spores of the BotaniGuard. This will alone only kill off 98% of the problem,,,they WILL come back! http://www.amazon.com/BotaniGard-22W...rds=botanigard
NOW 7 DAYS LATER DO THE FOLLOWING
#3: Get something called ORTHENE, the generic is far cheaper and is called ACEPHATE 97UP....Yes this is strong stuff,,,,,BUT at the level required for our use and the systemic duration of the chem it IS considered safe for our specific end use of the plant. Mix as directed (you will need a calculator to figure out the mix ratio per gallon. (4.7 grams per gallon?) please recheck my memory on this one as my grow notes from back then are not here at the house). Now put this into a spray bottle and LIGHTLY mist the TOP of the leaves on the entire plant. You DO NOT have to bury it in this stuff. It is a systemic and only needs a little to spread out into the entire plant, including the root system....The man at Bayer said to mist the top of the media you grow in also if you are in soil.....DO NOT DO SO IN HYDRO. Repeat in 7 Days!!!! This is it,,,,you've now killed off your problem in the plants.....BUT your not done yet! http://www.growerssolution.com/PROD/...ontrol/70-1105
LASTLY and JUST as IMPORTANTLY
PART #4: While you are waiting in between applications of the insecticides. You must now clean and STERILIZE everything in the grow!!!!!! Pot's, tools, walls, floors, gaps between every door,vent, any incoming air tube's, AC unit's, Heaters, etc, etc, etc......Don't leave anything out! The damn eggs are VERY persistent!!!! So be especially SURE ALL pots and anything that contacts your growing media is sterilized! For hydro,,,be sure that when the grow is over you DO the same for the COMPLETE system your using!!! Lines, pots, res. ANYTHING that contacted the feed solution and everywhere that it didn't!
This seems like overkill, I know. Here in Michigan this was never a problem until it was imported from Cali on Grape rootings and clones.
Some may say "I got rid of them doing this "X", or you may find someone saying that "I did "Y", and the internet bozo's suggested "Z".....
But "I" can guarantee you that they will return! And 5 years ago, we would Kill them and a month later they were back worse then before...... It took a lot of internet and phone time to get this squared away for good!
I'm here today to say that this IS what FINALLY ended the problem and "knock wood" it has not come back again......KEEP IT CLEAN!
I suppose you may get "LUCKY". But do you REALLY want to take the chance?