Trifecta Crop Control was designed with foliar applications in mind. There have been several times that we are aware that people have applied it as a root drench to treat various issues from root rot and fusarium, to root aphids and fungus gnats.
There are 2 concerns that Trifecta has with these type of applications.
1) Negatively impacting mycorrhiza. Certain essential oils in Crop Control were chosen for causing cell lysis in fungal species. This means that it can kill beneficial fungi also. If you use it as a soil drench, you will need to rebuild mycorrhiza colonies after treatment.
2) Phytotoxicity in your plant. The same oils that cause cell lysis in fungal species can have a damaging effect on plants. This exhibits itself as a slight curling in the leaves occasionally when Trifecta Crop Control is first applied. This effect is more pronounced on clones and younger vegetative growth, and with foliar applications is scarcely noticeable, and is manageable and not problematic. In soil drench applications, this concern is more significant.
Bear in mind that Crop Control wasn’t intended for Soil Drench Applications, and that we make no official recommendation regarding it’s use this way, but people have reported successful soil applications. IF you intend to try using Crop Control for this application we have heard that the best success happens when the plant is well fed and full of water so that it doesn’t drink high levels of Crop Control too quickly. For best results saturate the soil, with diluted Crop Control (likely 1oz to gallon is sufficient) and then rinse out with fresh water. Plan to rebuild mycorrhiza colony in soil after treatment.
There is a forum post where a user describes using Crop Control to treat Root Aphids with good success. Please follow the hyperlink for the forum link: