I’m attempting to grow goldenseal in my aquaponic system, but the roots of my plants have blackened and there was some yellow wax oozing out of them. What can I do?
When root systems become discolored or darkened this generally indicates disease. A common culprit is Phytophthera species, the genus of a plant-damaging water mold. Phytophthera thrive, grow, reproduce and infect plant roots in water, saturated soil, and along river banks and ponds. Flooded or saturated soils are not favorable for plant growth and can predispose plants to infection. Anywhere significant quantities of water collect, accumulate or flow, Phytophthora spp. can be found. The lack of oxygen in the water is typically what helps this fungus/mold flourish in ponds. Usually, because of the root failure, the plants will begin to wilt or fail completely.
It is possible that your situation could be a different pest, however. You can bring (or ship) specimens to a certified laboratory to get confirmation—just check the associated costs before proceeding with this. The downside of mailing away from answers is that diseases spread quickly, especially to other plants of the same variety.
The best way to control a phytophthora disease is before it starts. In the landscape, water regulation and good drainage is vital. In an aquaponic set-up, increase the amount of oxygen in the water with something such as an air pump or air stone. There are meters available for checking the level of oxygen. Make sure your pump runs at least 15 minutes each hour.
Overall, clean stock, crop rotation, sanitation, chemicals as needed, and host resistance are among the controls that can be implemented. Hydrogen peroxide has been successful in controlling the disease on the roots; however, in the case of aquaponics it may not be successful due to dilution issues. Do some research before trying this method.
Removing an infected plant from the water and rinsing the roots in a light concentration of hydrogen peroxide (three per cent), then returning the plant to the aquaponic system might help when done in conjunction with the addition of extra oxygen. As prevention is the best way to treat fungal diseases in the garden, you may need to remove the infected plants and discard them while you work to improve your water quality, and then re-insert new plants.