Black Root Rot
Most susceptible plants: pansy, vinca.
Black root rot can cause significant production losses in greenhouse crops. Although this fungal pathogen also has a very wide host range, the most serious problems occurr on pansy and vinca. Pansy and vinca plug infection has resulted in significant plant losses.
The black root rot fungus damages the root of the plant, effectively interfering with the root's ability to absorb nutrients. As a result of root injury, plants usually develop symptoms indicative of nutritional stress. Yellowing of the younger growth is a common symptom. Root examination of infected plants usually reveals a lack of healthy, white roots; infected roots are usually off-white, gray or black, depending on the stage and severity of infection.
Control of black root rot can be difficult if the pathogen becomes established within the growing area. Pay strict attention to sanitation. Do not reuse plug trays or plastic pots. Store media in a location that is protected from contamination. Spot-check all plugs introduced into the growing area by carefully examining roots for healthy, white color. Stress has been shown to greatly enhance black root rot. Adverse temperatures, excessive moisture in the root zone, excessive levels of soluble salts and excessive use of fungicides or other plant production chemicals have all been implicated in intensification of black root rot. Because plugs are vulnerable to a number of stresses, all plugs should be planted as soon as possible after arrival.
Several fungicides have proven effective. Use preventatively or at the first sign of infection for effective control. An acidic pH helps to manage black root rot; a pH range of 5.5-5.8 can reduce black root rot development.