A borescope-minirhizotron system was evaluated as a method for observing Phymatotrichum omnivorum in situ in both field and greenhouse situations. The borescape consists of an eyepiece, extension tube, and an objective head with a right angle objective lens. The minirhizotrons were constructed of plexiglass tubes 51 mm ID and placed in the soil at an angle 30' from vertical. Lighting was achieved using a quartz-halogen light source and fiber optic cables. The borescope is equipped with its own incandescent light source but due to excessive heating and glare, it was not used. Observations were recorded with a 35 mm camera or a video recording system.

The borescope proved to be an excellent tool for observing Phymatotrichum growing in situ. Strands were observed on cotton roots in the fields ten-days before any above ground symptoms appeared. Strands could also be seen growing around sorghum roots with discolored localized lesions appearing at points of root-fungus contact. In greenhouse studies germinating sclerotia were clearly visible, and strands of Phymatotrichum were observed attacking roots of cotton seedlings five days old. The borescope-minirhizotron system has the potential to become a very useful tool for study of soil borne organisms. The low cost and ease of installation of the minirhizotron tubes will allow sufficient numbers for statistical analysis. Tube installation results in minimal disturbance to the soil thus providing a more natural situation, for observing soil borne microorganisms. Finally, minirhizotrons of the proper diameter can also serve as neutron access tubes. This will allow studies relating fungal growth and disease progression to soil moisture in a natural, relatively undisturbed field situation.