We present observational evidence for the strong turbulence processes, namely, the oscillating two stream instability (OTSI) and spatial collapse of Langmuir waves in the source regions of solar type III radio bursts. The high time resolution observations from the STEREO/SWAVES experiment show that the Langmuir waves excited by the electron beams occur as localized wave packets with durations less than 10 ms and with peak intensities exceeding the strong turbulence thresholds. These localized Langmuir wave packets satisfy the criterion of the envelope solitons collapsed to spatial scales of a few hundred Debye lengths. The spectra of these wave packets contain the characteristics of OTSI: intense peaks corresponding to beam-resonant Langmuir waves, two or more sidebands corresponding to Stokes and anti-Stokes modes, and low frequency enhancements below a few hundred Hz corresponding to ion sound waves. The frequencies and wave numbers of these spectral components satisfy the resonance conditions of the OTSI. The tricoherences, computed using the trispectral analysis techniques show that the spectral components of the wave packets are coupled to each other with a high degree of coherency, as expected of the OTSI type of four wave interaction. The observed high intensities, short scale lengths, sideband spectral structures, low frequency enhancements and high levels of tricoherence are suggestive of strong Langmuir turbulence processes, namely, the OTSI and spatial collapse of Langmuir envelope solitons. The implications of these observations are that: (1) the OTSI and spatial collapse probably play key roles in the beam stabilization as well as conversion of Langmuir waves into escaping radiation at the fundamental and second harmonic of the electron plasma frequency, and (2) in the case of type III radio bursts, the Langmuir collapse probably prefers the route of OTSI instead of route of nucleation instability.