One of the hypotheses being tested, that of the pest Sufetula sunidesalis as the main cause of stagnating yields, is becoming increasingly probable over the other hypotheses. Neither the planting density, nor the height of the water table are to blame. The probability of a silica mineral deficiency is also diminishing as time goes by. On the other hand, we have more and more clues pointing to a depressive effect of Sufetula. Direct observation of roots through the panes of the rhizotrons has confirmed strong pest pressure on the root system. The soil cover trial (ferns/bare soil right from planting) shows that the difference in yields may be correlated with attack levels on the roots. The trial to eliminate Sufetula in the planting circle of young coconut palms by insecticide applications (untreated control palms/palms treated twice a month) shows that Sufetula attacks are increasing substantially on the untreated coconut palms. The percentage of roots affected at 15 months is still low, but increases as time goes by, and an effect on the aerial parts is expected in the medium term. As regards recommendations sent to the commercial plantation, we confirm switching to bare soil and to a KCl/NaCl mixture in the chlorine fertilizer.