The decline disease in date palm (Phoenix dactylifera L.) has become one of the most severe problems in date palm offshoots of the Egypt. Our previous studies have established that Lasiodiplodia theobromae (Syn: Botryodiplodia theobromae) is one of the fungi causing root rot diseases. This study was carried out in three governorates Bani-suef, Behara and Kaluobia. A survey of governorates was conducted in 2011 and 2012 to collect the root-rotted samples from rhizosphere of declined date palm offshoot and trees. Behara was the most affected governorate with 25.5% disease severity, while in Kaluobia it was 14.5% and in Bani-suef it was 13%. Bartamoda cultivar was the least susceptible to infection by the pathogenic fungus followed by Sakoty, Siwey, Sammany and Zaghloul. L. theobromae was most abundantly isolated fungal pathogen. Colony growth of L. theobromae was maximum at 35ºC and optimum temperature for disease incidence and severity was 30ºC. Relative humidity percentage of 70% is best for the growth of L. theobromae, while the optimum Rh% for disease incidence and severity it was 60%. Water salinity (ECw) at the concentration 15.63 ds/m2 was reduction linear growth of L. theobromae to 17.03%, while at water salinity concentration increased the severity of all cultivars tested. Root exudates from Bartamoda cv. the most effective on growth rate of L. theobromae at concentration 10%, it was reduction linear growth to 41.30%. Jojoba oil proved the best bioagent in vitro suppressing the growth of L. theobromae showing reduction of linear growth to 83.33% at 500 ppm. Plant guard was found the second most effective reduction to 52.96%. Marjoram showed the least efficacy against L. theobromae in all concentrations. Experiments in greenhouse to control the root rot disease proved the Jojoba oil gave the best results to decreased disease severity, followed by Plant guard and the least was Marjoram against L. theobromae at all cultivars tested.