The present experiments were carried out in El-Mattana Research Station (latitude of 25.25°N and longitude of 32.31°E), AgriculturalResearchCenter, Luxor Governorate, Egypt. The present work was conducted on two plant cane crops grown in 2015/2016 and 2016/2017 seasons to study the yield, quality and natural of infestation with lesser sugarcane borer, Chilo agamemnon Bles., and pokkah boeng disease (Fusarium moniliforme Sheldon) and other diseases of four sugarcane varieties (G.T.54-9, G.2003-47, Ph 8013 and C. 57-14) as affected by three levels of potassium fertilization (zero, 24 and 48 kg K₂O/fed.). The results showed that the difference in mostly traits between sugarcane variety G.T.54-9 and G.2003-47 was insignificant, they surpassed the other two varieties in number of millable canes and cane and sugar yield/fed. Also, they recorded the highest percentages of infestation with C. agamemnon Bles., and pokkah boeng, during the two successive seasons. The sugarcane variety Ph 8013 showed significant superiority in stalk weight, sucrose% and sugar recovery%. However, the variance between the two sugarcane varieties namely Ph 8013 and G.2003-47 in sucrose% and sugar recovery% was insignificant. Increasing the applied dose of potassium fertilizer up to 48 kg K₂O/fed. was accompanied by a significant increase in the values of number of millable canes, stalk weight/plant and sugar yields as well as decreased of percentage of infestation with C. agamemnon Bles., and pokkah boeng disease, during the two successive seasons. However, the variance between 24 and 48 K₂O/fed. in sucrose%, sugar recovery% and cane yields/fed. was insignificant during the two successive seasons. Fertilizing sugar cane crop by 24 and 48 kg K2O/fed. increased cane yield by 6.47 % & 7.51 % during the first season and 4.51 % & 11.34 % during the second season, respectively, compared with check treatment.