this research aims to determine the level of knowledge of the agricultural respondents about the extension recommendations for control onion diseases, through: determining the Level of knowledge of the agricultural respondents about the extension recommendations for control fungal diseases of the onion crop, bacterial diseases, viral diseases, and nematode and physiological diseases of the onion crop, and determining the relationship between the respondents' knowledge of the recommendations. Guidelines for combating onion diseases and the independent variables studied, identifying the obstacles facing the studied farmers in combating onion diseases, and the necessary proposals to overcome them. To determine the population of the research, an inventory of onion growers in Assiut Governorate was conducted: The research was conducted in Assiut Governorate, and their number reached 272 farmers, and then three administrative centers were identified: Al-Qusiya, Assiut, and Abutig, and two villages were selected from each administrative center: Bani Idris, and Manshia. Khashaba in Al-Qusiya, Dranka, Riva in Assiut, Bani Samie, and Al-Nakhila in Abutig. A simple random sample of 164 farmers was selected from onion growers to conduct field research. To determine the sample size, the Krejci and Morgan equation (1970) was applied, and they were distributed as follows: Qusia, 82 respondents, Assiut, 29 respondents, and Abutig, 53 respondents. The most important results of the research are summarized as follows: The respondents' knowledge of the guidelines for control onion diseases varied, as it was low for both fungal and nematode diseases, especially stem rot nematodes (20.7%) and root rot (24.4%); increased knowledge of the farmers surveyed about the guidance recommendations for combating onion bacterial, viral and physiological diseases; there is a positive significant correlation between the respondents' knowledge of the agricultural extension recommendations for controlling onion diseases and many of the independent variables studied: the level of education, the use of and benefit from information sources, agricultural tenure, and the area of the holding cultivated with onion crops, at significant levels of 0.01 and 0. 05.