This depends on the course:
BSc level courses are often taught in Dutch. You are expected to be fluent in Dutch to participate in these courses. Some BSc courses are (also) in English. In that case the requirements are almost the same as for MSc courses.
MSc courses are taught in English. The required level depends on the course. To get an indication, please check the page about English language proficiency (non-EU/EFTA).
You do not have to submit an English test when you apply for a WURth-while course. During the intake meeting your level of English will be assessed. If there are doubts, you may be asked to take a test at the Wageningen language centre.