Shen Collection, Upper Volume
Radical: Grass (cǎo)
蒮; Kangxi stroke count: 16; Page 1049, Entry 26
Pronounced yu (falling tone).
Erya (Erya): Explaining Grasses (Shicao) states that the zhuo refers to mountain chives.
Commentary (Shu): Chives that grow in the mountains are called zhuo.
Also acts as a variant form for the character (yu).
Wang Yinglin, Investigation of the Book of Odes (Shikao): In the sixth month one eats the wild grape and the zhuo. From the Han Odes (Hanshi) and the Commentary on the Erya (Eryashu).
Also, according to the Ancient Sounds of the Tang Rhymes (Tangyun guyin), citing the Book of Odes (Shijing), the line eating wild grapes and zhuo requires the character to be read in the departing tone, pronounced ao, rhyming with the subsequent shu, zao, and dao.