1)
Why does it say "va'Yman"?
1.
Radak: Hashem summonsed a worm at the time in the place of the Kikayon.
2)
What is the meaning of "va'Tach"?
1.
Rashi: The word struck the Kikayon. This is the feminine form of va'Yach. Radak - Tola'as is feminine, like "Ki Sochelenu ha'Tola'as" (Devarim 28:39).
3)
Why did it dry?
1.
Radak: It cut it below. After the moisture from the ground ceased, and it was cut, its leaves dried - they were the shade. His Simchah was for one day, and the next day, at dawn it was stricken and dried.
2.
Malbim: It cut it below at its root.
