From: Rabbi Moshe Sofer
To: Rabbi Avraham Katz
Wheat contaminated with small garlic-like growths raises concerns that their sharp juice constitutes mei peiros, which combined with water could accelerate leavening of matzah dough. The Chasam Sofer rules that ideally the wheat should be sorted and flour carefully sifted, but after the fact the matzah is not prohibited.
Source: Shu"t Chasam Sofer OC §126