Radak: This is destruction, like "Ga'arta Goyim" (Tehilim 9:6). "Lachem" is for you.

Radak citing Targum Yonasan: I will censure you with produce of the land...

Malbim: Chagai (2:18-19) and Zecharyah (Perek 8) promised them that from when they began to build the Beis ha'Mikdash and offered Korbanos, what they seed will be blessed. Now that you did not guard Mishmeres ha'Korbanos properly, I will destroy the seed so it will not sprout for Brachah.

Shabbos 151b: This refers to people who abandon Torah and make all their days like festivals [for feasting]. Three days [after death], the stomach bursts and falls to the face, as if to say 'take back what you gave to me'.

Rashi: I will cast excrement of the animals of your festivals in your faces. I.e. you will not receive reward from Me, only evil and shame.

Radak: Chageichem are animal Korbanos, e.g. lambs - "Isru Chag ba'Avosim" (Tehilim 118:27), "Chelev Chagi" (Shemos 23:18). The Korban is called Chag because most Korbanos are offered during the Regel. Just like you disgrace Me via Korbanos, I will disgrace you via them. The most disgraceful part of an animal is its excrement - I will strew it on your faces! I.e. I will disgrace you due to hunger. I will destroy the seed that you plant, and you will lack bread. You will be ashamed among the Goyim around you. Hunger causes shame - "u'Svatem Oso v'Lo Eten Eschem Od Cherpah ba'Goyim" (Yo'el 2:19). It is as if I strewed excrement on your faces.

Malbim: Since the Korbanos are Pesulim, nothing remains from them, only the excrement that you bring into the Heichal from the animals offered and their ashes.

Rashi: Excrement of the animals of your festivals will carry you to it, to be despised and disgraced, like it.

Radak: The sin will carry you to this disgrace, Midah k'Neged Midah. You disgraced Me, and you will be disgraced.

Malbim: The excrement of the Korbanos that you offer on your festivals will burn you. You will resemble the excrement and ashes.