The State Department is halting most visa processing for Mexican guest workers amid the coronavirus pandemic, prompting concerns from US farmers who rely on their labor to harvest crops.

Growers say the new restriction "threatens our ability to put food on Americans' tables."

The news comes while grocery stores across the country have been subjected to panic-buying, with many running out of staple products.

The crops most likely to go unpicked will be leafy greens, celery, broccoli, cauliflower, radishes, and melons, one growers' association said.

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The US government is halting most visa processing for Mexican guest workers amid the coronavirus pandemic, raising fears that farmers won't be able to harvest their crops while grocery stores across the country are already struggling to meet demand.

American fruit and vegetable producers have relied for years on the guest workers, who largely come from Mexico and use H-2A visas that allow them to legally work in the US for up to a year at a time.

The novel coronavirus sweeping the US has triggered mass panic-buying at many grocery stores, leaving a number of staple products such as meats, cleaning supplies, and toilet paper out of stock.

Now, farmers are concerned fresh fruits and vegetables could be the next to go.

"Under the new restrictions, American farmers will not have access to all of the skilled immigrant labor needed at a critical time in the planting season. This threatens our ability to put food on Americans' tables," Zippy Duvall, the president of the American Farm Bureau, said in a statement.

These crops are harvested by migrant farm workers, mostly from Mexico, some of who have seasonal work visas and some of who are undocumented. Andrew Lichtenstein/Corbis via Getty Images

Growers also said the labor shortages will likely hit fruit and vegetable farmers the hardest, since farmers who grow grains such as wheat and corn generally harvest their crops with machines rather than workers.

Farmers' associations told Reuters that as of Wednesday, new H-2A applications will not be processed, though returning seasonal workers will still be allowed to enter the US.

But the growers also said returning guest workers make up just 40% of farmers' labor needs.

In the last fiscal year, farmers hired 188,262 Mexican workers, according to The Wall Street Journal.

The crops most likely to go unpicked will be leafy greens, celery, broccoli, cauliflower, radishes, and melons, Dave Puglia of the Western Growers Association told Reuters.

"When the process is stopped midstream, it likely means those crews won't be there exactly when they're needed, if they get there at all. That means lost crops. That means lost food," Puglia said.