The might of a mite

Jenny Gessaman
An odd cylindrical bug, with a head that tapers in the front, dominates a surreal black and white landscape.

A wheat curl mite as seen through a scanning electron microscope.

Micrograph courtesy of Kansas State University

It’s smaller than a period, but can destroy acres of crops. It is so tiny, it crumbles into dust without enough moisture, but it can cost farmers thousands of dollars. Yes, the wheat curl mite has a powerful and bad reputation, despite its size.

Kansas State University’s Entomology Department describes the mite as white and cigar shaped, with four legs at its head. The insect is so small, it fits between the veins in wheat leaves. So how does something with such an innocuous description do such damage?

 As MSU’s Extension Plant Pathology Specialist, Mary Burrows is the perfect person to decode the mite’s effects: her job is all about decoding.

“I’m a translator between the university and citizens of the state,” Burrows said.

She depicted the wheat curl mite as a self-sufficient insect, capable of creating its own housing. The mite eats tiny holes into leaves, leaving a Swiss-cheese landscape. Burrows explained the holes make the leaves curl inwards, creating a namesake and a home.

“That makes a nice environment for the mite to reproduce in,” she said.

Despite the physical changes it causes, the mite doesn’t really damage wheat.

“There’s very little loss due to the mite itself,” Burrows said. “It’s only when it’s transmitting viruses that it’s a definite danger to the crop.”

She explained a plant getting a virus was similar to a human catching one: In both cases, the recipient gets sick. The wheat curl mite plays a role by carrying a virus from sick plants to healthy ones. Burrows said the wheat streak mosaic virus was the one most commonly associated with the insect.

“It infects the plant’s every cell,” she explained, continuing, “It’s just like a cold virus: It moves through your whole body.”

According to Burrows, wheat streak weakens the plant, making it difficult for roots to grow and photosynthesis to occur.

“And there’s no medicine you can give the crop,” she said.

Luckily, the mite can only taxi the virus around under certain conditions.

“The mite is favored by what we call the ‘green bridge’,” Burrows said. “That’s the presence of green plant material between the harvesting of one crop and the planting of the next.”

Fergus County MSU Extension Agent Darren Crawford summarized:

“That bridge of green material that carries the mite from this season into next season.”

He explained the mites prefer green, or younger, wheat plants that contain moisture.

“When they don’t have a living plant to eat, they tend to dry out quickly and die,” he said.

Farmers tend to want one growth cycle at a time in fields, so how does young plant material pop up in a mature wheat field?

According to Crawford, with the help of weeds and accidental seedlings. He said the mites could survive on weeds and native grasses. He also said wheat seed left after harvest or hail could sprout green bridge material for the insects to survive on until the next crop.

“Often times with hail, that’s when we have the biggest wheat streak issue,” Crawford said, explaining hail hitting the tops of wheat plants could scatter seeds across the ground.

So, with no medicine and a harmless mite carrying a harmful passenger, what can farmers do? They can shoot the messenger.

Burrow and Crawford recommend an extended period between the harvest of a wheat-streak-infected crop and the next planting. With no food, the mites die. Or, as Burrows put it:

“Everybody just has to recover from the flu.”



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