About 25 years ago on our ranch we started having a few cases every winter of what looked like pinkeye, in cattle pastured along the creek. Affected eyes were irritated and watering, sensitive to light and held shut. The eyeball became blue and in severe cases the animal would be temporarily blind in that eye; there was often an ulcerated protrusion on the eyeball.

We couldn't understand why cattle would get pinkeye so late in the year since pinkeye is a summer problem, spread from animal to animal by face flies. We treated the eyes with antibiotics injected into the inner surface of the eyelids, sewed the eyelids shut to protect the eyeball, and they all cleared up—but it sometimes took several weeks.

One fall our old gelding developed a similar eye problem. His eye turned blue and it was sore and watering, with ulceration on the eyeball. He kept that eye shut. Antibiotic ointments didn't help. It took two months for his eye to clear up.

The cause of the eye inflammations eluded us and our veterinarian. Then in 1993 we learned that some sore-eyed horses examined at the Virginia-Maryland Regional College of Veterinary Medicine had microscopic barbed slivers embedded in the eye—fragments from seed heads of the burdock plant. About the same time, veterinarians at Cornell and at New York State College of Veterinary Medicine found the same cause for mysterious eye problems in cattle and horses.

Burdock burrs stick to just about anything - including animals' fur, and slivers of the plant may get into the eyes.

We contacted these colleges to learn more about this problem. Dr. Martin Furr at Virginia-Maryland Regional College of Veterinary Medicine and Dr. William Rebhun at Cornell University told us that large seeds and pieces of hay or straw in the eye usually work their way to the corner where tears wash them out. Occasionally they are trapped under the eyelid and cause irritation and scraping of the cornea—the transparent covering of the eye. Any large foreign particles can usually be seen and flushed free or removed.

By contrast, tiny burr slivers can be hard to locate and remove. They often become entangled in folds of the eyelid lining. When caught under the lid, embedded in the lining, they create a sore by scraping against the eyeball each time the animal blinks.

Burdock burrs stick to fur, hair, horse's manes and tails or human clothing. The plant has large composite leaves and grows six feet tall or higher, with round prickly burrs. It grows in shady wet places like creek bottoms or along ditch banks. Cattle that go into the brush often become covered with burrs. The burrs can be difficult to groom out of a horse's mane or tail or fetlock hair.

When burrs are ripe in the fall and winter they release hundreds of microscopic barbed slivers. If a burr is shredded during attempts at removal, the seeds are scattered. Even if you pull off burrs that stick to your clothes some slivers remain, causing itching when the clothes are worn again. Slivers can become embedded in human flesh, causing irritation. The sliver is too small to see with the naked eye and very difficult to remove.

A sliver in the eye can cause inflammation and infection that may elude detection efforts. It usually gets caught in an eyelid or third eyelid, where it scratches the surface of the eyeball with every movement of the lid, creating irritation and pain. The cornea may become inflamed and ulcerated; the eye may turn cloudy and have a white spot or bulge.

When my husband and I learned about burdock eye problems, our "winter pinkeye" mystery was solved. The only cattle on our ranch that developed eye problems were pastured on fields with access to creek bottoms and thickets where burdock grows. The cattle on our mountain pastures never had this eye problem; there was no burdock there. The old gelding with the bad eye had a lot of burrs stuck in his mane and forelock. Several burdock plants grew along the ditch in his pasture.

Burdock growing in pastures resembles rhubarb to the untrained eye (rhubarb leaves are glossy, burdock are not).

The sliver from a burr is so small that the usual tools used to examine an eye (focal light and magnifying lens) may not be powerful enough to locate it. Dr. Furr said diagnosis is made by careful observation with a slit lamp—an ophthalmic instrument that magnifies. But inflamed and reddened tissue may hide the sliver. The veterinarian must narrow the search by looking at the portion of eyelid that neighbors the damaged cornea during normal eye movements and blinking.

Staining the eye with fluorescein dye makes it easier to locate an embedded sliver and remove it with forceps. If it can't be grasped it can still be removed by scraping the surface of the inflamed tissue, to snag the embedded sliver. Once the foreign object is removed, the inflammation and infection can be cleared up quickly with topical antibiotics, but an eye that has been inflamed a long time—with scarring—takes longer to heal, according to Furr. Eventually the sliver festers and comes out on its own.

Most injured or inflamed eyes respond to standard treatments and show signs of improvement after three or four days of medication. If an eye does not improve, you can suspect a burr sliver and it's a good idea to take the animal to a clinic with specialized equipment for eye examinations, where the sliver can be more easily detected and removed. A corneal ulceration or spot of inflammation near the eyelid or third eyelid should make the veterinarian suspicious that a small foreign body like burdock could be the cause.

Eradicating the pesky plant

Burdock can be controlled by chopping it down in early summer before it is mature enough to put forth seeds. It can also be controlled with herbicides. When we found that eye problems in our cattle were caused by microscopic burr slivers, we asked Don Morishita, Idaho State Weed Specialist at Twin Falls, Idaho, how to eradicate these plants. He told us that any broad-leaf herbicide will kill burdock, if done properly. Burdock is a biennial; it lives for two growing seasons. The first year, it doesn't grow tall stalks or bloom—it merely grows leaves and accumulates food reserves in its roots, like a carrot, another biennial. Morishita said burdock root is edible; the roots and leaves are used in herbal medicines—as a diuretic and a laxative.

The second year of the plant's life it grows a long, deep taproot, a tall stalk, flowers and burrs. Putting forth flowers and burrs exhausts food reserves in the root and the plant dies after burrs are mature. After the stalk comes up, it is harder to kill with herbicides; the plant is sending food up from the roots instead of down.

Burdock is easiest to kill in spring or fall. The first year it stays in a rosette stage with a circular cluster of leaves, and this is the easiest time to kill it. Apply spray when the plant is putting food into the root, to get herbicide into the root to kill the plant. Morishita recommends a broad-leaf herbicide like 2,4-D that can move down into the root. If you spray early in spring you kill the new young sprouts and last year's rosettes that are trying to create more food reserves in the root for a big push to complete second year growth and make burrs. You must spray early to get the second year plant. After the stalk comes up it is harder to kill. If you spray in fall you kill this year's rosettes—the plants that would mature and create burrs next year.

Fall is actually a good time to spray burdock, according to Morishita, to kill young plants that are storing food reserves in their roots for next year's growth. The first hint of cold weather is a trigger to send food to the roots, so this is a good time to spray. By contrast, in spring the second year plant is taking food from its roots to produce leaves and make the big push for a tall stalk and blooms. The food is going up, and it's harder to get the herbicide down into the root.

One thing to remember when using herbicides to kill burdock is to not overdo it, said Morishita. If you use too much, it quickly kills the top growth leaves and doesn't get down into the taproot. The root survives, to regrow. You want a slower kill so the leaves survive long enough to transfer the herbicide on down into the root, to kill the whole plant. Use the recommended rate and spray plants lightly—until they are barely wet but not dripping.

The dried burrs can be a real nuisance to animals and humans.

"Burdock is a bare-ground plant; it doesn't grow well where there's a lot of grass cover or competing plants," said Morishita. Chopping the plants is also effective for control, but you must do it at the right time or the plant will regrow from the root. The best time to chop is after the stalk is budding but before burrs are ripe. At that point the food reserves are so low in the root that it cannot regrow.

If you have burdock it may take several years of diligent control to eradicate it, since seeds can live a long time. Even though you chop or spray the plants, there may be seed in the ground from earlier years that will sprout and grow. Keep checking the patches, and get rid of new plants that grow up from old seeds.

For a number of years we chopped burdock every fall to get rid of burrs before we put cattle into burdock-infested pastures—so calves wouldn't be covered with burrs when we sold them, and so no animals would develop eye problems. Everyone in our family has developed sore, itching lumps in the skin after chopping and gathering burdock plants.

When we learned that burdock was the cause of mysterious winter eye problems, we began to control these plants because they were spreading after first appearing along a ditch that borders our place. Seed burrs were carried by wildlife and cattle to the rest of our lower fields. We began chopping the plants and hauling them off to burn, and discovered first-hand how irritating the burrs can be. If we gather burdock in the fall, we now use gloves and old long-sleeved shirts that can be thrown away afterward. If we spray plants in the spring before they develop blooms it greatly reduces our biggest patches. But we still have to chop down an occasional plant or patch that gets missed in the spring.

If we ride through thickets and get burrs on our horses, we carefully remove them after the ride. You can prevent shattering of burrs and scattering slivers on the wind, where one might lodge in an eye, if you coat the burrs with mineral oil or petroleum jelly before you pull them off.