“Cockleburs can take over the farm if they are not controlled.”
The neighbor farmer made that assessment many years ago, and it is probably correct.
Certainly, cockleburs can readily thrive in ditches, wasteland, waterways, pastures, and sometimes cropland.
They are most noticeable when the hard ripe brown ’burs become tangles in horse manes and tails. The ’burs are also frequently a problem for dogs readily adhering to their hair as well as other livestock.
Charles L. Mohler at Sustainable Agriculture Research and Education has provided key information about cockleburs and managing the weeds.
An erect summer annual herb, seedlings have short, thick stems with purple at the base. The stem becomes green and covered with upward pointing hairs as the plant develops.
Fully mature stems are green, one-to-four-feet tall, highly branched, hairy, and flecked with purple, brown to black spots. The semi-woody, broad and sturdy taproot can reach four feet deep.
“Fruit” is a woody, brown, egg-shaped cocklebur. Each ’bur is approximately one-inch long by 0.7-inch or less wide, is covered in hard quarter-inch spines, and has two beaklike projections at the tip.
Each ’bur contains oblong, pointed, light brown to black seeds, covered in a papery, silver-black membrane.
Cockleburs are extremely competitive weeds due to fast emergence and rapid growth supported by the large seed,” Mohler said. “Populations of one to three plants per 10 square feet can cause soybean yield losses up to 75 percent.”
Tine weeding and rotary hoeing have limited effectiveness because the seedlings can emerge from deep in the soil.
Because the seeds do not persist well in the soil, rotation to a sod crop will help control this weed. Rotation to a winter grain will also help because the burs do not mature by grain harvest.
“Plant a cover crop after grain harvest to prevent resprouting from the shoot bases and subsequent seed production,” Mohler suggested.
“Cockleburs often establish first on unmanaged areas like embankments and stream banks,” Mohler said. “So, if you see it there, eradicate it quickly before it can invade your tilled fields.”
Germination of seeds is promoted by microbial decay or mechanical seed coat damage. Cocklebur seeds can survive for nine years.
Most emergence occurs in mid-spring to early summer, with occasional pulses of seedlings later in the summer.
“Cockleburs emerge well from an inch of soil, and can emerge from as deep as six inches,” Mohler informed.
The cocklebur is drought tolerant,” Mohler noted. “Roots can extend seven-feet laterally and four-feet deep, allowing access to water throughout the soil profile. Yet, they tolerate only light frost.”
Cockleburs are an aggressive competitor partially because of capacity to take up more water than other plants under similar conditions. “However, growth and reproduction are, nonetheless, reduced by prolonged drought,” Mohler pointed out. “Yet, cockleburs can tolerate flooding.”
Highly responsive to nitrogen, cockleburs will store excess nitrogen and later use it to increase seed production.
“Small plants regrow quickly from buds at the base of lower leaves if plants are trampled or clipped,” Mohler explained. “Once flowers have been pollinated, ’burs produce mature seeds even if the shoot or branch is severed from the roots.”
Plants flower as days shorten, with flowering in August regardless of age or size. Seed maturation continues until a killing frost.
“Common cocklebur primarily self-pollinates, but up to 12-percent of flowers are cross pollinated by wind dispersed pollen,” Mohler said.
Vigorous, open grown plants produce from 500 to 5,400 ’burs, each of which usually contains two seeds. “The number of ’burs depends entirely on the size of the plant at the time flowering begins,” Mohler said.
“The spiny ’burs cling to animal hair, clothing, grain sacks, about everything,” Mohler reiterated. “They tangle particularly well in sheep’s wool and are dispersed when the animals or wool are transported.”
Cockleburs float and are readily dispersed in streams, lakes, irrigation ditches. and flooded fields.
“People do not consume common cocklebur, but the seeds have been used in herbal medicine,” Mohler said. “Larger plants have good nutritional value for livestock but are rough and unpalatable.”
Pollen of cockleburs produce hay fever symptoms in sensitive individuals and contact with the stems can a cause dermatitis. Mohler noted.
“Cocklebur weed management can be tricky,” Mohler admitted. Of course, because of its toxicity to animals, it cannot be controlled by grazing, as many other weeds can be.
“There are, in fact, very few natural biological control methods for getting rid of cocklebur weeds,” Mohler contended
“The parasitic plant, dodder, may be effective in choking out cocklebur plants, but it isn’t advisable,” he said.
“Studies show that the Nupserha beetle is effective in controlling cocklebur, but it’s not a native species,” Mohler said. “The most effective methods of cocklebur control are hand pulling or chemical controls.”
There are different preemergent and post emergent herbicides available for chemical control of cockleburs. However, stringent applications rules and recommendations that must be followed.
“A weed control specialist must be contracted for advice before ever using chemicals to control cockleburs,” Mohler demanded.