Puncturevine, a summer annual broadleaf weed that thrives on field borders, comes by its nasty name naturally. The spiny burrs that it produces can wind up in harvested forage, decreasing its palatability and intake, says Rick Boydston, a USDA-ARS weed scientist in Prosser, WA.
“Those burrs can also get lodged in the feet, mouths and digestive tracts of dairy and beef cattle, causing them distress,” says Boydston.
The nuisance weed can be toxic to sheep and goats if eaten in large quantities. “It causes sensitivity to light,” he says. “Blisters form on the insides of the animals’ mouths and on areas of their bodies where skin is exposed to sunlight.”
Puncturevine originated in the Mediterranean region and was discovered growing along railroad tracks in the Northwest in the early 1900s. It’s now found in almost every state, but is most abundant in those with milder winters, says the weed scientist.
The good news is that puncturevine doesn’t compete well against alfalfa, so it’s generally found on field edges. “It prefers areas where there’s very little crop canopy, but if it finds an open area, it can quickly take hold,” says Boydston.
It grows close to the ground, forming dense mats that can reach up to 12’ in diameter. It has hairy leaves and yellow flowers with five petals. After each flower is pollinated, a seedpod forms that is a cluster of five flat, spiny fruits or burrs that can contain up to five seeds each. Mature seedpods break apart and the burrs disperse, often getting lodged in machinery and truck tires and in the soles of shoes.
“Those burrs are then easily transported to areas where the weed’s not infested, enabling it to take hold there.”
Aggressive measures used over multiple years are usually needed to control it. A typical plant produces 200 to 5,000 seeds during a growing season and those seeds can survive in the soil for four or more years.
“The seeds within each burr have different dormancy levels,” explains Boydston. “If you have five seeds, one may germinate this year and the other four seeds may sit dormant for a few years or so before germinating. So even if you get rid of the seedlings that come up one year, you’re still likely to have problems in subsequent years.”
To minimize the spread of puncturevine, he recommends washing your shoes, machinery and tractor tires frequently to rid them of burrs. Keep it out of alfalfa fields by applying a pre-emergence herbicide, such as flumioxazin and norflurazon, in late winter when the crop is dormant. Puncturevine seedlings can be controlled with a postemergent herbicide such as bromoxynil or imazamox when the weed is less than 2” in diameter. Several other herbicides are also available, but read labels carefully.
To kill the weed in field borders, he advises repeated tillage at three- to four-week intervals. “Depending on moisture levels, the seed can continue germinating from early April through mid-August.”
One final suggestion: “Plant a competitive crop, such as grass, around field borders to minimize bare areas and crowd out the weed,” says Boydston.