A pint-sized invasive grass called ventenata is wreaking havoc on timothy acres in parts of Idaho, Washington and Oregon. The weed outcompetes timothy; its stems are high in silica and exporters refuse bales that contain it, says John Wallace, University of Idaho weed scientist.

“We had timothy we couldn’t sell to the export market,” exclaims Bill Fountain, Cusick, WA. “Timothy might be worth $250/ton to an exporter – with ventenata, all of a sudden the hay is worth $70.”

The small annual weed can be identified by its narrow leaves with brown to purple rings at the nodes and its distinct membrane between the grass blade and stem. When flowering, it resembles a miniature wild oat.

“It doesn’t take very long to damage your crop. Ventenata will spread out through the timothy and then, all of a sudden, the timothy will die,” says Fountain.

“We are puzzled as to why ventenata is such a great competitor,” observes Tim Prather, University of Idaho Extension weed scientist. He and Wallace are working with USDA-NRCS and researchers at other universities to find answers.

They know that its litter leads to more ventenata plants the following year – “similar to a snowball effect,” says Prather. And it grows in areas that overlap with cheatgrass and medusahead.

Herbicides can control ventenata in pastures. But, in timothy, registered herbicide options are more limited and Prather encourages growers to discuss them with their Extension agents. “There are always going to be species of grass injured by a herbicide designed to take grasses out of grass,” he notes. “That’s why local knowledge is so important.”

Fountain uses several weed-control strategies. Timothy fields heavily infested with ventenata are replaced years earlier than they would normally, he says. “Ventenata doesn’t seem to want to sprout in new soil. However, by the fourth year, it is back.”

Sometimes he harvests timothy early while ventenata is still green and cows will eat it.

Although there’s risk of damaging the timothy, Fountain has tried some herbicide applications with mixed success. “You want the timothy to be as dormant as possible,” he says.

Fence lines are sprayed with Milestone, which isn’t registered for timothy but sometimes reduces ventenata if applied before the weed emerges, he adds.

By next fall, Prather hopes that Axiom, from Bayer Crop Science, will be registered for use on timothy. It looks to provide good control of ventenata with little injury risk to timothy, says Prather.

Managing timothy for optimal growth is a strategy the researchers suggest. That includes cutting it higher than normal – to 4” – to give the crop a fighting chance against ventenata. “That’s the optimal amount of stem needed to store energy to produce new stems for the next year,” says Prather.

If needed, fertilize with phosphorus and potassium in fall for root growth and nitrogen in spring to develop stems and leaves.