This week’s joint meeting among the Sparks and Reno city councils and the Washoe County Board of Commissioners featured a dramatic public comment with an allegation that the City of Reno is spraying weeds along the Truckee River.
Is it true? Yes.
A better question is why.
City of Reno Parks Manager Jeff Mann said that the city does conduct weed control activities along the river, but does not spray herbicide into the river itself.
“Parks has sprayed herbicide to treat tall whitetop along the Truckee,” said city spokesperson Mary-Sarah Kinner. “They don’t spray into the water or within the river channel itself.”
Tall whitetop, or perrenial pepperweed, is an incredibly nasty weed. It’s on the state’s noxious weeds list for good reason. It’s invasiveness is so profound that it is incredibly difficult to remove and has severe natural resource and economic impacts.
The plant crowds out native and beneficial plants, enables mosquito breeding, harms wildlife habitat, erodes stream banks, reduces access to water ways and has eliminated in some areas agricultural production along the Truckee River.
And it spreads vigorously downstream, impacting agricultural production and threatening Pyramid Lake. “Mature stands can produce more than 6 billion seeds per acre.” After historic Reno floods, stream and river channels have become inundated with the weed. Portions of the South Meadows are still tall whitetop monocultures. And because it is a state noxious weed, allowing the weed to propagate is illegal under NRS 555.150.
Aside from grazing the plant with livestock, which is expensive and logistically improbable along river channels, herbicide is the most economical treatment of tall whitetop. Pulling the weed can expand its root system, causing more plants to grow. Mechanical methods are generally not effective.
According to the Truckee-Carson Irrigation District,
the nature of perennial pepperweed’s creeping root system negates most mechanical control measures. It is nearly impossible to cut the roots fine enough to prevent the sprouting of buds that form new plants.
“Sprouts from root segments grow very rapidly, often resulting in flowering plants in the same year that the parent roots are cut in tillage operations. Mechanically cut roots are very resistant to drying.
“Roots exposed on the soil surface over winter will sprout the next spring. The crowns of established plants become enlarged and very woody.”
That leaves chemical controls or herbicides.
“In most cases, herbicides are needed to provide effective control of perennial pepperweed. However, chemical control is made more difficult by the robust root system,” according to a University of Nevada Cooperative Extension fact sheet. (UC Davis concurs.)
Because treatment options are limited, using herbicide is likely the most efficacious and realistic of options. A UNR Cooperative Extension study identified the costs of delaying tall whitetop treatment and found that
Because of the peculiar characteristics of the ecological problem posed by tall whitetop and other invaders (i.e., explosive growth), the costs of control multiply rapidly over time. Therefore a failure to devote resources to infestation problems today requires the decision maker to spend appreciably larger sums of money even a small number of years from now. At the highest expansion rate modeled in our assessment (which is well within the range of data observed for invasive weeds in the West), even a four-year delay in beginning a control program would cause the eventual Year 1 control costs to nearly triple. A ten-year delay would cause Year 1 costs to rise by more than a factor of ten.”
Costs also go up by not using herbicides. Hand pulling and digging is laborious and expensive, and as indicated above, might not be effective. It is, however, an option in river channels, according to UNR’s Cooperative Extension:
Hand pulling or digging has been used in situations where only a few plants are present or in riparian areas where herbicides cannot be used due to the proximity of water or other management concerns…. This is a labor‐intensive method that is only appropriate in limited circumstances where herbicides are not an option.”
Indeed, Reno City Councilmember Paul McKenzie, after it was announced this week that city parks are going herbicide free, forewarned that there’s a cost associated with weed abatement absent chemical controls.
“We may have to increase staffing to continue this effort,” he said. “We’ll have to replace (herbicides) with man power.”