UCCE Master Gardeners of San Joaquin County
University of California
UCCE Master Gardeners of San Joaquin County

UC Garden Blogs

The Efficacy of Weed Killers

Here's an article by Paul Franson | Wines & Vines | 07.22.2014


Weed science advisor John Roncoroni explains that Roundup doesn’t do much for horseweed during a presentation about the use of herbicides in vineyards.

Napa, Calif.—Last week John Roncoroni, a Napa County UC Cooperative Extension weed science advisor, held a field demonstration about the efficacy of herbicides newly registered for vineyard application. He had laid out 25 treatment plots and rated the herbicides for weed control in vineyards.

The trials demonstrated that some new herbicides are very effective, especially if a mix of more than one is applied. But they also showed how ineffective some herbicides were against troublesome, newly arrived weeds.


Amounts given per acre mixed in 30 gallons of water. Ratings are the average of four replications and are based on control of four main weeds: panicle willowherb, horseweed, annual sowthistle and annual grasses. Source: John Roncoroni/UCCE Farm Advisor
The trial regimen

The test was held in south Napa Valley near Carneros. It was for pre-emergent herbicides, though each application included Roundup systemic herbicide in case any weeds had geminated unseen, plus AMSPro surfactant to improve penetration.

The plots had been cleared during the winter with glyphosate (such as Roundup) and Shark (carfentrazone, a contact herbicide that is mixed with glyphosate to help control some of the tolerant weeds). The applications were made in February just before significant rains (8.85 inches within a week).

The plots were 25 feet long by 6 feet wide under the vines, and they were swept clear of leaves before application.

The treatments were made at 30 gallons of water per acre at various rates and combinations of herbicides. They were applied with a CO2 backpack sprayer with two 8002 nozzles, each delivering 700 ml per minute. Roncoroni said that 30 to 50 gallons of water per acre seemed about optimum for adequate coverage.

No weeds were visible at the time of treatment.

All of the herbicides are registered. Roncoroni works exclusively with registered materials in Napa, saying: “The grapes are too expensive to destroy! Those trials are made with lower priced grapes in the Central Valley.”

Glyphosate is widely used in vineyards but some weeds have developed resistance to it, and others (some new to the region) are tolerant of it.

He applies the treatments in January or February, as they require rains to be activated, but they're only effective for 4 to 6 months. Vineyards may require mid-season spraying.

Rely is a preferred contact herbicide for mid-season and post-harvest spraying after pre-emergent herbicides have become ineffective and can't be applied again, but it is in short supply because of demand in the Southeast for use with cotton and soybeans fighting glyphosate-resistant weeds. Rely won't kill the vines if it gets on suckers, just the suckers, while glyphosate can get into the vine and cause problems in the spring.

“In the old days, they used paraquat,” said Roncoroni. Paraquat is still registered for use in grapes but requires special permitting and safety equipment for use.

Some of the new herbicides have some post-emergent properties, but one of the longest lasting, Alion (indaziflam), has none. In any case, Roncoroni emphasizes that mixes of two or more herbicides are generally more effective than a single product.


The herbicide Prowl performed nearly twice as well on vineyard weeds when combined with Alion or Matrix.
The results

Many of the herbicides did a pretty good job by themselves, notably Matrix (rimsulfuron), Chateau (flumioxazin), Goaltender (oxyfluorfen), and especially Alion at 5 ounces of product per acre.

However, the mix of Alion plus another herbicide such as Prowl (pendimethalin) and Zeus (sulfentrazone) was the most effective. Zeus plus Goaltender did particularly well, too.

However, the quantities obviously matter. Alion, for example, was significantly more effective at 5 ounces than at 3 ounces per acre. Some materials required much larger quantities per acre than others.


Panicle willowherb (above) and horseweed are new to the Napa area and represent some of the biggest challenges at present.
A note on some specific weeds

Roncoroni considers horseweed (Conyza canadensis) (often called mare's tail) and panicle willowherb (Ebilobium bracycarpum), both relatively new to the area and his biggest challenges at present

Willowherb can grow to 5 feet tall, getting into the clusters and even interfere with mechanical harvesting. It isn't resistant to glyphosate but tolerates it. Glyphosate can kill the top of the plant, but the weed will simply grow out from lateral buds. “It's really become a problem,” he said. It is killed by some pre-emergent treatments.

Horseweed (the preferred name) has gone from tolerance to resistance to glyphosate in the San Joaquin Valley. “It germinates almost year-round, so can crop up if you water after harvest,” said Roncoroni.

He said that it was relatively new in Napa Valley, and it's a real problem. “It can be 0.5 inches in diameter and 6 to 8 feet tall. It uses a lot of water and can interfere with harvesting.”

Fortunately, Matrix, Chateau and Alion are very effective in killing it, and the first two have some post-emergent effectiveness. “If it germinates in the fall, you need post-emergent herbicide to kill it.”

Glyphosate will only kill small plants (4-5 in. tall).

Rely can control both horseweed and willowherb, but again when they are relatively small.

Roncoroni added. “The only thing that will kill large willowherb or horseweed is iron—hardened on the end of a handle.'

Roncoroni noted that the pre-emergent herbicides aren't effective against field bindweed (Convolvulus arvensis), which has very deep rhizomes. It is best controlled with spot application when the morning-glory relative is blooming. This may take several years once established.

Turkey mullein (Croton setigerus) is a common weed, but Roncoroni says it isn't a big water user and doesn't grow very big so isn't a real problem. It prefers uncultivated soil, which is common in vineyards.

Roncoroni's trials showed that some of the new herbicides are very effective against weeds including tenacious types, but he noted that he didn't have information on price. Some like Alion are so new that other weeds may prove resistant to them in the future, but most resistance has been found recently in the overuse of post-emergent herbicides by themselves.


Organic herbicides

Roncoroni didn't include any organic herbicides in the trials since no new ones have been approved recently, though he expects some soon and will conduct trials with them. He fears, however, that they may be expensive and not effective against tough weeds.


Original source (Reprinted with permission from Wines & Vines)

Posted on Friday, July 25, 2014 at 2:40 PM
Tags: glyphosate (14), herbicide (28), vineyards (3)

So Beautful, So Exquisite

There's something about seeing a butterfly that makes your eyes light up, your smile widen, and your feet feel like skipping.

Nature's joy.  

So when I was over at Kaiser Permanente in Vacaville last Tuesday, I rejoiced at seeing a magnificent anise swallowtail, Papilo zelicaon, fluttering around the lantana flower beds near the entrance.

The butterfly flashed its brilliant yellow and black colors in the morning sun as it glided around the flower bed, touching down occasionally for a sip of nectar.

Such a beautiful, awe-inspiring, glorious creature. 

So I did what comes naturally—I pulled the camera out of my bag—somewhat like pulling the rabbit out of a hat because you never know what kind of magic may--or may not--happen.  Assuming my best "non-predator posture," I slowly trailed it from blossom to blossom, dropping down to capture its image.

It was then that I noticed a woman sitting on a nearby bench, smiling, as she watched the photographer follow the butterfly.

“I love butterflies," she said. "I collect butterflies—jewelry. I would never collect the real thing. They're too beautiful.”

“Me, either,” I said.  “I try not to disturb them—I just photograph them.”

Half an hour later, I returned to the area only to observe a stricken look on the woman's face.

“You have the last photo of that beautiful butterfly," she said. "A bird ate it." 

And right in front of the managed health care facility.

Anise swallowtail foraging on lantana. (Photo by Kathy Keatley Garvey)
Anise swallowtail foraging on lantana. (Photo by Kathy Keatley Garvey)

Anise swallowtail foraging on lantana. (Photo by Kathy Keatley Garvey)

Anise swallowtail about to take flight. (Photo by Kathy Keatley Garvey)
Anise swallowtail about to take flight. (Photo by Kathy Keatley Garvey)

Anise swallowtail about to take flight. (Photo by Kathy Keatley Garvey)

Anise swallowtail spreads its wings. (Photo by Kathy Keatley Garvey)
Anise swallowtail spreads its wings. (Photo by Kathy Keatley Garvey)

Anise swallowtail spreads its wings. (Photo by Kathy Keatley Garvey)

Posted on Thursday, July 24, 2014 at 9:54 PM

It's National Moth Week!

Greater wax moth, Galleria mellonella, a pest of bee colonies. (Photo by Kathy Keatley Garvey)
It's National Moth Week!

The event, which runs through Sunday, celebrates "the beauty, life cycles, and habitats of moths," according to its website. Scientists and citizen scientists are encouraged to document their findings. It's now a worldwide event.

A few nuggets from the website:

"Moths are among the most diverse and successful organisms on earth.

  • Scientists estimate there are 150,000 to more than 500,000 moth species.
  • Their colors and patterns are either dazzling or so cryptic that they define camouflage. Shapes and sizes span the gamut from as small as a pinhead to as large as an adult's hand.
  • Most moths are nocturnal, and need to be sought at night to be seen – others fly like butterflies during the day.
  • Finding moths can be as simple as leaving a porch light on and checking it after dark. Serious moth aficionados use special lights and baits to attract them."

Then there are, of course, the pests such as the greater wax moth, Galleria mellonella. This moth slips in at night to honey bee colonies and lays its eggs. The bees struggle to remove the larvae.  Beekeepers struggle with control of the  tell-tale evidence--damaged combs.

The honey bee bible, The Hive and the Honey Bee (Dadant Publication), says the wax moth female "produces less than 300 eggs during her life span of 3 to 30 days, but a few lay as many as 2000 eggs. Mated females fly to beehives one to three hours after dark, enter, and lay eggs until they leave shortly before daylight."

Sneaky little critters!

The Hive and the Honey Bee authors relate that "the presence of the wax moth larvae usually signals a major problem such as queenlessness, an infectious disease, poisoning and starvation."

Greater wax moths are probably not what the organizers of National Moth Week, founded by two naturalists in East Brunswick, N.J., had in mind when they launched this special week! (Unless, of course, they were anglers; the larvae make good fish bait!)

Wax moth larvae and a hive beetle (top left). (Photo by Kathy Keatley Garvey)
Wax moth larvae and a hive beetle (top left). (Photo by Kathy Keatley Garvey)

Wax moth larvae and a hive beetle (top left). (Photo by Kathy Keatley Garvey)

An infestation of wax moth larvae. (Photo by Kathy Keatley Garvey)
An infestation of wax moth larvae. (Photo by Kathy Keatley Garvey)

An infestation of wax moth larvae. (Photo by Kathy Keatley Garvey)

Posted on Wednesday, July 23, 2014 at 5:50 PM

Plant science students earn top honors at UC Davis Weed Day

From the Fresno State website Jul 18, 2014  by


A team of three Fresno State plant science students took first place in the weed identification category at the 58th annual Weed Day seminar hosted by University of California, Davis.

Seniors Sarah Parry of Sonora, Isaac Giron of Terra Bella and Mala To of Cambodia correctly identified 17 of 20 weeds to win the contest among almost 200 participants on July 10.  A fourth team member, graduate student Rama Paudel of Nepal, won second place.

They prepared under the tutelage of Dr. Anil Shrestha, professor of weed science in the Plant Science Department of the Jordan College of Agricultural Sciences and Technology at Fresno State.  Fresno State's team was accompanied by Steve Wright, farm adviser for the University of California Cooperative Extension in Tulare.

Each year, Weed Day brings together pest control advisers, farm advisers, chemical company cooperators, college faculty and students and regulatory officials to learn about current weed science research at UC Davis.

For the contest portion, contestants were asked to identify 20 different types of weeds during a tour of current weed research plots at UC Davis. The plots involved herbicide research in annual fruit and vegetables crops, crop safety and herbicide symptomology demonstrations, aquatic weeds and grassland weed invasion and restoration research.

The Fresno State students were invited to a dinner after the seminar for one-on-one interaction with UC Davis weed science graduate and post-doctoral students, extension specialists and professors.

“It was a great experience that opened my eyes to new opportunities in weed science and it has encouraged me to pursue my master's degree,” Parry said. “I'm excited to see what the future has in store.”

To said, “I was able to utilize my prior knowledge that I learned from Dr.  Shrestha's weeds class to successfully help me identify the various weeds in the Weed ID Challenge.”

For more information, contact  Shrestha at ashrestha@csufresno.edu.

Fresno State students with Weed Day 2014 Chair Brad Hanson

(Copy by Akyia Westley, University Communications news assistant.)

Original source

Posted on Wednesday, July 23, 2014 at 1:57 PM
Tags: announcement (109), students (1)

Using solar tents to inactivate invasive weed seeds

Graphic by Cynthia Stapleton, adapted from Journal of Pest Science 85:17-21

In the backyard or in the wild, roguing (selectively pulling or cutting weed plants) and herbicide spot treatments can help prevent small patches of invasive weeds from becoming large infestations. However, herbicide applications may be of little value...

Posted on Wednesday, July 23, 2014 at 10:00 AM
Tags: solar tents (1), solarization (4), weeds (12)

Next 5 stories | Last story

Webmaster Email: mdhachman@ucdavis.edu