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Chateau effective on alfalfa weeds

Chateau SW herbicide performed well against broadleaf weeds in University of California trials on established alfalfa during 2008 and 2009, although it required a tank-mixed companion material for grassy weeds, according to Kurt Hembree, Fresno County farm advisor.

“We found it to be a good fit for dormant alfalfa,” Hembree told an alfalfa and forage field day at the Kearney Agricultural Center at Parlier.

After a stand has gone through its first dormant season and has up to 6 inches of regrowth, “that’s a good time to start the program with it,” he said.

Approved for alfalfa in California on Oct. 1, 2008, the label for Chateau calls for not more than 4 ounces per acre during a single application and not more than 8 ounces per acre during a single growing season.

“If you make a split application, you have to wait 60 days from the first treatment in October-November until the second in January-February. It takes only about a quarter-inch of rainfall to set it,” he added.

Since the product has a 25-day preharvest interval, a treatment in mid-February could be followed by a cutting around March 15.

Among the weeds Chateau controlled in Hembree’s trials are groundsel, cheeseweed, henbit, horseweed, and chickweed. He said although fiddleneck is not on the label, he saw good control of it also.

Chateau should not be used with any type of emulsified concentrate material or adjuvant unless the treatment is made in the fall, when an herbicide such as paraquat can be tank-mixed with it to burn down existing weeds, Hembree said.

“Chateau does have some burn-down activity, but it’s not going to be a stand-alone material in most cases. There’s no question we will need tank-mixes to get the broader spectrum.”

It works well and is convenient, he continued, in ground water protection areas because it does not leach and doesn’t require the permits required for diuron products. It also has a shorter plant-back restriction than Velpar.

Hembree cautioned that Chateau needs to be applied with at least 30 gallons of water per acre for good ground contact.

“It’s like Goal, and if you lay it down and then disturb the soil, you lose activity. You’ll want to use Turbo TwinJet or TwinJet nozzles to increase coverage. And be aware that the more you drive over it, the more risk of kicking up the soil.”

Although dodder is not listed on the Chateau label, Hembree observed activity of the product against the parasitic weed.

“In a seed-alfalfa field we sprayed it as a contact material on less than 6 inches of regrowth in mid-June when the dodder was attached to the crown of the plant. We got about 95 percent control when we used 2 to 4 ounces per acre with a surfactant.”

Corn leafhopper has been an increasing concern in SJV cornfields during the past several seasons, but Albert Newton, staff research associate at KAC, said the insect, which vectors corn stunt, has been slow in making its appearance in new corn fields this year.

Typically, the hopper, distinguished by its tan color and about an eighth inch long, can be seen in the whorls of corn plants by September. Corn stunt is caused by Spiroplasma kunkelii, a complex of pathogens, and its symptoms are multiple ears that fail to fill and leaves that turn reddish in the fall.

Newton, who has worked for many years with Charles Summers, UC entomologist, said they don’t know why there are fewer of the hoppers. “It could be weather, or it could be they did not find favorable overwintering sites in winter cereals, which were planted later this year.”

USDA tests of sample leaves during the past several seasons, Newton added, confirmed that maize bushy stunt, another leafhopper-vectored disease, also occurs in the Valley.

In scouting fields in Merced County this year, Newton said he discovered Sipha maydis, also known as barley aphid, a species not previously detected in the SJV.

Common in Europe, the Middle East, and Central Asia, it transmits barley yellow dwarf. It was first detected in Santa Barbara County, but showed up later in Merced, Stanislaus, San Joaquin, and Fresno counties. It is not considered a problem in corn.

“It has been found to do significant feeding damage to wheat and barley in Argentina. If you follow corn with winter cereals, it could become a problem here,” Newton said.

Pointing to the various levels of genetic resistance to Septoria tritici, or stripe rust, in wheat varieties planted in California, Steve Wright, Tular County farm advisor, said growers are adjusting.

“We’ve seen a change in the varieties of wheat as they’ve slowly shifted over the years from those that are susceptible to stripe rust to those that are resistant to it.”

The 2009 season, with its dry and warm spring, saw low pressure from stripe rust and leaf rusts, although spring frosts in some areas cut yields by as much as 30 percent.

Stripe rust resistance ratings in 2009 statewide variety trials showed Cal Rojo, Redwing, and Ultra as the top three among the resistant group.

PR 1404, Blanca Royal, and Trical 118 were the top moderately resistant. Dash 12 and Duraking were in the moderately susceptible/moderately resistant category.

Susceptible/moderately resistant was Joaquin. Moderately susceptible were Clear White and RSI 59. In the susceptible group were Yecora Rojo, Blanca Grande, Kronos, Topper, and Orita.

Repeating his perennial message, Wright recommended growers choose more than one variety or grain type to reduce the impacts of weather, disease, harvest schedules, and economics.

“First and foremost,” he said, “select and plant varieties with good resistance along with high yield potential. Secondly, a well-timed fungicide application was shown to reduce the yield loss even in resistant varieties when weather conditions favor the disease.”

Wright reminded the participants that stripe rust develops new races to overcome existing resistance.

The best silage varieties can also be the high yielding grain varieties with high protein, resistance to disease and resistance to lodging and early maturity.

A dual-purpose variety gives options particularly when grain prices are high and silage prices are low, or vice versa, or when water may be limited, he said.

TAGS: Management
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