Extension Offers Weed Control Tips

7/6/2013 7:00 AM
By Philip Gruber Staff Writer

LANDISVILLE, Pa. — Extension weed control scientists Bill Curran and Dwight Lingenfelter led two seminars on their favorite subject last week at Penn State’s Southeast Research and Extension Center.

The first was the Agronomic Weed Control Tour in the evening on June 26. This highly technical event was peppered with the five-syllable names of organic compounds and focused on the results of the two researchers’ herbicide trials at the university’s Landisville laboratory farm and other sites around Lancaster County.

After discussing the testing, Curran encouraged the participants to inspect the tested fields for themselves.

Curran cut the tour short after thunder and lightning rolled in from the west. A windy torrential downpour forced the participants to huddle on one side of the tour wagons as they headed back to the barn for dinner.

The summer sun and heat returned the next day, however, for the Farming for Success field day. Curran and Lingenfelter spoke at the same field, but this time they spoke about pigweed and marestail, two of the most problematic weeds for crop farmers at the moment.

Agronomic Weed Control Tour

The 64 tested herbicides were generally effective for weeds in corn and soybeans, Curran reported. The pre-emergence spraying took place May 9, and the post-emergence applications on June 5.

The researchers did not find herbicide-resistant chickweed, but they found that groundsel is becoming more common.

Lingenfelter said the reduced-till corn herbicide trials benefited from getting a good rain right after planting. Harness came up short in broadleaf control, while Zidua and Sharpen only cleared around 80 percent of giant foxtail and large crabgrass.

In that trial, the Zidua/Verdict, Verdict, SureStart and Corvus/atrazine test plots showed 10 to 15 percent injury to the crops, including stunting, yellowing and leaf curling. Lingenfelter blamed the ALS (acetolactate synthase)-inhibiting properties of those chemicals.

According to the National Institutes of Health, ALS inhibitors prevent the creation of amino acids.

In a corn trial of market-leading products, Keystone, Instigate and Corvus achieved 90 percent grass control, while the other chemicals gave 95 percent control.

The Keystone, Corvus, Zidua/Verdict and Prequel plots had higher injury rates.

For soybeans, Curran and Lingenfelter highly recommended Bayer’s LibertyLink system. The product offered protection from lamb’s quarters and Canada thistle.

Marestail is increasingly showing ALS-inhibitor resistance, so LibertyLink, with an 85 to 90 percent effectiveness rate, is the go-to product for post-emergence marestail control, Curran said.

There were two products Curran could not recommend for soybeans. He found that Cadet caused leaf burns, while Flexstar caused 15 percent injury.

In off-site wheat testing, Powerflex, Maverick and Osprey reduced grass by 85 percent, while most other products had at least 90 percent effectiveness.

The 2013 trials included several new products. Curran and Lingenfelter researched versions of FMC’s Anthem (pyroxasulfone and fluthiacet) with and without atrazine. Anthem is for corn or soybeans.

Valent’s Fierce, used for corn, also includes pyroxasulfone but pairs it with flumioxazin.

Zidua is a straight pyroxasulfone from BASF to which the researchers dedicated a no-till soybean trial.

Optill is also from BASF and combines that company’s existing products saflufenacil (Sharpen) and imazethapyr (Pursuit). Optill Pro adds dimethenamid-p (Outlook) to the mix.

Two new DuPont products were tested. Instigate combines rimsulfuron with mesotrione. Trivence uses chlorimuron, metribuzin and flumioxazin.

Monsanto’s new acetochlor branded as Warrant was also investigated in the trials.

Penn State will hold another weed and insect tour on Wednesday, July 10, at the school’s Agronomy Research Farm in Rock Springs, Pa. For more information on that event, call Lisa Crytser at 814-865-2543 or Bill Curran at 814-863-1014.

Farming for Success

The redroot variety of pigweed is the most common variety of that problem weed in Pennsylvania, Curran said. Other varieties that have been common include smooth pigweed and spiny amaranth. Six of pigweed’s nine species are present in the state.

Palmer pigweed, common in Delaware, and waterhemp, the bane of Illinois and Indiana, are nearly identical and of special concern because they are Roundup-resistant.

Pennsylvania has fared better than some of the Midwest states have with pigweed so far because Pennsylvania has more crop diversity, but “it’s just a matter of time” until Palmer and waterhemp invade the state, Curran said.

Curran expects Palmer pigweed to appear in the area in two to three years. He asked farmers to contact their Extension office is they find the resistant varieties in their fields.

Palmer pigweed has a longer petiole (stalk connecting the leaf with the main plant stem) than redroot pigweed.

Waterhemp is distinguished by having leaves that meet the stem in a whirl pattern rather than at common nodes.

Compared with redroot, which has male and female parts on the same plant, waterhemp plants are either male or female. Waterhemp also has spikelike flowers that can grow a foot long.

Some varieties of pigweed may show resistance to ALS inhibitors, so to keep pigweed out of soybeans, Curran said farmers are relying on PPO (Protoporphyrinogen oxidase) inhibitors.

According to the USDA, PPO inhibitors interrupt chlorophyll production and cause the harmful buildup of oxygen in plant cells.

Of the PPO inhibitors, Valor has residual effects, while Sharpen does not.

Pigweed does not seem to have a preference for tilled or no-till soil, Curran said.

Lingenfelter said that marestail, a relative of the aster flower, is hard to control because its seeds can get caught in the wind currents and float for miles.

Also called horseweed, marestail has two germination periods, starting in roughly September and late March, and can grow 3 to 6 feet tall.

Roundup hurts but does not kill marestail. Applying that herbicide causes the plant to grow multiple stems.

Lingenfelter said using 2,4-D ester in burndown is a farmer’s “main shot” at controlling marestail, though Classic (chlurimuron) can give residual protection.

FirstRate is an effective post-emergence spray in the Mid-Atlantic, but Lingenfelter said that it is no longer effective in other parts of the country.

As he and Curran did at the weed control tour, Lingenfelter supported using LibertyLink soybeans with LibertyLink herbicides.

Though these beans are generally more expensive than other varieties of soybeans, the effectiveness at marestail control can boost yields enough to outweigh the expense, he said.


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