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Infrequent insect, new weed highlight sugar field day

(Blake Wilson at LSU Sugarcane Field Day 20162016/07/21) ST. GABRIEL, La. – Louisiana sugarcane growers and consultants heard about a sporadic insect pest and a new, unidentified weed on July 20 during the annual field day at the LSU AgCenter Sugar Research Station.

The West Indian cane fly has made an appearance in Louisiana sugarcane fields this year for the first time since 2012, said AgCenter entomologist Julien Beuzelin.

Although it’s generally not considered a pest, the cane fly this year is causing serious damage in sugarcane fields. "It sucks sap from leaves and exudes honeydew that leads to sooty mold,” Beuzelin said.

The insect was first identified in Louisiana in 1944 and has appeared in large numbers in 1969, 1997 and 2012. Because its appearance is so sporadic, entomologists haven’t established economic thresholds in the past, he said.

This year, the AgCenter recommends considering applying labeled insecticides when populations exceed 30 nymphs per leaf based on experiences from 2012. "We have a Section 18 crisis exemption declared by the Louisiana Department of Agriculture and Forestry to use Strafer or Intruder this year,” Beuzelin said.

Another emerging problem is a Chinese weed with no English name, said AgCenter weed scientist Al Orgeron.

It appears to be a nightshade species. Last year we thought it was Eastern black nightshade, but it isn’t, he said. A sample was sent to a taxonomist at the University of Tennessee, who identified it as an invasive species from China.

It can be controlled with dicamba or Callisto and atrazine, Orgeron said.

Orgeron also is looking at a new herbicide Armezon for post-emergence use to suppress bermudagrasss. The chemical, which appears to be effective when cane is actively growing, is not currently labeled for use in sugarcane.

Mexican rice borer has been moving steadily across the Louisiana sugarcane region from west to east, said AgCenter entomologist scientist Blake Wilson. "But it has not yet emerged as a damaging insect to sugarcane,” he said.

Traps at sugar mills during last year’s harvest did not detect any human-aided movement of the borer from production fields, he said.

Diseases affecting sugarcane this year include brown rust, smut and mosaic, said AgCenter plant pathologist Jeff Hoy.

Rust overwintered well because of the mild winter. "Chemical control options include multiple fungicides,” Hoy said.

Hoy’s research is focusing on when and how to use fungicides and evaluating different chemical combinations.

Conditions are favorable for the spread of mosaic by aphids. "It’s a tough disease to deal with,” he said.

Two factors – planting resistant varieties and a healthy seedcane program – will help deal with potential problems, Hoy said.

Growers should rely on tissue culture-produced seedcane to control smut and "flush this disease out,” he said.

Matt Foster, a graduate student in the School of Plant, Environmental and Soil Sciences, told about his research with harvest aids on soybeans.

He recommended applying harvest aids when the beans are at growth state R-6.5 or when the seeds are at physiological maturity.

Sugarcane breeder Collins Kimbeng said he is screening parent material used in developing new varieties and has discovered 80 percent of the parents are resistant to mosaic.

He also is screening clones for resistance to smut, mosaic and leaf scald to develop new parent materials with resistance to those diseases.

The newest sugarcane variety, HoCP 09-804, was released this year from the U.S. Department of Agriculture Sugarcane Research Unit in Houma. "It’s one of the better varieties that have come through the breeding program for a number of years,” said sugarcane breeder Michael Pontif.

The new variety made it through the program on the strength of its high sugar content and stubbling ability, he said.

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