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Sheath blight control, stink bug resistance study

An effective fungicide program is necessary for sheath blight and help from the Texas Department of Agriculture and the Environmental Protection Agency may be needed to help control the stink bug, said two Texas AgriLife researchers at the Texas Plant Protection Association annual conference in College Station last December.

Sheath blight is the most economically important disease and the rice stink bug is becoming increasingly difficult to control for Texas rice growers.

Young-Ki Jo, department of plant pathology and microbiology, said management practices such as rotation and selection of resistant varieties may reduce severity of sheath blight.

“However, adopting these cultural practices frequently does not eliminate the need for an effective fungicide program.” Rice farmers typically make at least one pre-emptive application of a recommended fungicide per growing season.

Last year Young-Ki evaluated 17 fungicide treatments for sheath blight control on main and ratoon crops.

“Inoculation of Rhizoctonia solani (the causal agent for sheath blight) in field plots produced an average 6 to 7 disease severity level rating in untreated check plots. Infection caused lesions that affected the lower two-thirds to three-fourths of the sheath area and the lower two-thirds of the leaf blades.”

He said a tank mix of strobilurin and trizole fungicides consistently provided the best control in both the main and the ratoon crop. That mix “also produced significant yield increases in the ratoon crop compared with the untreated control."

“Most fungicides significantly reduced sheath blight and promoted ratoon stands. Selecting the correct fungicides will be the key to control. Managing disease in the main crop is important for the ratoon crop.”

He said sheath blight survives in the soil. “Mycelium begins growing on the stem and as conditions become more favorable continues to grow.” The disease “causes little yield loss, but affects stands in a ratoon crop.”

Young-Ki said other diseases that affected Texas rice in 2009 include false smut, leaf smut, brown leaf spot, narrow brown leaf spot, and panicle blight. He said some varieties are susceptible to narrow brown leaf spot. “It may be severe in a ratoon crop.

“We see a lot of panicle blight (a bacterial disease) in Texas.” High temperatures (above 90 degrees) during the growing season favor the disease.

Future research efforts will include fungicide updates, studies on main crop production efficiency and the effect on improving the ratoon crop. He’s also looking at panicle blight management with seed treatment and biological control techniques.

M.O. Way, Texas AgriLife Extension and research entomologist, said the rice stink bug “is becoming increasingly difficult to control in Texas rice fields. Pyrethroids are commonly applied to control this grain-feeding pest.”

He said Texas farmers average three pyrethroid applications a year to control rice stink bugs. “Some farmers treat more frequently.”

He began work last year with entomologists from Arkansas, Louisiana and Missouri to monitor for possible resistance development in the stink bug. They collected rice stink bugs from four Texas locations – Beaumont, East Bernard, Ganado, and Round Mott – as well as from locations in the other states.

“Compared to data from other states, rice stink bugs are much harder to control in Texas,” Way said. “The average LC 50 for all four Texas populations is about three times higher than the average for the other states.”

Way will use this information to “help convince TDA and EPA to approve another Section 18 for Tenchu 20SG for Texas this year. This systemic insecticide has excellent residual activity against rice stink bug and received positive reports from Texas farmers and crop consultants in 2008 and 2009."

He said Tenchu 20SG controls the rice stink bug and some grasshoppers.

Way also reported on Cruiser Maxx seed treatment for water weevil, chinch bug, thrips, leaf hoppers and black bugs. “It does not control stalk borers, but it does control chinch bugs,” Way said.


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