Wilmington, Delaware-based Belchim Crop Protection USA has received a 2ee recommendation for use of Tenchu 20SG in Texas and Louisiana to control rice delphacid, should it appear in damaging numbers again this season.
The insecticide already has a full Section 3 registration for use in rice to control rice stink bugs.
After a decades-long absence, rice delphacid — also referred to as a rice planthopper — was confirmed in 2015 in several ratoon fields south of Houston. It was not reported during the 2016 and 2017 seasons but was again confirmed in a handful of Texas ratoon fields in 2018.
So far this season, Dr. Mo Way, a Texas A&M AgriLife entomologist in Beaumont, said he had heard of no reports of the invader as of Aug. 15. But he has put the word out to fellow entomologists as well as consultants in Texas and South Louisiana to be on the lookout for the pest.
In 2018, the first report came from Galveston County in a ratoon crop of Texmati, and the grower reported patches of hopper burn. Way subsequently found rice delphacid in Brazoria, Matagorda and Jackson counties and possibly Wharton County.
The recurring pest came to light in 2015 when a consultant reported symptoms of hopper burn — bronzing of the plants caused by planthopper feeding — in a ratoon rice field south of Houston. Subsequent inspections and sampling of rice fields using insect sweep nets found rice delphacid in five counties: Brazoria, Jefferson, Wharton, Colorado and to a lesser extent, Jackson.
Results from a non-randomized, small-plot insecticide experiment Way conducted in a commercial field in Brazoria County suggested pyrethroids were not effective, but dinotefuran was. In fact, the trials in 2015 found pyrethroids flared rice delphacid populations. Dinotefuran, a neonicotinoid, is the active ingredient in Tenchu 20SG.
Observations of infested fields found no difference in susceptibility among inbred and hybrid cultivars.
South American experience
In December 2017, Way traveled to the International Center for Tropical Agriculture (CIAT) in Cali, Colombia, to observe first-hand this insect and the virus it can carry that causes a severe rice disease called “hoja blanca.”
Translated, that means white leaf. Because the pest is endemic in that country, researchers can carry out field trials. For growers there, developing resistant varieties is the only economic solution.
The rice delphacid uses a piercing-sucking mouth part to feed on plant phloem — plant tissue that transports nutrients, including sugar, made during photosynthesis to parts of the plant where they’re needed.
The planthopper, roughly 1/4 inch long, damages rice plants through feeding as well as egg-laying. In addition, it is an important vector of a virus that causes hoja blanca, which can cause up to 50% crop loss in Central and South America.
Known scientifically as Tagosodes orizicolus, rice delphacid was reported in rice-growing areas of the Southeast United States from 1957-1959 and from 1962-64. During that time, hoja blanca was found in Florida, Louisiana and Mississippi. But because the vector never established, the disease has not been reported since then.