Begin scouting early to catch the pest before it can cause significant yield loss.
• By Vicky Boyd,
For three out of the past five years, growers and consultants have found the rice planthopper in scattered fields of second-crop rice south and west of Houston, Texas.
Dr. Mo Way, Texas A&M AgriLife Research entomologist, has told growers and consultants annually to be on the lookout for this ¼-inch-long pest, and his warnings appear to have paid off. The infestations in 2019 were caught early enough that growers were able to apply an insecticide and obtain good control that prevented yield loss.
“There are no economic thresholds, so I think the farmers did the right thing (to treat) because once they pop up, they can really expand quickly,” Way says.
Cliff Mock, an Alvin, Texas, crop consultant, says he specifically looked for the rice plant-
hopper last season in second-crop rice and only found very low populations.
“If I would not have been really looking for (planthopper), I would not have found it,” Mock says. “I would not have found it if I were walking across a field during normal stinkbug scouting. I had to work to find it.”
Last season, Mock says he could make 10 sweeps of a field with his net and pick up no more than two plant-
hoppers. Often times, the sweeping wouldn’t pick up any.
That compares to 2015, the first year the pest was confirmed in Texas, when growers and consultants were caught by surprise with damaging second-crop rice infestations. Back then, Mock says, he could make five sweeps and catch more than 2,000 planthoppers.
“We had them (in 2019), there was no doubt,” he says. “They just never reached the populations they did a couple of years ago.”
When he found planthoppers, Mock recommended Endigo ZC insecticide. The premix of thiamethoxam and lambda-cyhalothrin received a Section 18 emergency use exemption from the Texas Department of Agriculture for the pest. The Section 18 expires Nov. 9, 2021.
Rice farmers in Texas also can apply Tenchu 20SG to control the planthopper, Way says. This use is legal under a 2(ee) Recommendation because Tenchu 20SG already had a label to control rice stink bug. But farmers cannot apply Endigo ZC to control rice stink bug because it is not registered for that pest.
Planthoppers can damage two ways
The rice planthopper — also known as the rice delphacid — can damage rice by direct feeding, but it also can carry the virus that causes the “hoja blanca” disease. In both 2015 and 2018, Way sent dead, preserved delphacid samples to Dr. Ismael Badillo-Vargas, Texas A&M AgriLife Research virologist, for analysis. None tested positive for the hoja blanca virus. Samples collected in 2019 are still being analyzed for the virus.
In Colombia and other South American countries where the insect vector and disease are present, the only way growers are able to successfully produce a rice crop is by using resistant varieties.
In December 2017, Way traveled to the International Center for Tropical Agriculture (CIAT) in Cali, Colombia, to observe first-hand the relationship between the insect and hoja blanca. It was there he learned of CIAT’s program to breed delphacid-resistant varieties.
Delphacid infestation symptoms
A delphacid infestation starts as scattered circular spots of rice that are yellowing and/or have dying foliage. Often referred to as hopper burn, the discoloration is caused by excessive direct feeding by both nymph and adult planthoppers.
Because these symptoms also could be caused by diseases, such as narrow brown leafspot or Cercospora, Way says you need to sweep the area with a net to confirm the presence of planthoppers.
“You can’t just look at the field from the pick-up,” he says. “You need to get out in the field to check with a sweep net. In a heavily infested field, it’s really obvious with desiccated and bronze spots.”
Unlike some insect infestations that start at the edge of fields and move inward, Way says delphacid infestations will be scattered throughout the field.
“There’s no pattern,” he says. “Because they’re strong fliers, they’ll be in the middle and on the edge.”
As the infestation continues, the spots expand, eventually coalescing into even larger patches.
“So it’s really critical that the farmers get in the field and scout,” Way says. “They should be looking at it right from (plant) emergence on. I’m not sure why we’re only seeing it in the second crop.”
He bases his recommendation for early scouting on what he learned from Colombian colleagues.
Keep your eyes peeled
As with the Texas delphacid discoveries in 2015 and 2018, the 2019 finds were brought to Way’s attention by consultants who found the pest while scouting fields.
All of the infestations have been south and west of Houston, and none have been found to the east. The pest was not found in Texas during 2016 and 2017.
Whether the rice delphacid will return during the 2020 season is a big unknown, Mock and Way say. After the 2015 infestation, they monitored what had been a severely infested rice field and ryegrass pastures adjacent to that field over the 2015-16 winter and during the 2016 season. Ryegrass is a pretty good host, although rice is preferred, Way says.
They didn’t find a single planthopper.
Testing for varietal tolerance
Way also is working with Texas A&M rice breeder Dr. Dante Tabien and Louisiana State University AgCenter breeder Dr. Adam Famoso to obtain seeds from public inbred varieties. Those will be sent to Dr. Maribel Cruz, an entomologist at CIAT, so she can rate them for field tolerance to rice delphacid feeding.
In exchange, she will send some of their resistant varieties to Tabien and Famoso, so they can begin incorporating the resistance trait into their breeding programs.
The planthopper, known scientifically as Tagosodes orizicolus, 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 in the United States since then.
If you suspect a rice delphacid infestation, contact your state Extension entomologist. If you grow rice in Texas and suspect the pest, contact Way at 409-239-4265 or firstname.lastname@example.org.