Rice Farming

Grape colaspis is one of those unpredictable pests that can wreak widespread damage one year and cause minimal problems the following season. But knowing when and how to protect rice can help you manage the risk.

“Grape colaspis has been in Arkansas for nearly as long as there has been rice,” says John Bernhardt, a University of Arkansas entomologist. “Each year is different and the problem may be minimal, severe or somewhere in between. The problem may be local and scattered or it may be local and widespread.

“Consequently, I have years when there are no reports of severe damage and years when there are numerous reports of damage.”

Know the pest’s life cycle
Adult grape colaspis are smallish, oval golden brown beetles about 3/16 inch long. But it’s the larvae, or grubs, that actually damage rice. The 1/4-inch-long larvae have a brown head and can be differentiated from other white grubs by using a 10X hand lens. Grape colaspis larvae, sometimes called lespedeza worms, have abdominal segments with ventral fleshy projections bearing a few hairs on the ends.

The damage cycle begins when larvae from the previous year’s soybean crop move below the soil’s freeze line to overwinter. In the spring, the larvae become active and move closer to the surface.

If rice has been planted, the larvae will feed on and damage newly germinated seeds, tender young plants and roots. If the infestation is severe, they can easily remove all roots.

Another important feeding site is on the plant stem between the seed and soil surface. This type of damage, or girdling, causes plant stress by reducing nutrient and water intake to the plant above the ground. Plants with root damage often recover, but girdling damage often results in the death of plants.

“Problems with grape colaspis are most frequent on silt loam soils, especially those that are a little sandy,” says Bernhardt, who’s with the Rice Research and Extension Center in Stuttgart. “Rice on heavy clay soils does not appear to have the same problems.”

Chemical control
Fipronil seed treatment, marketed under the trade name Icon 6.2FS by Aventis Crop Science, is currently the only insecticide registered to control grape colaspis. Product use varies greatly, depending on the frequency of occurrence, soil type and rotation schedules.

Growers who produce host crops, such as soybeans or other legumes, for one or more years on soil conducive to grape colaspis must decide whether $12 to $15 per acre for a fipronil seed treatment is an economical insurance policy.

“I have been unable to conduct controlled experiments with the grape colaspis to answer many of the biological and ecological questions about the life cycle and alternate control methods,” Bernhardt says. “However, I have conducted large field tests and have shown that Icon gives excellent control.”

Cultural control
Some cultural practices may help protect rice against this problem. To reduce stand loss, Bernhardt advises growers to never allow the plants to become water stressed.

“Timely rains help, but flushing the rice may also be necessary,” he says. “I am sure tillage helps. Some growers try deep tillage in the fall and spring to disrupt the successful overwintering of larvae. Timely normal spring cultivation, not deep tillage, may be helpful if larvae have already left overwintering status and are in the upper soil.”

Seed treatment put to the test
But cultural controls may not be enough, especially in a severe infestation, like that of Scott Young of Portland, Ark. With his cooperation, Bernhardt conducted large-scale field tests with fipronil to determine its effectiveness under extreme conditions.

“Scott’s problems with grape colaspis were the worst I have ever seen,” Bernhardt says. “My tests results showed Icon did great.”

Young first noticed a problem 10 years ago after planting a rice field in the opposite direction from the previous year’s soybean crop.

“The rice was dying right down the still visible bean rows,” he says. “I called my Extension agent and we found these really little beetles eating on the rice.”

While Bernhardt was trying to find some badly infested fields to test Icon, Young called to say he had a major problem with grape colaspis beetle larvae. The following season, 300 acres were planted with fipronil and 300 were left untreated.

“We found there was just a marked difference right down to the drill row between the treated and untreated fields,” Young says.

He is now a fipronil fan and likes the added control it provides for rice water weevil in flooded rice.
“Icon is a significant investment, but I’m not apprehensive about spending the money since it works so well,” he says.

Besides vital insect control, Young says labor costs have gone down since the need to scout fields has dropped and yields have improved.

For questions or comments about this article, contact Rice Farming editor Vicky Boyd at (209) 571-0414 or vlboyd@att.net.

Hotlinks
University of Arkansas Extension Entomology—Grape colaspis
http://www.aragriculture.org/weedinsctdis/insects/rice/insects/grapecolaspis.asp

University of Missouri Extension rice guide—insect pests
http://aes.missouri.edu/delta/muguide/ricegsh.stm

Here one year, gone the next Learn when and how to protect your crop from unpredictable grape colaspis
By Amy Roberts Contributing Editor
Grape colaspis is one of those unpredictable pests that can wreak widespread damage one year and cause minimal problems the following season. But knowing when and how to protect rice can help you manage the risk. “Grape colaspis has been in Arkansas for nearly as long as there has been rice,” says John Bernhardt, a University of Arkansas entomologist. “Each year is different and the problem may be minimal, severe or somewhere in between. The problem may be local and scattered or it may be local and widespread. “Consequently, I have years when there are no reports of severe damage and years when there are numerous reports of damage.” Know the pest’s life cycle Adult grape colaspis are smallish, oval golden brown beetles about 3/16 inch long. But it’s the larvae, or grubs, that actually damage rice. The 1/4-inch-long larvae have a brown head and can be differentiated from other white grubs by using a 10X hand lens. Grape colaspis larvae, sometimes called lespedeza worms, have abdominal segments with ventral fleshy projections bearing a few hairs on the ends. The damage cycle begins when larvae from the previous year’s soybean crop move below the soil’s freeze line to overwinter. In the spring, the larvae become active and move closer to the surface. If rice has been planted, the larvae will feed on and damage newly germinated seeds, tender young plants and roots. If the infestation is severe, they can easily remove all roots. Another important feeding site is on the plant stem between the seed and soil surface. This type of damage, or girdling, causes plant stress by reducing nutrient and water intake to the plant above the ground. Plants with root damage often recover, but girdling damage often results in the death of plants. “Problems with grape colaspis are most frequent on silt loam soils, especially those that are a little sandy,” says Bernhardt, who’s with the Rice Research and Extension Center in Stuttgart. “Rice on heavy clay soils does not appear to have the same problems.” Chemical control Fipronil seed treatment, marketed under the trade name Icon 6.2FS by Aventis Crop Science, is currently the only insecticide registered to control grape colaspis. Product use varies greatly, depending on the frequency of occurrence, soil type and rotation schedules. Growers who produce host crops, such as soybeans or other legumes, for one or more years on soil conducive to grape colaspis must decide whether $12 to $15 per acre for a fipronil seed treatment is an economical insurance policy. “I have been unable to conduct controlled experiments with the grape colaspis to answer many of the biological and ecological questions about the life cycle and alternate control methods,” Bernhardt says. “However, I have conducted large field tests and have shown that Icon gives excellent control.” Cultural control Some cultural practices may help protect rice against this problem. To reduce stand loss, Bernhardt advises growers to never allow the plants to become water stressed. “Timely rains help, but flushing the rice may also be necessary,” he says. “I am sure tillage helps. Some growers try deep tillage in the fall and spring to disrupt the successful overwintering of larvae. Timely normal spring cultivation, not deep tillage, may be helpful if larvae have already left overwintering status and are in the upper soil.” Seed treatment put to the test But cultural controls may not be enough, especially in a severe infestation, like that of Scott Young of Portland, Ark. With his cooperation, Bernhardt conducted large-scale field tests with fipronil to determine its effectiveness under extreme conditions. “Scott’s problems with grape colaspis were the worst I have ever seen,” Bernhardt says. “My tests results showed Icon did great.” Young first noticed a problem 10 years ago after planting a rice field in the opposite direction from the previous year’s soybean crop. “The rice was dying right down the still visible bean rows,” he says. “I called my Extension agent and we found these really little beetles eating on the rice.” While Bernhardt was trying to find some badly infested fields to test Icon, Young called to say he had a major problem with grape colaspis beetle larvae. The following season, 300 acres were planted with fipronil and 300 were left untreated. “We found there was just a marked difference right down to the drill row between the treated and untreated fields,” Young says. He is now a fipronil fan and likes the added control it provides for rice water weevil in flooded rice. “Icon is a significant investment, but I’m not apprehensive about spending the money since it works so well,” he says. Besides vital insect control, Young says labor costs have gone down since the need to scout fields has dropped and yields have improved. For questions or comments about this article, contact Rice Farming editor Vicky Boyd at (209) 571-0414 or vlboyd@att.net. Hotlinks University of Arkansas Extension Entomology—Grape colaspis http://www.aragriculture.org/weedinsctdis/insects/rice/insects/grapecolaspis.asp University of Missouri Extension rice guide—insect pests http://aes.missouri.edu/delta/muguide/ricegsh.stm
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