I didn’t set out yesterday knowing the day would play out like it did, but in honor of Cinco de Mayo, we wound up with five insects to discuss. All of which we found in rice fields on Cinco de Mayo.
I’ve continued to get a lot of calls about some strange injury in rice – chewing at the base of plants, digging/tunnels in the soil, and declining stands. After lots of head scratching, research, and some conversations in the halls of the “ivory tower” with my colleagues, we finally started to put it together. All signs pointed to sugarcane beetle. A new Ph.D. student, Karen Nix, and I headed to the field in Jefferson-Davis Parish to scout with County Agent Barrett Courville and Crop Consultant Benet Augustin. I told Benet he’s going to get a prize for finding the most odd insects this season. I’m certain he’d rather do without that recognition…
The first thing Benet had described in this field was a reduction in stand in hybrid rice treated with CruiserMaxx. Cruiser had been used because of historical problems with chinch bugs in this particular rice field.
As we walked into the field, it was not difficult to find plants with soil disturbed at the base of the plant.
We dug around the base of the plant and in many places were able to quickly locate a large black beetle.
The sugarcane beetles are injuring the rice by chewing at the soil line in the crown of the plant. Some of the plants are dead or dying, while others may still recover by tillering.
I called Dr. Tara Smith (Sweet Potato Extension Specialist and Entomologist) to learn more about sugarcane beetle biology. Tara studied this insect for her dissertation research. The symptoms we are seeing in rice are very similar to what you will find in field corn (where the sugarcane beetle is causing some injury in Arkansas this season). I discussed treatment options with Tara. She confirmed that Thiomethoxam (the active ingredient in CruiserMaxx) does not have good activity against this insect.
Treatment recommendations are tied to the biology and behavior of the insect. Sugarcane beetles overwinter as adults, and then move into field crops and attack plants at the soil line. During this time of year, they will be flying, mating and laying eggs. Flying usually occurs from dusk to 10 pm. Thus, we advised treating with a pyrethroid sometime around dusk to increase the odds of insecticide coming into contact with the beetles – a spray applied during the day would probably be less effective because the beetles are down in the soil. Alternatively, bringing a permanent flood as soon as possible should also prevent further injury. In this field, the rice is not ready for a permanent flood.
I’ve never observed these insects in rice, and apparently, they are a rare problem. Is anybody else finding these in rice fields?
We moved on to another field after we confirmed the sugarcane beetle problem. This field was suspected to be infested with colaspis larvae. This was a field of hybrid rice which did not have an insecticide seed treatment applied. It was drilled into a stale-seedbed, which was planted in soybeans in 2010. Sure enough, we found a severe infestation of colaspis larvae that was reducing the stand.
It was not difficult to find colaspis feeding in the soil anywhere from 1/2 inch to 3 inches below the soil line.
It’s easy to see how these little larva can inflict injury on the roots of a rice plant when you look at the large size of their chewing mouthparts (mandibles).