Bollworm Emergence Causing Problems in Texas Cotton07/11/2018
Cotton producers who planted Bt pest-resistant varieties in some parts of the state are seeing damage from bollworms, so vigilant monitoring and management may be necessary to prevent losses, said a Texas A&M AgriLife Extension Service expert.
Dr. David Kerns, AgriLife Extension integrated pest management state coordinator in College Station, said there has been a “huge” bollworm egg lay throughout much of the Upper Gulf Coast and central Blacklands areas. The bollworm in cotton, known as the earworm in corn and the headworm in sorghum, feed as larvae on cotton fruit and grain on corn and sorghum.
This pest represents one of the most damaging for Texas agricultural producers, Kerns said. Infestations are airborne, arriving with the migration of moths that lay eggs in the three crops. Over the last two weeks, large numbers of eggs have been spotted in cotton fields.
Kerns said the bollworms appeared to have moved into cotton primarily from the previous generation that had infested corn. It is thought the current bollworm generation has developed some resistance to some cotton Bt technologies by feeding on similar technologies in corn. Bacillus thuringiensis, referenced as Bt, is a spore-forming soil bacterium that produces protein crystals toxic to many types of insects.
“Bollworms have shown a lot of resistance the last few years, and they’re persisting this year,” Kerns said. “We’ve seen a lot of damage in fields that have Bt technology. All of the cotton Bt technologies had experienced some degree of failure, except for varieties containing Bt-Vip technology, which seems to be holding up very well.”
Bt cotton was genetically modified with resistance targeting tobacco budworm in 1996, Kerns said. Since then the primary pest of concern has shifted to the bollworm. Bt technology in cotton started with one toxin, then evolved to include two toxins and most recently three Bt toxins. The larvae that feed on the plant expressing the Bt die.
Current Bt in cotton is specific towards caterpillar pests and is harmless to beneficial insects, Kerns said.
But like many pests, the bollworms’ resistance to toxins has evolved as well, and the data demonstrates that bollworms have developed resistance to all the Bt toxins in cotton except the Vip toxin, he said.
Kerns said cotton varieties containing Vip technology also include two additional Bt Cry toxins, and the combination of these toxins appears to be working on bollworms.
“It appears that any variety with just two Cry toxins is having problems and those with the addition of Vip look good,” he said. “We’re seeing extensive damage in test plots, but cotton producers are aware of the problem and are treating cotton as needed to prevent yield loss.”
Kerns said dryland fields that received moisture bounced back well, but infestations could put yields in jeopardy if not properly managed.
Bollworm eggs typically hatch in three to four days, and the larval stage continues for almost two weeks, he said.
Most producers are monitoring for bollworm and staying on top of the situation in individual fields, Kerns said. But multiple egg lays mean producers in the area need to monitor and producers in the northern Blacklands need to be watching their fields closely as moths produced from corn begin to emerge there.
Kerns said producers should not assume Bt cotton will prevent bollworm damage and they should stay vigilant and note numbers, especially in non-Vip Bt cotton fields. Treatment of fields with insecticides early before the worms make their way to the fruit is the best tactic for optimal control. In areas where Bt resistance has been previously noted, spraying on large egg lay areas has proven highly effective.
But Kerns said treatment of Vip cotton varieties should be based solely on damaged fruit with larvae present because treating those fields in most often not necessary.
“In non-Vip cotton in areas where we have had Bt-resistance issues, if I have a large egg lay, I’m going to spray,” he said. “With Vip cotton, they tend to work, so you can avoid the added cost of spray treatments by just letting them do their job.”
However, even Vip cotton can experience unacceptable injury from bollworms under certain conditions, and should be treated once 6 percent or more fruit injury occurs with larvae present, he said.
AgriLife Extension district reporters compiled the following summaries:
CENTRAL: Recent rains were not enough to keep pastures from burning up, and most producers didn’t get a second cutting on hay. Hay production was down drastically. Row crops were suffering and livestock were being supplemented. A lot of grain sorghum was cut for hay because heads were not making grain. A little more than half of the counties reported fair soil moisture. Overall crop, rangeland and pasture conditions were fair in more than half of the counties.
ROLLING PLAINS: Weather in the district remained hot, dry and windy with some spotty showers. Cotton farmers wrapped up planting, however some acres were replanted due to weather conditions. Early planted cotton acres avoided the disastrous weather and were in good condition but needed rain. Pastures and rangelands were in good condition but also needed rain. Grasses were drying out, and wildfires were becoming a concern. One county reported over 1,500 acres burned. Hay was being used as a supplement in dry pastures. Grasshopper damage was occurring in pastures and yards.
COASTAL BEND: Scattered showers limited access to fields to harvest sorghum and corn. Harvest-aid applications to prevent lodging were delayed on some sorghum. Moisture levels fluctuated in grain day to day from 13 percent to 18 percent following a tropical front. Cotton bolls were opening, and a few early planted cotton fields were defoliated. Herbicide application continued as weather allowed. Some hay was being made, but conditions were not great. Livestock were doing well.
EAST: Scattered showers eased dry soil conditions in many areas across the district. Water levels were still down in most lakes and ponds in Gregg and Cherokee counties, which caused difficulties for many livestock producers. Cherokee County was still in drought. Trinity County reported hard winds dried out soil following rains. Producers were still trying to find hay to purchase outside of Trinity County, and Smith County’s supply was running very low. Marion County reported some producers were having to start feeding hay and Gregg County producers continued hay feeding. Pasture and rangeland conditions were in fair to good condition throughout the district. Marion County gardens were drying up unless they were being watered. Subsoil and topsoil conditions were short. Livestock were in fair to good condition. Fly and mosquito numbers remained high in Henderson and Houston counties. Wild pigs continued to cause a lot of damage in Henderson County.
SOUTH PLAINS: Hot, dry weather kept subsoil and topsoil moisture levels low despite spotty showers. Most areas were still in extreme drought. Cotton fleahopper numbers continued to be very low to non-existent. Some early planted cotton was blooming, and areas fortunate enough to receive moisture looked good. Remaining cotton fields were struggling, and growers were going back in failed acres with either cotton or sorghum. There were no signs of sugarcane aphids in sorghum. Weed and pest control remained priority No. 1 for producers. Pastures and rangelands needed rain. Peanuts were doing very well with most fields in bloom and beginning to set pegs.
PANHANDLE: Temperatures were near average, but soil moisture was mostly short. Some moisture was received in parts of the district. Deaf Smith County producers all but wrapped up wheat harvest. Producers continued to run water on corn and cotton. Field work was ongoing with compost and manure trucks starting to operate. Mild weather and scattered showers in Moore County improved crop outlooks. Producers in Ochiltree County plowed and sprayed fallow ground and crops to control weeds. Sorghum planting was complete. Rangeland and pastures in some areas were in very good condition after heavy rains in June. Recent hail and high winds severely damaged or destroyed a large number of cotton acres in Wheeler County.
NORTH: Topsoil and subsoil moisture levels were mostly short due to extremely high temperatures and lack of measurable rainfall. Wheat harvest was completed, and yields averaged about 50 bushels per acre. Hay harvest continued, but yields were about half what they were last year due to lack of moisture. Cotton began to bloom. Pastures and hay meadows were stressed from no rain. Wild pig activity was low.
FAR WEST: Temperature highs were in the upper 90s with lows in the high 60s. Most parts of the district received rainfall ranging from trace amounts to more than 3 inches. Multiple pop-up rain showers combined with cooler temperatures and helped perk cotton up. Very few cotton acres survived, but acres that survived looked decent. Pest numbers increased. Spider mites were infesting corn and sorghum. Watermelon harvest was in full swing. Producers continued to water all crops. Shipping of kid and lambs was finishing up. Fire danger was less, but a few small grass fires occurred.
WEST CENTRAL: Conditions were hot and dry with isolated rain showers. Rain amounts ranged from a trace to 2 inches. Cotton planting was complete. Substantial cotton acres showed little to no emergence due to drought conditions, though some areas provided marginal stands. Some storm damage occurred in crops. Overall crop conditions were fair. Sorghum fields were in fair to good condition. Forage sorghum and hay fields were in fair to good condition, but were showing drought stress. Rangeland and pasture conditions were mostly poor to fair. Tank levels were still low, but rains helped.
SOUTHEAST: Parts of the district received significant rainfall while others received limited amounts. Galveston County received heavy rains, and some areas flooded. Walker County received scattered rains that helped soil moisture conditions. Moisture should help forages and vegetables. Livestock and crops were in good condition. Rangelands and pastures were very poor to excellent with fair ratings being most common. Soil moisture levels ranged from adequate to surplus with adequate being most common.
SOUTHWEST: Almost all counties reported rainfall and cooler temperatures. Conditions were so poor, little improvement was noted. Without more rainfall, pasture and rangeland conditions will continue to deteriorate. Areas severely damaged by drought will likely not recover immediately. Wildlife were expected to benefit from the rains.
SOUTH: Northern parts of the district reported continued hot, dry weather conditions with short to adequate moisture levels. Southern, eastern and western parts of the district reported hot weather, wet conditions and short to adequate soil moisture levels. Rain amounts in parts of the district ranged from 0.5 of an inch to 5 inches. Grain corn harvest began. Watermelon and food corn harvests continued. Cotton benefited most from rains and was setting bolls and making good progress. Some cotton acres were being prepared for harvest. Sorghum harvest was expected to begin soon. Some sorghum in drier parts of the district were plowed under. Pasture and rangeland conditions were poor, and supplemental feeding of livestock continued in drier areas. Areas that received rain reported improved pasture and rangeland conditions and reduced supplemental feeding. Cattle conditions remained fair. The live cattle market continued an upward trend.
Source: Texas AgriLife Extension