b'Corn rootworm has a number of characteristics that make it a problem. Probably the most significant is its ability to develop resistance to control tactics. Nick Seiter, a field crop entomologist with the University of Illinois, explains that populations of both western and northern corn rootworm have developed resistance to diverse tactics including insecticides, Bt hybrids, and crop rotation.In recent years, increasing levels of resistance to Bt traits in particular has led to higher populations and greater damage in some areas, particularly those areas where a lot of corn is grown following corn.As for eradication measures, Seiter says crop rotation is one of the best tools growers have.While there are rotation-resistant populations of both species, damage to first-year corn has been minimal in recent years (at least in Illinois), and its no coincidence that areas with less rotation have higher rootworm populations. In east central Illinois (formerly a hot spot for rotation-resistant western cornCorn rootworm can cause severe damage to corn as both larvae rootworm), we have had minimal problems with rootworm inand adults.PHOTO: SYNGENTArecent years.OBrien agrees and adds that crop rotation to a non-hostSmartStax Pro and RNAi Technologycrop is still the single most effective way to control corn root- While technology can work wonders in many areas of agricul-worm. This is because the adult beetles lay their eggs in cornture, when it comes to corn rootworm, Seiter says that no trait fields anticipating that when they hatch next season, there will beor insecticide is bullet-proof.corn roots there for larvae to feed on.However, depending on the area there may still be a good If in the following season a non-host crop like soybeansdeal of susceptibility to at least Cry34/35Ab1. Soil insecticides is planted, as the CRW eggs hatch there are no corn roots fortargeting corn rootworm remain pretty effective, though they larvae to feed on and they starve. There are exceptions in someallow a higher adult population to survive than an effective areas of the Northern and Eastern Corn Belt where CRW hasBt trait would. New RNAi trait packages have been or will be adapted to crop rotation. In the Northern Corn Belt, some eggsreleased over the next few years. These will provide a new mode of the Northern corn rootworm may have an extended diapauseof action for rootworm control but are still paired with Bt pro-where the eggs remain in the soil for more than one season andteins that in many cases are already compromised by resistance.hatch in subsequent seasons when corn may be planted again.This year, Bayer launched SmartStax PRO with RNAi Then, in areas of the Eastern Corn Belt, a variant of the WesternTechnology, the next generation of corn rootworm protection. It corn rootworm has begun laying eggs in soybean fields, so ifis the industrys first product offering with three modes of action corn is planted the following season those eggs hatch and feedfor corn rootworm control, including a novel RNAi based mode on corn roots. of action. He adds that in addition to crop rotation, management strate- This product will provide growers yet another tool to help gies including seed trait stacks like DuracadeViptera, soil appliedcontrol tough corn rootworm pests, says Hassan. In addition insecticides like Force, seed treatments like Avicta Completeto corn rootworm, SmartStax PRO will offer growers protection Corn 1250, and adult beetle control with Warrior II can be used inagainst European corn borer, southwestern corn borer, fall army-a multi-year plan to minimize CRW populations and damage.worm, black cutworm, and corn earworm, as well as tolerance to A unique trait product, like DuracadeViptera, provides anglyphosate and glufosinate herbicides.ideal foundation for a CRW control plan for several years butHassan says its best for growers to take a proactive approach different technologies should be used in some years through awhen managing corn rootworm. multi-year plan to prevent adaptation to a single technology. Growers need to plan ahead and make their management Seiter emphasizes that control decisions need to be madedecisions before the season starts as there are no effective prior to planting. This is because all effective controlsrotation,rescue treatments for corn rootworm. If you wait until you see Bt traits, insecticidesmust be applied at planting.damage, it is too late.When the larvae are active in late May to June, samplingTinsley agrees and adds, There are no post-planting rescue roots for larvae can give you an initial idea of how effective con- treatments available for corn rootworm, so management deci-trols have been. Digging roots and examining them for damagesions need to be made in advance of planting a corn crop. This in mid to late July is a more accurate way to determine how wellmeans that it is especially important for growers to scout for your controls worked out. Finally, monitoring adults in July tocorn rootworm during the growing season so that they can make August is the best way to determine your potential for rootworman informed decision about how they will manage the following damage the following year. years corn crop.SW120/ SEEDWORLD.COMDECEMBER 2022'