b'CORN ROOTWORM:Its a rather annoying pest that pops up across the Midwest and can become a problem for the field rather quickly. But thats not to say its immune to management. Troy Bauer, field technical representative for BASF, estimates that western corn rootworm has cost corn growers over $1 billion MANAGE CORN ROOTWORM in yield loss and control expenditures annually.Insecticides have been used to control corn rootworm since the late 1940s, he says. Adult corn rootworm beetles usually emerge above ground in early July and can be found in corn-fields throughout August and September. The insect consists of one generation per year, with females laying eggs in cornfields to over winter and hatch the following year.Bauer says most egg laying occurs from July through September, and a single northern corn rootworm female can lay more than 1,000 eggs in the growing season. On top of that, the western corn rootwormone of the more problematic species, as opposed to the northern and southern corn rootwormcan lay around 1,800 eggs in a season. Then, the larvae hatch and begin feasting on corn roots, which causes reduced nutrient uptake and increased lodging potential, Bauer says. This makes it difficult for plants to maximize photo-synthesis and these lodged plants are difficult to harvest. On top of that, Bauer adds that adult beetles can feed on silks and reduce pollination, further causing reduced yields for growers. As early as 1959, resistance to cyclodiene insecticides was identified, Bauer says. In some areas of the Midwest, such as Kansas and Nebraska, and other areas of the western corn belt,A corn rootworm larva found in the roots of a corn plant. growers adapted an adult management approach to reduce egg laying by relying on carbamates and organophosphate insec- The adoption of Bt crops has been beneficial; however, ticides. Corn rootworm beetles have developed resistance toresistance in western corn rootworm to corn hybrids expressing some of these foliar insecticides as well. Cry3Bb1 toxins was reported in 2009, Bauer says. Resistance to To beat some of these resistance issues, Bauer says oneCry34/35 was documented in 2018.common cultural practice to assist with corn rootworm controlAlthough these pesky and sneaky pests have developed is rotation away from corn for at least one year. However, thisnumerous ways to combat usual management styles, never fear. wasnt a catch-all strategy either.There are ways to combat and prepare for corn rootworm if it In certain geographies, corn rootworms have developed aappears in the field.strategy to overcome this by laying eggs into soybean fields in anticipation of planting corn the following year, Bauer says.How to PrepareThe western corn rootworm is the culprit for this sneakiness.First things first: find out if you have corn rootworm in your In addition to overcoming crop rotation in this way, anotherfield.corn rootworm speciesthe northern corn rootwormhas anThere might be some acres where farmers need to investi-extended period of the egg stage, where eggs can remain viablegate, for example, using a check strip of non-Bt corn, to deter-underground for 2-3 years before hatching. mine what pest pressures are like and whether they need all Bt Beginning in 2005, another potential solution was the intro- traits that are available, Krupke says.duction of Bt corn into rotation. According to Christian Krupke,Bauer agrees, and says growers need to continuously scout professor of entomology at Purdue University, Bt corn hastheir field throughout the year. helped growers in Indiana over the past 10 years.First, scout the fields throughout the year to determine the Corn rootworm has been going down in severity and preva- amount of root feeding present, as well as the level of corn root-lence in Indiana, he says. Part of the reason for that is that theworm adult beetles flying around, he says. Then, you can move vast majority of field corn in the state is Bt corn targeting root- on to determine management strategies for the following year. worms, as well as caterpillar pests. The majority of rootwormOne thing Krupke says to be aware of is what traits you need larvae die after feeding on Bt traited hybrids in Indiana. And theto use for the year, versus what traits you dont need. lower populations of the pest reflect that. But were really still man- We know we dont need every single trait every single year aging them as if we assume theyre going to be there every year.in all fields, he says. When commodity prices arent great, DECEMBER 2019SEEDWORLD.COM /105'