Western corn rootworm adult captures as a tool for the larval damage prediction in continuous maize

Continuous maize production in Croatia and Central Europe is at serious risk from western corn rootworm (WCR) (Diabrotica virgifera virgifera, LeConte) activity. When alternatives to sowing continuous are not feasible, farmers will need a reliable tool that will allow them to choose fields for continuous cultivation. The decision could be based on assessing the adult populations in fields from the previous year. Non‐baited yellow sticky traps [Pherocon AM (PhAM)] could be utilized as a practical tool for sampling. The main objective of this study was to determine which WCR adult population data collected by PhAM traps could most reliably predict the subsequent WCR larval population and damage. Adult WCR population densities in 30 cornfields were determined weekly over a 74 day period each year (24th to 35th week) from 2006 to 2009. In addition to root damage and plant lodging measurements, soil and root sampling were conducted to measure the WCR larval population in continuous maize fields. Larval infestation is best predicted by maximal weekly capture (MWC) but, root damage is better predicted by capture of adults in the 31st week of previous year. For the prediction of plant lodging, MWC, average daily capture (ADC) and the capture of adults in 29th week were found to be equivalent. To save money and to shorten the sampling period, farmers should employ PhAM traps between the 29th and 32nd week. The estimated WCR adult capture that could cause significant larval infestation is ≥22 adults/trap in the 29th week. Significant future root damage is predicted if ≥41 adults/trap are captured in the 31st week. Plant lodging is predicted if ≥36 adults/trap (for 90% of upright plants) or ≥32 adults/trap (for 10% of partially lodged plants) are captured in 29th week. Findings will help to develop economic threshold models and improved decision‐making for WCR management.