2011 Armyworm Populations Appear to be Following 2006 and 2008 Outbreak Levels

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Source: Doug Johnson, Extension Entomologist and Patty Lucas, Extension IPM Specialist, University of Kentucky

2011 captures of armyworm moths in UK-IPM pheromone baited traps so far mimic those seen in recent outbreak years (2006 & 2008). An "outbreak" year is simply one when the population reaches a size that requires control and/or produces crop damage that exceeds the cost of control. Armyworms overwinter in Kentucky and are found in fields every year. They usually do not reach damaging populations but producers and consultants should be careful not to overlook them until it is clear that damaging levels are not present.

The UK-IPM monitoring system provides a method of developing some degree of risk assessment. Because there are many years of trap capture data available and information on when populations resulted in crop loss, we can compare the current year to what has happened on a recurring basis in past years. See graphs of UK-IPM trap captures here.

Select the insect of interest from the list at the bottom center of the screen.

How the Graphs are Presented: Each graph contains at least two lines. The Blue line is a rolling five year average. This line does NOT include outbreak years; so it indicates a population trend that has little risk of crop damage. Weekly trap catches from the current year appear in Green. Capture from an outbreak year is plotted in Red and also in Black if there is a second outbreak year shown.

Using The Graphs: The risk from these populations can be viewed as follows. If the Green line appears to be occurring at about the same levels as the BLUE there is no evidence of elevated risk. The damage potential increases with the separation of the Green line above the Blue line. Increased scouting for armyworm damage will be needed if the Green line approaches or exceeds the Red outbreak line.

Applying the Information: Insect-trap graphs, provide a quick and simple way to assess risk from the current population trend each week and to adjust scouting priorities. At present, graphs are updated on Friday afternoon.

Restrictions: 

  • These data do not predict occurrences in specific fields. They only tell you when risk is elevated so you can target that time period for sampling. 
  • The absence of elevated risk does not mean there will be no damage. Armyworms are present in most fields every year so there is ALWAYS some level of risk. These data only describe when risk is greater than one would normally expect. 
  • The presence of elevated risk does not mean that damage will occur in an individual field. The graphs are only a snap shot in time of what is ordinary or out of the ordinary. 
  • These graphs represent the capture of adult moths. Moths are not the damaging stage. 
  • The larval (juvenile) or caterpillars are the damaging stage. Caterpillars will occur at some time after the moths are flying. This why the graphs provide an "Early Warning" before the damage occurs.
Scouting for the Damaging Stage: The graphs only show moth flight, one must scout for the caterpillars or damage to assess the damage potential. Using the moth capture as a beginning point (BioFix) one can use temperature data to make a general prediction as to when feeding damage can be expected. This is the stage that important to scout. This prediction has not yet been mechanized. So if the population continues to follow the outbreak year data, a prediction of the dates when caterpillars are expected to be present will be published in each Kentucky Pest News here, and the Grain Crops Blogspot at: Grain Crops blogspot.

Crops at Risk: Armyworms can feed on all grass crops including corn, timothy, millet, bluegrass, small grains and some legumes. In Kentucky the crops most commonly infested are corn, wheat and grass hay. Major damage is unusual, but this pest occasionally can inflict major losses.

See Entfact-111 Armyworms in Small Grains here and Entfact — 109 Armyworms in Corn here

These fact sheets will give a general overview of the insect's description, biology and damage.

Controls: Insecticides registered for use against armyworms may be found in Ent-16, 17 or 47; Insecticide Recommendations for Corn or Small Grains or Alfalfa and Pastures & Hay), available here.

Future Plans: It is hoped that in future the current graphs will also display estimations of when the caterpillar stage is likely to occur. At present this information is provided in Kentucky Pest News articles.

1 The armyworm, Mythimna interpunctella (Haworth), may be found listed in earlier publications as armyworm or true armyworm, Pseudaletia unipuncta (Halworth). The insect is the same, only the names have been changed.

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