Proper identification and detection of insect pests is the basis of deciding when to apply a pest management tactic. It is essential to the basic principle of IPM to take action against a pest only when 1) the pest is known to be present and 2) the pest is at a level that may cause economic damage.
Monitoring pest populations is important to determine the onset of the pest in the crop being protected, seasonal patterns of the pest population, movement of the pest in the crop, life stage of the pest, abundance and distribution of the pest in the crop, and finally to assess the effectiveness of management tactics.
Different methods can be used to monitor populations, including direct in situ counts (i.e. Japanese beetle); soil extraction (i.e. weevil larvae); beat trays (psyllids); sweep nets (i.e. cranberry fruitworm larvae); pitfall traps (i.e. ground-dwelling beetles); attractive traps for flying insects using pheromone (i.e. codling moth; Fig 1); feeding attractants (i.e. spotted wing drosophila); visual cues (i.e. apple maggot; Fig 2); lights (many nocturnal flying insects), among others. For some insects, it is sometimes best to monitor for the characteristic damage symptoms, for example with plum curculio and its crescent-shaped oviposition scars (Fig 3).
It is also important to monitor temperature to record daily low and daily high temperatures to determine heat accumulation in the form of degree days. Insects being cold blooded, their development is tightly linked to the ambient temperature, thus it is more appropriate to rely on degree days than calendar dates for tracking insect development. For numerous pest species, degree day models based on temperature have been established and help predict phenological stages of the pest of concern. For example, using temperature data from the NEWA weather station at the West Madison Agricultural Research Station (see previous issue for more detail on how to access and use the NEWA information), we are able to make informed decisions on when to apply a management strategy for specific life stages of the specific pest.
Once the pest of concern has been identified and is being monitored, population densities can be assessed and used to determine when a chemical control strategy should be applied. Economic thresholds also known as action thresholds are available for many insect pest species and are based on the economic-injury level (EIL) concept. The EIL is defined as the lowest number of insects that will cause economic damage. The economic threshold is the density of pest population at which a management practice should be implemented to prevent the population from reaching the economic injury level. It is important to remember that in many cases, plants can tolerate some injury without incurring a significant reduction in yield. A lot of research goes into establishing EILs and economic thresholds for specific pest species and EILs can be dynamic as they take into account market value of the commodity, management costs, environmental conditions, and changes in plant susceptibility (e.g. new cultivars that are more or less susceptible). An action threshold is an important decision rule that is used for managing numerous insect pest species. For example, the action threshold for apple maggot monitored with red sticky spheres is one fly per week on unbaited spheres or five flies per week on spheres baited with a chemical lure. In some cases, the pest is too detrimental and no threshold is established, e.g. spotted wing drosophila, and once the pest is detected, management strategies need to be implemented.
In practicing IPM, we thrive to know the biology of the pest of concern, how to identify and monitor for the pest, calculate degree days, and apply chemical control when the most susceptible phenological stage of the pest is present and we reach the established economic threshold.This article was posted in Insects and tagged IPM.