Concept 5: Pest damage relationships

The impact of pest attack on crop yield and revenue is clearly an important factor that determines the effectiveness of pest management.  

As shown above, two forms of relationship can occur between pest attack and yield:

Type 1 relationship - where the pest is a vector of disease, where it attacks the grain late in the crop, or where crop tolerance and compensation is limited.

Type 2 relationship - where the pest attacks at the vegetative stage of the crop and the crop's innate tolerance (e.g. more tillers than it can take through to maturity) or compensation mechanisms result in no loss of yield occurring, up to a threshold level of pest attack.  Most rice varieties produce more tillers than the plant can support through to maturity, providing "spare capacity" to tolerate pest or disease attack. Rice also has various ways in which plants can compensate for injury caused by pests and diseases so that yield loss due to pest or disease attack only occurs above a certain threshold of pest attack.