The damage webworm may cause in any one year is determined by how the paddock is managed in the year and weeks prior to seeding. The reasons for this can be seen in the life cycle and habits of the pest. Adults flying in autumn prefer to hide and lay their eggs in areas where dry grass residues are plentiful. It is in these areas that the survival of eggs and young caterpillars will be greatest. Bare paddocks or stubble paddocks are unsuitable for webworm development.
Some shade is essential for the small eggs to avoid overheating and drying up.
When the young caterpillars emerge, they are prone to starvation and shrivelling up. They have to find grasses growing from autumn rains. Moist conditions and undisturbed paddocks provide the best conditions for webworm and may allow hundreds of caterpillars per square metre to survive. Large numbers are often present in pasture but usually go unnoticed. Minimum tillage methods allow a high survival rate whereas weed control and soil disturbance reduce or eliminate the pest population.