There are over 800 noctuid species in the Pacific Northwest. This order of Lepidopteran may very well be the most destructive. Larvae will feed voraciously under outbreak conditions. Adult are nocturnal and often seen around lights.
Origin of common names
It is the behavior of the larvae that give rise to the common names. The term "cutworm" comes from the behavior of cutting the leaves or stems of weeds at the base. Generally, cutworms feed nocturnally and spend the days in the cover crop. These insects move up and down the tree daily between the shelter of the cover crop and the tree. The term "armyworm" comes from the movement pattern of larvae. These pests have the ability to move in mass from one feeding area to another. Fruitworm are more solitary in movement and sedentary within host plants.
Know your enemy
The first step to managing noctuid pests is to "know your enemy". A grower that suspects noctuid damage can sample all hosts showing damage. Larvae can be dislodged from a tree using a beating tray technique, or pull weeds dislodge larvae into a bucket by knocking them off the plant. Adults can be monitored with general purpose bucket-style traps baited with pheromone lures.
Results of intensive larval sampling indicate three main noctuid species are causing the majority of problems in Washington orchards. Spotted cutworm are the prevalent species in the early spring and late fall. Bertha armyworm are the most abundant species found in the ground cover. They appear to have a broad host range that includes tree fruits. Bertha armyworm are the primary noctuid pest of pear. L. subjuncta are the most abundant species found in apples, and the noctuid most often associated with fruit injury.
All noctuids that attack tree fruits prefer herbaceous plants. Weeds are generally considered a primary host while tree fruits are only secondary hosts. Armyworms and climbing cutworms characteristically move between the tree and weeds on the orchard floor, while fruitworms (including L. subjuncta) may complete their entire life cycle on tree fruits. The weeds most associated with these noctuid pests are lamb's-quarter, pigweed, dandelion, mustards, plantain, mallow, morning glory, and Canada thistle. Potatoes, sugar beets, hops, alfalfa, and mint also hosts for noctuid pests.
Natural population control
Weed control is the most effective method for controlling populations and preventing outbreaks. Eliminating weeds removes egg-laying sites and the preferred food. Mowing discourages oviposition. Biocontrol from insects, spiders, birds and rodents will also suppress populations. Larvae are susceptible to viral outbreaks. An infected larvae may climb a tree and die. Healthy larvae will feed on the viral ooze. Those species that overwinter as larvae are susceptible to high winter mortality (spotted cutworm). Under most years these natural control will keep natural populations under control.