Trapping and monitoring are not required for export inspections, but they can be helpful in timing control, knowing what pests are present, and avoiding surprises. To that end, it is important to know where and how to set traps. Traps that are poorly placed or set out at the wrong time can give incorrect information and a false sense of security.
Pitfall traps attract and trap a wide variety of ground crawling creatures. These traps are often covered with small boards with runners underneath to keep out rain and dirt. These traps are useful in checking for slugs, snails, root weevils, and ground beetles. They are a non-specific trap because anything that passes by can be captured.
For attracting and trapping slugs and snails, place beer or baking yeast in a 5% sugar-water solution in a pitfall trap or a pan set in the ground. Growers shipping to areas with slug or snail restrictions often bait areas where trees are stored and can use traps to monitor the presence or absence of molluscs.
Sticky monitoring traps are highly adhesive, water-resistant tags of various sizes and colors that insects adhere to when they fly into them. Various chemical lures and bait attractants are available, though few are specific to Christmas tree pests. These traps can be useful in monitoring Douglas-fir needle midge; however, they may also trap a variety of non-pest midges and other flying insects.
Funnel traps are made of nested black funnels (up to as many as 12). Insects fall through the funnels to a cup that is filled with a preservative. Funnel traps come in a wide range of sizes. Flying beetles and other insects may be attracted by chemical lures and captured in the trap base. Few lures specific to Christmas tree pests are currently available.
Yellowjacket attractant traps include chemical lures, colors, and trap designs to attract western yellowjackets. These traps are less successful with German yellowjackets. They are useful for monitoring worker activity but not for control.
Yellowjackets are the only Christmas tree “pest” for which there are specific chemical lures for attraction. Placing roughly 5 traps per 10 acres of field is sufficient for monitoring. The queen is the key to controlling population growth, and she only flies in March. Thus, early lure placement and trapping should help control some colony formation. Since the queen does not move outside the nest after this early period, later trapping only affects the worker population. There are currently no registered insecticides that may be used as toxic bait to eliminate the nest. Direct spraying of ground nests is allowed; traps may be useful in finding these ground nests. Ground nests can pose hazards to shearing crews and visitors, so control is also beneficial for safety.
A raised board trap with runners that is placed in a field provides a hiding place for slugs. Board traps without runners are effective for root weevil monitoring. For root weevils, the board should be placed lightly on the ground to allow space for the insect to shelter. Board traps are good monitoring tools because slugs and root weevils seek dark, protected sites during the day.
See the sections on slugs and root weevils for suggestions on the timing and placement of traps.
Needle midge traps consist of a box with a jar inserted into the top edge of one side. As adults emerge from the soil, they fly towards the light (jar) to escape. Place a moist towel inside the jar to catch the adult midges. The jar will contain other flying and crawling insects, so use a hand lens to help with identification.
See the section on Douglas-fir needle midge for suggestions on the design and timing of traps.
Pay particular attention to Douglas-fir fields that had Douglas-fir needle midge problems the previous year and to edge rows close to native Douglas-fir timber. Needle midges seem to prefer the “shady side” of trees, where there may be some vegetation; however, in a fully stocked field, this could be anywhere. The needle midge is one of the few pests for which there are degree-day models to track emergence, which can vary by 4 to 5 weeks from year to year (Appendix E). The degree-day models can help determine when to place traps. Placing five emergence traps per field of trees is good for monitoring a growing area. Place the traps with the jar side facing between rows so it gets as much light as possible. Check the traps frequently and count needle midges to get an idea of population numbers. Prolonged cool rain during emergence also helps control numbers.
Insect sweep nets are useful for capturing flying insects, such as Douglas-fir needle midge.
Beating boards and sheets are used beneath limbs to sample insects, such as adult weevils, that are easily knocked off.
Many pests are too small to see unaided. A hand lens with 10× or 16× magnification will help identify these insects.
