Annual Bluegrass Weevils

Diagnosis and Decision Making for Sustainable Annual Bluegrass Weevil Management 7 Figure 10. Standard U.S. penny with 1st through 5th larval instars (left to right). Compare width of the head capsule (amber – brown sphere at top of larva) to the width between two pillars on the Lincoln Memorial. • Place turf plugs individually, turf side up, into 16 oz. deli cups (Figure 9A) then fill each cup with salt solution just until plug is submerged (Figure 9B). Thatchy plugs often float, exposing turf and soil, and reducing the efficiency of the method. If this happens, place a heavy steel washer or small stone on top of the plug to keep it submerged. • Larvae often appear within the first 30 minutes. However, plugs should be left in salt water for at least 90 minutes to account for variability in soil type and larva location, both of which can affect the speed of extraction. • Monitor the surface of the solution for ABW larvae. Larvae can be collected using the tip of a knife blade or other small implement and should be moved to a separate dish or paper towel for counting and life- stage determination. Decision Making and Management– Larvae The density of larvae that turf can tolerate varies. Typically, action thresholds range from 30 to 80 larvae per square foot for generation one. However, stressed turf may experience damage at much lower densities. A general threshold would be to use an average of one larva per sample, however, more precise timing of larvicides can be achieved by assessing the different larval stages. Remember, the goal is to identify the time frame when larvae are emerging from the turf crown and into the soil where they are vulnerable to curative pest management efforts. Measuring overall body size and head capsule width is the most accurate method for determining larval stage. This can be done using a Figure 9. Salt flotation procedure. A – Turf plug being placed into deli cup. B – Turf plug flooded with saturated salt solution. good hand lens (~15x) and a penny. Place larva on the back of a standard penny, and use your hand lens to compare the width of the head capsule to the distance between two pillars on the Lincoln Memorial (Figure 10). The head capsule width on 1st through 3rd instar larvae fit easily between two pillars. The head capsule of the 4th instar larva, the stage at which larvae emerge from the turf crown, will just barely fit inside the gap between two pillars, and that of the 5th instar larva will be slightly larger than the gap between pillars. The goal of this scaling activity is not to measure every larva collected, but to develop a search image for gauging larval stages. Continue conducting weekly salt flotations until the majority of larvae recovered from your salt floats are 3rd to 4th instar. Using the general threshold of 1 larva per sample on average, along with the assessment of life stages and GDD will provide the best chance of accurately timing curative larvicide applications where necessary. Appropriate active ingredients at this stage include cyantraniliprole, indoxacarb, spinosad, and trichlorfon.