Sampling Recommendations for MRB larvae:
•Sample 1ft2of soil to a depth of 2-3” (include rhizomes)
•2 samples taken every 2-3 acres
•Minimum 25 samples per field
•Screen samples in the field or recover larvae with Berlesefunnel in the laboratory
•Treatment threshold = average of 2-3 larvae/ft2sample
Late Aug/early Sep is the time to scout for Mint Root Borer (MRB) larvae in the soil if fall control is being considered (i.e. Lorsban, Mocap, nematodes). MRB larvae drop from the foliage to the ground in August and tunnel into rhizomes, where they will feed into the fall.
Larvae are generally too small to see in August, while sampling in late September is too late as the damage is done.
Control treatments must be applied before larvae form hibernacula (overwintering, soil-based cocoons). Based on the insect development model, hibernacula formation in Grande Ronde Valley should be 5% by September 11th and will reach 50% by October 14th. Baker Valley should expect 5% hibernacula by Sept 26th.
Recently, a new invasive leafhopper species, known as Ligurian leafhopper (Eupteryx decemnotata Rey, Hemiptera: Cicadellidae) was reported by Bill Gerth, OSU Plant Clinic and this prompted us to look out for this insect while sampling the commercial mint field in Western Oregon. This insect species is of Mediterranean origin and is a pest of many plants in the family Lamiaceae which include peppermint, sage, basil, oregano, rosemary, lemon balm, and other culinary herbs.
Ligurian leafhoppers are tiny, less than 3mm long or 0.12 inches, yellowish-green leafhopper (see image) with a characteristic pattern of spots on the head and the wings.
The Ligurian leafhopper is an important pest in cultivations of plants from the family Lamiaceae. Just like other leafhoppers, they are sap-feeding insects causing damage by puncturing cells and removing their contents. The characteristic stippling is produced (see image) when pest density is high. The damage can be mistaken for thrips or mite injury. The occurrence of this insect pest in Northeastern mint production systems and damage potential in commercial fields is still unknown.
We are now at the optimal in-season application window at both Agrimet sites (the optimal window for Grande Ronde Valley will be closing soon).
Peak moth flight of Mint root borer adults was reached July 21st in the Grande Ronde Valley, optimal control extends from this time through peak egg-laying (Aug 1st). The NMME forecast still puts peak moth flight for Baker Valley on July 26th. Good control can be achieved with Coragen® from peak moth catch through peak egg-laying.
Variegated Cutworm larvae should be controlled before 5th instar when they drop to ground and become difficult to control. Treatment threshold is 0.6 larva/sweep or 1.3 larvae/sq ft.
Mint root borer capture rates in the pheromone traps were low and have yet to reach peak moth flight in Baker Valley. No variegated cutworms were found. Only one mint cutworm (See image below) was discovered during crop inspections and they are not generally considered a pest of economic concern as other cutworm species.
Recent cooler weather has pushed back the predicted peak flight activity by a couple of days.
The peak flight activity is approaching in the coming weeks.
This week’s newsletter presents “PAMS” – Prevention, Avoidance, Monitoring, and Suppression framework for mint IPM ranging from proactive to reactive approaches in bio-intensive to conventional settings.
Regular scouting and monitoring determine the presence and potential insect pest damage to mint fields in Oregon. Management practices, such as crop rotation, tillage practices, varieties used, etc., reduce the occurrence of many of these pests. This newsletter is a decision support system that utilizes resources such as Online phenology and degree-day models (http://pnwpest.org/dd/model), and the Pacific Northwest Pest Management Handbooks (https://pnwhandbooks.org/insect/crop-pests?combine=mint ) to facilitate the efficient use of chemical control options.
Archived Reports – 2019
We just finished the second week of trapping for MRB adults in Baker County and the numbers are very low so far. A total five (5) MRB moths have been capture over the two week period. We are not doing any area-wide monitoring in the Grande Ronde Valley but we are providing the phenology development updates based on predictive models for the GRV. As expected, GDD accumulation is running behind a few days compared to last year.