Control treatments must be applied before larvae form hibernacula (overwintering, soil-based cocoons). Based on the insect development model, hibernaculum formation began Aug 28th, with 50% hibernaculum formation expected by Sep 13th.
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 damage is done.
Control treatments must be applied before larvae form hibernacula (overwintering, soil-based cocoons). Based on the insect development model, hibernaculum formation begins Aug 28th, with 50% hibernaculum formation expected by Sep 16th.
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.
This is the first report of this insect’s occurrence in the commercial mint field and the potential of this insect to cause economic damage to Oregon mint production systems is still unknown.
It was a bit unexpected to see a high number of MRB adults (on average >18 moths per trap) in the pheromone traps in WV this week. We are going to use the data collected this year and from previous years to see if there is a need to make adjustments to the insect phenology models. We still encourage you to scout your local fields for insect activity and plan for applications if large MRB populations are found. If pheromone traps are unavailable, walkthrough mint fields looking for MRB moths in flight.
On average trap count in Willamette Valley was <10 MRB adults per site. Alfalfa loopers were found in sweep net samples. Looper and cutworm caterpillars are still mid-late instar, and VC are expected to reach peak 5th instar populations by July 30th. VC will readily drop from mint when plants are shaken or disturbed and can be found on the ground. Looper caterpillars are smaller and can be found with sweep nets.
The trap counts remained low this week (< 5 MRB adults) at all sites in Willamette Valley. No loopers were found in the sweep net sampling. We encourage you to keep scouting your mint fields for cutworm and looper activity.
Besides variegated cutworm, keep an eye for mint cutworm (Heliothis phloxiphaga) which are large, yellow, tan, or green larvae with black spots over the body (See image below), similar to corn earworm. Damage is similar to that of the variegated cutworm and alfalfa looper, but this insect seldom is a problem of economic importance on mint.
On average less than ten MRB adults were captured in the pheromone traps in the Willamette Valley. Few loopers were found in the sweep net sampling at all sites. Keep scouting the mint fields for insect activity as we are now close to the predicted peak flight period.
Few MRB (<5 adults) were captured in the pheromone traps in the Willamette Valley this week.
Few MRB were present in the pheromone trap captures this week. The predicted peak activity of moth flight is the next couple of weeks.
No MRB adults were found in the pheromone traps this week.
No insects were found in the traps this week. Fields were too wet for collecting sweep net samples.
Few mint root borer (MRB) adult moths (<10) were captured in the pheromone traps south of Corvallis. The first flight is predicted for June 4.
Archived Reports – 2019
Trap counts have begin to taper off, averaging 12/trap in the South Valley and less than 5/trap in Mid Valley. The window for optimal control of VC and MRB with chlorantraniliprole has passed, but adequate control can still be achieved before MRB migrate into stems and VC begin to pupate in the soil.
Trap counts remain high (up to 20/trap on average), and MRB moths can be seen actively flying in the canopy. Looper and cutworm caterpillars are still mid-late instar, and VC are expected to reach peak 5th instar populations by July 28th. If pheromone traps are unavailable, walk through mint fields looking for MRB moths in flight. VC will readily drop from mint when plants are shaken or disturbed and can be found on the ground. Looper caterpillars are smaller and can be found with sweep nets.
Trap counts have picked up in the South Willamette Valley, averaging 20 per trap. Trap sites in the mid valley remain lower (less than 5/trap), but MRB moths have been observed in flight and in sweep samples. Rain and cloudy weather may be responsible for the decreased cutworm and looper activity this week, but caterpillars are likely to on-track with degree day models based on previous field observations. Keep in mind that insecticide applications should never be made based solely on model predictions – knowledge of your fields’ historical MRB infestations and current observations of MRB activity are the only way to determine whether management is currently needed.
Trap counts are slightly higher, averaging 5 per trap. Cutworm and looper caterpillars were found in small numbers at multiple sites, appeared to be in the 1st and 2nd instars.
Pheromone trapping in the Mid and South Willamette Valley have found few adult MRB moths (<5 per trap) and only one looper moth.