July 10, 2024
With the heat wave over the last few days, insect development has been moving quickly, and model predictions are a few days earlier than we expected as of a week ago. The growing degree model predicts that peak moth catch is occurring today, July 10, in the Willamette Valley. If you are planning to use an in-season Vantacor application on your mint, the best time to spray is now. Try to complete your sprays in about the next 10 days, or before peak egg laying, which is predicted to occur on July 21. Check the app to stay up to date with any changes in these predictions.
Previous OSU studies suggest that the best time to apply Vantacor to get the best over all control of mint root borers, loopers and variegated cutworms is between peak moth catch and peak egg laying based on the mint root borer growing degree model. Vantacor is a systemic insecticide that is absorbed by the plant, and controls insects over an extended period. It works best on insects at the egg and early larval stages. Since insects lay eggs over a couple week period, you want to spay early enough that the earliest laid eggs are still vulnerable, but late enough that the product is still effective when the later eggs are laid.
Mint root borer moths have been captured in three of the five fields with traps this year. This week, an average of 14 and 3.5 moths per trap were caught in two of the fields, but no moths were found in the other three fields. These moth counts are just slightly higher than last week. No variegated cutworms or loopers were caught in sweep net samples in the fields yet. The model for variegated cutworms predicts that third instar larvae will peak on July 13.
July 3, 2024
Hello and welcome to the Mint Pest Alert for 2024. This email newsletter is designed to help you control mint root borers, variegated cutworms, and loopers in mint fields. Over the next couple weeks, I will share the results from a trapping program in your region. I will also include information from growing degree models for mint root borers and variegated cutworms. These models predict when the insects will reach various growth stages, which can help you figure out the most effective time to spray.
A new addition to the Mint Pest Alert this year is a growing degree web app. This means you can get updated model predictions any time. You can see the app by visiting the Mint pest alert blog site at https://blogs.oregonstate.edu/mintpestalert/production-regions/willamette-valley/.
We have pheromone traps in five fields in the Willamette Valley this year. The first mint root borer moths were caught in two of the fields this week. No loopers or variegated cutworms were caught in sweep samples.
The growing degree model is predicting peak moth catch for mint root borer moths on July 11. For variegated cutworms, peak egg laying was on June 24, and first instar larvae are expected to peak on July 4.
Archived Reports 2023
Fall Chemical Management
Late Aug/early Sep is the time to scout for Mint Root Borer (MRB) larvae in the soil if fall control is being considered. 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, 5% hibernacula formation was on August 18, and 50% is expected on September 3.
Sampling Recommendations for MRB larvae:
- Sample 1ft2 of 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 with Berlese funnels in the laboratory
Treatment threshold = average of 2-3 larvae/ft2 sample
Archived Reports 2022
Willamette Valley Mint Pest Alert Newsletter – August 31
Willamette Valley Mint Pest Alert Newsletter – August 10
Willamette Valley Mint Pest Alert Newsletter – August 3
Willamette Valley Mint Pest Alert Newsletter – July 28
Willamette Valley Mint Pest Alert Newsletter – July 20
Willamette Valley Mint Pest Alert Newsletter – July 15
Willamette Valley Mint Pest Alert Newsletter – July 6
Willamette Valley Mint Pest Alert Newsletter – June 29
Willamette Valley Mint Pest Alert Newsletter – June 24
Archived Reports – 2021
Willamette Valley Mint Pest Alert Newsletter – August 28
Time for fall treatment.
Willamette Valley Mint Pest Alert Newsletter – July 30
Plan to sample early for larvae in soil.
Willamette Valley Mint Pest Alert Newsletter – July 23
MRB captures can vary a lot between fields, so be sure to scout your fields.
Willamette Valley Mint Pest Alert Newsletter – July 16
Optimum application window closed.
Willamette Valley Mint Pest Alert Newsletter – July 10
The optimum application window for MRB and VC control with Coragen or Vantacor Ends July 11
Willamette Valley Mint Pest Alert Newsletter – July 3
The optimum application window for MRB and VC control with Coragen or Vantacor is now
Willamette Valley Mint Pest Alert Newsletter – June 25
Upcoming heat wave moves up optimum application window for Vantacor or Coragen
Willamette Valley Mint Pest Alert Newsletter – June 18 21
3-6 MRB per trap were found in two of four fields.
Willamette Valley Mint Pest Alert Newsletter – June 11 21
21 MRB moths were found in one field, but no MRB were captured in the other three fields. Three loopers, a variegated cutworm moth and a mint cutworm larvae were also found.
Willamette Valley Mint Pest Alert Newsletter – June 4
12 mint root borer moths were found in a field in the southern Willamette Valley. The first flight was predicted for June 1.
Archived Reports – 2020
Willamette Valley Mint Pest Alert Newsletter-_September 11
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
Willamette Valley Mint Pest Alert Newsletter- Aug 27
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.
Willamette Valley Mint Pest Alert Newsletter-August 5
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.
Willamette Valley Mint Pest Alert Newsletter-July 30
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.
Willamette Valley Mint Pest Alert Newsletter-July 23
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.
Willamette Valley Mint Pest Alert Newsletter- July 16
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.
Willamette Valley Mint Pest Alert Newsletter- July 09
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.
Willamette Valley Mint Pest Alert Newsletter- July 02
Few MRB (<5 adults) were captured in the pheromone traps in the Willamette Valley this week.
Willamette Valley Mint Pest Alert Newsletter- June 25
Few MRB were present in the pheromone trap captures this week. The predicted peak activity of moth flight is the next couple of weeks.
Willamette Valley Mint Pest Alert Newsletter- June 18
No MRB adults were found in the pheromone traps this week.
Willamette Valley Mint Pest Alert Newsletter- June 10
No insects were found in the traps this week. Fields were too wet for collecting sweep net samples.
Willamette Valley Mint Pest Alert Newsletter-June 03
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
Willamette Valley
Willamette Valley Mint Pest Alert Newsletter – Aug 29th
Willamette Valley Mint Pest Alert Newsletter – Aug 7th
Willamette Valley Mint Pest Alert Newsletter – July 24th
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.
Willamette Valley Mint Pest Alert Newsletter – July 18th
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.
Willamette Valley Mint Pest Alert Newsletter – July 11th
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.
Willamette Valley Mint Pest Alert Newsletter – July 5th
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.
Willamette Valley Mint Pest Alert Newsletter – June 27th
Pheromone trapping in the Mid and South Willamette Valley have found few adult MRB moths (<5 per trap) and only one looper moth.
Willamette Valley Mint Pest Alert Newsletter – June 19th