August 28, 2024
Post harvest larval sampling is the best way to measure mint root borer populations in your fields
Mint root borers damage mint stands by feeding on the roots and rhizomes in the late summer and fall. After hatching, larvae feed on mint foliage for a few days before dropping to the ground and searching for rhizomes to feed on. Correct timing is the key to successful larval scouting. If you scout too early (July and early August), the larvae are too small to be found reliably. If you scout too late (after mid-September), much of the damage has already been done, and larvae have started to form hibernacula, which protects them from insecticides. The best time to scout is late August to early September. At this time larvae are large enough to see, and control efforts will be effective at providing some crop protection.
To scout for larvae, collect soil/rhizome samples from 1 ft x 1 ft areas in the mint field. Samples should be 2-3 inches deep and include the mint rhizomes in that area. You should collect at least 25 samples, or two samples for every 2-3 acres. You can screen the samples in the field, or extract larvae using the Berlese funnel method. The treatment threshold is 2-4 larvae per square foot, depending on age and vigor of the stand, other pests or stresses, and oil price.
Based on the Growing degree model, 5% of larvae are expected to have formed hibernacula by August 31 near Madras, and September 12 near Powell Butte. 50% hibernacula formation is expected on September 19, and October 21, respectively.
August 1, 2024
The mint fields we have been monitoring this year will be harvested soon, so this was the last week of trapping for this season. No mint root borers were caught in traps again this week, which makes for a whole season with no mint root borer moth captures. No variegated cutworms or loopers were caught either.
Based on the growing degree-day model, peak hatch for mint root borers was on July 30 in the madras area and will be on August 4 near Powell Butte. 90% moth catch will be on August 2 and August 6 for Madras and Powell Butte, respectively. For variegated cutworms, 5th instar larvae peaked on July 31 near Madras and are expected to peak on August 5 near Powell Butte.
While we did not capture any mint root borer moths in the trapping program this year, populations could be higher in other locations, especially for older mint stands. Mint root borer larvae damage mint stands by feeding on the roots, so it is always a good idea to sample for larvae in the fall and treat when needed. A good time to sample is around 5% hibernaculum formation, which is forecast for August 23 and September 9 for Madras and Powell Butte, respectively.
July 25, 2024
The optimal spray window for Vantacor is wrapping up. The model-predicted peak egg-laying date, which marks the end of the best time to apply Vantacor in-season, was on July 21 near Madras, and will be on July 28 near Powell Butte. Peak egg hatch for mint root borers is expected on July 29, and August 5 for Madras and Powell Butte respectively. The growing degree model for variegated cutworms predicts peak fifth instar larvae on July 31 and August 5 for Madras and Powell Butte, respectively.
So far this year, we have not caught any mint root borer moths in the pheromone traps. No variegated cutworms or loopers were caught in sweep net samples.
July 18, 2024
The optimal spray window is now. If you are planning to use an in-season Vantacor application on your mint, the optimal application window started on July 13 near Madras, and July 17, near Powell Butte. Try to complete your sprays before peak egg laying, which is predicted to occur on July 21 or July 26 in Madras and Powell Butte, respectively. Check the app to stay up to date with any changes in these predictions. No mint root borer moths have been caught in traps this year.
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 should peak on July 16 and 20, near madras and Powell Butte, respectively.
July 10, 2024
If you are planning to use an in-season Vantacor application on your mint, the best time to spray will be starting in the next few days. The growing degree model predicts that peak moth catch will be on July 12 near Madras, and July 16 near Powell Butte. Try to complete your sprays before peak egg laying, which is predicted to occur on July 22 or July 28 in Madras and Powell Butte, respectively. 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 overall 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.
No mint root borer moths have been caught in the traps yet this season, and no variegated cutworms or loopers were caught in sweep net samples. The model for variegated cutworms predicts that first instar larvae peaked on July 7 near Madras and should peak on July 10 near Powell Butte. Third instar larvae should peak on July 15 and 20, respectively.
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/central-oregon/. Select the weather station closest to you using the options on the left.
No mint root borer moths have been caught in traps so far, and no cutworms or loopers were found in sweep net samples. The growing degree model Predicted first catch on June 14 for Madras and June 21 for Powell Butte, and is predicting peak moth catch for mint root borer moths on July 15 and 16 for Madras and Powell Butte, respectively. For variegated cutworms, first instar larvae are expected to peak on July 7 and July 12, respectively.
Archived Reports – 2023
Late Aug/early Sep is the time to scout for Mint Root Borer (MRB) larvae in the soil if fall control is being considered.
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 is expected September 3 near Powell Butte, and occurred on August 19 near Madras.
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
Archived Reports – 2021
Central Oregon Mint Pest Alert Newsletter – August 28
Time for fall treatment.
Central Oregon Mint Pest Alert Newsletter – July 30
Plan to sample early for larvae in soil.
Central Oregon Mint Pest Alert Newsletter – July 23
MRB captures can vary a lot between fields, so be sure to scout your fields.
Central Oregon Mint Pest Alert Newsletter – July 16
Optimum application window closed/closing.
Central Oregon Mint Pest Alert Newsletter – July 10
The optimum application window for MRB and VC control with Coragen or Vantacor is ending soon.
Central Oregon Mint Pest Alert Newsletter – July 3
The optimum application window for MRB and VC control with Coragen or Vantacor is now.
Central Oregon Mint Pest Alert Newsletter – June 25
Upcoming heat wave moves up optimum application window for Vantacor or Coragen
Central Oregon Mint Pest Alert Newsletter – June 18
6 MRB were found in 1 field
Mint Pest Alert Newsletter – June 11
No MRB were found in traps this week, and no insects of interest were found in sweep net samples.
Mint Pest Alert Newsletter – June 4
Two MRB were found in a trap on June 3. First moth catch was expected on June 4.
Archived Reports – 2020
Central Oregon Mint Pest Alert Newsletter- September 11
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 Madras/Culver will reach 50% by Sept 17th. Prineville/Powell Butte should expect 5% hibernacula by Sept 16th.
Central Oregon Mint Pest Alert Newsletter- August 28
Control treatments must be applied before larvae form hibernacula (overwintering, soil-based cocoons). Based on the insect development model, hibernacula formation in Madras/Culver should be 5% by Aug 31st and will reach 50% by Sept 22nd. Prineville/Powell Butte should expect 5% hibernacula by Sept 22nd .
Central Oregon Mint Pest Alert Newsletter-August 7
According to the GDD models, optimal application timing for in-season control of Mint Root Borer (MRB) and Variegated Cutworm (VC) has passed in Madras and Powell Butte area. Coragen or Orthene application now may still control VC in Powell Butte/Prineville area. Average MRB moth counts decreased between the last two trapping events, suggesting we are past peak moth catch. According to the model, VC are past or entering 5th instar, after which they will drop to the ground to pupate and cannot be controlled with sprays.
New Invasive Leafhopper Species
Recently, a new invasive leafhopper species, known as Ligurian leafhopper (Eupteryx decemnotata Rey, Hemiptera: Cicadellidae) was reported by Bill Gerth, OSU Plant Clinic . 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. Occurrence in Central OR mint production systems and damage potential is still unknown.
Central Oregon Mint Pest Alert Newsletter- July 24
Peak moth catch was last week in Madras, which is supported by our trap counts decreasing this week. In-season control for Variegated Cutworm (VC) with Coragen or Orthene is most effective at early instar stages. Peak 3rd instar of VC in Madras was July 19, and is now in PB area. VC 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.
Central Oregon Mint Pest Alert Newsletter- July 17th
We are now in the best application window for the in-season management of MRB and variegated cutworm.
Central Oregon Mint Pest Alert Newsletter- July 9th
The optimal window for insecticide application and peak moth flight is beginning next week.
Central Oregon Mint Pest Alert Newsletter- July 2nd
Trap counts remain high again this week with peak flight fast approaching in the coming weeks.
Central Oregon Mint Pest Alert Newsletter- June 26th
High number of MRB (33 moths) were captured this week. Peak flight is approaching fast.
Central Oregon Mint Pest Alert Newsletter-June 19th
Few MRB adults (9 moths) were captured in the pheromone traps this week.
Central Oregon Mint Pest Alert Newsletter- June 12th
The first flight of MRB adults was predicted this week for Central Oregon and we captured 4 moths in the pheromone traps.
Archived Reports – 2019
Central Oregon
Central Oregon Mint Pest Alert Newsletter – August 29th
Central Oregon Mint Pest Alert Newsletter – August 7th
Central Oregon Mint Pest Alert Newsletter – August 1st
Central Oregon Mint Pest Alert Newsletter – July 24th
Central Oregon Mint Pest Alert Newsletter – July 17th
According to the growing degree day model, peak moth flight of MRB was reached on July 15th in Culver/Madras area, and will be reached July 23rd. Moth counts in the Culver/Madras area decreased from an average of 4 moths/trap on July 11th, to 3 moths/trap on July 18th. This indicates the model prediction is in line with what we are finding in the field.
There was a minor increase in moth counts this week in the Powell Butte area. We continue to find alfalfa loopers in the field and small populations of cutworms. Continue scouting your own fields to make management decisions. If control is needed, now is the optimal time to apply Coragen for control of MRB, loopers and cutworms in the Culver/Madras area. See newsletter for more information.
Central Oregon Mint Pest Alert Newsletter – July 11th
Adult MRB counts in pheromone traps are picking up, with some sites at 8/trap while others remain at less then 5/trap. Reports in Central Oregon are also finding areas with increased MRB flight activity. Alfalfa loopers are showing up more frequently in sweep net samples, so please continue to scout fields over the next week to determine if populations are increasing in your fields.
Central Oregon Mint Pest Alert Newsletter – July 5th
Third week of trapping continues to find low adult MRB and cutworm/looper numbers – less than one per trap on average.
Central Oregon Mint Pest Alert Newsletter – June 28th
Second week of trapping has found very low adult MRB numbers, a total of four (4) have been collected in the last week. A few alfalfa loopers have also been found.