Crop Profile for Mint in Montana

General Production Information

Top producing states in the U.S. include Indiana, Michigan and Wisconsin. It also grows well in Oregon, Washington, Idaho, South Dakota and Montana because all these states are north of the 41st parallel, where the right amount of daylight produces good yield and quality of oil. 

Mint is a perennial plant that produces no seed. It is planted in rows, with state-certified, disease-free, root
stock or underground runners from existing plants. By the second year the plants spread out, creating a solid
mint meadow. 

The oil is stored in glands on the underside of the peppermint and spearmint leaves. An acre (0.4 ha) of mint
produces about 76 pounds (34.5 kg) of oil. 

Mint can be difficult to grow and special care must be taken to ensure only the finest quality finished oil.  

Production in the U.S.	About 75,000 acres all mints; about 2,160 tons oil.
Production in Montana	Approximately 1,800 acres of spearmint and peppermint (2002). 2.4% of total U.S. mint production. In previous years production was approximately 7,000 acres. Mint production in Montana is centered around Flathead county in western Montana

A soil test is obtained prior to planting to determine the soil pH and levels of available macronutrients. The pH of the soil should be kept slightly alkaline, between 5.5 and 6.5. The soil should have at least 100 pounds available phosphorus and 400 pounds available potassium per acre. If the soil test indicates levels lower than what is recommended, fertilizer should be applied prior to planting.

Since mint is grown as a perennial crop, it is important to have the soil as weed-free as possible prior to planting. Fall plowing and disking are done to reduce weed populations. Turning the soil over will also protect the plants from winter kill. Excessive weeds compete with mint and reduce yields, and may contribute off-flavors to the mint oil at harvest, resulting in lowered oil quality.

Roots are dug with a mint root digger (sometimes a modified potato digger).  The digger usually digs into a truck that hauls the roots to the field to be planted.  

Mint is planted in fall (mid October to early November) or early spring (late March to early May). An acre of well-established mint will usually yield enough stolons to plant 10-15 acres. Stolons are generally dug from a nursery bed in an existing planting. Roots are dug with a mint root digger (sometimes a modified potato digger).  The digger usually digs into a truck that hauls the roots to the field to be planted.  It is important to dig stolons from weed-free soils to prevent the introduction of insects, diseases, or perennial weeds such as quackgrass or toadflax into new plantings along with the mint. Small pieces of mint stolons are dropped in the row with a mechanical planter. Go to the Montana Mint Growers Association website for a graphic and description of this process. The furrows into which the stolons are planted must not be made too far ahead of time so that adequate moisture is present at planting time. The stolons are then covered with 2 to 3 inches of soil. Stolons can not be planted if they have sprouted more than 2-3 inches. New plants become established as roots and shoots grow from the nodes on the stolons.

This first planting outside of the greenhouse is called the nuclear generation.  Nuclear plants are sometimes hilled, and are not harvested for oil.  Nuclear generation roots are dug the fall after transplanting, or the following spring.

When the nuclear generation is replanted it becomes the foundation generation.  The next two years are generations #1 and #2, and are used to establish most oil production fields.  Healthy fields will produce for several years.

Fertilization takes place in late March to May. Generally not all nitrogen is applied at this time and some nitrogen is usually applied through the water in June through July.   Irrigation typically occurs from April through October, depending on weather. Irrigation is stopped about a week before harvest, then start again right after harvest, depending on weather. More irrigation during the summer and fall seems to make a big difference in winter survival. Typically Montana mint producers water once a week if it doesn't rain in the June through July time.  

Mint is cut and windrowed with a swather or sickle bar windrower. Recently growers have been using rotary windrowers because they move quickly through the field and cut closer to the ground so that oil yields per acre are increased. It also leaves the mint hay in smaller windrows so that it dries faster and is ready to distill sooner. Hay should be cut before it has reached 10% of full bloom to achieve high yields and high quality oil. After flowering the plant’s production of mint oil decreases and existing oil begins to deteriorate in quality.

After the mint is cut and windrowed, it is allowed to cure until the leaves are thoroughly wilted and partially dried. The hay should not be allowed to become too dry or left too green since it will be difficult to distill. The hay is picked up, chopped, and blown into the distilling tub by a conventional field chopper.

The essential oils are removed from the mint hay through on-farm steam distillation. Because the essential oils in mint are insoluble in water, steam may be used to extract these oils under pressure. Custom-built, wagon-mounted distillation tubs are commonly used. Steam is introduced to the tubs through perforated pipes that run along the bottom of the tub. A high-pressure boiler generates steam for the distillation. After distillation, the steam-vaporized mint oil is run through a water-cooled condenser to recondense the oil which floats on top of the water and can be easily extracted in its pure form.

Mint is usually plowed under after the first killing frost to protect the stolons from winterkill. Stolons can not be plowed more than 4-5 inches under or they will not survive. There are many theories on how to plow. The concensus is that roots and stolons need to be on a slant after plowing to allow for shallow to deep placement of residue. This helps to insure that somewhere on the slant, the rootstock will survive.

The harvesting season for mint is mid-June to late September, depending on the location of the fields. 

Worker Activities

Pest Management In Mint

Prevention

Planting Pest and Disease-Free Certified Material

General Pest Control Considerations For Mint Grown in Montana

Weeds are a major problem in mint production.  Weeds reduce mint hay and oil yields by competing for light, moisture, and nutrients.  Mint oil quality can also be reduced, since some weeds can impart objectionable colors, odors and flavors.

A number of broadleaf and grassy weeds are known to reduce yields and cause economic injury to mint by imparting off-flavors to the oil. Since mint  spreads by stolons (aboveground runners), mint is planted in wide rows and plants are spaced apart. This and the fact that mint breaks winter dormancy late in the spring allows for weeds to gain the upper hand. Since tillage can spread Verticillium wilt, the mint producers rely on a number of registered herbicides (Sinbar, Stinger, Goal, Buctril, Basagran, Paraquat, and others) to manage the majority of weed problems.

Weed control starts in the year of establishment by selecting fields that have a history of low weed pressure.  High quality, disease-free root stock should be planted at a population high enough to ensure a uniform stand.  Cultural practices which result in a competitive mint crop also help to reduce weed invasion.  This includes the use of optimum irrigation and fertilizer inputs, as well as minimizing and control insect and disease outbreaks.  Mechanical cultivation will effectively control early season weeds.  However, if verticillium wilt is a concern, tillage should not be used. 

In Montana, spraying for weeds occurs from  late March through June, depending on weed pressure. There may be more than one application.

Many insect pests complete their disruptive life cycle in underground plant parts where treatment is difficult, thus enabling populations to increase to devastating levels. A field of mint is typically left in production for 3 to 5 years, enabling pest populations to increase over the life of the stand.

Key insect pests in Montana include: spider mites (Tetranychus urticae), various cutworms and loopers (Family: Noctuidae),  and aphids (Ovatus crataegarius).

Several insecticides (Comite, Dyfonate, Kelthane, Lorsban, Lannate, Malathion, Metasystox, and Orthene) are registered and used to combat these pests in mint. Many of these registered compounds are disruptive to beneficial insects and counterproductive to establishing and maintaining IPM programs. Plant stress caused by insects, notes and other arthropods, also result in similar types of interactions with Verticillium wilt and other pests as those previously discussed. These arthropod pests, especially the immature (larval) life stages, are spread by infested plant material.

Description: Two species of loopers feed on mint leaves. Alfalfa looper, Autographa californica, and cabbage looper, Trichoplusia ni, vary in color from light to very dark green. Mature larvae range in size from 1 to 1 1/2 inches long and eat ragged- edged holes through the leaves or in from the leaf margins. Loopers are distinguished from cutworms and armyworms by their "looping" behavior when moving and by having only two pairs of abdominal prolegs (cutworms and armyworms have four pairs). Both species commonly overwinter as pupae in cocoons in plant debris. Adults begin emerging in late March or April. Eggs are usually deposited singly on weed hosts, particularly wild mustards. They hatch in 3 to 5 days and the larvae feed for about 2 weeks before pupating in cocoons on the host plant or in plant debris. The total development time from egg to adult requires about 30 days. The second generation adults emerge shortly afterwards. There are two to three generations each year. Larvae of the second generation cause the most serious damage on mint, particularly during late June and July. Larvae of the alfalfa looper and cabbage looper may occur at the same time as the variegated and spotted cutworms and the western yellowstriped and Bertha armyworms.

Management of Loopers: Alfalfa and cabbage looper larvae are usually found in mint from mid-June to early August. Take 10 straight line sweep net samples in at least five different sites in fields up to 30 acres. Add an additional sample site for every additional 10 acres. Count the number of larvae and calculate an average number per sweep net sample. Field inspections for loopers are usually done at the same time as sampling for variegated cutworm. Loopers and variegated cutworm will both be found in sweep net samples and ground search samples. Loopers, unlike the variegated cutworm, can usually be found on foliage during the day.

The number of loopers and other foliage-feeding cutworms can be combined to determine whether or not to apply an insecticide. Early in the season (early June) populations of loopers alone may not need control because, in most cases, feeding occurs on leaves that will be shed by the plant as a result of shading prior to harvest (Coop, 1987). Also, the percentage parasitism or diseased loopers usually exceeds 50 per cent in most fields most seasons and does not cause significant leaf injury. Parasitized loopers can usually be distinguished from nonparasitized loopers by the presence of a black spot on the back of the looper near the back end. Parasitism can be detected by selecting some of the larger loopers from the sweep samples, cutting off the head of each, and pulling each larva apart. A smaller parasite larva will be found inside the looper larva. It is important for growers and consultants to realize that many loopers found in samples are parasitized and will not cause leaf injury. If treatment is justified, refer to the insecticide table for registered insecticides and rates for control of loopers. 

The biological insecticides, Biobit HP (Valent - Bacillus thuringiensis (Bt)) and Dipel DF (Valent - Bt) are registered in Montana and may provide very good control of loopers and small cutworms when applied by ground with a sticking agent and in sufficient water to provide thorough coverage.

In Montana, insecticide spraying for worms (loopers, cutworms, and/or army worms) occurs from April though July if they occur at high enough levels. Cutworms can severely set back or kill the plants in the spring (April - May) by chewing them off right below the ground, generally on the sandier areas of a field. Army worms and cutworms come on again in July. Loopers generally come on in July, but don't generally cause less damage than the army worms. Since the mint oil is extracted from the leaves, July cutworm damage causes decreased oil yield.  

Confirm (Dow Agrosciences - tebufenozide) is labeled in Montana for alfalfa  loopers and Bertha armyworms. 6 to 8 lbs/A for early season applications and 8 to 16 lbs/A for mid to late season applications. Post harvest interval (PHI) is 14 days.

Lannate (Dupont-methomyl) is labeled in Montana for variegated cutworm and alfalfa looper (3 pt/A, 14 day PHI) and flea beetles (2 1/4 to 3 pt/A, 14 day PHI)

Description: Twospotted spider mites, Tetranychus urticae, are tiny (0.25 to 0.5 mm long) eight-legged arthropods with two large spots on both sides of the body. Mites are typically found on the undersides of leaves but may colonize entire plants during outbreaks. Silk webbing on the undersides of leaves, and bronzing, stippling and burning of leaves are characteristic signs of spider mites. 

The female mites overwinter in the soil and in plant debris in and around mint fields. Females become active in the spring as temperatures warm, and they begin depositing eggs on the undersides of leaves. Eggs hatch in 4 to 5 days and the entire life cycle from egg to adult may require 1 to 3 weeks, depending on the temperature. Infestations of mites may occur as early as March during warm weather. During the summer months, mite populations can increase very quickly, particularly in hot, dry weather, along dusty roads, during periods of water stress and even in response to insecticide applications. Therefore, fields should be inspected at least weekly to detect the buildup of damaging populations.

The practice of spring flaming mint fields west of the Cascade Mountains to control rust contributes to the suppression of spider mite populations . Additionally, predator mites occur in mint fields and can be a significant factor in limiting spider mite populations and problems. Learn to distinguish between spider mites and predator mites.

Management of Mites: Two spotted spider mite has become progressively more important as a pest of mint throughout the Northwest. Probable reasons may include: 1) development of resistance in populations of mites in mint fields which have been repeatedly treated with miticides such as Kelthane (dicofol), 2) reduced use of flaming for spring rust control, 3) changes in production practices or pesticide use patterns, causing increased mortality of natural enemies, or 4) improved awareness of their pest status and the use of proper sampling methods. Either fall plowing or spring flaming of mint contributes greatly to the cultural control of mites in mint fields by reducing early season populations that are initiated from overwintering female mites .

Correct sampling procedures for spider mites involve close observation of leaf samples taken from different areas in a field . Include leaf samples from plants in areas that are high, excessively dry, and have had past problems with mites, such as dusty areas or field margins. The use of a 10X or 15X hand lens will enable growers to distinguish between spider mites and predator mites (see below). By walking in a "Z" or "M" pattern in the field, randomly collect stems and inspect the leaves from the bottom, middle and top of the stems for mites (count adults, nymphs and eggs). Classify the leaves as "infested" or "not infested" if the mites (adults and nymphs) number five or more. For each 30 acres, 14 individual field sites should be monitored for mites by examining a total of 45 leaves (15 leaves each from the bottom, middle, and top) from 15 randomly selected mint stems per site. It also is important to count the number of predator mites on each leaf. These natural predator mites help reduce spider mite populations below economic levels through harvest. If predator mites are present, the field may not require immediate treatment and should be rechecked at a later date. Treatment of spider mites is justified if there are no predator mites and if 18 or more of the leaves in the 45-leaf sample taken at each site are infested with five or more spider mites. It is also important to estimate the number of spider mite eggs on the leaves, because their number will help predict an emerging infestation. 

Injury to mint plants begins to occur when populations of spider mites reach five per leaf. Feeding injury caused by densities greater than five mites per leaf increases water stress, reduces photosynthesis, and alters terpene metabolism, resulting in elevated levels of menthol and neomenthol and decreased levels of pulegone . Peppermint leaf phenolics reduce spider mite fecundity and increase developmental time .

Spider mite populations can increase rapidly during hot, dry weather and even after an insecticide application. Fields should be inspected twice weekly during these times. 

Spring flaming, used  for rust control west of the Cascade Mountains in Oregon and Washington,  reduces the incidence of spider mites early in the growing season. This may result in fewer applications of miticides during the growing season . Fewer miticide applications will help delay the development of mite resistance, protect beneficial predators, and reduce production costs.

In Montana, insecticide spraying for spider mites if the occurs mainly in July.  

Metasystox-R (Gowan - ) is labeled in Montana for the control of aphids and mites at 3 pt/A.

Description: Variegated cutworm, Peridroma saucia, is a common pest of many vegetable and field crops, including mint. They overwinter as half grown larvae in soil or under plant debris in or around mint fields, begin feeding in April, and mature in late April and May. Larvae pupate in earthen cells in the soil. Adults emerge in May and early June and deposit eggs in clusters of 200 to 500 on the undersides of leaves. Eggs hatch in 4 to 7 days and larvae begin feeding on plant foliage. Larvae feed for 4 to 6 weeks and then pupate in the soil. Summer generation adults emerge in late August and deposit eggs. Larvae hatching from these eggs feed until cold weather and then become inactive and overwinter. There are two overlapping generations each year. 

Often the larvae of other species occur on and defoliate mint at about the same time as the variegated cutworm. Life cycles are about the same as that of the variegated cutworm. However, at times Bertha armyworm larvae may be present before detectable populations of variegated cutworm. Because its leaf feeding damage usually occurs earlier in the growth of mint and its population density is generally less than that of variegated cutworm, it is important to distinguish between the two species. An early insecticide application against this species may not necessarily control variegated cutworm. One well-timed remedial application for cutworms and loopers reduces cost and pesticide load on the field, and minimizes other possible problems, such as the induction of spider mite problems, destruction of beneficial insects, and increased pressure for resistance development in pest insects.

Management of cutworms: Foliage feeding cutworms and armyworms include the variegated cutworm and other foliage-feeding cutworms such as spotted cutworm, Amathes c- nigrum, western yellowstriped armyworm, Spodoptera praefica, and the Bertha armyworm. These different cutworm species may occur together in the same field during July and early August. The sampling program and treatment threshold described below for the variegated cutworm may also be used for the aggregate of these species.

For variegated cutworm, inspect fields closely from mid-June to just prior to harvest, remembering that if an insecticide application is considered, the preharvest interval (PHI) must be observed. Growers may want to consider harvesting earlier to avoid further crop injury. Sweep net samples can be used to sample small larvae (first, second, and third instars). Usually 10 straight line sweeps at 5 different sites in fields up to 30 acres are sufficient to evaluate larval populations. Add an additional site for every additional 10 acres. Largest collections of these smaller larvae will occur on cool, overcast days, or when fields are sampled early in the morning or near dusk on still days. Avoid sweep net sampling when mint is water-stressed or foliage is wet. Very often, more than 50 per cent of the cutworms found in samples will be parasitized; this may alter the treatment thresholds.

The decision to apply an insecticide is usually based on the average number of larvae found per 1,000 sq cm (cm2)(an area slightly larger than 1 sq ft) on the soil surface. To estimate larval populations of fourth, fifth, and sixth instars, inspect the soil surface by first vigorously shaking mint foliage and closely observing and recording the number of larvae per 1000 cm2 randomly through the field. Take a ground search sample every 5 acres for fields up to 30 acres. Add an additional site for every 10 acres in fields that exceed 30 acres. Look very closely for small and curled-up larvae under and in folded leaves on the ground. Remember that larvae can fall into cracks on the soil surface. When leaf-chewing is quite evident and cutworm counts from ground searches are low, consider returning after dark and sampling with a sweep net when the larvae actively feed on the foliage.

Sequential sampling plans have been developed for variegated cutworm using sweep net samples to estimate larvae (instars 2 to 4) and for ground search samples (1000 cm2) to estimate larval instars 4 to 6. Using these plans, treatment of larval instars 2 to 4, sampled with a sweep net, is recommended if 60 larvae are collected from a minimum of 11 different field sites (a minimum of 10 sweep net samples should be taken at each site). Treatment is not recommended if fewer than 44 larvae are collected in sweep net samples. For ground search sampling, treatment of larval instars 4 to 6 is recommended if 24 larvae are collected in 1000 cm2 samples taken from a minimum of 18 different sites. Treatment is not recommended if fewer than 17 larvae are collected in the 1000 cm2 samples.

A sex pheromone is commercially available and can be used to detect and monitor adult males of the variegated cutworm in the spring. Trapping males could provide valuable early season information to growers concerning the potential need to control cutworm larvae during June and July. Sticky traps baited with this lure can be set in fields in late April and monitored weekly or biweekly through June. Although action levels for an insecticide or Bt treatment have not been developed based on moth catches, it is likely that large and continual catches greater than 25 per week will result in similarly large populations of larvae being observed approximately 2 weeks following peak trap counts. The real value of pheromone traps lies in the fact that they signal when to begin inspecting fields for larvae, thereby greatly improving timing of an insecticide application, if one is necessary. Also be aware that, occasionally, large trap catches will not result in large larval populations. This is particularly true when the mint field does not have a resident population of variegated cutworm and the trap catches are a result of males being lured into traps from other crops. Conversely, a small trap catch does not necessarily mean that an action level will not be exceeded by the larvae.

Naturally occurring predators and parasites play an important role in suppressing cutworm populations throughout all mint-growing areas in the Northwest. The principal parasites of cutworms and loopers on mint are Meteorus communis, Nepiera sp., Campoletis sp., and Copidosoma sp. Growers and consultants are urged to consider that it is likely that a significant proportion of the larvae in samples may be parasitized. Leaf consumption by parasitized larvae is much reduced and there is very little reduction in oil yield caused by these larvae. Parasitized larvae can be distinguished from nonparasitized larvae only by dissection. Select some of the largest larvae from the sweep or ground search sample. With each, cut the head off, and pull the larva apart. If the larva is parasitized, another smaller larva of the pasrasite will be found inside the cutworm larva. If time permits, larvae can be reared in the laboratory to determine the number parasitized. Depending on the percentage of larvae parasitized, you can increase the suggested action thresholds.

Orthene generally has been more effective in controlling larger cutworm and looper larvae and grasshoppers. Lannate controls smaller larvae and has been shown to prevent egg hatch in laboratory studies and field observations in other crops. Lannate also satisfactorily controls populations of adult mint flea beetle when present at the time of application -- Orthene does not. Research has shown that variegated cutworm feeding on peppermint is less susceptible to insecticides because the terpenes found in mint leaves induce enzymes that detoxify the insecticides. On the other hand, certain peppermint terpenes have been shown to increase mortality of variegated cutworm larvae and pupae.

Bacillus thuringiensis (Bt) applied at 1 to 2 quarts/acre can reduce populations of small cutworms. It benefits from the addition of a spreader sticker or wetting agent and is more effective if applied at night, when larvae are actively feeding on foliage being sprayed, and in the absence of direct sunlight and extreme temperatures. It does not control pests other than loopers, cutworms, and armyworms. Activity on variegated cutworm and other cutworms and armyworms is variable, depending on the trade product and its formulation. The major disadvantage of the use of Bt is the fact that the dense mint foliage prevents penetration and coverage of the leaves with Bt.

In Montana, insecticide spraying for worms (loopers, cutworms, and/or army worms) occurs from April though July if they occur at high enough levels. Cutworms can severely set back or kill the plants in the spring (April - May) by chewing them off right below the ground, generally on the sandier areas of a field. Army worms and cutworms come on again in July. Loopers generally come on in July, but don't generally cause less damage than the army worms. Since the mint oil is extracted from the leaves, July cutworm damage causes decreased oil yield.   

Confirm (Dow Agrosciences - tebufenozide) is labeled in Montana for alfalfa  loopers and Bertha armyworms. 6 to 8 lbs/A for early season applications and 8 to 16 lbs/A for mid to late season applications. Post harvest interval (PHI) is 14 days.

Lannate (Dupont-methomyl) is labeled in Montana for variegated cutworm and alfalfa looper (3 pt/A, 14 day PHI) and flea beetles (2 1/4 to 3 pt/A, 14 day PHI)

Lorsban 4E (Dow Agrosciences - chlorpyrifos) is labeled in Montana for armyworms and cutworms at 1 to 2 pt/A.

Orthene (Valent - acephate) is labeled in Montana for the control of cutworms, army worms and aphids at a rate of 1 lbs/A with a 14 day PHI.

These small, soft-bodied insects feed on plants by sucking the plant sap. They are typically found on the undersides of leaves. When aphid numbers are great enough, the plant’s leaves may curl or the entire plant may be stunted. In severe cases, plants may die. Aphids are also vectors of diseases that can be more damaging than the aphid feeding itself.

Mint aphids overwinter around the bases of plants, on roots, beneath plant debris, and in cracks and crevices in the soil. Females give birth to mobile nymphs in the spring. A single generation may be completed in 7 to 10 days and as many as 12 to 15 generations may be produced in a year. The higher the temperature, the faster the rates of development and higher the population densities. Mint aphid is a minor problem on both peppermint and spearmint.

Mint root borer, Fumibotys fumalis, overwinters as a prepupa within an earthen cell 1/2 to 1 1/2 inches below the soil surface. Pupation occurs within the cell during April and early May. Adult emergence begins in June and early July, continuing through the summer until early August . Peak emergence occurs during July. Females deposit eggs that resemble tiny scales along the leaf veins on both lower and upper surfaces. Each female can deposit 100 to 200 eggs during a 1-to-2 week period. Eggs hatch in 5 to 10 days, and first-stage larvae feed on leaf surfaces for 1 or 2 days before dropping to the soil surface to tunnel into rhizomes at the bases of buds. Individual larvae feed in rhizomes for 70 to 80 days during August, September, and early October. They emerge from rhizomes and construct earthen cells in October in which to overwinter. There is a single generation each year. The mint root borer occurs on peppermint and spearmint in all growing areas in the Northwest. 

Mint root borer larvae cause damage by feeding inside peppermint and spearmint rhizomes from late July through mid-September. Damage resulting from feeding injury weakens mint stands, which overwinter poorly and regrow slowly in the spring.

Inspect fields during the growing season when adults are active. When disturbed, adults fly a few feet and land on the underside of a leaf. Collect moths by sweeping foliage, then shaking net contents to the bottom and slapping lightly against a hard surface. Empty net contents onto a light background. Presence of adults in a field should serve as a signal to take soil samples before harvest or as soon as possible after harvest in August. If samples are taken in July or early August, larvae will be very small and only found by the most skilled observer and should be extracted with Berlese funnels. Late September and October soil samples will usually only detect larvae after damage is done and results of chemical control will normally be poor. Soil samples (1 sq ft in size) should be taken from several locations in the field. We recommend that two samples be taken for every 2 1/2 acres. Take a minimum of 25 samples per field at several different sites. Samples should include soil and rhizomes to a depth of 2 to 3 inches. These samples also may be used to estimate the population of root weevil larvae and symphylans in the fall, although the depth of samples may be too shallow to collect a representative sample. Samples may be sorted by hand in the field, but we recommend the use of Berlese funnels to separate the larvae from the sample. If using Berlese funnels, separate the soil and rhizomes to enhance recovery of larvae. If samples are inspected in the field, be sure to inspect rhizomes for damage and larvae which may be within the rhizome. Depending on soil texture and moisture, the use of screens to sieve soil may speed up the process of locating larvae in the samples that have exited rhizomes.

Treatment is justified if an average of two to three larvae are found per square foot sample. The only insecticide registered to control mint root borer is Lorsban, which should be applied after harvest. See the insecticide table for rates to apply. Lorsban must be immediately irrigated into the soil to be effective and, since Lorsban has low solubility in water and may tie up in the carbon and organic matter layer on the soil surface, it requires at least 1 inch of water. Treat only the acreage that can be irrigated immediately. Lorsban 4E may also be applied through sprinkler irrigation systems as a postharvest broadcast application to control mint root borer. Before applying Lorsban through a sprinkler irrigation system, thoroughly read and follow the directions on the label. Consult with Montana Department of Agriculture before applying this product through a sprinkler system.

Tillage after harvest has been shown to significantly reduce mint root borer. In southcentral Washington and parts of Idaho, strip tillage combined with Lorsban applied prior to mid-September provides 90 per cent or more control in furrow- irrigated mint fields. In sprinkler-irrigated fields, plowing and double disking mint fields in late October or early November or in the spring during February or March provides 80 per cent or more control. Tillage may spread verticillium wilt; growers should use this practice only in fields with a low incidence of verticillium wilt. Growers may observe benefits from tillage, such as stand rejuvenation, suppression of some weed species, redistribution of nutrients, disruption of the layers of accumulated carbon and organic matter, and the establishment of uniform pH levels in the upper 4 to 6 inches of soil.

A sex pheromone is available commercially to sample for mint root borer adult males. The successful development of this sex pheromone in a trapping system could provide valuable early-season information to growers concerning the need to control mint root borer larvae. Revealing the presence or absence of mint root borer adults in a field, concentration of adult activity in a certain area, and/or size of an infestation based on trap catches are examples of how pheromones have been used to successfully manage pests in other crops. 

Lorsban (chlorpyrifos - Dow Agrosciences) is registered in Montana. Apply at a rate of 4 pints/A. One postharvest application per season.  PHI is 90 days.

Verticillium wilt of mint is caused by the fungal pathogen Verticillium dahliae. Either directly or indirectly, our Integrated Pest Management programs revolve around managing this disease. This disease along with other pests, was transported throughout the Midwest on contaminated root stock during the 1930's and growers have kept moving to new land because of the spread of this disease. All major U.S. mint growing areas are presently experiencing difficulties with various levels of this disease as well. Wilt symptoms may appear in the first year of production if the mint is grown from plant material contaminated with the mint strain of Verticillium dahlias.

Once a field has become contaminated with wilt, the microsclerotia can remain in the soil for long periods of time and inhibit future mint production.  Once the plant becomes stressed from Verticillium wilt, the severity of other pests (insects, diseases, weeds) increases proportionally. This disease is considered to be the major pest threat to mint production in the U.S. and is spread by the planting of contaminated material.

Rust of mint, caused by the pathogen Puccinia menthae, is another major problem in several mint growing districts.Planting material originating from areas or fields infested with rust contributes to the spread and severity of this problem.

Powdery mildew is another concern to mint growers. This disease is especially a problem in spearmint production, but has increased in severity in peppermint as well. Current control consists of multiple applications of elemental sulfur. Sulfur has been shown to eliminate beneficials, especially predator mites and also imparts undesirable flavor characteristics to mint oil.  This disease is also spread by planting of contaminated material.

Plant parasitic nematodes. The root-lesion nematode (Pratylenchis penetrans) and rootknot nematode (Meloidogyne hapla) are major pest problems in all mint growing regions. The needle nematode (Longidorus sylphus) has also been shown to drastically affect peppermint plants. Vydate is register in Montana (1/2 to 1 1/2 gallon/A) and applied in the spring to control these nematode pests. Vydate has a 21 day Post Harvest Interval (PHI). Destruction of the root system by these pests adversely affects the vigor of the crop and it's ability to ward off other pests over the course of it's entire production cycle. The reduction in vigor adversely affects the crops ability to withstand additional stresses such as those caused by insects, diseases, and weed pressure. Contaminated planting material is a primary source for the introduction and spread of the nematodes in mint.

Harvest and Distillation

Harvest is generally in August to early September. The crop is swathed and let dry 2 to 5 days in normal drying conditions. Then it is chopped into tubs and hauled to the distillery.  After harvest the fields are checked for mint root borers. If the population are high enough they should be treated. 

In the distillery, pressurized steam shoots through tubs vaporizing the mint oil. An excellent description of this process is located on the Montana Mint Growers website.  The oil vapors and steam pass through a line at the top of the tubs to water-cooled condensers, where they return to a liquid state. In a separator, the mint oil rises to the top and is drawn into huge drums. Samples are then tested and the oil is either bought or rejected. Oils accepted for purchase are stored in a temperature-controlled warehouse. 

Equipment and Facilities for Essential Oil Extraction

Steam Distillation Unit

Boiler -To generate high pressure dry steam used in vaporizing and extracting the oil. Cost depends upon size of the boiler. Allocate approximately 100 hp for every stall used (or tub being distilled). A new 200 hp boiler may cost approximately $40,000 while a 400 hp may cost approximately $70,000. 

Tubs -These are the mobile tubs that are brought to the field, filled up with chopped plant material and then brought back to the distillation building. It contains headers and steam lines at its floor where steam is passed and dispersed throughout the tub. Depending upon size - approximately $15,000-$20,000 each. 

Condenser - Condenses the steam and the oil vapors coming out of the tub. The vertical condenser is now commonly used. Approximately $2000.00 each. 

Receiver - Receives the condensate or liquefied water vapor and oil coming out from the condenser. It also makes it easy to separate the oil (which usually floats) from the water. Approximately $600.00 each. A distillation unit with 4 stalls can process 400-500 acres of essential oil crops. 

Site preparation (water, gas, drainage, power needs) and plumbing, sensors, fittings, etc. are needed to complete the whole distillation systems.

Field Production Equipments

In addition to standard farm equipments such as cultivators, harrows, sprayers, fertilizer applicators, swather, forage pickup/chopper, tractors and trucks, a mint digger and planter is needed to produce a mint crop. The digger is used to dig the stolons from the mother plants for planting by the mint planter. Each equipment costs approximately $20,000.00.

An acre of mint stock can plant approximately 5-10 acres of new land.

Reeves Petroff, Montana State University Pest Management Center, (406) 994-3518, rpetroff@montana.edu

Montana Mint Growers Association - http://www.montanamint.addr.com/

Robert Stougaard, Northwestern Agricultural Research Center, Kalispell, Montana. (406) 755-4303

Crop Profile for Mint in Idaho - http://pestdata.ncsu.edu/cropprofiles/docs/IDMint.html

Integrated Pest Management on Peppermint - Oregon State University - http://www.orst.edu/Dept/entomology/ipm/ipmp2.html

Irrigating Peppermint - http://eesc.orst.edu/agcomwebfile/edmat/html/em/em8662/em8662.html

Integrated Pest Management on Peppermint - http://ippc2.orst.edu/mint/ipmpdemo.htm

Midwest Vegetable Production Guide - http://www.entm.purdue.edu/entomology/ext/targets/ID/IDpdf2000/ID-70-76.00.pdf

Minnesota Grown Opportunities - http://www.mda.state.mn.us/mgo/publication/mint.pdf

Mint In Michigan - http://www.geo.msu.edu/geo333/mint.html

Mint in Wisconsin - http://ipcm.wisc.edu/piap/mint.htm

Mint Industry Council - http://www.pesp.org/1996/mirc96.htm

Montana Mint Growers Association - http://www.montanamint.addr.com/

National Agricultural Statistics Service - Crop Summary http://usda.mannlib.cornell.edu/reports/nassr/field/pcp-bban/cropan01.txt

Nitrogen Uptake and Utilization in Mint - http://ippc2.orst.edu/mint/nitrogen.htm

Northwestern Agricultural Research Center - http://ag.montana.edu/nwarc/default.htm

Seasonal Peppermint Plant Growth - http://ippc2.orst.edu/mint/mintgrowth.htm

Weed Management Handbook For Montana, Utah and Wyoming, 2001-2002. 

Weed survey of peppermint fields in the Flathead valley, Montana - http://jgg.unl.edu/grasses/wildoat/montras.htm