Key to the major mint pests from damage symptoms

Identification of peppermint pests and beneficials
Use mouse to select area of plant injured

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INSECTS FEEDING ON MINT LEAVES

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1. Plants cut-off slightly below or above the soil surface; leaves with ragged- edged holes and above ground stems with notches eaten out. CUTWORMS such as: VARIEGATED CUTWORM {bmc larvai.bmp}(Figs. 3, 4 PNW Pub. #182), SPOTTED CUTWORM{bmc larvai.bmp} (Fig. 5 PNW PUB. #182), BERTHA ARMYWORM, WESTERN YELLOWSTRIPED ARMYWORM {bmc larvai.bmp} (Fig. 6 PNW Pub. #182), REDBACKED CUTWORM {bmc larvai.bmp} (Figs. 1, 2 PNW Pub #182), and BLACK CUTWORM. Damage from redbacked cutworm and black cutworm usually occurs in April, May, and June. Other cutworms typically cause injury in July and August.

2. Ragged-edged holes eaten through the leaves and around the leaf margins particularly on leaves mid-way and higher on the plants. LOOPERS including: ALFALFA LOOPER {bmc larvai.bmp} AND CABBAGE LOOPER (Figs. 7, 8, PNW Pub #182).

3. Terminal leaves and buds tied together with silk. Upper surfaces of leaves skeletonized or with small holes. FALSE CELERY LEAFTIER {bmc larvai.bmp} (pg. 5, PNW Pub. #322 and (Figs. 17, 18, PNW Pub. #182)

4. Ragged or completely eaten leaves present on plants around the field margins at first, later entire field with a ragged appearance. GRASSHOPPERS {bmc ghi.bmp} (Fig. 22 PNW Pub #182).

5. Small semicircular holes or irregularly shaped notches chewed in the leaf margins. STRAWBERRY ROOT WEEVIL ADULTS {bmc srwi.bmp} (Fig. 14 PNW Pub #182).

6. Very small holes in leaves giving a shot-hole appearance to the leaves. MINT FLEA BEETLE ADULTS {bmc mfbai.bmp} (Fig 12 PNW Pub #182).

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INSECTS FEEDING ON RHIZOMES AND ROOTS

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1. Plants cut-off at or slightly below the soil surface in the spring (April, May, early June). Lower foliage with ragged-edged holes. Cutworms found beneath soil surface during the day and feeding on above-ground foliage at night. REDBACKED CUTWORM {bmc larvai.bmp} and other Euxoa species (Figs. 1, 2 PNW Pub. #182) and BLACK CUTWORM. Redbacked cutworm occurs only east of the Cascade Mountains.

2. Plants show wilted appearance above ground during August, September and early October. Rhizomes with tunneling around the nodes or rhizomes hollow. MINT ROOT BORER LARVAE {bmc larvai.bmp} if 1/2 inch long with three pairs of true legs (pg 3 PNW Pub. #322, Fig. 9 PNW Pub. #182). If larvae smaller, 1/8 inch long, C-shaped, white legless grub found feeding inside mint stems near the soil surface in Idaho or eastern Oregon, then MINT STEM BORER LARVAE {bmc larvai.bmp} (Fig. 15 PNW Pub. #182.)

3. Plants slow to grow in the fall and early spring. Surface feeding injury on the rhizomes, roots and stems. Small C-shaped white legless larvae1/4 to 1/2 inch long with brown head may be found inside roots or in the soil around or beneath roots. STRAWBERRY ROOT WEEVIL LARVAE{bmc larvai.bmp} (Fig. 13 PNW Pub #182). Also includes other weevil species such as black vine weevil, obscure root weevil, and rough strawberry root weevil.

4. Plants slow to grow in the spring. Feeding injury evident on surface of roots or just beneath root epidermis, brown "tracking" evident just beneath root epidermis Very small white larvae 1/8 inch long with three pairs of legs and a brown head may be found inside the roots or in the soil around roots. MINT FLEA BEETLE LARVAE {bmc larvai.bmp} (Fig. 11 PNW Pub. #182).

5. Plants stunted in irregular spots in the field, plants often very slow-growing in the spring. Small, 1/8 to 1/4 inch long, white centipede-like animals feeding on small roots leaving few root hairs, roots stunted and discolored with prunned appearance. Found principally west of the Cascade Mountains. GARDEN SYMPHYLAN {bmc symphi.bmp} (Fig. 21 PNW Pub. #182).

6. Plants appear stunted and slow growing from feeding injury on roots and rhizomes. Tan or dark brown, shiny, segmented larvae, 1/2 to 3/4 inch long, with three pairs of legs and key-hole-like structure on the last abdominal segment. WIREWORM LARVAE {bmc larvai.bmp} (Fig. 19 PNW Pub. #182).

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SUCKING INSECTS ON LEAVES OR STEMS

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1. Feeding injury caused by small and soft-bodied insects often found in large numbers on the undersides of the leaves and along the stems. Feeding may cause stunting, discoloration and leaf curling. Leaves often covered with sticky substance (honeydew) and black sooty mold growing on honeydew. MINT APHID {bmc aphidi.bmp} (Fig. 24 PNW Pub. #182).

2. Feeding injury caused by small, soft-bodied animals with eight legs visible under 15X magnification. Large numbers found on the underside of leaves. Leaves may have webbing on the undersides. Feeding causes speckled appearance on the leaves. Leaves may turn brown or bronze and drop from the plant, particularly late in the growing season. TWOSPOTTED SPIDER MITE {bmc mitei.bmp} (Fig. 23 PNW Pub. #182). Predator mites also may be present on the leaves (Fig. 36 PNW Pub. #182).

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BENEFICIAL INSECTS & MITES

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Many other insects, spiders, predators and parasitoids are often found in mint fields. Most of these other animals are not pests and may be either predators or parasites of pests. All beneficial insects and mites should be conserved by using insecticides only when necessary to control a pest that has exceeded the treatment threshold.

Predators effectively control many small, soft-bodied pests such as aphids, mites, small worms, and insect eggs. The most commonly found predators include:

LADY BEETLE ADULTS {bmc ldbgai.bmp} are about 4mm long, oval and convex in shape, reddish-orange or black, usually with spots on the winds. LARVAE {bmc ldbgli.bmp} are gray or bluish-grey, with numerous yellow, white, or red spots (Figs. 25, 26 PNW Pub. #182).

SYRPHID FLY LARVAE {bmc syrphli.bmp} (Fig. 28 PNW Pub. #182) are about 12 mm long, wrinkled or slug-like in appearance,tapering to a point at the head. GREEN LACEWING ADULTS {bmc lcwgai.bmp} are green to yellowish-green with four, delicate transparent wings with many veins and crossveins. LARVAE {bmc lcwgli.bmp} are slender, mottled gray or yellowish-gray and about 9.5 mm long (Figs. 29, 30 PNW Pub. #182).

BIGEYED BUG ADULTS {bmc miridi.bmp} are about 3 to 6 mm long, buff gray or blackish in color with large, prominent eyes. Nymphs resemble adults except in size and absence of wings (Fig. 33 PNW Pub. #182).

MINUTE PIRATE BUG ADULTS {bmc minpi.bmp} are oval-shaped, about 3 mm long, very flat, and marked conspiciously with black and white. Nymphs and adults have piercing-sucking mouthparts enclosed in a long beak (Fig. 34 PNW Pub. #182).

DAMSEL BUG ADULTS are tan or gray, with piercing-sucking mouthparts and enlarged front legs for grasping their prey. They have slender bodies, and are 10-12 mm long. NYMPHS {bmc damai.bmp} resemble adults, except they are smaller and have no wings (Fig. 35 PNW Pub. #182).

SPIDERS are important but often overlooked predators in peppermint. They feed on most insects especially in the younger stages. A list of the spiders found in peppermint has been compiled (McIver and Belnavis, 1986).

BIRDS are frequent predators of cutworms and loopers, especially as the insects reach the middle and later larval stages.

In some areas, BATS can be important predators of flying insects, including cutworms and loopers.

PREDATOR MITES {bmc predmi.bmp} are similar to the twospotted spider mite in size, 0.25 to 0.5 mm, but are more flattened and lack spots (Fig. 36 PNW Pub. #182).

PARASITES (also known as parasitoids) are important in the control of many cutworm and looper larvae, particularly variegated cutworm and the loopers. Most are tiny wasps which are easily over-looked. However, they play an important role in controlling insect pests in mint. In most instances, larvae that have been parasitized die before causing significant plant injury. Parasites are either Hymenoptera wasps {bmc ichai.bmp} (Figs. 31, 32 PNW Pub. #182) or Diptera flies, which resemble common house flies.

PARASITIC NEMATODES {bmc nemai.bmp} are tiny parasites that enter soft- bodied insects and release a symbiotic bacterium that reproduces and kills the host (Fig. 37 PNW Pub. #182). They control soil pests in mint: mint root borer, strawberry root weevil, and mint flea beetle.