This month, Northern Gardening hosts Diane Booth and Joan Farnam talk to Jeff Hahn, U of M. Extension entomologist and author of “Insects of the North Woods” about the insect invasion in our gardens this year, and local gardener Charlie Butter talks about his square-foot gardens and a new vegetable garden project at the hospital that he has developed.
Some garden insect pests that are being seen this year in Cook County include the following:
1. Flea beetles
• Numerous species: striped flea beetle, western black flea beetle, spinach flea beetle, potato flea beetle
• 1/16 – 1/8”
• Black, bronze, bluish or brown to metallic gray, stripes
• Large black legs used for jumping when disturbed
• Overwinter as adults in the leaf litter, etc.
• Early spring adults lay eggs in small holes in roots, soil, leaves
• Common on radishes, broccoli, cabbage, turnips, eggplant, peppers, tomatoes, potatoes, spinach, melons,
• Following egg hatch they feed on roots – little damage except to potatoes
• Adults cause most of the problems feeding on foliage.
• Typical damage are small rounded, irregular holes usually < 1/8” diameter looking like shot-holes.
• Monitor with yellow sticky cards
• Use floating row covers
• Plant a trap crop – radishes before you plant your main crop
2. Onion maggots
• A fly (Delia antique) lays eggs in early spring at the base of an onion and in nearby cracks in the soil.
• The larvae form is what burrows into the onion bulb or lower part of the onion.
• The foliage wilts or is stunted as the first sign.
• If you pull the onion you will usually find the culprit burrowed into the bottom part of the onion. They feed on the bulb and rot invades as well.
• A floating row cover can protect your plants from having the adult fly lay their eggs.
• Rotate your onions so you don’t plant them in the same place.
3. Variegated cutworm
• Eggs of the variegated cutworm, Peridroma saucia, were found in large numbers on windows, siding, screens this spring.
• Apparently, variegated cutworm moths from outbreaks in southern states were blown north over a period of a few weeks in May and eggs were laid at night on emerging crops, gardens, fence posts, buildings, trees and almost anything that holds still long enough.
• All these eggs will hatch, yielding tiny, translucent caterpillars with a few dark hairs and over-sized, black heads. They will be hungry. And, they have an extremely wide host range: most vegetable garden plants, fruit trees, rhubarb, raspberries, strawberries, ornamental plants, shrubs, hostas, canola, wheat, corn, sunflower, clover and other row crops. Cutworms feed at night and rest during the day so it is hard to find them, but the damage will be easy to spot: seedlings nipped off at ground level and large holes eaten out of leaves all season long.
• The variegated cutworm is also called the climbing cutworm because mature caterpillar stages will spend both days and nights on their host plants in contrast to most other species of cutworm. After feeding, they'll pupate in the soil, emerge as moths and start another generation, likely in July. Adults created from this generation will migrate south in October to other states in order to overwinter.
• Projections for next year…. what can we expect? Will they pupate and overwinter in our soil, adults fly south to overwinter? If we have a cold winter, the cutworms will not survive it.
• Variegated cutworms are beginning to show up in alfalfa in SW MN. The variegated cutworm is a migrating moth that makes its way into the region and occasionally arrives early and in large enough numbers to cause problems. Alfalfa is one of several host crops the moths are attracted to for laying eggs. The most distinguishing characteristic of the variegated cutworm is the 4 to 7 pale yellow, circular spots on the back of the larva. Its general body color is variable (olive to nearly black), but usually brown. The underside of the caterpillar is cream colored. There is a narrow, orange-brown stripe along the side.
• Became noticeable in Minnesota in the 1990’s.
• Forficula auricularia
• Many areas of Minnesota experienced high earwig numbers last year. Cook County had a high infestation two years ago and we are seeing some again this year. Be on the watch for them in your garden this summer.
• Earwigs are about 5/8 inch long, with a flat, reddish brown body and very short wings. They look like a cockroach or a rove beetle but are distinctive because of the pair of pinchers (cerci) on the tip of their abdomen. Nymphs are similar to adults except they are smaller and generally lighter in color.
• They love moisture and usually come out to feed at night.
• They are scavengers that often feed on decaying plant or insects. They will also feed on healthy plant tissue including flowers and vegetables.
• The damage often looks like slug damage except there isn’t a slime trail.
• Oil traps vs. rolled up newspaper traps in the garden. You can set out rolled up newspapers or similar objects to trap earwigs. You can also place old tuna fish cans baited with fish oil or vegetable oil. Set them out during evening in areas where you are seeing earwigs in your garden. In morning, shake the traps above a pail of soapy water to remove and kill the insects.
• Keep the top of the soil dry in your garden.
• Permethrin around the perimeter of your home may help deter them from coming inside. It is best to caulk everything and prevent them from getting into your indoor space.
5. Spotted milk millipede
• Blaninlus guttinlatus
• Snake-like slender body (whitish / translucent) with pinkish spots on the side
• Soil inhabitants that feed on decaying plant material.
• They have been found here eating zucchini plants – feeding damage to the root system. They can also attack other plants especially when we have dry weather.
• Last year they were especially bad for one grower in Cook County.
6. Imported Cabbageworm / Cabbage Butterfly
• Pieris rapae
• Winter is spent as a pupa amongst plant debris.
• Adult females lay yellow bullet shaped eggs on leaves.
• 2-4 generations a year
• Like broccoli, cauliflower, cabbage
• Use of exclusion with reemay
• Bacillus thuriengensis
7. Strawberry Root Weevil
• Otiorhynchus ovatus
• Very small, ¼ inch long, black or dark brown with rows of pits along their back
• Feed on roots of strawberries, evergreens, raspberries, grapes, etc.
• Adults emerge in early summer and feed on the edges of foliage, leaving a characteristic notched appearance
• In hot dry summers, they can become invaders in your home looking for cool, damp conditions. They are attracted to moisture.
• They are being found this year near water on docks, lakeshores and in basements, sinks, bathtubs.
8. Colorado Potato Beetle
• Leptinotarsa decemlineata
• Found occasionally in Cook County
• Adults 3/8” long, yellow and black stripes on back
• Larvae are reddish / red-orange with a dark head
• Usually one generation a year
• Hand pick
9. Potato Leafhopper
• Empoasca fabae
• Pale green, 1/8” long, move sideways when disturbed
• Yellowing of tip of leafs followed by browning, cupping, distortion.
• ‘Hopper burn’
• Rose leafhoppers similar, but nymphs cannot move sideways. Pale yellow to creamy white color.
• White apple leafhopper is also similar.
10. Four-lined Plant bug
• Poecilocapsus lineatus
• Adults are yellow usually with 4 dark lines on their back.
• ¼ -1/3” long / immature forms are bright red-orange with black dots on the thorax
• Feeding damage is little round circles of necrotic tissue damage
11. Tarnished Plant Bug
• Lygus lineolaris
• Adults are generally oval, about twice as long as wide, and about ¼ inch long. Generally brown with some yellow and reddish markings.
• Feeds on developing leaves, flowers, fruits, killing the areas around the feeding site.
• Catface injuries to fruit; hard nubbins for strawberries, etc.
12. Tobacco or Geranium Budworm
• Heliothis virescens
• Caterpillars can reach 1.5” and feed on flowers and buds. Found in Cook County by holes in geranium and petunia buds.
• Hand pick or use Bacillus thuriengensis
13. Corn Earworm
• Helicoverpa zea
• Migration of adult moths can occur in our county. (Don’t overwinter here)
• Eggs are laid on the silks of the corn
• The small larvae tunnel down into the corn and eat for about 4 weeks.
• Mineral oil on the silks when moths are around?
• Cut off the damage to the end of the ear of the corn and use the rest.
14. Japanese Beetle
• Popillia japonica
• Overwinter as a nearly full-grown grub below frost line in winter.
• Adults emerge in late June and early summer, feed on foliate, mate, and return to lawn areas. Females lay eggs in small masses in soil cavities 2-4” deep. One year cycle but can extend to 2 years.
• Adults feed on foliage of more than 300 species: rose, mountain ash, willow, linden, grape, Virginia creeper, birches, ornamental apple, plum, cherry, etc.
• 1,300 species+
• Normal reproduction is asexual. Sexual forms usually occur in one generation a year.
• Suck sap from the phloem of plants and can cause injuries including transmit viruses, etc.
• Honeydew that is secreted can be associated with sooty mold.
• Common: apple aphids; lupine aphids; balsam twig aphid;
16. Leafhoppers carrying Aster Yellows
• What leafhoppers are most common for this? Aster leafhopper? (Macrosteles quadrilineatus)
• Phytoplasma that is picked up by the leafhopper, develops for up to 10 days or 3 weeks before it can be transmitted through saliva from the leafhopper to another plant.
• 1-5% of all leafhoppers carry the aster yellows phytoplasma during the growing season.
17. Gladiolus thrips, iris thrips, daylily thrips
• Thrips simplex
• Feeding at the base of emerging leaves produces silvery scarring that later turns brown.
• Infestation of the flowers produces scarring and distortion.
• Corms can be corky, sticky when infested with thrips.
• Store corms at 35-40 degrees for 4 months to kill thrips.
• Napthalene flakes can be added to the corms in a tight paper bag for storage?
18. Eriophyid Mite Galls
• Erinea (red felt-like patches) on maple leaves
• Maple bladder galls
• Ash flower galls
19. Iris Borers
• Macronucutua onusta
• ‘Water logged leaves’ are a typical sign. Larvae feed at the base of leaves and hollow out the rhizomes. Wound areas are frequently colonized by rots and the plants may be killed
• Larvae are pale pink with a distinct brown head; adults are dull brown moths
Charlie Butter has been working with square-foot gardening in his yard for the last few years and has seen some impressive results.
• The square-foot gardening technique is based upon the book by Mel Bartholomew by that name first published in 1981.
• Use a square foot system to make the most use of your garden space allowing you to raise only the amount of food you really need and will eat.
• 1 square foot = 4 lettuce plants, 1 pepper, 9 spinach or bean plants, 16 carrots or onions or radishes.
• Defines boundaries so that you take care of the plants you do have – less work, carefully grown plants – higher production.
• Vine crops are grown vertically to take advantage of smaller spaces.