IF You See This…. Early Season Vegetable Insect Pests

Weather patterns have been inconsistent so far this growing season, causing a wide level of variation in vegetable garden growth.  However, one aspect that is probably consistent across all gardens is that early season insect pests are present and starting to munch their way through our gardens.  Some are worse than others, in regards to the level of damage they will do to plants, but all of them merit monitoring and management.

The first step in properly making management decisions is identification.  If you don’t know what you’re facing, you will have much more difficulty effectively managing the critters or knowing if it is worth your effort to do so.  Let’s review the key insect pests that you may be seeing and the vegetables on which you may find them, or their damage.  The links at paragraph ends take you to factsheets that offer much more information about the specific pests.

The most general insect at this time of the year is the black cutworm.  It is also probably the most frustrating, as it can simply make plants disappear overnight.  The caterpillars are fairly robust, dark gray with a few darker spots, and are generally only active at night, so they are very difficult to find.  Their name describes what they do – they physically chew through and cut off young plants and either eat the entire thing right there, leave the cut off portion laying on the soil surface, or dig into the soil and pull the plant with it.  As mentioned, they do this at night and during the day they are hidden in the soil, usually somewhat close (within 1 foot or so) to the last plant on which they fed.  https://vegento.russell.wisc.edu/pests/black-cutworm/


Predicting cutworm damage is difficult, as they feed on both seedlings and transplants of almost all vegetables.  Transplant damage is more economically important, but may be a bit simpler to stop.  Placing a physical barrier around the plant stem is the simplest way to accomplish that goal.  You can use barriers that wrap directly on the stem, but they are a bit trickier to apply and need to either expand, degrade, or be removed as the plant grows.  Larger diameter barriers such as cans, pvc pipe pieces, sturdier plastic bottles/jugs, or other suitable materials do very well, and many gardeners save bags full of them to place around each tomato, pepper, cabbage, cauliflower, eggplant, or any other transplant which they put into the garden.  If you see damage in seeded rows, do some digging in the top inch of soil around the area of newest damage and you can hopefully find and kill the caterpillar before they continue their way down the row.

Most other insects are more particular about which plants they want to eat.  The next most general insect is the corn seed maggot.  And, of course, its preferred food is not corn, but beans.  The adult fly lays their eggs in freshly worked soil and the maggots feed on imbibing seeds and developing seedlings.  They really like lima beans, wax beans, green beans, cucumbers and melons, squashes, and, of course, corn and a few others.  Effective management methods are few, but planting multiple times to ensure missing the primary flight is one possibility.  Another is to put a layer of clean wood ash over the row after planting.  This changes the texture enough that they are less likely to lay their eggs there.


For the cabbage family, the imported cabbageworm is the most serious pest and this day-flying white butterfly is already out and about.  They lay their eggs on all vegetables in this family, but are most damaging on cabbages, as they can chew into the head and create opportunities for fungal pathogens to cause further damage.  Catching and killing the adult butterflies is an option, as well as physically controlling the caterpillars on the plants.  Insecticides are also available, including Bt products and others, most commonly including the active ingredient carbaryl.


Another cabbage family critter is the cabbage maggot, very similar to the corn seed maggot already discussed.  Their maggots feed on roots, though, and create very poor quality, often inedible, radishes, turnips, and rutabagas.


Vine crops are not immune to insect damage.  The earliest one that we can see is the cucumber beetle.  First generation adults emerge to feed and to lay eggs in the soil.  Their feeding can be serious enough to kill seedlings and their larvae can substantially decrease vigor of developing plants by feeding on roots.  Squash bugs can also overwinter and cause early season damage.  Both of these insects are a bit more difficult to control, but there are insecticides labelled for their control, or you can use physical control or mesh coverings if you only have a few plants.

https://cdn.shopify.com/s/files/1/0145/8808/4272/files/A3755-E.pdf for squash bug information.

https://cdn.shopify.com/s/files/1/0145/8808/4272/files/A3751-E.pdf for cucumber beetles.

Our earliest vegetable, asparagus, also has a pair of beetles which affect it – the common and spotted asparagus beetles.  Adults chew holes on the edges of spears, causing misshaping and quality decreases.  They lay their eggs directly on the spears, as well.  The eggs are small, dark projections which look like bristles.  If they hatch, the larvae crawl up the stalk and feed inside the developing seed pods.  After harvest is complete, insecticide options are valid, but physical control works best until harvest is over.  Squish the adults and scrape off the eggs for simplest effect.


Although there are other insects you may find, the last ones we’ll discuss are underground generalists – grubs and wireworms.  Usually, these are only serious on garden edges that border lawns or grassy areas or in newer garden sites.  These immature beetles feed on roots and can cause seedling death or plant stunting, if found in sufficient numbers.  There are not any highly effective control methods in the home garden, unless you happen to have a pet skunk.

https://cdn.shopify.com/s/files/1/0145/8808/4272/files/A3758-E.pdf to learn about wireworms.


There are many ways to find out more information about these, and other, insects.  One web site which has very detailed information is the Pests page of the UW-Madison Vegetable Crop Entomology group, found at https://vegento.russell.wisc.edu/pests/  This web site is oriented toward commercial vegetable growers for control methods, but has a very thorough listing of vegetable affecting insects.  Homeowner-oriented information for most garden affecting insects can be found on two different Extension websites, at the main Extension publications site under the lawn & garden section, at https://learningstore.extension.wisc.edu/ or on the vegetables section of https://hort.extension.wisc.edu/links/

Locally, you can contact Scott Reuss, UW-Madison Division of Extension Marinette County Agriculture & Horticulture Agent, with any questions that you may have about horticulture or agriculture topics.  He will help you accurately identify the pest your plants are facing and help you consider management options.  He can be reached by e-mail at scott.reuss@wisc.edu or via telephone at 715-732-7510.