Sweet corn in Washington gets damaged at three stages: seed and seedlings right after sowing, leaves while the plant grows, and silks and kernels once ears form. The first thing you see is a symptom, such as a gap in the row, a ragged leaf, or a chewed ear tip. The county office of Washington State University Extension can put a name on the cause. A full guide to the crop is in Growing Sweet Corn in Washington.
Which pests attack corn in Washington
Washington State University Extension is the service that documents garden pests in the state, and its county offices are where a damaged plant gets a name. A statewide pest list runs long, and most of it has nothing to do with a corn row. Insects that live on tree fruit, conifers, or ornamental shrubs stay on those hosts, because they feed on bark, buds, or foliage that corn does not have. A corn patch deals with a much shorter list, and the quickest way to sort it is by the part of the plant being eaten.
What eats corn seed and seedlings?
Seed and young seedlings are the most exposed stage. Anything that feeds on germinating seed, or on the soft stem at the soil line, shows up here, and the damage is easy to miss because the evidence is a plant that never appeared. Soil-dwelling insects and animals that dig up seed both fit this group. Cold, wet spring soil makes it worse, since seed sitting in the ground for extra days is seed that something can find. The stage of the plant tells you which group to suspect first.
What chews leaves, silks, and kernels?
Once seedlings are up, the next group is leaf chewers. They leave holes and shredded edges, often first in the tight whorl at the center where new leaves unfold. The last group feeds on the ear itself: silks, then the kernels underneath. Birds and other wildlife also take ripening ears, though that damage looks different from insect feeding, with whole ears pulled down or stripped rather than small tunnels and nibbled tips.
A Washington garden rarely has all of these at once. Which ones show up depends on the county, the soil, and the neighbors, and that is a question for the extension office rather than a guess from a photo of a leaf.
When each one shows up, and what it does first
The calendar here starts with the freeze window at the Seattle reference station. NOAA NCEI Climate Normals put the mean last spring freeze between February 27 and March 18, and the mean first fall freeze between November 13 and November 30, using the 30 to 70 percent probability band. That is western Washington, mild and maritime. Eastern Washington, beyond the Cascades, is high desert with a far shorter season, so those dates do not apply there.
When does damage start after planting?
A mild last-freeze date does not mean corn goes in the ground that week. Sweet corn needs soil above 60 F, according to Utah State University Extension, and that warmth arrives well after the last freeze. Clemson Extension is more specific: “Do not plant before the soil temperature at the 4-inch depth is at least 50 ºF. Wait to plant extra-sweet varieties until soil temperatures reach 65 °F.” An extra-sweet (sh2) seed sown at 50 F tends to rot rather than sprout, which looks like pest damage but is not.
The first sign of seed or seedling feeding is a gap in the row in the first weeks after sowing: a missing plant, a seedling cut at the base, or a dug-up hole where seed was. Dig a few spots before deciding. A hollowed or chewed seed points to a feeder. A soft, intact seed points to cold, wet soil.
When do leaf and ear damage show up?
Leaf chewing appears as the plant grows, and the first sign is a row of ragged holes across the unfolding whorl leaves. Ear damage starts when silks emerge. From silk emergence, watch the ears closely, and that is the stretch when chewed silks, damaged kernels at the tip, or ears torn open by animals show up. This clock is separate from the other one. Sixty to ninety days from planting tells you whether a variety fits the season before the first fall freeze, while the silk clock tells you which week to pick. Late plantings that run into November meet the end of the window with ears still filling. The question of fit is covered in Will Sweet Corn Ripen in Washington?
Telling the damage apart from everything else
Many corn problems look like insect damage and are not. Dry soil, cold nights, nutrient shortages, wind, and poor pollination all leave marks that get blamed on bugs. Dig up a missing seed and look at it before you blame an insect. The table below gives the sign that separates each look-alike. It does not name what is in your garden. For that, take a sample to your county extension office.
| What you see | Possible causes | What settles it |
|---|---|---|
| Gaps in the row, seed missing | Feeding on seed, or rot from cold wet soil | Chewed or hollowed seed versus soft, intact seed; soil temperature at 4 inches when sown |
| Pale, stunted young plants | Cold soil, or a nutrient shortage | Uniform yellowing that clears as soil warms versus yellowing that starts on the lower, older leaves in a V shape |
| Leaves rolled or gray at midday | Water stress | Leaves open again by evening or after watering; no insects or chew marks |
| Torn leaves, snapped stalks | Wind or hail | Clean tears and a pattern across the whole patch after a storm; no feeding trace |
| Spots or lesions on leaves | Disease | Defined spots with edges rather than holes or missing tissue; a sample at the extension office confirms |
| Ears with scattered missing kernels | Poor pollination, or ear feeding | Gaps spread across the ear with no chewing versus chewed kernels and damaged silks at the tip |
Summer heat is rarely the cause in western Washington. The Seattle reference station averages 3.0 days a year at 90 F or more, so heat scorch is uncommon there, and rolled leaves are more often a watering problem. Pollination failure, on the other hand, is common in patches planted as a single row or two, which is one reason corn is grown in blocks.
What actually works here, and what is a waste of time
What works on a short, cool season?
On a season this tight, timing does more than any product. Sow by soil temperature at 4 inches, not by the calendar. At 50 F for ordinary sweet corn and 65 F for extra-sweet, seed germinates fast and spends less time in the ground where it can be eaten or rot. When to Sow Sweet Corn in Washington goes through how to read that for your area.
A physical barrier set at the right moment works better than a treatment applied late. Row cover or fencing goes on before seedlings emerge or before ears ripen, not after the damage is done. Plant in blocks of three or more rows, as Utah State University Extension advises. A block pollinates better than a long single row, and a compact shape is easier to cover and watch.
Keep the types apart in time as well. Utah State University Extension notes that sweetness is lost if su, se, and sh2 types tassel at the same time, so separate plantings so they do not tassel together. Then pick on time. The signs come together: dry brown silks, husks still moist and green, and milky juice from a punctured kernel. Clemson Extension adds that “Sweet corn loses sugar from the kernel rapidly at high temperatures… Sweet corn can be stored under optimal conditions for about five days, but will lose sweetness with each day of storage.”
What is a waste of time?
Spraying before you know what is feeding on the plant often hits the wrong target and can harm insects that do no damage. Treating a look-alike problem, like drought or cold-soil rot, does nothing at all. Planting early because the last freeze is mild is another trap, since cold, wet soil and low light hold corn back well past that date. The extension office is the only source that knows what is registered for home use in Washington, so this site names no products.
Where to check this for your own county
Washington State University Extension has an office in each county, and that office knows what is moving through local gardens in a given season. A pest that is common on one side of the Cascades may be rare on the other, and conditions can differ from one valley to the next, or between a river-bottom garden and one on a slope. What is documented across the state does not tell you what is in your own rows.
Local weather matters just as much. The freeze dates given earlier come from one western Washington reference station, and an eastern Washington garden will have a different window, a different soil warm-up, and different insects. The county office can tell you what is local, what to look for this season, and what is registered for home use. Bring a fresh sample or a clear photo, along with the date and the stage of the plant.
Contact your county WSU Extension office before you spray, and ask what has been reported nearby this season.
Common questions
Can I plant sweet corn right after the last freeze in western Washington?
Not by the freeze date alone. Soil at 60 F comes well after the last freeze. Clemson Extension says not to plant before the soil at the 4-inch depth reaches at least 50 ºF, and to wait until 65 °F for extra-sweet types. Measure the soil at that depth.
How do I know when ears are ready so animals do not get them first?
Look for three signs together: dry brown silks, husks still moist and green, and milky juice from a punctured kernel. Count from silk emergence, watching the ears closely until picking. Do not rely on any one sign alone.
Does the layout of the patch matter?
Yes. Plant in blocks of three or more rows, not a single long row. Keep su, se, and sh2 types from tassel overlap, since sweetness is lost if they tassel at the same time.
Who can identify a pest I cannot name?
Your county WSU Extension office. Take a sample and a photo of the damage, and note the plant stage and date.