Know Your Pests
Know your pests. Protect your yield.
Healthy crops can tolerate some feeding. Stressed crops cannot. This guide covers the insects and mites that hit corn and soybean hardest, how to identify the damage they leave behind, and how to build a system where pest pressure is easier to manage before it turns into a rescue situation.
Pests don't pick fields at random
Insects are not just looking for food. They are looking for plants they can actually digest. The healthier the crop, the harder it is to feed on, and the more likely an insect is to fly past it and land somewhere weaker.
Plants leak information all the time. Stressed plants release distinct volatile compounds, alcohols, aldehydes, and simple sugars that pest insects can detect from surprising distances. Healthy, fully-fed plants release a different chemical signature and produce sap that is too dense and too complete to nourish a soft-bodied feeder.
That is what the Brix reading is really telling you. Plant sap sugar content is a fast, in-field readout of how well the plant is photosynthesizing, moving nutrients, and building complete sugars instead of weak, attractive ones.
Healthy plants are not just more tolerant of pests. At a high enough Brix level, the sap itself becomes indigestible, and in many cases toxic, to the insects trying to feed on it.
The Plant Health Scale
Volatile Compounds
Stressed plants release a different bouquet of compounds: ethanol, simple aldehydes, and stress-linked terpenes that travel on the wind. Many pest insects are wired to detect that signature and orient toward it. A healthy plant simply does not advertise itself the same way.
Simple vs. Complete Sugars
Low-Brix sap is loaded with simple sugars and free amino acids that soft-bodied insects can digest easily. As Brix rises, the plant builds those into complete sugars and complete proteins. The sap gets denser, more nutritionally complete, and much harder for piercing-sucking insects to process.
Defense Chemistry
A truly healthy plant doesn't just become harder to digest. It produces secondary metabolites, defense compounds the plant can only afford to make when it has full nutrition and active soil biology supporting it. At high Brix, those compounds can sicken or kill the insects that try to feed on it.
The takeaway for the field
You cannot spray your way into healthy sap. You build it through soil biology, balanced minerals, root function, and stress reduction. The pest pressure you feel in a given field is partly an outcome of those choices.
Four kinds of pests, four different scouting patterns
The first question is not what to spray. The first question is what kind of feeding is happening, where it is happening, and whether it is crossing an economic threshold.
Chewing Insects
Chewing insects remove tissue. They clip seedlings, skeletonize leaves, prune roots, or feed on silks, pods, and kernels. Damage is visible, but risk depends heavily on crop stage.
Piercing-Sucking Insects
These pests remove sap, inject saliva, or transmit disease. Damage often shows up as yellowing, stippling, curling, stunting, or poor pod fill rather than obvious missing tissue.
Borers & Internal Feeders
Internal feeders are harder to scout because damage happens inside stems, stalks, seeds, or growing points. Look for entry holes, frass, deadhearts, tunneling, and lodging.
Mites & Soil Pests
Some expensive pest problems start below the canopy or below the soil surface. Aboveground symptoms can look like drought, nutrient deficiency, or disease until you dig.
Pests that hit corn and soybean hardest
Tap any pest for ID notes, crop risk, damage signs, scouting tips, and management priorities. The goal is not to kill every insect. The goal is to keep pressure below economic damage while protecting the beneficials that are helping you.
Damage recognition, by feeding type
Pest damage is a pattern. Missing tissue, clipped seedlings, stippling, tunneling, pod damage, and root pruning each point you toward a different group of pests and a different management decision.
Defoliation
Missing leaf tissue looks dramatic, but not all defoliation is equal. Soybeans can tolerate more leaf loss during vegetative stages than most growers think. Corn damage depends heavily on whether the growing point is protected and whether the pest is still actively feeding.
- Round holes in soybean leavesBean leaf beetle, green cloverworm, early defoliators
- Skeletonized leavesJapanese beetle, grasshoppers, heavy leaf feeding
- Ragged whorl feeding in cornArmyworm or fall armyworm
- Edge feeding firstGrasshoppers, Japanese beetles, migrating pests from field borders
Stand Loss
Stand loss can come from insects, cold stress, planter issues, seed quality, herbicide injury, or seedling disease. Digging is what separates a guess from a diagnosis.
- Plants clipped at soil lineBlack cutworm
- Seed missing or hollowed outSeedcorn maggot, wireworms
- Uneven emergence after cool, wet conditionsSeedcorn maggot, seedling disease, cold stress
- Deadheart in young cornStalk borer, wireworm, cutworm, early whorl injury
Root Damage
Root pests are easy to miss because the aboveground symptoms look like stress. Rootworm, grubs, wireworms, compaction, and disease can all create uneven, weak-looking plants.
- Pruned corn rootsCorn rootworm larvae
- Goosenecked or lodged cornRootworm injury, wind after root pruning
- Wilting in patches with weak rootsWhite grubs, wireworms, rootworm, compaction, disease lookalikes
- Soybean stunting with weak rootsNematodes, grubs, disease, compaction
Stippling & Yellowing
Sap-feeders do not chew holes. They pull from plant tissue and can shift plant energy, reduce fill, or cause yellowing and bronzing that looks like weather stress.
- Tiny white or yellow specks on leavesSpider mites, thrips, leafhoppers
- Bronzed soybean leaves in hot dry weatherTwo-spotted spider mite
- Curled soybean leaves with sticky honeydewSoybean aphid
- Yellowed field edgesSpider mites, grasshopper feeding, drought stress
Boring & Tunneling
By the time you see the plant response, the pest may already be inside. Split stems and stalks when the aboveground symptoms do not make sense.
- Frass at stalk entry holesEuropean corn borer, stalk borer
- Broken stalks or dropped earsEuropean corn borer, stalk rots, wind
- Deadheart in cornStalk borer or early-season borer injury
- Soybean stems breaking near harvestDectes stem borer
Silks, Pods & Seeds
Late-season feeding needs a different eye. The crop has less time to recover, and feeding can open the door for disease, molds, poor grain quality, and harvest loss.
- Silks clipped before pollinationCorn rootworm beetles, Japanese beetles
- Kernels chewed at ear tipCorn earworm, western bean cutworm, birds, ear molds as secondary issue
- Pod scarringBean leaf beetle
- Shriveled or damaged soybean seedStink bugs, pod feeders, seed disease
The conditions that turn pest presence into pest pressure
Weather and field conditions set the stage, but crop vigor decides how much damage shows up. A stressed crop can be hurt by pest levels that a healthy, fast-growing crop would outgrow or tolerate.
Hot & Dry
Hot, dry weather favors spider mites, grasshoppers, and sometimes chinch bugs. Drought-stressed plants also tolerate feeding poorly, so the same pest level can cause more economic damage.
- Field edges burning down first
- Soybean leaves bronzing
- Grasshoppers moving from roadsides or pastures
- Mite flare-ups after broad-spectrum insecticides
Cool & Wet at Planting
Cool, wet soils slow germination and give seed and seedling pests more time to feed. Fields with fresh manure, green cover crop residue, or decaying organic matter can be more attractive to seedcorn maggot.
- Delayed emergence
- Stand gaps
- Fresh green residue ahead of planting
- Organic matter or manure attracting egg-laying flies
Late or Uneven Crop Stage
Late or uneven fields can act like magnets. They stay attractive longer, line up with later pest flights, and often become the field pests choose when everything else is past the preferred stage.
- Late-planted corn during moth flights
- Later soybean fields during beetle movement
- Green islands after surrounding fields mature
- Uneven stands with multiple growth stages
The four-layer pest defense
A real pest program starts with crop health, scouting, and biological balance. Insecticides are a tool, but they belong at the end of the decision tree, not the beginning.
Crop Vigor & Stress Tolerance
A crop that emerges fast, roots well, and keeps photosynthesis moving can tolerate low-level feeding better than a crop that is already stressed.
- Plant into fit conditions whenever possible
- Build early root growth and seedling vigor
- Keep calcium, boron, manganese, zinc, copper, and potassium in balance
- Avoid excessive soft growth from over-applied nitrogen
- Reduce compaction and drought stress before pests expose it
Scouting & Thresholds
Pest management starts with knowing what is actually in the field. Presence is not the same as economic damage.
- Scout by crop stage, not just calendar date
- Check field edges and interior separately
- Use sweep nets, root digs, sticky traps, and visual counts where appropriate
- Estimate percent defoliation honestly
- Treat when thresholds are met, not when pests are simply present
Beneficial Biology & Cultural Control
Beneficial insects and soil biology are part of the pest control system. The goal is to make the field less friendly to outbreaks and more friendly to natural suppression.
- Rotate crops to disrupt rootworm and residue-linked pests
- Manage weeds and green bridges before planting
- Protect predators and parasitoids whenever possible
- Use cover crop termination timing wisely
- Build soil structure so the crop outgrows early feeding
Chemical Intervention, Last Ditch
Insecticides can be valuable when thresholds are reached, but routine broad-spectrum sprays can flare secondary pests by killing beneficials.
- Use thresholds and crop stage before spraying
- Choose the narrowest effective product when possible
- Avoid spraying when beneficial populations are controlling the pest
- Watch for spider mite flare-ups after pyrethroids
- Rotate modes of action to slow resistance
Beneficial insects are part of the program
Not every insect in the field is a problem. Some are doing quiet work every day. A good pest program protects the predators and parasitoids that keep small problems from becoming outbreaks.
1Predators eat the pest directly
Lady beetles, lacewing larvae, minute pirate bugs, spiders, ground beetles, and predatory mites consume aphids, eggs, larvae, mites, and small caterpillars.
2Parasitoids stop the next generation
Tiny wasps lay eggs inside or on pest insects. The pest may still be visible, but its ability to reproduce has already been disrupted.
3Broad-spectrum sprays can reset the field
A pyrethroid may knock down the target pest, but it can also remove the beneficials holding mites, aphids, and caterpillars in check. That is how one spray can create the next problem.
4Diversity supports control
Flowering field borders, reduced unnecessary insecticide use, soil cover, and habitat diversity help keep beneficial populations present before pests arrive.
The bottom line: A clean field is not the same as a healthy field. The goal is not zero insects. The goal is a balanced system where pest populations stay below economic thresholds and the crop keeps moving.
Pest decisions, by growth stage
A good pest program is a sequence. You are watching different pests at different crop stages, and the right action depends on crop stage, pest count, field history, and beneficial activity.
Rootworm pressure, cover crop termination, residue, manure, weedy field edges, and fields with past stand loss.
- Review last year's rootworm beetle counts and lodging
- Plan rotation or trait strategy
- Terminate green cover crops early enough to avoid green bridge issues
- Watch fields with manure or heavy decaying residue for seedcorn maggot risk
- Scout emergence and stand uniformity
- Dig missing plants before blaming seed
- Look for clipped plants, hollowed seed, larvae, and feeding tunnels
- Track black cutworm moth flights where available
- Estimate defoliation accurately
- Dig corn roots in rootworm-risk fields
- Check grassy borders and cover crop fields first
- Do not spray cosmetic feeding below threshold
- Check silk clipping before pollination is complete
- Scout soybean aphids during reproductive stages
- Watch edges separately from whole-field pressure
- Protect beneficial insects when aphid pressure is below threshold
- Scout hot, dry field edges for mites and grasshoppers
- Check pods and seed quality risk
- Watch ear feeding that opens the door for molds
- Use thresholds before making late-season applications
Harvest losses, lodging, root injury, pest history maps, and fields where rescue treatments were needed.
- Evaluate rootworm injury
- Map lodged or edge-damaged fields
- Plan next year's rotation and hybrid placement
- Review whether sprays helped or only followed symptoms
Common pest misdiagnoses
A lot of insect damage calls are actually weather, disease, planter issues, herbicide injury, or nutrient stress. The pattern usually gives it away.
Bronzing soybean leaves
Both show up in hot, dry conditions. Mites leave stippling, webbing, and tiny moving specks on the underside of leaves.
Missing corn plants
Planter skips leave a clean absence. Cutworm injury leaves clipped plants, wilted plants, or cut stems at the soil line.
Goosenecked corn
Wind can knock corn over, but rootworm-pruned roots explain poor anchoring and plants that try to grow upright again.
Curled or yellow soybean leaves
Aphids cluster on undersides and stems, often with honeydew and sooty residue. Nutrient stress follows soil or application patterns.
Leaf symptoms
Insects remove tissue. Diseases discolor or kill tissue. Holes, ragged edges, scraping, and frass point toward insects.
Strange field patterns
Herbicide injury often follows spray patterns, overlaps, or drift edges. Insects usually follow crop stage, field borders, weeds, or patchy population buildup.
Pest ID Quiz
See if you can identify pests from photos and damage patterns. Start with obvious examples, then move into tougher field calls where threshold thinking matters.
Pick a level to start
Each level shows pest photos and asks you to pick the right answer from four options.
Level Complete
Seeing something in your field you can't place? Get in touch with AgriBio Systems.