Pocket Guide to Grass Seed Pests and Beneficials: Identification, Monitoring, Management

Using the guide

This pocket guide provides information on pests and beneficial organisms found in grass seed production fields across the state of Oregon.

Pests are organized alphabetically within each category. The guide includes common occurrences; where pests are found; arthropod pest status; identification; biology; symptoms of damage; what you might mistake one for; thresholds, if known; ways to monitor; prevention tools and management; and a pest scouting calendar based on crop stage.

Current registered chemical management options can be found in the
PNW Insect Management Handbook.

A step-by-step guide to diagnosing plant problems

Incorrectly identifying a pest problem will lead to a poor management decision. Monitor agricultural sites regularly for pests. Closely follow a plant’s health as it grows to discover pest problems before economic damage occurs. Identifying pest problems is detective work; be inquisitive.

Describe the plant abnormality or problem. Ask questions:

• What should a normal plant look like at the time of observation?
• Am I giving the plant what it needs (water, nutrients, light)?
• Are the problem symptoms found on new or old growth, in the whole field or localized, on the stem or on other plant parts?

Collect evidence from living organisms (biotic)

• Do you see pest signs on the damaged plant? These can include: frass (large caterpillar droppings, pepperlike excretions), slime trails, stickiness from honeydew, molted insect skins, webbing, eggs, fungal spores or bacterial ooze, or the organism itself, invertebrates (such as insects, mites, symphylla), vertebrates (rats, mice, birds, rabbits, raccoons, possums, deer), weeds (dandelions, ragwort, bindweed, thistle), pathogens (mildew spores, scabs, galls).
• Do you see plant “symptoms” from abnormal conditions? These can include: plant tissue rolled up, folded or chewed; leaves stippled with small white spots, viral mosaic patterns, fungal and bacterial leaf spotting, wilting, stunting or distortion.

Collect evidence from nonliving factors (abiotic)

• Chemical: A film or residue, plant or leaf distortion (epinasty), yellowing or necrotic spots due to chemical phytotoxicity, runoff, inadequate chemical agitation of mixture, fertilizer sensitivity, mix of noncompatible chemicals.
• Environmental: High winds, extreme temperature or other weather-related factor (heat, frost, hail, sunburn), moisture (drought, overirrigation, poor drainage area).
• Mechanical: Injury, such as plant breakage or bruising from a person or nearby construction, transplanting or equipment.
• Other disorders: Nutrient, soil pH, previous crop history causing weakness, yellowing with distinctive patterns, wilting or stunting.

Look for patterns

• Uniform damage over a large area? If so, the cause is generally due to nonliving factors (chemical, environmental, mechanical or other plant disorders).
• Scattered or random damage over a few areas? If so, the cause is generally due to living organisms (insect pests, mites, slugs, rabbits, moles, rodents, deer, geese, disease).

Assess how damage spreads

• Is there a clear pattern or line between damaged and undamaged plants in the field?
• For nonliving factors, damage is typically immediate, rather than progressive.
• Pests (living organisms) will generally multiply over time and increase in spread and damage.

Major and minor pests, beneficial organisms

See the PDF.

Scouting

Scouting tools

Monitor for pests by scouting plants at a pest’s known critical activity time or at a specific time of plant development that is known to attract certain pests (see pest scouting calendar).

Regular scouting helps ensure early detection, determines level of pest presence and optimizes the timing of treatments.

Baited traps

• For symphylans, wireworms, slugs. Potato for symphs; seed for wireworm; and metaldehyde pellets for slugs.

Beat sheet

• Insects can be easily collected by beating the plants low to the ground and placing a beat sheet next to the plant. A beat sheet is basically just a piece of heavy-duty cloth 1 square meter stretched across two diagonal pieces of wood joined at the center. They can be purchased or made. Beat sheets can vary in size, but a typical beat sheet is about 3 feet square. For flying insects, an aspirator can be used to suck up the bugs.

Berlese funnel

• A 20- to 40-watt incandescent light bulb slowly dries out the sample over a few days that sits above samples. Insects slowly migrate down following the moisture gradient as soil dries. They then fall into a jar of alcohol and can be counted and recorded.
• Used to extract insects from sod soil cores, or plant roots, crowns and foliage.

Microscope

• A microscope is used to see objects that are too small to be seen by the naked eye.

Pheromone traps

• For Lepidopteran pests (sod webworm, armyworm, various cutworm species).
• The traps use pheromones to lure insects into them. Sex pheromones and aggregating pheromones are the most common types used.

Pitfall traps

• Plastic cups with a protective lid to protect from rain and birds that remove insects that drop in. Sunk in field at ground level, marked with flag.
• Inspect for insects twice a week.

Soil sieve

• Wood- or metal-framed, with different size wire mesh screens, to sieve soil and separate insect pests from soil and organic matter (for symphylans, wireworms, cutworms, weevil larvae).

Shovel and auger soil sample

• A shovelful of soil dug and placed on a tarp for examination of pest (for symphs, cutworms, root weevil larvae, mites).

Sweep net

• Thresholds for controlling pests are often based on average numbers of pest insects per straight-line or 180-degree sweep of this net. Ten consecutive straight-line sweeps dipping the net halfway into the foliage are taken as one walks. Insects are counted, divided by 10 for an average number per sweep and recorded in field notebook. This is done in at least 10 different locations in a field to gain a representation of the population.

Visual inspection

• Hand lens, jeweler’s loupe or OptiVisor.
• Simple tools for viewing small-pest life stages in the field.

Water trap

• Yellow-colored plastic buckets or pans with a drop of soap added to reduce surface tension will attract flying insects like aphids and thrips.

Yellow sticky trap

• Sticky cards are useful for monitoring for thrips and aphids. The cards will trap the flying stages of flying adult insects. Yellow for aphids; blue for thrips. Hang sticky cards near plants attached to a stick.

Grass seed pest scouting calendar

Based on crop stages. An entry indicates when a life stage of the pest can be seen.

Glossary

Cauda: The “tail” or appendage at the end of an aphid’s abdomen.

Cornicles: Pair of dorsal, tubular processes on dorsal, posterior end of an aphid’s abdomen (“tailpipes”); corniculi.

Crochets: On moth larvae (cutworms, armyworms, webworms), the bottom of prolegs can have a series of hooklike structures arranged in rows, bands, circles or half-circles that are helpful in identification to family level.

Economic threshold: The density of a pest at which damage can occur and control is warranted.

Entomopathogenic nematode: A nematode (roundworm) infecting insects only.

Frass: Excrement or droppings left by insects.

Honeydew: Sugary, liquid excretions released from the anus of aphids, leafhoppers and mealybugs.

Immature stage:

• Grubs are generally referred to as immature beetle larvae.
• Larvae, or caterpillars, have wormlike bodies with legs and are different from the adult (for example, moths and beetles).
• Maggots are wormlike without legs (fly larvae, for example).
• Nymphs molt, wings develop, and they resemble the adult form (grasshoppers and leafhoppers, for example). They do not reproduce.
• Pupa/pupae, or hibernaculum, is the resting or overwintering stage of an insect.
• Neonates are young, immature, nonreproductive slugs.

Molted skins: Sloughing or shedding of the insect skin.

Prolegs: Small, fleshy, stubby-looking legs found on the posterior of wormlike larva body that help them grip.

True legs: Six jointed legs located near the head of the larvae. True legs are retained through adulthood.

Source: CAB Direct

Resources

Berry, R.E. Insects and Mites of Economic Importance in the Northwest, 1998. Oregon State University.

Dreves, A.J., N. Kaur, M. Bohle, D.B. Hannaway, G. Fisher, S.I. Rondon. 2020. Invertebrate Pest Management for Pacific Northwest Pastures. Oregon State University Extension, PNW 750.

Lamp, W.O., R.C. Berberet, L.G. Higley and C.R. Baird, editors. Handbook of Forage and Rangeland Insects. 2007. Entomological Society of America, APS Press.

Hollingsworth, C.S., editor. 2019. Pacific Northwest Insect Management Handbook, Corvallis, OR: Oregon State University Extension.

Hooven, L., R.R. Sagili, and E. Johansen. March 2016. How to Reduce Bee Poisoning from Pesticides, PNW 591.

Shewmaker, G.E., and M.G. Bohle, editors. Pasture and Grazing Management in the Northwest. 2010. PNW 614.

Potter D.A. 1998. Destructive Turfgrass Insects — Biology, Diagnosis, and Control. Ann Arbor Press.