6.1 Pest Types, Identification & Characteristic Damage

6.1 Pest Types, Identification & Characteristic Damage

Every New Hampshire category examination tests pest recognition. Pes 304.09(b)(4) spells out what that means: the common features of pest organisms and the characteristics of damage needed in identification, recognition of relevant pests, pest development and biology relevant to problem identification and control, and alternative methods of control under IPM. The private-applicator standard in Pes 305.06(c)(1) says the same thing more plainly - the applicator must be able to "recognize the pests, their damage and their control common to the applicant's situation."

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What makes something a pest

A pest is any organism that injures or interferes with a desirable plant or animal, damages a structure or product, or annoys or transmits disease to people and animals. Pest status is contextual, not biological:

• White clover is a weed in a putting green and a nitrogen-fixing cover crop in a hayfield.
• A paper wasp nest is a public health problem beside a school door and a beneficial caterpillar predator in a hedgerow.
• Carpenter ants foraging in a woodlot are decomposers; in a sill plate they are a structural pest.

The practical consequence is that the first question is never "what will kill this?" but "is this actually causing unacceptable injury, and is it the organism responsible?"

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The five pest groups

+------------------------------------------------------------------+
|  PEST GROUP        |  EXAMPLES          |  TYPICAL EVIDENCE       |
+--------------------+--------------------+-------------------------+
|  INSECTS &         | beetles, aphids,   | chewed leaves, tunnels, |
|  RELATED ARTHROPODS| mites, ticks,      | stippling, honeydew,    |
|                    | termites           | frass, exit holes       |
+--------------------+--------------------+-------------------------+
|  PLANT PATHOGENS   | fungi, bacteria,   | spots, cankers, wilts,  |
|                    | viruses, phyto-    | mosaics, rots, molds,   |
|                    | plasmas            | blights                 |
+--------------------+--------------------+-------------------------+
|  WEEDS             | annual, biennial,  | competition, shading,   |
|                    | perennial broad-   | stand thinning          |
|                    | leaves and grasses |                         |
+--------------------+--------------------+-------------------------+
|  NEMATODES &       | root-knot nematode,| galled roots, stunting, |
|  MOLLUSKS          | slugs, snails      | slime trails, holes     |
+--------------------+--------------------+-------------------------+
|  VERTEBRATES       | rodents, birds,    | gnawing, droppings,     |
|                    | deer, moles        | browse lines, runways   |
+--------------------+--------------------+-------------------------+

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Insects: read the mouthparts

The single most useful identification shortcut in entomology is mouthpart type, because it determines both the damage you see and the control you choose.

Chewing mouthparts

Beetles, caterpillars, sawflies, grasshoppers, and grubs remove tissue. Look for:

• notched or ragged leaf margins, shot-holing, skeletonizing (veins left behind);
• frass - granular excrement - on foliage, in bark crevices, or at the base of a stem;
• tunneling and galleries in wood, stems, or fruit, with exit holes whose shape often identifies the insect (round, D-shaped, oval).

Chewing insects are controlled effectively by stomach poisons and by baits, because they ingest treated tissue.

Piercing-sucking mouthparts

Aphids, scales, leafhoppers, plant bugs, thrips, whiteflies, and mites insert a stylet and withdraw fluids. Look for:

• stippling or flecking - a fine pale mottling where individual cells were emptied;
• distortion: cupped, curled, or puckered new growth;
• honeydew, a sticky excretion, followed by black sooty mold growing on it, and often ants tending the colony;
• cast skins and fine webbing (spider mites).

These insects rarely ingest surface residues, so contact and systemic materials work where stomach poisons do not. Piercing-sucking insects are also the group that transmits plant viruses, which is why an aphid population that looks tolerable may still require action in a virus-susceptible crop.

Life stage matters

Insects develop by complete metamorphosis (egg, larva, pupa, adult - beetles, flies, moths, wasps) or gradual metamorphosis (egg, nymph, adult - true bugs, aphids, grasshoppers, cockroaches). In complete metamorphosis the damaging stage and the visible stage are often different: the adult Japanese beetle skeletonizes foliage while its larva feeds on turf roots, and the two require entirely different treatments at different times.

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Plant pathogens: look for the pattern

Disease requires three things simultaneously - a susceptible host, a virulent pathogen, and a favorable environment. This is the disease triangle, and it explains why fungicides so often fail when nothing was wrong with the fungicide: if the environment stays favorable and the host stays susceptible, the pathogen keeps arriving.

A field diagnostic clue that separates the abiotic from the biotic: living agents spread over time and produce a gradient; abiotic problems - frost, herbicide injury, compaction, road salt, nutrient deficiency - tend to appear all at once, across species, and follow a pattern that matches the physical cause (a drift plume, a driveway edge, a hardpan).

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Weeds: classify by life cycle

Weeds also separate into grasses (parallel veins, fibrous roots, growing point at or below the soil surface) and broadleaves (netted veins, taproot common, exposed growing point). That distinction drives herbicide selection more than any other single trait.

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Getting the identification right

Ways to identify a pest include the organism's own physical features, the characteristic damage it leaves, the host and site where it is found, the time of year, and the geographic distribution of candidate species. When the specimen itself is absent - the borer has left, the deer has moved on, the fungus has sporulated and collapsed - characteristic damage is often the only evidence available.

New Hampshire resources:

• UNH Cooperative Extension - the Pesticide Safety Education Program, the Education Center Infoline, and the plant diagnostic laboratory.
• The state entomologist, who sits on the Pesticide Control Board, and the NHDAMF Division of Plant Industry.
• The category fact sheets that UNH Extension supplies with each commercial and private manual - these are required study material for your category exam, and they are the state-specific pest list you are accountable for.
• Regional resources such as the New England Vegetable Management Guide and the New England Tree Fruit Management Guide.

Submit a good sample: fresh material showing the transition between healthy and affected tissue, roots included for a suspected root problem, in a sealed bag without added water, with a written history of the site, variety, weather, irrigation, fertility, and every pesticide applied.

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Worked example

A turf manager reports patches of yellowing on a fairway that pull up easily like loose carpet, with birds and skunks digging at the edges.

• Loose turf that rolls back indicates the roots are severed - a root-feeding larva, not a foliar disease.
• Birds and skunks digging confirms a substantial larval food source below.
• The likely agent is a white grub, the larval stage of a scarab beetle; the adult stage feeds on entirely different plants and at a different time of year.
• Confirming the species matters because treatment timing keys to egg hatch, not to the appearance of damage, and the relevant degree-day model differs by species.
• Had the patches instead shown stippled, papery blades with fine webbing, the diagnosis would swing to a piercing-sucking mite, and had the margins been chewed and ragged with frass, to a surface-feeding caterpillar - three different pests, three different products, all producing "a yellow patch."