What are Biorational Pesticides?

A biorational pesticide (insecticide) is one that is environmentally friendly, organic, and commercially produced. (See Table 1.)

Table 1. Biorational pesticides
Biorationals Target Pest
Bacillus thuringiensis var. kurstaki Caterpillars, gypsy moth
B. thuringiensis var. tenebrionis Leaf-feeding beetles, Colorado potato beetle
B. thuringiensis var. japonesis Scarab larvae, including white grubs
B. popilliae Japanese beetle larvae
Beauveria bassiana Larval stages and soft-bodies adults
Horticultural oil Scale, aphids, mites, lacebugs
Insecticidal soap Soft-bodied insects (aphids, scale crawlers, mites)
Neem Thrips, caterpillars
Nematodes Soil dwelling and boring insects

The routine examination of garden plants, or scouting, helps to determine when pest problems are reaching a critically damaging threshold. Scouting also helps to determine the stage (larva, pupa, adult) of the insects. Insect traps can be used to monitor insect populations before they build up to harmful thresholds. If damage is noticed before an insect population is firmly established and when the insect is at a vulnerable stage, many problems can be easily thwarted by environmentally-kind measures ranging from hand-picking to hosing off the insects with water to using soaps and oils.

Gardeners must make decisions on when to apply a pesticide, by analyzing their expectations of "perfect" produce and recognizing the trade-offs involved in seeking the perfect product. Damage thresholds are related to both the level of damage a plant can tolerate, called injury threshold, and the amount of damage a gardener can tolerate, called aesthetic tolerance. Such trade-offs include potential harmful effects to soil and water quality, encouraging resistance to pesticides within pests, and possibly killing beneficial insects. Caution: honey bees actively forage in your garden during the day, so to avoid bee kill apply insecticide in the evening after the bees return to their hives.

When chemical pesticides are necessary, use the least toxic one available and only spot spray. Carefully follow the label instructions and wear gloves, goggles, and long-sleeved clothing. Ready-to-use, premixed products are convenient and avoid the problem of disposing of out-of-date, unused chemicals. For your safety and the safety of others, securely lock up all pesticides. (See Table 2.)

Table 2. Organic pesticides: botanicals
Organic Pesticide Target Pests Mode of Action
Neem Chewing insects (caterpillars, beetles) Is a feeding deterrent; stops growth of insect
Nicotine Aphids, thrips, other sucking insects Toxic to ground and soil pests by contact
Pyrethrum Most insects Injestion, contact
Rotenone Leaf-feeding caterpillars and beetles, insects with sucking mouthparts Paralyzes insects on contact
Ryania Codling moth, caterpillars, leaf beetles, thrips Acts on contact; is a stomach poison
Sabadilla Leaf-feeding caterpillars Paralyzes insects on contact

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