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Aphids

There are at least 4,000 species of aphids worldwide, with over 1,200 occurring in North America. Aphids can prove to be difficult pests to control in the home garden.

The final, last-resort tool in an Integrated Pest Management (IPM) program is the chemical arsenal.

IPM does not specifically require organic, but recommends the chemical product that can achieve control with the least environmental impact. Knowledge of the specific plant-pest interaction informs the practitioner whether an organic or conventional product is in order for that instance. Chemical controls are last in an IPM program in relation to other arsenals — bringing out the “big guns” after other methods have failed. Ideally, other control methods make chemical use unnecessary. In practice, rigorous use of the other arsenals reduces pesticide use, maintaining it as an option for true need. Let’s take a look at pesticide use in an IPM framework.

Correct pest identification: Chemicals applied for the wrong pest have a low probability of success and contribute to resistance issues. Extension agents can help you get the correct identification of the problem at hand, so an effective product can be chosen. It’s not unusual for Extension staff to learn that a client has repeatedly applied a fungicide (used for plant disease) for an insect issue before calling, frustrated with poor results. Use your local Extension Service to correctly identify the problem when unsure — then identify the correct pesticide. Extension staff will typically suggest active ingredients rather than brand names to maintain neutrality.

Right formulation: After correct active ingredient, formulation must be considered. Examples of formulations are granules, liquids, emulsifiable concentrates, and solutions. A single active ingredient comes in multiple formulations appropriate for different plant situations. Formulations vary in how they are applied, concentration of active ingredient, residue longevity, and risks to pollinators and other non-target organisms. For example, a contact insecticide kills any insects it touches, while a systemic formulation will only affect organisms ingesting some of the plant material. Contact insecticides should be timed for application when pollinators are not present, systemic ones managed to minimize residues of the chemical in subsequent pollen.

Timing of application: A poorly timed insecticide application is wasted time and resources. Insect life cycles vary: there may be a huge time lag between when pesticide application is useful, and when the pest is noticed. Apple codling moth is a perfect example: telltale piles of frass show up on apples, after it’s too late to apply pesticide. The correct time is when the small, brown, hard-to-see adults are mating and laying eggs. For codling moth and many other pests, entomologists develop “degree-day models” to predict adult emergence. Models inform when pests are most likely to be present, and enable proper matching of insecticide treatments to the insect’s life cycle for maximum effect with the least product.

Rotating mode of action: Especially difficult pests like aphids, scale, and spider mites may require multiple applications of insecticide, especially if the problem remained unchecked too long. Cases of extreme infestation more frequently require chemical controls — one reason regular scouting is such an important part of an IPM program.

Insects like aphids can have many generations per year, and building populations that overwhelm plants. Frequent reproduction also contributes to aphids’ ability to become quickly resistant to pesticide chemistry. Rotating modes of action is an important tool against this kind of pest. Instead of spraying the same item twice, the second time a product with a different active ingredient and chemical pathway is used. While generally successful, this tactic is tough for some to adopt. For home growers who’d prefer no pesticide at all, two is hard to swallow. For commercial producers, possibly applying products to considerable acreage, this strategy can be cost prohibitive despite effectiveness.

Understanding the risk: Frequently, interest in organic gardening is driven by desire to avoid “those nasty chemicals.” While organic pesticides are derived from natural rather than synthetic sources, ultimately their purpose (killing things) is the same. In pesticide application, finding the most environmentally friendly choice is not as easy as organic vs. conventional. The potency of some synthetic pesticides means tiny amounts can be effective, where some organic products don’t persist long enough in the field and are replied repeatedly. Copper based fungicides, used in both conventional and organic agriculture, are responsible for serious soil contamination in older vineyards. For a deeper look at the effects on wine producers visit https://bit.ly/3aT5zd6. No pesticides are without risk. Factors influencing risk include amount and frequency of application, how product was applied, and combining multiple products. Even wind and rainfall play a role.

Becoming adept at applying IPM principles is a process, using previous pest and disease experiences to predict the future challenges, then being prepared with a menu of management options derived from the different arsenals. Many IPM practices include a degree of latitude for maneuvering different situations and pests, but that is never true for pesticide application. When applying pesticide, the label is always the law.

Nicole Sanchez is horticulture faculty at OSU’s Klamath Basin Research and Extension Center. For more information on this or other gardening topics, contact Sanchez at 541-883-7131 or Nicole.sanchez@oregonstate.edu, or attend a “Garden Gab” session at Leap of Taste, fourth Friday of each month, 8:30 to 9:30 a.m.