Q. Mike: Applying systemic chemical pesticides is a nuisance, and the products can be so dangerous that ORTHO has taken its systemic pesticides off the market. I have tried using products like Pyola, Neem Oil, etc. but they don't seem to have an effective residual presence on plants like my roses. Gardens Alive and other natural gardening catalogs feature a vast array of pesticide and fungicide products. My Question: Which ones kill on contact, and have good residual effectiveness? Last summer I used a combination of natural and Ortho products every 7 - 10 days. Is there a better method?
- ---Frank in North Andover, Mass.
A. Let's begin with some definitions. The word "pesticide" refers to any substance used to control something undesirable, including insects, slugs and snails, rodents, weeds, and disease. So insecticides, molluskicides, rodentacides, herbicides and fungicides are all grouped under the 'pesticide' umbrella.
And despite what many people believe, the word pesticide does not automatically mean the control is a chemical. Pesticides can be natural/organic products or toxic man-made chemicals. That's right—if it's sold for use against a pest, it has to be called a pesticide, regardless of whether it's a natural soil organism like one of the Bt's or a persistent, deadly chemical like DDT.
'Contact pesticides', like insecticidal soap and horticultural oils, must actually strike a pest to harm it. If you spray soap or oil on a pest, the pest will be smothered and die. Spray soap or oil on a leaf in advance of a pest being there, and you waste your time and money. (And run the risk of being mocked by the pest when it does show up.)
Most pesticides are 'residual'; that is, they cling to the surface of a plant and remain active for a certain amount of time. BTK—an organically approved naturally occurring soil organism that's deadly to caterpillar pests—is a good example. You spray it on a plant being eaten by caterpillars and the caterpillars currently feeding on the sprayed leaves die, and so do any new ones that show up to feed for a while. How long that 'while' lasts depends on variables like temperature, rain, and sunlight.
'Systemic' pesticides are taken up inside the plant, typically through the root system, so that every part of the plant then contains the chemical. (I say 'chemical' here because I can't think of any organic systemics.) As you can imagine, systemics on food crops are an especially bad idea. In fact, in one of their very first uses, the string beans they were "protecting" became as poisonous to people as the attacking bean beetles.
Now, you specifically mention roses, and we don't eat our roses (that's what Japanese beetles are for), so what could be the problem with systemic pesticides there? Jay Feldman, long-time Executive Director of the great watchdog group Beyond Pesticides, in Washington, DC didn't have to think about the question more than an instant.
"Merit is the most widely used systemic pesticide", he explained, "and the active ingredient in Merit is the chemical most implicated by researchers in the Colony Collapse Disorder decimating honeybee hives around the world. Growers use Merit to protect their plants, bees ingest the chemical when they collect pollen from those plants, and boom—the bees are poisoned because the chemical is in every part of the plant, including the pollen. And this isn't specific to just Merit; its just one example of how these types of pesticides can have a profound and deadly impact on non-target organisms like pollinators."
And of course, without pollinators, we got no food or flowers.
You also speak of having to treat your plants every week to ten days. That's a huge red flag. If you're using ANY pesticide—chemical or organic—that often, something is badly out of whack in your garden.
If disease is the problem you're battling, are your roses getting morning sun and good airflow? Do you have wood, bark or other disease-harboring mulch incubating illness underneath your plants instead of a mulch of disease-preventing compost? Do you invite even more disease by wetting the leaves of your plants when you water?
If aphids—a common 'target pest' of systemics—are the issue, have you tried blasting them off the plants with sharp streams of water? Researchers found this 'mechanical technique' to be as effective as any pesticide against aphids—and it won't foster disease if you do it first thing in the morning, when the sun can dry the plants off immediately afterwards. Aphids are also well controlled with insecticidal soaps, light horticultural oils and/or boric acid traps at the base of the plants if ants are 'farming' and protecting the aphids so they can dine on the sweet honeydew the aphids excrete.
And finally, are you feeding your plants harsh chemical fertilizers? The fast, weak unnatural growth these chemicals cause makes plants much more attractive to pests and prone to disease.
Switch to compost, practice good sanitation and prevention, and watch your problems shrink and your plants prosper. Because in the end, a natural feeding program based on improving the health and life of your soil is the most reliable 'systemic' response to virtually any problem.