February 2009
Earlier this year I attended the Western Orchard Pest and Disease management conference in Portland Oregon. One of the reasons I attend is to keep tabs on new pesticides working their way through the registration process. Research folks from across the country (sometimes around the world) report on the trials they've conducted using a new product against various pests. A new material first shows up as a numbered compound such as Dupont's DPX-E2Y45. After a few more years it's given a trade name. In this case, Altacor. Registration and projected release targets are then announced. It's not uncommon to return the following year and find that a registration has been postponed for one reason or another. It's a long, expensive venture to bring a new pesticide to the marketplace. One newsletter I read from Syngenta mentioned 5 years and a $184 million to register a new product!
At this year's conference only one numbered compound, and two new named products were discussed. The product development pipeline is far from being full. With this registration scenario it's important that we get the most mileage possible out of the pesticides we currently have! Thanks to a couple of new materials, I've watched long term codling moth problems disappear in several blocks of fruit. But how long until resistance becomes a factor and we struggle once again to keep a pest in check? RESISTANCE MANAGEMENT IS ENTIRELY A PROACTIVE BATTLE! You must be ahead of the curve. OK... here's a bit of bug management 101.....
Ecological backlash: is defined as the counter-responses of pest populations in the environment that diminish the effectiveness of pest management tactics. Ecological backlash mainly manifests in the form of Resistance, Resurgence, and Replacement. The three "R" s of pest management awareness.
Resurgence: is defined as a situation where a population, after having been suppressed (sprayed), rebounds to numbers greater than before suppression occurred. Spider mites are great at this.
Replacement: also referred to as a secondary pest outbreak, occurs when a major pest is suppressed and is continued to be suppressed by a pest management tactic, but is replaced by another pest previously with minor pest status. A few years ago I watched an apple block get sprayed for wooly apple aphid (WAA). The application went a long way towards eliminating the WAA problem, but within a week the block was overrun with green apple aphid.
During secondary pest outbreaks, the tactic has an effect on the primary pest, but has no effect on the secondary pest.
Three major causes have been suggested to explain resurgence and replacement.
1) Reduction of natural enemies along with the primary pest
2) Direct favorable influences on physiology and behavior of pests
3) Removal of competitive species
Resistance: Natural selection by an insecticide allows some initially very rare, naturally occurring, pre-adapted insects with resistance genes to survive and pass the resistance trait on to their offspring. Through continued application of insecticides with the same mode of action (see below), selection for the resistant individuals continues so the proportion of resistant insects in the population increases, while susceptible individuals are eliminated by the insecticide. Under permanent selection pressure, resistant insects outnumber susceptible ones and the insecticide is no longer effective. The speed with which resistance develops depends on several factors, including how fast the insects reproduce, the migration and host range of the pest, the availability of nearby susceptible populations, the persistence and specificity of the crop protection product, and the rate, timing and number of applications made. Resistance increases fastest in situations such as greenhouses, where insects or mites reproduce quickly, there is little or no immigration of susceptible individuals and the user may spray frequently.
Mode of Action (MoA): Pesticides are grouped by class or mode of action. To be effective in combating resistance you must rotate from one class to a different one. For example, Guthion and Imidan are both organophosphates, switching from one to the other will not help. It's the same story with Rally and Rubigan, they're both sterole inhibitors. Changing MoA's from one insect (or disease) generation to the next goes a long way towards preventing resistance.
I've copied the table below from the latest Fruit Grower News. Michigan State University (Larry Gut and his team) assembled it for codling moth control. I've included not only for that purpose, but because it shows a number of currently used insecticides and their class.
I once heard a “rut” described as a grave with both ends kicked out. If your spray program is in a rut, (same materials and timings year after year) it's likely the pests you're after are building resistance! STAY AHEAD OF THE CURVE!
Pest control is like a three legged stool. Remove one leg and it's a tough place to sit! The three legs: Timing, Coverage and Material. If you're struggling with control of a pest, one of these legs is broken. My bet is usually on timing or coverage. Do you use the sound of your neighbor's sprayer as an alarm clock? Have you ever stopped spraying and walked back to a look at the coverage, to look for dry spots? If your stool keeps falling over, take a look at each leg (timing, coverage and material) one at a time and determine where it's broken.