- Judging IGRs like Confirm a Matter of Delayed Gratification
Managing Editor
Insect growth regulators are a prime example of how this learning curve is working. Confirm 2F, an IGR from Rohm and Haas, is now labeled everywhere for pome fruits (apples and pears), with New York added as of May 8. It has gained a label this year for blueberries. The product had already been labeled for vegetables, walnuts, pecans, sugar cane, cotton and forestry ornamentals.
Target pests on pome fruit include codling moth, obliquebanded leafroller (OBLR), pandemis leafroller, tufted apple bud moth, eyespotted moth, fruit tree leaf roller, redbanded leafroller, variegated leafroller, lesser apple worm and green fruitworm. Target pests on blueberry include OBLR, redbanded leafroller, cranberry fruit worm and cherry fruit worm.
Rohm and Haas is marketing the product as “smart insecticide technology” because it uses a new kind of chemistry with a unique mode of action. Confirm (common name tebufenozide) is a target-specific material aimed at controlling larvae by initiating a fatal, premature molt. This material works differently than other insecticides such as organophosphates and carbamates, which are nerve poisons and kill the target insect quickly on contact.
“Confirm is a unique compound that can provide some opportunities for the Michigan fruit industry. However, it is unique enough that there is a learning curve involved,” said John Wise, Michigan state fruit entomologist and coordinator of Michigan State University’s Trevor Nichols Research Station in Fennville, Mich.
“Confirm is a mimic of a natural hormone that exists in the larvae of lepidopteran insects that stops natural development. Because of this, it has to be consumed by the insect. It takes time for it to work because the insect responds over time as opposed to a fast-acting nerve poison,” he explained.
This means that for growers and researchers alike, there is a difference in how IGRs are applied (especially in the areas of coverage and timing) and how their effectiveness is judged as opposed to more traditional types of insecticides. If those issues are successfully handled by the applicator, Confirm has shown good results, according to research and use data.
Orchard results
Research evaluating the performance of Confirm on apples at Walker, Mich. show two of three treatments of the insecticide against OBLR surpassed the grower standard performance of 90.8% of clean fruit. A regime of three summer sprays at 18 fluid ounces per acre showed 95.3% control. Another regime of one petal fall application plus three other applications at 18 oz/a yielded the 97.4% rate of clean fruit.
In a research plot in Hartford, Mich. on OBLR and codling moth, a treatment of Confirm 2F (18 ounces) plus Latron B-1956 (8 ounces) and one quart of Guthion helped result in a 98% clean crop compared with the grower standard of 96%. The same comparison but without the Guthion was made in Traverse City and Sparta research plots. In Grand Rapids (both pests), the Confirm+Latron treatment had 95% clean fruit, compared to the grower standard material’s performance of 90.5%. The Sparta breakdown vs. just OBLR was 95.4% to 90.6% in favor of Confirm and Latron. Similar results were found at Peach Ridge sites.
Albion, N.Y. grower George Lamont has battled OBLR in his orchards for 20 years. He has been working with Rohm and Haas to evaluate 36 different pesticide combinations against this pest. Now that he has learned to work with Confirm, Lamont said, “we have almost completely wiped obliques out of a block of Cortlands, our toughest variety.”
Cause of confusion
Because of the different mode of action exhibited by IGRs, some growers have reported confusion and even doubt that the product is working. Specifically, after using the product, they still see caterpillars crawling around the orchard whereas with other types of insecticides, the creatures would be dead.
If a grower is using a contact poison, the target insect just needs to come in contact with the insecticide as it moves through the tree. The chances of this increase with species that have higher mobility, such as fruit flies. Lower rates of these materials can thus be used.
“But insect growth regulators have to be where the insect is feeding,” said Wise. “A leafroller can hatch and walk across an IGR with minimal or no effect. But once that insect walks to the tip of an actively growing terminal, feeds and ingests the compound, our data suggests it works quite effectively. If you don’t have good coverage, or the compound is not in a place where it will be ingested, the likelihood of having control is reduced.”
Judging the performance of Confirm is a more complicated matter than “either you kill the bug or you don’t.” Research has shown IGRs do indeed cause mortality – but visual evidence of their lethality does not come as quickly as with conventional insecticides. Up to a week may pass before the lethal effect can be observed.
However, this does not mean that larvae that have ingested the IGR are eating their way through your orchard. These IGRs have a number of sublethal effects that are typically not measured when judging the performance of an insecticide, says Wise.
“One of these effects is the cessation of feeding. We see this effect to two degrees in the field. One is where the animal will completely stop feeding. It may still be sitting there, but it isn’t doing any damage. Another degree is where there is actually some, but damage you see is pinpricks on the fruit as opposed to the tunneling you might see in an untreated area,” he said.
Wise said another sublethal effect researchers are still learning about is how IGRs affect the next generation of insects. There is some level of adult sterility in that generation. Insects that do not die immediately will often not survive to pupate and emerge as adults. Wise has worked with Confirm and other IGRs at the Trevor Nichols station, applying them three consecutive years in the same plots. He has seen the pest population in these blocks dropping.
An indirect population effect comes from the nontoxicity of Confirm to natural enemies of the target pests. Wise says this is a real effect, but difficult to measure.
“If you are going to judge the performance of an IGR, you must take all these things into account to judge it fairly,” he said.
Timing and coverage
IGRs are more effective on smaller, younger larvae as compared to conventional insecticides. They tend to be more effective when the egg mass or individual egg is covered with the compound before it hatches. When the larvae eats its way out of the egg mass, it will ingest a lethal dose of Confirm.
The recommended timing in Michigan for Confirm against codling moth is biofix plus 150 degree days base 50&Mac251;. Come back with a follow-up spray 14 days later. The recommendations for OBLR are not so firm, but the safest bet is to apply at biofix plus 300 degree days base 42&Mac251;. Researchers are still trying to determine the best time to use the product against leafrollers.
The current rate recommendation for Confirm is 20 fluid ounces per acre on apples and 16 ounces per acre on blueberries. The maximum seasonal active ingredient allowed is 80 ounces for apple and 64 ounces for blueberries. The pre-harvest interval is 14 days for each crop.
Ready for the future
Insecticides like Confirm could be the wave of the future. In fact, there is another IGR on the market called Esteem, manufactured by Valent. This product mimics the juvenile hormone of the insect and prevents its normal development to the adult stage. It is labeled in apples and pears for control of codling moth, San Jose scale and pear psylla. Many of the considerations already noted about how to judge the performance of Confirm apply to Esteem – or to any kind of IGR.
“I would encourage growers to gain experience with these kinds of new compounds,” said Wise.
This can be done by setting aside a relatively small acreage that has light to moderate pest pressure and that can be monitored carefully. Until you gain experience, don’t use IGRs during periods of peak egg hatch and high risk of fruit damage. Instead, apply them earlier or at the tail end of the emergence period where, if infestation occurs, it will be more manageable. Another reason to get experience with IGRs is as a resistance management tool.
Perhaps the major motivation to get acquainted with IGRs is the Food Quality Protection Act and the effect it may have on the availability of many traditional, proven crop protection materials in the future.
“There may be a time in the future when we will be forced to rely on compounds like IGRs,” said Wise. “If that occurs, growers will be thankful they gained some experience during a time when it was their own choice to learn how to use them.”
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