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You asked: "This is the second year that we have had to treat the lawn for chinch bugs. How do we eradicate?"
Chinch bugs are impossible to totally eradicate. And especially so with the products available today. Even in the old days, chemicals would knock out a lot more, but I'd hesitate to say that they totally eradicated them.
Adult chinch bugs overwinter under the shrubs, along the house or garage- anywhere it is a bit warmer or protected. They return to the lawn in May-June. They mate and start laying eggs. A female chinch bug may deposit 500 eggs over a 2-3 week period.
Even if all the chinch bugs on your lawn were controlled, the adult chinch bugs that overwintered on a neighbour's lawn could come over to your lawn and start laying eggs. So sometimes chinch bugs can be a problem for several years in a row.
Do mow your lawn at 3" high. Chinch bugs like warm, sunny conditions. A little bit extra grass blade will shade the soil and keep it a touch cooler. This may not prevent chinch bugs altogether, but it does help to tilt the balance in your favour.
When overseeding, make sure to use a mixture that contains a Perennial ryegrass that contain an endophyte. These endophytes help to deter chinch bugs.