We start our scab control program when pollinated nuts show the first sign of nut enlargement. This actually occurs a couple of weeks after pollination when the egg inside the pistillate flower becomes fertilized and the embryo starts to grow. It is interesting to note that pecan nut casebearer moths seem to lay their eggs only on nuts that have viable, growing embryos. Because these two pests attack nuts at the same time in the life cycle of the pecan, we usually combine our first fungicide treatment with an insecticide to control both scab and casebearer.
Depending on weather conditions a second fungicide application may be required 2 weeks after the first application. Last year we sprayed our native pecans twice and high-value, scab-susceptible cultivars 3 times. I'll be posting this year's scab spray program as the season progresses.