Friday, September 6, 2013

Rainfall and pecan weevil emergence

Pecan weevil larva feeding on pecan kernel tissue
   A large part of being a successful pecan grower is learning how to adapt to changing weather conditions. This year nut development was delayed by a cool spring and has remained at least two weeks behind normal all season long. But this summer we also experienced  above average rainfall in late July and early August that promoted early pecan weevil emergence.
    Late developing pecans. Early weevils. This year's weather patterns have created a unique pest control challenge. In the chart below, I've recorded both rainfall and weevil trap catches. We had over 15 inches of rain from July 21 until August 12. Since that time, the rain has completely stopped and at this point things are starting to look dry again.
    We captured our first weevil on July 31 with emergence peaking from August 5 to August 21.  As our soil has started to dry out the number of weevils we have captured dropped off dramatically.


     The combination of early weevil emergence and late kernel development has meant that, for the entire month of August, adult weevils could not find a place to lay eggs. However, pecan weevils are patient creatures. They simply feed on developing pecans (causing nut drop!), while they wait for the pecans to start creating kernel.  Because of the large number of weevils that emerged in early August, we sprayed our pecan grove starting August 14. Now I'm wondering, when it rains again this month, will we get a second flush of weevil emergence? Late emerging weevils will find plenty of places to lay eggs now that our pecan crop has started to fill kernel. And I certainly don't like finding weevil larvae in my cracked pecans at harvest time. This year, we'll be checking our weevil traps well into October.