Thursday, June 16, 2022

Pecan nut casebearer arrives late


    Every year I scout my pecan orchard for pecan nut casebearer damage to young nuts. Damage from this insect is easy to recognize by the pile of insect frass at the base of a nut and the silken threads that connect the damaged nut to the pedicel (photo at right). Left unchecked, a single pecan nut casebearer larvae will destroy 3 to 4 nuts in a cluster. 

    The first evidence of casebearer nut damage this year occurred a week later than normal. However, now that this first summer generation has started, the above average temperatures predicted for the next 10 days will cause the casebearer population to expand rapidly. I found the first damaged cluster on Wednesday June 16th and started spraying early Thursday morning.

    When spraying during a heat wave, I try to start at first light and quit around 11:00 am. Once temperatures start to approach 90 degrees F spray droplets can evaporate before they ever hit the foliage. 

Pollinated flowers vs. Fertilized Nuts

        Long before I found the first casebearer damaged nut, I knew things were running late by watching the developing nuts. When a female flower becomes pollinated the stigma becomes dry and black, however, it takes a little time for the pollen tube to grow down into the nut and become united with the ovule. Once the nut is fertilized, it starts to swell and the sepals (leaf like projections just below the stigma) will point straight up. This year, nuts didn't show the normal signs of fertilization until June 14th. A day after most sepals were pointing up, I found my first casebearer. Over the years, this relationship between nut development and the first sign of casebearer activity has been very consistent.  In fact, I now use observations of nut development as the primary method for timing a pesticide application to control casebearer.