Post-pollination nut drop

    When I'm scouting for pecan nut casebearer, I always notice some level of post-pollination nut drop. The other day, I was able to photograph a single nut cluster that exemplifies two common causes of post pollination nut drop.

     In the photo at right, note the small, rusty-colored nutlet that has completely separated from the peduncle and is just about to fall to the ground. This type of nut drop is due to poor pistillate flower development. In other words, the tree didn't have enough energy to fully create a healthy female flower. In most cases, pecan trees shed these weak flowers early in the growing season, usually during the pollination season.
    The olive colored nut at the top of the peduncle is an example of a second type of nut drop. This pistillate flower was most likely pollinated but the egg inside the ovary was never fertilized. Lack of fertilization can be the result of improper pollen tube growth or a genetic miscue between egg and sperm.  In the photo you can also seeing the beginnings of an abscission zone forming on the peduncle right above the healthy nut (small crack). In shedding the unfertilized nut, the tree will also shed the upper part of the peduncle above the abscission zone.
    This year we are experiencing an "on" year for pecans. The vast majority of our pistillate flowers were healthy and are now developing into a bumper crop of pecans. In contrast, during "off" years we seem to see a lot more post-pollination nut drop of both types illustrated by the photo above.    

Pecan nut casebearer: May 28th Update

    We scouted our native pecan grove this morning and found 2.67% of the nut clusters damaged by pecan nut casebearer. I'm still seeing a bumper crop of nuts on the trees so we do not plan to control this year's casebearer population.
     Recent weather conditions have been ideal for the development of pecan nut casebearer--dry and hot. The slow rate if damage increase we've seen so far points to a relatively light casebearer infestation for 2012. However, we need to keep watching.

Pecan nut casebearer: 1st entry May 25th

     This morning we found 1.67% of our pecan clusters with pecan nut casebearer damage (photo at right). You can identify casebearer damage by the pile of brown frass at the base of the nut and the appearance of fine webbing between nut and peduncle.
    It usually takes 2-3 nuts to satisfy the hunger of just one insect.  Damage levels will peak in 7 to 10 days after first entry. If you plan on controlling this pest, you will need to spray before damage levels hit 5% cluster infestation.

Curled-up pecan leaves

    Growers are seeing some curled-up leaves in their orchards this year. Over the past week, I have spotted two types of leaf distortions in our pecan grove.
     In the photo at right you can see that the 5 leaflets on the end of this leaf are twisted and cupped. This type of damage was caused by the potato leaf hopper during the period of leaf expansion. The holes in the leaflets were caused by sawfly feeding, also earlier this growing season.

    If you take a close look at the underside of a curled-up leaflet, you will note brown necrotic areas along the main midrib and all major veins  (photo at left). When the leaflet was small and very tender, the potato leaf hopper inserted it mouth parts into the vascular system of the leaflet to feed on nutrient rich plant sap. This feeding behavior causes the vascular system to become clogged, stopping the flow of carbohydrates needed for further leaf expansion. Areas of the leaf that rely on those clogged veins for water and nutrients become yellow (lack of nutrients) or turn brown (lack of water). The leaflets curl because affected areas stop expanding while areas that are adjacent to functioning veins continue to expand.
     Potato leaf hoppers migrate through our area every spring. The damage caused by this insect varies from year to year and you will see several trees species affected (including pecan, walnut, ash, & maple).  We do not recommend treating for this transitory insect and just let the tree grow additional leaves to replace the damaged ones.

     A second type of curled up leaf is caused by the leaf roll mite. In the photo at right, note that the margin of the leaflet is rolled into a tight, hardened gall-like structure. As the mite feeds on the edge of a leaflet during leaf expansion, it causes distorted cell growth, creating the "leaf roll".  Leaf roll mites are fairly rare in a native pecan grove and we don't take steps to control what amounts to minimal damage.

Pecan nut casebearer update

     Three times a week we scout our native pecan grove for signs of pecan nut casebearer feeding. As of Wednesday, May 23rd we have found almost every terminal bearing nuts but only 1 damaged nut. The cool evening temperatures we've experienced over the last three days have slowed both nut development and insect activity way down. However, the weatherman is predicting much warmer temps for the second half of the week. That means we should see increased casebearer activity by the weekend.
    This year's crop load is very heavy (photo at left) so we will not be spraying our grove for casebearer this year.  Instead we will be concentrating our pesticide dollars on scab control.  The weather has been unseasonably dry lately so current scab pressure remains low. However, when we do get a change in the weather, we'll be ready to spray our trees with a fungicide.