Back to April 2015

Predicting casebearer activity using PNC forecast system


Here you can see an egg that a pecan nut casebearer laid on this nutlet. (Photo by Bill Ree)

Monitoring pecan nut casebearer PNC moth activity with pheromone traps is now a standard practice for managing this import insect pest. Trap counts indicate when male PNC moths are first active in the spring and their relative activity during each generation. The best use of trap counts is to enter the information into the PNCforecast System which predicts when first generation PNC moths will be laying eggs in the orchard. The result is a picture of egg-laying activity expected during the next two to three weeks that is customized to the unique conditions of the orchard where the trap data were collected. This information can then be used to time orchard scouting and anticipate when to apply an insecticide if needed. The PNCforecast System is available online.

The PNCforecast System calculates dates when first generation eggs are expected to be present in the orchard and the optimum dates to begin scouting the orchard for PNC eggs. Egg laying activity can vary by as much as two to three weeks, so knowing when to look for eggs can save time and help reduce the risk of missing egg laying activity.

These nutlets are suffering from extensive pecan nut casebearer damage. (Photo by Bill Ree)

To generate a PNCforecast, you need to know the date when PNC moths begin flying in your orchard. To be sure you capture the first PNC moths in the spring, you must place your traps in the orchard before the first moths fly. In south Texas, traps should be in the orchard by Apr. 1; in central and southwest Texas by Apr. 10; and in north and northwest Texas by Apr. 20. Record the number of captured PNC moths every one to two days. If no PNC moths are present, enter a zero for that date. Once traps are in the orchard, there should be several inspection dates when no moths are captured to be sure the first moths that appear in your traps are indeed the first ones of the spring flight.

Selecting the date when you first capture PNC moths in your traps is very important. Sometimes one to two PNC moths are captured and then none are captured on subsequent dates. Ignore these early “stragglers” if no new PNC are present in your traps on the next inspection date. Once you capture moths on two consecutive dates, the sustained moth flight is underway. Choose the first date of the two consecutive dates as the date of first moth capture. Table 1 shows trap captures in three orchards, A, B and C, and the determination of the date of the “first“ moth. Once you know the date of first moth capture, no additional trap data is needed to generate a PNCforecast, but you can continue to record trap captures to compare year to year PNC activity.

Once you know the date of first moth capture in your traps, you are ready to generate a PNCforecast for your orchard. Log onto: Pecan ipmPIPE. At the home page, select ”Maps” and then under PNC Forecast Map click on “Forecast PNC risk”. After reading the “Warning” statement, close the text box using the X at the top right. At the top left, select “Choose Location” and use the arrows in the circle at the top left to find you orchard on the map. Use the magnifying glass to zoom in and out on the map. Once the map is fully magnified and the cursor is at your orchard location, right click. This will place a red pin at your orchard site. The PNCForecast will use the average temperature expected at this location during the next 2-3 weeks to predict PNC development. Next, at the top right of your screen, at “Set Biofix”, click on “Select Date” and use the calendar to enter the date on which you captured the first PNC moths in traps at this orchard location. Once you enter this date, the site will then generate a PNCforecast both as a graph and table.

This pheromone trap captured a number of moths and can be used to plan your pecan nut casebearer management. (Photo by Bill Ree)

The PNCForecast table lists the dates when 10, 25, 50, 75 and 90 percent of all first generation PNC eggs are expected to be present in the orchard. In the example shown in Table 2, 25 percent of total eggs expected should be present on May 10 and the egg-laying period should be almost complete by May 19 (90 percent of all eggs deposited). Begin scouting your orchard for PNC eggs on the dates when 25-50 percent of all eggs are expected to be present. If PNC egg numbers are not at a treatment threshold (consult your local Extension service for threshold levels for your state) at that time, return on the dates of 50-75 percent egg-lay (two to three days later) and scout for eggs again. If the numbers of eggs and larvae are still below the threshold, scout a third time on the dates when 75-90 percent of the eggs are expected to determine if PNC infestations have increased to a threshold level justifying an insecticide treatment.

This example shows the number of PNC moths captured in pheromone traps in three orchards and the calculated date of first moth capture. The date of first moth is entered into the PNCforecast System.

The percentages in the table are NOT the expected percent of nutlets infested with eggs, but an estimate of what proportion of total eggs are expected to be present on a given day. The orchard must be sampled (scouted) for PNC eggs and nut entry to determine if the PNC infestation justifies treatment and if so when to apply the insecticide. Treatment decisions should not be based solely on a PNCforecast output. Growers should base management decisions regarding PNC on their assessment of numbers of PNC eggs and larvae and nut set as determined by scouting in their orchards.

This is an example of a PNCforecast. Dates indicate the percent of total eggs expected during a generation. Begin assessing first generation PNC egg infestations on the dates of 25-50 percent.

PNC activity at other sites across the pecan belt as reported by cooperating growers is also available online. At this site, under Maps select PNC Risk Map. The Decision Window refers to the dates when 25-50 percent egg lay is predicted and indicates when orchards near that site should be sampled to determine if infestations justify treatment.

A list of supplies of PNC traps and lures is available online.