Pecan IPM Using Black-Eyed Peas as a Trap Crop

Pecan IPM Using Black-Eyed Peas as a Trap Crop

Summary

Stinkbugs occur throughout the South and cause kernel damage to pecans in all pecan growing states. In Texas, most stinkbug damage occurs August through November when stinkbugs move from nearby crops and weeds. Stinkbugs cause a direct loss of three to five percent of the economic returns from southern region pecans, although losses within individual orchards can reach 40 to 50 percent.

Using their needle-like mouthparts, stinkbugs pierce the pecan shells and feed on the maturing kernels. The resulting damage is a dark, sunken, bitter-tasting spot on the pecan kernel (kernel spot). Farmers are not paid for stinkbug damaged kernels.

Preliminary information suggests that small plantings of black-eyed peas in pecan orchards can help pecan growers manage stinkbugs. The bugs are attracted to the black-eyed peas on which they feed preferentially, reducing pecan kernel damage. The grower’s goal was to utilize the trap crops in one or more of four ways. They first used the trap crops to monitor populations of stink bugs (it is much easier to sample black-eyed peas than pecans). Second, they used the trap crops to attract and hold the stink bugs, thereby preventing nut damage. Third, if large numbers of stink bugs were found, the growers could spray the trap crop. By not spraying the trees, the growers would avoid creating the secondary pest outbreaks of aphids which commonly occur when broad spectrum insecticides are used on pecans in West Texas. Lastly, if stink bug populations in the orchard reached numbers at which high levels of kernel damage were imminent, they could spray the trees, using the population levels in the trap crop as a decision making tool.

Approach
The growers used two orchards in this study. In the first, southern pea trap crops were established on about 1.5 percent of a 650 acre irrigated orchard. The second orchard, 20 miles north of the first, was not planted with trap crops and was used as a control.

Each year, scouts sampled the pea trap crops on a regular basis with a standard (15-inch hoop) sweep net to determine stink bug species, infestation levels and population changes. They used this information to make management decisions on insecticide application.

At harvest, 100 samples of 20-22 nuts were taken at various distances from the trap crops to assess the activity and success of using trap crops to protect pecans from stink bug damage. Farm-wide levels of stink bug damage were estimated by pooling these data.

In 1994, eight cowpea trap crops of two rows with two beds/row (about five acres total) were established at 800 to 1,200 foot intervals. They were planted between the tree rows, ran the same length as the tree rows and were planted on July 19 and August 1. Sweep net samples were taken on September 12, 20, 23, 27 and October 7, averaging 2500 sweeps/sampling date (range 1,600 to 3,300). The growers applied no pesticides to either the pecans or the trap crops as a result of the sweep data.

The growers sampled pecans on October 21 and October 27 by taking approximately 100 nuts at 22 locations (total of 2409 nuts). They took four replications of 100+ nut samples at 0-10 feet, 90-110 feet and 290-310 feet from the cowpeas to assess how distance from the trap crop affected stink bug damage. Another set of samples were taken from 0-10 feet to 2000 feet from the cowpeas. They examined the sample nuts for evidence of stink bug damage.

In 1995, nine pink-eye purple-hull pea trap crops of 4 rows with one bed/row (about 10 acres total) were established at 800 to 1,200 foot intervals in the first orchard. The plantings were again established for the length of the tree rows in between the rows. The trap crops were planted on August 1 and 10. Sweep samples were taken on August 28, September 5, 11, 19, October 2, 9, 16 and 27. An average of 2255 sweeps were taken per sampling date (range 1,900 to 2,900). Using the sweep data as the basis for treatment decisions, no insecticides were applied to the trap crops or the trees.

The growers took nut samples from the trees planted with trap crops on October 31, November 10 and 18. Twenty samples of approximately 100 nuts (total of 2, 065) were taken. The growers took six samples at 90 to 128 feet, six samples at 290 to 317 feet, and two samples at 619 to 620 feet from the trap crops. As they did in 1994, they examined the nuts for stink bug damage. No differences in stink bug damage to pecan kernels were observed 0, 100 and 300 feet from the trap crop plantings in either 1994 or 1995. The growers did note a trend toward increased damage at 600 feet from the tree rows.

The growers noted strong reductions in stink bug damage when comparing the orchard with trap crops to the orchard without trap crops. In 1994, the trap cropped pecans sustained only 70 percent of the damage sustained by the non trap cropped pecans. In 1995, a year with low stink bug problems in the region, the trap cropped pecans sustained 91 percent of the damage of the non-trap-cropped pecans.

The cowpeas used in the 1994 study performed well. They maintained good growth, leaf color, flowering, and pod set for 45 days. The pink-eye purple-hull peas used in the 1995 study were chlorotic (yellow) in spite of an expensive iron treatment. They demonstrated poor growth, blooming and pod set and were a poor choice for a trap crop planting in west Texas.

Results
When the growers compared the average dollar losses from stink bugs between the trap cropped sites and the non- trap-cropped sites they found that the non-trap-cropped sites sustained $29.29 more stink bug associated losses than did the trap-cropped orchards. It cost the growers approximately $2,112.50 (about $211.25/acre of peas) to establish and maintain the trap cropped peas. When spread over the 650 acres of the pecan farm being affected by the presence of the trap crops, the growers spent $3.25/acre (of pecans) to establish and maintain the trap crops. The growers determined for every dollar they spent establishing and maintaining the trap crops, they prevented $9.01 in kernel damage from stink bugs.

Outreach
At project completion, results were presented at the Texas Pecan Growers Association meeting, the Permian Basin Pecan Conference, and to the Southwestern Irrigated Pecan Growers.

December 1998.