Progress 01/01/05 to 12/31/05
Outputs
Weekly during the growing season in ten alfalfa fields in Kent County, Delaware the number of alfalfa weevil larvae and adults, number of potato leaf hoppers, number of pea aphids, number of leaf blotch miners, and number of tarnished plant bug nymphs and adults were monitored. Throughout the growing season outbreaks of alfalfa weevils, potato leafhoppers, pea aphids and tarnish plant bugs did occur and exceeded the economic threshold. Because of successful USDA-ARS classical biological control projects, insect pest control for alfalfa has been biologically-based. However, about 70 percent of the alfalfa growers still relied on spraying for control. All tarnished plant bug (Lygus lineolaris) nymphs were taken to the USDA-ARS Beneficial Insect Introduction Research Lab and reared to adults to determine degree of parasitism. Three indigenous parasitoid species, Leiophron uniformis, Peristenus pallipes and Peristenus pseudopallipes, were recovered from tarnished plant
bug nymphs, but levels of parasitization were extremely low, less than 1 percent on average. The tarnished plant bug, not only feeds on alfalfa but it is a pest of over half of the 30 most important crops in the U. S. It has been brought under control in most areas north on 40.5 degree N latitude (corresponding to New York City) by Peristenus digoneutis, a nymphal parasite of European origin established by USDA-ARS scientists in the 1980s. Unfortunately, this species has not spread south of New York City, so more southern populations of tarnished plant bug have not been impacted by this parasitoid. Personnel from this USDA-ARS Lab are rearing the Peristenus stygicus, the dominant parasite of lygus bugs in southern Europe for release in alfalfa fields in Delaware during summer of 2006. A second objective was to establish economic thresholds for potato leafhopper in resistant (Glandular-haired) cultivars of alfalfa. Five glandular-haired and two susceptible cultivars were established.
The glandular-haired cultivars were: WL-346LH, Mycogen 4375LH, DKA-3720, Trailblazer 4.0 and PEGASUS. Susceptible controls were Saranac AR and Cimarron. To achieve different levels of pest pressure in 2005 potato leafhopper densities of 0, 40, 80 and 160 per cage were caged over an area of 0.21 m/sq and randomly assigned with all four densities in each plot for 30 days. At potato leafhopper infestations of 40, 80 and 160, susceptible cultivars showed yellowing of the foliage, reduced yield, quality and dead plants. All glandular-haired cultivars demonstrated high resistance to potato leafhopper at both 80 and 160 levels of infestations and difference among cultivars. A graduate student has collected one year of data and needs another year of data to graduate in May 2007 and earn a Master of Science degree in Plant Science from Delaware State University.
Impacts
If the tarnished plant bug can be brought under control in areas south of 40.5 degree N latitude by establishing Peristenus stygicus, the dominant parasite of lygus bugs in southern Europe for release in alfalfa fields in Delaware, it has the potential of saving food and fiber producers an estimated 350 million dollars annually, similar to money being saved with controlling the alfalfa weevil biologically. Although the leafhopper can be controlled with insecticides, the recent development of resistant cultivars promises to greatly reduce the use of pesticides needed to control this pest, but separate economic thresholds for these varieties are needed. Thus, the establishment of economic thresholds for potato leafhopper in resistant (glandular-haired) varieties of alfalfa will result in using less insecticides and lower production costs.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/05
Outputs
The project was a joint effort with the USDA ARS Beneficial Insects Introduction Research Lab, Newark, Delaware. Alfalfa introduced into U. S. in 1736 from near Iran was grown on 8,954,656 hectars in 2005 producing forage valued at $7.3 billion nationally and $2.7 million for Delaware. Due to successful USDA ARS classical biological control projects, insect pest control for alfalfa has been biologically based. At present, the potato leafhopper, a native species, is the major insect pest in both the Northeast and Midwest. Although the leafhopper can be controlled with insecticides, the recent development of resistant cultivars promises to greatly reduce the need for pesticides. Moreover, it is not known to what extent other pests can interact with potato leafhopper to exacerbate the damage caused by the leafhopper. The tarnished plant bug, another native species, has been brought under control in areas north of New York City by Peristenus digoneutis, a nymphal parasite
of European origin. Unfortunately, this species has not spread south of New York City. To meet these needs, our objectives were: 1) establish economic thresholds for potato leafhopper in resistant (glandular haired) varieties of alfalfa, 2) assess the over abundance of and damage by alfalfa insect pests in Delaware and see whether there are any synergistic effects between the different species in the complex, and 3) attempt to establish Peristenus howardi, the dominant parasite of lygus in western U. S., to control populations of tarnished plant bug in alfalfa fields in Delaware. The research was conducted in Kent County, Delaware. Results were as follows: (for objective 1): 1) none of the 7 cultivars (5 glandular haired and 2 susceptible) of alfalfa showed complete resistant to potato leafhopper, 2) the resistant cultivars were not as affected by potato leafhopper as were the susceptible cultivars in 2005, 3) the glanduler haired (resistant) varieties exhibited a greater yield
potential than susceptible varieties when under potato leafhopper conditions in 2005, (for objective 2): 4) the abundance of potato leafhopper was strongly (P<0.0001) and positively correlated with the abundance of tarnished plant bug (r=0.619), alfalfa plant bug (r=0.378), height of alfalfa (r=0.345), and the previous weeks leafhopper counts (r=0.547), 5) there was a weak negative (r=0.063, P<0.05) correlation with precipitation (cm) the week of sampling, 6) there was no correlation with abundance of pea aphids, precipitation during the previous week, mean temperature or spraying, 7) hopper burn was strongly (P=<0.0001) and positively correlated with leafhoper counts on the same (r=0.331) and previous weeks (r=0.364) sampling date, the abundance of tarnished plant bugs (r=0.362) and alfalfa plant bugs (r=0.332), and height of alfalfa (r=0.252), and for (objective 3): 8) during the study all tarnished plant bugs were taken to the USDA ARS lab and reared to adults to determine degree
of parasitism and results indicated less than 1% of the tarnished plant bug nymphs were parasitized by parasites and none by the newly released Peristenus howardi parasite.
Impacts
If the tarnished plant bug can be brought under control in areas south of 40.5 degree N latitude by establishing Peristenus howardi, the dominate parasite of lygus bugs in southern Europe for release in alfalfa fields in Delaware, it has the potential of saving food and fiber producers an estimated 350 million dollars annually, similar to money being saved with controlling the alfalfa weevil biologically. Although the leafhopper can be controlled with insecticides, the recent development of resistant cultivars promises to greatly reduce the use of pesticides needed to control this pest, but separate economic thresholds for these varieties are needed. Thus, the establishment of economic thresholds for potato leafhopper in resistant (glandular-Haired) varieties of alfalfa will result in using less insecticides and lower production costs.
Publications
- Peiffer, R. A. , R. A. Barczewski, R. W. Fuester, P. B. Taylor and L. N. Gibson. 2006. Assessing overall abundance and damage by insect pests of alfalfa. Fourteenth Biennial Research Symposium, Association of Research Directors, Inc., Atlanta Georgia, April 1-5, p 299.
- Gibson, L. N., R. A. Peiffer, R. A. Barczewski, R. W. Fuester and P. H. Taylor. 2006. Thresholds for potato leafhopper for glandular haired cultivars of alfalfa. Fourteenth Biennial Research Symposium, Association of Research Directors, Inc., Atlanta Georgia, April 1-5.
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Progress 01/01/04 to 12/30/04
Outputs
The first objective is to assess the overall abundance of damage by primary alfalfa insect pests in Delaware and to establish Peristenus stygicus, the dominant parasite of lygus bugs in southern Europe and Peristenus howardi, the dominate parasite of lygus bugs in the western U. S., to control populations of tarnished plant bugs. Weekly during the growing season data on insect populations was collected from ten alfalfa fields in Kent County, Delaware. Releases of Peristenus stygicus were made in 2002. Throughout the 2004 growing season outbreaks of alfalfa weevils, potato leafhoppers, pea aphids, leaf blotch miners and tarnished plant bugs did occur and exceeded the economic threashold. About 70% of the alfalfa growers relied on spraying and the other 30% relied on beneficials for control. All tarnished plant bugs were taken to the USDA-ARS BIIRL, Newark, Delaware and reared to adults to determine degree of parasitism. Results indicated less than 1% of the tarnished
plant bugs nymphs were parasitized by parasites and none by the newly released Peristenus stygicus parasite. The second objective is to establish economic thresholds for potato leafhopper in resistant (glandular-haired) varieties of alfalfa. At two locations in Kent County, Delaware, five glandular-haired and two susceptible cultivars were seeded on September 9 and 12, 2003. The glandular-haired varieties were:'WL-346LH', 'Mycogen 4375LH', 'DKA-3720', 'Trailblazer 4.0' and 'PEGASUS'. Susceptible controls were 'Saranac AR' and 'Cimarron.' During the first regrowth period at one location in 2004 potato leafhoppers were caged on alfalfa to achieve four different levels of pest pressure (0, 15, 30 and 45 per cage per cultivar times 4 reps). Prior to setting out the cages the freshly cut alfalfa was sprayed with the insecticide permethin to kill existing insects. After 30 days the cages, covering a land area of 0.21m sq, were removed and no potato leafhopper nymphs or adults were found
suggesting that not enough time elapsed between spraying and introducing the potato leafhoppers. However, the mean value of alfalfa dry matter recovered inside the 112 cages was 2.13 Mg/ha compared to 4.14 Mg/ha for alfalfa growing outside the cages, a 48% reduction in forage yield. At another location in 2004 the same experiment was repeated using second regrowth alfalfa and without spraying permethrin. After 30 days potato leafhopper nymphs were recovered from the cages; however, the 0, 15, 30 and 45 levels of infestations were not high enough to affect the resistant cultivars. The two susceptable cultivars did show some characteristic yellowing of the leaves on alfalfa plants outside the cages from the wild potato leafhopper population.For the 2005 growing season the levels of infestations will be increased to 0, 40, 80 and 160 per cage.
Impacts
If the tarnished plant bug can be brought under control with a biological method, it will save U. S. food and fiber producers an estimated 350 million dollars annually similar to money saved with controlling the alfalfa weevil biologically. Although the potato leaf hopper can be controlled with insecticides, the recent development of resistant cultivars promises to greatly reduce the use of pesticides needed to control this pest, but separate economic thresholds for these varieties are needed. Thus, the establishment of economic thresholds for potato leaf hopper in resistant (Glandular-haired) varieties of alfalfa will result in using less insecticides and lower production costs.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Throughout the growing season data was collected from 12 alfalfa fields in Kent County, Delaware. Weekly counts of insect pests of alfalfa indicated that at some point during the growing season, alfalfa weevil, potato leaf hopper (PHL), aphids and tarnished plant bugs reached the economic threshold. About half of the alfalfa growers relied on spraying and the other half relied on beneficials for control. Both practices worked good for controlling the alfalfa weevils and pea aphids; however, it was more difficult keeping the potato leafhopper under control. No alfalfa grower sprayed specially for the tarnished plant bug, but they were sprayed when other pest were sprayed. Tarnished plant bug nymphs were collected weekly and reared to adults. Results indicated < 1% of the tarnished plant bug nymphs were parasitized by existing parasites. Thus, releases of Peristenus stygicus, the dominate parasite of lygus bugs in southern Europe, will be released in 2004 to control
populations of tarnished plant bugs. Use of promising new PLH resistant alfalfa varieties will aid in controlling the PLH; in addition, to reducing the need for spraying. However, there is a need to determine the economic threshold for PLH for these new glandular-haired cultivars of alfalfa; thus, five glandular-haired (WL-346LH, Mycogen 4375LH, DKA-3720, Trailblazer 4.0 and PEGASUS) and two susceptible cultivars (Saranac AR and Cimarron) were planted at two locations in Delaware on September 12, 2003.
Impacts
If the tarnished plant bug can be brought under control with a biological method, it will save U. S. food and fiber producers an estimated 350 million dollars annually similar to money saved with controlling the alfalfa weevil biologically. Although the potato leaf hopper can be controlled with insecticides, the recent development of resistant cultivars promises to greatly reduce the use of pesticides needed to control this pest, but separate economic thresholds for these varieties are needed. Thus, the establishment of economic thresholds for potato leaf hopper in resistant (Glandular-haired) varieties of alfalfa will result in using less insecticides and lower production costs.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
The project is a three year study starting October 1, 2002 running through September 30, 2005. Two areas, one at the University of Delaware's agricultural farm at Newark, Delaware and the other at Delaware State University were planted with five glandular-haired and two susceptible cultivars. The glandular-haired varieties were: `WL-346LH,' `4375LH,' `DKA-3720,' `NK-EXPLH' and 'PEGASUS.' Susceptible controls were `Cimarron' and `Iroquois.' Cultivars were arranged in a randomized complete block design with four replications. Starting in 2003 potato leafhoppers will be caged on the alfalfa to achieve different levels of pest pressure. Leafhopper densities of 0, 15, 30, and 45 the first year and 0, 40, 80, and 160 in subsequent years will be randomly assigned to each cage, with all four densities in each block. Economic injury level trials will be conducted during the second, third and fourth cutting periods each year. In addition, the project is currently advertising
for a graduate student to work on the project. Thereby, that student will earn a Master of Science degree in Pant Science from Delaware State University.
Impacts
The alfalfa test plots were established as stated earlier and we are close to recruiting a graduate student to work on the project.
Publications
- No publications reported this period
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