S_TEMP1102: Improved Systems for Management of Economically-Important Arthropod Pests Attacking Pecan
(Multistate Research Project)
Status: Inactive/Terminating
S_TEMP1102: Improved Systems for Management of Economically-Important Arthropod Pests Attacking Pecan
Duration: 10/01/2002 to 09/30/2007
Administrative Advisor(s):
NIFA Reps:
Non-Technical Summary
Statement of Issues and Justification
Pecan (Carya illinoinensis (Wang.) K. Koch ) is the most economically-important native nut crop in the U.S. It provides annual farm gate revenues > $300 million to diverse producers; most with < 100 acres and some with > 1000 acres. Uncultivated native stands are managed in river valleys that empty into the Gulf of Mexico but also in vegetatively propagated and seedling orchards across the south-central U.S. Growers rely on arthropod pest management strategies that are developed through regional entomology research dispersed across the pecan growing region. Regional coordination increases the feasibility of completing multiple research projects. Pecans are produced in 18 states but only GA, AL, LA, TX, OK, KS, and NM conduct research to control pecan pests. However, regional cooperation among pecan entomologists has provided research-based strategies for pest management in all states by effectively pooling resources, coordinating research and testing new technologies. Success of the regional research project is measured by the creation of new pest management tools and successful adaptation of new technology into IPM strategies widely used by pecan producers.
Improving systems to manage pecan arthropod pests requires regional research that includes: improved systems to monitor pests, improved control systems for pests and development of pest biocontrol systems. Technical feasibility to complete this research is high given past regional accomplishments. Non-renewal would negatively affect our stakeholders by diminishing collaborative research between regions and limiting opportunities for direct transfer of information between scientists. This replacement proposal is directly related to Goal 4 (Greater harmony between agriculture and the environment) Part F (Integrated pest management systems, including biologically-based tactics) of the SAAESD Programmatic Plan priority areas for multistate research activities.
Pecan production differs across states requiring validation of monitoring and control techniques at different locations. In improved southeastern orchards, the pecan weevil (PW), HSW, aphids, and kernel-feeding hemipterans are important pests and minimized pesticide sprays during the early season conserves beneficial insects. In improved western orchards, pecan nut casebearer (PNCB) and aphids are important pests but others, e.g., PW, are not established. Insecticides may be applied to southwestern orchards for early season PNCB control, mid-season for PNCB and August for PNCB plus aphids. Management of native groves emphasizes control of PW and PNCB; one early application for PNCB and 2-3 fall applications for PW.
Pecan pest management changed considerably in the past 5 yr due to improved monitoring and chemical controls. The Circle trap improved PW detection and spray application. Pheromone monitoring of PNCB, HSW, and Euschistus spp. stink bugs was refined. Development of pheromones may allow for mating disruption to manage lepidopteran pests. Advances in biocontrol were made against aphids, pecan leaf scorch mite and PW. Orchard IPM was advanced by testing and recommending reduced-risk insecticides targeting specific pests but conserving natural enemies. However, rising costs of monitoring and control demand optimized management strategies. Aphid and mite resurgence remains a problem when broad spectrum insecticides are used against nut pests. Thus, implementation of more economical, target-specific insecticides and biocontrol measures are needed.
Non-chemical control of PW is needed. Carbaryl sprays for PW are often amended an insecticide to prevent aphid and mite resurgence because carbaryl destroys their natural enemies. Alternative control tactics include: biocontrol with nematodes and fungi, early nut harvest, improved trapping, soil moisture control, host plant attractants and cultivars with low vulnerability to oviposition. Regional research efforts are needed to integrate such new tactics into an overall IPM strategy.
The importance of this research to agriculture is in innovation to improve pest controls that protect and conserve this important native tree nut crop. The value to science is in using basic research to solve practical problems. Basic chemistry elucidated insect pheromones now used to monitor pests. Basic ecology developed aphid population models, predatorprey interactions and energy budgets for pest populations. Basic entomology delineated trophic relations between aphids and aphidophaga, lepidopteran pests and parasitoids, and weevils and pathogens. Insect behavior research led to better trap designs and alternative control tactics.
Related, Current and Previous Work
Related and Current Work: The Current Research Information System (CRIS) of the USDA was searched and 156 research projects were found that currently or recently involved some degree of research or association with pecan research. The search revealed that 64 of these projects were at least loosely related to pecan and insect research, whereas, 26 projects were more tightly linked to research on pecan and arthropod problems by scientists in the USDA and the SAES systems. The following narrative cites projects, by author and agency, for pecan research projects more-relevant to pecan entomology that were active during 1998 and afterward. Pecan cultivar resistance to insect damage has been and continues to be an important part of a pecan breeding program in Texas (Thompson and Grauke, ARS 6202) and in Georgia (Conner, CSREES GEO). Biological control of pecan insects is being carried out by several disparate projects (Shapiro-Ilan, Cottrell and Wood, ARS 6606; Ellington, CSREES NM; Dutcher, CSREES GEO; Mizell, CSREES FLA; Hunter, CSREES ARZT). Development and implementation of the Circle trap in pecan orchards for monitoring pecan weevil has proved successful by assisting in timing application of insecticides (Mulder, CSREES, OKL). Trapping Euschistus spp. stink bugs with pheromone-baited traps showed the seasonal occurrence and vertical distribution of two different species in pecan orchards. In addition, improvements were made to the trapping system that enhanced stink bug catch (Shapiro-Ilan, Cottrell and Wood, ARS, 6606). Use of pheromone traps to refine timing application of insecticides against the HSW and PNC has been done resulting in enhanced control and cost savings to growers (Mulder, CSREES OKL; Harris and Ree, CSREES TEX). Reduced-risk insecticides (e.g., imidacloprid) are available for certain pecan pests thus allowing for pest management strategies that focus on increasing natural control by minimizing the impact of chemical insecticides on beneficial species. Implementation of these reduced-risk insecticides into pecan pest management also will help to meet future grower needs as more broad-spectrum insecticides are lost due to the Food Quality Protection Act (FQPA) (Harris and Ree, CSREES TEX; Dutcher, CSREES GEO, Ellington CSREES NM, McVay, CSREES ALA). In addition, trap crops have been tested and can provide relief to pecan from stink bug damage and other kernel-feeding Hemiptera thereby further reducing insecticide usage in pecan orchards (Hall, SAES LA.B). Pecan insect management strategies are being developed for native pecan groves (Reid, CSREES KAN). Many of the projects are authored by S-293 technical committee members and the biological control group has expressed interest in developing cooperative work through the new regional projects.
Previous Work - Pest Monitoring Advances: New techniques for monitoring and control have been improved through regional research. Most recently, effective control and monitoring systems for pecan nut casebearer, stink bugs and black pecan aphids have been developed, field tested, and implemented in commercial orchards.
A highly effective monitoring and control system was developed for pecan nut casebearer by combining a pheromone monitoring system, a sequential sampling plan, a prediction model, and insecticides (Harris 1995, Harris et al. 1994, 1995a, 1995b, 1997). Important factors in pheromone trap catch were dose, lure age, and trap design (Knutson et al 1998). Research has found ways of replacing broad spectrum insecticides with tebufenozide (Confirm 2E, Dow AgroSciences, Indianapolis, IN), a biorational pesticide for pecan nut casebearer control. Pecan nut casebearer monitoring has been adjusted to predict first nut entry for different areas of pecan production (Davis 1993, Layton 1993, Mulder 1997, Ree 1995). Biological research continues to improve our understanding of oviposition and nut entry behavior of pecan nut casebearer (Aguirre et al 1995) and the interaction of pecan nut casebearer, pecan weevil and masting of pecan (Chung et al 1995, Harris et al 1996). Pecan nut casebearer spray timing has been linked to geographic information systems (GIS) to generate maps with isoclinal lines showing when to make control decision dates; maps are updated weekly during the first summer generation. Prediction models for first nut entry have been developed for use in Georgia and Texas. Evaluation of both models in Oklahoma by Grantham et al. (2002a, 2002b) showed that the Texas model performed best for Oklahoma orchards. Additionally, pheromone trapping across the southern U.S. validated the Texas model (Stevenson et al., 2003).
Stink bug monitoring was improved with a new trapping technique. A pyramidal pecan weevil trap was painted yellow and a screen trap was affixed to the top (Mizell and Tedders 1995, Mizell et al., 1997). An aggregation pheromone, attractive to brown and dusky stink bugs, was used in conjunction with this yellow pyramidal trap. Seasonal occurrence of brown and dusky stink bugs was monitored (Yonce and Mizell 1997). Using this trapping technique, differential trapping of brown and dusky stink bugs was discovered in orchards; more brown stink bugs near the ground and more dusky stink bugs in tree canopies (Cottrell et al. 2000). Stink bugs cause damage in pecan in the fall and anytime when droughty conditions surround the orchard area. At these times alternate host plants in adjacent border crops are harvested or senesce, these areas become less desirable for stink bugs and the stink bugs migrate into the pecan orchard. The influx of stink bugs from harvested peanut fields into pecan can last 30 days (Mizell et al 1997). Irrigated pecan orchards are highly attractive to stink bugs and feeding before shell hardening can cause the nut to abort within 7 days (Wood and Tedders 1996).
A sampling technique for black pecan aphid was developed to detect low population levels and give the growers an early warning for each infestation. The sample unit was changed from the compound leaf to the terminals and complete enumeration of the aphids is replaced by rating the terminals as having 0, 1 or 2+ aphids and whether or not nymphs are present. The older sampling technique underestimated small populations and overestimated large populations. By noting the presence of adults and/or nymphs, a lag period can be identified between the appearance of the first adult aphids and exponential population growth (Dutcher 1997a).
In addition, insect monitoring and prediction systems have been improved for other very important arthropods, including pecan weevil and hickory shuckworm. A pheromone mixture of the male pecan weevil was identified (Hedin et al 1997) that is attractive to female pecan weevil. Pecan weevil mating is diurnal, peaking in the mid-afternoon (Collins et al 1996). Pecan weevil trapping has been improved with pyramidal cone traps (Tedders and Wood 1994, Tedders et al 1996) and circle traps (Mulder et al 1997) and a pheromone trapping system is in development (Hedin et al 1996, 1997, Collins et al 1996). The activity of pecan weevil adults after emergence from the soil is better understood from recent research (Cottrell 2001). This research indicates that pecan weevil emergence rate increases at dusk each day to nearly double the rate during the day, night or dawn. When weevils emerge, 60% crawl on the ground to the tree trunk and 40% fly to the trunk before ascending into the tree crown. After ascending into the large (15 m in ht.) trees in this study, weevils oviposited in a higher percentage of the pecans in the lower third of the canopy than in the middle or upper thirds. Weevils were also easily intercepted with traps set between trees at 5, 8 and 12 m indicating frequent flight of weevils between trees.
A pheromone for the hickory shuckworm is commercially available and researchers have been developing pheromone based monitoring systems. This research has revealed two new compounds with attractiveness to male moths (M. T. Smith et al. 1994). In controlled field experiments, male moth response to the new components was mixed (M. T. Smith 1995a). Analysis of trap catch data indicates that the populations have a clumped distribution that becomes more uniform as the population size increases. These results indicate a need for more traps per orchard to measure moth flight accurately. The current recommendation is 1 trap/10 acres (M. T. Smith 1995a). However, hickory shuckworm pheromone trap catches are lower than black light trap catch (Collins et al 1995), especially during the mid-summer, even though adults are present and larvae cause significant nut drop (Yonce and McVay 1994). Research continues to identify and evaluate additional pheromone components (M. T. Smith et al 1994, M. T. Smith 1995a), trap design and placement (McVay et al 1995), emergence patterns and population trends (McVay et al 1994, Yonce and McVay 1994). In controlled field experiments, male moth response to the new components was mixed (M. T. Smith 1995a). Biological studies have measured the response of hickory shuckworm larvae and larval parasitoids to cold temperatures (Nava-Camberos et al 1996, Yonce et al 1996).
Current Chemical Control: Chemical control of pecan insects is a critical issue in pecan production. Many insect problems are solved with chemical controls. Cancellation of the registration of principal pecan insecticides, development of insecticide resistance in aphids, and a reduction in the number of new registrations has reduced the chemical control options for pecan growers. Many growers rely on biological controls of early season insect problems, but the high investment in the crop has to be conserved with effective late season insect controls, especially for nut protection. Chemical control of pecan weevil, hickory shuckworm and kernel-feeding hemipterans is the most effective way to conserve the crop. Chemical control of black pecan aphid is the most effective way to conserve the foliage through the season and reduce alternate bearing. New chemical controls continue to be evaluated for control of pecan insect pests. A reduced-risk insecticide, imidacloprid, is currently used on pecan for control of pecan aphids. However, control of the seriously-damaging black pecan aphid is less than control of the blackmargined or yellow pecan aphids. Biorational materials such as tebufenozide have been used against pecan nut casebearer and hickory shuckworm on pecan. Usage of phosmet, methidithion, and formulations of B.t. toxins, has increased due to the canceling of the registration of phosalone (Harris 1998). Phosmet and methidithion are the only two insecticides with high efficacy against black pecan aphid that are readily available to pecan growers. Reduction in spray frequency by growers is a result of improved insect monitoring techniques. The number of carbaryl sprays for pecan weevil management has been reduced through improved trapping methods for pecan weevil. New traps and trunk sprays of carbaryl are being tested yearly (Mulder et al. 2003, Cottrell and Wood 2003). A pyrethroid, zeta-cypermethrin, looks promising for control and is currently registered. All other chemicals have to be sprayed out once per week to be as effective as carbaryl for three seasons and then Dipel for hickory shuckworm control during late season of the fourth and fifth seasons is effective in reducing pecan weevil. The two year hiatus from carbaryl allows natural controls to reduce aphid and mite infestations. Weevil damage was less than 2% damage in untreated pecan trees. These results indicate that pecan weevil may be locally controlled with reduced spray frequency for several seasons after a three year intensive control program (Dutcher 1997b). Pecan nut casebearer can usually be controlled when the monitoring system is used with one well-timed spray. Hickory shuckworm still requires two sprays of a contact insecticide, timed by monitoring pecan nut phenology and black light trap catches. Pecan aphids were found to develop insecticide resistance in the field within two seasons of the introduction of use of pyrethroids or organophosphates. Combinations of insecticides were also losing efficacy over time (Dutcher 1997c). Black pecan aphids have shown some tolerance to insecticide applications and populations are increasing across the southeast (McVay and Estes 1995). More specific aphid insecticides were found to effectively control the aphids and resistance development studies are underway for these new insecticides (Dutcher 1997b). The impact of pesticides on beneficial insects and aphid pathogens was determined in field and laboratory experiments (Hurej and Dutcher 1994a, 1994b, 1994c) and indicated that ladybeetles were not tolerant to any insecticides tested and lacewings were tolerant to certain insecticides. A pesticide usage survey in Texas indicated a reliance on organophosphate insecticides and strong participation in IPM approach to control (Harris et al 1993). Characteristics of concentrate and dilute spraying techniques were compared (Harris 1997).
Integrated Control Measures: Research has developed pecan pest management programs for control programs of pecan weevil, hickory shuckworm, pecan nut casebearer and the aphid complex based on integration of chemical and biological controls (Harris 1983). Alternatives to broad spectrum insecticides for pecan pest control were developed (McVay and Hall 1998). In addition to control of pecan nut casebearer, tebufenozide effectively controls gregarious caterpillars and hickory shuckworm without destroying predacious insects of aphids and mites (Dutcher 1996). Pecan weevil control is still reliant on sprays of carbaryl to the foliage as an adulticide (Tedders and Wood 1995). The specific aphidicide, imidacloprid (Provado 1.6E or Admire 2E, Bayer Chemical Co., Kansas City) effectively controls pecan aphids that tend to increase rapidly after carbaryl is applied for weevil control during the late season (Dutcher 1994b, 1995a, 1996, 1997a, 1997b). New biological controls such as a rickettsiella-like organism (Adams et al 1997) may be a potential biological control agent against pecan weevil. Habitat diversification techniques have been identified as effective in pecan production. Trap cropping has been shown to be a viable alternative to chemical control for reducing the incidence of hemipteran kernel damage on pecan (M. T. Smith 1996); trees adjoining trap crop areas had an overall reduction in damage of 55%. Research in the area of trap cropping in pecan is a major initiative and is a recommended practice in some IPM programs. Differences in the seasonal occurrence of brown and dusky stink bugs may be important to the effectiveness of trap crops. Brown stink bugs are trapped more readily on the ground than dusky stink bugs that are more abundant in the tree canopy (Cottrell et al 2000). Intercrops of warm and cool season legumes have shown promise as sources of alternate prey aphids for aphidophaga that also feed on pecan aphids. Intercrops stimulate an increase of populations of alternate prey aphids and aphidophaga in the orchard and a decrease in pecan aphids in the tree crown. When coupled with control of secondary predation of aphidophaga by red imported fire ant, the pecan aphids are further reduced (Dutcher 1993, 1995b). Pecan aphid control was demonstrated with conservation of aphidophaga by intercropping with summer crop of sesbania, controlling secondary predation by red imported fire ant and spraying predator attractants (Bugg and Dutcher 1993, Kaakeh and Dutcher 1992, 1993c, Dutcher 1993, 1994a, 1995b, 1998). Reductions in the frequency of fungicide sprays conserve entomophagous fungi that regulate pecan aphid populations (Pickering et al 1990). Pecan arthropods were influenced by cool season intercrops (M.W. Smith et al 1994, 1996a, 1996b) and methods were developed for screening potential intercrop plants (M.W. Smith et al 1996a, 1996b). Native pecan production was found to be profitable with limited insect control (Reid 1993, Reid and Mulder 2003). Organosilicone surfactants were found to control pecan aphids for a short time (Wood et al 1997). Higher action thresholds and inundative release of aphidophaga was an effective and economical control for pecan aphids in New Mexico (LaRock and Ellington 1996). Blackmargined aphids and associated honeydew attracts aphid predators to the pecan foliage and may ameliorate biological control of aphids (Harris and Li 1996). Red imported fire ant commonly occurs in pecan orchards and is an important predator of pecan weevil (Dutcher and Sheppard 1981) as well as certain aphidophagous insects (Tedders et al 1990, Dutcher et al 1999). The environmental factors affecting pecan aphid population dynamics were determined (Kaakeh and Dutcher 1993a, 1993b); the aphids have a wide range of tolerance to high temperature and are temporarily reduced by rainfall. The Texas pecan IPM program has been evaluated and found IPM oriented producers experienced cost savings in excess of $1 million/annum (Harris et. al 1998, Harris 2001). An excellent resource that integrates and updates information on new biologically oriented management methods for pecan production is the National Center for Appropriate Technology (Diver and Ames 2000).
Biological Control: Biological control in pecan production can offer alternatives to the use of broad spectrum insecticides (Ellington et al. 2003). Accomplishments of ongoing biological control projects include: identification of virulent strains of entomopathogenic nematodes active against larval and adult pecan weevil (Shapiro-Ilan, 2001 a, b, Shapiro-Ilan 2003, Shapiro-Ilan et al. 2003a, b, Shapiro-Ilan et al. 2004a); efficacy of trunk-perimenter applications of an entomopathogenic fungi against pecan weevil (Shapiro-Ilan et al. 2004b); discovery of differential susceptibility between a native lady beetle species and an exotic lady beetle species both important to pecan aphid control (Cottrell and Shapiro-Ilan 2003); documenting differential predation on native versus exotic lady beetle species eggs in the laboratory (Cottrell 2004); efficacy of application of predatory mites to manage damaging pecan leaf scorch mites; established biological control in the Mesilla Valley of New Mexico in pecan orchards; investigated heat tolerant species of lacewings for biological control of pecan aphids in Arizona and developed and tested intercrops, ant controls and predator attractants as enhancements for aphidophaga in Georgia pecan orchards.
Host Plant Resistance: Significant advances have been accomplished in host plant resistance of pecan insects on pecan cultivars. Resistance of Pawnee and Navajo cultivars to blackmargined aphid has been demonstrated in greenhouse and field evaluations (Thompson and Grauke 1998). These cultivars are not immune to aphid infestation but resistance enhances current recommended control techniques. These results are consistent with lab and field research in Georgia (Kaakeh and Dutcher 1994) where blackmargined, black pecan and yellow pecan aphids were found to have lower reproductive rates and altered probing behavior and lower infestation levels on Pawnee and Cape Fear cultivars. Black walnut, butternut, pecan and several hickory species were investigated as potential sources of resistance factors to aphids (M. T. Smith et al 1993, M. T. Smith 1995b). Blackmargined aphid adults lived longer and had higher reproductive rates on pecan, water, scrub, shellbark hickory, and hican than on black walnut, butternut, and several other hickory spp. Percent survival of blackmargined aphid nymphs to the adult stage was lower on most hickory and walnut species than on pecan, hican or water hickory. Yellow pecan aphid adults lived longer and had higher nymph survival on pecan than on hickory or walnut. Black pecan aphid had similar adult longevity over all tree species but reproduced and developed from nymph to adult only on pecan. Pecan cultivars have variable susceptibility to black pecan aphid feeding damage as measured by the amount of chlorosis. Certain cultivars have a water-soluble antibiotic factor on the leaf surface that suppresses black pecan aphid populations (Wood and Reilly 1998). Two new cultivars - Kanza and Creek - have some resistance to hickory shuckworm and Kanza" is highly resistant to phylloxera species (Thompson 1996a, 1996b). A leaf disc bioassay was developed to evaluate pecan cultivars for host plant resistance to black pecan aphid (Estes 1995). Pecan cultivars differed significantly in susceptibility to hemipteran kernel damage in a recent evaluation over four seasons (Dutcher et al 2001). The majority of the cultivars in the experiment that had consistently low levels of kernel spot also had highly desirable horticultural characteristics and these cultivars were recommended for planting. Most cultivars with consistently high levels of kernel spot were also not recommended for planting (Worley and Mullinix 1997, Thompson 1996a, 1996b).
Objectives