S1049: Integrated Management of Pecan Arthropod Pests in the Southern U.S.
Statement of Issues and Justification
The pecan industry now has a highly effective and sophisticated insect and mite pest management system in place that conserves the foliage and nut crop. This was achieved through research by the USDA/CSREES regional research projects in collaboration with extension specialists, private industry and cooperating pecan growers. Pecan foliage can be protected from aphid and mite feeding injury with bottom-up control methods where fertilizers, pesticides and ground cover plants are applied to the soil or with top-down control methods where the foliage is treated directly (usually with an airblast sprayer) with: insecticides; miticides; repellents; biological control agents, such as, insectary-reared insects and mites or cultured-microbes or their byproducts; natural products, primarily plant extracts; or soaps and surfactants that modify the leaf surface. Pecan nuts are currently protected by top-down controls with insecticide sprays timed to be applied when the pest populations occur in the orchard in sufficient abundance to cause economic injury to the crop. The key to effective nut pest control is to have an effective insect monitoring program ongoing in the orchard from budbreak to harvest. Pecan growers, throughout the U.S., have many control options including both federally registered insecticides and miticides and proven biological controls. Scouting techniques are also effective, well-known and used by a significant portion of growers. The system is not static and changes from season to season because of four main factors. First, INNOVATION leads to the development of new and more effective control methods each year. Second, REGULATION of insecticides and miticides can result in the gain/loss of their registration for use on pecan. Third, SELECTION within pest populations can develop a tolerance or resistance to certain chemical controls. Fourth, STATUS of the orchard changes with each season with respect to: climate; types and abundances of pests; value and size of the nut crop locally and across the region; and costs of production. The regional research approach has been an effective forum for finding alternative insect and mite controls and monitoring methods for pecan growers in the southern region of the U.S. since 1976. The current project S-1017, terminates on September 30, 2010 and the following narrative outlines our research plans for 2010 to 2015 seasons. Cooperating States Agricultural Experiment Stations and Agencies are: (Alabama, Florida, Georgia, Louisiana, Texas, USDA).The need for research as indicated by stakeholders - Pecan growers universally demand improvements in insect and mite pest management. No pecan growing region is without some type of arthropod pest problem and multiple problems are the norm. Differences occur between the pecan growing regions in the portion of the insect or mite pest complex that is abundant at a sufficient level to cause economically significant injury to the trees, foliage or the nut crop. California, Arizona, New Mexico and West Texas pecans typically have aphid and mites on the foliage and pecan nut casebearer and hickory shuckworm as nut pests. In East Texas and north to Oklahoma to southeastern Kansas then east through to the east Atlantic Coast of Georgia the major pecan insect and mite pests are: aphids, pecan weevil, pecan nut casebearer, and hickory shuckworm. Pecan leaf scorch mite and Prionus root borers are key pests east of the Mississippi River in the southeastern U.S. Recent crop profiles for pecan production in Georgia (Guillebeau 2001) and Texas (Smith et al 2002), Kansas (Kadir et al 2001), North Carolina (Parker et al 1999), and Arkansas (Johnson et al 2003) indicate that the pecan weevil and kernel feeding hemipterans are the major late season kernel pests facing the U.S. pecan industry. Insecticides are the main controls used for reducing damage by these two pest problems. The research committee of the Georgia Agricultural Commodity Commission for Pecan ranks black pecan aphid as the most serious foliage feeding insect pest. Stakeholders also want better resources placed on the internet to aid their in-season decision making on key pests.
The importance of the research work, and consequences if it is not done - Since 1976, regional research in the southern states on pecan entomology has produced effective methods for detecting, predicting and managing insect and mite outbreaks in pecan orchards. Pecan orchards that are not managed for insect and mite control each season will typically stop producing a significant nut crop within two seasons. The damage potential of the nut feeding insects is sufficient to injure or destroy the entire nut crop each year and foliage insects can defoliate the trees early in the season throwing the trees in to a non-productive period that can last for several seasons (Dutcher et al 1984).
The technical feasibility of the research The primary problem in accomplishing pecan research goals is the establishment of a research site for field experiments to test new control methods. Prior to 1976, most of the field experiments were run on the farms of cooperating growers often without nontreated controls and only limited (or no) local controls, randomization and replication of treatments. Since 1976, several experimental sites have been planted and are available for controlled field experiments under more uniform conditions at state agricultural experimental stations (SAES) and the USDA field stations. The work at these locations has produced control methods that are thoroughly tested, interpreted, analyzed, refined and retested in statistically valid experiments. The trials determine the efficacy as well as the probability of achieving the efficacy. Methods developed at these sites are readily transferred to commercial orchards. Also, efficacy trials at the SAES sites have found methods that are ineffective or cause ancillary problems, such as, resurgence of secondary pests, or insecticide resistance and pest replacement problems. Biological control methods are new to pecan growers. Advantageous interactions between cultural methods and pest populations are recently measured and just now being understood and manipulated by growers. Considerable extension and educational efforts will have to be initiated to ensure that growers understand how to use these new ideas in the field. As examples: identification of beneficial insects and mites will become important and is not a skill that most growers have at this time; more frequent application of reduced rates of fertilizer coupled with aphid and mite scouting information is not currently practiced by growers; the use of clover as an intercrop is widespread but the movement of predators from the cover crop to the tree with food sprays and sicklebar mowing is not a common practice; identification of the fungi that attack aphids and coupling reduced frequency of fungicide sprays to encourage these fungi is not commonly used by growers. The implementation of these known positive interactions is typically not associated with increased input costs and has been shown to be effective in research trials and limited grower demonstrations. Additionally, new developments in Information Technology provide a novel opportunity to develop deliverables with complex underpinnings using the computer and posting results on the internet. The initial phase for this has been established at http://pecan.ipmpipe.org/
The advantages for doing the research work as a multistate effort The advantages of working as a team of entomologists across the pecan growing regions are: 1. Methods can be innovated at one location and then tested under a broad range of conditions and then altered to fit the conditions at each region; 2. Information of recent work can be presented and discussed each year by all participants so that scientists can access the results before the material is published since the publication process can take a year or more; 3. Regional experiments can be conducted during the same season to measure the influence of environmental factors on the efficacy of the control methods and seasonal occurrence of the pests; 4. Extension specialists and growers and publicists can be invited to the annual meetings to make presentations on important issues giving the technical committee members a better perspective on conditions in the pecan industry.
What the likely impacts will be from successfully completing the research work -Compare the % mortality required to prevent annual increases in the insect and mite populations (Table 1) with the relative efficacies of the current control methods (Table 2) and it is obvious that improved control methods are needed against all the key insect and mite pests listed. Table 1. The mortality that is needed each season to cause a reduction in the season to season abundance are estimated from literature values for the reproductive capacity (RC) and generation time (GT) for certain pecan insect and mite pests with the formula:
% Mortality = 100´ (1 (1 ¸ (SR ´ RC)GT)).
Pest* Reproductive Capacity Generation Time % Mortality
Pecan weevil 75 eggs/female .33 or .50 gen/yr 3053/season** Pecan nut casebearer 50-150 eggs/female 2 gen/yr 99-99.9/season Hickory shuckworm unknown 2-5 gen/yr unknown Black pecan aphid 35 nymphs/female 26 gen/yr 99.9/season Yellow pecan aphid 38 nymphs/female 32 gen/yr 99.9/season Black margined aphid 125 nymphs/female 16 gen/yr 99.9/season Pecan leaf scorch 9-36 eggs/female 7-8 gen/yr 99.9/season Mite Fall webworm 300-1000 eggs/female 4 gen/yr*** 98-99.9/season Walnut caterpillar 120-880 eggs/female 2 gen/yr 99-99.9/season
* Kernel feeding hemipterans are not listed since they invade the orchard and do not breed in the orchard. ** 97.3 % mortality per generation is required to prevent pecan weevils from increasing in the orchard. 30 % (53%)mortality per year will control weevils with a 3 (2)year life cycle. *** 2 overlapping broods occur each season
Table 2. Control methods for the eight major pecan arthropod pests in North America.
Pest Control method for pest Relative efficacy
Pecan weevil Broad spectrum insecticides High Curculio caryae (Horn) Quarantine High Risk rating and spot treatment Moderate Trunk treatment Moderate Entomopathogens, nematodes Low Red imported fire ant as predator Low Pecan nut casebearer Broad spectrum insecticides High Acrobasis nuxvorella Biorational insecticides High (Neunzig) Mating disruption Low
Hickory shuckworm Broad spectrum insecticides High Cydia caryana Fitch Biorational insecticides High Sanitation Moderate
Black pecan aphid Organophosphate insecticides High Melanocallis caryaefoliella Neonicitinoid insecticides Moderate Davis Insecticidal soap High Harmonia axyridis (Pallas) Moderate Interplanting crape myrtles Low
Yellow pecan aphid Soil applied systemic insecticides High Monelliopsis pecanis Bissell Neonicitinoid insecticides High Insecticidal soap High Harmonia axyridis (Pallas) Low Introduced parasites Low
Blackmargined aphid Soil applied systemic insecticides High Monellia caryella Fitch Neonicitinoid insecticides High Insecticidal soap High Harmonia axyridis (Pallas) Low Introduced parasites Low Pecan leaf scorch mite Miticides High Eotetranychus hicoriae Sulphur High (McGregor) Predatory mite release Moderate Dormant oil sprays Low Kernel-feeding Hemipterans Broad spectrum insecticides Moderate Pentatomidae and Coriedae Trap crops Low Removing alternate host plants Low
* Control methods listed in the table have shown benefits greater than the costs.
** Efficacy ratings: Total = 100%; High - 96% to 99%; Moderate 80 to 95%; and, Low < 80%.
The impact of the research is nothing short of saving the U.S. pecan crop each season from devastating insect and mite injury. The reproductive potentials of the insect pests translate into significant damage potentials when the insects and/or mites occur at levels of abundance that cause economic injury to the tree, foliage and nuts. The new control and delivery methods will however require more extension and educational efforts to be effectively applied by pecan growers. Training is needed in the identification of beneficial organisms and interactions between methods.
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