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United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Emerging Pests and Pathogens Research

2013 Annual Report

1a. Objectives (from AD-416):
1: Characterize fungal strains associated with insects (including insect pathogens and symbionts and plant pathogens vectored by insects) and develop methods to enable their rapid identification and tracking. 1a. Develop molecular assays to detect and quantify plant pathogenic oomycetes vectored by insects to verify transmission. 1b. Identify the primary fungal symbiont associated with Asian ambrosia beetles and assess the genetic diversity of these fungi from beetles in the eastern United States. 1c. Evaluate fungal delivery, establishment and persistence in target populations of invasive wood-boring beetles. 2: Determine and improve the effectiveness of fungi for use within integrated management systems for greenhouse, horticultural and landscape pests, including but not restricted to thrips, whiteflies, ambrosia beetles and emerald ash borer. 2a. Develop a biologically-based IPM program for western flower thrips infesting greenhouse crops. 2b. Compare the efficacy of Beauveria bassiana and Metarhizium anisopliae against the Q biotype of Bemesia tabaci. 2c. Develop available microbial control agents for management of Asian ambrosia beetles and their symbiotic fungi. 2d. Integrate pathogenic fungi with other biocontrol agents for emerald ash borer and evaluate non-target impacts.

1b. Approach (from AD-416):
The goals of this project are to integrate entomopathogenic fungi into management systems for selected insect pests of horticultural, nursery and landscape plants and to track fungal strains in these environments. The work comprises fundamental laboratory studies as well as applied greenhouse and field research. This project will develop basic information on the biology of fungal and oomycete pathogens associated with insects, their genetic and phenotypic variability, and their survival and transmission in greenhouse and field environments. Integration of fungal pathogens will be accomplished for management of key pests: a biologically based program will combine use of pathogens and predators for control of western flower thrips infesting greenhouse crops; efficacy of fungal pathogens will be determined for Bemisia whiteflies (B. tabaci Q biotype); microbial control agents will be developed for management of Asian ambrosia beetles; and a fungal mycoinsecticide will be integrated with other biocontrol agents used against emerald ash borer. Fungi used in the ways developed in this project will provide safe, effective biological alternatives to synthetic chemical insecticides and/or rotational partners for insecticide resistance management.

3. Progress Report:
Initial testing of Beauveria bassiana soil-drench applications for control of western flower thrips have been encouraging. Three or four applications of conidial suspensions to potted impatiens at rates equivalent on an area basis to previously tested foliar-spray applications reduced initially high pest populations by an average of 25% on flowers and 44% on foliage. Though representing inadequate levels of control from a greenhouse pest management perspective, treated plants produced 31% more undamaged flowers than control plants and these levels of pest population reduction were observed under high ventilation, low ambient relative humidity conditions that have been found to render foliar applications almost completely ineffective. Field assays were done to test means for effective sampling of Xylosandrus germanus. Small bait logs soaked in ethanol were more heavily attacked by adult beetles than those soaked in water or isopropanol. Increasing ethanol concentration above 15 percent did not result in increased attacks. Logs placed close to the ground were attacked more heavily than those placed 1 to 2 meters above. Logs treated with a preparation of two commercial mycoinsecticides received fewer beetle attacks than water-treated logs. Parasitoids of the emerald ash borer have been recovered at six of eight release sites in two infested areas of New York. A second season of parasitoid releases at these sites is underway. Additional releases are underway in a third infested area.

4. Accomplishments
1. Fungal pathogens and antagonists of the granulate ambrosia beetle. The granulate ambrosia beetle, Xylosandrus crassiusculus, is an invasive pest difficult to control because it spends most of its life cycle within the wood of a wide range of host nursery trees. In a laboratory study, ARS researchers at Ithaca, New York, in cooperation with Cornell University scientists, evaluated the susceptibility of Xylosandrus crassiusculus to three commercial strains of entomopathogenic fungi and its effects on gallery formation and brood production among females coupled with exposure to a mycoparasitic fungus, Trichoderma harzianum. All three entomopathogens were virulent. Females exposed to beech stems treated with entomopathogenic fungi at the highest dose had lower survival rates and produced fewer galleries. All doses tested, however, resulted in females with fewer offspring compared to control. Those exposed to T. harzianum produced galleries with sparse, patchy, or no symbiont growth, many of which had no or few brood present. These results show the potential of entomopathogenic or mycoparasitic fungi in controlling X. crassiusculus, either directly by killing adult females and preventing or reducing brood production or indirectly by suppressing growth or establishment of their fungal symbiont in galleries.

2. Sampling trees for emerald ash borer colonization. The intensity and distribution of emerald ash borer attack on individual ash trees was examined by ARS researchers at Ithaca, New York in cooperation with scientists from the SUNY College of Environmental Science and Forestry. Beetle distribution was modeled by sampling one meter increments of 71 ash trees. The probability of detecting emerald ash borer was highest at tree diameters of 19 centimeters and at heights of 14 meters. The degree of bark roughness was not a useful predictor of beetle presence. Results are being used by forest managers to improve emerald ash borer detection and estimate densities. Knowledge of colonization patterns has led to development of more efficient management tactics for this invasive pest.

3. Insect pathogenic fungi exhibit low virulence against foxglove aphid. Biological control of mixed infestations of foxglove aphid and green peach aphid in greenhouse ornamental crops has proven a difficult challenge, and additional natural enemies with broad host ranges are needed to control these pests. In a series of laboratory assays, Cornell University and ARS researchers at Ithaca, New York investigated the microbial biocontrol potential of novel and commercial strains of Beauveria, Metarhizium and Isaria fungi against foxglove aphid. None of the fungal strains exhibited more than moderate virulence against this aphid. These results are in accord with our previous studies of other key greenhouse aphid pests and indicate that these microbial control agents should be applied for aphid control only in conjunction with other biological or chemical control agents in fully elaborated IPM programs.

4. Control of foxglove aphid by a predatory midge is reduced by presence of green peach aphid. Foxglove aphid (FGA) has emerged from its former status as a sporadic pest to become the second most important aphid pest of greenhouse ornamental crops after green peach aphid (GPA). These aphids frequently occur in mixed infestations so that growers are faced with a dual control problem. In small-scale greenhouse tests, researchers from Cornell University and ARS researchers at Ithaca, New York assessed the efficacy of Aphidoletes midges against FGA alone and in mixed infestations with GPA. Female midges exhibited a strong preference for laying their eggs among patches of GPA, which inhabits primarily young leaves in the tops of plants or the basal parts of flowers, passing over many patches of FGA, which was found to prefer older leaves near the bottoms of plants or flower petals. Consequently, control of FGA in mixed aphid infestations was inconsistent and generally inadequate from the standpoint of pest management. Results indicate that effective use of these predators for control of aphid infestations will require careful scouting of pest populations and integration with other control agents.

5. First report of Phytophthora capsici as a pathogen of Osteospermum, Calibrachoa, and Lupinus. Phytophthora capsici is a devastating, long-lived soilborne pathogen with a wide host range that includes many vegetables in the Cucurbitaceae, Solanaceae and Fabaceae families and Fraser fir Christmas trees. Michigan State University researchers and ARS researchers at Ithaca, New York tested the susceptibility of three floriculture crops to P. capsici and other Phytophthora spp. Phytophthora capsici infection was rated as 2.0, 4.3 and 3.0 (1=healthy, 5=dead) on Osteospermum, Calibrachoa, and Lupinus, respectively. These research results reveal that the host range of P. capsici includes valuable ornamental crops, and alert growers and plant-disease scouts to the potential presence of this pathogen in their greenhouses.

6. Impatiens downy mildew symptoms delayed by fungicide drench treatments at the production greenhouse. A new and lethal downy mildew disease of impatiens has begun to seriously affect the U.S. flower industry. Cornell University researchers and ARS researchers at Ithaca, New York assessed the potential use of systemic fungicides to protect plants moved to the landscape after drench treatments in the greenhouse. Impatiens were treated in late June and then moved outside to a shade house with overhead irrigation; mildew inoculum was provided by adjacent infected impatiens. Nontreated controls deteriorated rapidly, showing mildew sporulation by mid-July and uniform mortality by late August, whereas plants treated with SubdueMAXX at 1.0 fl oz per 100 gal alone or in combination with an experimental phosphonate at 20.0 fl oz per 100 gal did not show sporulation until much later (early August). Plants receiving the combination treatment still retained their leaves by the last rating in early September. These results show that pre-sale drench treatments by impatiens producers may enable landscapers to grow impatiens successfully, even in areas with high risk of downey mildew outbreaks.

7. Pot size affects severity of Pythium Root Rot of geranium. Greenhouse flower growers are continually challenged by quality reduction and crop loss caused by Pythium root rots. Cornell University researchers and ARS researchers at Ithaca, New York evaluated the effect of pot size on control of root rot caused by Pythium aphanidermatum in geraniums when applying the strobilurin fungicide pyraclostrobin: seven treatments were made to geraniums in 3-inch and 6-inch pots of ProMixBX at 14-day intervals. Only the highest rate of pyraclostrobin tested (Empress at 3 fl oz per 100 gal) protected plants in 3-inch pots, similarly to azoxystrobin (Heritage 50WG at 1 oz per 100 gal), whereas in 6-inch pots Empress at rates of 0.5 to 3 fl oz per 100 gal protected geraniums from root rot. Growers will be able to apply the information that container size can affect the severity of the disease and the effectiveness of strobilurin treatments when they make decisions on which containers to use for Pythium-sensitive crops.

8. Management of impatiens downy mildew with fungicides. Downy mildew has recently become a serious threat to impatiens, a US floriculture industry worth $102.5 million wholesale in 2012, a drop of almost $3 million in value from 2011. Researchers of Michigan State University and ARS researchers at Ithaca, New York tested 9 oomycete-specific and standard fungicides applied as foliar sprays or drenches in treatment programs varying from a single application to multiple applications at 7-day intervals in three trials. A single drench of Alude L (phosphorous acid), Vital (phosphorous acid), Subdue MAXX EC (mefenoxam), Vital + Subdue MAXX EC, Adorn SC (fluopicolide), Plentrix SC (azoxystrobin + metalaxyl), and a single foliar spray of Micora SL (mandipropamid) completely prevented downy mildew infection, as did a program of six 7-day applications alternating among Adorn + Subdue MAXX drench, and sprays of Dithane 75DF (mancozeb) and Micora SC. This research provides urgently needed recommendations to commercial growers of bedding impatiens so that they can grow healthy plants and regain consumer’s confidence in this popular shade plant.

9. Standardizing sample processing for routine and forensic applications. Multiple protocols are available for manipulation of diseased plant samples for routine examination; however, differences among these protocols makes comparison of results difficult, which can complicate epidemiological studies and disease management. Furthermore, the lack of thoroughly validated and statistically sound protocols prevents the use of plant pathological samples in forensics. Researchers of Oklahoma State University and ARS researchers at Ithaca, New York and Fort Detrick, Maryland developed a protocol for processing plant samples infected simultaneously with multiple pathogens. The protocol, based on next generation sequencing and newly developed computational biology tools, has been published in the Journal of Microbiological Methods and validated for detection of Phytophthora ramorum and Pythium ultimum (reported in a M.S. thesis). These protocols will allow the simultaneous and accurate detection of multiple fungal plant pathogens infecting a plant sample without the need of isolation and generation of pure cultures, reducing the time to diagnosis from weeks to hours. Furthermore, results produced by validated protocols can be used as evidence in forensic investigations.

10. Phytophthora cryptogea and P. drechsleri, two pathogens of ornamental crops, vary in host range and aggressiveness. Phytophthora cryptogea and P. drechsleri are very closely related “sister” species, but researchers at NC State University in Raleigh and ARS researchers at Ithaca, New York recently found differences in their host ranges and aggressiveness to common floriculture crops. In tests of three C. cryptogea isolates on African marigold, annual stock, dusty miller, fuchsia, gerbera daisy, osteospermum, snapdragon, and verbena, only annual stock and gerbera daisy were attacked by all three isolates. Only two isolates caused root rot on osteospermum, even though it is in the same plant family as gerbera daisy. Work at NC State is the first with P. drechsleri isolates from floriculture crops; two of three isolates of P. drechsleri were pathogenic to all 8 plants, but one isolate caused disease only on osteospermum. This work expands the host range of P. drechsleri to include osterospermum, snapdragon, and annual stock; shows that P. drechsleri is generally more aggressive than P. cryptogea against ornamentals; and indicates that nonsymptomatic plant material shipped between growers may account for spread of these pathogens. These findings alert growers and plant-disease scouts to potential disease problems, particularly in ornamental crops not previously known to be susceptible to these pathogens.

Review Publications
Jandricic, S.E., Wraight, S.P., Gillespie, D.R., Sanderson, J.P. 2013. Oviposition behavior of the biological control agent Aphidoletes aphidimyza (Diptera: Cecidomyiidae) in environments with multiple pest aphid species (Hemiptera: Aphididae). Biological Control. 65:235-245.

Ugine, T.A., Wraight, S.P., Sanderson, J.P. 2013. Assessments of the microbial biocontrol potential of novel strains of Beauveria bassiana s.l. against greenhouse shore fly, Scatella tenuicosta: virulence, mass production capacity, and effects on shore fly reproduction. Biological Control. 65:348-356.

Braun, S.E., Sanderson, J.P., Daughtrey, M.L., Wraight, S.P. 2012. Attraction and oviposition responses of the fungus gnat Bradysia impatiens to microbes and microbe-inoculated seedlings in laboratory bioassays. Entomologia Experimentalis et Applicata. 145:89-101.

Last Modified: 06/26/2017
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