1997UC IPM Competitive Grants Program
Biorational Use of Biotic Agents or Chemicals
This biorational use category includes development and evaluation of methods of applying or using biotic agents or regulated pest control materials more effectively and in an environmentally sound manner. Examples might include efficient production and quality control of biotic agents; application or delivery technology, effective application and use of plant growth regulators, pheromones, attractants, or repellents; methods of reducing the impact of pesticides on beneficial organisms; and methods of improving the safety, reducing environmental contamination, or reducing the total amount of the control agent needed for effective control. Research on biotic agents may include the development of technologies to maintain their survival and/or residual activity and to effectively deliver them to target sites. Research on the development and testing of environmentally safe chemicals is also considered if on-going research has shown that no reasonable alternatives exist.
New Projects Funded for 1997-98
Objectives: Develop a computer-based, disease forecast system to optimize fungicide timing for controlling black mold (Alternaria alternata) in tomato.
Determine the period for A. alternata infection under different regimes of relative humidity, leafwetness, and air temperature.
Evaluate timing of fungicide application on control of black mold disease.
Develop and validate a forecast model for black mold disease.
INCREASING EFFECTIVENESS OF NEMATODES FOR GRUB CONTROL
Synergism of imidacloprid and entomopathogenic nematodes: a novel approach to white grub control in turfgrass. (Year 1 of 3; $18,345)
Principal Investigators: H. K. Kaya, Nematology, Davis; A. M. Koppenhöfer, Nematology, Davis
Objectives: Test the feasibility of combinations of the chloronicotinyl insecticide, imidacloprid (IMI), and entomopathgenic nematodes (EN), with emphasis on the scarab-specific Steinernema kushidi, for the control of white grubs in turfgrass.
Determine (1) the effect of combined applications of IMI and EN on 3rd instar masked chafer (Cyclocephala hirta), and Japanese beetle (Popillia japonica); (2) the direct effect of IMI on EN infective juveniles; (3) the effect of IMI on EN recycling in white grub hosts; and (4) the pathogenicity of S. kushidai and its capacity to recycle in various life stages of the scarab pests.
Continuing Projects Funded for 1997-98
WHAT IS THE IMPACT OF LACEWINGS?
Ecology of predatory green lacewings: Quantifying the impact of higher-order consumers. (Year 2 of 2; $20,000)
Principal Investigator: J. A. Rosenheim, Entomology, Davis
Objectives: Measure the seasonal abundance of green lacewings in tomato fields and grape vineyards and quantify mortality factors acting on lacewings in the egg, larval, pupal, and adult stages.
Quantify the seasonal abundance of other dominant species of generalist predators in tomato fields and grape vineyards and experimentally evaluate their impact on larval lacewing survivorship.
Determine the diet of predatory green lacewings, including their rate of consumption of key tomato and grape pests, through detailed field observations of foraging lacewings.
Summary of Progress: The utilization of generalist predators in biological control systems is increasing due to the wider adoption of augmentative release strategies using commercially-reared natural enemies and due to the increased use of cover crops designed to increase resident populations of generalists. The ecology of these generalist predators, however, is poorly understood.
We studied predatory green lacewings and other key groups of generalist predators in six crops in Yolo and Solano counties: grapes, tomatoes, alfalfa, cotton, almonds, and walnuts. Lacewing populations were found to peak early in the season in grapes (reaching 11,000/acre), alfalfa (reaching 58,800/acre), almonds (reaching 23,000/acre), and walnuts (reaching 7,000/acre). In cotton the highest numbers (26,000/acre) were reached during the late summer. No lacewings were recorded in tomatoes.
Many lacewing eggs occurred in crops despite the presence of very low densities of prey species (aphids, mites, and thrips). Variation in lacewing densities between crops, between sites within a crop, and seasonally underscores the importance of sampling fields before recommending augmentative releases; however, in many cases augmentative releases can produce meaningful increases in lacewing densities. Lacewing egg parasitism appeared to be significant only in grapes where 50% were killed; mortality of lacewings at the pupal stage was often heavy. Other dominant predators included spiders, minute pirate bugs, predatory mites, and ants. Direct observations of foraging lacewing larvae have been initiated and indicate that lacewings feed on extrafloral nectar as well as on arthropod prey.
PARASITES FOR PRUNE APHIDS
Introduction and evaluation of parasitoids attacking aphids as a component of the developing IPM program on prunes in California. (Year 2 of 3; $18,169)
Principal Investigator: N. J. Mills, Environmental Science, Policy and Management, Berkeley
Objectives: Acquire, import, and produce nonindigenous species and biotypes of parasitoids that attack prune aphids.
Field release the parasitoids and then collect them from release sites for distribution to new localities.
Monitor parasitoid establishment and impact on pest aphids in prune orchards, and establishment on aphids on the obligatory alternate host plants in California.
Survey for and monitor the populations of native arthropod parasitoids and predators that attack prune aphids in California orchards and on their alternate host plants.
Summary of Progress: A total of 44,700 individuals of a biotype of the aphid parasitoid Aphidius colemani originally obtained from the Czech Republic in 1995 were field released on the mealy plum aphid from May 2 to October 3 in three prune orchards and on nearby cattails, an alternate host of this aphid. Intensive sampling revealed no reproduction by this biotype at any of the release sites.
Another parasitoid species, Ephedrus plagiator, and a Spanish biotype of Aphidius colemani specific to the mealy plum aphid were imported in September. Totals of 3,250 E. plagiator and 1,927 of the Spanish A. colemani were liberated at three orchards in October and early November. Sampling on November 27 revealed that A. colemani had reproduced at all three orchards and E. plagiator reproduced at two of the orchards.
Three orchards were sampled through the season to monitor the abundance of the mealy plum aphid and indigenous predators. Aphid abundance declined in June in two of the orchards due to migration of aphids to cattails, their summer host. Aphids persisted through July in the third young orchard that had continuous shoot growth, indicating that some aphids can relocate and remain in an orchard rather than migrate. The most important indigenous predators were the lady beetle (Harmonia axyridis), the green lacewings (Chrysopa oculata and Chrysoperla carnea), and the silver fly (Leucopis sp). The predators were particularly abundant on heavily infested prune trees early in the season and declined when aphids migrated to cattails in June.
Projects that Ended in 1996-97
IMPROVING MONITORING TOOLS FOR WALNUT HUSK FLY
Field test of more effective traps for the walnut husk fly.
Principal Investigators: C. Pickel, UC IPM Project, Sutter/Yuba counties; S. Opp, Biological Sciences, CSU, Hayward
Objectives: Field test two different trap types (yellow panel and green ball) and three lures (Trece supercharger, Pacoast membrane-release lure, and the walnut volatile caryophyllene) in three commercial walnut orchards, each in a geographically distinct area of northern California. These field tests will give us information to develop a walnut husk fly trap that will better detect or predict onset of egglaying so that pesticide sprays can be better timed.
Determine the effects of trap height (low or high canopy) in trees for optimal walnut husk fly detection in early season and in low fly density orchards.
Summary of Progress:. We field tested two types of traps (yellow sticky panel and green sticky ball) paired with three different lures/attractants (Trece Supercharger, and the walnut volatile caryophyllene at two different concentrations, 100% and 10%) and a control (no lure) for attraction of walnut husk fly (WHF) in three commercial walnut orchards in northern California. In the second year, we found a pattern similar to the first year: yellow sticky panels baited with ammonia (Trece Supercharger) captured the greatest numbers of walnut husk flies, especially females, although some variation in trap capture on the other trap and lure combinations occurred in the three orchards (in Gridley, Yuba City, and Vina).
We repeated the field test for the effect of trap height. Each tree had two identical traps hung low and high in the canopy. In all three orchards, the high traps caught more WHF than the low traps. We also tested two different concentrations of caryophyllene in pentane (100% and 10%) to determine if we could better predict the onset of husk fly egg laying in walnuts. The 100% caryophyllene seemed to capture more males and females than the 10% caryophyllene, and better corresponded to when we first detected walnut husk fly eggs in walnuts. Nevertheless, the Trece Superchargers attracted the most flies overall.
We also dissected female WHF to check for mature eggs in their ovaries (fecund females) and dissected walnuts to find WHF eggs and stings (oviposition holes). In two orchards, spraying occurred within 10 days of detection of two or more fecund females on traps. These two orchards remained free of WHF eggs in walnuts for the next month and did not need a second treatment for WHF that season. Thus, effective control of WHF occurred prior to egglaying.
In the third orchard, WHF eggs were detected in walnuts 11 days after fecund females were found on traps, but spraying was unavoidably delayed for more than 2 weeks. This orchard required a second treatment for WHF less than a month later. We conclude that the most efficacious control occurs when orchards use Trece Superchargers to detect fecund females and are sprayed within 1 week after fecund females are found. Dissection of WHF females for presence of mature eggs is critical for timing control treatments.
Objectives: Determine the current distribution of the eucalyptus snout beetle (ESB) in southern California and monitor its spread and rate of increase.
Optimize conditions for rearing and propagating a natural enemy of ESB, the egg parasitoid Anaphes nitens.
Conduct field releases of A. nitens and monitor establishment.
Evaluate the efficacy of A. nitens in controlling populations of ESB and its impact on damage to Eucalyptus caused by ESB.
Summary of Progress: Since first being detected in 1994, the eucalyptus snout beetle (ESB) has spread throughout Ventura County, and northward and southward into neighboring Santa Barbara and Los Angeles counties. Populations of the beetle reached epidemic proportions in many areas, resulting in nearly complete defoliation of eucalyptus during 1995. The 1994 release of the biological control agent Anaphes nitens, a minute parasite of the beetle's eggs, has rapidly brought ESB under control.
Anaphes nitens has proven adept in dispersing and locating infestations of ESB on eucalyptus trees, and has in fact naturally colonized all areas where ESB infestations have been discovered to date. Parasitism rates of A. nitens commonly exceed 90% of ESB eggs, and this high mortality rate has resulted in a sharp decline in the abundance of ESB within a few months time. At almost all sites, the decimation of ESB populations by the parasite has been followed by a swift recovery of eucalyptus trees, with rates of defoliation falling to negligible levels. Resurgence of ESB at one site was apparently due to drift of agricultural insecticides. In most areas, A. nitens is such an effective biological control agent for this severe pest that no further control measures need be taken.
CAN REDUCING OVERWINTERING INOCULUM HELP CONTROL BROWN ROT?
Cultural approaches to control brown rot of stone fruits in California.
Principal Investigator: T. J. Michailides, Plant Pathology, Davis/Kearney Agricultural Center, Parlier
Objectives: Determine the importance of Monilinia fructicola apothecia as a source of primary inoculum in stone fruit orchards in the San Joaquin Valley.
Study the conditions that favor the stromatization of mummified fruit by M. fructicola that enhance the production of apothecia capable of initiating blossom infections in the spring.
Determine the importance of thinned fruit as a source of inoculum during the season, and whether thinned fruit can become stromatized, overwinter, and produce apothecia in the spring.
Summary of Progress: Apothecia of Monilinia fructicola, the mushroomlike sexual reproductive structure of the brown rot pathogen of stone fruit, were commonly observed in commercial orchards during our springtime disease survey in March and in our own experimental orchards where infected and mummified stone fruits were added. At this time conidial sporulation of M. fructicola was not observed in the orchards surveyed although they could be induced in the laboratory.
Blossom blight was less severe in research plots where mummified fruit were removed when compared to plots where mummified fruit were left on the ground. Subsequently, preharvest fruit brown rot was also less severe in plots where mummified fruit were completely removed when compared to plots where infected fruit were left on the ground. A similar relationship was observed for postharvest fruit brown rot in both 1995 and 1996. In addition, preharvest fruit brown rot was reduced in plots where the orchard floors were disked, herbicides were applied to berms in the tree rows, and orchard sanitation was practiced by removing mummified fruit; the above plots were compared to no-till, no-herbicide, and nonsanitized plots.
These results suggest that apothecia may function as a significant source of primary inoculum for initiating the brown rot disease of stone fruits in the San Joaquin Valley of California. Also, blossom blight and fruit brown rot may be reduced by eliminating mummified fruit from orchard floors and by creating an unfavorable microclimate for apothecia development by disking and applying herbicides during winter.
Preharvest fruit brown rot was less severe in treatment plots where thinned fruit were completely removed when compared to plots where thinned fruit were not removed and where the thinned fruit from the "removed" treatment was also added. Similar results were obtained from similar plots in five nectarine orchards in 1995 and 1996. Postharvest brown rot was also less severe in treatment plots from one nectarine orchard in 1996 where thinned fruit were completely removed, when compared to plots where thinned fruit were not removed. No difference was observed in both pre- and postharvest brown rot of fruit from treatment plots where thinned fruit were raked from "dry" berms into "wet" irrigation drenches when compared to treatment plots where thinned fruit was left untouched in two nectarine orchards 1995.
Our results suggest that thinned fruit can readily become infected by M. fructicola and function as a significant source of the secondary inoculum for brown rot of both immature and mature nectarines, and that brown rot could also be lessened by removing or destroying readily infected thinned fruits from nectarine orchards.
CAN HONEYDEW MANAGEMENT INCREASE PARASITE EFFECTIVENESS?
The role of honeydew or nectar in the biological control of armored scales by Aphytis melinus in San Joaquin Valley citrus groves.
Principal Investigator: R. F. Luck, Entomology, Riverside
Objectives: Identify the sources of carbohydrates likely to be encountered by Aphytis melinus in San Joaquin Valley citrus groves.
Determine whether Aphytis actually feeds on these carbohydrate sources in the field.
Determine the frequencies with which groves and trees within groves have carbohydrate on their leaves, quantify its availability, identify the source, and determine how it varies seasonally.
Determine whether the application of carbohydrate in a grove will increase the Aphytis population and decrease California red scale or yellow scale populations.
Summary of Progress: This study seeks to determine the role of honeydew in the efficacy of parasitoids in San Joaquin Valley citrus groves. These parasitoids suppress red and yellow scale, yielding less costly pest control while maintaining fruit quality. From previous research we know that instituting a biologically-based pest management program in groves under transition from a traditional, broad-spectrum pesticide program is problematical. Transition takes 1 to 3 years. Natural enemies, especially those we release, occur at low numbers or are absent from these groves. We suspect their absence arises from an inconsistent carbohydrate source without which the natural enemies cannot persist.
Honeydew in citrus groves comes from two sources: Homoptera (such as soft scales, mealybugs, and aphids) and nectar. Bare ground in most groves and citrus' short bloom period make nectar an undependable source. A complex of nonpest homopterans is present in southern California groves but is uncommon in sprayed San Joaquin Valley groves. It takes time for this complex to re-establish. We monitor honeydew quantity in a grove during the season. Not all of the sugars in honeydew can be used by parasitoids. Thus, we are identifying the sugar comprising each honeydew and the homopteran that produces it. We have identified most of the carbohydrate sources and their composition. We also are determining whether they are used by the important natural enemies in the field. Two benefits arise from this study: development of monitoring techniques to identify carbohydrate deficient groves and an ability to manipulate carbohydrate sources.
MANAGING PEACH YELLOW LEAFROLL
Evaluation of control practices for peach yellow leafroll disease.
Principal Investigator: B. Kirkpatrick, Plant Pathology, Davis
Objectives: Determine if premature defoliation or late season insecticide applications can decrease the incidence of peach yellow leafroll (PYLR) disease in four high risk peach orchards located in northern California.
Determine what effect, if any, zinc sulfate mediated defoliation has on peach yields under northern California growing conditions.
Monitor and determine the infectivity of mycoplasmalike (MLO) insect vectors caught in yellow sticky traps placed in the four high risk orchards.
Determine what PYLR-MLO strains are causing new infections in the four test orchards and other orchards that are currently using pheromone disruption practices.
Summary of Progress: Diagnostic assays performed in 1996 showed that, except for one tree, all of the peach trees in four test orchards that had symptoms of peach yellow leaf roll (PYLR) disease were infected with a mycoplasmalike organism (MLO) that infects pears and is transmitted by pear psylla. Because pear psylla migrate out of pear into peach only in fall, we hypothesized that PYLR transmissions could be reduced by defoliating peach trees with zinc sulfate or by protecting trees with pyrethroid insecticides in late fall.
Zinc and insecticide treatments were established in four orchards that previously experienced high PYLR losses. In 1996 we found only 22 new PYLR infections in the four test orchards and there were similar numbers of infected trees in each of the treatment plots. Because of the comparatively low numbers of new infections and their apparently random distribution in the test orchards, it was not possible to evaluate the efficacy of the treatments applied in 1995.
Because of concerns that zinc defoliation could adversely affect fruit yields, we have been evaluating the impact of zinc defoliation since 1993. Blossom set and fruit yields on zinc-treated trees were indistinguishable from untreated controls in 1994 to 96, which indicates that zinc defoliation could be a feasible management practice.
Comparatively low numbers of pear psylla were caught in all test orchards in 1996. Initial testing of insect vectors caught on yellow sticky traps placed in the test orchards showed approximately 3% of the pear psylla, and none of leafhoppers, were infected with the PYLR-MLO, providing additional evidence that psylla are the primary insect vectors of this disease.