1996UC IPM Competitive Grants Program
Biorational Use of Biotic Agents
This 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 will be considered if on-going research has shown that no reasonable alternatives exist and that there is a good potential for their use. Highest priority will be given to research that involves materials that are environmentally benign.
If the proposal involves the eventual registration of a pesticide, modified microorganism, etc., the PI must indicate how and when registration data will be obtained and the mechanism and time frame for pursuing registration. It must be made clear whether registration will delay use of the product in the field.
New Biorational Use Projects Funded For 1996-97
WHAT IS THE IMPACT OF LACEWINGS?
Ecology of predatory green lacewings: Quantifying the impact of higher-order consumers. (Year 1 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.
PARASITES FOR PRUNE APHIDS
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.
BIOLOGICAL CONTROL FOR A NEW EUCALYPTUS PEST
Establishment and evaluation of a biological control program against the eucalyptus snout beetle, Gonipterus scutellatus gyll. (Year 2 of 2; $30,240)
Principal Investigators: L.M. Hanks, Entomology, Riverside; T.D. Paine, Entomology, Riverside; J.G. Millar, Entomology, Riverside
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: The eucalyptus snout beetle (ESB) is apparently confined to Ventura County, but its populations continue to spread outwards. It is probably inevitable that the beetle will eventually range throughout the coastal areas of California wherever its preferred hosts, Eucalyptus globulus and E. viminalis, occur. A parasite of ESB eggs, Anaphes nitens, was imported and reared, and hundreds were released in fall 1994 at the site where ESB was first discovered. By June 1994 the parasite was killing nearly 100% of ESB eggs at this site, with the result that larvae virtually disappeared and the beetle population crashed by the end of the year. Eucalyptus trees at the site are now recovering and putting out new foliage.
During 1995 multiple releases of A. nitens were carried out at three more sites in Ventura County at the edges of the ESB distribution. More than 7,000 A. nitens were released, and they quickly established in at least two of the sites. In addition, the parasitoid dispersed on its own to stands of eucalyptus adjacent to the original release site. At all of these sites the parasitism rates have approached 100%, and beetle populations are declining sharply. A. nitens is proving to be such an effective biological control agent for this severe pest that no further control measures need be taken at the release sites used so far. The second year of this project will focus on implementation, releasing the parasite at the spreading fronts and at new isolated infestations of the beetle population to establish controls before ESB can become an important pest in new areas. By responding rapidly to this potentially devastating insect pest, we hope to avert major widespread damage statewide.
IMPROVING MONITORING TOOLS FOR WALNUT HUSK FLY
We also tested for the effect of trap height. Each tree had two identical traps hung low and high in the canopy. In Esparto, in an unsprayed orchard, the high traps always caught more flies than the low traps. In Gridley the high traps caught more flies early in the season, before the first spray of Guthion. After the first spray, the low traps caught more WHF than the high traps for the rest of the season. However, in Vina, trap height was not significant in the early season or for the entire season. In general, however, traps placed high in the canopy captured more flies than traps hung lower.
The caryophyllene lures attracted the most males and females at times that corresponded to the onset of husk fly egglaying in walnuts. We dissected female WHF to check for mature eggs in their ovaries and dissected walnuts to find WHF eggs. In each orchard, about 10 days elapsed between first detecting females with mature eggs and detection of walnuts infested with WHF eggs. Thus, both the caryophyllene lures and dissection of female WHF for detection of mature eggs in the field may provide valuable information about the onset of egglaying and may help to better predict when to spray. These findings will be further tested in year 2 of this study.
CAN REDUCING OVERWINTERING INOCULUM HELP CONTROL BROWN ROT?
Cultural approaches to control brown rot of stone fruits in California. (Year 2 of 2; $21,280)
Principal Investigator: T.J. Michailides, Plant Pathology, Davis
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: The plant pathogenic fungus that causes brown rot of stone fruit, M. fructicola, can produce apothecia from infected and rotten fruit, called "mummies," either on or below the soil surface. Apothecia are mushroomlike structures that release ascospores, capable of causing infection and blossom blight, into the air in the spring when fruit trees are blooming and their blossoms are susceptible.
Our initial research has shown that not all rotten fruit mummies can produce apothecia. Rotten peach and nectarine mummies were collected from several orchards and placed in experimental plots. Some mummies were fresh fruit mummies found on the ground after harvest, others were collected from trees in the winter. "Winter mummies" are called stromatized or sclerotinized mummies because they have had several months to dry on trees and form resistant fungal structures, called stromata. Winter mummies are quite hard and not easily decomposed.
Both fresh fruit and stromatized mummies were placed either on the soil surface or buried, for 7 months, from August to February. Apothecia were counted in these plots in February-March. The fresh fruit mummies decomposed quickly and never produced apothecia. Mummies buried in August-September and January-February did not produce apothecia either.
Only winter mummies, which were placed on the soil surface or buried in October-December, produced apothecia. These results indicate that growers need not worry about the large quantities of rotten fresh fruit mummies on the ground during or after harvest; but that they should try to remove the dried down mummies on the trees in the winter. In the same orchards, where mummies were either placed on the soil surface or buried, there were also plots where mummies were removed. These plots were and will continue to be evaluated at harvest for blossom blight, the incidence of latent infections, and brown rot. Initially, we have observed an overall trend towards less brown rot in the plots where winter mummies were removed.
Nectarines thinned after pit-hardening were found heavily infected and sporulating with M. fructicola conidia. From approximately 1,200 thinned nectarines per tree, 36.2% showed M. fructicola sporulation 4 weeks after thinning. If the fruit was racked into irrigation trenches it became infected more quickly but was also more decomposed by harvest. We consistently observed a trend towards less brown rot at harvest if the thinned fruit had been removed. Our field observations indicate that infected thinned fruit is an important source of secondary inoculum in the epidemiology of brown rot in the San Joaquin Valley, and we are currently studying in more detail their influence on disease severity.
CAN HONEYDEW MANAGEMENT INCREASE PARASITE EFFECTIVENESS?
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: During the last 4 months we have purchased young citrus trees and have inoculated these plants with four species of soft scales: (1) citricola scale, (2) brown soft scale, (3) black scale, and (4) hemispherical scale. We are collecting the honeydew from these scales and sending them to our collaborator at The Western Cotton Research Laboratory, Phoenix, Arizona, for analysis. The analyses will identify the types of sugars that are present in the honeydews. Honeydews are composed of numerous carbohydrates (sugars). We are interested mainly in the simple sugars, the mono and disaccharides. These are the ones that Aphytis feeds on for energy. In their absence, Aphytis dies within 1 or 2 days. In their presence, Aphytis can live several weeks, parasitizing a substantial number of red scale in the process. Thus, groves that lack such energy sources are unlikely to support substantial Aphytis populations. The analysis of honeydew will allow us develop simple tests to assay a grove for the presence of the appropriate sugars.
Also, we have conducted preliminary experiments in which parasitoids were fed honeydews to test whether the honeydews from different homopteran species are of a similar value as an energy source. We found that the lifespan of parasitoids fed honeydew from either black scale or citricola scale is shorter than that of parasitoids fed 70% honey. We suspect that this is due to the low percentage of the simple sugars present in the honeydews. Thus, it is the continuous availability and renewal of the honeydews that may be crucial to the persistence of a parasitoid population in a citrus grove.
MANAGING PEACH YELLOW LEAFROLL
Evaluation of control practices for peach yellow leafroll disease. (Year 3 of 3; $21,606)
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 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: Molecular diagnostic assays performed in 1994 and 1995 showed that all of the peach trees in our four test plots, as well as other orchards located in Yuba County that had symptoms of PYLR disease, were infected with a mycoplasmalike organism (MLO) that infects pears and is transmitted by pear psylla. Because pear psylla only migrate out of pear into peach in late fall, we hypothesized that PYLR transmissions could be reduced by prematurely defoliating peach using zinc sulfate or by protecting leaves with pyrethroid insecticides late in fall. Randomized treatment blocks were established in four orchards that previously experienced high PYLR losses, and growers applied zinc or pyrethroid insecticides in late fall 1994 and 1995. The very low number of new infections that occurred in the four test orchards during 1995 made it impossible to evaluate the efficacy of the defoliation and insecticide treatments that were applied in 1994. The lack of new PYLR infections also correlates with the comparative low number of MLO vectors that were captured on yellow sticky traps in these test plots during 1994 and 1995.
Because there was some concern that premature defoliation could adversely affect fruit yields, we have been evaluating the impact of zinc defoliation on trees located at UC Davis since 1993. Blossom set and fruit yields on zinc-treated trees were indistinguishable from untreated controls in 1994 and 1995.
WALNUT HUSK FLY ATTRACTANTS
Evaluation of host plant volatiles as attractants for walnut husk fly.
Principal Investigators: C. Pickel, UC IPM Project, Sutter-Yuba counties; S. Opp, Biological Sciences, CSU, Hayward
Summary of Accomplishments: Volatile chemical odor components of walnut leaves and husks were tested individually and in multiple-component blends for attractiveness to male and female walnut husk flies in the field. Fifteen chemicals were presented individually on rubber septa hung from yellow sticky panel traps in walnut trees. Trees were located in an unsprayed walnut orchard (Payne variety) in Newark, CA and in a commercial orchard (Hartley variety) in Modesto, CA. In Modesto, 3 weeks of data were collected prior to husk fly suppression with insecticides. Data from 8 weeks of testing in the unsprayed orchard in Newark indicated that male walnut husk flies were differentially attracted to the various walnut odors and that one chemical, caryophyllene, was the most attractive single chemical. Female flies showed little attraction to any of the odor components. Attraction of flies to the lures was very low in early season (prior to onset of female egglaying) and in late season (after most walnuts were already damaged). Trap captures of males dramatically increased in Newark as female flies began to lay eggs. Because increased male attraction to particular walnut volatiles, especially the commercially available caryophyllene, appears to coincide with onset of female egglaying, we feel a selective male trap could be developed which would lead to more accurate timing of insecticide sprays to control walnut husk fly.
TRAPS FOR WALNUT HUSK FLY
Development of more efficacious and selective attractants and traps for the walnut husk fly.
Principal Investigators: C. Pickel, UC IPM Project, Sutter-Yuba counties; S. Opp, Biological Sciences, CSU, Hayward; D. Light, USDA ARS, Albany; S. Kint, USDA ARS, Albany; R. Teranishi, USDA ARS, Albany
Summary of Accomplishments: We compared the relative attractancy and duration of attractancy to walnut husk flies (WHF) of commercially available ammonia-emitting lures and an aqueous ammonia lure we developed. Although our aqueous lure showed the greatest initial attractancy, the commercial lures lasted longest in the field. Because all ammonia lures fade over time, we suggest growers using any commercial lures should replace lures every 3 to 4 weeks, regardless of WHF activity. Using laboratory-released marked WHF, we demonstrated that the most attractive ammonia-based lures were also nonselective lures, attracting WHF of different sex, age, and feeding history equally, regardless of the type of trap used. Walnut-derived lures were selective for male WHF, although fewer flies were attracted to walnut odors than to ammonia. Trap captures of the marked flies very closely mimicked the capture patterns of wild flies, indicating that our marked flies were good predictors of wild fly behavior in the field. Marked flies were not captured on traps in the first 3 to 10 days following release. Older flies (reproductively mature) were captured significantly sooner than younger flies, and the green sphere traps baited with ammonium carbonate captured the released flies most quickly. We also found evidence that traps placed high in the tree canopy were more effective at capturing flies than traps lower in the trees.
Indications are that both ammonia and walnut volatile baited traps, whether yellow panel or green sphere, can play important roles in WHF monitoring and pesticide application decisions. Walnut volatiles are more selective lures and may give better indications of the onset of egglaying so that growers can make more informed decisions about when to begin pesticide applications. Ammonia lures are best used to provide estimates of the severity of WHF infestations.
BIOCONTROL OF FUSARIUM WILT
Biological control of fusarium wilt of sweet potato by antagonistic fungi
Principal Investigator: R.N. Campbell, Plant Pathology, Davis
Summary of Accomplishments: Biological control of Fusarium wilt of sweetpotato has been reported using saprophytic fungi and would be desirable because it could avoid the use of benomyl. Ten candidate isolates of Fusarium spp. originating in California were tested in the greenhouse in 1992 both for lack of pathogenicity to sweetpotato and for protective ability against Fusarium wilt. The most promising biocontrol fungus was evaluated in field trials in this project. Although the fungus provided some protection, it was not adequate in field conditions. These trials have shown the need for field evaluations at an early stage of testing.
An evaluation of the physiological specialization of the isolates of the Fusarium wilt fungus obtained in these trials has given evidence for a different race of the fungus in California. Isolates have been provided to collaborators in Louisiana and North Carolina where breeding programs are in progress and include resistance to Fusarium wilt.
IMPACT OF IGRS ON WHITEFLIES AND THEIR NATURAL ENEMIES
Evaluation of juvenoids for control of sweetpotato whitefly on poinsettia and compatibility with natural enemies
Principal Investigators: L. Harshman, Entomology, Davis; M. Parrella, Entomology, Davis
Summary of Accomplishments: Insect growth regulators (IGRs) offer the potential to control the silverleaf whitefly and may fit well into an integrated pest management program. Many of these materials have characteristics that are favorable for an insecticide in the l990s: low mammalian toxicity, reduced residual activity, short re-entry intervals after application, no hazard to the health and safety of farm workers, lack of problems with ground water contamination, good activity against the target pest, compatibility with natural enemies, and no impact on nontarget organisms. Although it is rare to find all these qualities in a single material, the IGRs (and particularly the juvenoids) are gaining a great deal of attention. Many of these materials are used for whitefly control in other parts of the world (Europe, Japan, Israel, etc.) and registration is being pursued for some of these materials in the United States.
We evaluated four insect growth regulators (buprofezin, pyriproxifen, kinoprene and fenoxycarb) for their ability to kill the various immature stages of the silverleaf whitefly and for their potential compatibility with natural enemies of this pest. The materials buprofezin and pyriproxifen provided the best control, and activity was highest against the early instars of the whitefly. In addition, buprofezin was the only material to impact the egg laying of adult whiteflies exposed to fresh residues. Buprofezin was the only material capable of providing whitefly control as a stand alone product. The other materials, acting alone, may be insufficient to control the silverleaf whitefly. However, all the IGRs evaluated in this project may fit into an IPM program where both the natural enemy complex and the insecticide cause mortality to the whiteflies. Adult parasitoids readily oviposited in whiteflies treated with any IGR and parasitoid emergence was recorded from all treatments. Parasitoid survivorship was recorded after treatment with all the IGRs and these parasitoids were viable. However, only pyriproxifen showed no significant difference in parasitoid emergence when compared to the control. Similar results were found when these materials were evaluated for compatibility with a predatory coccinelid beetle.