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Annual Reports

1996UC IPM Competitive Grants Program

Applied Field Ecology

Research in the area of applied field ecology focuses on the interactions among pests, their hosts, their biocontrol agents, the beneficial biota, and environmental factors that affect pest population dynamics, survival, and crop damage. The emphasis is on applied ecology with attention given to the understanding of how pest-host and weed-crop interactions, and biocontrol agents are affected by both abiotic and biotic factors. Studies might determine the environmental factors that affect the ability of the biocontrol agent to effectively suppress pest populations or develop a better understanding of the mechanisms by which the biocontrol agent suppresses pests. Laboratory studies are expected to be closely related to field experimentation.

Because of the general nature of field ecology, it is expected that projects here would include components found in other research categories. For example, studies on the interactions among organisms would involve the development and use of monitoring techniques (possible research areas might include studying dynamics of pest populations or natural enemy and antagonist populations, development or improvement of optimal cropping system design, host-pest-environment interaction studies, or research on the mechanisms affecting interactions between organisms).

Highest priority will be given to field-oriented research that demonstrates a high potential to lead to the control of pests or a reduction in pesticide use.

New Projects Funded for 1996-97
Continuing Projects Funded for 1996-97
Projects that Ended in 1995-96
Final Reports for Projects that Ended in 1995

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New Projects Funded for 1996-97

INTEGRATING BIOCONTROL AND HOST RESISTANCE

Evaluation of interactions among Russian wheat aphid, an effective parasite, and plant resistance. (Year 1 of 3; $21,724)

Principal Investigator: D. González, Entomology, Riverside

Objectives: Assess impact of Aphelinus albipodus, an effective introduced parasite, on Russian wheat aphid (RWA) in combination with two resistant cultivars displaying different resistance mechanisms.

Assess impact of extant (naturally occurring) parasites (especially D. rapae) and predators against RWA on resistant plants with open (uncurled) leaves.

Implement releases of A. albipodus against RWA on the most promising plant resistant cultivar.



CONTROL BY FIRE

Photo of Yellow Starthistle
One new project will investigate the effect of controlled burning on yellow starthistle control and establishment of native plants.
The use of fire to control yellow starthistle (Centaurea solstitialis L.) and enhance native plant diversity. (Year 1 of 3; $14,632)

Principal Investigator: J.M. DiTomaso, Vegetable Crops and Weed Science, Davis

Objectives: Determine the effectiveness of 1, 2 and 3 years of controlled burning on yellow starthistle control and native plant composition and diversity.

Examine the time-course of yellow starthistle reinfest-ation following three consecutive annual burns. From these findings, develop a sustainable management strategy utilizing periodic controlled surface fire.

Elucidate the factors responsible for enhancing the success of native plants following burning.



BIOLOGICAL CONTROL OF CITRUS PEEL MINER

Bionomics of the citrus peel miner and its parasites in the Coachella Valley. (Year 1 of 2; $16,711)

Principal Investigator: J. M. Heraty, Entomology, Riverside

Objectives: Identify the species of gracillariid leaf-mining moths attacking grapefruit, leader and willow, and identify the source of infestations in Coachella Valley citrus groves.

Identify the parasitoid species attacking the citrus peel miner on citrus, leader, and willow.

Evaluation emergence patterns, temperature thresholds, longevity, survivorship, and levels of infestation of the peel-miner and its parasitoids on citrus and oleander in the Coachella Valley.

Evaluate the origin of the peel miner as native or foreign and suggest or develop an appropriate biological control strategy.

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Continuing Projects Funded for 1996-97

ANT REPELLENTS

Developing an IPM-compatible technology for using semiochemicals and related chemicals to disrupt foraging of ants. (Year 2 of 3; $30,775)

Principal Investigator: H.H. Shorey, Entomology, Davis

Objectives: Using two quantitative laboratory bioassays that discriminate between chemoreception by olfaction alone vs. olfaction and gustation operating together, determine the relative biological activity of candidate repellents to three ant species as it relates to chemical structure, duration of activity, and mode of chemoreception.

Evaluate a number of different schemes for formulating the most effective ant repellents, so as to arrive at one or more long-duration delivery systems that are appropriate for banding perennial crops.

Determine for a variety of perennial crops the long-term phytotoxic effect of candidate ant repellents and formulating materials.

Summary of Progress: Two different laboratory bioassays are used to determine the effect of crude plant-produced, as well as synthetic, semiochemicals as repellents against foraging workers of the Argentine ant, the native fire ant, and the native gray ant. One assay is based on the ability of ants to cross barriers of beeswax containing differing concentrations of test chemicals; the other is based on repellency of the ants to airborne chemicals and, therefore, only measures olfactory responses. Both assays permit construction of dosage/response curves and determination of a BI-50 (the amount of chemical providing 50% repellency). The olfactory bioassay was used to determine the foraging-disruptant effect of volatiles from dichloromethane extracts of 58 different combinations of plant species and plant parts. Extracts of anise seed, clove buds, and allspice seedpods, which were among the most repellent plant materials, each produced BI-50's from about 1 mg of extracted plant material placed in the olfactometer; anise seed and clove buds each appear to produce more than one active semiochemical, and the blend of their semiochemicals may be stronger than any of the components separately. Crude macerates of anise seed and clove buds lose disruptive activity over time, with a half life of about 12 hours.

Early results indicated that Carnauba wax might be highly effective as a carrier for semiochemicals, although a field test in which citrus trees were banded with a mixture of Carnauba wax and farnesol showed that this method is not yet suitable for commercial use. When young citrus, plum, and cherry trees and rose bushes were banded with mixtures of semiochemicals (farnesol or methyl eugenol) and carriers (stickem or tree tanglefoot) a high level of phytotoxicity developed.



SHEEP FOR WEED CONTROL

The manipulation of sheep grazing pressure for weed control in seedling alfalfa. (Year 2 of 2; $8,990)

Principal Investigators: C.E. Bell, UC Cooperative Extension, Imperial County; J.N. Guerrero, UC Cooperative Extension, Imperial County

Objective: To compare different sheep grazing pressures in seedling alfalfa for their effect on weed control, crop yield, crop cover, lamb weight gain, and soil compaction.

Summary of Progress: Five and one-half acres of `CUFl01' alfalfa were planted at the rate of 30 lb seed per acre in mid-October in three blocks and irrigated our plots. The winter of 1996-97 was quite unusual: it was quite mild, it never got cold, and precipitation was nil. Consequently the "normal" crop of winter annual weeds in seedling alfalfa was very subnormal. We did have some broadleaf weeds, mostly goosefoot, some volunteer wheat, but winter annual grasses were almost nonexistent. In some of our past research, the winter grasses have been prevalent. We will be repeating this experiment an additional year, and hopefully the winter climate will be more normal.

Grazing commenced on January 5, 1996 and continued until March 1, 1996. We had two lamb weigh periods, each being about 28 days. The paddock size was .1 acre, each paddock having four lambs. To evaluate the differences in grazing pressure on weed control, lambs were grazed for 2 to 16 days in each of the treatments. Measurements of lamb weight gain and standing forage in the paddock were taken. First year data have been computed but not statistically analyzed.

The correlation of grazing pressure to the different estimates of standing forage DM after grazing should be quite revealing and is the primary objective of the research project. The second year should provide sufficient data for some interesting correlations, as well as answers to the following questions: Does putting more sheep on subsegments of a paddock for a shorter period of time assist weed control in seedling alfalfa? Do these additional lamb movements and labor costs benefit lamb gain?



PREDICTING WEED PROBLEMS

Phenology predictions of common annual weeds in California. (Year 2 of 2; $41,056)

Principal Investigators: J.S. Holt, Botany and Plant Sciences, Riverside; T.S. Prather, UC IPM Project, Kearney Agricultural Center

Objectives: Quantify phenology, including emergence, flowering, and seed production, of common annual weeds planted in two different field locations.

Determine the effect of planting date on phenology of these weeds.

Correlate phenological data from two locations and four planting dates with air and soil temperature to evaluate the utility of degree-days to predict phenology of these weeds.

Summary of Progress: Seeds were collected in the vicinity of UC Riverside and Kearney Agricultural Center of weeds common in each location. Current collections in each location include several weeds from each of 10 or more plant families; many of the species are found in both collections, as well. Germination experiments were conducted on all seeds in the collections to determine percent and rate of germination at 25deg.C. These data were used to select the species to be studied further and to determine the number of seeds to plant in field experiments. Experiments were begun on a temperature gradient bar, using three species at a time, to establish lower and upper temperature thresholds of germination for each species from both locations for use in developing predictive models. The first field experiment was planted in November 1995, using the same species in two locations to quantify phenological events. Experiments are planted in a randomized complete block design with six blocks. Weed species constitute the treatments; nine species are planted in the first experiment, including members of five plant families. Plots are being watered by overhead sprinklers; weed control is accomplished by hand-weeding unwanted plants. Data collection is being made at 2 or 3 day intervals and includes time to emergence, number of leaves, number of branches, and time to flowering. Once flowering occurs, subsequent data will include time to first seed set.

This research will generate information about the phenology of important annual weeds in California. Predictions of emergence, growth, and reproduction of weeds could help growers plan cultivations and post-emergence herbicide applications in order to control the greatest number of weed species possible with the least amount of herbicides used. Information about weed emergence can also be used to choose crop planting dates when weeds will not occur, to improve timing of seedling management or seedbed preparation, to exploit the competitive advantage of early crop establishment, and to identify potential hosts of beneficial insects, hosts of pest insects that act as bridges, and hosts of insect vectored diseases.



MONITORING MITES ON HENS

Off-host ecology and sampling of northern fowl mites in poultry systems. (Year 2 of 2; $17,843)

Principal Investigators: B.A. Mullens, Entomology, Riverside; N.C. Hinkle, Entomology, Riverside

Objectives: Document the practicality of a previously developed, sequential, direct bird examination sampling plan for northern fowl mites on caged laying hens.

Correlate estimated mite numbers with actual mite numbers on hens.

Determine the relationship between estimated on-host numbers of mites and numbers of mites appearing on the eggs.

Examine off-host distribution (eggs, cages, manure surface) of northern fowl mites relative to time of year, time of day, temperature, and estimated level of infestation of hens.

Summary of Progress: We are trying to test a previously developed, direct hen sampling plan for northern fowl mites and to see whether we might be able to sample eggs as an easier means of gauging infestation levels. The study is in its early stages, but already is quite interesting. Mite counts on eggs do seem to be related to overall infestation level in the house, but mites on any particular hen do not relate as strongly to mites on the hen which laid the egg. Mites apparently do not get on the egg as it is laid. Rather, we suspect that mites often move off the host bird and crawl on cage wires; some end up on the eggs for variable periods of time.

Examining 100 arbitrarily-chosen eggs in a regular pattern in the house results in a fast, easy mite count. It takes much less than half as long as examining the hens directly. Thus far, RaVap treatments for mites have done a good job of reducing mite numbers on eggs, but a mediocre job of reducing mite numbers on the hens. We suspect that acaricide residues on cage wires kill mites off-host, but penetration problems (inadequate pressures?) are preventing good control. There also seems to be a lag period before treatment effects are seen, perhaps due to egg hatch after some of the adult mites are killed.

We are just beginning to relate our estimates of mite numbers to actual numbers of mites on the hens. It is likely that visual scoring results in vastly underestimated mite numbers, especially at higher levels of infestation.



WHY DON'T INSECTICIDES ALWAYS WORK?

Photo of cotton aphid morphs
Different colored morphs of the cotton aphid (shown here, the light and dark) appear to differ in their susceptibility to commonly used cotton insecticides; this may help explain erratic patterns of control.
Agronomic and environmental factors influencing control of cotton aphids with insecticides. (Year 2 of 3; $16,707)

Principal Investigator: L.D. Godfrey, Entomology, Davis

Objectives: Examine effect of cotton aphid morph on the susceptibility to commonly used insecticides in cotton IPM.

Examine effects of several agronomic factors in cotton production, such as plant nitrogen level, plant water status, plant age, and boll load, on cotton aphid susceptibility to commonly used insecticides in cotton IPM.

Study susceptibility/response of cotton aphids reared on various host plants to commonly used insecticides.

Summary of Progress: The cotton aphid (Aphis gossypii) has emerged as a significant pest of cotton in the San Joaquin Valley; insecticidal control of this pest has been extremely erratic, often necessitating repeat applications. These repeat applications of broad-spectrum materials exasperate the disruption of biological control of other key cotton arthropod pests. Cotton aphid field populations are comprised of several color morphs. A pale yellow morph and a dark green black morph are the most apparent with a gradation of color forms between these extremes. In laboratory studies, these morphs have been shown to possess different biological characteristics, such as developmental rate, number of offspring produced, size, etc. These morphs may also differ in susceptibility to commonly used insecticides. During the first year of this project, a field study was conducted on this question and a laboratory study is ongoing. For the field study, bioassays (discriminating dose and dose response curve analyses) were conducted on cotton aphids from cotton in the southern San Joaquin Valley. Discriminating dose mortality differed between the light and dark morphs among the four insecticides tested. The dark morph cotton aphids were generally less susceptible to chlorpyrifos than light morphs, whereas light morphs were more difficult to kill with bifenthrin compared with dark morphs. There were no consistent trends between the morphs with endosulfan and triazamate. Dose response curves showed higher LD95 and lower slopes values (low homogeneity) for field-collected dark morph than for light morph cotton aphids. However, dose response curves for the two morphs were quantified about 2 months apart because of aphid morph availability in the field; therefore these data must be considered in light of the differing environmental and plant conditions. The influence of some of these agronomic and environmental factors on cotton aphid susceptibility will be examined in future studies.



HABITAT MANAGEMENT FOR PIERCE'S DISEASE

Management of riparian vegetation for control of Pierce's disease in coastal California (Year 2 of 2; $22,334)

Principal Investigators: A.H. Purcell, Environmental Science, Policy and Management, Berkeley; J.R. McBride, Environmental Science, Policy and Management, Berkeley

Objectives: Manipulate the structure and composition of forest plants bordering a typical intermittent-flow coastal stream near commercial vineyards by selective plant removal and control and by planting of tree and shrub species to reduce breeding of the blue-green sharpshooter and its dispersal to adjacent vineyards.

Monitor the effects of riparian vegetation management on population density, dispersal and infectivity with Xylella fastidiosa of the blue-green sharpshooter vector of Pierce's disease.

Summary of Progress: In this first year of a 4-year project to manage vegetation along a coastal stream in order to reduce damage caused by Pierce's disease of grapevines, we removed selected plants in the treatment area of riparian vegetation along Conn Creek next to Napa Valley vineyards. Replanting was delayed by the record floods of winter 1996, that delayed plant removal, followed this fall by record dry weather that delayed replanting.

The abundance and activity of the blue-green sharpshooter vector of Pierce's disease was monitored by direct sampling with sweep net and vacuum collector. Sweeping proved to be preferable because of its simplicity and low labor costs and gave similar results to vacuum collecting. Yellow sticky trap catches revealed that trap location was most important. This is most reasonably explained by the proximity of favored host plants. Trap catches were about as high or higher in the proposed treatment area as in the unmanaged control plot and highest in the portion of the site in which a buffer strip of Douglas fir and redwood will be planted. Blue-green sharpshooters collected in the study area were tested for their ability to transmit the Pierce's disease bacterium (Xylella fastidiosa). Natural infectivity rates ranged from about 10 to 20%, but test plants need to be rediagnosed by culture or other methods to calculate final figures.

Negotiations with participating growers and agencies are underway to begin a second replication of the experiment. If successful in reducing the populations of the Pierce's disease vector and their rates of infectivity with the Pierce's disease bacterium, the methods developed in this research should reduce damage caused by Pierce's disease in vineyards near riparian vegetation and also improve the environmental quality of the riparian habitat along coastal streams bordering vineyards.



GROUND COVERS: HELP OR HINDRANCE FOR TRUE BUGS?

Photo of Walt Bentley
Walt Bentley samples for true bugs in pistachios as part of his research project looking at impact of orchard floor vegetation on pest numbers.
Manipulation of orchard-floor vegetation for control of hemipteran pests of pistachio. (Year 2 of 2; $24,102)

Principal Investigators: W.J. Bentley, UC IPM Project, Kearney Agricultural Center, Parlier; P.G. da Silva, Center for Biological Control, Berkeley; K.M. Daane, Center for Biological Control, Berkeley

Objectives: Determine whether species composition and population densities of the major hemipteran pests are influenced by the presence or absence of vegetative ground cover in San Joaquin Valley pistachio orchards.

Determine whether hemipteran-caused crop damage is influenced by the presence or absence of vegetative ground cover in San Joaquin Valley pistachio orchards.

Summary of Progress: The pistachio market is one of California's fastest-growing agricultural commodities. While once considered virtually pest-free, pistachios are now attacked by a variety of pests. One group of insect pests is commonly referred to as the "big bugs," and includes the relatively large hemipteran pests in the families Coreidae and Pentatomidae most notably the leaffooted bug, the redshouldered stink bug, the southern green stink bug, and the green stink bug. These "big bugs" are not as abundant during the first half of the season as other hemipteran pests (e.g., Lygus); however, during the latter half of the season they can increase in numbers and cause direct damage to the pistachio nut. Therefore, development of a control program for these pests is an industry priority.

Many pistachio growers have already begun experimenting with different management practices for both the "small bug" and "big bug" hemipteran pest species. One common practice is the use of vegetative ground covers to act as a trap crop or shelter for beneficial insects and spiders. Such practices have generated a great deal of discussion in the pistachio industry; however, detailed studies are lacking. To determine the effects of ground vegetation on the migratory habits and pest status of the stink bugs and leaffooted bugs we established large, replicated blocks of cover and no-cover management systems in cooperative growers' pistachio orchards.

Throughout the 1995 season, we measured the development of plant covers and the populations of the hemipteran pests and their natural enemies. To date, results have shown no major differences in the numbers of hemipteran pests or natural enemies between cover and no-cover treatments. We believe one reason for this lack of differences was the very low levels of hemipteran pests in 1995. For example, Lygus, a very common pistachio pest, was found at only one of three field sites. Because the floor vegetation might act to attract migrating hemipteran pests into the orchard, one of the important questions was the preference of big bug pests to different plant species found in the cover crop system. The importance of certain habitat preferences of pests and natural enemies was confirmed; for example, common invading plant species are London rocket and Russian thistle, both of which are proving to be preferred host plant material to some big bug species. We also found that planting a cover crop did not prevent these "undesirable" plant species from establishing in the pistachio orchards studies. In 1996 we will continue to study pest and natural enemy densities in the field plots and complete laboratory studies on the development and host plant preference of some of the big bug pest species.

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Projects that Ended in 1995-96

SPIDERS AND GRAPE IPM

Photo of spider
Overall spider populations were not significantly correlated with ground covers in grapes.
Effects of spiders on pest populations in vineyards: Determining their role in grape IPM.

Principal Investigators: K.M. Daane, Laboratory of Biological Control, Berkeley; M.J. Costello, UC Cooperative Extension, Fresno County

Objectives: Determine spider species composition and relative abundance, and evaluate and refine a spider sampling procedure.

Evaluate the role of the more common vineyard spider species on leafhopper densities through laboratory and field feeding studies.

Determine the effect of cover crops on the spider species composition and relative abundance in the vines.

Summary of Progress: To better understand the ecology of the vineyard spider complex, we have refined a sampling method that has enabled us to better estimate spider species composition and density in the grape vineyard. Three spider sampling methods were evaluated: (1) beat and shake onto a drop cloth, (2) beat and shake into a cloth funnel suspended from the trellis wire, and (3) D-vac (insect vacuum). All methods were compared to a control in which we stripped off and searched the foliage of entire vines. The D-vac altered the proportion of spider species sampled, collecting a significantly higher percentage of some species (e.g., jumping spiders) than the control, indicating a sample bias by this method. Spider species composition was not altered by either the beat or funnel methods. The funnel method has the advantage of speed without a significant decrease in accuracy.

We are also using immunochemical methods to analyze the stomach contents of spiders and determine what they are feeding on in the field. Using whole hemolymph antisera (polyclonal antibodies) to leafhopper extract, we achieved positive reaction to leafhopper extract exclusive of certain other Homoptera. However, these results could not be duplicated with ascites. Therefore, we have initiated the process for production and isolation of leafhopper specific monoclonal antibodies.

To test the hypothesis that maintenance of ground covers between vine rows encourages the density of predator populations, we sampled spiders and other predators from vines with and without ground covers, in both table grape and raisin grape sites. At the table grape site, we found no evidence that the total spider population varied significantly between ground cover and cultivated treatments, although early season density of Oxyopes scalaris was highest in plots without cover, and Neoscona oaxacensis were highest with ground covers. At the raisin grape site, there were higher levels of total spiders in plots with ground covers in three out of the five sampling dates. However, only one spider, Hololena nedra, had a consistent pattern of higher densities where ground covers were present.



CONTROLLING CRABGRASS WITH LESS HERBICIDE

Photo of Clyde Elmore
Clyde Elmore monitors plots in research to determine cultural practices that will improve weed control in turf.
Crabgrass management in turfgrass: understanding invasion and improving control with reduced herbicide use.

Principal Investigators: C.L. Elmore, Vegetable Crops/Weed Science, Davis; A. Harivandi, UC Cooperative Extension, Contra Costa and Santa Clara counties; M. Rejmanek, Evolution and Ecology, Davis

Objectives: Evaluate the utility of using tall fescue cultivars and timing and rate of overseeding of tall fescue for crabgrass control.

Determine the relationship of gap size and the ability of smooth and hairy crabgrass to invade tall fescue turfgrass.

Use selected tall fescue cultivars to reduce preemergence herbicides.

Develop overseeding of cultivar methods for crabgrass control in tall fescue turfgrass.

Summary of Progress: Smooth and large crabgrass are the most prevalent summer annual grass weeds found in turfgrass in California. Commonly, preemergence herbicides are used annually in the late winter or early spring for control. In this project, we have found that both crabgrass species germinate but do not establish well in new fall seeding of turf-type tall fescue cultivars. In spring plantings smooth crabgrass is more competitive than large crabgrass and will establish as a weed in the turf irrespective of the tall fescue cultivar. The very dwarf variety `Bonsai' or the older forage type `Fawn' allow more crabgrass to germinate and establish than the intermediate turf-type varieties. An opening (gap) in turf is needed for crabgrass to establish. When 4- to 8-inch openings are made in the turf leaving bare soil, smooth crabgrass can germinate and establish if seed is present. When the turf is scalped once, or clipped to 0.5 inch, the regrowth of tall fescue is rapid enough that little or no crabgrass will establish. A few smooth crabgrass will establish in large closely clipped areas, compared to a single scalping. Large crabgrass did not establish until there were 4 inches or more of bare soil. By understanding the gap or hole size for the two crabgrass species to establish, we can have a guide for when to overseed bare spots. Also, fall seeding is preferable to spring seeding to give the greatest competitive edge to the turf over crabgrass.

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Final Reports for Projects that Ended in 1995

COVER CROPS DON'T HELP SAN JOSE SCALE PARASITES

Improving biological control of San Jose scale using flowering cover crops.

Principal Investigators: G.E. Heimpel, Entomology, Davis; J.A. Rosenheim, Entomology, Davis

Summary of Accomplishments: We tested the hypothesis that flowering cover crops can lead to improved biological control of insect pests. In particular, we asked whether plantings of dill within an almond orchard could improve biological control of San Jose scale, Quadraspidiotus perniciosus, by the parasitoid Aphytis aonidiae. Laboratory studies showed that dill nectar can increase the lifespan of A. aonidiae. In the field, we established dill plantings in an almond orchard in Northern California and compared adult parasitoid abundance, parasitism rates, and scale densities in these plots with plots left to resident vegetation. No differences were found in any of these measures of parasitoid activity between the dill and control plots. Thus, dill plantings did not improve biological control of San Jose scale in our experiment.

The failure of dill to improve biological control of San Jose scale can probably be attributed in part to a lack of movement of wasps from the almond trees to the flowers. Although a number of other parasitoid species were observed feeding on dill nectar in the field, no Aphytis were seen on dill plantings. Only a single Aphytis was recovered by shake sampling into alcohol-coated pans, and no differences in sticky-trap catches of Aphytis were detected between dill and control plots. A chemical assay designed to detect nectar sugar in the guts of parasitoids indicated very low amounts of feeding, if any. We recommend that methodologies may need to be devised to deliver food into the tree canopy itself.

Our observations also indicated that A. aonidiae females were subject to a substantial amount of predation by generalist predators. Predators included Argentine ants, assassin bugs, and spiders. The risk of mortality from predation rivaled the potential risk of mortality from starvation during the time of year when Aphytis were most abundant. Thus, the lifespan of parasitoids may be limited by predation as well as by food. Under these conditions, the provision of supplemental food may have little effect on biological control.



NEW APPROACHES TO OLIVE KNOT CONTROL

Integrated control of the olive knot disease.

Principal Investigators: M.N. Schroth, Environmental Science, Policy and Management, Berkeley

Summary of Accomplishments: The hypothesis was proven true that olive knot bacteria internally inhabits apparently disease-free wood of olive trees and that this can be a major source of contamination of wood used for propagation purposes. This appears to be a principal reason why young, previously healthy olive orchards rapidly become severely diseased, especially following a hail storm or other environmental conditions that favor the disease. The populations of internal olive knot bacteria vary greatly from year to year and throughout the season. They are also affected by proximity to diseased wood. Populations up to one million per gram of tissue were detected. Wounding of apparently healthy wood also indicated that the bacteria were systemic as knots frequently developed at the sites of wounding. Pruning experiments, where wounds were made and subsequently inoculated with knot bacteria, showed that pruning should be done during dry warm weather when populations of internal bacteria appear to be low and moisture is not available to promote infections of wounded tissues. June appears to be an ideal time. Work focusing on improving the efficacy of copper compounds to control olive knot was successful. The incorporation of iron to copper compounds enhanced efficacy. Also, it was discovered that the surfactant that is incorporated in standard Kocide 101 did not provide the "wetting" to enable the copper to diffuse into natural openings (leaf scars) and provide protection. Other surfactants were superior.

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