Annual Reports

1998—UC 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 is 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 1998-99
Continuing Projects Funded for 1998-99
Projects that Ended in 1997-98
Final Reports for Projects that Ended in 1997

New Projects Funded for 1998-99

Principal Investigator: K. M. Daane, Center for Biological Control, Environmental Science Policy and Management, Berkeley/Kearney Agricultural Center, Parlier

Objectives: Develop a research-oriented sampling program for grape mealybug that shows pest abundance, development and seasonal movement on different parts of the vine.

Determine the effect of cultural practices on grape mealybug ecology, including: pest status, growth parameters, and natural enemy abundance and species composition.

Principal Investigator: J. J. Stapleton, UC IPM Project, Kearney Agricultural Center, Parlier

Objectives: Augment existing database of thermal death dosages of fungal pathogens with data for selected nematode and weed species important in California agriculture.

Validate the database during field solarization in several California growing areas.

Principal Investigator: A. H. Purcell, Environmental Science Policy and Management, Berkeley

Objective: Determine if pruning can eliminate Pierce’s disease from grapevines with symptoms of the disease.

Principal Investigator: H. S. Costa, Entomology, Riverside

Objectives: Determine the effects of reduced ultraviolet light levels on insect (thrips, whitefly, and aphid or leafminer) immigration rates and host finding ability.

Evaluate the effectiveness of commercially available ultraviolet-absorbing plastic film in reducing insect infestations and suppressing pathogen incidence in greenhouse grown crops.

Continuing Projects Funded for 1998-99

The Use of Fire to Control Yellow Starthistle (Centaurea solstitialis L.) and Enhance Native Plant Diversity.

Principal Investigator: J. M. DiTomaso, Vegetable Crops, Davis

Objectives: Determine the effectiveness of one, two, and three years of controlled burning on yellow starthistle control and native plant composition and diversity, examine the time-course of yellow starthistle reinfestation following three consecutive annual burns.

Develop a sustainable management strategy utilizing periodic controlled surface fire and elucidate the factors responsible for enhancing the success of native plants following burning.

Summary of Progress: Around 1984, yellow starthistle began to spread rapidly throughout the grassland areas of the Sugarloaf Ridge State Park near Sonoma. In July 1993, and again in 1994 and 1995, we conducted a prescribed burn of a 30 acre infested test site when yellow starthistle was in the early flowering stage. An additional 155 acres was burned in July 1996 and June 1997. While a single year of burning did not control yellow starthistle, it increases the native forb populations, as well as total plant diversity. Two consecutive years of burning, however, gave 68% control of yellow starthistle, and three years gave over 90%, while still maintaining high native plant diversity. The effectiveness of a three year burn cycle was reflected in a 99.5% reduction in yellow starthistle seeds in the soil. Native perennial grasses increased by over 3-fold with three consecutive years of burning. When the area burned from 1993-1995 was left unburned in 1996, the seed bank of yellow starthistle increased by 30-fold compared to the previous year. This corresponded to an increase in yellow starthistle seedlings in spring 1997, and mature plants that summer. The recovery in starthistle correlated to a reduction in plant diversity (particularly forbs) in the site left unburned following a three year burn. Thus, the rate of yellow starthistle re-invasion is rapid, even in areas undisturbed by human activity or grazing. Consequently, prescribed burning can be a valuable tool for starthistle suppression, and stimulation of native plant diversity and perennial grass populations, but should be incorporated into an integrated management system incorporating other control methods.

Evaluation of Interactions Among Russian Wheat Aphid, an Effective Parasite, and Plant Resistance.

Principal Investigator: D. González, Entomology, Riverside

Objectives: Assess impact of Aphelinus albipodus, an effective introduced parasite on Russian wheat aphid (RWA) in combination with 2 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.

Summary of Progress: In this report we present results from two plantings, each with four replications of all plots. The spring planting was in March and corresponds to the most common planting date for wheat and barley in northern California. It is the growing period that has the greatest potential for high numbers of RWA on cereal plants. The summer planting began in early May and provided continuity with the spring planting in providing susceptible plants from early May through mid July for RWA infestations. High temperatures in June and July severely reduced the potential for RWA increase in numbers. The low numbers of RWA in the summer planting provided the opportunity to assess the plant-RWA-parasite interactions under two significantly different densities, under optimal mild temperatures in spring and under severely restrictive (very hot) summer temperature conditions. During the spring and summer a total of 1,439 tillers were sampled and counts were made as planned.

Ecology of Fannia spp. (Diptera: Muscidae) in Poultry Systems.

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

Objectives: Determine moisture preferences of adult Fannia spp. for oviposition and document influence of moisture on development and survival of immature Fannia spp. in the laboratory.

Document the field microdistribution of immature Fannia spp. in the manure, with particular reference to moisture, temperature, and depth.

Test for competitive interactions between the two dominant Fannia spp. in the laboratory.

Summary of Progress: Trials to date have shown that both the little house fly, Fannia canicularis, and the other species found in poultry manure, F. femoralis, can develop successfully when early stage larvae are placed into manure with moisture levels between 35% and 65%. Emergence is slightly reduced and flies are somewhat smaller at 35% moisture, indicating some stress, but we have shown that Fannia spp. can develop in much lower moisture than house flies can. Preliminary observations on oviposition behavior indicate that dry manure which becomes wet must age 2-3 days before flies lay well on it. Uneven features on the manure surface are required to stimulate egg laying. In the laboratory, larvae of F. canicularis remain closer to the manure surface than do those of F. femoralis, suggesting that the two species may segregate in the habitat by depth. This will be determined in the field over the next few months.

Integrating Crop Competitiveness with Herbicide Applications to Improve Weed Control and Reduce Herbicide Use.

Principal Investigators: T. C. Foin, Environmental Studies, Davis; J. E. Hill, Agronomy and Range Science, Davis

Objectives: Establish critical emergence periods for weeds beyond which interference by the rice crop alone is sufficient to suppress weed growth.

Identify and test mechanisms by which rice interferes with weed growth with a particular emphasis on the importance of competition in the rhizosphere.

Evaluate the effect of rice cultivar and seedling rate on the suppressive ability of the crop.

Summary of Progress: Rice yields increased when broadleaf control was delayed up to 28 days after seeding. This supports earlier work that suggested broadleaf control could be improved by delaying herbicide applications until the rice plants were large enough to suppress the growth of weeds that emerged after the herbicide was applied. There was no advantage, however, in delaying the application of herbicides to control watergrass. In fact, rice yields decreased with delays in watergrass control.

Root competition reduced the growth of both rice and watergrass more than shoot competition. This suggests, contrary to the widespread belief that rice and weeds compete primarily for light, competition for nutrients was the primary mechanism. If the rice crop is to be used to improve watergrass control, researchers will have to increase their emphasis on the dynamics of below-ground competition.

The effect of the main factors differed between the two experiments. Watergrass dry weight at the end of the season was significantly affected by all three main factors. Herbicide rate had the greatest effect on watergrass growth, but M202, the more competitive cultivar, produced higher yields than A301, even at lower herbicide rates. Rice seed rate had little effect on watergrass growth; differences were only significant (p<0.05) between the 50 and 150 to 200 lbs. seed/acre treatments. The data suggests that the choice of cultivar is the most promising avenue for reducing herbicide use.

Spatial Distribution and Water Relations of Armillaria mellea in Pear Orchards.

Principal Investigators: D. M. Rizzo, Plant Pathology, Davis; K. A. Shackel, Pomology, Davis

Objectives: Evaluate the spatial distribution of Armillaria in commercial orchards and the relationship of the pathogen to tree crown symptoms and plant water status.

Determine the effects of irrigation type on the susceptibility of pears to Armillaria root disease in a controlled field study.

Determine the effect of soil moisture and temperature on growth of Armillaria under field and laboratory conditions.

Summary of Progress: A survey was conducted to produce a map of tree water stress around an Armillaria infection center in Lake County. A pattern of stress was observed for trees which bordered the infection center, but not replant trees within the infection center. This may indicate that Armillaria requires many years to develop a significant effect on tree water status. However, spatial patterns of stress were not limited to the borders of the infection center. This is in agreement with on the spatial distribution Armillaria in pear orchards. Excavations of pear root systems confirmed that rhizomorphs are the primary means of spread for Armillaria. Infection does not always start at the periphery of the root system; it often starts directly at the root collar or at scattered locations around the root system. To determine the effects of irrigation on disease development, we established a pear orchard at the Armstrong Research Plots at UC Davis. Three different rootstocks were planted in a randomized block design utilizing both flood and sprinkler irrigation systems. Inoculations were done in May 1997 and will be monitored over the next several years. In addition, we have initiated a number of experiments to test for the growth of rhizomorphs through soil at various moisture contents. Measurements of tree water stress indicated only minor differences between trees in the flood irrigation and the two sprinkler irrigation treatments (recommended versus excessive application). These treatments will be followed to determine their effect on both tree growth and Armillaria infection and spread.

Projects that Ended in 1997-98

Agronomic and Environmental Factors Influencing Control of Cotton Aphids with Insecticides.

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) is one of the most damaging insect pests of cotton in the San Joaquin Valley. Presently, insecticides are a major tool used to control cotton aphids in cotton. However, in recent years, insecticide control in California has become erratic and unpredictable. The present study shows that some agronomic and environmental factors can influence the response of the cotton aphid to different insecticides, which could explain in part the insecticide failures observed in the field. The dark vs. light aphid morph experiment indicated that the dark-morph aphids possessed a significantly lower susceptibility to most insecticides than the light morphs. In addition, the planting-date experiment showed that aphids reared on late-planted cotton were less susceptible to most insecticides than the aphids reared on early-planted cotton. Finally, the nitrogen-level experiment suggests that aphid susceptibility to some insecticides (two of the five tested) may decrease with higher levels of nitrogen in the plant, although the opposite result was observed with one of the insecticides. Our study also shows that nitrogen may also affect the population dynamics of aphids. Additional work is needed to test if any of these changes in insecticide susceptibility are significant in a field situation, and also to determine the physiological mechanisms behind these changes. By a better understanding of the role that agronomic and environmental factors play in the insecticide susceptibility of this pest, an increase in the predictability and effectiveness of insecticide control could be achieved and possibly a reduction in the number of insecticide applications.

Bionomics of the Citrus Peel Miner and its Parasites in the Coachella Valley.

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

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

Identify the parasitoid species attacking the citrus peelminer on citrus, oleander and willow.

Evaluate emergence patterns, temperature thresholds, longevity, survivorship, and levels of infestation of the citrus peelminer and its parasitoids on citrus and oleander in the Coachella Valley.

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

Summary of Progress: In 1995-96, the citrus peelminer, a new species of Marmara (Lepidoptera: Gracillariidae) reached extraordinary levels of infestation on grapefruit in the Coachella Valley. Peelminer larvae attack the fruit, forming serpentine mines between the epidermal layers and rendering the fruit unacceptable for the fresh market. In the Coachella Valley, oleander is a common alternate host plant for the peelminer. Of 95 stands of oleander identified in the commercial citrus region of the Coachella Valley, 65% were infested by peelminer. Peelminer was generally absent in oleander from areas distant to commercial citrus. Other host plants identified in California and Arizona include tree tobacco (stem-miner), cotton (stem-miner), avocado (fruit- and stem-miner) and questionably mango (fruit-miner). Results of all morphological analyses support the notion of a single species of Marmara with a broad host range. Marmara are able to complete development on mature or senescing fruit, enabling them to infest new fruit in June and early July. Therefore, oleander is not the only source of spring infestations.

Peelminer populations were generally low throughout the Valley during 1996 and 1997, with fruit damage generally below 10%, although early season damage reached 35% in some study blocks. Early season population increases in July (1997) and August (1996) were quickly controlled by an undescribed species of Cirrospilus (Hymenoptera: Eulophidae). In both years, the parasitoid eventually parasitized over 95% of the peelminers in all orchards being sampled, and by September very few live larvae were found in plots being monitored for population changes.

Field Test of More Effective Traps for the Walnut Husk Fly.

Principal Investigators: C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter/Yuba counties; S. Opp, Biological Sciences, CSU, Hayward; C. Lauzon, Biological Sciences, CSU, Hayward

Objectives: Field test two new lure substances, 3-methyl, 1-butanol, and putrescine, alone and in combination with ammonia for attractiveness to gravid female walnut husk flies in a walnut orchard.

Determine optimal dosages of the lure components in the field for monitoring walnut husk fly activity.

Summary of Progress: We field tested two new lure substances, 3-methyl, 1-butanol, and putrescine, alone and in combination with ammonia. Putrescine was not tested alone as Opp et al. (Unpubl.) determined its unattractive nature to walnut husk flies. While some variation occurred among blocks (typical patch dynamics associated with walnut husk flies), walnut husk flies generally were more attracted to ammonia in combination with the low dose of the butanol than any other lure either alone or in combination with ammonia during the first three weeks of testing. By the fourth week of testing, however, walnut husk flies were more attracted to ammonia and this strong attraction continued to the end of the 10 week study. Also, during the first four weeks of testing, both high and low dosage butanol lures alone captured more flies than control traps. Later in the testing season, however, control traps caught more flies than traps containing either dose of butanol with or without putrescine. Gravid female flies were first captured during the second week of the study. The attraction of flies to the butanol/ammonia lure shows promise toward specifically detecting gravid females under low population conditions and immature flies who are not attracted to ammonia. It appeared that high dosage butanol with or without putrescine in combination with ammonia diminished the attractive power of ammonia. This suggests that a repellent effect may have taken place when ammonia was mixed with high butanol alone or with putrescine. More tests need to be conducted to understand why low butanol and ammonia together are most attractive to flies early in the season, why this attraction does not continue, and if we alter dosage can we extend the attractive nature of this combination. In addition, the possible repellent effect of butanol should be examined for possible use in new trapping strategies.

Development of a Knowledge-Based Advisory System as an Aid for Decision Making in Nematode Management.

Principal Investigators: E. P. Caswell-Chen, Nematology, Davis; B. B. Westerdahl, Nematology, Davis; R. F. Walters, Computer Science, Davis

Objectives: Develop a user-friendly, knowledge-based ("expert") system that will aid growers in making nematode management decisions, specifically regarding nematicide application, and crop and cultivar selection.

Make the knowledge-based system available via the Internet and World Wide Web (WWW).

Summary of Progress: Scientific progress, with attendant proliferation of reductionist knowledge has led to overwhelming amounts of information, and a proliferation of informational databases. Because of the projected loss of methyl bromide by the year 2000, there is a critical need to be able to access and interpret knowledge on nematode management. During this one year project, our objective is to demonstrate that we can successfully develop a functional prototype of a World Wide Web addressable knowledge-based system that will aid growers in assessing and making nematode-management decisions. During the current year we started this project by initiating an assessment of the data contained within NEMABASE, a host-nematode interaction database, to see if all the information contained therein warranted inclusion as reference in a knowledge-based system. We concluded that two significant sources that were included within the database should not be included, so, we eliminated them. We have initiated the development of a summary nematicide database derived from the DPR pesticide database, and from the US EPA pesticide database. We have initiated the development of a user interface that will allow users to enter queries via the WWW.

Management of Riparian Vegetation for Control of Pierce's Disease in Coastal California.

Principal Investigators: A.H. Purcell, Insect Biology, 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: The third year of this multiyear project evaluated continuing experimental management of riparian vegetation to reduce Pierce's disease in adjacent vineyards while preserving or enhancing environmental attributes of riparian habitats. The removal of breeding plants of the principal Pierce’s disease vector, the blue-green sharpshooter (BGSS) and their replacement by planting a diversity of native riparian hardwood species continued to exceed our original projections for the degree of reduction of BGSS. At our first experimental site at Conn Creek, near Yountville, catches of BGSS on sticky traps used to monitor vector activity showed that BGSS activity were dramatically lower (99% less) in the plot where vegetation had been removed and replaced compared to an adjacent undisturbed control. The growth of trees planted in areas where mature trees had been removed in 1995 continued to greatly exceed the growth of trees planted near established trees. A second experimental site, along the Napa River near Yountville, that had been cleared in 1996 also had large reductions (more than 70%) in activity of the BGSS; catches at a single trap near adjacent undisturbed vegetation accounted for a majority of the BGSS activity that we detected in the vegetation management plot. A third site, along Mayacamas Creek in Sonoma County, was monitored for BGSS activity to be used for comparisons in future years. Clearing at the third site began in fall, 1997. Increased community involvement and support was encouraged by activities of the North Coast Pierce's Disease Task Force and by University of California Cooperative Extension workshops and presentations. An Internet site (www.cnr.berkeley.edu/xylella) for plant diseases caused by Xylella fastidiosa was maintained for information and as a forum for communication on Xylella diseases world-wide.

Final Reports for Projects that Ended in 1997

Off-Host Ecology and Sampling of Northern Fowl Mites in Poultry Systems.

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 Accomplishments: Studies at a caged-layer ranch confirmed the practicality of sequential sampling for mites. Direct hen examination took as little as 15 minutes/house. Visual mite scores by three individuals correlated with each other and with actual infestation scores derived by removing infested feathers and extracting mites. Very low-level infestations (<10 mites) often were overlooked. Scores underestimated actual numbers of mites on the hens; estimation errors often exceeded 10-fold at high infestation levels.

The percentage hens infested usually was over 60%; average egg infestation level was 8.5%. Molting eliminated vent feathers and reduced mite numbers nearly to zero. Treatments with Ravap eliminated mites on eggs, but not mites on hens. Surveying 100 eggs required 5-6 minutes. While not as sensitive as hen examination, looking for mites on eggs is considerably faster and easier than looking at hens. Mites on eggs were related to the infestation level of hens near those eggs.

Mites introduced into an empty cage in a row of hens took 4-6 weeks to spread five meters. Dispersing mites stopped at the first host encountered and then did not spread to an adjacent hen until they had reproduced.

Management of Riparian Woodlands for Control of Pierce’s Disease in Coastal California.

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

Objectives: Test the effectiveness of manipulating the structure and composition of riparian woodlands to reduce populations of Pierce's disease vectors.

Manipulate the structure and composition of riparian woodlands bordering typical coastal streams adjacent to commercial vineyards by selective plant removal and replanting of tree and shrub species to reduce breeding of the blue-green sharpshooter (BGSS), its infectivity with the bacterium Xylella fastidiosa, and its dispersal to adjacent vineyards, and assess through monitoring the effects of riparian vegetation management on population density and dispersal of the blue-green sharpshooter vector of Pierce's disease and its infectivity with Xylella fastidiosa.

Summary of Accomplishments: Pierce’s disease of grape in the coastal valleys of California is caused by the bacterium Xylella fastidiosa, which is transmitted to grapevines by blue-green sharpshooters (BGSS) that enter the vineyard from adjacent riparian zones. This project showed that the most effective control of BGSS was to experimentally manage the vegetation in these narrow corridors of native and exotic vegetation by removing those plants that serve as BGSS breeding habitat and bacterial infection sources and replacing them with native trees and shrubs in a manner that preserves and enhances the environmental attributes of riparian habitats. Sticky traps and sweep net sampling used to monitor BGSS continued to exceed our original projections for the degree of reduction of BGSS from vegetation management. At our first experimental site at Conn Creek, near Yountville BGSS activity was dramatically lower (99% less) in the plot where vegetation had been removed and replaced compared to an adjacent undisturbed control for the second consecutive season. The growth of trees planted in areas where mature trees had been removed in 1995 continued to greatly exceed the growth of trees planted near established trees. A second experimental site, along the Napa River near Yountville, that had been cleared in 1996 also had large reductions (more than 70%) in activity of the BGSS; catches at a single trap near adjacent undisturbed vegetation accounted for a majority of the BGSS activity that we detected in the vegetation management plot. Infectivity of BGSS with X. fastidiosa from the control sections remained high (5 to 45%). The lack of BGSS in the treatment plots made tests for infectivity impossible. A third site, along Mayacamas Creek in Sonoma County, was monitored for BGSS activity in 1997 to be used for comparisons in future years, and plant removal began at the third site in fall, 1997. Studies are in progress by other researchers to evaluate environmental impacts of riparian vegetat ion management. Increased community involvement and support was encouraged by activities of the North Coast Pierce's Disease Task Force and by University of California Cooperative Extension workshops and presentations. Internet site (www.cnr.berkeley.edu/xylella) for plant diseases caused by Xylella fastidiosa was maintained for information and as a forum for communication on Xylella diseases world wide.

Phenology Predictions of Common Annual Weeds in California.

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

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 Accomplishments: Our research has enabled us to predict the growth of 17 weed species. Determining the starting point (biofix) for beginning the growth will simply become the planting date for a number of annual crops, making application of degree-day approach straightforward. Other crops, particularly the perennial crops present challenges to find a starting point, particularly for weeds that emerge during the late fall and winter periods. These degree-day models allow us to begin applying phenological predictions to the management of weeds in a variety of cropping systems. Identifying the time of emergence of some weed species in perennial crops allows for application of pre-emergent herbicides to just prior to emergence, maximizing the duration of control. Post-emergent control strategies benefit in at least two ways. First, identification of species with similar emergence and growth patterns allows for control to be timed to the last species that emerges within a growth stage assembly of weedy species. Spraying or cultivating in the middle of an assembly means not controlling the later emerging members of that assembly. Missing weed species reduces the efficiency of control by requiring subsequent control activities. A second benefit is identifying the post-emergent control window with respect to time of year. Calculations from the degree day models indicated that many species required twice as long to reach the 2-leaf stage in March versus July. Identifying control windows aids in planning to ensure control of problem species. For example, annual weeds should be controlled when they are at the cotyledon to 4-leaf stage for flex-tine cultivators to be most effective. Plants develop rapidly past the 4-leaf stage during the summer months making planning of cultivation and irrigation critical for successful use of this type of cultivator. Application of these models should optimize both pre-emergent and post-emergent control activities.

The Manipulation of Sheep Grazing Pressure for Weed Control in Seedling Alfalfa.

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

Objectives: Measure the effects of different lamb grazing pressures on seedling alfalfa on lamb performance and on alfalfa regrowth.

Summary of Accomplishments: The main effects, year, land within year, or cycle, did not affect (P >. 05) lamb weight gain. The grazing pressure treatments did affect (P = .05) lamb weight gain. When lambs were placed in paddocks and grazed the paddocks unimpeded for the 14 to 16 days, they gained more weight (.17 kg/d) than when the same number of lambs grazed the same size paddock divided into eight equal portions (.13 kg/d). There were no differences (P > .05) in lamb average daily gains between the two intermediate grazing pressures, the paddocks halved (.13 kg/d) or split into quarters (.15 kg/d). This research demonstrated that the longer the lambs can selectively graze, lamb average daily gain will increase. Conversely, when grazing selectivity decreased, lamb average daily gain also decreased.

At the first cutting after grazing, there were no differences (P > .10) in hay yields in experimental paddocks between grazing pressure treatments or between the grazed paddocks and ungrazed (P > .10) alfalfa. At the first cutting after grazing, there were no differences (P > .10) in weed DM estimates in experimental paddocks between grazing pressure treatments or between the grazed paddocks and ungrazed (P > .10) alfalfa.

Manipulation of Orchard-Floor Vegetation for Control of Hemipteran Pests of Pistachio.

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

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 Accomplishments: 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 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. Many pistachio growers have begun experimenting with ground covers to act as a trap crop or shelter for beneficial insects and spiders to improve control of hemipteran pests, their natural enemies, and to determine whether the kinds and numbers of hemipteran pests, their natural enemies, and crop damage are influenced by the presence or absence of vegetative ground cover.

We established large, replicated blocks of cover and no-cover management systems in commercial pistachio orchards. Throughout the 1995 and 1996 season, we measured the development of plant covers and the populations of the hemipteran pests and their natural enemies. Results suggest that migratory pest bugs in the families Miridae (small bug pests, e.g., Lygus) and Pentatomide (e.g., stinkbugs) initially attack plants on the orchard floor, but then move up into the pistachio canopy as the ground vegetation declines in quality. There they attack the developing crop. Parasites and predators, while present, apparently have little effect on this migration. We found that careful attention to ground cover in and around the orchards is one key to effective hemipteran pest management. Therefore, control techniques that should be considered or studied include 1) elimination of all herbaceous vegetation in the orchard, 2) maintenance of cover crops to be used as monitoring strips for hemipteran pests, 3) use of trap crops that are treated with an insecticide to kill migratory hemipterans, 4) use of trap crops combined with the augmentative release of natural enemies, and 5) use of cover crops that are not attractive to hemipteran pests.

Developing an IPM-compatible Technology for Using Semiochemicals and Related Chemicals to Disrupt Foraging of Ants.

Principal Investigator: H. H. Shorey, Entomology, Riverside/Kearney Agricultural Center, Parlier

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 and 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 Accomplishments: Two laboratory bioassays were developed to determine the effect of plant-produced, as well as synthetic, semiochemicals as repellents against foraging workers of Argentine, southern fire, and native gray ants. One was based on the ability of ants to cross barriers of beeswax containing test chemicals and, therefore, only measured olfactory responses. Both permitted construction of dosage/response curves and quantitative measurements of loss of inhibitory activity over time. The olfactory bioassay was used to determine the inhibitory effect of volatiles from 58 different plant species. Volatiles from anise seed, clove buds, and allspice seedpods were among the most repellant. Using the beeswax barrier assay, synthetic chemicals which are components of anise seed, clove buds, and other semiochemical-producing plants were compared to determine chemical characteristics associated with high levels of repellency. Benzene derivatives, especially including three isomers of methoxybenzaldehyde (which are volatiles from anise), were highly inhibitory to foraging ants of all three tested species. Various long-chain alcohols and esters, but not corresponding acids, were highly inhibitory to foraging Argentine ants, but not to the other two species. No more effective plant-banding material than semiochemical plus stickem (as a carrier) impregnated into cotton string was found, although a search for other, more commercially acceptable banding means was made. Most young citrus trees and rose bushes banded with mixtures of the semiochemicals, farnesol and methyl eugenol, plus stickem, impregnated in cotton string, were killed. The semiochemicals are sufficiently phytotoxic that means will have to be developed to keep them from direct contact with plant stems.

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