1997UC 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 1997-98
WALNUT HUSK FLY LURES
Optimization of lures to predict egglaying by female walnut husk flies. (Year 1 of 1; $9,853)
Principal Investigators: C. Pickel, UC IPM Project, 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.
Field test optimal lure combinations and dosages in two commercial walnut orchards for attractiveness to gravid female walnut husk flies at the critical time when control measures are needed.
WHAT FAVORS LITTLE HOUSEFLY IN POULTRY HOUSES?
Ecology of Fannia spp. (Diptera: Muscidae) in poultry systems. (Year 1 of 2; $23,314)
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.
Integrating crop competitiveness with herbicide applications to improve weed control and reduce herbicide use. (Year 1 of 3; $34,814)
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 selection and seeding rate on the suppressive ability of the crop.
SOIL-WATER FACTORS IN ARMILLARIA ROOT ROT
Spatial distribution and water relations of Armillaria mellea in pear orchards. (Year 1 of 3: $29,459)
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.
EXPERT SYSTEM FOR NEMATODE PESTS
Development of a knowledge-based advisory system as an aid for decision making in nematode management. (Year 1 of 1; $19,984)
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 applications and crop and cultivar selection.
Make the knowledge-based system available via the Internet and World Wide Web.
VEGETATION MANAGEMENT FOR PIERCE'S DISEASE
Management of riparian woodlands for control of Pierce's disease in coastal California. (Year 1 of 1; $21,164)
Principal Investigators: A. H. Purcell, Environmental Science, Policy and Management, Berkeley; J. R. McBride, Environmental Science, Policy and Management
Objectives: This project will test the effectiveness of manipulating the structure and composition of riparian woodlands to reduce populations of Pierce's disease vectors; specifically:
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, its infectivity with the bacterium Xylella fastidiosa, and its dispersal to adjacent vineyards.
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.
Continuing Projects Funded for 1997-98
Summary of Progress: Preliminary results indicate that certain characteristics of plant resistance can be combined very effectively with biological control agents to control Russian wheat aphid (RWA) whereas other plant resistance characteristics are not as effective in both short- and long-term assessments.
Three types of plant resistance were evaluated: (1) antibiosis, (2) tolerance, and (3) reduced leaf curling following feeding by RWA. In antibiosis there were relatively few RWA on plants, and surviving RWA were very small, less than half the size of RWA on the tolerant or susceptible plants. In tolerant plants, RWA were much more abundant and aphids were of normal size. In plants with antibiosis there was practically no leaf curl, and in plants with tolerance there was only a slight curl. Reduced leaf curl is highly significant because it leaves RWA exposed to all predators and parasites whereas curled leaves prevent access of most native predators and parasites to RWA.
From both short- and long-term perspectives, plants with tolerance plus reduced leaf curl were significantly more effective than plants with antibiosis in maintaining low numbers of RWA for the following reasons: (a) plants with antibiosis had few aphids, all greatly reduced in size. Consequently, there was a very low number of suitable hosts for predators and parasites. Tolerant plants allowed a buildup of large numbers of predators and parasites. On tolerant plants, newly introduced, more effective parasites also increased in number to be available to attack RWA in overwintering native grasses where presently there are no effective RWA enemies; (b) tolerant plants combined with large numbers of predators and parasites are more likely to slow up the process of RWA resistance to new plant cultivars.
The buildup of large numbers of predators and parasites on RWA also serves as a field insectary of natural enemies that can then attack other aphids on the same crop or in surrounding crops.
CONTROL BY FIRE
The use of fire to control yellow starthistle (Centaurea solstitialis L.) and enhance native plant diversity. (Year 2 of 3; $15,342)
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 reinfestation 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.
Summary of Progress: Around 1984 yellow starthistle began to spread rapidly throughout the grassland areas of Sugarloaf Ridge State Park, in the northern coast range near Sonoma. In these infested areas, no existing control options were practical or acceptable. In July 1993 and again in 1994, we conducted a prescribed burn of a 30-acre, infested test site when yellow starthistle was in the early flowering stage. In July 1995 the same 30-acre region and an additional 155 acres were burned, and in July 1996 the 155-acre plot and a separate 200 additional acres were burned.
Our results indicate that while a single year of burning does not control yellow starthistle, it significantly increases the relative cover and frequency of native forbs as well as total plant diversity. Two consecutive years of burning, however, gave 68% control of yellow starthistle, and 3 years gave over 90% control while still maintaining high native plant diversity. The effectiveness of a 3-year burn cycle was reflected in a 99.5% reduction in yellow starthistle seeds in the soil. While native perennial grasses were slightly reduced by a single year of burning, they increased by nearly eight-fold with 3 consecutive years of burning.
When the area burned each year from 1993 to 1995 was not burned in 1996, the seed bank of yellow starthistle increased dramatically compared to the previous year. Thus initial measurement suggests that the rate of yellow starthistle reinvasion may be rapid, even after a substantial level of control.
BIOLOGICAL CONTROL OF CITRUS PEELMINER
Bionomics of the citrus peelminer and its parasites in the Coachella Valley. (Year 2 of 2; $16,254)
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 peelminer on citrus, leader, and willow.
Evaluate emergence patterns, temperature thresholds, longevity, survivorship, and levels of infestation of the peelminer and its parasitoids on citrus and oleander in the Coachella Valley.
Evaluate the origin of the peelminer as native or foreign and suggest or develop an appropriate biological control strategy.
Summary of Progress: Over the last few years the citrus peelminer, a species of Marmara (possibly salictella; Lepidoptera: Gracillariidae), reached extraordinary levels of infestation on grapefruit in the Coachella Valley. 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 (stemminer), cotton (stemminer), avocado (fruit- and stemminer), and, questionably, mango (fruitminer). The identity of Marmara on all of these plants has yet to be determined, but initial results suggest it is probably one species with a very 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 fruit damage was below 8%. A population increase in August was quickly controlled by an undescribed native species of Cirrospilus (Hymenoptera: Eulophidae). The parasitoid eventually parasitized over 95% of the peelminers in all of the orchards being sampled, and by the end of September no live larvae were found in plots being monitored for population changes.
WHY DON'T INSECTICIDES ALWAYS WORK?
Agronomic and environmental factors influencing control of cotton aphids with insecticides. (Year 3 of 3; $17,391)
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 populations and their 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. This insect has gone from a minor, sporadic pest (before 1986) to primarily an early season and late season cotton pest (about 1986 to 1992) to a season-long cotton pest (after 1992). Insecticidal control of this pest has been extremely erratic, often necessitating repeated applications. Insecticide resistance from this selection pressure partially accounts for these control failures. However, reduced susceptibility in aphids can also be induced by environmental and agronomic factors.
The effects of four of these factors on cotton aphid susceptibility to insecticides were evaluated in 1996. Field plots were established with cotton plants of four developmental stages, three water status regimes, four nitrogen levels, and four boll loads. Field observations and previous research have shown that all of these factors could be important. Laboratory-reared cotton aphids were placed on these plants and, after 3 weeks of exposure, susceptibility to insecticides from five chemical classes was evaluated. Plant age and boll load influenced susceptibility, as indicated by our laboratory bioassays. However, the differences were very small and probably not of overriding importance from a field control standpoint. In addition, the influence of plant age, plant water status, nitrogen level, and boll load on cotton aphid population development was quantified.
Three of the four factors influenced aphid reproduction. Plant age (more aphids on younger, i.e., later planted cotton), water status (more aphids on adequately watered vs. deficient conditions), and boll load (more aphids on plants with bolls missing from first position sites compared with plants with a full boll load) were found to be important. A four-fold range of population difference was found across the boll load treatments.
Projects that Ended in 1996-97
SHEEP FOR WEED CONTROL
The manipulation of sheep grazing pressure for weed control in seedling alfalfa.
Principal Investigators: C. E. Bell, UC Cooperative Extension, Imperial County; J. N. Guerrero, UC Cooperative Extension, Imperial County
Objective: 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: There appears to be no difference in lamb weight gain between grazing pressure treatments; whether the lambs graze the weedy seedling alfalfa paddock over an extended period of time (12 to 16 days) or they graze the paddock in sections apparently makes no difference in lamb weight gain. If these results remain the same during the second year, they will indicate that the grazier will have to make fewer costly lamb pasture changes to attain the same weight gain. Furthermore, the whole-plot treatment requires less total fencing.
Before grazing, about 60% of the forage dry matter in the experimental paddocks was alfalfa and 40% was weeds. Prior research at this location demonstrated that lambs in a weedy, seedling alfalfa field consume the weeds before they eat the alfalfa. Apparently, these treatments did not differ in their effect on alfalfa weed infestation. Earlier grazing, while the weeds were presumably quite palatable, resulted in a somewhat better job of weed control than grazing mature weeds.
The effects of weeds on seedling alfalfa are transitory. At the first cutting, all grazed paddocks had increased weed control when compared to ungrazed. By the second cutting, there was no difference between grazed and ungrazed paddocks; all were virtually weed-free. Grazing in winter is risky; lambs can do substantial damage to the field if not moved out immediately following rainfall.
Uneaten forage, sampled soon after lambs left the experimental paddock, was also quantified into alfalfa and weed portions. Long-term effects of grazing will be measured by sampling the experimental paddocks prior to the first cutting of the second year.
PREDICTING WEED PROBLEMS
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 Progress: Seeds of the most common weed species were collected at UC Riverside and Kearney Agricultural Center. Germination experiments were conducted on a temperature gradient bar ranging from 15deg.C to 37deg.C using three species at a time from both locations. Four conventional indices and a repeated probit analysis were utilized to determine lower and upper temperature thresholds of germination for each species.
Field experiments were planted in November 1995 and April, July, and October 1996 using the same species in both locations to quantify vegetative and reproductive phenological events. Experiments were planted in a randomized, complete block design with six blocks. Weed species constituted the treatments; nine species were planted in the first experiment, including members of five plant families, and more species were planted in subsequent experiments. Plots were sprinkler- irrigated and unwanted plants were hand-weeded. Data were collected at 2 or 3 day intervals and included times to emergence, 1 to 10 leaves, 1 to 10 branches or tillers, flowering, and first seed set. These event times were converted to cumulative degree-days (C day-1) for each species using the simple sine method, based on daily maximum and minimum temperatures and species-specific temperature thresholds from gradient bar experiments.
This research will generate predictions of weed phenology that can help growers plan management practices to control the greatest number of weeds with the least amount of herbicide, choose the crop planting dates when weed germination is least likely, improve timing of seedling management or seedbed preparation, and exploit the competitive advantage of early crop establishment. Furthermore, accurate weed phenology predictions can assist IPM programs by identifying potential hosts of beneficial insects, alternate hosts of pestilent insects, and hosts of insect-vectored diseases.
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 the second year of this multiyear project we began to experimentally manage riparian vegetation to reduce Pierce's disease in adjacent vineyards while preserving or enhancing environmental attributes of riparian habitats. At the first experimental site, three vegetation management treatments were established: a conifer buffer plot, a plot where vegetation was selectively removed and replanted, and an undisturbed control.
Sticky traps used to monitor blue-green sharpshooter activity showed that sharpshooter (BGSS) activity dropped dramatically where vegetation had been removed and replaced. This is not surprising because replanted trees were very small in the area where vegetation had been removed. Buffer-strip plantings of Douglas fir had no effect on BGSS abundance or movements into adjacent vineyards, as expected for this early in their growth. One new experimental site, along the Napa River near Yountville, was approved for addition to the project and selective clearing of vegetation was begun. The second new site, along Mayacamas Creek in Sonoma County, will be added to the project next year. Transplanted hardwood seedlings established in cleared areas at favorable survival rates, but extensive direct seeding is planned for planting new sites.
Increased community involvement and support was encouraged by activities of the Napa 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 established at UC Berkeley as a forum for regional and international information and communication on Xylella diseases.
MONITORING MITES ON HENS
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 Progress: We are trying to test the practicality of 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. Direct hen sampling using the preexisting sequential sampling plan works well, particularly for assessing the effectiveness of an acaricide application. Mites on any particular hen do not relate strongly to mites on the hen which laid the egg. Mites apparently do not get on the egg as it is laid. Rather, 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. RaVap treatments at the study ranch 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 feather penetration problems are preventing really 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. Presence of mites on eggs, while less sensitive than direct hen examination, appears to be a good indicator of both the distribution of mites in the houses and the intensity of general infestation.
Visual mite scores by three experienced individuals were highly correlated with each other and with actual infestation scores derived by removing infested feathers and extracting mites. Very low-level infestations (<10 mites) were overlooked fairly often by one or more of the observers. Mite scores consistently underestimated mite numbers relative to actual numbers of mites on the hens; estimation errors of mite numbers often (40% of the time) exceeded 10-fold.
GROUND COVERS: HELP OR HINDRANCE FOR TRUE BUGS?
Manipulation of orchard-floor vegetation for control of hemipteran pests of pistachio.
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 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.
To improve control of hemipteran pests, many pistachio growers have begun experimenting with ground covers to act as a trap crop or shelter for beneficial insects and spiders. Our first objective was to determine whether species composition and population densities of the hemipteran pests were influenced by the presence or absence of vegetative ground cover. To determine the effects of these practices we established large, replicated blocks of cover and no-cover management systems in commercial pistachio orchards. Throughout the 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 of the families Miridae and Pentatomidae initially attack plants on the floor upon invading the orchards but then move up into the canopy as the ground vegetation declines in quality where they attack the developing crop. Parasites and predators, while present, apparently have little effect on this migration. The main implication of these findings is that careful attention to ground cover in and around the orchards is the 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
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 laboratory bioassays are used 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 is based on the ability of ants to cross barriers of beeswax containing test chemicals; the other is based on repellency of ants to airborne chemicals and, therefore, only measures olfactory responses. Both permit 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 repellent. Using the beeswax barrier assay, synthetic chemicals that are components of anise seed, clove buds, and other semiochemical-producing plants are compared to determine chemical characteristics associated with high levels of repellency. Benzene derivatives, especially including three isomers of methoxybenzalde-hyde (which are volatiles from anise), are highly inhibitory to foraging ants of all three tested species. Various long-chain alcohols and esters, but not corresponding acids, are highly inhibitory to foraging Argentine ants, but not the other two species.
No more effective banding material than semiochemical plus stickem (as a carrier) impregnated into cotton string has been found, although a search for other banding means continues. Most young citrus 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.
Final Reports for Projects that Ended in 1996
CONTROLLING CRABGRASS WITH LESS HERBICIDE
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/Santa Clara counties; M. Rejmanek, Evolution and Ecology, Davis
Summary of Accomplishments: Smooth and hairy crabgrass are common summer weeds in turfgrass in California. Preemergence herbicides are often used annually at rates from 3 to 10 lb/acre for season-long control. We evaluated 10 new tall fescue cultivars by planting in the spring or fall for their ability to exclude smooth and hairy crabgrass during the summer months. We also evaluated how large a gap (hole) is required in the turf for invasion of crabgrass to occur.
There was a range of vigor and growth differences between cultivars. 'Fawn' tall fescue is an old cultivar with seedling vigor but as the stand matures crabgrass seedlings germinate and establish. 'Bonsai' tall fescue is a very dwarf cultivar that has low seedling vigor and grows less during the season (less vigorous), allowing smooth crabgrass to establish in low numbers. The remaining cultivars were all vigorous and reduced crabgrass germination and establishment equally.
Fall plantings of tall fescue were more effective than spring plantings in controlling both crabgrass species the first season. All cultivars except 'Fawn' and 'Bonsai' cultivars reduced crabgrass over 95% when the turf was planted in the fall. Crabgrass stands ranged from 5 to 35% of the turf when planted in spring. The following year, however, after the turf had an opportunity to establish, crabgrass populations were less than 5% with all cultivars. Following the turf stand for 3 years, crabgrass was not a problem weed in the turf at the end of the study period.
A gap or hole of 4 inches (10 cm) of bare soil is required for smooth crabgrass to germinate and establish in turf-type tall fescue turf. A gap size of 8 inches (20 cm) is required for large crabgrass to establish. If the turf is scalped once, then allowed to regrow, a gap size of 8 inches is required before smooth crabgrass will establish. Large crabgrass will not establish in turf that has been scalped a single time. When the turf was cut repeatedly at a height of 3/4 inch, a gap size of 4 to 6 inches (10 to 20 cm) is required for smooth crabgrass to establish.
Over-seeding 'Olympic' tall fescue in fall in a smooth crabgrass site with 5 or 10 lb/1000 sq. ft. and mowing the turf at 3 inches reduced smooth crabgrass as much as an application of preemergence herbicide when evaluated 2 years after planting.
SPIDERS AND GRAPE IPM
Effects of spiders on pest populations in vineyards: Determining their role in grape IPM.
Principal Investigators: K. M. Daane, Center for Biological Control, Berkeley; M. J. Costello, UC Cooperative Extension, Fresno County
Summary of Accomplishments: To better understand the ecology of the vineyard spider complex, we refined a sampling method to estimate spider species composition and abundance in vineyards. Three sampling methods were evaluated: (1) beat and shake onto a drop cloth, (2) beat and shake into a cloth funnel, and (3) D-vac (insect vacuum). 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.
The use of cover crops is popularly associated with the attraction of beneficial insects and lower pest densities. However, the role of cover crops in vineyard IPM is not well understood and studies in vineyards have not shown consistently lower pest densities in cover cropped vineyards. We tested the hypothesis that ground covers increase spider abundance on the vines, leading to lower leafhopper densities. We found no evidence that the total spider population was consistently increased on vines in cover cropped plots.
Although cover crops rarely affected total spider numbers, cover crops can influence the relative abundance of the spiders. For example, in one vineyard the abundance one spider (Trachelas pacificus) was 60% higher in August and September in plots with ground covers. Spider species composition is important because each species will impact pest populations differently. In laboratory studies, Trachelas ate ~12 leafhopper nymphs per day while other common spider species ate <2 nymphs per day. Of course, overall predator abundance in cover cropped vineyards (cover crops and vines) increased because many predators reside in the cover crop. However, our results suggest that there is little movement between cover crops and vines, and therefore the cover crops do not provide an important alternate habitat for vine dwelling spiders. The addition of cover crops often resulted in a statistically significant reduction in late-season leafhopper nymph abundance. In most instances the level of reduction was not economically important (commonly near 15%). Because there was not a consistent increase in predator numbers in cover cropped plots, we believe the change in pest density is partly attributed to changes in vine condition. Ground covers that are managed season-wide can compete with the vines for water and nutrients and, under some circumstances, the resulting reductions in vine vigor will lower leafhopper numbers.