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Annual Reports

1995UC IPM Competitive Grants Program

Cultural Controls

Cultural control methods include a broad range of normal management practices that can be modified or manipulated to manage one or more pest problems. Such factors as crop rotation, tillage, timing of planting and harvesting, cover crops, choice of plant cultivar and animal strains, fertilizer or irrigation practices, tail water and waste management, sanitation, solarization, and postharvest treatment of a commodity all have significant influences on pest species prevalence, development, damage, and survival. Relatively small changes in even one practice, e.g., the early harvesting of almonds, can have significant impacts on pest damage.

Proposals submitted for the cultural control area of research must include a description of how proposed new practices would be integrated into the current production system. If current production practices must be altered to ensure the successful adoption of the research, these changes should be outlined. All projects must be designed to produce practical guidelines, tools, and methods by the end of the project. Investigators should describe how the methods or tools will be implemented in the field. The IPM Project does not fund development or screening of resistant cultivars.


New Projects Funded for 1995-96
Continuing Projects Funded for 1995-96
Projects that Ended in 1994-95
Final Reports for Projects that Ended in 1994

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New Projects Funded for 1995-96

Reduced Herbicide Rates at Layby

Trifluralin application at varying rates across the bed for layby weed control. (Year 1 of 2; $10,452)

Principal Investigators: W. T. Lanini, Vegetable Crops, Davis; T. S. Prather, UC IPM Project, Kearney Agricultural Center

Objectives:
Evaluate reduced rates of trifluralin applied at layby, relative to standard constant rate applications in processing tomatoes, and their impact on weed control, weed seed production, tomato yield, tomato quality, and economics.

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Continuing Projects Funded for 1995-96

Water/Nitrogen Management Reduce Hull Rot

Effect of nitrogen fertilization and deficit irrigation of hull rot of almond. (Year 3 of 3; $14,004)

Principal Investigator: B. L. Teviotdale, Plant Pathology, Davis/UC IPM Project, Kearney Agricultural Center

Objectives:
Determine the effects of deficit irrigation and nitrogen fertilization on incidence and severity of hull rot disease of almond.
Summary of Progress: Hull rot disease may be caused by either of two fungi, Monilinia fructicola or Rhizopus stolonifer. Spores of the fungi enter the almond fruit through the natural opening of the hull after it splits during the ripening process. Infections of the hull tissues result in the production of a toxin which is transported from the hull into the shoots and leaves where it kills these tissues. The edible nutmeat is not harmed but fruiting wood is destroyed and future yields compromised. No chemical treatments are available to control the disease, and cultural practices have long been suspected of affecting hull rot incidence. We are investigating the effects of two cultural practices - irrigation and nitrogen fertilization - on this disease.

The experiment compared the normal 39 inches of water (the control) to three deficit amounts (34, 28, and 22 inches) of water per season. Within each of the three deficit groups, the deficit was applied as a constant reduced portion of the normal in one treatment (85, 70 or 55 percent of normal) and as shorter intervals of 50% reduction of normal in the other two treatments. We inoculated fruit in the control and two each of the 34 and 28 inches water deficit irrigation groups with M. fructicola and R. stolonifer, monitored the moisture content of the hulls, observed the loosening of the hull from the fruit stem, and evaluated natural incidence of hull rot at harvest. We found that the amount of hull rot decreased with decrease in water and that a 50% reduction of applied water during a single two week period reduced the amount of hull rot by more than half. Hull moisture content also decreased with decreasing water and hulls loosened from the fruit stem more rapidly in the drier water treatments.

The nitrogen experiments entailed application of 500, 250, 125 and 0 lbs nitrogen per acre per year since 1989. We performed the same inoculation experiments described above for the irrigation experiment. The natural incidence of hull rot increased with increasing amounts of applied nitrogen. Unlike previous years, this relationship was not found in our inoculation treatments. Hull split was delayed in the high nitrogen treatments thus we were unable to inoculate fruit in all treatments on the same date. M. fructicola caused more leaf death than did R. stolonifer in this and the irrigation experiment.


IPM for Yellow Starthistle

Using subterranean clover with sheep grazing and mowing to control yellow starthistle in pastures. (Year 3 of 3; $11,967)

Principal Investigators: W. A. Williams, Agronomy and Range Science, Davis; D. W. Pratt, UC Cooperative Extension, Solano County

Objective:
Develop an effective long-term control program for yellow starthistle using an integrated approach of subclover establishment, sheep grazing, and mowing.
Summary of Progress: Previous research has demonstrated that controlled grazing and timed mowing are useful methods for managing many yellow starthistle infestations. However, to obtain long-term control it is necessary to establish replacement vegetation that has the ability to persist. Our two experiments are designed so that the final results will be applicable to both pastures and nongrazed areas. In one experiment the treatments are subclover seeding with grazing and mowing, grazing and mowing with no subclover seeding, and a control, with no subclover, grazing or mowing. In the seeded paddocks we grazed three times (February 1, March 13, and May 18) and mowed once (July 1). In the unseeded paddocks we grazed twice and mowed once. The treatments in the second experiment are subclover seeding with mowing, mowing with no subclover seeding, and a control, with no subclover or mowing. We mowed three times (February 5, June 8, and July 27) in the seeded paddocks and twice in the unseeded paddocks. The later mowings in both treatments were targeted to starthistle's early flowering stage and regrowth. In both experiments starthistle suppression was excellent in all treated plots. Both seeded and unseeded plots had very low amounts of starthistle remaining. Next year we will be able to comment on subclover's effectiveness as a competitor against starthistle since we had excellent regeneration this past fall.


Fertilizer/Bacteria Relationships in Trees

Control and exploitation of exogenous bacterial 3-indoleacetic acid production to reduce pesticide inputs to tree crops.(Year 2 of 3; $28,890)

Principal Investigators: S. E. Lindow, Environmental Science, Policy, and Management, Berkeley; G. McGourty, UC Cooperative Extension, Mendocino County; N. O'Connell, UC Cooperative Extension, Tulare County

Objectives:
Determine the rates and form of nitrogenous fertilizers that will most effectively interfere with bacterial IAA production on trees, thereby reducing fruit russeting of pear and apple.
Determine the fraction of IAA-producing strains on pear and apple tissues in different locations whose biosynthesis of IAA is repressed by nitrogenous compounds.
Determine the efficacy of IAA-producing bacteria in inhibiting drop of navel orange fruit from trees and retention of buttons of lemon fruit in storage.

Summary of Progress: Three different nitrogenous compounds were sprayed onto pear trees weekly for three weeks starting at petal-fall to determine their ability to reduce pear fruit russeting. Nitrogenous compounds were applied both to trees inoculated with a strain of capable of producing 3-indoleacetic acid (IAA) in culture, as well as to trees naturally colonized by IAA-producing bacteria that appear to be common incitents of fruit russet. In both studies the severity of fruit russet was reduced from 3- to 4-fold by foliar sprays of either ammonium sulfate, calcium nitrate, or urea. No significant difference in control of fruit russet was observed when either 200 or 400 ppm solutions of these materials were applied, suggesting that the low rate is sufficient to inhibit IAA production on trees as was observed in culture. No significant increase in the total bacterial population size, nor of populations of particular species such as the fire blight pathogen, Erwinia amylovora , or of ice nucleation active bacteria was observed on trees treated with nitrogenous compounds, suggesting that bacterial population sizes were limited by environmental extremes and/or carbon availability rather than by the abundance of nitrogenous compounds on this species. Collections of IAA-producing bacteria have been made from untreated apple, pear and navel orange trees during 1994; the strains are being evaluated for the pathway by which they produce IAA and whether IAA-production in the strains is always inhibited in the presence of ammonium ions or other nitrogenous compounds. Navel orange trees, while having a much lower total bacterial population size than apple and pear, appear to support a higher frequency of bacterial strains that produce IAA in culture. While the majority of IAA-producing bacteria on pear and apple resemble E. herbicola , the majority of IAA-producers on navel orange are non-pigmented enteric bacteria with substantial differences from E. herbicola. Mixtures of IAA-producing strains of Pseudo monas fluorescens, E. herbicola and unidentified bacteria from navel orange have been sprayed onto the foliage and fruit of navel orange in trials initiated in November, 1994 in an effort to enhance fruit retention in the spring. The bacterial mixtures were applied both in water alone and in a nutrient solution composed of sugars and the amino acid tryptophan; bacterial population sizes are higher on citrus leaves receiving nutrient sprays in addition to the bacterial mixtures, suggesting that bacterial colonization of citrus leaves is more limited by nutrient availability than on other crop plant species such as pear.


Reducing Disease in Potatoes with Drip Irrigation

Integrated management of potato diseases with drip irrigation. (Year 2 of 3; $9,666)

Principal Investigators: G. T. Browne, UC Cooperative Extension, Kern County; R. M. Davis, Plant Pathology, Davis

Objectives:
Examine effects of drip irrigation as compared to sprinkler irrigation on development and integrated management of several potato pests and diseases in California.
Evaluate efficacy of drip applications of metham sodium as compared to sprinkler applications of the material.
Measure microclimate parameters under drip and sprinkler irrigation and use published information to evaluate environmental effects of the differential irrigation methods on pests and diseases.
Evaluate the potential cost effectiveness of drip irrigation as a tool in integrated pest management of potatoes.
Summary of Progress: Equipment was secured for monitoring of wetness and temperature conditions under drip and sprinkler irrigation practices. Surface and subsurface drip irrigation systems have been installed in various configurations for comparisons with conventional sprinkler irrigation at the Shafter Research Station. Research on effects of the irrigation methods on crop microclimate and disease management will formally begin with the cropping season in February 1995.

Some preliminary experiments have been completed. Efficacy of preplant chemigation was compared between drip and sprinkler systems. Each of the irrigation systems was used to apply metham-sodium (Vapam, 57 gal./A in 2 in. of water) to plots in which sclerotia of Sclerotium rolfsii were buried at various positions after plant beds were formed. The inoculum was retrieved after chemigation to determine viability of sclerotia (and effectiveness of chemigation). Conventional sprinkler chemigation with metham eradicated inoculum more effectively under furrows than within plant beds; the reverse was true for subsurface and surface drip chemigation in single-row beds. Subsurface drip chemigation of double-row beds (one drip line per two-row bed) was relatively ineffective. After planting of potatoes and infestation of soil with additional inoculum of S. rolfsii, subsurface drip irrigation resulted in reduced incidence and severity of stem and tuber rot as compared to results with surface drip and sprinkler irrigation. Reductions in stem and tuber rot with subsurface drip irrigation were correlated with reduction in moisture level near the soil surface. Yield and water use efficiency were improved for variety Russet Norkotah by single-bed subsurface drip irrigation as compared to conventional sprinkler irrigation.

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Projects that Ended in 1994-95

Nematode Resistant Cultivars

Effectiveness of heat stable and heat sensitive root-knot nematode resistance genes in desert vegetable production.

Principal Investigator: P. A. Roberts, Nematology, Riverside

Objectives:
Determine the effectiveness of root-knot nematode resistance genes, which are known to differ in sensitivity to high temperature (heat stable or heat unstable), for protecting selected vegetable crops from nematode infection under hot desert production conditions.

Summary of Progress: In attempts to determine the potential for using host plant resistance to control root-knot nematodes in desert vegetable production systems, a selection of cultivars and lines of several vegetable crops known to have root-knot resistance genes are being tested in field and controlled-environment conditions. In four field experiments, 16 plant types representing tomato, carrot, common bean, cowpea, Lima bean, and pepper have been compared in split plots with or without nematode inoculum. Plants were assessed for their tolerance to infection based on top growth, and their resistance based on the ability of nematodes to reproduce in and to gall the root systems. Two experiments were started in late September, one located in the hot Coachella Valley and the other in the coastal Tustin area. Two other experiments were conducted in spring-early summer at the Coachella site, one in 1993 and one in 1994. Almost all of the resistant selections remained effective even under the desert spring growing conditions, where early season soil temperatures in the root zone were at or above 28-30°F (82-85°F). These temperatures are known to cause some breakdown in nematode resistance in some crops. Resistant carrot and Lima bean were found to be quite susceptible under these desert temperature regimes. That these temperatures did not induce loss of resistance in most genotypes suggests that fluctuating (day-night variation) high soil temperatures may not cause resistance breakdown as found with constant high temperature. The resistance in the various plant types was effective in the cooler Tustin location and desert fall planting as expected. Susceptible Henderson Lima bean planted after the vegetable treatments is a useful bioassay for indexing effects of resistance on nematode population change across all crop plots. Screening of the resistant plant selections with the same nematode isolates in controlled-environment chambers at high and moderate temperatures has verified the fiel d results of temperature effects on resistance. Field experiments are being repeated at both sites in the 1995 spring-early summer growing season for final validation of seasonal soil temperature effects on resistance expression.


Robotic Weed Control

Development of a computer vision system for weed detection and control.

Principal Investigators: D. C. Slaughter, Biological & Agricultural Engineering, Davis; P. Chen, Biological & Agricultural Engineering, Davis; R. F. Norris, Agricultural Botany, Davis

Objectives:
Develop the basis for an intelligent weed removal machine by transferring and building upon recent advances in computer vision technology, knowledge-based decision theory, and robotics.
Develop a computer vision system that can distinguish between processing tomato plants and weed plants in the seedline to allow automated control of weed plants located between crop plants.
Summary of Progress: An off-line computer vision algorithm to automatically distinguish between tomato plants and weeds was developed. Results indicate that computer recognition of plants is more accurate when no portion of the plant is hidden by other plants and that tomato plants at the cotyledon to first true leaf stage, were easiest to identify because tomato plants at these stages were less likely to be hidden by other plants. Results from real-world images collected in commercial processing tomato fields indicate that the new computer vision algorithm is capable of correctly locating and identifying the tomato plants between 60% and 70% of the time, while mistakenly identifying weeds as tomato plants less than 3% of the time.


Nematode in Easter Lilies

Cultural techniques to reduce groundwater contamination in the easter lily cropping system.

Principal Investigator: B. B. Westerdahl, Nematology, Davis

Objectives:
Determine the population dynamics of the lesion nematode, Pratylenchus penetrans, on Easter lilies and pasture and the feasibility of using fallow as a management technique.
Determine if hot water treatments of Easter lily planting stock can replace chemical treatments of soil.
Evaluate the relative host status of 22 rotation crops for Easter lilies.

Summary of Progress: Easter lilies have been the most important crop in Humboldt and Del Norte counties since the early 1940's. This is the only area of the United States in which Easter lilies are grown commercially. Approximately 600 acres of lilies are grown each year in a three to six year rotation with pastures for cattle and sheep grazing; so that approximately 6,000 acres are part of the cropping system. The industry is the area's largest employer and very important to the local economy. Yearly farm gate value of the crop is approximately five million dollars. Bulbs are sold to greenhouse operations for forcing to produce flowering plants for sale each Easter. The finding in 1982 that groundwater had been polluted by nematicides which had been applied to control the crop's major pest, the lesion nematode, Pratylenchus penetrans, has had significant adverse impacts on both the water consumers of these counties and on the bulb industry. Since this finding, growers have used other chemicals for nematode management.

Basic principles of nematode control dictate that effective management requires a combination of clean planting stock and clean soil as well as an understanding of the biology of the pests involved. It makes little sense to clean up the soil only to reinfest it with infected plant material. Likewise it makes no sense to clean up the planting stock only to plant it in infested soil where it will immediately become recontaminated.

This project is examining the feasibility of hot water treatment to kill nematodes in the planting stock, determining the length of time land would need to be left fallow for nematodes to starve to death, and testing the relative host suitability of various pasture crops to minimize nematode reproduction during crop rotation. We have determined that hot water treatments do have promise for reducing nematode numbers without harming lily bulbs and are determining the optimum times and temperatures for these treatments. We have shown that lesion nematodes can persist in fallow soil for at least two years and have preliminary evidence that several pasture crops support significantly less nematode reproduction than a number of others tested.

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Final Reports for Projects that Ended in 1994

Suppressive Soil for Fungus Control

Development of an integrated pest management system to control ornamental and vegetable bedding plant seedling and root diseases.

Principal Investigators: J. G. Hancock, Entomology & Microbiology, Berkeley; A. H. McCain, Entomology & Microbiology, Berkeley

Summary of Accomplishments: In separate experiments in commercial glasshouses in Elkhorn and Salinas, the incidence of carnation wilt caused by Fusarium oxysporum f. sp. dianthi was reduced consistently up to 40% when methyl bromide treated bedding soils were amended with small amounts of a soil from Soledad. Results of two experiments indicate that suppressive qualities in this soil can be transmitted to a sterilized compost and that a filtered extract of the suppressive soil (SS) imparts suppressiveness when applied to fumigated bedding soils. In contrast to results with SS, amendments of bedding soils with sewage sludge or composted sludge alone increased disease whereas crabmeal and the biological control agents Mycostop and Blue Circle Strain A had no effect on disease progress. Adaptations of SS for control of Fusarium wilt in commercial settings are promising, especially uses of the findings that suppressiveness can be transmitted to sterilized composts and be filtered.

Nonchemical methods for reducing seedling diseases in the vegetable and ornamental transplant industry were tested, including SS, composts and selected biologicals. Testing was centered on Blue Circle Strain A (Pseudomonas cepacia), which was found to be most effective against Rhizoctonia and Pythium root diseases of cauliflower when seedlings were grown in vermiculite inoculated with the agent prior to transplanting into pathogen-infested potting mixes or sandy soil. Overall effectiveness of Strain A against Rhizoctonia solani root diseases of vegetables was judged significant but modest. Other promising biological control agents (Streptomyces sp. S 57, Trichoderma harzianum, Pythium oligandrum, composted sewage sludge and garden waste) and raw soils did not retard Rhizoctonia seedling diseases or were not as effective as Strain A. Preliminary tests with a soil that is strongly suppressive to Rhizoctonia diseases showed that disease suppression did not transmit to peat-based potting mixes. These results indicate that Blue Circle Strain A is a promising control agent for seedling diseases in the bedding plant industry.


UV Treatment of Recirculated Wastewater

Management of fungal root pathogens in recycled irrigation water.

Principal Investigator: J. D. MacDonald, Plant Pathology, Davis

Summary of Accomplishments: Many nursery and glasshouse growing facilities in California have been required to sharply limit discharges of irrigation wastewater. Regulations limiting effluent runoff have been adopted primarily to prevent nitrate-laden leachates from contaminating surface or groundwater resources, and also to force greater water conservation. While the need to conserve water and prevent the pollution of drinking water resources is clear, wastewater recirculation introduces a significant risk of spreading plant pathogens within affected nurseries.

In surveys of recirculating systems at several commercial nurseries, we found that irrigation effluents contain large numbers of fungal propagules. Some of the fungi in recirculated water are known to be plant pathogens, and we have detected them in the irrigation water being applied to crops. In effect, plants are being inoculated with pathogenic fungi each time they are irrigated with recycled water. Experiments showed that daily irrigation of healthy plants with artificially- or naturally-infested water caused substantial root infections within 10 weeks.

Experiments with two root-infecting fungi frequently detected in irrigation water showed that spores suspended in distilled water were killed following relatively brief exposure to UV radiation, or low concentrations of chlorine or ozone. However, when spores were suspended in nursery effluent water, which contains soil particles and organic impurities, treatment efficacy was significantly reduced. Treatment dosages or contact times had to be increased by a factor of 2-10, depending upon water quality. Under such conditions, we found a UV-emitting excimer laser to have greater efficacy at high throughput capacity than a commercial UV water purifier. A simple baiting-ELISA method, utilizing commercially-available test kits, was developed to help growers detect one of the most common and important root pathogens in irrigation water.


User Friendly Nematode-Host Database

Host status of crop and weed species to plant-parasitic nematodes in California: Development and release of a PC/Mac-platform database.

Principal Investigators: H. Ferris, Nematology, Davis; E. P. Caswell-Chen, Nematology, Davis

Summary of Accomplishments: Since 1992 we have been developing a database that provides accessibility to information on the host status of plants to nematodes in a format that is easily usable by our clientele. The database allows selection of non-host crops and determination of the availability of resistant cultivars for species and races of plant-parasitic nematodes. It allows rapid search of the available knowledge base for novel species of crops or cover crops that warrant testing in a cropping systems for their effect on resident nematode populations.

Our initial emphasis was the assembly of information on the nematodes and crops of California (1992-93). Since then we have taken a more global perspective and recognize the power of that approach. Search of the database reveals native plant species in various parts of the world that are listed as resistant or non-hosts to nematode species that are, at least nominally, the same as important California pests. That prompts testing of novel plant species or cultivars as cover or rotation crops in California agriculture.

As of January, 1995, there are 35,540 records from 70 countries which include information on 5,030 plant taxa identified at the genus, species or variety level and 688 nematode taxa identified at the genus, species or race level. That information has been extracted from 3,295 articles published over the last 90 years in six journals that deal primarily with plant-parasitic nematodes and in widespread reports assembled in earlier compilations of host records. The extractions are not yet complete and there are data in several other important sources that need to be assembled.


Hosts for Root Knot Nematodes

Management of root knot nematode through crop rotation with agronomic crops.

Principal Investigator: M. V. McKenry, Kearney Agricultural Center

Summary of Accomplishments: A host-suitability list for 47 annual-type crops in the presence of 13 field populations of root knot nematode was developed. Seven of the plants are identified as relative nonhosts. These include two species of Velvetbean, Piper Sudan Grass, Merced Rye, Mesi Daikon, Black-Eyed Susan Daisy, and Cowpea #5.

Although this work confirmed previous work that gel electrophoresis provides repetitive and stable identification of the dominant species in a population, host preferences of any field population were found not to be predictable based on a species determination. One may actually have a better chance of predicting nematode buildup based on a host suitability list such as the one developed here. However, there are too many different plant varieties and root knot nematode populations to ever develop an adequate listing.

Root knot nematode juveniles present within chopped cucurbit roots or peach roots become immobilized and largely ineffective presumably due to leachates also released by the roots. One result is that estimates of nematodes/gram of root tissue from these crops is greatly underestimated if a mist chamber is used for the extraction process. The planting of cucurbits followed in four to eight weeks by rotovation and a two or three inch irrigation should be evaluated as a new method of nematode management.

The six most aggressive root knot populations come from sites where perennials (e.g. alfalfa or grape) were in the recent planting history. Aggressive populations are those which develop to higher final populations on a wide variety of hosts. A measurement of population aggressiveness seems to have more practical value than does population speciation.

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