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Annual Reports

1996UC 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.

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

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New Cultural Control Projects Funded for 1996-97

COMBATING STAR-THISTLE

Using subterranean clover with combinations of mowing and sheep grazing to control yellow starthistle. (Year 1 of 1; $18,600)

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

Objectives: Develop an effective long-term control program for yellow starthistle using integrated approaches of subterranean clover plantings, mowing, and sheep grazing in pastures and ungrazed areas.



MULCHES FOR CONTAINERS

Photo of Cheryl Wilen
Cheryl Wilen, shown here, is working with Ursula Schuch to evaluate mulches and other alternative weed controls for ornamentals grown in containers. (Photo by Marcella Grebus)
Controlling weeds in containers with mulches and method of irrigation. (Year 1 of 2; $10,000)

Principal Investigators: U. Schuch, Botany and Plant Sciences, Riverside; Cheryl Wilen, UC IPM Project, San Diego County

Objectives: Identify which single treatment or treatment combinations of herbicide, mulch, and irrigation will result in maximum weed control without negative impacts on plant growth.

Evaluate three organic mulches for their potential to control weeds in container plants and their effects on plant growth.

Examine how two methods of irrigation affect weed control and herbicide efficacy.

Determine the potential for weed control in containers using a plant-based herbicide (corn gluten meal) by comparing it to a traditional, registered herbicide



THRESHOLD FOR CYST NEMATODE

Developing damage/economic thresholds for sugarbeet cyst nematode on cole crops. (Year 1 of 3; $25,289)

Principal Investigators: B.B. Westerdahl, Nematology, Davis; E.P. Caswell-Chen, Nematology, Davis

Objectives: Develop damage/economic thresholds for sugarbeet cyst nematode on cole crops.



ROTATION FOR VERTICILLIUM WILT

Rotation with broccoli to target Verticillium wilt control: A potential alternative to soil chemical fumigants. (Year 1 of 2; $10,000)

Principal Investigators: K.V. Subbarao, Plant Pathology, Davis; R.M. Davis, Plant Pathology, Davis

Objectives: Determine the effects of a broccoli crop on the dynamics of Verticillium dahliae microsclerotia in soil.

Determine the interactive effects of broccoli residue incorporation, irrigation methods, and water regimes on the dynamics of V. dahliae microsclerotia and incidence of Verticillium wilt on cauliflower.

Determine the threshold number of microsclerotia below which Verticillium wilt does not occur on cauliflower.

Elucidate the mechanisms of broccoli-mediated pathogen suppression..

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Continuing Projects Funded for 1996-97

FERTILIZER/BACTERIA RELATIONSHIPS IN TREES

Control and exploitation of exogenous bacterial 3-indoleacetic acid production to reduce pesticide inputs to tree crops. (Year 3 of 3; $27,922)

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

Objectives: Determine the rates and form of nitrogenous fertilizers that will most effectively interfere with bacterial indoleacetic acid (IAA) production on trees, thereby reducing fruit russetting 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 3 weeks starting at petal fall to determine their ability to reduce pear fruit russeting. Nitrogenous compounds were applied to trees naturally colonized by IAA-producing bacteria that appear to be common incitants of fruit russet. The severity of fruit russet was reduced about two-fold by foliar sprays of either ammonium sulfate, calcium nitrate, or urea. The reduction of fruit russet was similar irrespective of whether either 100, 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. Applications of nitrogenous compounds made 2 or 3 weeks after petal fall caused a greater reduction than sprays made at earlier times.

While not significantly different, like in 1994, urea and ammonium sulfate were more effective in reducing fruit russet than calcium nitrate. No significant increase in the total bacterial population size nor of populations of particular species, such as ice nucleation active bacteria, was observed on trees treated with nitrogenous compounds in most plots, 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.

All of the IAA-producing bacteria collected from untreated apple, pear and navel orange trees during 1994 are inhibited in IAA production in the presence of ammonium ions in culture. 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. Mixtures of IAA-producing strains of Pseudomonas fluorescens, E. herbicola, and a mixture of unidentified bacteria from navel orange sprayed monthly onto the foliage and fruit of navel orange from November 1994 to March 1995 delayed the time when fruit dropped from trees, particularly when nutrients were added to bacterial inoculum.

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. Modest reduction in the frequency of button abscision of lemon was observed on fruit treated with a bacterial suspension in the presence of nutrients.



REDUCED HERBICIDE RATES AT LAYBY

Photo of Brian Correiar
Student Brian Correiar shows how weeds are sampled in research being conducted by Tom Lanini and Tim Prather to evlauate how herbicide rates can be reduced with layby treatments.
Trifluralin application at varying rates across the bed for layby weed control in tomatoes. (Year 2 of 2; $10,882)

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

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.

Summary of Progress: In processing tomatoes, layby herbicide treatments are soil incorporated, placing the herbicide into the upper soil layers. The incorporation of the layby herbicide dislodges most emerged weeds, thus weeds emerging after this time come from seed or perennial propugales. Tomatoes often produce rapid vegetative growth shortly after layby herbicide treatment, generally in response to the sidedress fertilizer application (applied 1 to 7 days before layby). The tomato canopy can block light, preventing further weed growth, and reducing the need for herbicide near the crop row. The farther from the crop row, the less the competitive effect. Competition from the tomatoes may reduce the need for herbicides. Variable rate treatments were evaluated relative to constant rate treatments at eight locations throughout California. Variable rate applications were made using a five nozzle boom with the center nozzle positioned over the furrow, the outside nozzles positioned near the crop row, and the interior nozzles on the shoulders of the bed. Rates were varied on the boom by changing the nozzle size, with smaller nozzles used near the crop to reduce the quantity of herbicide applied. Some mixing of the treated bands occurred during incorporation.

Variable rate treatments reduced herbicide used by 40% (medium rate) or 60% (low rate-no herbicide put near the crop row) compared to the standard, constant rate. Trifluralin was used in all studies with 0.85 lb/a applied as the standard rate. An untreated control was also included at each site where no herbicide was used, but was cultivated by the incorporator. Tomato yield and quality were not affected by layby treatment; untreated, constant rate, and varying rate treatments all had equivalent yields. Weed density and cover were generally greater on untreated plots compared to other treatments, but did not differ between varying rate and constant rate treatments. Weed seed production was also greater on many untreated plots, but again did not differ between varying rate and constant rate treatments.

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Progress Reports for Projects that Ended in 1995-96

WATER/NITROGEN MANAGEMENT REDUCES HULL ROT

Effect of nitrogen fertilization and deficit irrigation on hull rot of almond.

Principal Investigator: B.L. Teviotdale, Plant Pathology, Davis/Kearney Agricultural Center, Parlier

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.

Irrigation. 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 normal in one treatment (85, 70 or 55% 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. The natural incidence of hull rot decreased with decrease in water, and a 50% reduction of applied water during a single 2-week period at the beginning of hull split reduced hull rot by more than half. Both pathogens responded similarly to the irrigation treatments in inoculation experiments, though M. fructicola caused more hull rot than did R. stolonifer in inoculations. Hull moisture content also decreased with decreasing water, and hulls loosened from the fruit stem and split more rapidly in the drier water treatments.

Nitrogen. 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 as described for the irrigation experiment. The natural incidence of hull rot increased with increasing amounts of applied nitrogen. A similar trend occurred in the inoculation experiments but the response was not as definite, and the two pathogens caused equivalent amounts of hull rot. Hulls tended to split, loosen from the fruit stem, and dry more rapidly in the lowest nitrogen treatment.



REDUCING DISEASE IN POTATOES WITH DRIP IRRIGATION

Integrated management of potato diseases with drip irrigation.

Principal Investigators: G.T. Browne, Plant Pathology, Davis; 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 the information to evaluate environmental effects of the 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 Accomplishments: Sprinkler irrigation and several configurations of drip irrigation were compared at the Shafter Research Station for effects on efficacy of chemigation with metham sodium and effects on development and management of late blight, early blight, southern blight, white mold, root knot nematode, and weeds.

In preformed plant beds, preplant drip chemigation with metham sodium was consistently more effective than sprinkler chemigation with the material for killing sclerotia of Sclerotium rolfsii, but under furrows beside the beds, the sprinkler chemigation was more effective than drip irrigation. On level ground, drip and sprinkler methods of preplant metham sodium chemigation were similar in effectiveness for control of S. rolfsii sclerotia and root knot nematodes.

Comparative effects of subsurface drip and conventional sprinkler irrigation on severity of late blight were inconsistent over 2 years of experiments, given that sprinkler irrigations occurred in early morning, no fungicide was applied, and preplant metham chemigation was applied with resident drip or sprinkler systems. In contrast, incidence and severity of southern blight consistently were lower with subsurface drip irrigation than with sprinkler irrigation. Regardless of irrigation treatment, incidence and severity of early blight was negligible, and no white mold occurred. Similarly, soil sampling indicated that at Shafter no significant populations of root knot nematodes had developed under any of the irrigation treatments. Weed populations were reduced by subsurface drip irrigation as compared to sprinkler irrigation.

The low incidence of southern blight and low populations of weeds were associated with a relatively dry soil surface that resulted from subsurface drip irrigation; the intermittently wet soil surface under sprinkler irrigation favored germination of weeds and infection by S. rolfsii. Soil temperatures occasionally were slightly greater with subsurface drip irrigation than with sprinkler irrigation, but overall, soil temperature, air temperature, relative humidity, and hours of leaf wetness were generally similar in magnitude, regardless of method of irrigation, given that sprinkler irrigations were applied in early morning. It is possible that sprinkler irrigation at other times of day would alter comparative effects of the different irrigation methods on environmental conditions and some diseases such as late blight.

Subsurface drip irrigation of potatoes is technically feasible, but cost-effectiveness is less certain. In 3 years of experimental comparison with conventional sprinkler irrigation, semipermanently buried single-bed subsurface drip tubing delivered water reliably and uniformly, reduced irrigation water requirements (by 17 to 35%), and increased yields of No.1 potatoes (by 13 to 46% with variety Russet Norkotah; by 6 to 27% with variety White Rose). Semi-permanently buried double-bed subsurface drip (one drip line per two potato rows) resulted in similar water savings but no consistent yield improvement. Given current prices, the most effective drip irrigation system would require several consecutive years of use before costs of the system could be offset by increases in yield revenues and reductions of input costs.

Our data suggest that subsurface drip irrigation may be an effective tool for management of southern blight. The practice may also offer several advantages for management of late blight that were not addressed in our experiments.



IPM FOR YELLOW STARTHISTLE

Photo of grazing sheep
A combination of controlled grazing , timed mowing, and seeding of subclover can be used to manage starthistle in pastures.
Using subterranean clover with sheep grazing and mowing to control yellow starthistle in pastures.

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

Objectives: Develop an effective long-term control program for yellow starthistle using an integrated approach of subclover establishment, sheep grazing, and mowing.

Summary of Progress: Our previous research has demonstrated that controlled grazing and timed mowing are useful methods for managing yellow starthistle infestations without herbicides. However, to obtain long-term control it is necessary to establish replacement vegetation that has the ability to persist. We are testing this with two experiments using combinations of seeding, sheep grazing, and mowing in a pastured and ungrazed situations. In the pasture experiment the treatments are (1) subclover seeding with controlled grazing (short duration, high-intensity) and timed mowing, (2) grazing and mowing with no subclover seeding, and (3) a control, with no subclover, grazing, or mowing. The seeded (October 1993) paddocks were grazed on February 7, March 24, and May 26, 1995 and mowed on July 3, 1995. The unseeded paddocks were grazed on March 24 and May 26 and mowed once, July 3, 1995.

The treatments in the ungrazed experiment are (1) subclover seeding with mowing, (2) mowing with no subclover seeding, and (3) a control, with no subclover or mowing. The seeded plots were mowed two times. Mowing on February 11, 1995 was done to enhance clover growth by reducing competition from tall-statured grasses. The second mowing (June 26) was timed to yellow starthistle's early flowering stage. In the unseeded plots we mowed once (June 26), also in yellow starthistle's early flowering stage. Our second year findings are that the seeded plots in both experiments resulted in improved starthistle control compared to other treatments. The best control came from seeding and mowing (3 times in 1994 and 2 times in 1995), where starthistle was essentially eliminated this year.

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Final Reports for Cultural Control Projects that Ended in 1995

ROBOTIC WEED CONTROL

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

Principal Investigators: D.C. Slaughter, Biological and Agricultural Engineering, Davis; P. Chen, Biological and Agricultural Engineering, Davis; R.F. Norris, Weed Science Program/Vegetable Crops, Davis

Summary of Accomplishments: Both off-line and real-time computer vision systems were developed to automatically distinguish between tomato plants and weeds. 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 developed for this study is capable of correctly locating and identifying the tomato seedlings between 60 and 70% of the time, while mistakenly identifying weeds as tomato plants less than 3% of the time.



NEMATODE IPM IN EASTER LILIES

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

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

Summary of Accomplishments: Easter lilies have been the most important crop in Humboldt and Del Norte counties since the early 1940s. 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 3- to 6-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 $5 million. 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 that 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, nor to clean up the planting stock only to plant it in infested soil where it will immediately become recontaminated.

This project determined the feasibility of hot water treatment to kill nematodes in the planting stock, examined the length of time land would need to be left fallow for nematodes to starve to death, and tested 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. Optimum times and temperatures under the conditions of our experiments were 115°F for 90 minutes or 120°F for 45 minutes. We have shown that P. penetrans can persist in fallow soil for at least 3 years. Of the crops tested, fescues (Festuca sp.) were the poorest hosts and clovers were the best hosts.



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

Summary of Accomplishments: The potential for using host plant resistance to control root knot nematodes in desert vegetable production systems was tested in field and controlled-environment experiments using cultivars and lines of several vegetable crops known to have root knot resistance genes.

In five field experiments, 16 plant types representing tomato, carrot, common bean, cowpea, Lima bean, and pepper have been compared in plots with or without nematode inoculum. Plants were assessed for their tolerance to infection based on top growth, and their resistance to nematode reproduction and root-galling.

Two experiments were planted in late September 1992, one in the hot Coachella Valley and the other in the coastal Tustin area. Three other experiments were conducted in spring/early summer at the Coachella site, in 1993, 1994, and 1995.

Most of the resistant selections remained effective even under the desert spring-summer growing conditions in 1993 and 1994, when early season soil temperatures in the root zone were at or above 28° to 30°C (82° to 85°F) on certain days. 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. Resistance in the other crops was not affected probably due to fluctuating (day-night variation) temperature regimes.

In 1995 soil temperatures were above 28°C (82°F) following nematode inoculations, and nematode resistance was broken in tomato and commercial cowpea, as well as in Limas and carrots. Resistance in pepper and some cowpea lines with new resistance remained effective. The field results were supported by the controlled-temperature tests.

Our findings have shown which resistance genes in various crops can be used effectively in desert vegetable systems to manage root knot. This is valuable for implementation of existing cultivars and also for determining which resistance traits should be combined with heat tolerant crop types.

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