Annual Reports

1998—UC 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.

All projects must be designed to produce practical guidelines, tools, and methods by the end of the project. Investigators must have a plan for how the methods or tools will be implemented in the field and how proposed new practices would be integrated into the current production system.

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: M. McGiffen, Botany and Plant Sciences, Riverside

Objectives: Quantify light interpretation, growth, and other ecophysiological processes related to varietal tolerance of weeds.

Derive INTERCOM model parameters for H8892, Boss 3155, and 145B-7879 tomato varieties and black nightshade.

Validate model for processing tomato and black nightshade.

Use sensitivity analysis to evaluate characteristics that confer varietal tolerance.

Principal Investigator: J. M. Duniway, Plant Pathology, Davis

Objectives: Characterize Verticilliam dahliae populations in strawberry cropping systems in California for biological diversity (vegetative compatibility) and variation in virulence on main strawberry cultivars.

Determine the relationships between inoculum of V. dahliae in soil and Verticillium wilt development in strawberry.

Evaluate effects of organic amendments on population dynamics of V. dahliae in soil and Verticillium wilt in strawberry.

Principal Investigators: L. D. Godfrey, Entomology, Davis; R. Hutmacher, Agronomy and Range Science, Davis/UC Cooperative Extension, Shafter Field Station

Objectives: Study the life history of cotton aphids in California, including host plants/weeds utilized, population buildup in crops other than cotton, overwintering strategy, presence of a sexual stage, and other aspects of the life cycle.

Study the influence of early-season cotton management (nitrogen fertilization regime and lygus bug management) on cotton aphid population dynamics and seasonal buildup in cotton.

Continuing Projects Funded for 1998-99

Sugarbeet Cyst Nematode: In-Field Assessment of Damage/Economic Thresholds on Cole Crops and Reproductive Potential on Weeds.

Principal Investigators: B. B. Westerdahl, Nematology, Davis; E. P. Caswell-Chen, Nematology, Davis; R. F. Norris, Vegetable Crops and Weed Science, Davis

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

Quantify development and reproduction of Heterodera schachtii on weeds that are common in California sugarbeet and cole crop fields.

Determine how H. schachtii reproduction on weeds may alter the rotation interval necessary for nematode management.

Summary of Progress: Development of damage thresholds for the sugarbeet cyst nematode (SBCN) will permit nematicide use only when justified by expected damage and economic returns. Our preliminary data from Brussels sprouts in 1996 suggested that the damage threshold may be as high as 20 eggs/cubic centimeter (approximately one teaspoon) of soil at planting. The preliminary analysis of our field trial in Brussels sprouts during the summer of 1997 confirms this finding. Our initial field trials with broccoli have not allowed us to estimate a threshold. Several growth chamber experiments revealed that Brussels sprouts, broccoli, and cabbage seedlings are significantly damaged by five juveniles per g of soil.

The host status of weeds Sinapis arvensis, Raphanus raphanistrum, Capsella bursa-pastoris, Chenopodium album, Amaranthus retroflexus, Solanum nigrum, and Portulaca oleracea to SBCN was investigated in lab, greenhouse, and microplot. Juvenile SBCN penetrated the roots of all the weeds. Greater numbers of swollen juveniles and a higher ratio of swollen to vermiform juveniles occurred in roots of sugarbeet, S. arvensis, and R. raphanistrum compared to the other weed species. Greater numbers of cysts and eggs were recovered from S. arvensis, R. raphanistrum, and C. bursa-pastoris than other weed species. By calculating the ratio of egg production on weeds to egg production on B. vulgaris a relative reproductive index (RRI) was obtained. The RRI indicated that S. arvensis was a good host, R. raphanistrum and C. bursa-pastoris were intermediate hosts, and C. album, A. retroflexus, S. nigrum and P. oleracea were poor hosts of SBCN.

Management Practices for Long-Term Yellow Starthistle Control and Enhanced Rangeland Productivity.

Principal Investigators: S. Orloff, UC Cooperative Extension, Siskiyou County; J. M. DiTomaso, Vegetable Crops, Davis; D. Drake, UC Cooperative Extension, Siskiyou County

Objectives: Develop a long-term sustainable approach to controlling yellow starthistle and improving the quality and productivity of California rangeland.

Test the effectiveness of 1, 2, or 3 years of herbicide treatment (clopyralid) on yellow starthistle management and seed bank depletion in a rangeland system in Siskiyou County.

Evaluate the impact of herbicide application on rose clover and wheatgrass establishment. Determine the ability of fall-seeded rose clover or late winter-seeded wheatgrass to compete with yellow starthistle in untreated or in areas treated with clopyralid for 1, 2, or 3 years.

Measure and contrast rangeland productivity, forage quality, and water infiltration rates in (a) unimproved yellow starthistle-infested rangeland with no chemical control, (b) unimproved rangeland with chemical control, and (c) rose clover-or wheatgrass-improved rangeland treated with clopyralid for 1, 2, or 3 years.

Economically evaluate all treatment combinations to determine the most cost-effective method of yellow starthistle management in rangeland.

Summary of Progress: Yellow starthistle is the most troublesome weed in northern California rangeland. Available control measures have been largely ineffective and too costly for widespread use in range. Two trials were established in late winter of 1997. The first examined the affect of clopyralid at several rates and application timings on yellow starthistle control and desirable forage species. The second is a long-term study combining a reseeding program (rose clover and wheatgrass) and clopyralid application for yellow starthistle control and improved rangeland productivity.

Excellent control of yellow starthistle was achieved at clopyralid rates between one and four oz ai/A. Early applications (February and March) were more effective than April and May treatments. The February application timing also produced the highest forage quantity, and this decreased significantly with each month delay in clopyralid application. These results suggest that a early season treatment is preferred for cattle ranchers where the desired outcome is both yellow starthistle control and improved forage quality and quantity.

Initial evaluations of the long-term reseeding study showed that clopyralid application had a dramatic effect on rangeland species composition. The percent cover of yellow starthistle decreased from 58% in untreated plots to 4% in clopyralid-treated plots. Furthermore, clopyralid treatment increased the cover of plant species preferred by livestock (e.g., filaree, annual grasses, perennial grasses, wheatgrass and alfalfa). Because of the competitiveness of yellow starthistle, wheatgrass was unable to become established in plots without clopyralid treatment. Total late fall forage, including yellow starthistle, was not statistically different among the treatments.

Cultural Control Measures for Management of Belding's Ground Squirrels.

Principal Investigators: D. Whisson, Wildlife, Fish and Conservation Biology, Davis; S. Orloff, UC Cooperative Extension, Siskiyou County; D. Lancaster, UC Cooperative Extension, Modoc County; D. Putnam, Agronomy and Range Science, Davis

Objectives: Investigate cultural techniques to minimize damage due to Belding's ground squirrels in alfalfa.

Assess damage caused by Belding's ground squirrels to provide a basis for determining the level of expenditure which can be justified for squirrel management.

Investigate the effects of spring versus fall ripping of fields on mortality of ground squirrels. Evaluate the potential of using physical barriers to reduce invasion of ground squirrels into new fields.

Summary of Progress: Study sites have been selected in Siskiyou County. A search for sites in Modoc County is currently underway. Because the timetable for this study is dictated by the season of squirrel activity (March to September), the majority of work will commence in February 1998.

Projects that Ended in 1997-98

Controlling Weeds in Containers with Mulches and Method of Irrigation.

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

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 (pine bark, fir bark, and pecan shells) for their potential to control weeds in container plants and their effects on plant growth.

Examine how two methods of irrigation (sub-irrigation and top-irrigation) affect weed control and herbicide efficacy.

Evaluate the herbicidal activity and utility of a plant-based herbicide (corn gluten meal) in container production by comparing it to a traditional registered herbicide.

Summary of Progress: A 2.5 cm deep layer of coarse organic mulch (pine bark, composted green waste, or pecan shells) was adequate for pre-emergent control of annual broadleaf weeds (common groundsel, creeping woodsorrel, cudweed, and northern willow herb) in five gallon containers for at least six months in the nursery. Copper hydroxide treated fabric disks used to cover the potting mix surface also controlled broadleaf weeds. These nonchemical treatments reduced weed numbers, coverage, and dry weight to a level equivalent to that obtained using a commercially available herbicide. The fabric mulch and the pecan shells were the best mulch treatments for controlling overseeded ryegrass. Applying herbicide to the mulch did not improve the efficacy of mulches used alone. We also tested corn gluten meal, a plant-based product reported to have herbicidal activity. This product did not control any of the broadleaf weeds examined but did reduce the number of ryegrass seedlings in the containers as compared to the controls. However, the reduction was not adequate for this product to be considered an effective weed control treatment for nursery crops.

In another experiment, the effect of various depths of pine bark mulch and method of irrigation for plants in five-gallon containers was evaluated for weed control. Results indicate that sub-irrigation, regardless of mulch depth, provided excellent weed control and sub-irrigated treatments reduced water loss to a greater extent than those that were top-irrigated, even when the latter treatments were mulched.

Developing Area-Wide, Simultaneous Control of Four Major Lepidopterous Pests of Agricultural Crops through Disruption of Sex Pheromone Communication.

Principal Investigators: H. Shorey, Entomology, Riverside; P. Phillips, UC IPM Project, UC Cooperative Extension, Ventura County

Objectives: Determine the optimum strategy for placement of puffers releasing beet armyworm (BAW), cabbage looper (CL), corn earworm (CEW), and diamond-back moth (DBM) pheromones, as well as the optimum timing and amounts of pheromone lures used as bait within the blocks. Using 40-acre, 160-acre, 1 section (640-acre), and 4-section blocks of lettuce, cole crops, stock, celery, tomatoes, and other associated vegetable and floricultural crops in the Lompoc and Santa Maria valleys of Santa Barbara County.

Develop whole-season crop protection for DBM by treating 40-acre blocks in the Lompoc Valley using the optimum strategy determined earlier in this experiment.

Determine by sampling in transects through the blocks the extent of penetration of already mated female moths of this species into the pheromone-protected areas.

attempt whole-season crop protection for the three noctuid species by treating the entire Lompoc Valley.

Determine by sampling in transects through the valley the extent of penetration of already mated female moths of each species into the pheromone-protected area using the optimum strategy determined previously.

Summary of Progress: Trials were conducted in one-square-mile plots to evaluate strategies for releasing BAW pheromone from puffers for mating disruption. One puffer per ca 10 acres gave a better disruption than did per 40 acres. Deploying all puffers around perimeters of square miles appears to be as effective as deploying them in grids throughout the treated areas. As little as 10 g of BAW pheromone released per acre per season may give effective disruption. With flight ranges being measured in miles, multiranch acreages may need to be permeated with pheromones to suppress mating of such noctuid moth species. The fourth pest, DBM, has more limited flight than noctuid species. Various numbers of puffers continuously releasing either 2 or 10 mg of DMB pheromone per puff at 25-min intervals were placed around perimeters of stocks fields of various sizes near Lompoc, CA. Early season (through June, 1997) use of puffers releasing 2 mg puffs gave about 80% reduction in DBM larvae in 40-acre blocks. Later season (July, August, September) use of up to 30 perimeter puffers releasing 2 mg puffs in block sizes of ten acres gave little or no larval control; we feel this poor control resulted from inflight of mated females from outside the areas of puffer protection (centers of elongate ten acre blocks were only 50 m from the nearest edges) combined with very high moth population densities. Late season application of pheromone in 10 mg puffs from 40 puffers surrounding a 40-acre field resulted in greater than 80% larval control during the first half period of crop growth.

Using a Longer Harvest Interval to Control Nutsedge in Alfalfa.

Principal Investigator: R. Kallenbach, UC Cooperative Extension, Riverside County/Blythe

Objectives: Determine if longer harvest intervals during the summer can control nutsedge growth and reproduction in alfalfa.

Document how this cultural control method compares to chemical control of nutsedge in alfalfa.

Determine if cultural control is an economically viable method to suppress nutsedge growth in alfalfa fields.

Summary of Progress: Hay yields (alfalfa and nutsedge combined) were the same for plots that received Eptam or were left untreated for similar harvest intervals. When combined across chemical treatments, hay yields from April through September were 4.34, 4.95, and 4.81 tons per acre for hay harvested every 28, 35, or 42 days respectively.

Forage samples from plots harvested every 28 days and that received Eptam contained 32% nutsedge compared to 43% for untreated plots. In plots harvested every 35 or 42 days hay average 35% nutsedge and the botanical composition was unaffected by either the use of Eptam or cutting interval. These data suggest that Eptam is only beneficial when harvesting alfalfa on a short cutting interval.

Nutsedge density averaged 82 plants per m² at the beginning of the study. Fourteen days after each harvest we counted these populations again. In plots harvested every 28 days, nutsedge declined by 81% to 15 plants per m² when Eptam was applied. In plots harvested every 35 or 42 days, an Eptam application reduced the nutsedge population to 11 and 12 plants per m² respectively. In untreated plots, regardless of the number of days between harvests, the nutsedge population remained the same as at the beginning of the study. These data demonstrate the effectiveness of Eptam as means of controlling nutsedge in alfalfa.

Final Reports for Projects that Ended in 1997

Control and Exploitation of Exogenous Bacterial 3-indoleacetic Acid Production to Reduce Pesticide Inputs To Tree Crops.

Principal Investigators: S. E. Lindow, Plant and Microbial Biology, 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 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.

Summary of Accomplishments: The severity of fruit russet was reduced from about 20% to 60% by foliar sprays of either ammonium sulfate, calcium nitrate, or urea sprayed onto pear trees weekly for four weeks starting at petal-fall. The reduction of fruit russet was reduced irrespective of whether solutions containing 100, 200, or 400 ppm N in the form of these materials were applied, suggesting that the low rate is sufficient to inhibit IAA production on trees as was observed in laboratory cultures of IAA-producing bacteria. Applications of nitrogenous compounds made two or three weeks after petal fall caused a greater reduction than sprays made at earlier times. While seldom significantly different, urea and ammonium sulfate were more effective in reducing fruit russet than calcium nitrate. Bloom-time nitrogen sprays thus are an effective and inexpensive procedure for fruit russet control. 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 trials, suggesting that bacterial population sizes were limited by environmental extremes and/or carbon availability rather than by the abundance of nitrogenous compounds on tree crops. 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 with nutrients from November to January delayed slightly the time when fruit dropped from trees in about half of the trials. The effects of application of IAA-producing bacteria on fruit retention of navel orange are too small and variable to recommend at this time.

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

Objective: 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 Accomplishments: In processing tomatoes, layby herbicide treatments are soil-incorporated. Incorporation of the layby herbicide dislodges emerged weeds, thus weeds emerging this operation come from seed or perennial propagules. Tomato growth is rapid after layby herbicide treatment, responding to the sidedress fertilizer application (applied 1 to 7 days before layby). The rapid expansion of the tomato canopy helps to block light and prevents or reduces weed growth, and thus reducing the need for herbicide near the crop. The farther from the tomato row, the less the competitive effect. Herbicide rates can be varied on a spray boom by changing the nozzle size. In this study, variable rate applications were made using a boom with the center nozzles positioned over the furrow and outside nozzles near the crop; the center nozzles applied full rate, while nozzles near the crop were one-half the size and applied half rate. Variable rate treatments reduced herbicide the amount of herbicide applied by 40% compared constant rate. Variable rate treatments were compared to constant rate treatments at eleven locations throughout California. Trifluralin was used in all studies with 0.85 lb/a applied as the standard rate. An untreated control was also included with no herbicide, but was cultivated by the incorporator. Tomato yield and quality were not affected by layby treatment. Weed density and cover were generally greater on untreated plots compared to other treatments, but did not differ at any location between varying rate and constant rate treatments, regardless of the weed species present on a site. Weed seed production also did not differ between varying rate and constant rate treatments. Implementation of variable rate layby treatments requires a simple nozzle change on the layby application equipment, using a nozzle size smaller (1/2) than that used in the furrow area.

Principal Investigators: K. V. Subbarao, Plant Pathology, Davis/U.S. Agricultural Research Station, Salinas; R. M. Davis, Plant Pathology, Davis

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

Summary of Accomplishments: The impetus for this project came from the observation that the extensive broccoli crop grown in the Salinas Valley remained unaffected despite the severe losses suffered by its sister crop, cauliflower from Verticillium wilt caused by V. dahliae. Based on this and other experimentally proven evidence, we hypothesized that rotations with broccoli may reduce soilborne microsclerotia, and subsequently, the incidence of Verticillium wilt on cauliflower. Field experiments were conducted to test this hypothesis. The populations of V. dahliae microsclerotia were not affected during the broccoli crop. Within a month after the broccoli residue incorporation, however, the numbers of microsclerotia declined significantly and this reduction continued during the subsequent cauliflower crop. The populations of microsclerotia in soil at the end of the cauliflower crop were about 70% less in plots where broccoli residue was incorporated compared to either stable or significant increases in plots without broccoli. The Verticillium wilt incidence and severity in the subsequent cauliflower crop in plots rotated with broccoli were also significantly lower than in plots with no broccoli crop. The intensity of microsclerotia that formed on infected cauliflower roots was significantly lower in plots previously rotated with broccoli than in plots without broccoli. In a related research project supported by other funding, we have determined that for maximizing the broccoli-mediated pathogen attrition in soil, the residue should be incorporated when the soil temperatures are at least 20 C. Thus, the growers in the Salinas and adjacent valleys may rotate cauliflower and other Verticillium wilt-susceptible crops with broccoli, and incorporate the residue after commercial harvest when the soil temperatures are at least 20 C. This recommendation would be compatible with current production practices and is therefore immediately adaptable by the growers in coastal valleys for Verticillium w ilt management. Over the past two years, a number of growers have field-tested rotations of both cauliflower and lettuce with broccoli, and determined that this technique not only is effective against Verticillium wilt but also on lettuce drop caused by Sclerotinia minor.

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 integrated approaches of subterranean clover plantings, mowing, and sheep grazing in pastures and ungrazed areas.

Summary of Accomplishments: Our previous research demonstrated that controlled grazing and timed mowing are useful methods for reducing yellow starthistle infestations without herbicides. However, to obtain long-term control, we hypothesized that competitive vegetation should be established. We tested this over a four-year period with two experiments using combinations of subclover seeding, phosphorus fertilizer, sheep grazing, and mowing in grazed and ungrazed paddocks. In the pasture experiment we tested: 1) subclover seeding with controlled grazing (short duration, high-intensity) and timed mowing, 2) grazing and mowing with no subclover seeding, and a 3) control, with no subclover, grazing or mowing. The seeded (once in Oct. 1993) paddocks were grazed three times between early February and late May, and mowed in early July each year. The unseeded paddocks were grazed in late March and late May and mowed once in early July. The treatments in the ungrazed experiment were: 1) subclover seeding with mowing, 2) mowing with no subclover seeding, and a 3) control, with no subclover or mowing. The seeded plots were mowed two times, once in February to enhance subclover growth, and a second time in mid-June during yellow starthistle's early flowering stage. In the unseeded plots we mowed only once, also in yellow starthistle's early flowering stage.

Our results indicate that there were weed control benefits from planting subclover as a competitive plant, but the tested varieties declined substantially after four years. The best control came from subclover seeding with phosphorus fertilizer and mowing. The grazed treatment was less effective because the vegetative canopy was removed during a critical period. Maintaining a dense spring canopy of vegetation is an essential ingredient for optimal yellow starthistle control. Yellow starthistle responds to the increased sunlight from spring defoliation by producing plants that are more prostrate and with growing buds closer to the ground, making plants less susceptible to control with defoliation by later spring grazing and mowing.

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