Annual Reports

1997—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 1997-98
Continuing Projects Funded for 1997-98
Projects that Ended in 1996-97
Final Reports for Projects that Ended in 1996

New Projects Funded for 1997-98

GROUND SQUIRREL MANAGEMENT

Cultural control measures for management of Belding's ground squirrel in alfalfa. (Year 1 of 3; $27,850)

Principal Investigators: D. Whisson, Wildlife, Fish and Conservation Biology, Davis

Objectives: Investigate 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 that 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.

Developing areawide, simultaneous control of four major lepidopterous pests of agricultural crops through disruption of sex pheromone communication. (Year 1 of 1; $15,000)

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

Objectives: Using four different sized 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, determine the optimum strategy for placement of puffers releasing beet armyworm, cabbage looper, corn earworm, and diamond-back moth pheromones, as well as the optimum timing and amounts of pheromone released in puffs, to prevent male moths from locating female moths or pheromone lures used as bait within the blocks.

Develop whole-season crop protection for diamond-back moth by treating 40-acre blocks in the Lompoc Valley, and determine 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, and determine the extent of penetration of already mated female moths of each species into the pheromone-protected area.

Using a longer harvest interval to control nutsedge in alfalfa. (Year 1 of 2; $9,020)

Principal Investigators: R. Kallenbach, UC Cooperative Extension, Riverside County; D. Cudney, Botany and Plant Sciences, Riverside; E. Takele, UC Cooperative Extension, Riverside County

Objectives: Determine if longer harvest intervals during 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.

Management practices for long-term yellow starthistle control and enhanced rangeland productivity. (Year 1 of 3; $18,120)

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

Objectives: Using IPM principles, 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 and on rose clover and wheatgrass establishment in a rangeland system in Siskiyou County.

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

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

Continuing Projects Funded for 1997-98

IPM Advisor Cheryl Wilen checks plants as part of research to evaluate impact of irrigation practices and mulches on weeds in container-grown plants. Photo by Yvonne Thompson.

MULCHES FOR CONTAINERS Controlling weeds in containers with mulches and method of irrigation. (Year 2 of 2; $10,000) Principal Investigators: U. Schuch, Botany and Plant Sciences, Riverside; C. 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 plus a spun fabric for their potential to control weeds in container plants and their effects on plant growth.

Examine how two methods of irrigation in combination with different depths of mulches affect weed control.

Determine the potential for weed control in containers using a plant-based herbicide (corn gluten meal).

Summary of Progress: In a study examining the utility of various mulching materials for preemergent weed control in containerized plants, we found a 1-inch layer of coarse mulch or a fabric disk treated with copper hydroxide covering on the potting mix surface controlled broadleaf weeds (common groundsel, creeping woodsorrel, and northern willow herb) in 5-gallon containers for at least 6 months in the nursery. The organic mulches tested were pine bark, fir bark, and pecan shells. These nonchemical treatments reduced weed numbers, coverage, and dry weight to a level equivalent to that obtained using a commercially available herbicide. 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, in this study. This product did not control any of the broadleaf weeds examined.

In another experiment, the effect of various depths of pine bark mulch and method of irrigation for plants in 5-gallon containers was evaluated for weed control. Preliminary 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. Mulching and top-irrigating also controlled weeds. We will harvest plants at the end of the year (1996) to evaluate the treatments' effect on plant growth. The potting mix in many of the sub-irrigated treatments remained excessively wet during the course of the experiment and this may be a limitation in using this technique in commercial production due to concerns about plant disease and root growth.

Developing damage/economic thresholds for sugarbeet cyst nematode on cole crops. (Year 2 of 3; $26,428)

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

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: Approximately 25% of the nematicides used in California are for preplant reduction of populations of the sugarbeet cyst nematode (Heterodera schachtii, SBCN) on cole crops. Development of damage thresholds for SBCN will permit growers to utilize nematicides only when justified by expected economic returns; this holds promise for producing a rapid reduction of nematicide use in this cropping system. Preliminary data analysis for a trial on Brussels sprouts indicates the damage threshold is above 20 eggs/cubic centimeter (approximately 1 teaspoon) of soil at the time of planting.

A quantitative assessment of weed host status for SBCN will lead to increased management efficacy, will allow appropriate assessment of weed management, and will reduce nematicide use. The preliminary data indicate that several common California weeds support nematode reproduction, and that cyst production and clutch size varies among weed species. It is clear that Brassica rapa (field mustard) and Brassica kaber (wild mustard) are very effective hosts for the nematode; Capsella bursapastoris (shepherd's purse), Amaranthus retroflexus (redroot pigwood), and Raphanus raphanistrum (wild radish) are less effective hosts; and Solanum nigrum (black nightshade), Portulaca oleracea (common purslane), and Chenopodium album (lambsquarters) are relatively poor hosts.

Projects that Ended in 1996-97

FERTILIZER/BACTERIA RELATIONSHIPS IN TREES

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. 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 4 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 from about 20 to 60% by foliar sprays of either ammonium sulfate, calcium nitrate, or urea; the reductions in fruit russet were smaller than in 1994 and 1995 and were attributable to the low level of fruit russet in 1996. The reduction of fruit russet was similar irrespective of whether 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 and 1995, 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.

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 with nutrients from November 1995 to January 1996 delayed slightly the time when fruit dropped from trees. Bacterial population sizes were 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.

Trifluralin application at varying rates across the bed for layby weed control in tomatoes.

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 upper soil layers. Incorporation dislodges emerged weeds, thus weeds emerging after incorporation 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 tomato canopy can block light, preventing weed growth, and reducing the need for herbicide near the crop. The farther from the crop row, the less the competitive effect. Competition from tomatoes can reduce the need for herbicides.

Variable rate treatments were compared to constant rate treatments at eight locations throughout California. Variable rate applications were made using a boom with the center nozzle(s) positioned over the furrow and outside nozzles near the crop. 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. Variable rate treatments reduced herbicide use by 40% compared to constant rate. Trifluralin was used in all studies with 0.85 lb/acre 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 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.

Using subterranean clover with combinations of mowing and sheep grazing to control yellow starthistle.

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.

Summary of Progress: To obtain long-term control of yellow starthistle it is necessary to eliminate seed production and, where possible, establish competitive vegetation that has the ability to persist. For 3 years we have been testing combinations of cultivation, subclover seeding, timed mowing, and controlled sheep grazing in two experiments involving five treatments. The best control came from plots that were cultivated, seeded, and mowed.

Prior to seeding in October 1993 we cultivated the plots to prepare a seedbed. The cultivation was done the previous spring before yellow starthistle had produced any seed, which helped reduce the seed bank. Each year after establishing the subclover, we mowed in late winter to enhance the subclover stand and during yellow starthistle's early flowering stage (late June) to remove yellow starthistle biomass and to reduce reproductive output. The cumulative effect of 4 years of control with preplant cultivation, subclover seeding, and timed mowings nearly eliminated seed production and depleted the seed bank to the level that yellow starthistle eradication may be possible in the subclover plots within a few years, if 100% control is maintained.

Seeding and mowing treatments were less effective when combined with sheep grazing. Seeded paddocks were grazed three times (winter, mid- and late spring) to utilize subclover and yellow starthistle as a forage and mowed in July during yellow starthistle's early flowering stage. Establishing or maintaining a dense spring canopy of associated vegetation is an essential ingredient for optimal yellow starthistle control in a mowing program. In appropriate settings, certain subclover varieties can be useful for this purpose.

Rotation with broccoli to target Verticillium wilt control: A potential alternative to soil chemical fumigants.

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.

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, by Verticillium wilt. 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 crop. Field experiments were conducted to test this hypothesis.

The populations of V. dahliae microsclerotia changed little 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 were 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 20deg.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 20deg.C. This recommendation would be compatible with current production practices and is therefore immediately adaptable by the growers in coastal valleys for Verticillium wilt management.

Final Reports for Projects that Ended in 1996

Hull rot of almonds can be substantially reduced by careful water and nitrogen management.

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

Summary of Accomplishments: Hull rot disease is caused by either of two fungi, Monilinia fructicola or Rhizopus stolonifer. Fungus spores enter the almond fruit through the natural opening of the hull after it splits during the ripening process. Infections of the hull lead to death of fruiting wood, reducing future yields. The edible nutmeat is not harmed. Chemical treatments do not control the disease.

We investigated the effects of deficit irrigation on hull rot control by comparing the normal 39 inches of water (normal) to three deficit amounts (34, 28, and 22 inches) per season. We inoculated fruit in the normal irrigation treatment and in some of the 34- and 28-inch water-deficit irrigation treatments with M. fructicola and R. stolonifer, monitored the moisture content of hulls, observed the loosening of the hull from the fruit stem, and evaluated natural incidence of hull rot at harvest. Hull rot incidence 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. Hulls were drier and loosened from the fruit stem and split more rapidly in the drier water treatments.

The effects of nitrogen on hull rot incidence were examined among trees fertilized with 500, 250, 125, and 0 lb nitrogen/acre/year since 1989. We performed the same inoculation experiments as described for the irrigation experiment. Hull rot increased with increasing amounts of applied nitrogen and a similar trend occurred in the inoculation experiments but the response was not as definite. The two pathogens caused equivalent amounts of hull rot. Hulls tended to loosen from the fruit stem, split, and dry more rapidly in the lowest nitrogen treatment.

Growers should limit nitrogen fertilization to the minimum required for good tree growth, reduce irrigation near hull split, and harvest as soon as possible to reduce damage from hull rot.

Integrated management of potato diseases with drip irrigation.

Principal Investigators: G. T. Browne, Plant Pathology, Davis; R. M. Davis, Plant Pathology, Davis

Summary of Accomplishments: No report received yet (11/97).

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