Weeds continue to have a tremendous impact on crop yield losses in Canada and the United States, despite efforts to control them with chemicals. Biological control offers an additional means for reducing weed populations while reducing the reliance of the agri-food industry on chemical pesticides. Effective biological strategies that are compatible with good soil conservation practices would benefit farmers while maintaining environmental quality and a sustained production for the future. Inundative biological control of weeds with microbial agents involves the mass production and application of high concentrations of a plant pathogen to a target weed. Historically, biocontrol agents used on weeds have been foliar fungal pathogens. More recently, the soil has become a source for microorganisms, such as rhizobacteria, for development as biological control agents. Several naturally occurring rhizobacteria have weed suppressive properties, where growth and development of weeds such as downy brome, wild oats, leafy spurge, and green foxtail are significantly inhibited. Although the focus in weed biocontrol has been on the eradication of weeds, rhizobacteria may be used to improve seedling establishment of the crop by reducing the weed competition. This can be achieved through a reduction in weed growth, vigor, and reproductive capacity and improvement in the ability of the crop to compete with the weed. Current research in weed biocontrol with microorganisms and its application to weed management systems will be discussed.
One of the main difficulties in controlling root diseases biologically has been the inability of biocontrol agents to establish and persist in the rhizosphere. The inability of biocontrol agents to establish and persist is often attributed to competition from indigenous microorganisms for space and nutrients and to fluctuations in environmental conditions. The use of biocontrol agents over the entire geographic range of a crop also has been limited by differences in environmental and edaphic conditions from field to field and region to region. An advantage of hydroponic crop production in greenhouses is that environmental conditions such as temperature, moisture, pH, and growth medium can be consistently controlled in a house and from site to site. An additional advantage of many hydroponic systems is that they are virtually sterile upon planting. This initial period of virtual sterility greatly reduces competition for an introduced biocontrol agent. In addition, these systems are usually pathogen-free upon planting allowing the establishment of a biocontrol agent prior to pathogen introduction. Last, the temperatures, high moisture levels, and pH ranges of hydroponic systems can be ideal for the proliferation of many biocontrol agents. With all of these advantages for the use of biocontrol agents in hydroponic systems, our company, and many labs around the world, have focused their attention on developing biological control agents for these systems. I will provide a review of research focused on controlling root diseases of vegetables grown in rockwool and other hydroponic systems.
Plant growth-promoting rhizobacteria (PGPR) enhance plant development by many mechanisms. Indirect growth effects result from PGPR activities that displace soilborne pathogens and thereby reduce disease. Direct effects include improved nutrition, reduced disease due to activation of host defenses, and bacterial production of phytohormones. An understanding of the mode of action is essential for exploitation of PGPR for field use. For instance, bacteria that act as biological control agents can only be of benefit at locations where disease occurs. PGPR that stimulate plant growth directly will likely have more universal uses and greater impacts. Thus, we have been developing model systems for identifying PGPR with such traits. In this presentation, the effects of bacterization of tissue culture-grown plants, plug transplants, and seed with a growth-promoting Pseudomonas sp. (PsJN) will be described. Potential uses for this and other PGPR will also be identified. The talk will consider the advantages and limitations of: a) screening methods used for selection of PGPR, b) model systems available for studying the mechanisms of action, and c) why transplants offer an ideal delivery system for rhizobacteria. Results from field trials with PGPR with different modes of action will be presented and their future role in agriculture considered.
The susceptibility of third-instar larvae of Anastrepha ludens (Loew) to the entomopathogenic nematodes Steinernema carpocapsae (Weiser) (All and Tecomán strains), S. feltiae (Filiipjev), S. glaseri (Steiner) (NC strain), S. riobrave (Cabanillas, Poinar & Raulston), and Heterorhabditis bacteriophora Poinar (NC, Patronato, and Tecomán strains), was evaluated under laboratory conditions. Sterile distilled water (1.0 mL) with 4000 infective juvenile nematodes were applied on 300 g of moistened sterile soil into 1000-mL pots, and 20 third-instar larvae were placed on the soil surface, 1 mL of distilled water without nematodes was applied as control. Each nematode treatment was replicated four times. After nematode application, pots were incubated at 25 °C. Mortality of larvae and pupae was evaluated 6 and 12 d after inoculation. Cadavers of larvae and pupae were dissected and examined for the presence of nematodes. Our results showed that Mexican fruit larvae were susceptible to entomopathogenic nematodes. S. riobrave and S. carpocapsae All strain caused 90% of larval and pupae cumulative mortality, H. bactetiophora NC strain and S. feltiae killed more than 80%, whereas H. bacteriophora Tecomán and S. glaseri caused a 52.5% mortality. These results suggest that the nematodes S. riobrave and S. carpocapsae All strain have a potential as biological control agents against A. ludens.
English walnut (Juglans regia) producers in California compete with many insect and disease pests to produce an acceptable crop. Traditional control strategies work reasonably well for most pests. However, environmental concerns, loss of certain pesticides and new or impending regulations threaten the use of many traditional techniques for control of many of the pests. Codling moth (Cydia pomonella), walnut husk fly (Rhagoletis completa), and walnut aphid (Chromaphis juglandicola) are the major insects that affect California walnut production. Control strategies that use integrated pest management programs, beneficial insects, mating disruption, insect growth regulators, improved monitoring techniques and precise treatment timing based on the insect's life cycle are leading edge techniques currently available for insect control in walnuts. Major diseases include walnut blight (Xanthomonas campestris pv. juglandis), crown gall (Agrobacterium tumefaciens) and crown and root rot (Phytophthora spp). Both copper resistant and copper sensitive strains of the walnut blight bacterium are best controlled with combinations of copper bactericides and maneb instead of copper materials alone. A new computer model, Xanthocast, used to forecast the need for walnut blight treatment is under evaluation. Crown gall is managed using a preplant biological control agent and a heat treatment to eradicate existing galls. Phytophthora crown and root rot is dealt with primarily by site selection, irrigation management and rootstock selection.
The efficacy of Tilletiopsis pallescens Gokhale, a naturally occurring ballistosporeforming yeast isolated from mildew-infected leaves, was evaluated as a biological control agent against rose powdery mildew [Sphaerotheca pannosa (Wallr.:Fr.) Lév. var. rosae Woronichin]. Two trials were conducted on potted rose (Rosa sp.) plants (1-year-old cv. Cardinal Pink) under commercial greenhouse-growing conditions during the summer (June to September) when mildew was most severe. Mildew-infected plants were subjected to one of four treatments: a T. pallescens spore suspension applied three times (3–4 d apart), distilled water (applied three times), one application of T. pallescens spore suspension, or one application of culture filtrate without spores. Two weeks after treatment began, mildew development was evaluated by enumerating conidial density on sampled leaflets. Sporulation was significantly reduced (by 97%–98%) on plants treated with three applications of T. pallescens spore suspension, compared to a 47%–57% reduction on plants treated with three applications of distilled water. There was no significant difference in conidial density between plants treated with one application of T. pallescens spore suspension and plants treated with one application of its culture filtrate, with a 78%–94% reduction in conidia, which was significantly higher than for the water treatment. The mode(s) of action of T. pallescens appears to be eradicant and associated with enzymes or metabolites produced in the culture filtrate. The results from this study demonstrate the potential for biological control of rose powdery mildew under commercial growing conditions in British Columbia.
Trichoderma virens (Gliocladium virens) (Miller et al.) von Arx is a soilborne fungus with a high degree of rhizosphere competence that produces a potent herbicidal compound, viridiol, and therefore has potential for development as a bioherbicide. We investigated the possibility of using composted chicken manure (CCM) as a medium for the production and deployment of T. virens. We chose CCM since the safe disposal of chicken manure presents significant logistic problems, and composted manures, as well as serving as an organic source of nitrogen, have been shown to support the activity of other biological control agents. Composted chicken manure supported the growth of T. virens and the rapid production of high concentrations of viridiol, but only when it was supplemented with large quantities of nutrients, including sucrose (16% w/w). Viridiol was not stable when stored in CCM, with a rapid decline in viridiol concentrations observed in T. virens-inoculated CCM cultures. Clearly, a cheaper alternative to sucrose is required as a carbon source for T. virens in CCM or similar media, and effective storage methods would need to be found for a T. virens-based bioherbicide product. Importantly, CCM did not need to be sterilized to support the growth of T. virens and its concomitant production of viridiol, suggesting that on-farm production systems may be feasible. Trichoderma virens-colonized CCM reduced the emergence and seedling growth of redroot pigweed (Amaranthus retroflexus L.) in a greenhouse experiment and dramatically reduced the emergence of a mixed community of broadleaf weeds in the field.
Abstract
Concern over pesticide pollution of the atmosphere and increased resistance of numerous species of insects to insecticides has caused entomologists to seek alternate means of control of pest insect populations. Recently the term “pest management” has been coined for the Integration of the various available control measures for pest populations into Systems that minimize the use of insecticides. New emphasis has been placed on the potential utilization of biological control agents for the control of pest populations. Basically, the following presentation will consider ecosystem analysis of the use of parasites and predators both in attempts to establish the agents as permanent, recurring controls and in inundative release attempts to replace insecticides on a short-term basis. The examples cited pertain mainly to two cotton pests, the pink bollworm, Pectinophora gossypiella (Saunders), and the bollworm, Heliothis zea (Boddie). The bollworm is a horticultural pest attacking corn, tomatoes, beans and a host of other crops; the pink bollworm is restricted to cotton. However, the concepts and the approach to the introduction of integrated control is similar, regardless of the crop under consideration. An analytical approach will be employed. However, a paralleling use of the data for the development of models for insect population dynamics is possible (20).
Abstract
Cold storage of cut ‘Sonia’, ‘Royalty’, and ‘Gold Rush’ roses (Rosa hybrida L.) at reduced humidities (50% to 80% RH) significantly decreased the severity of Botrytis cinerea Pers. infections that developed from naturally occurring or experimentally applied inocula, compared to storage at saturated humidity. The disease reduction was attributed to the absence of free water on the petals. Wrapping the flowers in cellophane sleeves before reduced-humidity storage decreased water loss but also impaired disease control. No deleterious effects of reduced-humidity storage on poststorage fresh weight gain or visual quality were observed, whether the wrapped flowers are stored with or without vase solutions. Two biological control agents, the yeast Exophiala jeanselmei and a Coryneform-type bacterium, controlled B. cinerea infections during storage at 2.5°C when applied 0 to 48 hr after inoculation with the pathogen. The level of disease control achieved with the biological antagonists during storage was comparable to that achieved with the fungicide vinclozolin, but the biological antagonists did not control poststorage disease development as well.
Abstract
The effects of peat: vermiculite mixes on increased growth response of radish (Raphanus sativus L. ‘Early Scarlet Globe’) induced by Trichoderma harzianum Rifai (isolate T-12) were investigated. Canadian sphagnum peat and vermiculite were mixed in various ratios to form 0-100% peat mixes. Four levels of T-12 amendment were added to these mixes—0%, 2%, 5%, and 10% (v/v) or 0%, 0.1%, 1%, and 10%. In general, increasing levels of T-12 amendment induced linear increases in radish dry weights after 4 and 5 weeks. Greatest increases were seen in mixes containing 20% peat or 80% peat. The smallest increases were observed when T. harzianum was added to 0% peat or 100% peat mixes. There was no effect on the population densities of T-12 after it was introduced into the mixes. No Pythium spp. or root disease were detected in the mixes, suggesting that T. harzianum, a biological control agent, can increase plant growth independent of any detectable root pathogens.