W. E. Grey

Biological control as a means of enhancing the sustainability of crop/land management systems

Abstract Biological control can contribute to the sustainability of crop/land management systems by reducing the inputs currently derived from non-renewable fossil energy sources. Biologically based technology will have to be developed and gradually integrated into management systems that will include some chemicals for a long time to come. A researchable paradigm is presented: using “weed-suppressive soils” for biological control of weeds in crops. This example requires extensive knowledge of the ecology of soil microflora and how various populations are affected by management strategies. These management strategies are structured to foster microbial populations in soils that will provide timely suppression of early flushes of annual weeds. Biological seed treatments using microbial antagonists will have to be developed to “safen” the crop against the active biological factors in the “weed-suppressive soils”. As these and other biological alternatives are adopted, the concept of “sustainability” will move closer to reality.

A root-injection method to assess verticillium wilt resistance of peppermint ( Mentha × piperita L.) and its use in identifying resistant somaclones of cv. Black Mitcham

Three studies were initially conducted using five mint cultivars with known disease reactions to verticillium wilt to determine if inoculation method, root-dip as compared to root-injection, had an affect on the plant growth and disease reaction. The planting media did not affect the development of wilt symptoms in susceptible varieties, however, the soil/peat based medium resulted in higher shoot fresh weight at harvest than the perlite/vermiculite medium. Black Mitcham had the highest susceptible disease rating and greatest reduction in fresh shoot weight from inoculation with Verticillium dahliae at two inoculum concentrations, 104 or 106 microconidia/ml. Native spearmint was resistant and Mentha crispa was moderately resistant, whereas, Murray Mitcham peppermint and Scotch spearmint were moderately susceptible to verticillium wilt with a corresponding lower fresh shoot weight. Scotch spearmint was less susceptible at the low inoculum concentration than at a higher level of microconidia, indicating a low level of disease resistance. Overall, the two inoculation methods resulted in similar cultivar responses to verticillium wilt, although the root-injection method was more applicable for large plant populations. Thus, the root-injection method of inoculation was utilized to screen 743 Black Mitcham derived somaclones for wilt resistance, of which nine somaclones were found resistant in repeated inoculation tests.

Effect of soil water content on wild oat (Avena fatua) seed mortality and seedling emergence

Abstract Field experiments were established in fall 1999 and 2000 near Huntley, MT, to determine the effects of soil water content on wild oat seed mortality and seedling emergence. Four supplemental irrigation treatments were implemented from June through September to establish plots with varying soil water content. Wild oat seed mortality during the summer increased linearly as soil water content increased. For seed banks established in 1999 (1999SB), seed mortality increased, on average, from 36 to 55% in 2000, and 15 to 55% in 2001 as soil water content increased from 6 to 24%. For seed banks established in 2000 (2000SB), seed mortality increased, on average, from 38 to 88% in 2001 and 53 to 79% in 2002 as soil water content increased from 6 to 24%. Increasing soil water content likely increased the activity of microorganisms that cause mortality in wild oat seeds. The increasing seed mortality rates (due to increasing soil water content) resulted in greater annual declines of wild oat seed banks and ...

Mycoses of Wheat Stem Sawfly (Hymenoptera: Cephidae) Larvae by Fusarium spp. Isolates

ABSTRACT A complex of Fusarium spp., including F. pseudograminearum, F. culmorum, F. avenaceum, F. equiseti, and F. acuminatum, was isolated from field-collected larval cadavers of wheat stem sawfly at two locations for 2 yr. The Fusarium spp. isolates caused mortality in both diapausing larvae in a topical bioassay and in developing larvae feeding in infected stems in a greenhouse experiment. Larval mortality was >90% in both experiments at the highest dose. The pattern of correlation between integument discoloration, hyphal growth, and larval mortality showed that the Fusarium spp. isolates actively infect larvae and kill them, rather than colonizing larval tissue as secondary postmortem invaders. The versatility of Fusarium spp. as plant and insect pathogens enables colonization that results in disease in wheat plants and subsequent mortality of the wheat stem sawfly larvae developing within the same tissue.

Biological Control of Take-all Disease of Wheat Caused by Gaeumannomyces graminis var. tritici Under Field Conditions Using a Phialophora sp.

A Phialophora sp. (isolate I-52), originally isolated from soil in a wheat field exhibiting suppression of take-all disease caused by Gaeumannomyces graminis var. tritici , was tested under field conditions for its ability to suppress this disease in winter and spring wheat. I-52 was grown on a variety of autoclaved organic substrates, including oat, millet and canola seed. All of these gave significant disease control when added to the seed furrow with inoculum of the take-all fungus. W hole seed of I-52 substrate was as effective as particles < 0.5 mm in diameter. Placing I-52 in powdered form directly on to wheat seed was ineffective in controlling take-all. Rates as low as 2 g of I-52/3.3 m of row added with the seed provided some control of take-all, and nearly complete control in winter wheat was obtained using 15 g/3.3 m. The winter wheat host cultivar did not influence the degree of control of take-all by I-52.

Spring Wheat Production and Associated Pests in Conventional and Diversified Cropping Systems in North Central Montana

Producers in the northern plains are diversifying and intensifying traditional wheat (Triticum aestivum L.)-based cropping systems by reducing summer fallow and including legume and oilseed crops. This study examined the influence of diversification and intensification on spring wheat yield and quality and associated insects, diseases, and weeds. Research was conducted during the 1998 through 2000 period in farm fields in north central Montana. Conventional rotations included either hard red spring wheat–spring barley (Hordeum vulgare L.)–fallow or spring wheat–fallow. Diversified rotations included replacement of fallow with either annual pulse crops or cool-season oilseeds. Preplant soil water was less in diversified rotations, but residual nitrate was not influenced by rotation type. Insect pests and beneficial arthropods were in greater numbers in conventional rotations. Incidence and severity of crown and root rots of wheat were similar between rotation types, but foliar leaf spot diseases were greater for wheat in conventional rotations. Weed densities were not influenced by rotation type. Spring wheat yield, tiller density, and test weight were greater in conventional rotations. Spring wheat in diversified rotations had greater drought stress. Diversification and intensification of spring wheat systems may reduce pests and decrease wheat productivity, particularly when precipitation is inadequate.

Dalmatian Toadflax (Linaria dalmatica): New Host for Cucumber Mosaic Virus

To date, there have been no reports of Dalmatian toadflax serving as a host for cucumber mosaic virus (CMV). Infestations of Dalmatian toadflax may serve as a reservoir of CMV, thereby facilitating aphid transmission of CMV to both agricultural crops and native plants. The goal of this study was to determine whether Dalmatian toadflax is a host for CMV. Dalmatian toadflax seedlings were randomly assigned to two treatments (18 replicates/treatment): no inoculation (control) and inoculation with CMV (Fast New York strain). The Dalmatian toadflax seedlings were inoculated by standard mechanical methods and tested for the presence of CMV using enzyme-linked immunosorbent assay (ELISA). Ten of the 18 CMV-inoculated toadflax plants tested positive for the virus; 6 of the 18 displayed systemic mosaic chlorosis and leaf curling. All control plants tested negative. Transmission electron microscopy obtained from CMV-positive plants confirmed the presence of CMV based on physical properties. To verify CMV infestation, tobacco plants were assigned to the following treatments (six replicates/treatment): no inoculation (control), CMV-negative (control) inoculation, and a CMV-positive inoculation. Plants were inoculated by standard methods. Five of the 6 tobacco plants treated with the CMV-positive inoculum tested positive for CMV using ELISA. All control plants tested negative for the virus. Nomenclature: Dalmatian toadflax, Linaria dalmatica (L.) Mill. LINDA, tobacco, Nicotiana tabacum L, cucumber mosaic virus