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1424. Cook, R.J.. 1988. Management of the environment for the control of pathogens.. Phil. Trans. R. Soc. London B 318:171-182.
Pathogens can be controlled by management of the environment of 1) the host plant, to maximize resistance, 2) non-pathogens associated with the pathogen to enhance antagonisms, and 3) the pathogen itself, to limit its activity or longevity directly. Often only the slightest change in the environment will bring about a major change in disease activity, such as drying of the soil. The quality and quantity of non-pathogens are both important, and contribute to more complexity, and usually more biological stability. Fusarium foot rot of wheat first was a serious problem in the low- to intermediate-rainfall areas, particularly with the more progressive farmers. This was traced to the occurrence of severe plant water stress triggered by excessive nitrogen fertilization. By managing plant water potentials, the parasitic activities of Fusarium culmorum are virtually prevented. By leaving standing stubble, the saprophytic activities of this fungus are virtually prevented. Pythium root rot generally requires control only in the intermediate- to high-rainfall areas. The most effective controls are combinations that 1) minimize wheat straw on the surface or in the top 10-15 cm soil, 2) keep the soil surface exposed to drying winds and sun, especially in early growth, and 3) keep soil matric potentials in the top soil drier than -0.4 to -0.5 bar. Straw can be eliminated by burning, burial, or rotation (peas, lentils). Fumigation of the soil, not the straw, is necessary to eliminate the pathogens. Pythium is also limited by early seeding, and is less prevalent in soils without a tillage pan. To maximize take-all antagonism, tillage and delayed seeding can be used. Also the use of ammonium rather than nitrate fertilizer suppresses take-all, and any fertilizer will suppress it on an N-starved soil.
3200. Strand, L.L (ed.). 1990. Integrated pest management for small grains.. Univ. Calif. ANR Publ. 3333, Oakland, CA. 126 pp..
This publication is part of a series on major crops in California. It is a well-written volume with a wealth of information. There are many figures and pictures included to help in diagnosing pest problems. Cultural, biological, mechanical, and chemical controls are included.
6359. Smiley, R., D. Wilkins, W. Uddin, S. Ott, K. Rhinhart, and S. Case. 1989. Rhizoctonia root rot of wheat and barley.. OR Agr. Expt. Sta. Special Report 840, p. 68-79..
Rhizoctonia root rot is now considered the most severe root disease of barley in the PNW. It is more important than take-all and Pythium on wheat produced in drier areas (<16" precip.). Based on long-term plots at Pendleton, different management systems are unlikely to greatly influence the biological resistance of soils to Rhizoctonia. Rotational crops susceptible to Rhizoctonia include wheat, barley, peas, chickpeas, lentils, and rapeseed. The disease is less apparent on small grains after legumes than after cereals. Rhizoctonia damage is always highest on no-till systems, but yields may not suffer due to improved water relations under conservation tillage. Australian research indicates that applications of N and P fertilizers can reduce the disease. There appear to be detrimental herbicide interactions with Rhizoctonia, particularly Glean on high pH soils. Also, the use of glyphosate increased disease incidence, perhaps by signalling the pathogens to move from the dying plants to newly seeded ones. A delay of at least 2 weeks is suggested between chem kill and planting of a new crop.
6370. Smiley, R.W.. 1990. Seed treatment fungicides for wheat and barley.. Sherman Station Field Day handout, OSU, Moro, OR.
Seed applied fungicides failed to improve yields of winter wheat or were inconsistent from site to site and/or year to year. The most consistent treatment for winter wheat was a combination of Apron and Vitavax 200. This mixture increased wheat yields by 3%. Fall barley yields were either unchanged or reduced, while spring barley showed the best economic response. Thus, an economic response to seed treatment is unlikely in the absence of damaging amounts of smut disease. Since control of smut depends on the combination of fungicide seed treatments and genetic resistance, which has been stable for decades, the use of untreated seed is discouraged to avoid the loss of genetic resistance by cereal cultivars.
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March 31, 2004