I must say I'm a little puzzled by this. If I accept the
admittedly anthropocentric definition of weeds--"weeds are plants that are
out of place"--i.e., ANY plant that humans don't want in a particular
spot (wheat seedlings in a soybean field, soybeans in a corn
planting, etc., etc.), then what is to account for the apparent
selectivity of these DRB? Will they weaken the soybeans in the corn
field but only the wheat in the soybean field? And what of the
plants that are clearly only weeds to our (agri)culture, such as
purslane, chuffah (nutsedge) and dandelions--plants that are crop
plants in other cultures or times? What about amaranth=pigweed?
I guess I'll have to wait to see some of the published research.
> From: vcz1@cornell.edu
> Date: Fri, 30 Jun 2000 22:14:12 -0400 (EDT)
> To: sanet-mg@ces.ncsu.edu
> Reply-to: vcz1@cornell.edu
> Subject: Cropping systems influence biological weed control
> CROPPING SYSTEMS INFLUENCE BIOLOGICAL WEED CONTROL
>
> Boosting organic matter in soil creates a healthy
> environment for
> soil-dwelling bacteria that suppress weeds. That's
> according to
> Agricultural Research Service scientists who for the
> first time have
> determined which cropping systems provide the best home
> for these
> beneficial bacteria.
>
> ARS scientists report that to create ideal soil
> conditions, farmers should
> rotate their crops, reduce tillage and keep herbicide
> applications to a
> minimum.
>
> The beneficial microbes, called deleterious
> rhizobacteria (DRB), live on or
> within millimeters of--weed roots, and they feed on
> substances that ooze
> from those roots. As the name DRB implies, these
> bacteria are bad for
> weeds. Although they suppress weed growth, DRB normally
> don't interfere
> with crop plant growth.
>
> Robert J. Kremer, a microbiologist with the ARS
> Cropping Systems and Water
> Quality Research Unit in Columbia, Missouri, says many
> DRB keep weed seeds
> from germinating and produce toxins and excessive
> concentrations of plant
> growth hormones that put the life processes of weed
> seedlings in
> "overdrive." Consequently, root cells may rupture and
> leak, replenishing
> the DRB diet. Once weakened by DRB, weeds are less able
> to compete with
> other plants, and they become more vulnerable to other
> control measures.
>
> Kremer and graduate student Jianmei Li researched
> cultures of DRB
> associated with the most dominant species of weeds in
> six different
> cropping systems. In general, the highest numbers of
> weed-suppressing DRB
> came from fields where crops were rotated, chemicals
> and tillage were
> minimal, and organic materials like composts were
> added. DRB fared best in
> a corn-soybean-wheat-cover crop rotation. An organic
> strawberry system with
> compost was a close second.
>
> The researchers believe the research information can be
> used to modify
> current cropping practices or design novel ones to
> promote development of
> DRB and take advantage of their natural
> weed-suppressive effects.
>
> ___________________________________________
>
> Scientific contact: Robert J. Kremer, ARS Cropping
> Systems and Water Quality
> Research Unit, University of Missouri, Columbia, MO.,
> phone (573) 882-6408,
> fax (573) 884-5070, KremerR@missouri.edu.
>
>
>
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