Cropping Systems Influence Biological Weed Control (fwd)

Lawrence F. London, Jr. london at
Tue Jun 27 13:21:03 EDT 2000

---------- Forwarded message ----------
Date: Tue, 27 Jun 2000 10:43:53 -0400
From: ARS News Service <isnv at>
Subject: Cropping Systems Influence Biological Weed Control 

Cropping Systems Influence Biological Weed Control


ARS News Service
Agricultural Research Service, USDA
Ben Hardin, (309) 681-6597, bhardin at
June 27, 2000

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

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 at
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