Discriminating Weed Sprayer
Dr. Lei Tian, University of Illinois, Ag
Eng. Dept., 1304 W. Pennsylvania Ave., Urbana, IL, 217-333-7534,
Source: Ag Eng. News
Several manufacturers are looking at a prototype sprayer developed
at the University of Illinois. The "smart sprayer" uses
video cameras mounted ahead of the spray boom to determine the
size and density of weeds between the crop rows and creates a
weed map and application prescription. The two-dimensional image
sensor array has higher resolution than the WeedSeeker's photo
The University of Illinois smart machine sprays a 10 percent
rate of herbicide across the entire field but automatically calculates
and increases the rate at each spray nozzle to match weed size
and density. "Young weeds may only require a 20 percent rate
of the herbicide, whereas areas with large numbers of large weeds
may need a full rate," explains Dr. Lei Tian, professor of
ag engineering at the University of Illinois. The machine can
apply a different variable rate of herbicide from each nozzle,
whereas the WeedSeeker nozzles can only be turned on or off.
"We've found that many fields are only 10 to 30 percent
infested with weeds that need to be sprayed. Our average herbicide
savings has been 52 percent," Tian says. He has been using
Roundup Ready herbicide on Roundup Ready crops, but a selective
herbicide could be used on conventional crops instead. Like the
WeedSeeker, the University of Illinois machine does not distinguish
between crops and weeds or different weed species at this time.
Green Manure Crops Enhance Natural Disease Control in Soils
New research results from the 2000 growing season show that green
manure cropsbuckwheat, oats and sorghum-sudangrasssignificantly
reduced root disease in alfalfa. The green manure crops enhanced
the natural disease-suppressive activity of the soil microorganisms,
according to Linda Kinkel, University of Minnesota plant pathologist.
In the first two years of the trials, Kinkel and colleagues focused
on identifying green manure crops that could enrich the activity
of natural soil antagonists.
During the third yearthe 2000 growing seasonthey
initiated studies on disease control potential of the best green
manures. They found significant control of Phytophthora
root rot in alfalfa preceded by a single planting of green manure
crops. Buckwheat, oats and sorghum-sudangrass crosses all enhanced
the soil's natural disease control activity and provided significant
disease control. "Not all green manure crops enhance natural
antagonists of soil pathogens," Kinkel says. "Of 13
green manure crops we've studied, some do nothing to enhance soil
antagonists." So although crop rotations that include green
manures help reduce soil pathogen levels and prevent disease build-up,
they don't necessarily enhance natural disease suppression activity.
Kinkel says oats, buckwheat, canola and sorghum-sudangrass have
been the most successful crops for enhancing activity of natural
soil antagonists to control pathogens.
Much of Kinkel's work has involved diseases of potatoes. "Using
green manure crops should increase profits, since they involve
no added costs. In the longer term, we'd like to develop three-
to five-year cropping systems involving green manures and crops
such as potatoes, corn, green beans and alfalfa, where the green
manures would enhance natural disease control. These integrated
cropping systems could provide broad-based disease control for
all crops." "Some inoculative biological controls work
incredibly well," Kinkel says. "But many fail completely
for reasons that are difficult to discern."
Bringing Back Native Soil Fungi
When you think of endangered species, you never think of soil
fungi. Yet the fungi that make plants hardier have had their numbers
greatly reduced by the intensive agriculture practiced in the
United States since the 1950s. ARS scientists are trying to figure
out how to put these beneficial soil fungi back, as farmers make
the transition to using less chemicals. One approach researchers
are evaluating is to mix the fungicalled mycorrhizaeinto
potting soil planted with grass or other host plants. Farmers
would buy these "inoculated" seedlings and plant them
in compost. Then, after the fungi multiplied, farmers would apply
the colonized compost with manure spreaders.
The mycorrhizal fungi are beneficial organisms that live on plant
roots and help them extend their reach for water and fertilizer.
In exchange, the plant gives the fungi the sugar they need to
grow. The most common type lives inside root cells and extends
long, rootlike threads in the soil.
Farmers today have to rely on whichever of these native fungi
survived years of chemical use--from synthetic fertilizers to
fungicides. An ultimate goal is to produce the fungi in large
quantities efficiently and economically, without host plants.
They would then be applied as a biofertilizer before planting.
Building Wheats with Multiple Resistance to Leaf Rust
Genetic markerstools of modern biotechnologyare being
used by scientists to fortify wheat with longer-lasting resistance
to leaf rust, a disease that costs wheat farmers millions annually.
ARS plant geneticist Gina Brown-Guedira in Kansas, is building
gene complexes using markers closely linked to leaf rust resistance.
The markers are made of genetic material called DNA.
Brown-Guedira is combining leaf rust resistance found in two
ancestors of modern wheat: Aegilops tauschii (also known
as goatgrass), a weedy wheat relative found from Afghanistan to
Syria, and Triticum timopheevii from Iran, Iraq and Turkey.
Ultimately, genes from these ancestors can be combined and moved
into germplasm from which new resistant wheat varieties can be
Leaf rust is caused by a fungal pathogen called Puccinia triticinia.
In addition, leaf rust seriously affects the milling and baking
qualities of wheat flour. In the past, wheat-breeding programs
have released resistant varieties with only a single leaf rust
resistance gene. A few years later, these varieties usually begin
to lose their effectiveness against the rapidly changing fungus.
The result is a boom and bust cycle of wheat disease for farmers
in the major wheat growing areas of the world. Scientists currently
must use time-consuming classical genetic studies to determine
if a plant has more than one resistance gene. In contrast, Brown-Guedira
can look for the DNA markers at any stage of plant growth without
having to infect plants with the fungus. Because the markers are
closely linked to the resistance genes, there is a good chance
the genes are present.