Number 4
October 18, 2005
1. Control of woody plants in rangeland _____________________________________ 1
2. Starter fertilizers for late-planted wheat ___________________________________ 3
3. Sorghum regrowth considerations _______________________________________ 4
1. Control of woody plants in rangeland
Shrubs and trees are natural competitors with grasses and forbs on rangeland in Kansas. It
is not practical, or even desirable, to control all woody vegetation on rangeland. Woody
plants have value to cattle and wildlife around streambanks and ravines, for example. But
excessive amounts of woody vegetation on grazinglands will reduce the livestock
carrying capacity and should be controlled. Proper grazing with cattle will slow down
woody plant invasion to some extent, but cattle do not consume large amounts of browse.
Prescribed burning is the primary means of woody plant control on Flint Hills bluestem
range. Annual mowing in the spring, once woody plants have leafed out, can also be
effective.
With root-sprouting plants, the timing of control measures is especially important. The
goal is to damage the plants when they reach their low ebb in food reserves. Almost all
woody invaders of rangeland can sprout from the roots.
With plants that do not root sprout, primarily eastern red cedar, mowing or burning can
be effective at any time of the year. If eastern red cedars are mowed or cut, producers do
not have to treat the stump with an herbicide since eastern red cedars do not root sprout.
Producers should make sure eastern red cedars are cut off below the lowest green branch,
however. If any branches are left, regrowth is possible.
A combination of prescribed burning and mowing may be needed if there is a mixture of
root sprouting woody plants that reach their low ebb in food reserves at different times of
the season. For example, buckbrush should be burned or mowed in late spring (late April
to mid-May). Control measures taken at that time, however, will have no effect on
smooth sumac, which reaches its low ebb in food reserves about a month later.
For this and other reasons, there may be areas of rangeland with highly concentrated
stands of woody plants that were not controlled by fire or mechanical means. If those
areas have good potential for producing desirable forage, producers should consider
making spot treatments of the woody vegetation before it becomes unmanageable. Fall is
a good time to make those treatments.
Scattered stands of individual trees or shrubs should either be treated individually using
the basal bark method (for labeled plants less than 4-6 inches in diameter) or the cut
stump treatment method. The basal bark and cut stump treatments will not be effective if
there is standing water or ice around the base of the plant so that the plants cannot be
treated down to the soil line. Producers can treat smaller susceptible woody plants
individually this fall by spraying the basal stem parts with triclopyr plus diesel fuel. The
lower 12-15 inches of the stems or trunks of susceptible small trees and shrubs should be
thoroughly wetted with a triclopyr-diesel mixture. Triclopyr goes by the tradenames
Remedy and Pathfinder II. Pathfinder II is a ready-to-use product and does not have to be
mixed with diesel. PastureGard is a premix of triclopyr and fluroxypyr, and can be
applied as a basal bark or cut-stump treatment as a 50% solution in diesel.
If the woody plant is 4-6 inches in diameter or more, the best method is to cut it off at
ground level and treat the cut surface and sides of the stump with triclopyr and diesel fuel
within 30-60 minutes, before the sap seals over the exposed area. The stump of
cottonwood, elm, and oak species can be treated with a 1:1 ratio of dicamba (Banvel,
Clarity) in water instead of triclopyr if desired. As mentioned earlier, the stumps of
Eastern red cedars do not need to be treated.
Common honeylocust can resprout from a wide diameter area around the main plant
because of root suckers, so producers should make a basal bark treatment to kill the entire
plant in the fall. Then the main plant can be cut down in subsequent years once the tree is
dead.
Tordon RTU can be used on cut surfaces in noncropland areas such as fence rows and
roadsides. However, Tordon RTU is not labeled for use on range and pasture.
-- Walt Fick, Rangeland Management
785-532-7223
whfick@ksu.edu
2. Starter fertilizers for late-planted wheat
Producers applying starter P fertilizer for wheat often place the fertilizer either with the
seed or deep-banded with nitrogen as a preplant application (dual applications, deep
banded). Generally, both these application methods give the same excellent results.
However, as wheat seeding is delayed well past the optimum seeding date in the fall, the
more placement of the P fertilizer directly with the seed is favored. The later the planting
date, the more fall root development is slowed, making it more difficult for preplant
banded P to get into the roots. The closer the fertilizer is to the seed, the sooner the plant
roots can get to it.
Applying the starter P directly with the seed may mean that producers will have to limit
the amount of nitrogen applied as compared to preplant dual applications. Urea and UAN
solution should not be placed in direct seed contact.
-- Dale Leikam, Nutrient Management Specialist
785-532-6183
dleikam@ksu.edu
3. Sorghum regrowth considerations
Grain sorghum may start sending out basal tillers, or suckers, at this time of year. Suckers
will slow drydown, but there’s not a lot that can be done about it except to spray the field
with glyphosate after the grain reaches physiological maturity. This helps speed drydown
of late sorghum. If glyphosate is applied to sorghum that sent up late suckers, then the
grain in those sucker heads probably will not be at physiological maturity. If possible, the
combine header should be set high enough to avoid harvesting any of those sucker heads
low in the canopy.
Grain sorghum that has been harvested may start sending out regrowth this fall. Regrowth
can occur anytime until a hard, killing freeze of 25-28 degrees has occurred. High levels
of nitrate or prussic acid can occur in sorghum regrowth, or in the stems of stubble where
there is no regrowth. Under normal conditions, grain sorghum contains little free prussic
acid, or cyanide. However, when freezing, drought stress, wilting, or mechanical injury
damages plant tissue, free cyanide is produced.
Grazing can continue on grain sorghum stubble until frost, or even after frost if the plants
are allowed to turn brown before they are grazed. Do not graze frost-damaged or stunted
grain sorghum until they have been killed (turn brown) by the frost. If plants begin to
grow again after being frost damaged, they should not be grazed until the regrowth is 18
inches tall or the entire plant is killed by frost and turns brown.
There are some important precautions producers should be aware of before grazing or
utilizing grain sorghum stubble fields.
1. Don't graze on nights when a frost is likely. High levels of the toxic compounds are
produced within hours after a frost occurs. When only plant tops have been frosted, new
shoots may regrow at the base of the plants. These can be very dangerous because of high
prussic acid content, and because cattle will selectively graze them. Do not graze frosted
summer annuals until regrowth of shoots is 15 to 18 inches tall, or until several days after
the entire plant and shoots are killed by subsequent frost.
2. Don't graze or green chop grain sorghum for at least 4-6 days after a killing frost, or
until the plant is dry. Plants that are frozen may release high concentrations of prussic
acid for several days. After wilting, prussic acid release from plant tissues will decline.
Dead plants have less free prussic acid. Prussic acid concentrations are higher in fresh
forage than in silage or hay because HCN is volatile and dissipates as the forage dries.
However, if the forage had an extremely high cyanide content before cutting, or if the hay
was not properly cured, hazardous concentrations of prussic acid could remain.
3. Before a frost has occurred, grain sorghum stubble is usually safe to graze, but small
green shoots of sorghum or shattercane may develop in the stubble. Abundant regrowth
can be dangerous. Young plants or regrowth after grazing contain higher concentrations
of prussic acid and should not be grazed until plants have reached a height of 18 inches.
Never turn hungry animals into questionable forage.
Prussic acid does dissipate from plant tissue; therefore, hay that has been properly cured
is safe to feed. Properly ensiled forage is also safe to feed. When forage is being utilized
as green chop, it is important to feed the green chop in a timely manner. If the green chop
is allowed to heat, cyanide is released and the forage becomes toxic. If questionable
forage must be grazed or utilized as green chop, feed dry hay along with the fresh plant
material.
Grain sorghum, forage sorghum, sudangrass, sudan-sorghum hybrids and pearl millet are
notorious nitrate accumulators. Nitrate content generally is highest in young plant growth
and decreases with maturity. Sorghums and sudangrass are exceptions because
concentrations usually remain high in mature plants. If plants are stressed at any stage of
growth, they can accumulate nitrate. Nitrates normally accumulate in stems and
conductive tissues. Highest nitrate levels occur in the lower one-third of the plant stalk.
Concentrations tend to be low in leaves because nitrate reductase enzyme levels are high
there.
Nitrates accumulate in plants during periods of moderate drought. During a severe
drought, lack of moisture prevents nitrate absorption by plant roots. Following a rain,
however, the roots rapidly absorb nitrate and accumulate high levels. A light frost can
damage plant leaf area and reduce photosynthetic activity. With less available energy,
nitrates accumulate in the plant.
The same precautions for prussic acid poisoning will help prevent nitrate poisoning.
-- Jim Shroyer, Crop Production Specialist and State Extension Agronomy Leader
785-532-0397
jshroyer@oznet.ksu.edu
These e-Updates are a regular weekly item from K-State Extension Agronomy. All of the
Research and Extension faculty in Agronomy will be involved as sources from time to
time. If you have any questions or suggestions for topics you'd like to have us address in
this weekly update, contact Jim Shroyer, Research and Extension Crop Production
Specialist and State Extension Agronomy Leader
785-532-0397 jshroyer@oznet.ksu.edu