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Corn & Soybean News August,
2007, Volume 7, Issue 7
Cooperating
Departments: Agricultural Economics, Biosystems and Agricultural Engineering,
Entomology, Plant and Soil Sciences, Plant Pathology Editor:
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In this
Issue: 1. Drought and Weak Corn Stalks 2. Mycotoxin Risk Higher During Drought 5. Ryegrass Cover Crop Challenges |
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Weak
Corn Stalks from Drought The
drought conditions most likely have weakened corn stalks. Stands will need to
be checked prior to harvest this year. Corn
plants require water to receive most nutrients from the soil. In drought
conditions, those nutrients cannot be pulled from the soil at high rates.
Corn kernels need nutrients to develop properly. If the roots are unable to
take in nutrients from the soil at adequate rates, then the corn plant will
pull nutrients from the stalks to fill out the kernels. This
cannibalization of the roots will leave them with poorer structural
integrity. Corn plants are more likely to fall over with heavy winds or heavy
rains. Ear drop from the stalks is more likely as well. Corn
fields will need to be scouted for stalk integrity. Grab stalks above the ear
and pull them about 10 to 12 inches from center. Let go. If the stalks return
to their normal upright position, then stalk strength is acceptable. If the
stalks fail to return to their normal position, then weak stalks are likely a
problem. Be
prepared to harvest fields as soon as moisture levels are acceptable. Corn
may need to be harvested wet and dried to 15 or 14% moisture. |
· Lack of water usually
weakens stalks. · Cornfields should be
scouted for stalk strength. |
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Mycotoxin
Risk Higher During Drought Paul
Vincelli, Plant Pathology Mycotoxins
are toxic substances produced by fungi that can develop in grain before
harvest or during improper storage conditions. Fumonisins are a class of mycotoxins which cause
toxicity to horses, swine, and other animals. There is also concern about
possible detrimental health effects of fumonisins to humans. Fumonisins
commonly are produced by the fungus Fusarium
verticillioides, the fungus that causes Fusarium ear rot. Fumonisin
contamination in the field is often associated with hot, dry weather prior to
and during silking, conditions many fields experienced this summer.
Fumonisins also have been reported following late- season rains on corn where
harvest has been delayed. Aflatoxins are probably the most well-known mycotoxin,
because they have been long regulated by the US Food and Drug Administration.
Although aflatoxins are very uncommon in Kentucky corn as it comes out of the
field, they can occur preharvest in crops that were exposed to sustained
drought stress and high temperatures during grain fill. In
a year like this with conditions that might enhance mycotoxin risk, prompt
harvest will help reduce the risk of contamination. Leaving a crop in the
field for an extended period increases the risk of mycotoxin buildup. It also
may be advantageous to harvest at a moisture concentration of 25 to 28% and
dry down the grain to no more than 15.5% within 24 hours. Rapid dry down of
the grain should help to reduce the risk of fumonisin buildup, as compared to
letting the crop dry down in the field. Keep
in mind that, even if the corn was not contaminated in the field, mycotoxins
can accumulate in corn in storage, if environmental conditions permit. Spores
(microscopic fungal "seeds") of mycotoxin-producing fungi can be
present on the outside of kernels as the grain is harvested and stored. By
themselves, the spores do not produce significant levels of mycotoxins.
However, when warm, moist conditions develop in storage, the spores can
germinate and infect the harvested grain, which can then result in
contamination. For these reasons, it is recommended that grain be cooled to
60 degrees F or lower as soon as possible after drying to control storage
temperatures and mold and insect activity. If
there is any doubt about the condition of corn already in storage, it should
be inspected for mold and tested at the UK Grain Quality Testing Laboratory. Additional
Resources More information on
fumonisins in corn is available online at http://www.ca.uky.edu/agc/pubs/id/id121/id121.pdf. More information on
aflatoxins is available at http://www.ca.uky.edu/agc/pubs/id/id59/id59.pdf Grain storage
recommendations are available in the Extension publication, Principles of Grain Storage (AEN-20). Information on
laboratories that do mycotoxin testing is available at http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-1.pdf A multi-state Extension
publication entitled Moldy Grains,
Mycotoxins, and Feeding Problems is available at http://www.oardc.ohiostate.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm
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· Dry weather at key
periods favors fumonisins and aflatoxins. · Early harvest and quick
dry down of grain will reduce the risk. |
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Charcoal Rot Likely to
be a Problem this Season Don Hershman, Plant Pathology With the excessively dry conditions
that exist in most parts of the Commonwealth, I believe the odds are quite
high that many soybean fields in The disease increases as the stressed
soybean plants approach maturity and premature death of affected plants is a
common outcome. Yield can be severely compromised by charcoal rot. However,
because the disease is most common during drought conditions, most producers
attribute low yields in dry years to lack of sufficient soil moisture and do
not usually realize that charcoal rot has also taken a toll. Under moderate
drought conditions, affected plants usually occur in patches associated with
compacted soils or on hills. In a severe drought, large percentages of fields
may show evidence of disease. Symptoms
and Survival Plants affected by charcoal rot will
show a light gray or silvery discoloration of the surface tissues of taproots
and lower stems. Leaves from infected plants are smaller than normal and
plants may wilt and eventually die as symptoms progress. When the surface
tissues of lower stems and taproots are removed by scraping with the thumb
nail, extremely small, jet-black fungal structures called microsclerotia will
be found embedded in the diseased tissue. These structures are usually so
numerous that they resemble charcoal dust (or "pepper") and provide
the name for the disease. Splitting the taproot often reveals dark gray to
blue-black streaks within. Seed may become infected in severe cases, as is
evidenced by “blackseed”, which is often cracked with embedded
microsclerotia. The fungus survives between seasons as
microsclerotia in plant debris or in soil under dry conditions. Control
Options for this Year Because of the widespread distribution
of M. phaseolina in
Control
Options for Next Season Genes for tolerance or moderate
resistance to charcoal rot have been identified by researchers, and one or
more of these may be incorporated into varieties available for planting in
some maturity groups. However, few seed companies have good information about
charcoal rot tolerance or resistance for the varieties they sell. Still, it
is a good idea to ask your seed salesman for that information just in case
they have access to it. Rotating affected fields to non-host crops, such as
cereals (1 to 2 years), or to corn or grain sorghum (3 years or more), may
help reduce charcoal rot by lowering soil populations of microsclerotia,
which serve both as the infectious and the survival unit. Avoidance of the disease with irrigation
during the reproductive stages is an option next year. Where irrigation is
not possible, it may help to avoid excessive seeding rates and low soil
fertility, both of which stress plants and predispose them to charcoal rot.
Maintaining soil moisture by planting soybeans no-till, may also help
moderate the disease. Finally, it may be possible to avoid charcoal rot using
planting date and maturity group combinations that avoid the most common
drought period from late-July through August.
According to
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· Charcoal rot is usually a
problem with dry weather. · Once the disease is
present, management options are limited. |
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Soybean
Forage: A Rescue Option? The
dry weather has some farmers concerned about whether or not double-crop
soybeans will complete seed fill. Many of the plants in these fields are only
about 15 inches tall and have not filled the canopy. Farmers are hoping to
capture some yield from drought-stressed soybeans by harvesting them for
forage. Soybeans
for hay will yield about 2 tons/acre of dry matter under the most ideal
conditions. Soybeans that are only 15 inches tall may yield less than 1
ton/acre of dry matter. Ideally,
soybeans should be harvested when green, plump seeds fill the pod cavity (R6
growth stage) to maximize yield and quality. When harvesting drought-stressed
soybeans, seed size will be much smaller, meaning that much of the feed value
will come from the leaves. Ensiling or wrapping the soybeans for balage will
retain more leaves and may be a better option than baling the soybeans for
hay. Soybeans
harvested for silage should be about 35% dry matter for trenches or upright
silos, but 40 to 50% dry matter for balage. Crude protein could exceed 15%
and TDN could exceed 50% if seed fill is completed and most of the leaves are
retained. Small soybeans harvested before seed fill may have very different
feed values. Before harvesting the soybeans, try to estimate yield. Harvest an area of soybeans (for example, 10 square feet) and weigh the harvested soybeans. Take a subsample of the soybeans, weigh them and then dry them to get a dry weight. Using these numbers, you can calculate dry matter concentration of the soybean plants and ultimately, dry matter yield. In some cases, yields may be so low, that they soybeans are not worth harvesting for forage.
Check the labels of all herbicides and other pesticides used on the soybean crop to for any restrictions for grazing or harvesting soybeans as a forage. Harvesting
soybeans for forage should be the very last option employed. If yields appear
to be adequate and you can properly ensile the soybeans, then harvesting them
for forage could be the last best option. |
· Soybeans can be harvested
for forage. · Ensiling is a better
option than trying to make hay. |
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Ryegrass
Cover Crop Risks in James
R. Martin, William W. Witt, and J.D. Green, Plant and Soil Sciences Seeding
annual ryegrass as a cover crop has been promoted in a number of areas in
annual and perennial cropping systems.
While there may be benefits with this practice, grain crop growers
need to be aware of the potential drawbacks encountered when seeding ryegrass
as a cover crop in Corn Problems Ryegrass
can compete with young corn plants during early spring and often harbor
rodents that eventually feed on corn seed.
Therefore, killing ryegrass vegetation well in advance of planting
no-till corn is necessary to avoid these problems. Controlling
ryegrass in no-till corn requires good management skills and additional
expense. A high rate of glyphosate may
provide acceptable control, but it requires several weeks for ryegrass to
die. This slow activity of glyphosate
during early spring may not be acceptable for managing a heavy infestation of
ryegrass prior to planting no-till corn. It
is important to recognize that sequential programs will not provide 100%
control of annual ryegrass consistently. Furthermore, sequential programs
require extra time and additional expense that can range from $ 10.75 to $
31.50/A. Transitioning to Other Crops The
risk of ryegrass emerging as a ‘weedy’ plant in subsequent crops is another
factor to consider when using ryegrass as a vegetative cover in a grain crop
rotation. This problem is very likely to occur where ryegrass plants
initially escape control in corn and are able to produce viable seeds that
germinate the following fall. Carryover
of seeds in the soil can also contribute to future problems with
ryegrass. While most ryegrass seeds
germinate soon after exposure to a favorable environment, research has shown
that a small percentage of seeds can remain viable in soil six to seven
years. Therefore, even if a ryegrass
cover crop is completely killed, there is a chance that seeds remaining in
soil can develop as a problem in subsequent crops such as wheat. Wheat Problems Ryegrass
is especially competitive in wheat because it can emerge quickly in the fall
and grow rapidly in early spring. One
ryegrass plant per square foot can reduce wheat yield by approximately 4
percent. Management
skills are as important in wheat as they are in corn. Sporadic emergence patterns of ryegrass
challenges the grower in determining the optimum time to spray for this
weed. Preventing ryegrass plants from
producing seed is particularly important since its seeds are easily spread
during the harvesting process. A few
ryegrass plants that escape control in wheat can evolve into a major infestation
in subsequent crops in a short period of time. A
large drawback in dealing with ryegrass in wheat is the cost of using
herbicides which can range from $16.75 to $29.50/A. Potential “Fit” for Ryegrass Good
seedling vigor, fast emergence, and low cost make ryegrass attractive for
certain areas prone to erosion. A seed
mixture of ryegrass with tall fescue may help establish a sod cover for
waterways or highly eroded slopes that are not used for grain crop
production. Nevertheless, these areas
need to be properly managed to limit spreading ryegrass seed to fields used
for producing grain crops. This
includes clipping or mowing these areas before ryegrass plants mature to
limit new seed production, especially areas in close proximity to fields used
for grain production. Keeping mowing
equipment clean of seed will also help contain ryegrass. References: ● Lacefield, G.,
M. Collins, J. Henning. Tim Phillips, M. Rasnake, R. Spitaleri, D. Grigson,
and K. Turner. Annual Ryegrass.
AGR-179. 2005. ● Liebel, R. and
A.D. Worsham. Interference of Italian
Ryegrass (Lolium multiflorum) in
wheat (Triticum aestivum). Weed
Science, 1987. Vol. 35: 819-823. ● Martin, J.
R. Ryegrass – Crop or Weed. Kentuckiana Proceedings, Dec 1993. ● Martin, J. R.,
W. W. Witt, and D. L. Call. Feb. 1999. Managing Italian Ryegrass in Wheat and
No-tillage Corn. Proc. of the 4th
National Wheat Industry Research Forum. pp. 31-33. ● Martin, J. R. and C. H. Slack. 2005. Factors
Affecting Burndown Control of Italian Ryegrass with Glyphosate. 2005.
Proc. of Southern Conservation Tillage Systems Conference. 27: 166. ● Martin, J. R., D. Call, and J. James. 2003.
Italian Ryegrass Control with Wheat Herbicides. Proc. of Southern Weed
Science Society. 56: 307. ● Martin, J. R., ● Nickel, K. l.
Going Deep with Annual Ryegrass. CTIC Partners. Oct, 2006. Vol. 24, No 3. ● Rampton, H. H.
and T. M Ching. Persistence of Crop
Seed in Soil. Agronomy Journal, Mar-Apr 1970, Vol. 62: 272-277.
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· If ryegrass is to be used
as a cover crop, careful attention to management must be followed. · Any mistakes could lead
to weed problems for subsequent crops. |
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Corn
is in the dent stage across much of Kentucky. Drought conditions will reduce
yield potential. |
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