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This summer, thanks to the efforts of our many Soybean rust/aphid
sentinel plot monitoring network volunteers, we have accumulated
a large amount of statewide information regarding soybean pest occurrence.
This information has documented the absence of soybean rust and
a general sub-economic population of soybean aphids in NY this season.
In addition to those two key soybean pests field observers
have reported the presence of "White Dwarf" soybean aphid forms,
white mold, and the first documented NY occurrence of two soybean
diseases sudden death syndrome (Fusarium solani f. sp. glyines)
and brown stem rot (Phialophora gregata f.sp. sojae). This
information will help to improve the data upon which to base management
recommendations and guide future research efforts.
The potential threat of soybean rust this season has passed and
soybean aphids should soon begin developing their winged forms signaling
their movement out of fields and to their winter hosts. Soybean
monitoring efforts will continue until first frost or soybean dry
down. This time of year soybean producers should be on the lookout
for field symptoms which can indicate the presence of soybean cyst
nematodes (SCN). Fortunately, this pest has not been reported in
NY. However, our environmental conditions are similar to Ohio, Pennsylvania
and Ontario, Canada where SCN has been confirmed in the last two
decades.
The soybean cyst nematode (SCN), Heterodera glycines,
is a parasitic eelworm that damages root systems, interferes with
uptake of water and nutrients, causes stunting, reduced stand populations,
crop yield and can predispose plants to root infecting diseases.
Symptoms of SCN damage can be mistaken for other crop production
problems such as stand establishment issues, seedling diseases/blights,
nutrient deficiencies, and soil compaction.
Nematode populations build up over the summer and signs of their
impact can be seen in field symptoms in the fall. Symptoms of SCN
injury can be mistaken for damage from compaction, iron deficiency
chlorosis and other nutrient deficiencies, drought stress, herbicide
injury, or other plant diseases.
A description of SCN and it's injury to soybeans can be found
in the IOWA STATE UNIVERSITY factsheet:
"Soybean Cyst Nematode"
prepared by Greg Tylka, extension plant nematologist.
The following information is taken from that reference.
"The first obvious symptom of SCN injury to soybeans is the appearance
in the field of circular- or oval-shaped areas of stunted, yellowed,
less vigorous plants. These infested areas will vary in their size,
often showing a sharp dividing line at the edges between stunted
and apparently healthy plants.
In areas with high pH soils, the yellowing of soybeans due to
SCN often is confused with iron deficiency chlorosis. However, there
are differences between symptoms of the two problems. Iron deficiency
chlorosis symptoms usually appear in early June, whereas yellowing
due to SCN will more likely occur in July and August. The yellowing
caused by iron deficiency chlorosis typically affects the areas
between the veins of the upper leaves. Yellowing due to SCN usually
starts at the edges of the leaves, and can affect leaves on the
entire plant. Iron deficiency chlorosis and SCN may occur in the
same field and even on the same plant.
An area of SCN damage often will appear elongated in the direction
of tillage operations. Most severe damage is often in the center
of the area, with damage decreasing towards the margins. Such areas
frequently develop near a field gate, entrance, wherever equipment
enters a field, or near fences where wind-blown soil may accumulate.
The above-ground symptoms of SCN damage can range from nonexistent
to severe depending on the age and vigor of the soybean plants,
SCN numbers, soil fertility, moisture levels, and other environmental
conditions. Injury usually is more severe in light, sandy soils,
but it also occurs in heavier soils.
One cannot rely upon above-ground symptoms for identification
of SCN infestations. If soybean yields in any field have decreased
for no apparent reason, more thorough examination of plants for
below-ground symptoms and a soil analysis for SCN are needed.
Below-ground Symptoms
Roots infected with SCN are dwarfed or stunted. SCN can decrease
the number of nitrogen-fixing nodules on the roots. SCN infections
also may make the roots more susceptible to attacks by other soil-borne
plant pathogens. Often it is difficult to recognize if roots are
stunted and have fewer nodules unless they are compared to uninfected
soybean plants.
The only unique symptom of SCN infection is the presence of adult
female nematodes and cysts on the soybean roots. These structures,
which appear as tiny, lemon-shaped objects on the roots, are white
initially, but turn yellow and then tan to brown as they mature.
They can be seen with the unaided eye, although observation with
a magnifying glass is easier. Roots must be carefully removed from
the soil for examination or the cysts may be dislodged. Observation
of adult females and cysts on the roots of soybean plants is the
only accurate way to diagnose SCN infestation in the field."
NY Soybean Cyst Nematode Survey 2006
A limited soil survey of 19 soybean sentinel plots for soybean
cyst nematode is being conducted in September through the Cornell
Plant Diagnostic Clinic. We are interesting in supplementing
this survey with soil samples from other soybean fields where there
is visual evidence of SCN-induced symptoms or where characteristic
cysts (egg sacks) have been found on soybean roots.
If you monitor a soybean field with symptoms similar to those
described above and you suspect SCN injury please contact
Gary Bergstrom (gcb3@cornell.edu),
Keith Waldron (jkw5@cornell.edu),
or Mary McKellar (mem40@cornell.edu)
for further information on sampling methods and sample submission.
New York State Soybean Rust Information Center
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