Soybean Vein Necrosis Virus; North Central Soybean Research Program

My name’s Daren Mueller I’m a Iowa
State extension soybean plant pathologist I am Kiersten Wise I’m an extension specialist for field crop
diseases at Purdue University Hi I’m Damon Smith extension field crops pathologist for the University of Wisconsin-Madison What we’re looking at soybean vein necrosis virus Soybean vein necrosis is a
Tospovirus similar to tomato spotted wilt virus. This is the
first tospovirus however in soybean and we actually don’t know very much
about it however we do know that it is transmitted by thrips vectors One other things we
want to talk about is the symptoms of this disease and then also how to differentiate it from other
foliar diseases The symptoms that we sometimes see include a yellowing as
well some browning along with eventual necrosis
of the leaves, or death of the leaves, then eventually defoliation So it’s very important that we get down
into the canopy and look at the lesions that are on the leaves So the symptomology that we see with soybean vein necrosis virus can vary from this type of the yellow vein
syndrome which we see early on and sometimes you can even see the
injury from the thrips factors which entails very very small holes near the veins where they have fed. As the disease progresses the symptom then becomes more of a brown or necrotic lesion on the leaves which you can see
here. The most severe symptom you’re looking at here where we have
necrosis and chlorosis which is yet browning and yellowing respectively of the leaf and you can see the edges of the leaf are beginning to curl and shrivel up Even more severe cases the lesions will crack and fall from the plant and
eventually this leaf will defoliate from the plant itself. It’s very easy to
confuse soybean vein necrosis virus with many of the other diseases that we see
in soybeans Really as you start digging you can see
all sorts of different types of spots you can see little yellow spots in the
lower canopy you can see tattered leaves you can see a whole array of things and so one other
things you want to be doing is you want to notice where exactly are the
leaves coming from so you have a different type of symptom
sometimes in the lower canopy than you would see
in the upper canopy and so we’re gonna sort of walk through what spots
that we see in different parts of the
soybean plant In the lower canopy we commonly see diseases such as brown spot this is one that’s in most indiana
soybean fields every year it’s got some small angular brown spots
that can sometimes be surrounded by a yellow halo and then as the leaves senesce the
entire leaf can turn yellow A second disease that we see is called
bacteria blight and this is shown here as again you have
brown spot so can be confused with Septoria brown spot but this is
oftentimes seen in the upper canopy and so this is one where, fairly young symptoms, where you see the black or darker lesion was
followed by a yellow halo and eventually it’s going to grow to the
point where you see some of these halos growing together, some of these lesions, growing together and then the leaves dropping part of the leaf
tissue so it has tattered appearance and so this is bacterial blight on soybean again it’s and usually found in the
upper canopy So a third disease is downy mildew and this is one that is a little bit
different than bacterial blight or brown spot because it doesn’t usually have
brown spots that are associated with it so this disease is usually a lighter
green color an is usually fairly irregular shaped
lesions and so this shows up most likely in the upper
canopy can be in the mid canopy as well one of the best ways to confirm that is
downy mildew is to actually turn that leaf over and
then use a hand lens, and I’m not going to
use it properly, but you can put that hand lens over that lesion and you can see white growth, sometimes
in the morning you can see that white growth without the
hand lens or without without any any magnification but it is one the
best ways to confirm it Now there’s another disease in this
canopy that’s known as frogeye leaf spot and this is in the upper canopy as you
see here and frogeye leaf spot gets its name because its looks like a frog’s eye it’s got kind of a gray to brown center lesion that’s surrounded by a
purple or dark halo and this will be very small lesions
that can coalesce into larger lesions on these trifoliates One of the other foliar diseases that
you can see at least while the leaves are still attached is
called sudden death syndrome and this is very very young symptoms of sudden death syndrome where you see the yellowing just starting to occur on
the leaf and as this disease progresses you’ll
see there’s actually some brown or necrosis that is also occurring this we usually occur in between
the veins, eventually as this disease progresses the leaves will drop and and and the
petioles will remain At this point in time we don’t recommend
management for this disease since we don’t know the economic impact
of the disease in soybeans There’s much ongoing research we
understand a little bit about this however we’re still gonna look into cultivar resistance and also which vectors are important.