So I'll start first with the problems we find on onions.
The most common one we see is portrayed as neck rot.
It's caused by a fungus, Bortrytis aclada or Bortrytis
alii.
And that fungus likes temperatures in the field
of 60 to 70 degrees Fahrenheit.
You will not see symptoms on your onions
while they are in your garden or in your field.
The symptoms will show up later in storage.
But it will cause an infection of your plants.
The spores will be on the leaves and in the neck of the onion
and they survive in the soil.
And infections usually occur during moist and cool weather.
But they will remain unnoticeable.
And when the necks are not dry before you put the onions
in storage, then the infection becomes active
and about four to six weeks later in storage
when you take your onions out and you cut them open,
they will be rotten.
And you can lose up to 100% of your onions
in a really bad year.
So here's what the symptoms are.
And I don't know if you can see the cursor.
So the infection starts on the neck of the onion.
And then the fungus migrates down and in the process,
starts rotting the onion bulbs.
And eventually, the entire bulb will be rotten.
You do not always see spores developing on the onion bulbs,
but occasionally you can see them on the top.
It's that gray, powdery mycelium that you
see on the top of the onions.
Management for Bortrytis neck rot is actually very easy.
You just have to wait before you cut the leaves off
until they are dry.
If you cut them off when they're still
green and fresh and juicy, then you
will see Bortrytis neck rot.
So here, this onion that's here on the left,
it still has green leaves.
They're starting to dry up but they have not dried down yet.
And so this neck is still very moist and wet
and would be an ideal place for the fungus to colonize and then
start rotting the bulb.
So you want to wait until this neck is dry
and the onions look similar to this here.
And then you can cut the neck off.
And we do have a fact sheet on Bortrytis neck rot
that provides the information in more detail.
It's on the UPPDL website.
And you can find a lot more information about it.
And we have seen 100% yield loss of onions in commercial onion
fields due to this disease.
Another pathogen that's also a fungal pathogen that
can cause storage rot of onions is Fusarium basal rot.
It's a Fusarium oxysporum, from another soil-borne pathogen.
It also infects other plants like garlic, chives, shallots.
This particular strain of Fusarium oxysporum
will only go to onions and relatives of onions.
Its optimum temperature is 78 to 82 degrees Fahrenheit.
You can see above ground symptoms in the field.
You might get yellowing of leaves, leaf necrosis,
the leaves are starting to die back,
and you can get wilting of onions.
And if you cut the bulbs open, they usually
have tissue discoloration at the base
of the onion, which is kind of brown and watery looking.
So this is the basal plate of the onion.
This is where the fungus enters.
You see that these bulbs have no roots.
The roots have rotted already.
And then the fungus just moves up into the bulb.
And instead, a Bortrytis neck rot came from the top down
and Fusarium basal rot goes from the bottom up.
And this is what you can see in the field or in your garden
if onions have Fusarium basal rot.
But these symptoms on onions do not only
apply to Fusarium basal rot, they apply to some insects too.
If you have bulb mites feeding on the basal plate
of your onions, they are tiny, these mites.
But with a strong hand lens, you can see them.
They're like little white shiny droplets that move around.
Also maggots can get into the base of those onions
and feed on the roots.
Once the roots are gone, the plant
can't take up any more nutrients and water
and the leaves will start to die back
and the plant starts to wilt.
So it's very important to determine what the cause is.
If you have a hand lens, you can look for maggots and bulb mites
and if you can't see any, you might
want to contact Nick or me and we can take a look
and see if it might be Fusarium basal rot.
Management for Fusarium basal rot,
you have to use crop rotation three to four years
at least Since the fungus is soil born.
There are some resistant onion varieties you can use.
And if you do store onions, you want to store them
at 39 degrees or less.
Another fungal disease that you can also
find on onions that you buy at the store
is black mold caused by aspergillus niger.
It can survive on dead plant material
and it's not specific to onions.
It can colonize any dead plant material or sometimes also
other vegetables.
The spores are both in the soil and airborne.
It also likes it warm.
It likes temperatures of 82 degrees
to 93 degrees Fahrenheit.
The symptoms you initially see as a black discoloration
in the neck area of the onion.
The dark lesions with spores develop and the fungus
has dark black spores.
That's where the name niger comes from.
And you see those on the outer scales.
If you look at onion bulbs in the stores,
you can sometimes see that.
It's under the outer scales.
You see a line of dark black spores.
Sometimes this fungus can be mistaken
for smut, which is another fungal pathogen.
But we rarely see that one in Utah.
I've only seen it once whereas I see black mold all the time.
But if you have a microscope available,
you can send us a sample.
Then we can take a look and tell you if it's bulb rot
or if it's smut.
And then eventually the bulbs will start rotting.
So here on the right, this is what I mentioned initially
under these scales.
These scales were peeled back and you can
see the rows of black spores.
And then eventually, the rot will progress
and you get the entire bulb, the inside to rot.
It provides entrance points for other pathogens to get in
and your bulb will, in the end, be just mush.
To manage black rot or black mold,
you want to prevent the wounding or bruising of bulbs
during harvest.
Store the bulbs below 59 degrees Fahrenheit.
If you transport bulb somewhere at a higher temperature,
even if the fungus is not growing
at the moment, as soon as the temperatures get above 59
degrees Fahrenheit, it will resume the growth
and it will eventually rot the bulb.
Another disease that we sometimes
see, especially on white onions, are pink spots.
You can also find that on bulbs in the store.
There are two potential causes for that.
There is pinking, which is a response
to bruising during harvest.
And there's another Fusarium species, Fusarium proliferatum,
which can sometimes cause that.
Most of the time this disease is only
on the outer scales of the onion bulbs.
If you peel those off, onions below are perfectly fine.
In rare cases, Fusarium proliferatum,
if that's the cause, it can cause a bulb rot.
But I've tried it and I had to really create
the perfect conditions for this fungus
to get it to actually rot the bulb.
This is more of a cosmetic issue, I would think.
Now we move on to potatoes.
This is not really a tuber rot in storage,
but most of the time people won't notice it
until they have their potatoes in storage.
Zebra chip disease is caused by a non-culturable bacterium
called Liberibacter solanacearum.
It's most important on potatoes.
You can find it as well on tomatoes and peppers as well.
And the name Zebra chip disease comes from the potato chips.
So the symptoms you see here, when you cut a fresh tuber,
you get these brown striations.
If you just boil the potatoes and mash them,
you won't even notice that they were infected.
There's no flavor difference.
It's not harmful to you.
But if you are in the potato chip business
and you want to sell your potatoes to let's
say Frito-Lay or somebody else or you want
to make your own potato chips, these infected tubers
get these very dark brown rings and striations.
And nobody wants potato chips that look like that.
And that's where the name Zebra chip comes from.
The bacteria are transmitted by potatoes psyllids.
They're very small insects.
They look like winged aphids.
They're black.
And if you have a hand lens and you can get a hold of one,
they have this big white stripe across the back, which
allows you to identify them.
The nymphs you can see here in the middle.
They're very hard to see without a dissecting microscope.
You need to go to fairly high magnification.
They look like little armored personnel carriers.
And then the eggs are laid on stems right
along the margin of the leaves.
And they're so small that you can almost not see them even
with a dissecting microscope.
Above ground the symptoms, you see
can resemble nutrient deficiencies.
You get purpling and yellowing of leaves.
It's a reaction of the plant to the feeding psysillids.
The saliva of the psyllids has a toxin
and it causes the plant to react in that way.
But the only way to differentiate
between a nutrient deficiency and Zebra chip disease
is to test for the presence of the bacteria in the plant
or get a nutrient analysis to see if there's any potassium
or phosphorus deficiency.
Management of Liberiabacter or Zebra chip disease
is difficult. You can scout for potatoes psyllids,
put out yellow sticky cards and regularly
look at them with a hand lens.
You can start controlling the psyllids,
if you have them, with imidacloprid starting early
in the season.
Good weed management to reduce the amount of host plants
for the psyllids.
But once a plant is infected, there's no cure for it.
But like I said, most of the time
you won't even notice that your potatoes have
an infection until you actually have them in storage
and you cut one open that's raw.
Another disease of potatoes that we see in storage
is bacterial soft rot.
It's caused by the bacterium Pectobacterium carotovorum.
It also goes to other root crops like carrots
and sometimes onions.
The bacteria are usually found on seed pieces.
They can also be in the soil.
And initially, you see just some tissue discoloration
on the outside.
Then over time, the bacteria continues to rot the tubers
and the bacteria produces enzymes that
can dissolve the cell walls.
So all the cell contents will pool
in the center of the tuber.
And when you cut them open, you have all this liquid inside.
They have a very foul odor.
If you have a rotten potato in your fridge, you will know it.
It smells very strongly.
The bacteria enter through lenticels, cracks,
or other injuries that are caused to the tubers
during cultivation and harvest.
And to manage soft rot, crop rotation to non-tuber root
crops can help.
Buy seed pieces that are free of rot symptoms.
Avoid overwatering and avoid tuber injury during harvest.
Internal heat necrosis is something that I've noticed,
especially buying russet potatoes at the store.
This is not a real disease.
It's a physiological problem that
occurs if you have very high day and night temperature
temperatures in both the air and the soil
and you have low soil moisture.
So this year, when we had these very high temperatures early
in the season and we have a drought,
it could be that you might encounter this more often
and there's some varieties that are more susceptible like Yukon
Gold, Russet potatoes, as well as Atlantic and Chieftain
varieties.
And most of the time those tubers are very firm.
So unless you actually cut them open,
you will not see that this core is discolored.
Management of internal heat necrosis, avoid heat stress.
You can do that by having a healthy canopy that
shades the hills and reduces the soil temperature.
Proper nutrient management to promote a good vine and tuber
growth.
And avoid harvesting the bulbs during very high soil
temperatures.
And then we have rhizopus on little pumpkins.
That was an unusual storage disease.
These pumpkins were harvested right
after we had very strong winds with heavy dust and sand being
blown across some fields.
And you couldn't see anything obvious,
but as soon as these pumpkins went into storage,
rhizopus started growing right around the stem.
And this was caused because these little pumpkin
fruits have been sandblasted.
And so there were all these minute wounds that
were created during that storm.
And then as soon as they were in storage,
the temperature was reduced in the storage.
There was higher humidity.
That fungus starts growing.
Rhizopus takes any vegetable, fruit, bread, anything
it can grow on that provides any nutrients.
It's not very picky what it eats and it grows very, very fast.
It enters the fruit through wounds created by insects,
blowing sand, or equipment.
And the only way you can reduce the injury
is by reducing the injury to plants.
Now Nick asked me to talk a little bit
about watermelon rind necrosis.
It's not a storage disease but he had quite a few questions
about this problem this year.
The actual cause for watermelon rind necrosis is not known.
Bacteria have been isolated.
A lot of different bacteria have been found.
But they have never been definitely linked
to these symptoms.
You can take a perfectly healthy watermelon
and take samples out of the rind and you
will get bacteria to grow.
There's a lot of non-pathogenic bacteria
that just hang out on watermelons.
So there's a hypothesis that the symptom is actually
triggered by stress and that this stress causes
a hypersensitive response in the watermelon
if there are any bacteria present.
And it just has the tissue die back
trying to prevent these bacteria from growing.