• Training
  • ▶ Introduction to Crop Scouting
  • ▶ Crop Staging, Stand Counts, and Soil and Tissue Sampling
  • ▶ Scouting for Crop Nutrient Deficiencies
  • ▶ Basic Insect Identification for Crop Scouts
  • ▶ Basic Weed Identification for Crop Scouts
• Resources
  • 2025 Pest Management in Wisconsin Field Crops (A3646)
  • Corn Diseases Booklet (Iowa State University)
  • Soybean Diseases Booklet (Iowa State University)
  • A Farmer’s Guide to Corn Diseases (Iowa State University)
  • A Farmer’s Guide to Soybean Diseases (Iowa State University)
  • A Farmer’s Guide to Wheat Diseases (Iowa State University)
  • Scouting tools, checklists, and communication templates

0:05
All right, good afternoon everybody and welcome to our final installment of the Foundational Crop Scouting webinar series.

0:14
Today we are going to be covering our introductory to crop diseases.

0:18
So we’ll cover a handful of diseases in corn, soybean, wheat and alfalfa.

0:24
All right.

0:25
And then without further ado, we’re going to start jumping in and talking about plant diseases.

0:30
So the first thing we need to do when we’re thinking about plant diseases is to define what a plant disease is.

0:36
A plant disease is an abnormal change in a physical form or function of a plant caused by a living Organism.

0:42
Those living organisms could include things like fungi, oomycetes,  viruses, bacteria, and nematodes.

0:51
I bolded fungi on this slide because fungi is the leading cause for a lot of the diseases that we see here in the state of Wisconsin.

0:59
So that is the most common type of Organism causing disease.

1:08
So what is required for a plant disease to occur?

1:11
Well, I’m sure many of us are familiar with the plant disease triangle where we need the susceptible host, a disease causing pathogen and an environment suitable for the disease to develop in order for any sort of disease to occur.

1:27
A susceptible host is a plant that is infected by and is providing food source for the disease causing pathogen, usually usually at the expense of a crop in its own ability to develop and reproduce.

1:40
A pathogen is a disease causing agent, much like what we just highlighted in the previous slide.

1:48
And they’re capable of entering a plant in many ways, such as through wounds or natural openings on the plant.

1:54
And some pathogens are transmitted through insect feeding as well.

1:59
And then lastly, you need a favorable environment.

2:01
Diseases won’t develop without a favorable environment, and the favorable environmental conditions varies by pathogen.

2:10
Even if you have a host and a pathogen present, symptoms will not be present when temperature and moisture conditions are not conducive for disease development.

2:18
So that is a really key piece of the disease triangle is we could have pathogens and hosts present in a field, but if the environmental conditions are just not right for that disease to develop, we won’t have that disease occur.

2:35
Now, much like insects, diseases also have a life cycle in a sense, and that disease cycle is a series of events that occur for a plant pathogen to develop.

2:46
Many plant disease cycles include the following stages.

2:49
So step one is the initial production of inoculum.

2:53
That inoculum or inocula are forms of pathogen capable of spreading and facilitating host infections.

3:02
We can have primary inoculum which is dispersed initially to a host and then we also can have secondary inoculum that is dispersed from one host to another or from leaf to leaf.

3:14
The second stage is dispersal of the inoculum to a suitable host.

3:19
That dispersal is accomplished when wind, water, animals or people move that inoculum.

3:25
And that inoculum can survive in places that include plant residue, infected seed, insects and soil.

3:31
And again, that is going to depend on the type of pathogen.

3:36
Step 3 is the penetration of the host and then Step 4 is the infection of the host.

3:41
Once that host has been penetrated and infection occurs, the pathogen establishes a food or energy relationship with the host.

3:50
Step 5 is the colonization of host tissue and incubation.

3:54
So colonization occurs as the pathogen develops in or on plant tissue.

3:59
Depending on the pathogen and the disease, development may involve only a few types of plant tissue and occur only during certain stages of crop development.

4:11
During the incubation process, symptoms are not always evident on the infected plant and during both the incolonization and incubation process.

4:20
If the environmental conditions are not conducive or favorable for disease development, those things will cease and symptoms may not materialize after that leading into step 6, which is the development of symptoms.

4:34
Again, if we have those environmental conditions there, we have our plant that will develop symptoms from the disease and then step 7 is the initiation and completion of that secondary disease cycle.

4:46
Again, this is dependent on the type of disease or pathogen that we might see, but this is a potential secondary disease cycle can occur when new inoculum is produced in or on a host.

4:59
This can also lead to the spreading of the pathogen and infecting surrounding plants or additional parts of the same plant.

5:08
And then lastly, step 8 or stage 8 is the survival of the pathogen.

5:13
So some pathogens can survive in the soil like we said it in residue and then again some of these pathogens not in the living host will need to find favorable conditions to survive in overwinter.

5:30
So now that we know the basics about diseases, some things to consider before we head out into the field.

5:37
We might want to take note of the field history and note if there have been history of certain diseases out in the field.

5:44
Again, if we have with our crop rotations and we have a history of disease that that disease over winters, we could see that disease pop up again on a year to year basis.

5:56
So knowing the field history, knowing the history of the disease in the area or region.

6:02
So certain regions of the state might be more susceptible to certain plant diseases.

6:07
Noting the planting date and the crop stage is also really important because certain diseases will occur at certain crop stages.

6:15
So knowing what to look for before you head out just based off of crop stage is very helpful if you can find out the information.

6:24
I know as a crop scout, we might not always be given the information about the crop hybrid, but if we can find out some information about the susceptibility of that hybrid might also narrow down what we need to look for while we’re in the field.

6:38
Also note those weather conditions.

6:40
Think through where have the recent weather conditions been conducive for disease development.

6:45
If they have, then we should be looking for certain diseases.

6:48
If it’s so.

6:49
If it was hot and humid, we might be looking for different things and if it was cool or dry and then in general, just as a good reminder, when we’re looking for diseases and we are unsure, we should always try to take a sample and submit that diseased plant to an expert to get it verified.

7:07
So we know for sure that that is the disease that we’re looking at.

7:11
And this can be done by consulting an expert or by sending it into the plant Disease diagnostic lab.

7:20
All right, so we’ve considered all of the things before entering the field, but now we’re going to enter the field and scout for diseases.

7:28
So when we do that, we’re gonna want we’re gonna want to walk throughout the field making that W pattern, which is pretty similar to when we’re scouting for insects or weeds.

7:40
We want to check those low areas and field boundaries and look for areas where there is low stand or missing plants or any stunted plants, as there could be a disease causing those stunting plants or low stand or missing plants.

7:54
And then also keep in mind that headlands could have a higher risk of disease just due to those compaction issues.

8:00
When we’re going out to Scout, it’s good to bring with you a notebook or any sort of notes app so you can write down certain notes about where you are in the field.

8:09
Keeping plastic bags and a permanent marker with you in the vehicle is really helpful, especially if you do want to take any samples to submit to a plant diagnostic lab that’ll be able to keep the the sample fresh for when you submit it.

8:25
A shovel is helpful if you’re going to be doing any sort of root digging or need to submit an entire plant sample and dig up the roots.

8:34
Most of us always have a cell phone or a cell phone with us of some kind.

8:39
So a cell phone or camera so we can take pictures if we have any questions, we can take a picture instead of taking a sample.

8:47
A hand lens if we need to really look for some defining features about the disease symptoms we’re seeing.

8:53
That cooler is really helpful for keeping samples fresh if we are taking anything that needs to be submitted to the plant diagnostic lab.

9:01
And then if you would like to have some sort of guide with you or reference book that has disease examples in it so you can kind of page through and figure out or narrow down what disease it might be that you’re looking at, that can be really helpful as well.

9:19
When we are thinking about scouting, one of the key pieces of scouting diseases is estimating the severity of foliar disease.

9:30
It can be tricky to calibrate your your eye because we do tend to want to overestimate severity.

9:37
So here are two examples of what estimating foliar disease looks like for corn and for soybean.

9:44
Now corn we only have 3 examples.

9:46
We have one percent, 5% and 10%.

9:49
I know personally I would look at the 10% and definitely overestimate that to 15 or 20.

9:54
So making sure that we’re calibrating our eyes so that we know what we’re looking at or even having a sheet with us so we have a key so that we can look while we’re out there and and estimate as accurately as we possibly can on that severity.

10:10
That will come into hand, come in handy when we’re trying to make management decisions.

10:17
Like I said previously, we do want to make sure we’re verifying the diseases by either consulting an expert or submitting samples to the disease diagnostic lab.

10:27
So the Plant Disease Diagnostic Clinic at UW has both a digital photograph submission but also a physical sample submission.

10:36
So you have two options there.

10:37
You could take some really, really good photos, submit them that way, and try to get it verified.

10:42
It is helpful to take a physical sample just in case it can’t be identified by the photograph itself.

10:47
Or again, you could just take the physical sample and send it in.

10:54
There are some general sampling techniques that we do need to talk about because it is important to grab a sample when we are not sure what we could be looking at.

11:02
Again, we want to gather that pertinent background information.

11:05
A lot of that is really similar to what we’re thinking through before we go out and scout.

11:10
When we’re actually collecting a plant specimen, if we’re not just collecting a leaf tissue of some kind, we want to make sure we’re digging plants and not just pulling them.

11:19
We don’t want to cause any breakage or any damage to the plant itself.

11:23
If we can, we want to collect the entire plant and we want to collect several different plants of varying ranges of symptoms.

11:30
So we might want to collect a completely healthy plant, a really diseased plant, and then maybe one in the middle if we can Keep samples as fresh as possible, so in a plastic bag, in a cooler, keep foliage from being contaminated with soil as that can cause issues with actually diagnosing the disease.

11:51
And send those plants as immediately as you can to the diagnostic lab so that they are nice and fresh again.

11:58
UW Plant Disease Diagnostic Lab has guidance on their website about these proper sampling techniques, so definitely follow the submission guidance from the lab you choose to use.

12:11
All right, now we’re going to get into identifying some corn diseases.

12:16
So here we have our generalized calendar of corn diseases.

12:20
This is in conjunction with insects as well for corn, a lovely UW publication. Today

12:28
We are not going to go through every single disease on this list.

12:31
We would be here for hours, but we are going to go through some of the the more important ones that we see more frequently in our corn fields.

12:44
The first disease we’re going to talk about is Gray leaf spot.

12:48
It is caused by a fungus that survives in corn residue.

12:53
The graphic on the side kind of shows the life cycle of Gray leaf spot and that fungus and how it can overwinter in our corn residue.

13:02
And then that fungus will then spread via wind and rain and those spores will attach themselves to the leaves, germinate and infect those leaves and this cycle will continue regularly.

13:15
Symptoms of Gray leaf spot, they start on the lower leaves about two to three weeks before tasseling as those long narrow tan or Gray rectangular leaf lesions.

13:26
Favorable conditions for Gray leaf spot are when we have warm, so around 80°F and humid weather.

13:33
And the best time to scout for Gray leaf spot is the V-15 to R4 stage.

13:41
Next we have northern corn leaf blight.

13:43
Again we have the life cycle chart here.

13:45
It does overwinter in corn residue, so again it’s spread by wind and rain.

13:50
Those spores attach themselves to the leaves caused by that fungus that over winters in corn residue.

13:58
The symptoms are lesions that can start as these small light colored lesions but will eventually grow larger in size and be elliptical in shape.

14:09
They are a Gray green and they can turn a pale Gray or tan color.

14:14
We usually call this a looks like a cigar shape in a way.

14:19
Favorable conditions for corn leaf blight development is when we have leaf wetness that is over six hours and warm temperatures, so between 64 and 81°F.

14:30
So if we have periods of really high humidity or really wet conditions, we could see increase in severity of northern corn leaf blight.

14:39
The best time to scout for northern corn leaf blight is the V15 to R4 stage.

14:48
Next we have southern rust.

14:50
So southern rust is a little different than the other two diseases we’ve seen so far.

14:55
It is caused by a fungus.

14:56
That fungus is spread by weather events, so it overwinters outside of the United States in more tropical areas and will move up with weather currents into the northern region of the United States.

15:10
Symptoms of southern rust, Well, it gets its name because it shows up as those orange, orange circular pustules that can be very densely scattered on the leaf surface and they do occur on that upper leaf surface.

15:24
So they won’t be under on the underside of leaves on the upper side.

15:28
Favorable conditions for southern rust is when we have high humidity and high temps.

15:32
And so we do need to keep in mind that because this is a disease that comes up on weather fronts that we could have different instances of it on a yearly basis based on our weather patterns.

15:44
Best time to scout for southern rust is our Vt to R4 stage.

15:52
Next is tarspot.

15:54
So tarspot has been a disease that has been popping up more frequently in the last several years.

16:00
It is caused by a fungus.

16:03
In this particular fungus overwinters in residue as stromata.

16:08
The stermata releases ascospores that can move to other fields and infect foliage when moderate temperatures coincide with extended leaf wetness.

16:17
Symptoms of tarspot can occur 14 to 21 days after infection, and this cycle can repeat several times.

16:26
The symptoms of tarspot is flecking and yellowing on leaves, stalks and husks.

16:32
They can look like small raised black spots.

16:35
That small raised black spot is actually the fungal fruiting structures of of Tarspot.

16:40
And as we can see in the photograph in the the lower photograph, we see that that tan yellow surrounding some of those black spots as well.

16:49
So that is a a sign of tarspot.

16:54
Tarspot can be confused with southern rust in the late season, but the biggest difference between tarspot and southern rust is that tarspot can’t be scraped off of the leaf tissue, but rust on the other hand can.

17:11
Favorable conditions for tarspot is when we have high 60s to low 70s, so kind of cooler summer temperatures, nightly leaf wetness, and then those high dew points and humidity.

17:24
Best time to scout is R3 through R6.

17:27
Again, we want to do our due diligence and look for tar spot signs early on because the earlier the better.

17:33
We can then make some fungicide applications or management decisions based on how early we catch it.

17:43
The next corn disease is Fusarium stalk rot.

17:46
It is caused by several different Fusarium subspecies of fungi that overwinter in the in residues.

17:56
The kind of telltale sign of fusarium stalk rot is that shredded pith and sometimes it can have a whitish pink to salmon color.

18:04
So we see in the the middle picture here we see that kind of pink salmon color in the shredded pith.

18:11
This does lead to premature death.

18:14
There can be sometimes on the outside of the stalk you can see those brown streaks especially on our lower internodes.

18:22
One thing to be concerned, if we have really severe stock rot, we could have lodging be an issue, especially if we have really severe weather come through.

18:30
Those weakened stalks are going to be likely to lodge.

18:34
Favorable conditions for development of Fusarium stalk rot are warm temperatures, so 80 to 100°F, so really warm compared to some of the other diseases we’ve seen.

18:45
And then when it’s wet mid season following really early dry weather, best time to scout for Fusarium stalk rot is that R5 to R6 stage.

19:00
Now we’re going to talk about some ear rot.

19:02
We have Fusarium ear rot.

19:04
This is the most common ear rot disease in Wisconsin.

19:08
It is caused by several fungi in the Fusarium genus.

19:12
Symptoms are white to pink or salmon colored cottony mold that occurs on single or multiple kernels scattered or clustered on the ear.

19:21
Decay often begins with insect damaged kernels and infected kernels are frequently tan or brown or have white streaks so you can identify if those kernels have been infected by some some discoloration.

19:37
Favorable conditions for fusarium ear rot are when we have hot dry weather during and after silking.

19:44
So this is one of the few that was hot and dry and not hot and humid.

19:48
Best time to scout is R5 through R6 stage and then our last corn disease we’re going to talk about is Gibberella ear rot.

19:59
It is caused by a fungus that overwinters in corn residue as well as wheat residue.

20:05
Symptoms are when we see a red or pink colored mold that begins at the ear tip.

20:13
One thing with Gibberella ear rot is that it is this fungus is a mycotoxinogenic fungus.

20:24
And it produces a vomitoxin and some other toxins that can cause these issues.

20:33
And then the best time to scout for Gibberella ear rot is the R5 through R6 stage.

20:41
And the favorable conditions are we have cool and wet conditions during that grain fill period

20:46
And our silks are most susceptible 2 – 6 days after emergence.

20:50
So it’s important to get out there and and look ahead of time for for signs of this.

20:58
Now we’re going to move into identifying soybean diseases.

21:02
We’re going to start by looking at that generalized calendar.

21:04
There are quite a few different soybean diseases that we could talk about, but I’m really going to focus us on the root and stem diseases down at the bottom.

21:17
The first disease we’re going to talk about for soybean is the Phytophthora root, root and stem rot.

21:23
It is caused by an oomyce that survives in the residue or in soil.

21:29
The symptoms of Phytophthora are a dark brown lesion on lower stems that extend up from the taproot to the plant.

21:39
We can also see early early season symptoms like seed rot or pre and post emergence damping off.

21:48
Again, the most characteristic symptom is that dark brown lesion on the lower stem which we can see in the the upper picture.

21:55
The lesion can often reach as high as several nodes and it can girdle the soybean, the soybean stems and restrict the flow of nutrients and water which can stunt or kill the plant.

22:08
Phytophthora root rot is more severe in no till no till fields, poorly drained fields or low lying areas that are prone to flooding and the oomyces really thrives in those wet conditions.

22:21
The best time to scout for Phytophthora root rod are those VE through R1 stages and then one to two weeks.

22:28
After excessive rains this can develop further.

22:35
Next we have our Pythium seedling blight and root rot.

22:39
This is again also caused by an oomycete that overwinters in residue or soil.

22:46
This can cause pre or post emergence damping off we have infected seeds will appear rotted and the soil will stick to that.

22:56
Much like in that upper picture, we have kind of the soil all stuck to the the seedling.

23:02
Infected seedlings will have water soaked lesions on the hypocotyl or cotyledons that can develop into a brown soft rot and diseased plants are easily pulled from the soil because of those rotted roots.

23:18
Favorable conditions for the development of Pythium are those cool temperatures, so 50 to 60°F and wet soil conditions.

23:25
So if we have really cool wet conditions really close to when we planted our soybeans, we could have development of pythium seedling blight or root rot.

23:34
Best time to scout is that VE through V2 stage.

23:43
Next on our soybean disease list is soybean cyst nematode, which is abbreviated as SCN.

23:50
This is caused by a nematode that overwinters as eggs within dead females in the soil.

23:56
So here we have the life cycle of what a cyst nematode is.

24:01
So we have our soybean root where we can see the adults and the juveniles that are in and out and then the adult females with the eggs are kind of in the root itself.

24:13
And eventually that cyst will burst and the the cycle will start all over again where we’ll have the juvenile in the egg.

24:22
The juveniles will hatch, penetrate those roots, live their life in the actual soybean root, develop as the females, will develop eggs, and then it will continue.

24:34
Damage from SCN may not be obvious in high yielding fields or during years when soil moisture is plentiful.

24:40
However, we can see some heavy yield losses in other conditions.

24:50
Symptoms of SCN are stunting, slow or no canopy closure.

24:55
Oh, here chlorotic foliage and poorly developed roots.

24:59
And you can actually the top picture is an example of the actual cysts on the soybean roots where those females will end up dying and the the juveniles will come out of. Favorable conditions for SCN soybean cyst nematode like the exact same growing conditions as soybeans.

25:20
So it makes this a pretty prevalent issue and those eggs that will overwinter in the soil will survive for several years in the absence of a soybean crop.

25:33
So even with crop rotation, we could still have issues with SCN if we do have it in our field. The best time to scout for soybean cyst nematode is 6 weeks after planting until three to four weeks before harvest.

25:50
So a pretty large window.

25:51
So we always kind of want to have an eye out looking for anything that might be considered SCN.

25:57
If you do think that there is SCN in your field, there are different sampling protocols that you can do that will take both the plant species itself, but also the soil around the plant species or around the soybean plant and it will verify whether or not you have SCN and then you can make management decisions moving forward from that.

26:22
The next soybean disease is stem canker.

26:24
This is caused by a fungi.

26:25
There are two different types of stem canker, so they are caused by two different varieties of the Diaporthe genus fungi.

26:35
We have northern stem canker and southern stem canker.

26:39
The symptoms of stem canker are well, the first symptoms are often dead plants and they’ll have dry leaves attached to the petioles.

26:49
But we can have lesions that start on nodes away from the soil line and on the main stem and they’ll move upwards.

26:55
So we can see the those characteristics and that first upper picture where it starts at the node and the Browns.

27:03
The brown lesion starts to move upward.

27:07
The lesion will expand and become more brown and Gray with a red border.

27:11
It can lead to girdled stems, leaf flagging as well as plant death.

27:16
Favorable conditions for stem canker or cool and wet conditions that are early in the season.

27:21
And then we can see it an increased disease severity in no till fields and fields rotated with alfalfa.

27:29
Best time to scout soybeans for stem canker is mid to late growing season.

27:40
Next, we have sudden Death syndrome.

27:42
This is abbreviated as SDS.

27:45
It’s caused by a toxin produced by a Fusarium fungus that overwinters in both residue and soil.

27:54
Symptoms of SDS are scattered yellow spots between the leaf veins and those spots will grow to form chlorotic and necrotic blotches between the leaf veins, while the mid veins and major lateral veins will remain green.

28:09
So the upper picture here of the soybean leaf is very characteristic of SDS.

28:16
So we’ve got those veins staying prominently green and all of that, that kind of browning or chlorotic and necrotic blotches in between the leaf veins.

28:29
Favorable conditions for SDS are when we have high soil moisture and significant rainfall during specifically the reproductive stages of soybeans.

28:38
So our best time to scout is R1 through R6 stages.

28:48
All right.

28:48
And our last soybean disease that we are going to talk about is white mold or Sclerotinia stem rot.

28:54
It is caused by the fungi Sclerotinia scleroserum that survives in soil and it can survive for several years as sclerosia.

29:05
So the upper picture on this slide is what the actual sclerosia or overwintering bodies look like of the fungus.

29:14
The disease cycle begins when mushroom like structures called Apothecia are formed on the soil surface from sclerocia and those spores from the apothecia infect are senescing soybean flowers and the fungus will eventually grow to the stem.

29:32
This disease is more the favored conditions are cool, wet or humid season and we’re fields where canopy closes during flowering and pod development stages.

29:42
The symptoms for white mold are pretty characteristic I think relatively easy to spot.

29:47
It’s that Gray or white lesion on the stem with white fluffy mold and we can also see leaf tissue between major veins turn a a Gray green cast and eventually will die and turn brown.

30:00
But we typically see that white fluffy mold and can recognize that this is white mold.

30:08
Best time to scout is R4 through R6 growth stage and a little scouting tip.

30:13
You should check plants in areas where moisture collects due to fog and extended dew periods and also in pockets of low air movement as those areas are going to have a higher risk of developing white mold.

30:31
All right, we are now going to move into identifying some wheat diseases.

30:37
Here we have our general generalized calendar of wheat diseases.

30:41
In this section, we are going to identify Fusarium head blight, which is I think listed on here, leaf rust, powdery mildew, stripe rust, tan spot, and Septoria leaf spot.

30:55
First, we’re going to talk about leaf rust.

30:57
It is caused by a fungus.

30:59
It’s also known as brown rust.

31:02
The fungus causing leaf rust requires living tissue to survive, so it does not overwinter in northern areas.

31:11
And each year the spores for leaf rust will blow N on wind currents from those tropical areas.

31:21
Symptoms of leaf rust in wheat are those orange to brown rusty colored pustules.

31:26
They can be scattered all over the leaf and they’re not linear.

31:29
So they’re they’re pretty erratic.

31:32
Spores turn from that orange brown to dark brown and black color.

31:36
And then the the dark brown and black spores on wheat don’t don’t easily rub off.

31:41
So they’re not going to the rub off.

31:43
Favorable conditions for leaf rust.

31:46
Well, first we need those weather fronts from the tropical areas to bring the spores in.

31:50
Once we have that weather system, move spores.

31:54
In favorable conditions for the development of this disease in wheat is high humidity.

32:03
High humidity and temps between 65 and 77°F.

32:10
Under favorable conditions we can have secondary infections occur and the life cycle of this fungus will just continually repeat.

32:29
Next is powdery mildew.

32:30
It is caused by a fungus.

32:34
The symptoms are a fluffy Gray white fungus that we can see on upper surfaces of leaves as well as on our our wheat heads, and then the undersides of the leaves where there might be infection or powdery mildew on top will have a chlorotic spot on the backside of it.

32:55
If tillers are severely infected early in development, there might not be any heads that form, and then in certain susceptible varieties, stems and heads may also have mildew, much like the image we see here.

33:08
And if diseases advance, small brown to black fungal fruiting bodies may form within the fluffy white growth which we can see some of those black spots developing in the picture with the leaf.

33:22
The powdery mildew on the wheat leaf Favorable conditions for powdery mildew when we have mild winters and then we have cool, humid spring weather.

33:35
Once daily temperatures reach between 79 to 81°F, the the disease progress of powdery mildew will either slow or cease altogether.

33:50
Excess nitrogen and high planting populations or conditions that encourage heavy tillering, we can see increase of the severity of powdery mildew as well.

34:00
So some things to keep in mind if we know anything about the management of the field we’re scouting.

34:08
Next, we have stripe rust.

34:10
It is caused by a fungus that does not readily overwinter in areas without snow cover and below 14°F.

34:21
Symptoms of stripe rust.

34:23
They started as those yellow orange flecks on the leaves, and then those pustules will cluster in patches and they’ll form a linear stripe pattern.

34:32
We can see on this image that there are some more linear striped patterns on this picture, which is different than leaf rust that was kind of more erratic in the late season.

34:46
Those pustules can turn black on the leaf, so they’ll turn from that orange color to a black color.

34:53
Favorable conditions for stripe rust development are prolonged dew or wet Leafs.

34:58
Infection will occur in temperature conditions between 45 to 65°F and then we can have more sporulation in temperatures between 50 and 75°F.

35:10
And again with stripe rust, we can have secondary infections when conditions are favorable for rust development as the cycle will just continually repeat with stripe rust.

35:26
Next, we have tanspot.

35:28
This is also known as yellow leaf spot.

35:30
It is caused by a fungus.

35:36
The fungus that causes tan spot can infect wheat seed as well, and if this occurs, our kernels may develop a red, dirty appearance known as red smudge.

35:47
Leaf symptoms will look like small brown spots on the leaf, much like we see in the upper picture on this slide.

35:55
We can also see that those small spots have that yellow halo around them as well and spots will enlarge to more of a tan color.

36:05
Lesions can form a large blotchy necrotic region much like what we can see at the bottom picture where we’ve got several different leaves that have kind of overall developed a more chlorotic look at the tips.

36:19
Favorable conditions for tan spot development are wet and windy weather, 6 to 24 hours of continuous moisture.

36:27
So if we get a lot of continuous rain and we have temperatures between 68 and 75°F, we can have instances of tan spot.

36:40
Next we have septoria leaf spot.

36:43
It can also be called septoria Tretisi blotch.

36:49
Yeah.

36:50
Caused by overwintering fungus.

36:53
Symptoms of septoria leaf spot look like tan, brown lesions on lower leaves.

36:57
They’re elliptical in shape, and they do follow the leaf veins, and lesions on the upper leaves can have more of a straight edge.

37:07
As the disease progresses, the center of the lesion can become necrotic and the fungus can produce a dark fruiting body, giving the lesion a more speckled appearance.

37:18
If weather is humid opposed to wet, a translucent curling thread of whitish ooze may appear from those dark speckles when viewed through a hand lens.

37:29
So this is where having a hand lens might be helpful when we’re out trying to diagnose a field.

37:36
And then the disease will progress through infection cycles when the weather remains cool, wet and rainy.

37:44
And then we can also see increased likelihood of Septoria leaf spot when we have short rotations and high levels of residue that encourages disease development.

38:02
Next we have Fusarium head blight.

38:04
It is caused by several different Fusarium species.

38:09
Fungi in the symptoms can look like bleached spikelets.

38:16
We might see orange, like a orange or salmony color spore mass or pink, white fungal masses.

38:24
And then we also could see shriveled, chalky and white, pink kernels which we see down in the bottom picture.

38:31
We see those pink kernels.

38:34
The middle picture, we can clearly see that there is that tinge of orange or like that salmony color that is starting to develop.

38:41
And the top photo shows a really good instance of those bleached spikelets. With those with the infected spikelets, those kernels, they’re called tombstone kernels.

38:56
They’re lightweight and they’re highly contaminated with mycotoxins and they can often blow away with chaff.

39:02
So something to think about and consider when we’re looking at this disease.

39:07
Favorable conditions for a fusarium head blight.

39:10
So warm, wet weather with high humidity, specifically during flowering and early grain formation.

39:19
All right, we are going to move into identifying alfalfa diseases and wrapping this presentation up relatively quick.

39:30
So here we have the generalized calendar for alfalfa diseases.

39:32
Again, I’m not going to go through all of these.

39:35
In fact, the ones that we do go through, I will go through the root and stem diseases individually.

39:41
But I’ve lumped all of the foliar diseases together because the management for a lot of the foliar diseases is the same.

39:48
So it’s really the key of just identifying them.

39:53
One thing to consider when we are thinking about alfalfa diseases is that.

40:01
Disease pressures can change with the cutting and then also the stand year.

40:06
So the in in most cases we have seedlings can have pretty high risk of or probability of disease occurrence or severity.

40:18
The 1st and 2nd year is a little less and then the 3rd and 4th year kind of increases.

40:22
Again, this is dependent on the disease that we’re looking at, but it is good to keep in mind that certain diseases are going to be more prevalent in the first cutting versus the 3rd or 4th cutting and vice versa.

40:36
So something to keep in mind while we’re discussing alfalfa diseases.

40:42
The first disease for alfalfa I’m going to cover is anthracnose crown and stem rot.

40:47
It is caused by a fungus that can survive on crop residue and within within infected crowns.

40:55
So it can hang around for quite a while in the soil and this disease can be pretty devastating when it occurs on the crown as it causes plant death.

41:06
Our lesions for crown and stem rot typically occur on lower stems and are a large oval or diamond shape with a sunken appearance.

41:18
They can also be tan with dark borders and sometimes have those black specks in them as well.

41:23
That bottom picture is a really good example of what we call a shepherd’s crook, which is when the stem die and has the appearance of that like wilted stem, the wilted plants, but it’s starting to crook over.

41:41
Favorable conditions for anthracnose crown and stem rot are warm and wet weather as that favors pathogen infection and then also disease development.

41:56
Next, we have a fan, aphanomyces root rot.

42:00
It’s caused by an oomycete that survives in residue or soil.

42:05
And we know that alfalfa productivity is reduced when seedlings die or when the the chronic root infection occurs.

42:13
So it can have it in our established plants, we can have reduced root mass and decay of lateral roots in our seedlings.

42:21
We can have stunted growth, chlorotic purplish cotyledons as we can see on the top photo as well as leaf yellowing.

42:29
And then there can also be tan to Gray discoloration of the root and hypocotyl and eventually it will become brown.

42:38
Favorable conditions for aphanomyces

42:41
Root rot development is poorly drained or wet soils and we can have the decay of lateral roots.

42:47
You can tell in the bottom picture we have some reduced root mass as it’s not lateral roots are not as prevalent as they should be in that crop picture.

43:02
We also can have foliar yellowing and stunting that can appear to established stands and that can appear pretty similar to nitrogen deficiency, which as we know, alfalfa makes its own nitrogen.

43:15
So something to keep in mind if you start or if you’re walking out in an alfalfa field and you’re thinking this looks like it has nitrogen deficiency, there might be instances of aphanomyce root rot.

43:29
Next we have phytophthora root rot.

43:31
It is also caused by an oomycete that survives in the soil as oospores.

43:36
Symptoms for Phytophthora root rot.

43:39
When we’re thinking through our stem and roots, we can see light to dark brown lesions, lesions that they’ll start at the root tip where the taproot is connected to the lateral roots.

43:53
And then older lesions will eventually turn red, brown and look more sunken.

43:57
In older plants we can have those lesions will eventually girdle the taproot, so you could have plant death as well, or you could have the entire crown or taproot completely rot.

44:15
For foliar symptoms, we can have leaf yellowing much like we see in the upper picture, as well as redditing of the lower leaf surface.

44:23
And then we can also have wilted shoots and stunting as well.

44:28
Disease development requires prolonged wet soils with temperatures above 60°F.

44:37
So I am going to switch gears a little bit now.

44:38
We’re going to talk more about those general foliar diseases for alfalfa.

44:44
First, we’re going to look at common leaf spot, which is caused by a fungus that reduces yield, plant vigor and hay quality through defoliation.

44:54
And that fungus overwinters in leaf debris on the surface of the soil.

44:59
It also develops Ascospores that spread to alfalfa leaves during warm and moist spring weather.

45:06
Symptoms of common leaf spot will appear on lower leaves but progress upward on the plant, and symptoms can include small brown or black foliar lesions that rarely coalesce so they will not all kind of join together and form one big lesion.

45:23
A single brown pseudoapotheocium, which is the fungal reproductive structure generally forms in each lesion on the upper leaf surface and disease leaves will become yellow and fall from the plant and then dry and warm summer weather can reduce symptom development, but cool moist conditions of the fall can favor disease development.

45:49
And so when we see a stand, we can still see kind of that speckling occurring and the Leafs kind of turning that white color.

46:00
Now we’re looking at leptosphaerulina leaf spot, which is caused by a fungus.

46:09
It’s also known as lepto leaf spot for those of you who can’t pronounce leptosphaerulina like I can’t and is among the most common foliar diseases of alfalfa.

46:19
Symptoms are symptoms most often observed on the new leaves as small dark lesions or pepper spots as we can see in this picture here.

46:32
Those lesions can increase in size to become eye spots and are oval and brown with dark margin and yellow halos and these lesions will form parallel to leaf veins.

46:45
Leaf spot is favored by cool, wet weather on the fungus, survives on infected leaf, infected leaf debris and spreads to newly developing leaves.

46:55
Disease risk for lepto leaf spot is higher during the spring, early summer, and in the fall.

47:06
And then here is what lepto leaf spot can look like in the stand itself.

47:17
All right, the last two foliar diseases we’re going to talk about are spring black stem and summer black stem.

47:23
Spring black stem is caused by a fungus and is among one of the most devastating alfalfa diseases that we can see.

47:31
This particular fungus will survive in the soil, on seed and in infected plant debris and within infected crowns and taproot.

47:41
It can decrease yield, forage quality, seed weight and root mass, and reduce stand survival.

47:48
Symptoms of spring black stem appear on the lower leaves but but progress up the plant over time.

47:55
We can see these as small dark lesions.

47:58
Otherwise, we can call them as tar spots and they enlarge and they will coalesce so they all will become one giant lesion.

48:07
Leaves can be stunted and deformed, while petioles can develop lesions and become girdled.

48:12
Stems initially can show a small sunken dark spot that may enlarge to cover a large portion of the stem and the crown and roots may also show show disease symptoms.

48:25
Spring black stem is its development is favored by cool and moist conditions which is different than summer black stem.

48:36
Summer black stem and leaf spot is caused by a fungus as well that survives within infected stems and again reduces yield and forage quality and generally impacts the second and third alfalfa cuttings versus the first where spring will affect the first alfalfa cutting.

48:56
Summer black stem symptoms first appear on lower leaves but progress up the plant over time.

49:02
They’re irregular brown lesions with yellow halos.

49:05
The presence of fungal spores can cause the lesions to turn a silvery color, which we can kind of see in the image above.

49:15
We can have defoliation occur even when leaves only have about two lesions.

49:21
The stems will initially show a small dark lesion and that may grow to cover a large portion of the stem.

49:28
Summer black stem really, really likes high humidity and warm temperatures within a dense plant canopy.

49:36
That is how we will see more summer black stem instances.

49:42
So that kind of wrapped up identifying these diseases.

49:46
But I did want to talk about just a few scouting and disease resources out there for you to potentially use.

49:55
I will like to highlight, so Iowa State University has two really great publications on corn diseases and soybean diseases.

50:03
These are really cut and dry and mainly meant for you to look through and read about the diseases itself.

50:11
In the middle we have a farmer’s guide to either wheat, soybean or corn diseases.

50:16
These were created by a group of land grant university specialists who all kind of came together to develop this guide.

50:25
This is very much geared for in in the field identification and does include some management information as well.

50:34
And then I always like to highlight a 3646 that pest management in Wisconsin field crops.

50:39
It’s updated every year and does include Wisconsin specific management for all of the diseases we’ve highlighted today.

50:49
There is a really cool tool out there you could also use.

50:53
It is the Wisconsin Disease Forecasting Tool.

50:56
So it is a web-based platform that does some modeling based off of UW research and so it can notify you whether or not you have a low, moderate, or high risk of developing certain disease.

51:12
The diseases that are covered on the disease forecasting tool currently are tar spot, Gray leaf spot, frog eye leaf spot, and then white mold.

51:21
So you just have to find your location.

51:23
It pulls weather data information from a weather station point that is all the map points on here and then you can go based off of where your location is.

51:33
If you have a high risk, it’s probably a good idea to think about management strategies or getting out there and looking around to see if you see any signs of that disease.

51:42
developing. A few other web resources that might be helpful.

51:48
The Badger Crop Net Network is a new website that the UW specialists here in Wisconsin have kind of come together to put all of their resources together.

51:59
So this includes the Badger Crop doc, Wisc weeds, the corn agronomy website, as well as the the Cool Bean website as well.

52:09
So they’ve put all their information on one, one stop shop for you to find all things UW related.

52:18
And then lastly, the Crop Protection Network, which is a group of land grant universities that have come together to pool resources, has a really awesome encyclopedia of insects, weeds and diseases, as well as reference material that you can use is free to the public.

52:37
They also have their own crop disease forecasting tool.

52:41
So if you are somebody who might be traveling outside of Wisconsin and want to see what might be worthwhile for scouting, you can check out that disease forecasting tool as well.

52:54
Again, my name is Jordan Kampa and if you have any questions, now would be the time to ask.

53:00
I realize we only have about 5 minutes left, but got a question for you, Jordan.

53:06
Thanks for a great talk there.

53:09
So going back to some of the the ear rot diseases, is there some type of like rescue treatment that can go along with once those are detected or what?

53:22
I guess, yeah.

53:23
What do you do once you find that that type of disease on the on on a corn ear?

53:29
Yeah, it’s a really great question, Dane.

53:32
I think the biggest thing with finding those ear rots is just to be mindful because they can have those toxins that if you are harvesting it and can lead to issues at the at the grain elevator, especially with corn where they might not take your take your grain because of the the mycotoxins in it.

53:57
OK, Thank you.

53:59
Yeah, that makes sense.

54:01
We do have a few minutes left, so I will stick around if anybody does have any last minute questions.

54:07
But we do really appreciate everybody attending the Foundational Crop Scout webinar series and the the Intro to Crop Diseases today.