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Disease Management in Low Margin Years, Field Crops


Hi, I’m Damon Smith, extension field crops pathologist from the University of Wisconsin-Madison. Today I want to talk about some smart disease management decisions, especially in years when we have a low margins for grain production. First I just want to say that don’t forget your integrated pest management decision-making processes. The things that we’ve learned years ago are still applicable today. However I want to cover five specific disease management decisions which I think will be really helpful in a year like we’re about to come into. First I think it’s important for you to consult your records and field history notes to prepare for the upcoming season. We can make a lot of disease management decisions just based on the field history. We can use that history to make variety or hybrid selections we can also make decisions about rotating in particular fields and it can also provide us at some information on what we might expect in terms of disease issues. The second point I want to make is that choosing the right variety or hybrid for your particular location with a high level of resistance is a really cheap way to reduce the amount of disease that you might see in a field. Spend some time studying the variety hybrid test results from the state of Wisconsin and then choose varieties or hybrids that are rated well for the particular diseases that you know you have in your fields. The third point is to rotate crops. Many diseases that we deal with are residue borne. So if we can simply rotate out of a field for one or even two years, that’s achieved method for managing specifically those residue borne diseases. The fourth point: plan on time. Delaying planning in Wisconsin will often set us up for the crop to be at a susceptible growth stage at a period where diseases really start to become an issue. Typically in Wisconsin our disease issues don’t get here until late July or early August. Thus if we plan on time the crop is not at a susceptible stage at that time when those diseases arrive. The fifth point I want to make is to plan some time for scouting or higher certified crop advisor to assist you in scouting. In-season scouting will help in some decision-making especially on the fungicide application decision that you’ll need to make in season. So let’s talk a little more about each of these points in detail. First consulting records as I mentioned this can help you in variety and hybrid selection. It can help you make a decision about rotation and it gives you an idea of the risk in a particular field as it relates to diseases. Let’s use an example here. I will talk a little about white mold of soybean. You’ll remember that white mold results from infection by spores that erupt from these little apothecia here, these little mushroom like structures. The formation of apothecia is critical for white mold and soybean. We have to have the formation of those little mushroom structures during the time that soybeans bloom. And the majority of infections in soybean occur due to apothecia from inside the field. In other words, where the disease has happened in years past is typically where we see the higher pressure areas of a particular field. Thus this particular disease is considered an aggregated type disease or a disease that occurs in localized areas whether or not a particular field. Let’s look at this in a little more detail. This is some apothecial scouting data from 2015 and some research plots. We actually had two separate plots here. I depicted by this grid being the first plot. Here’s the second grade depicting the second plot and then we have the days after seeding here along the bottom along with a growth stage of the soybean crop in these particular locations. The intensity of red in each of these quadrats tells us how many apothecia there were. So the brighter the red, the more apothecia. The more pink color, the fewer apothecia and white indicates no apothecia. And you can see, as we proceed through the season and we get to the R2 grow stage, in other words, full bloom in soybeans, we see that there’s a large flush of apothecia in these plots, but you also note that the primary aggregation that inoculum especially in this particular grid here is over to the left side of the field. You can see that aggregation continues with a little bit of more apothecia appearing here a little later on and then by the time we get to the R3 growth stage, you’ll see that the number of apothecia quickly fall off and by the time we get to R4, we don’t have any apothecia in that field, again. Now let’s look at this a little different way. We can look at the number of spores as it relates to the number of apothecia in the field. These blue bars here indicate the average apothecia per plot and then the red line indicates the spores that erupt from those apothecia. And as you can see here, as the number of apothecia increase, the number of spores we trap increase and then as the apothecia go away, the number of spores that we trap goes down to zero. Okay, so we have to have those apothecia in the field and those apothecia basically give rise to most of the infections that occur inside that field. Now we can actually look at the disease severity index levels in that particular field and what you’ll notice right off the bat is that as we do our ratings through time here again days after seeding underneath each of these grids, you’ll notice that the disease severity index scores are primarily higher in those areas where we saw the higher levels of apothecia. So the moral of the story here is that if you know where you have high levels of disease in a particular field in a given year those are typically going to be the problematic areas of those those fields in the future especially for white mold. So knowing where those are and which fields those are help you make some decisions about varieties and rotations and those sorts of things. The second point I made early on was to choose an appropriate variety or hybrid. I would encourage you to consult the extension documents A3653 and also A3654. These are their corn hybrid performance trials and also the soybean variety performance trials. These are conducted each year by our corn and soybean agronomists here in the state of Wisconsin and these are an excellent resource to consult to choose the proper varieties of hybrids for your location. It also provides you some information about particular disease resistance traits, which can be very helpful especially if you know something about the disease levels in your particular field. Let’s take an example here. We’ll look at phytopthora root rot on soybeans. Phytopthora root rot is caused by the seed organism: phytophthora sojae. Mortality is usually prevalent in fields that are wet or have heavier soils that hold water. If you plant early in the season and it’s cool you’ll oftentimes see some issues early on with emergence or even some damping off. Now the primary methods of managing phytopthora root rot would be to use some seed treatments or also resistant varieties. And I would encourage you to really look at the resistance ratings on whatever variety you’re going to choose for your particular field especially if you know you’ve had phytopthora root rot issues in the past. Let’s look at some genes that are effective for controlling phtopthora here especially in the state of Wisconsin. There are various genes that are deployed against the specific races that you have in a particular field. Now some sampling years ago in Wisconsin has shown that the Rps 1K gene here is effective against the majority of the races that are found here in Wisconsin. In fact, that data suggests that about 99% of the fields this Rps 1K gene should be effective. Rps 1c is another common gene that’s deployed in many of the varieties grown here in Wisconsin. That particular gene would be effective in about 75% of the fields. So, if you’d known you’d had phytopthora issues in the past, and you’ve struggled with that, I would encourage you to look at the soybean resistance gene. It was deployed for phytopthora in that particular variety and then maybe choose one if it wasn’t Rps 1k, maybe try to choose a variety that has the Rps 1k traits. Where can you find information about those genes? Well, in Table 11 in the soybean variety book out of the state of Wisconsin, over here in this column, you can see that the Rps genes are actually listed here for phytopthora root rot. You’ll see the Rps 1c and then the rps 1k genes listed depending on the varieties. Again, if you’ve struggled in past years try to look for varieties that have that Rps 1k. Now, the third point that I made was to rotate crops. Many diseases are residue borne, so managing that residue can reduce the level of initial inoculum in a particular field. Tillage can be helpful from this standpoint. However, in areas where we want to practice conservation tillage or we’re running a no-till system, that obviously isn’t an option. So rotation would be the next of way that we would manage that residue and rotation really is a cheap option. Let’s look at an example here: anthracnose stalk rot on corn. So anthracnose of corn is caused by colletotichum graminicola. There are several phases of this particular disease. We can have a leaf blight phase, which you see here in this image here on the left. We can also have a top dieback and stalk rot phase, which you see here in this image in the right. So one thing I’ll say is that, you know, usually early in the season we often see the leaf blight phase year in and year out. This doesn’t really impact or have anything to do with how much stock rot we will see. So I will say don’t get too excited about seeing this type of damage. This usually happens year in and year out. However, we want to do some scouting later in the season again for your field history notes in your records to chart whether you’ve had stalk rot in the past. In 2016, that year was a year where we did have high levels of anthracnose stalk rot at the end of the season and that did impact some of the corn hybrids here in the state. So scouting at harvest time or near harvest-time can help with that record-keeping. Now we know that anthracnose, the anthracnose stalk rot pathogen is a residue borne pathogen, meaning it overwinters on corn residue in those fields. It makes spores on that residue and those spores are then rain splashed onto the corn plants in season. Now this particular fungus is a poor competitor outside of corn residue. So simply managing that residue can reduce the amount of spores that are available in season to infect those plants. Therefore tillage or rotating can help manage this. Again if tillage isn’t an option for you, rotation can be and I would say this is a very cheap option and something that you should consider especially in fields where you’ve struggled with stalk rot, you had known stalk rot issues and you know you’ve been corn on corn for several years in a row. Some other treatments that might help would be chemical control. Seed treatments have been shown to reduce some of the damage from anthracnose stalk rot or the anthracnose fungus and then also again consult the resistance ratings for the particular hybrid you’re interested in. Now the fourth point I made was to plant on time and let’s look at example here with northern corn leaf blight. Now northern corn leaf blight usually is a major concern in years where it’s above average in terms of rainfall and below average for temperatures. Those are usually the conditions that lead to high epidemics of northern corn leaf blight for us here in Wisconsin. Now in 2015 and 2016 we had some major epidemics but one thing that helped us here in the state was that those epidemics started late or later in the season. They really didn’t get a foothold until July or into August. Those farmers who planted on time at the end April, early part of May were able to push the crop to a growth stage that wasn’t highly susceptible once the epidemic started and they were able to actually escape a substantial amount of yield reduction and grain because the crop was not susceptible at the time of arrival. Now had we planted the crop later, let’s say mid-may or something like that, then the crop would have been at a more susceptible growth stage and this major epidemic would have been more impactful during that time or in that scenario. Now the fifth point I want to make is to take some time scouting. Scouting can help you not only in your record-keeping, but it also helps you in making some decisions. If you don’t have the time to scout in your operation, I would encourage you to hire a CCA to assist with that scouting. From a fungicide application decision standpoint, this is really critical because we know the fungicide application decisions are based on or need to be based on disease risk, how much pressure is there as it relates to the particular growth stage that you’re looking at. So let’s talk about this a little more in-depth. Each year we run fungicide trials here in the state of Wisconsin. We usually conduct these at the Arlington Agricultural Research Station. You’ll see a number of particular foliar fungicides here applied at different growth stages on corn. VT here indicates that that application was made at tasseling. V6 would have been at the vegetative growth stage earlier on in the season and then you’ll see some V12 or two pass applications of fungicide, such as this preemptor application here. We rate these plots for various diseases each year and other traits including lodging and greening. We also look at ear rot and then of course yield. We’ve sorted the table from highest yield to lowest yield and one thing you’ll note here in the 2016 trial is that really when we look at the statistics we didn’t have any statistically significant differences for any of the ratings here. However, you’ll note that we have a wide range of yields from high to low here. So what’s going on with these treatments and is it really economically viable to use fungide on hybrid corn here in Wisconsin and when is the best time to use fungicides? So first before I drill down into some of these questions, I just want to give you some breakeven scenarios for corn. So if we look at primarily strobilurin plus DMI Pre-Mix product. So these are things like quilt excel or headline amp which you might be familiar with. These products are very commonly applied to corn now here in the Upper Midwest and especially here in Wisconsin. The pricing of these products as of today would range at the rates that were using them would range from about twenty dollars an acre to upwards $35 an acre, including a seven dollar application charge. So there is a wide range of about fifteen dollars here and you can see the pricing across the top. Along this column here we have the corn price in dollars per bushel. So if we consider say a corn price today of maybe about three to four dollars per bushel and we’re looking at a range of twenty to thirty-five dollars for fungicide application cost, the amount of corn we need over not treating and our treated plots would range somewhere between five to almost 12 bushels. Okay, so keep this in mind as we talk a little more in detail about responses that we see on some of these fungicides here in Wisconsin. Now we’ve looked at a four-year data set now primarily from trials at Arlington, Wisconsin we’re especially interested in these Pre-Mix fungicide products. So again the DMI plus strobilurins. We have a number of replicated treatment observations now at various timings for these particular products, actually upwards of 51 replicated treatment observations here from 2013 to 2016. Now what we can do with this type of data is we can do some things like look at frequency distributions, the mean yield advantage over not treating and then we can actually look at the return on investment calculations and see what are the odds of actually getting our money back where we use these products. Let’s take a look at the frequency distribution here for these 51 treatments that we have over the last four years. These bars indicate the yield difference for each of the observations —replicated observations that we made over the non-treated control. So bars that are going down below the zero line indicate there is actually a loss compared to the non-treated control where we applied fungicide bars that are going up indicate a positive gain and yield over the non-treated plot. You can see on average here not accounting for anything in these trials other than just looking at the premix fungicides, we can see that we average about a one bushel per acre game. Okay, so it is a positive game but we only have about a forty seven percent frequency of positives in this data set. So you know there’s there’s something else here that’s going on and we need to look at this in a little more detail. So what we did is based on some previous data we split out the treatments where we had high levels of disease and low levels of disease. So these are the same 51 observations you saw on the previous slide, but now we’ve broke them out into a situation here where we have low disease. In other words on ear leaves, where we’ve rated for specifically northern corn leaf blight in this case, we take the cases where the severity ratings on those ear leaves are five percent or less. In those cases they’re here in this upper upper box with the yellow bars. In the lower box with the red bars we have the cases where foliar disease was what we consider high or above that five percent threshold. Now if we look here and do some simple statistics we see that about thirty-one percent of the time in the low disease situation we have some success. However, overall the mean yield is actually negative at about negative four and a half bushels. Now if we take the high disease situation here in the lower box, we actually see that seventy-four percent of the time we have positives with a mean yield of about five-and-a-half bushels. So we can see the disease levels really do impact our success here in terms of getting our money back out of these fungicide applications. Now we can look at this a little further. We can actually take the statistics from the frequency distributions and we can actually calculate the probabilities of recovering our fungicide application costs. So I ask you to remember that we were looking at a range in our strobular + DMI fungicides of somewhere between $20 and $35 here. So you’ll see along this lower access here we have that fungicide application cost, we’ve got the probability along the y-axis here, and then each colored line indicates different pricing scenarios for corn. So, you remember we’re using the three to four dollar example, so we want to look at the green and purple lines here, and I’ve boxed in here 20 to 25 dollar range for an average fungicide application cost. In our low disease situation then, the probabilities of actually recovering our fungicide application costs are about ten to fifteen percent. They’re not zero, but they’re not great. Okay, now let’s look at the high foliar disease situation. Now the situation changes quite a bit. So you’ll see again along the horizontal axis here, we have the fungicide application costs. Along the vertical axis, we again have the probability and then each colored line is a different pricing scenario for corn. And now, on the high disease situation, you can see the probability or chance of getting our money back goes up. Our range now is somewhere between 35 and fifty-two percent, if we assume that it costs somewhere between twenty and twenty-five dollars an acre for our fungicide applications. So the disease levels really do matter here when it comes to fungicide applications on hybrid corn. So just to summarize, I think it’s going to be really important, if you’re interested in using fungicide and hybrid corn, you need to do some scouting and consider how much disease pressure is there in that field. What’s the right growth stage to do this? I would say immediately prior to tasseling; that’d be the best time. We know from some other work that the tasseling application or the tasseling growth stages and growth stage where we get the most responsive out of these fungicide applications. So, targeting that time in for the application and doing some scouting prior to that time can be really helpful for you to make that decision. Other things to consider if fields where you have corn on corn, you planted late, you’re irrigating or you know you have a susceptible hybrid, those fields would be at higher risk in would elevate those chances of recovering your cost from a fungicide application. Now during your scouting, for example, of northern corn leaf blight, if you see fifty percent or more plants with ten percent severity on ear leaves, or, I’m sorry, on leaves below where the ear would form, you’re going to have a higher risk for disease later in the season and you’ll probably see some impact out of that fungicide or at least positive impact out of that fungicide application. Now let’s take soybeans and look at some similar return-on-investment calculations like we have done the corn. The primary disease of concern in soybeans in Wisconsin would be white mold. Each year we run a white mold fungicide efficacy trial. This is one trial at the Hancock Research Station. You’ll see in the column here we have disease incidence and then disease severity index score and then we have yield and we’ve sorted these from the highest yield to lowest yield and then the non-treated control falls right here in the table. I’ve also included the yield advantage over not treating here in this column over here to the right. One thing you’ll notice and this is pretty consistent from each year in our trials is that we generally have a couple of treatments which usually float to the top. This approach at nine fluid ounces, R1 followed by an R3 application, this usually is one of our better treatments followed by the Endura eight ounces with a single application at R1. And we consider this our positive control in this particular trial. You can see here that we, in the approach 2 pass application, we had almost, or over seven-and-a-half bushels gained over the non-treated in that particular treatment and with the single application of Endura, we had almost four and a half bushes gained over the non-treated. Other treatments in here also gave us some positive gains, but we’re actually on the bubble in terms of being economically viable here. Let’s look at another trial here. We know that Aproach and Endura are usually really efficacious products. However, the timing of the application really is important. This trial here was also conducted at Hancock in a different field. You’ll see we had really intense pressure in this particular field, high disease incidence scores, high disease severity index scores, again, we have yield here in this column and we’ve sorted the table from highest yield to lowest yield. You’ll see again we have Aproach and Endura and then now Proline in here because these are usually products that perform fairly well for us in our efficacy trial. But, you see the timings vary with these products. And what you’ll notice inside the yellow boxes is typically products that were applied at the R1 to R3 growth stage are usually the ones that give us the best responses. And you’ll notice that if we go really early at the V5 growth stage, or really late after about the R4 growth stage, we can have the best product out there, but if we miss that growth stage window of opportunity, you’ll see that we don’t get much of a response out of these particular products. So the moral of the story here is to target your applications for white mold if you know you have a field with an issue, target that window of opportunity between the R1 and R3 growth stages and if you plan on applying fungicide after R4, I would recommend you not do that, as you’re not going to get a positive return on investment. Now let’s just look at a little bit of pricing here in terms of the better treatment. So if we consider the Aproach two-pass program and the Endura single-pass program, the range here would be somewhere between 35 and 40 dollars for those particular programs. If we think we can get nine to, say, ten dollars a bushel for our soybeans, then we need somewhere between three and a half and four and a half bushels to break even on that particular program and you remember from the previous slide if we get the timing right, we’re using those Aproach or Endura programs we easily made that three and a half or four and a half bushels and then some in those particular treatments. Now let’s look at a case where white mold isn’t a problem. So each year we also run some trials where we just look at foliar fungicide applications on soybeans just for foliar disease control. The primary foliar disease that we run into here in Wisconsin is Septoria Brown Spot. You’ll see that we take in some severity ratings on this trial that was conducted at the Arlington AG Research Station in 2016 and we sorted this table from highest yield to lowest yield and I’ve given you the yield advantage over the non-treated control over here in the right hand column. You’ll see that we did get some advantage over not treating, but really the averages were somewhere around two bushels per acre over the non-treated and this is pretty consistent year in and year out. But, that’s going to be under what we would need to recover our investment. We really need something more like four bushels, which we see here out of the Stratego yield at the four fluid ounce at R3 application timing here. However this treatment is not necessarily consistent year in and year out. We do see certain treatments respond differently depending on the year, so, what I’m saying here is, you know, usually in Wisconsin in most years you’re not going to need a foliar fungicide treatment on soybeans for foliar disease control. You’re primarily going to need that fungicide targeted at white mold and fields with white mold risk. So just to summarize here, if white mold isn’t a concern, application fungicide has not resulted in significant increases in yield for the fourth straight year in Wisconsin field-testing trials, but if white mold is a significant problem, the Endura, Aproach, or Proline/Stratego yield program seem to be the best programs for us here in Wisconsin. However, I would encourage you to make sure you get the growth stages right on the soybeans and get that window of application correct. Again, we want that R1 to R3 window to be the optimum timing. After about R4, you’re not going to see much success out of those programs. With that, if you’re looking for any more information about fungicides or disease management or just disease idea in general, I would encourage you to consult my website. The link is here and then of course my contact information with phone and email here. Thank you.

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