Soybean Leaf Diseases

Soybean Leaf Diseases


(Music) Well good afternoon My name is Connie Strunk and I serve as an Extension Plant Pathology Field Specialist in the Sioux Falls Regional Extension Center and I’m going to talk to you today about soybean disease concerns. We’re going to kind of focus on one that’s been kind of hot for South Dakota and that’s Sudden Death Syndrome with soybeans. What it is is it is a soil borne fungal pathogen. Which means you know it’s very slow-moving, it resides in the soil, is not going to move and spread to your entire field overnight. Is going to start out in patches, kind of throughout your field over time innoculum can build up and eventually can spread out, but it’s very slow-moving. Unlike the name of Sudden Death Syndrome. So it attacks the soybeans very early in the growing season. You know just as those soybeans start to emerge and start the emerge and come out, and they’re very young, very vulnerable at that point in time. When it attacks, so it attacks very early, but you’re not going to see those symptoms right away. So it could be unbeknownst to you that your soybeans are being attacked by this pathogen. Over time, you know we fast-forward to the reproductive ages, so we started to have some flowering, some pod fill, that’s when ideally you’re going to start to see some of those foiler symptoms. So you start going to start to see some of the leaves show symptoms of having SDS. So what do you see on those leaves? Well by the time you first start to see symptoms, the path, the pathogen is already producing a toxin. Okay. Within those foiler symptoms, what you’re going to start to see early on, if you catch it early enough on the plant, is some very pale green small circular spots on those leaves, over time they’re going to enlarge, they’re going to darken in color, they will enlarge into like a striking irregular yellow flashing ,a very bold color formation on those leaves. Now that’s the first thing we look for for SDS. You’re going to look for those for the other symptoms. Over time so it’s very suddenly those leaves are going to continue to enlargen, they’re going to turn brown and eventually those leaves will prematurely drop off the plant. So if you’re starting to see those pre-mature leaf drop on that color discoloration on the leaves, chances are you have SDS. But that is not the only thing we look for, we need to take a look at the roots. We are working with the soil borne pathogen so you need to take a look at those soybean roots, pull the plant, if those roots pull out very easy, are rotted and discolored , perhaps you have a plant infected with SDS. But one of the diagnostic markers if you’re taking a look and you see a light blue fungus on those roots, you are probably more than likely than not working with a plant that’s infected with SDS. But we can’t just look at leaves and that blue colored fungus alone. We need to kind of take a look at the pith color, so within that plant you know split that plant, take a look at that pith. If that pith is a white to creamy white in color, chances are it points to being a Sudden Death Syndrome infected plant. Now if you’re looking at the pith color and it’s discolored brown, darkened you have a Brown Stem Rot infected plant which is also a fungal disease common in South Dakota. SDS unfortunately has a few different, few different diseases that mimic SDS here in South Dakota. Brown Stem Rot is one of them. So taking a look at that pith color is very important. I do have pictures in your handouts of what the foliar symptoms will look like on those leaves, on that blue colored fungus, and also that pith color here in the handout. You know so really when we talk about SDS,. well what is the yield loss? Well really truly, it can be anywhere from very minimal to a hundred percent. Kind of depending on how big of a patch, how big of an area has been affected, because again like I said, it’s very slow-moving this soil borne pathogen but when it takes hold and over time if you’re planting varieties that are very susceptible to SDS, you could lose your entire yield in that area that has been infected with SDS. I’m just going to keep moving ahead here. So what kind of infection favors SDS. Well what we have found is cool and wet soils favor SDS infection. If you’ve planted early in the growing season, if your fields perhaps have poor drainage, and unseasonable cool temperatures prior to and during flowering and pod set. Which our temperatures this year kind of fall into that very cool temperatures. We have had again like I said some positive SDS confirmations, which unfortunately are not showing those very vivid striking leaf symptoms. You know we’re talking a lot about textbook. This is in a diet and in an ideal world, what things are going to look like. So knowing that where would you look for SDS? We encourage you to take a look at wet fields. Take a look at fields that have uneven growth and the big one is we’ve seen a correlation with SCN, so if a field has had a known history of SCN take a closer look there for SDS. So how do we manage SDS, well unfortunately foliar fungicides are not going to do it for you. It has no control. It does not work for SDS. Same goes with seed treatments. We have found them to be not effective against SDS management. So what can you do? Well we encourage you to plant later in the spring when those soils are a little bit warmer, a little bit drier. Plant high-yielding SDS resistant varieties. You know manage for soil compaction and again sample and manage for SCN and also harvest your corn fields cleanly. We’ve found that if you’ve had a messy harvest, this pathogen resides on the corn kernels and you’re setting yourself up for further problems. So what is this correlation between SCN and SDS? Well SCN, when it feeds on the roots of the soybean plant causes a wound on that roort which leads as a means of entry into the plant for Sudden Death Syndrome. So we want you to take closer look for fields that have been infected with SCN. What is SCN? It is Soybean Cyst Nematode. It is the most important soybean pest in the world and in the United States. Oftentimes when you’re taking a look at your fields, you’re going to see very few symptoms out there until your numbers start to become pretty heavy. Generally when you’re taking a look at a field you may not see any stunting or yellow discoloration and you’re already having a yield reduction of 10 to 30 percent. When we really start to see those stunted fields and those yellowing looking plants, you’re probably in the area of a 30 to 70 percent yield loss occurring to SCN infection. SCN you can start to see with your naked eye when you pull up the roots and you take a look at the plant. When you look at that roots, she she’s very small very tiny, but the size of a pencil point. You know very tiny but you can see her. She’s very vivid white to kind of a creamy white in color. A very sizeable difference between the nitrogen-fixing nodules, but until you get comfortable looking at cysts on roots you may misdiagnose it for a grain of sand. So she’s very small But once you start going you can see her if you use a hand lens, you can see here very clearly. SCN again is not a new problem to South Dakota. We first found it in 1995 in Union County and last year in 2012 we found SCN in Beadle County. It is up and down, up and down the eastern part of South Dakota in most of our soybean producing counties. We imagine that it’s in other counties. We just have not stumbled across the field or gotten a sample in that is indicated as such. So how do we prevent the spread of SCN? Well, we want to work with sanitation and thinking about SCN can go anywhere soil can move. So you want to prevent the spread of soil SCN. So take a look, disinfect, clean out your tillage equipment, tires even your feet. SCB can spread in small soil peds after you harvested you’re soybean field. Well, not only that but if it goes anywhere, soil can go, wind can move SCN, same with water and animals. So how do we manage for SCN? You want to rotate to non-host crops such as our corn, alfalfa, wheat, and oats. We also encourage you to use resistant varieties, they’re very critical. There used to be a yield drag acclmated to them, but that’s not the case anymore, our varieties have come a long way. We’re not seeing that, there’s the different resisting resistance like the Pekings, the different P-I’s out there. There’s the different race typing and the HG typing. Really the more you know about your field and what’s going on in that area will help you to be able to pick the right tools for you to combat and work with this problem. So to kind of summarize SCN management. Well the first one I would encourage you to do, if you don’t even know if you have an SCN problem or if you do have it, you need to test your soil. Find out what your levels are and if you do have a problem. SCN testing is currently free for South Dakota growers. It is underwritten by the cut by the South Dakota Research and Promotion Council, so I encourage if you’ve not sampled in a number of years, go out and sample. It doesn’t cost you anything but a little bit of your time. Gets a good idea as to what those numbers are. If you’ve sampled in the past, sample again, see how your numbers are holding. Are you using the right type of resistance? You know, what are you doing? Again utilizing resistant varieties. You want to also rotate with non-host crops and prevent the spread of SCN. So again utilize the sampling. Samples can be sent to the diagnostic clinic. We are working with the survey, targeted towards counties that are that appear on the map and the handout that have not identified SCN. So we encourage samples to be set in there, just so we can kind of screen to see if sen is a problem that area. So we can get more education out. The last disease, I’m just going to highlight here quick Phytophthora. It is a root rot. I’ll pass around some plants that are putting them out here, so you can kind of see it. With our cool temperatures and wet early on, our Phytophthora is a root rot. Again at favors that cool, wet weather, poorly drained soils, compacted, heavy clay. Usually you’ll see identification is like a tan to brown chocolate brown lesion that starts at the soil line and moves its way up on the plant. There are some photos in the handout for a little closer identification. So some of the management for Phytophthora would include keeping track of your field history. Have you had a problem with phytophthora or different root rots in the past. You want to plant varieties and utilize different races, preferably if you can stack them together because Phytophthora, there’s many different races out there so it’s starting to combat a lot of the resistance that we do have available to us. You want to select varieties with higher levels of field tolerance. That’s more of our general or generic tolerance out there. Again, you want to improve that soil drainage and utilize the seed, a fungicide seed treatment. If there’s been a known problem with damping off in the past. Any suspected samples regardless of any diseases that we’ve talked about today, can be sent to the diagnostic clinic. Same goes with those SCN samples, so I encourage you to do that. We just want to highlight two websites, and then I’ll wrap up here. If you have not visited iGrow.org, I encourage you to do that and same with our Pest and Crop Newsletter. If you don’t currently receive that you can sign up for that on the website. With that I just want to thank you and we’ll take any questions at this time. That’ll just kind of give a shout out here quick for our SCN day which will be held on August 28th at 6:30 down at the Beresford Research Farm again, that’s August 28th that’s 6:30 working with and talking about Soybean Cyst Nematode education. (Music)

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