 I'm Michael Vunch, I'm the plant pathologist at the Carrington Research Extension Center. One of the crops that we work with very extensively is sunflower. And the disease that we've been working on in sunflower is sclerotinia head rot. And the research program that we've had here on the management of sclerotinia head rot is the most expansive, conducted arguably anywhere in the world. And we've been running a very extensive and expansive program targeting improved management of sclerotinia head rot here for the entire decade that I've worked here. And one of the critical questions that we sought to address early in that research is when are some fliers susceptible to sclerotinia head rot? There has always been a lot of talk that the head rot must come in at R7 when there are depressions in the back of the head and water builds up in the back of the head. And the heads are starting to synast, i.e. you've got some dead tissue in that yellowing back of the head. And so we sought to address the question of when the head rot develops. We did this by inoculating some flowers at different growth stages. We inoculated during full bloom during R6 growth stage when all the ray flowers and the disc flowers are fully wilted but they're still attached to the head, R7 and R8. And we did this with confection hybrids, with oil seed hybrids, with susceptible oil seed hybrids and partially resistant hybrids, highly susceptible to confection hybrids and partially resistant confection hybrids. And we also did it by bagging the heads or leaving the heads unbagged. With the idea that if we bag the heads we trap humidity around the head and create conditions even more favorable for head rot. We inoculated the heads, we put out sprinklers over the top of the sunflowers to facilitate keeping the heads wet throughout those growth stages. These sprinklers were on a timer so the heads just stayed moist to the touch on the front but there wasn't so much water that the sunflowers would lodge. And what we found in testing conducted across three locations in North Dakota across, gosh we started in 2011 and we finished this testing in 2018. So eight years of testing, what we found very consistently is that sunflowers are very susceptible to head rot during bloom, R5 growth stage. By the time they reach the R6 growth stage, when the ray flowers and disc flowers are wilted, the susceptibility drops very sharply and they can only develop head rot if it's extremely cool and wet. And after that they are not susceptible to head rot anymore. And during the bloom period there are differences in susceptibility depending on the stage of bloom. So when the sunflowers are entering bloom, what we would call an R5.2, R5.3, i.e. about 20 to 30 percent of the disc flowers, those little flowers in the middle of the head, in bloom or completed bloom, this is early bloom. Sunflowers are not very susceptible to head rot at this stage. They are susceptible but not highly susceptible. As bloom progresses, here we have a head that's probably about R5.5, about 50 percent of the disc flowers in bloom or completed bloom. These are much more susceptible than that last head, okay? And then as bloom progresses even more, here you have a head that's probably R5.8, maybe even R5.9, 80 to 90 percent of the disc flowers in bloom or completed bloom. Now this is even more susceptible than that last head to head rot. And this head right here, which has 100 percent of the disc flowers either in bloom or completed bloom, is even more susceptible yet. So as the percentage of these disc flowers in bloom or completed bloom increases, the susceptibility to head rot increases, okay? And then once you hit R6, oh, the ray flowers have dropped off of this because of abrasion, just hitting other heads. But when I picked this, all the ray flowers were on here, but they're all wilted. And notice that all the disc flowers are completed in bloom. At this stage, even though there are dead blossoms on here, this head is much less susceptible to head rot. And the hypothesis that we've come up with as well as other people in the industry is that it's probably because the kernels are starting to melanize, which gives them a bit more of a protection against infection, okay? And but they can still develop head rot at this stage, but only when it's extremely cool and wet in our experience from, again, multiple years of testing under very rigorous, rigorous testing and different regimes. The reason why we don't see the head rot usually develop until R7, R8 is not because infections occur later. It's because there's a long incubation period. And this is true for white mold in general. It's true on soybeans, it's true on dry beans. On sunflowers, it's particularly true. That disease infects through the front of the head, through senescent blossoms on the front and possibly even live blossoms on the front of the head. And then it must colonize, must run into that head and colonize that head tissue and then work its way all the way through that thick head until it comes out to the other side. And where you see head rot, and there's quite a delay there. And you will not see the disease until R7, R8 under most circumstances. And that's just because the time it takes for the pathogen to work its way through the head. And we know that for certain because of these inoculation studies we have done where we have inoculated different growth stages and left non-inoculated checks. And so we know when we inoculate it and we can see we got the disease involved and it didn't occur until that R7, R8 growth stage in most circumstances. And so this is very useful information because once you know when the sunflowers are susceptible, you know when you have weather conditions that are likely to cause risk. And you also know that if you're thinking about using a fungicide, which we'll discuss in the next video segment, when that might be applied. And if you're interested in assessing the susceptibility of sunflower hybrids to this disease, how you must go about screening those in a non-bias manner. If you have any questions, go to the NDSU Carrington Research Extension Center website. Click on Plant Pathology and scroll down to the section on sunflower sclerotinia head rot. And you'll see data slides that summarize the information I just presented. Thank you.