to introduce Dr. Mark Renz, an extension weed specialist here at the University of Wisconsin, Madison.  He does most of his research in the biology and management of weeds in perennial cropping systems and natural areas.  Mark has over 15 years of experience conducting weed management research throughout the United States.  With that please help me welcome Dr. Renz.  (audience applause) - Thanks Jeff.  It's a pleasure to be here today.  I have two goals in this session, in this presentation.  The first and most important is to get you out early so you can get in the front of the lunch line, cuz i'm sure it will be a long one.  And then the second, I wanna just talk about when we're developing weed management and utilizing a burndown program, some simple concepts that you can utilize to potentially improve control, particularly with some of your perennial weeds that you have in that system.  But first let's talk about why do we do burndown treatments? What's the ultimate goal? I have several split up here, but I want to emphasize the number one goal of our burndown treatments is what? It's simply to prevent that early season competition during that crop emergence and establishment. 

 Just remember that.  I think in general we do a pretty good job with our burndown treatments in accomplishing that one goal.  But there are also some opportunities to get some enhanced weed control, some of it will come at an additional cost, from our burndown treatments.  Some of those additional benefits may be some additional weed management.  We can use some herbicides in our burndown treatment that have residual activity that can delay weed development, that can particularly allow us to delay some of our post herbicide applications, and maybe reduce some of our weed population densities.  From a weed perspective, some of our opportunities really are to this is an opportunity to reduce and manage some of our weed populations.  Now I was tasked with focusing on perennial weed management, how we can increase some of our weed management on perennial weeds with our burndown treatments.  But I'm also briefly and initially gonna talk about winter annual weeds.   So why did I change and add this topic on to our system? Well, I want to first remind you guys what a winter annual weed is.  A winter annual weed is one that is gonna germinate in fall to the early winter. 

 What's gonna happen is, when springtime hits and everything gets going, those are gonna be really widespread, flowering and very troublesome and very competitive.  And here's a great picture that was taken by Jerry Dahl showing in early May, we can have a carpet of weeds that can be extremely, extremely competitive.  Well, why am I talking about winter annual weeds when the title has perennial weeds in here? Because I expect large populations this spring.  Remember how nice and pleasant it was in October? Well, what happened during that time frame is many of those winter annual weeds I would have expect have germinated and developed pretty actively.  We have a nice snow cover throughout much, if not all, of the state.  They're likely overwintering well, and I expect bumper crops that we're gonna have to deal with in spring, so I want to bring that to your attention.  What are some of these culprits? Chickweed species are some of those you need to be aware of.  We have two main species, although there's several in Wisconsin, Mouse-eared and common chickweed.  Prostrate growth, opposite leaves.  The mouse-ear can be very hairy while the other chickweed species are not as hairy. 

 Fairly easy to identify with the white flower.  Really be on the lookout for this one.  Shepherd's purse, this is one over the last 10 years I've seen really rapidly expanding throughout Wisconsin in many of our no tell fields.  Easy to identify.  When it's flowering it has those heart shaped fruits that are present, white flowers.  But also we'll see this right when the snow melts.  It'll be growing right away and have highly divided leaves.  It's easy to identify as well.  Finally, the third one I want you to be on the lookout for is pennycress.  Some may refer to this as a crop. 

 I would not call this a crop.  I would definitely call this a large problem and a weedy species, and I expect lots of it.  Easy to identify by having these wavy to serrated leaves that clasp the stem.  If you crush it, it has a very bitter smell.  Some say it's garlicky.  And clearly easy to identify when it has fruit present because those fruits have that clear dime shaped fruits that have a notch in the tip of them.  Just be on the lookout for those three species this spring.  There's a few others to be looking out for too.  I expect it to be a bumper crop this year.  The good news is, they're fairly easy to manage. 

 And they're fairly easy to manage with some of the tools that we commonly utilize.  A wide range of products are effective and economical.  Glyphosate alone or in conjunction with 2, 4-D are really effective.  And there's a lot of other products that are effective as well.  Applications can be applied in the fall, so if you did your applications this fall, those are the most consistent, good for you.  But we can still get really good results in the spring.  We do have to be aware that as these weeds get over six inches tall, some of the herbicide labels will be in that six inches or less time frame, so we wanna try and get 'em early versus later.  That's enough of my talk for my predictions.  You can come and see me in April and May and tell me how wrong I am.  That winter annuals weren't a problem at all. 

 I'm gonna now shift gears and really focus about how we can improve some of our perennial weed management issues.  We can do this with burndown treatments.  There are effective options.  But there's challenges associated with these in our northern climate.  Timing specific challenges and weed specific challenges.  Really these concepts overlap quite a bit, so I'm gonna go through these and talk about these.  The first thing I wanted to do, and this was kinda an interesting exercise, I wanted to talk about what are the top 10 perennial weeds that we see in our corn and soybean systems in Wisconsin? What I did is looked at some of the past surveys done over the last six or seven years by Ross Recker and Nathaniel Fickett.  And classified those to come up with what are the top weed species that we have in our Wisconsin system.  No surprise, common dandelions was the most common perennial weed species that we had.  I had lots of quackgrass, yellow nutsedge. 

 White cockle or white campion was another one.  Canada thistle and field bindweed.  Those were the top eight.  Some of the surprising species that you may not have thought of is white clover was really common in many of our fields.  That's one that we may not consider a weed.  And volunteer alfalfa is one that we're seeing more and more of showing up in our corn and soybean fields.  Finally, plantain species and horsetail were ones that rounded up the top 10.  These are ones that we commonly see, although there are a range of other species as well.   When we think about managing these species, we have to think about, well, when are they present in this system? These species emerge and show up all at different timings as we'll talk about more later.  I wanna emphasize that when they emerge and when they are actively growing is really critical to know in order to dictate how we're gonna mange these species. 

 We have some species that are actively growing early in the spring.  As I'll talk about, these are great ones to target for increasing control with some of our burndown treatments.  Like dandelion, quackgrass, even clover and volunteer alfalfa.  These are ones that are growing really early in spring and even late into the fall, and we can really effectively target in our burndown treatments.  But, we have other species such as yellow nutsedge, Canada thistle, our bindweed species and horsetail, that don't grow actively during those burndown time frames, in the fall and more towards that spring time frame.  So those are ones that we really don't have as good an opportunity to control in our burndown time frame.  We need to realize that a lot of these results are gonna be very species specific.  Okay, so now we're gonna take a step back and go back into Weed Science 101 looking at how herbicides work to maximize control on some of these perennial species.  In order to maximize control of perennial weeds, we need to get that herbicide absorbed into the plant, and then we need to get that herbicide to move or translocate into those perennial tissues.  That could be roots, rhizomes, tubers; it just depends on the species we're talking about. 

 I'm gonna talk in a little bit more detail on each of these with reference to burndown treatments.  How do we maximize absorption of herbicides that we're applying in a burndown situation? It depends.  Are these herbicides gonna be taken up by the foliage or by the roots? If these herbicides are gonna be taken up foliarly, by the leaves, we want to treat when there's as many leaves present to absorb that herbicide as possible, right? That's a really important characteristic to remember.  Then the second thing we need to remember is when you wanna treat when conditions are conducive to allow for absorption of that herbicide.  What do I mean by that? Well, those leaves aren't drought stressed.  The leaves aren't dead due to frost damage, or something like that.  And most importantly, that temperature is warm enough that absorption can occur.  Temperature's a really important factor in herbicide absorption into those plants.  Usually temperatures above 50 degrees.  Now secondarily, if that herbicide is gonna be taken up by the roots, we need those roots to be actively absorbing that nutrients, water, and those herbicide will be moving up with them as well. 

 We'll briefly talk on this, but we have a little bit more flexibility in temperature with that.  So what do you think? What do you think how most of these herbicides are absorbed when we're applying them in a burndown situation, foliarly or by root uptake?  Silence.  Foliarly, right? So that's really what I'm gonna focus on here.  But we do have herbicides that can be absorbed by the root too, and those are some opportunities to increase control as we'll talk about.  How do we maximize translocation of foliarly applied herbicides? Well, we want to apply at the right timing so that that herbicide can translocate into that perennial tissue.  The timing is very phenology and species specific, but really the two key timings I wanna mention are the timing when flower buds to early flowering is one good timing, and then in the fall when green tissues are present and right before those plants syness.  Those are the two key timings to maximize translocation into the roots.  Now that can be some challenge with some of these species to hit that flower bud to early flowering timing so that fall timing might work a lot better with some of our burndown treatments, as we'll see.  The key thing I want to emphasize though is the worst timing to apply these for translocation is early in the spring just after that plant emerges.  That's when it's really a challenge to get a lot of that herbicide deep into that perennial tissue. 

  So spring or fall when we're applying a burndown treatments which is our most effective time frame? Experiments have been done in Wisconsin and other states throughout the region, and it's always clearly been shown, even when we're making applications in the fall in the middle of November as you can see with this example here, we're always getting significantly better control with fall applications versus spring applications.  Whether they're herbicides that are only gonna be absorbed through the foliage versus herbicides that can be absorbed through the foliage and the roots.  So if you can get these on in the fall, that's by far gonna give you the best results with the example with dandelion here.  And it can be quite dramatic in some years, as you can see by this picture.  So now the question is, living in Wisconsin, is how late in the fall can we go? This was clearly a great year this past fall to do some of these fall burndowns so hopefully you were able to do that.  But how late in the fall can really vary depending on what herbicide you use, what the weather's like, and the status of the weed.  How resilient is that weed? Can it grow late into the fall or not? How stressed it is, how much leaf, how much leaf area is present.  As a general recommendation, to kind of sum up all of these factors that I mentioned, we recommend that you can make an application when temperatures exceed 50 degrees Fahrenheit for several hours the day of application or within one to three days of that application.  So that's to counter many of these factors I just talked about.  So when does that happen in Wisconsin? Any guesses? Pick a fall and it will be guaranteed to be different every fall versus the other fall. 

 Here's some data to show you that this 50 degree Fahrenheit time frame is really a good reference.  This is some work we did on alfalfa suppression.  We did it with a very low rate of 2, 4-D, just one pint.  And we did it at two different locations at four timings in the fall.  That blue bar was a late September timing.  That purple to reddish bar, I'm color blind so if I'm gettin it wrong tell me, is middle of October.  The lighter yellow bar is Halloween, October 31.  And then that light blue bar is middle of November.  What you see that there is some variation between two of those locations, but that November time frame is where that control really dropped off, right? So let's look at the temperature and how that temperature changed in that time frame.  This was done in 2008. 

 What we see with these arrows that are green and that last one that's red are our four different application times.  As you can see looking at the air temperature that yellow bar is that 50 degree Fahrenheit time frame.   That September time frame, middle of October time frame, well above 50 degrees Fahrenheit, good absorption of those herbicides, and as a result, effective control.  When we got to that Halloween day application, we saw it was pretty cold.  That day of the application it didn't get above 50.  But we had some warm temperatures that day after it was able to get above 50.  And we got some fairly decent control.  Little bit more variability, but decent control.  Look at that middle of November time frame.  That's really where the roof fell out from underneath us. 

 And we were much lower than that 50 degree Fahrenheit level.  So as a good rule of thumb, if we can get to that 50 degree Fahrenheit level, we can get good control.  This experiment really demonstrates that at two different locations in Wisconsin.  Okay, so how late, in Wisconsin, how late can we go and still expect to see those temperatures above 50 degrees? What I did is I took this information from our Wisconsin state climatology office.  These are maps that show you the average 30 year maximum temperatures over a 30 year time frame.  And what we see on the left there is October.  And what we see throughout most of the state we can find in October days where temperatures will get above 50 degrees.  Obviously, these are averages so there's gonna be time frames when we're below there.  But if we look at all of those numbers, we see they're all 50 degrees or above on average in October.  So, likely well into October we can have success. 

 On the right side, we see November.  There what you don't see is any temperatures above 50 degrees.  And so we're really rolling the dice when we get into November.  I think October's a good time frame.  Probably you can go late into October in southern Wisconsin and northern Wisconsin you're gonna struggle to get past middle of October in many years too.  But November is really when it's gonna be a challenge.  But it's a crap shoot.  We had many days in November  above 50 degrees this year too.  So it's highly variable from year to year.  All right, so let's say you wanna do a fall burndown treatment, but you can't get those temperatures above 50 degrees Fahrenheit. 

 What are some things that you can do? One of the options that we found, is increasing the rates.  Make sure they're within label, but increasing your herbicide rates can offset some of those low temperatures.  We did some work with alfalfa again.  What we found, if we doubled the rate of 2,4-D, we were working in Roundup Ready Alfalfa, we could get similar levels of control in controlling that alfalfa if we doubled the rate of 2,4-D in temperatures less than 50 versus higher than 50.  So what we're doing is just adding more herbicide.  So even though a smaller percentage is absorbed, we have more herbicide that gets into that root.  The other thing that we found with a lot of our dandelion research has been shown that some products can still be root absorbed in those lower temperatures even if we're getting poor foliar absorption.  Tank mixing some of these herbicides like Autumn, Canopy, Express, these do have the ability to be absorbed by the roots, can offset some of those lower temperatures as well.  So that's another thing you can do.  Key thing though is we don't wanna make those applications when the soil is frozen, but just when those cooler temperatures exist. 

 The third option is what? Wait til spring.  And that's often what we do because of other activities.   So if we are gonna go in with some of these spring burndowns, what are some things that we need to consider? Number one item we need to think about is, is those perennial weeds we're targeting emerged? We not only need to have them emerged, but we need to have considerable growth so that they can actually a, absorb that herbicide from having a lot of leaves present, and then two, hopefully that phenology's close where it can actually translocate it into the roots or perennial system.  We have a tool called the weedometer that actually allows you to predict when emergence of some of these species is gonna be and when flowering is in Wisconsin.  You can just google weedometer or you can go to the URL that I see there.  You can enter a lot of things.  You can actually shift the location, so it can help improve the prediction.  If you're in northern versus southern Wisconsin.   Just for the sake of time, I've showed you a screenshot of some of the results with some of the common perennial species.  What you see here are these green bars. 

 These green bars are the average emergence time of these weed species that I've highlighted there.  That's the range with the green dot being the average.  Then the yellow bars are the range of flowering of these species with the yellow dot being the average.  This was taken from the weed garden at the Arlington Ag Research Center.  Worked on there by Jerry Dahl in the late 1990s and early 2000, that can create these.  But you can adjust the location and it will come up with an estimate.  What you see here is many of our species emerge in late March to early April such as quackgrass, dandelion, white campion and yellow rocket.  These are really good candidates for a late April burndown treatment to be effective.  They're gonna be very well developed, have lots of leaf tissue and be close to flowering.  But some of our species as you see like Canada thistle, and more importantly, field bindweed and nutsedge, they're not even gonna emerge until after the first of May. 

 So we really shouldn't expect to get effective control from our burndown treatments.  What are some other things besides emergence to consider if you're doing a spring burndown treatment? The other important thing is to think about what those plant-back restrictions are for the products that you wanna utilize.  Much of my talk is gonna focus on glyphosate and 2,4-D.  Why am I gonna focus on that? Because in surveys that's what the majority of people are utilizing, and they have very minimal plant-back restrictions present on the labels.  A lot of other products are effective and can be utilized and have a lot of benefits such as residual control, but we need to be really careful that we don't screw up some of those plant-back restrictions on the label.   So what I thought I'd do now is show you one of our demonstrations that we did to highlight what happens long term with various spring burndown treatments.  This is gonna highlight some things that you can vary to help improve your control.  This is work we've done with Dan Heider, with our IPM group here at UW on campus.   He applied either glyphosate, 2,4-D or combinations of the two as burndown treatments to some of his plots that were in continuous corn or soybeans.  He applied them a little bit late, May 20, so keep that in mind. 

 Then he planted these treatments two weeks after treatment.  So what we did is we went in and took a range of measurements in these plots to look at both the initial and then the long term benefits of some of these different treatments that I'm gonna show you.  What were the measurements? Well, we came back 30 days after treatment and looked at all the treatments, and all the treatments had 100% dandelion control.  This is really important.  It's showing you just using a burndown treatment, any of these, prevented that early season competition with those crops which is our primary goal.  So they're all effective in that.  Now what we're gonna look at with our data is, how can we improve some of that longer term control? And we're really gonna make the assumption that that longer term control means we're killing some of those dandelions versus just suppressing that early season growth.  How we collected that data was we didn't look at the cover of those plants, but we actually physically counted the number of dandelions that emerged.  So if it was one dandelion that really looked injured but it was emerged, we counted it the same as a dandelion that was robust and actively growing, had a bunch of leaves.   We came in in late July and evaluated this. 

 And what we saw is, on the y-axis here we have the percent reduction in the number of dandelion plants.  So we're comparing it to an untreated control.  We can see if we applied glyphosate at three-quarters of a pound, Roundup at 22 fluid ounces in our corn or soybean fields, we were killing around 50% of those dandelions.  So we are getting some long term suppression, but again we're probably only killing about half of those populations.  The other half are probably the taller, older, more mature plants that we're struggling to kill.  If we increase that rate from 22 fluid ounces or three-quarters of a pound to a pound, what happens? Now all of a sudden our mortality jumps up, almost doubles, gets around 85% in corn and soybeans.  So that's pretty good.  That's one simple trick that we can utilize, just simply increasing our rate.  What happens if we add 2,4-D into the mix with a low rate of glyphosate? Well, again we get a similar response that we do with increasing the rate of glyphosate.  We're getting an increase in control, controlling anywhere between 80 to closer to 100% of those dandelions. 

 Any guesses as to why we're seeing better control in corn versus soybean? Remember these are continuous corn and continuous soybean plots.  Soybeans have a lot less residual cover.  We're probably getting much more robust populations of dandelions in those continuous soybeans populations just due to less competition for light.  That's my guess as to what we're seeing.  Then we had a 2,4-D alone treatment and we're seeing that combination of glyphosate and 2,4-D was also giving us some better control than the 2,4-D alone.  We also did have treatments where you apply glyphosate at three-quarters of a pound and a pint of 2,4-D.  We saw in the corn plots we saw similar control to the glyphosate at one pound.  But in those soybean fields we saw a lot more variability in those results.  Think it's due to it's right at that tipping point of effectiveness and adding that more 2,4-D really did benefit it in the soybean systems.   Are other herbicides available besides glyphosate and 2,4-D? These are the ones I'm talking about and absolutely they're available and they tend to be very effective. 

 But their effectiveness is specific to the weed species and the time of application.  A lot of 'em have very specific restrictions in place that just really prevent me to talk about them in detail.  Some like we've done research with like Autumn, can be applied late into the fall and are extremely effective.  Many of those that we utilize that are cost effective like Autumn and Basis are really effective but we still need to tank mix other products like 2,4-D or glyphosate are recommended to get that enhanced control.  The good news is some of these other options are pretty effective and they're generally very similar in cost.  But again, they have very specific restrictions.  Plant-back restrictions.  Some of 'em have very specific geographic restrictions that limit their use in Wisconsin.  And some have weight restrictions.  So read those labels carefully. 

 To sum things up, what are some tricks that we can do to increase our effectiveness on perennials with burndown treatments? Number one, scout those fields.  Know those weed species that are in your fields, and know when they're emerging and when they're sensitive to these applications.  Time those applications based on their growth.  I gave you some resources to help with that.  If you can, utilize fall applications when possible.  Hopefully, last fall you did a lot of that.  This is a really effective time frame to do that.  I know it's a struggle and it's a challenge.  We have lots of things going on in the fall.  If we have late harvest, it's hard to get it in every year. 

 So take advantages of those good falls like we had that year.  If we can't make those applications when temperatures are above 50, try to use some products that also can be absorbed by the roots.  We see some benefits that can occur from that.   If your gonna apply in the spring, some options that you can do is first, know those species that you're targeting in the spring.  Delay those applications as long as possible until you reach that optimum timing, so you can maximize that movement of the herbicide into the perennial tissue.  Increasing that rate of glyphosate with dandelions did show some benefit in increasing that, so that's one option you can look at.  Adding additional growth regulator herbicides  like 2,4-D or even Dicamba, if fitting in with the plant restriction is another good option to utilize as well.  Realize that some of our species are really not emerging during that time frame like horsetail and bindweed, and really need to be managed in crop is probably your best solution.  That was that last bullet point that I said right there.  Hopefully, I haven't gone over too much time. 

 I would like to answer some questions, but before I do I wanna mention that another option is just planting perennial crops.  This is a great example of alfalfa in a dandelion infestation and just having a perennial crop on the landscape can really do a lot of wonders for suppression as well.  Okay, if I have time for questions before lunch, I'd love to answer 'em.  (audience applause) Thank you.  (audience applause)