Field Crops Webinar Series - Herbicide Efficacy Under Weather Stress
Print
EmailMarch 3, 2019
Dr. Erin Burns discusses how weather stress can affect herbicide activity and how to design a program to improve your weed management by planning to buffer weather impacts. Future climate scenarios for the Great Lakes Region predict increasing temperatures and more precipitation in heavy rainfall events, leaving more days during the growing season that have little or no precipitation, polarizing the wet and dry periods. Herbicide efficacy and potential crop damage are highly influenced by weather conditions. For example, herbicides are less effective when weeds are drought-stressed and herbicide movement into the soil is less, reducing weed control. This webinar will focus on herbicide efficacy under various weather stressors (cold, hot, wet, dry conditions) and how to design robust weed management programs to buffer weather impacts and achieve consistent weed control and crop safety.
Video Transcript
- All right as Jim already mentioned we're gonna be talking about herbicide efficacy under weather stress. We'll start off a talk about weather here in Michigan. I'll give a little overview on historical norms and then where we are projected to go in terms of various climate variables. And the first is that as many of you know since the 20th century and since we really started recording temperatures in general Michigan has had over a two degree in Fahrenheit increase over time. So when you're looking at this figure on the horizontal we have the year so from 1900 all the way projecting into the future and then the temperature in degrees Fahrenheit, the orange squiggly line are actual observations and then we have both two different scenarios depending on different C02 emissions so red meaning more CO2 emissions projected increase in temperature going up and then the teal color being lower but still seeing that increase over time. Temperatures in 2000s have been higher than any other period we've experienced as you can see on the graph. And then in 2012 which is this data is a little bit dated we've surpassed that as the hottest year on record with a statewide average temperature of 48.4 degrees so you can think of our state as fairly large and has a lot of different temperaturisms so that was the average across the whole state which is a five degree above our long-term average. Moving on to precipitation we've also seen a wide range in precipitation from a low end of 23 inches in 1930 and the higher being 39 inches in 1985. Once again so this graph is now grouped into five-year periods and then the total precipitation in inches and this black horizontal line right here that I'm pointing out is the average historical norm. So anything below that line means we've experienced less precipitation than normal and then above the line would be more precipitation than normally observed historically. The driest multi-year period was in the 1930s and 1960s these are those yellow boxes that were fairly dry then as of late the most wettest multi-year periods have been the 80s, 90s and then now the 2000s in which we have data for which those bars are above that average line meaning more precipitation. And 2013 was the wettest on record for the state with over 38 inches of rain. Over the past decade we've also seen differences in the extreme amount of precipitation so these are characterized in two-inch rain events the same time or more so once again we have the year and then this black line is the norm so these are rain events in which two or more inches falls at a period once again below meaning lower than the record then high being more than the average. So these extreme precipitation events in Michigan are projected to increase so as you can think of this might have increasing in flooding durations and also might have implications on springtime activities out on the field so delayed planning and other activities. This is just a snapshot of the amount of precipitation that we got during the growing season this past year. So the gray would mean historically normal on average and then any greens or blues or purples mean higher than average in inches amount of rain and then as you'll see the yellow and red colors mean the drier regions so lower than what we would normally expect. So in April pick where you're located in the state and track the precipitation over time. Then in May various parts of the state except The Thumb and regions of the EP were fairly wet, wetter than normal. Then the state as a whole largely dried out in June. This carried through till July, then in August large portions of the state once again saw fairly large precipitation events, it got wetter, some regions more than eight inches over normal. And then once again in September things evened out again. So keeping this in mind of these events where we go from months that were fairly wet to strings of months that were dry and how this is gonna play a role in herbicides and weed control in general. So this next part of the talk will go into just different implications of weed control on our various weather extremes so we'll start with precipitation, I'll start with drought. And drought events may become more frequent given these climate projections. So you just saw in some of these figures we've seen that more precipitation is gonna fall in these very heavy events and this is gonna lead to large strings in time where we're not gonna see any precipitation so large times where there is no precipitation events happening. These have a number of implications on weed control, the first mainly weeds and crops compete for water for growth and also herbicide efficacy. So we have weed competition and then also how effective those herbicides are. And post-emergence herbicides are less effective when weeds aren't growing so they're not growing, they're not absorbing those herbicides and this reduces absorption, so how can the herbicide get in the plant and then translocation, can it get to its target site where it needs to be effective to kill that weed and then also metabolism of those herbicides. And then there's a large number of implications on residual herbicides. Residual herbicides are the ones that we apply to the soil and they have activity for weeks after we apply them and precipitation is quite critical in the efficacy of these categories of herbicides. And the first is that it actually moves the herbicide down into the soil surface so we don't lose anything from the soil that evaporates or volatiles through the soil surface on the top. It also needs to get the herbicide down into the zone where those weed seeds are germinating so any of those herbicides inhibit weed seed germination and growth. And then also those weeds need to have precipitation in order to germinate to be controlled. So it really has a three-step implication on the residual activity of these herbicides and often shortens it if there's not enough precipitation present after you apply these herbicides. To get down into that a little bit more is herbicide breakdown and lots of herbicides are degraded through microbial or chemical degradation and these both rely on soil moisture. And when the soils are really dry herbicides are broken down by microbial activity is slowed quite a bit. So in this figure we have our normal saturated soil, so these brown or black bobs are soil colloid particles, the little blue areas are the areas inside the soil pores where we have that moisture and then the orange and the yellow dots represent the degradation of the herbicides by the microbes and those microbes need those water areas to survive and thrive so that's where they are present. And then under dry conditions, you'll see a lot less blue space around these soil pores so not as much microbial activity and the degradation of those herbicides is prolonged which will have implications both on crop rotations and also herbicide efficacy of the weeds in the current season which we'll go over in a bit. Also has implications on chemical degradations so it slows microbial degradation but the chemical degradation also is required by a critical step with water so even very dry soils always have some amount of water along each one of those colloids so again this is that same figure looking at our soil particles and then the water that is around each one of those. And the herbicides can either be attached to the actual soil particles or within that thin water layer and then they are susceptible to chemical attack when they are in that water layer. And the rate of this chemical degradation may actually increase in drier soils because they tend to be hotter. And those hotter temperatures in those soil areas actually increase these chemical reactions and you might see an increase in chemical degradation of those herbicides at a faster rate than what you would normally observe if temperatures were more on par for that time of the year. We group herbicides, we know a lot about some of them and some we know that are primarily degraded by microbial activity are atrazine and then I put the active ingredients and then also the trade name of some of those herbicides that you might be common with. So things like Python and then the fomesafen herbicide so Flexstar, Reflex there's a quite a few others that contain this active ingredients. The imidazolinones so those are ALS inhibitors or HMIS so Pursuit and Raptor are also primarily degraded via microbial action. Callisto which is mesotrione which is in a lot of other herbicide. Premix is also Dual. Metribuzin then sulfentrazone these are known to be primarily degraded by microbes and soil. And then there's categories of herbicides that we know that have a combination of the two which would both be impacted by drought and flooding conditions which we'll go over in a bit. And the main difference here are various chemicals and then the big group are these ALS inhibitors, the sulfonylureas, things like Classic, Permit, Osprey, Matrix, Resolve there's quite a few others. These are mainly chemical and microbial component so knowing which herbicides are normally in your program you can look back at these and have a better idea of what kind of degradation pathways would occur. So on the flip side of the precipitation is heavy rain and flooding events. And the first is that heavy rain and flooding events damage the crops, the crop's injured, it's not growing as well as it normally would be and this allows weeds to compete. Weed competition can have two factors both for the injured crop and then also there will be bare areas potentially left after those rain and flooding move and evaporate off the soil so this leads to weed germination in those bare spots and then also that crop canopy might not close as fast so you don't have that competition from the crop. And there are two main options for weed control after a heavy rain or flood and this really depends on the status of the crop so if the crop recovers or if it doesn't recover. First we'll discuss if the crop recovers so once fields have dried there are gonna be newly emerging weed seedlings that need to be controlled and your choice of herbicides is really dictated by the stage that the crop is present. So the herbicide label and I'll show you a few other locations and our weed guide that you can look up clearly states what's the maximum growth stage of the crop that that herbicide can be used. And it's possible depending on the timing of the flooding event that they might beyond a window of application of a herbicide you might typically use in your program. So you wanna avoid applying any herbicides to stressed crops so those crops aren't growing as well they're not gonna metabolize the herbicide and they're not gonna respond to that herbicide as well as they normally would be and you have a copy of our weed guide so this is the 2019 weed guide version. You can get it on the extension website, I'll show a link at the very end of this talk and where you can purchase one of those with your various other events also. I just took a highlight of one of our tables so this is broken up for each one of the crops. We'll have the herbicide, then also the height that they are the most effective on for the weeds but then when we were talking about applying these herbicides potentially after a flood we have the maximum height so this is an example of corn so inches depending on the stage it will tell you in colors depending on how large those plants can be and some of them have no restrictions also so this is a quick table that you can use as references when trying to pick out a herbicide that you might use later in the season than you normally would. So when I was talking about crop damage and saturated soils these are largely because they cannot metabolize that herbicide so crops normally can metabolize herbicides and that's why they still live and weeds don't, 'cause weeds can't metabolize those herbicides to non-toxic compounds. And one way that saturated soils really aids in this crop injury we view is how herbicides are absorbed in the root system and this is through diffusion. So this diffusion process will continue to go regardless if that crop is actually growing. So diffusion's just when you apply a herbicide to a soil surface, very concentrated at that location and herbicide particles and any kind of colloids like this in general want to move from areas of high concentration to areas of low concentration so for our example the roots. So this in saturated system will keep going to their roots and the herbicide will be absorbed by the plant. That plant is growing as fast and as vigorously as it normally would be you can see crop damage through this process of this continuing diffusion. Those are your options if the crop recovers largely focusing on herbicide choice and overall crop health. The second is if the crop doesn't recover and weeds as you know are great at growing in all different conditions so some of them may survive that flood and set seed and some will have new flashes of emergence after that water subsides. So there's three main options for controlling weeds if the crop doesn't recover these include mowing and tillage and then herbicides. So if you decide to mow many of the weeds might survive this you might need multiple mowing events to ensure that those weeds that survive don't produce any new seeds but obviously this isn't an option if it's too wet. Also tillage so not minimal tillage but a vigorous tillage event will destroy the weeds that are currently up and many that are germinating so also help aerate the soil once again will depend on if you can get the equipment out to do so depending on how wet that soil surface is and then herbicide applications. And we recommend non-selectives things like Roundup, Liberty other herbicides with similar broad-spectrum activity that didn't have any kind of residual activity. Since we've learned about the microbes and the chemicals those are chemical degradation pathways are highly affected by the water that's in the soil surface ensuring that you're not applying a herbicide that might take longer to degrade in the soil due to those saturated conditions. And this often an option if it's too wet to tell and you're still able to go over and spray. And to know any of these tactics may need to be repeated multiple times throughout the season as new flashes of weeds continue to germinate because you have a field without any crop in it. Some considerations of years after a flood or very high rainfall events are to be alert for new problems after a flood. As you know flood waters can deposit new ground soil depending from your neighbor's field on to yours and vice versa and so the textures are quite diverse here in Michigan so depending on where you are the soil texture of your neighbors may be different than yours so this can move new soil onto your field which will have different texture pH and organic matter. And these soil factors influence herbicide performance in crop safety and often with some of our herbicides we actually choose the rates depending on organic matter and pH so being able to take soil samples of those highly impacted areas is essential to be able to take both the rates and which herbicides you're gonna use in those years after a flood. Further considerations on floods as we mentioned earlier herbicides are degraded by microbes so these flooding conditions depending on how severe they are can actually make your soil profile be anaerobic or have no oxygen available. Many of those microbes need oxygen to function and degrade the herbicides so this can lead to prolonged carryover, longer than what would normally be observed if those are completely anaerobic conditions. And some herbicides that will either be slower or faster in these anaerobic conditions, the first are triazines, this is atrazine, metribuzin type herbicides these are actually slower under anaerobic conditions so potential for longer impacts on carryover. Then we have Treflan, Sonalan or Prowl, these are faster along with your group 15 herbicides so Dual, Outlook, Harness, these are all soil-applied herbicides that will degrade faster under anaerobic conditions. This is Roundup or glyphosate as a reference has no impact not microbial degraded so it won't have an impacts on this. And then there's SU herbicides those ALS herbicides are chemically degraded so these are more impacted by soil pH than by anerobic conditions and then largely the ACCase inhibitors that you may use in some grass crops have no difference under these anaerobic conditions. It's just a snapshot of the diversity of degradation pathways of these herbicides and big classes that you may use and how they may be impacted due to these anaerobic soil conditions. We also highlight this in the weed guide so once again I just took a few snapshots of the different ways it's mentioned in the weed guide. So for each one of the herbicides we'll have the herbicide name and then the rate but also we call this the remarks limitations section and in here we'll highlight various things, one stage you can apply it up to, what rates and also lots of times if they do have an interaction of those carryovers with the amount of precipitation you get we'll mention that here so this one talking about 20 inches in different rotation intervals often to sensitive crops is when this plays a large role. And this is Curtail so just another herbicide that I highlighted from the guide I just picked a handful and this once again says it will have an interaction with the precipitation how much we get and then that will tell you what they carry over and how long that crop rotation restriction needs to be extended. Also at the end of the weed guide we put a table together that looks at herbicide crop rotation restrictions and anything with a star is often ones that have interactions with the amount of precipitation and you can go and then look at that specific herbicide to see how that will be affected. So these are just some quick ways if you do have our weed guide that you can look through to get an idea of some of those impacts. So we're gonna move away from precipitation and go towards temperature. So I'll first start with cold this first came to my mind it's a winter and it's pretty cold tonight so that's what we'll start with. And these are the temperatures after herbicide application can both impact crop safety and then weed control. So cold temperatures influence crop safety and weed control from those herbicides. And this is as I mentioned a few times, crops and weeds degrade herbicides by metabolism and this metabolism in crops is slowed due to cool or cold conditions. One of our recommendations is that you avoid applying herbicides when nighttime temperatures are gonna be below 40 degrees as often these cold wet conditions is when we see crop injury typically that we wouldn't see if the temperatures were a bit warmer. And also the effect of cold on herbicides varies by weed species and size so we know it causes crop damage but it also reduced weed control. An example of this when you might be spraying herbicides when it's a little on the cooler side for some of those spring burndown treatments. And if it's a little cooler this will retain effectiveness on those summer annual weeds, any weeds that recently germinated after the snow resided and it thawed out. But it also potentially reduced weed control of overwintering so winter annuals so things like horseweed or marestail are a big player in this or biennials or perennials. An Ohio State study, found that control with dandelion with glyphosate 2,4-D when temperatures were warmer was totally 100% and then decreased to near zero when they applied these herbicides under periods of cold weather. So having an idea of looking at the weather forecast, looking at the time of burndown treatments will be essential for some of those harder to control winter annuals or biennials that we're targeting during those burndown treatments in the spring. So moving on to hot, weeds will also have a harder time growing under hot and dry conditions. And they can become potentially more tolerant to herbicides so plants will actually develop a thick waxy layer, a cuticle layer on the leaf surface and this is so that it helps the plant keep in moisture to be effective for plant growth but it acts as a barrier for herbicide absorption so you can think of that waxy layer being a barrier that the herbicide cannot be absorbed as well and this will lead to reduced movement within the plant and the soil rate at actually controlling those weeds. So applications, herbicides during really hot weather we recommend going in in the morning after those plants have had a period of cool overnight to really bounce back and continue growing so that you get the best control out of your herbicide application if you are applying them potentially later in the season. We do see some of these warm spells that we've seen the past few summers. Also many contact herbicides will actually become more active as temperature increases and this increasing activity can have potential better weed control but it can also lead to crop injury. And some contact herbicides that this plays a role in are listed here, things like Aim, Basagran, Ultra Blazer, Cadet, Cobra these are all herbicides which contacts are when you spray them on the plant they don't translocate they just control where they landed on that leaf. So Flexstar, Gramaoxone or paraquat, Liberty, Resource, Sencor, Sharpen, these all have interactions if the temperature is increased to usually over 85 degrees or above is when we wanna start considering not applying those herbicides potentially leaving some crop injury during those pretty hot periods. An interesting thing that I found when I was doing some research for this presentation was actually looking at water temperature and herbicide performance. So this was a study that was done in Purdue. They wanted to look at impacts of the water that was actually in the spray tank and how that might interact with both crop damage and weed control so you can think of, if you have water in a tank potentially like this that's left out for a few days, eventually it's gonna be the same temperature as what the ambient air is, so the air just surrounding it. So we think lower temperatures in the spring and fall and potentially higher temperatures in the summer so they wanted to look at, how does this play a role in weed control? They used a neutral water source, they tried to use water that was not hard water, it didn't have any cations or suspended particles, had a neutral pH. They had four different temperature treatments. so they considered cold was 41 degrees, moderate 72, warm 102 and then the hottest temperature water that they evaluated was 133 degrees. And they wanted to look at, is there any interaction with how long those temperatures are sustained after you mix those herbicides. They mixed the herbicide with those various water temperatures and either waited 24 hours to spray, 6 hours or they sprayed immediately. The herbicides that were evaluated in these trial were 2,4-D, Liberty, Callisto and then they looked at a premix of Roundup and dicamba. Overall they found that storage times did not affect herbicide efficacy so it didn't matter if they waited 24 hours or 6 hours or zero after spraying. They had the same herbicide efficacy but they noted that this isn't a broad spectrum that you can apply to every herbicide 'cause there's lots of different herbicide groups that actually have detrimental impacts if you mix them and then wait too long to spray them. And these are group two herbicides so those ALS inhibitors can actually undergo hydrolysis in that spray solution if it's left too long and then group one herbicides depending on what kind of a herbicide spray tank you're using can break down if too much UV light actually gets in over time. So this isn't just a blanket statement but for the herbicides they tested they did not see any influence. But they did observe an influence of water temperature and overall they found, so we have our herbicide treatments here and then the water temperatures in degrees Fahrenheit. And they found that the extremes, so at 41 degrees and then all the way over here at 133 degrees they observed reduced performance so the herbicides weren't effective at controlling the weeds as they were during these middle two temperatures. So they are not affected at 72 or 102 so really this reflects what we've gone over earlier, spraying when it's too cold and also too warm so keeping the idea of what kind of water suits you're using throughout the year and how long that's been in the spray tank. So those are largely implications of temperature and precipitation on herbicide efficacy and the chemistry itself. They also have impacts on how well the crops and the weeds are growing in different emergence patterns. So the first is looking at water in what we consider the duration of the critical period of weed control. So the critical period of weed control is a period during which crop growth and weeds must be controlled to prevent unacceptable yield losses. So understanding how long this period is is really how we formulated when you wanna go in and apply those post-emergent herbicides. So this figure is looking at how you establish the critical period of weed control. So they have on here this is for corn, they have weeds that they allow to compete until V1 and then they remove them V2, V3 and so on and the percent yield loss. And this is looking at different nitrogen rates but overall the main take home is this dotted line is 5% yield loss so that's where they were deeming unacceptable and if weeds are allowed to compete for a long period of time you gotta control them by V1 or else after that and then as we increase the nitrogen rate we could extend the period of waiting to apply those herbicides but this is also dictated by when those weeds are emerging. So I think water has a role in this, water helps those weeds emerge throughout the season so there's been studies looking at this critical period which mean various different crops the study just highlighted was soybean and common ragweed and they found in a drier, this period was only two weeks but in wetter years study was extended to four weeks and overall they did a survey of these studies and they found that there was a slight tendency for drought to actually favor the crop by reducing the impact of the weeds and this was largely due to, there's a lower yield potential of the crop when they have water stress. So in a drought yield potential isn't as high as a normal year so there's a potential that because we already have this reduced amount of yield that this lack of water doesn't have as big of an impact than the weeds have than just this initial reduction in yield but this was species specific. Also temperature impacts weed seedling emergence so as you can think one of the primary factors that really dictates when weeds emerge is temperature and they are able to sense this and germinate depending on different diurnal temperatures so this is the difference between the day temperature and the night temperature and we can look at this in growing degree days so we have growing degree days established for crops we can apply the same kind of model for weeds. An example of this is effects of temperature on competition between soybean, cocklebur and smooth pigweeds. The study looked at the effect of weed seedling emergence on soybean yield and they found that during early growth periods cocklebur and soybean were both equivalent competitors to smooth pigweed and this is regardless of any kind of temperature impact but they did find an impact that the pigweed was not as competitive when the daytime temperature of 79, nighttime was 63 but then when they increased these temperatures so you can see an increase for both the day and night temperature, pigweed paths became much more competitive with the crop. So overall the take home from that would be that these pigweeds are more effective in potentially later planted soybeans. So when those temperatures are warmer that are syncing up to these and then cocklebur they found was competitive regardless of the planting date. But you can apply this to the concept of scouting so knowing what weeds are present in your field and either differences in what we can learn about what weeds are out there so thinking about some of the more aggressive pigweeds species and being cognizant of when we planted and what herbicides need to be applied at the correct stage depending on these weed emergence. And they also have impacts on those potential spring flooding events so if we do get in and plant later than normal the temperatures may be a little bit more increased than what you would normally planting and knowing that some of those weeds may have already emerged and grow and have faster growth rates under higher temperatures. Taking all these into consideration there's many different weed prep management programs that we can use to buffer these weather stressors and keep in mind looking at different kinds of forecasts and planning during the winter months. Now I've grouped these really into broad categories. I was thinking about what kind of herbicide programs we have and largely in relation of when we are applying so you can go and PRE only programs. These are applying one herbicide before the crop has emerged and the benefits are they save time and money you only have to go over once. Potential cost is rainfall timing as I mentioned earlier if we don't get that rainfall event right after we've applied those herbicides the herbicide won't move into the soil profile to have contact with those germinating weed seeds and we also might see some soil or less amount of herbicide that gets down then also prolonged weed emergence. So we are starting to see weeds such as marestail or horseweed also water hemp and poly amaranth which will show this extended emergence throughout the entire growing season so if we're only putting a herbicide up front it will control those weed seedlings early but if we have any of that emerge later on in the season they can become both yield-limiting and then also they'll produce new seeds that go into that seed bank to have a heavier population the following year. Next group of herbicides are early post herbicides so this is also the benefits of using a one-pass early post program be they save time and money. Potential costs are high weed densities so if we're having lots of weeds that are emerging and are growing potentially when we've decided to apply these early post programs might be too late and that critical period has extended and we'll see some yield loss also those weather impacts. So critical timing with these are applying since you're going in post the weeds have emerged if you have any rainfall event, wind, other things that prevent you from getting out in the field to apply herbicides this will have more days you wait the weeds will continue to grow and you'll see some yield impacts and also crop injury that I mentioned earlier most herbicides have that maximum crop height in which they can be applied so if you've missed that window you may see some crop injury and then early weed competition as we mentioned those weeds will be competing with the crop plants. The final group of herbicides programs that I've grouped are those two-pass programs. So going in with a pre herbicide and a post herbicide. The benefits are consistent weed control over a range of conditions so I'll elaborate that in a slide or two. And this also gives you time so it lengthens your application window for post herbicides so you apply the pre that will do some weed control then depending on various activities but for this type of weather we have various weather events, we'll have some more time to go in with those post herbicides as we wouldn't in these other two programs. But the cost of these programs are that it increases time, labor and ultimately costs to some of these herbicide programs. So when do we decide to use these and these can really be specific to the fields and the weed pressure that you have in those fields. So when you wanna use a one-pass program so if you're best for a pre, you wanna target low risk fields that have overall fairly light weed infestations you wanna make sure there's no large-seeded broadleafs or perennial weeds as many pre only herbicides don't have very good wide spectrum of control in some of these large-seeded broadleaf weeds. You need to ensure there's adequate timely rainfall for these residual herbicides so that we see those weeds are in control which is the goal until that crop canopy closes and then we can use the benefit of crop competition. So if you go with a pre only program we recommend scouting regularly to ensure that you have that consistent weed control until the crop canopy closes and then you can use that. Early post programs once again targeting fields with low risks or light weed infestation. The timing here is essential so many herbicides control weeds fast when they're small. So normally we say a range of two to four inch weeds is when we wanna go in and control them. So if we're not getting in at the right time due to some of those weather events, weeds might be six, 12 inches, you're not gonna see as good a control as you would if they were smaller when you applied those herbicides. You wanna make sure for any one-pass program in general, they have excellent activity over the entire weed spectrum you have in your field so if you have grasses and broadleafs you wanna make sure that the herbicides that you're using have multiple effective sites of action both on the width and breadth of the weeds that you have present but also when we're considering and talking about herbicide resistance programs we wanna make sure that we have multiple effective sites of action for each one of your most troublesome weed species so looking at the weed species you have and using your herbicide program in diversity in those programs. And you ultimately want to control the weeds for a sufficient duration so making sure those residual herbicides get a good activating rainfall and that they will provide excellent weed control until the crop canopy develops. When might you use a two-pass program? These you wanna target high risk fields, so these are harder to control weeds. So these weeds that show extended emergence or if they are perennials but also gives you the benefit of lengthening the time that you have to apply those post herbicides. So these are great for later emerging weeds but also helps buffer that environmental variability. So any of those precipitation, wind, temperature, any of those events that we've gone over will have an impact on potentially getting into one of those post herbicides if you applied a pre this gives you a bigger window to apply. Helps minimize early weed competition and give you overall control. So this I liked to see if any state near us has done a longer term study looking at two-pass or single pass control and then also cost. So this study was from Wisconsin back in 2006 so these prices might not be accurate to today but the difference will be, so they found on average they went to a number of different growers and had sites all over the state and did an average cost of single pass programs is 33 dollars, this is increased by seven dollars for two-pass programs, so you can think of applying that to today's costs but having a similar ratio in price changes. And they looked at overall, do the yield that you get out of using a two-pass program is that a way that increased cost. So anything on this side of the figure, if those bars are above zero means that those yield increases outweighed the cost of the additional pass of herbicides. And then on the right-hand side so they found 20 trials achieved that and overall 13 trials did not. So this is that extra cost didn't resolved in that overall yield difference. But overall what they saw was that 12 trials around this side improved profit greater than 20 dollars per acre. But so which is great, so looking at that really range so this whole scale over here and those two-pass programs having a greater profit even given that they cost a bit more. In contrast they only found four trials that decreased their bottom line by 20 dollars per acre or more so only four as compared to 12 on this side. They also looked at weed control and overall they found that weed control was equivalent or better than the single pass. So certain conclusions that can be drawn from this entire topic, so you know weather plays a large role in herbicide efficacy and also weed biology so emergent competition on the chemistry side and then also the weeds physically growing by themselves. We looked at precipitation extremes and also temperature extremes. Then when you're designing your weed management program think about these impacts, potential weather stressors and ultimately also looking at we really focused just on herbicides today but cultural and mechanical techniques which will also have implications on weather so looking at weed emergence depending on those cultivation events that you reach those peaks in weed emergence or not. And we have posted all of our, so Dr. Christy Sprague and I share a weed science website, we post all of our research results, so we group them into those pre, early post and two-pass programs on our website which is, msuweeds.com so you can go and visit that website and look at all the different research that's being conducted, I believe we have the results back from 2006 to 2005 and then also any other kind of extension materials and back sheets we post on the website. And also this is my email then my phone number so I know we covered a lot today so you could jot those down and ask any questions we might not get to during the rest of the time that we have.