Speaker 1: Good afternoon. My name is Vince Davis. I am the Annual Cropping Systems Weed Science Extension Specialist at the University of Wisconsin Madison.
This afternoon, we are out here, it is early July. It’s actually July 11, 2012. We have been experiencing extremely dry conditions. Rated at moderate drought in our area for southern Wisconsin this year. It has been an interesting year, from that standpoint, to see the visual symptomology of crop stress due to a lack of early season weed control or weed competition, if you will. We have had less than two inches of rain up to this July time period. We experienced around three tenths of an inch of rain for the entire month of June.
What I am standing in is a visual effect of soybeans, where we start out in a system that had a pre-emergence herbicide and good early season weed control timely post-emergence applications. You can see these beans I’m standing in here, are developing quite nicely. They are at about the R2 growth stage. They are stressed a little bit for water and moisture, obviously. It would be nice if they were a little bit fuller and closer to canopy, but there is very little weeds in here competing for moisture. The way these plots were set up, as we move throughout the rest of this presentation, and as you can see across these fields, you can see the crop stress response increases as you get further away from the camera. We will walk over there in a minute. The difference has been the aggressiveness of early season weed competition and also the timing of post-emergence application has been delayed as you see that crop stress increase as we move across there.
Here we are, as I have moved across. Here is a system now that experienced later applications of post-emergence herbicides. In this year where droughty conditions have been prevalent, relying on post-emergence herbicides has made control of some weed species, particularly common lambsquarters very difficult where even glyphosate, which is usually has good efficacy, has struggled with common lambsquarters quite a bit in these droughty conditions. You can see here that the soybeans where we have some common lambsquarters escapes still persisting, is that these soybeans here although, still look somewhat similar to what we are in weed free, is still showing more stress and much more visible stress. It will be interesting to see how this comes out from a yield reduction standpoint.
Here we are, where we have moved on across to where we relied on basically a very late glyphosate application. You can see the lambsquarters were very tall at the time of application. Again, the efficacy was very poor and highly variable. This not only is going to dramatically decrease yield, and that is clearly visible by the amount of stunting on these soybeans and the high level of stress that is occurring, because these weeds are being so competitive and in this year, particularly for water resources. In addition to the yield and crop stress problems with this system is, it’s also a very poor glyphosate resistance management strategy, if the post-emergence strategies for lambsquarters control was to rely solely on glyphosate. It usually is with this weed problem from a post-emergent standpoint, because a lack of other non-glyphosate options is going to be efficacious waiting to a late post-emergence timing, like was done in this particular field.
In comparison, you can see the heavy lambsquarters pressure we had at this location, and the extreme stress the soybeans, if you can see the soybeans in this weedy mess, are under in this situation where an application has not been applied.
I’m over in front of our corn plots, which are set up the same way I just walked you through the soybean plots. That is where we started out with good pre-emergence herbicide weed control and strove for weed free conditions. You can see, this corn is starting to roll a little bit. There is clear visual stress response in this corn, but in comparison to a lot of the grower’s fields around here this year, this looks pretty normal. If you look at the efficacy control, down in these rows, pretty good control with only a few minor lambsquarters escapes.
I’m going to walk down here to the corn plots, just as I did in the soybean plots, and I want you to observe the change in corn stress response as well as corn height reduction as we walk down. Really, the difference is the later post-emergence application timing and the decrease in lambsquarters post-emergence control, as you come down. Until you get to the point where you see here in these late post-emergence application timings, where there is extreme crop stress and likely to be, extreme crop yield losses. Again, we can end up to where you can see the pressures and admittedly this is a high level of pressure. Both in the soybeans and in the corn that I’ve talked about today. These are annual weed species that can be very competitive and in a year like this, where water competition is important, is very visual.
I’m back here, and we’ve moved to a different part of the farm, into a block that is actually a no till block we have here. In Wisconsin, our number one weed problem in no till is dandelion. Dandelion is a weed that is highly competitive with water, because of its effective perennial simple tap root it has. It can really absorb water out of the root profile much more effectively than our annual crops. Where I’m standing in this corn, again was mid-May planted corn, but this corn that I’m standing in, although it looks severely stressed, is planted in a plot where there was a fall herbicide application to mostly control the dandelion. The dandelion control is not perfect, but it was good enough for this crop to actually get established. What’s quite interesting, although you might say that this does not look very good, and you would be correct, is that at the same planting date where the dandelions were thick and uncontrolled, has basically been total crop failure. The carcasses that are left here were planted in this row at the same timing this was planted. As you pan behind me, you can see the remnants in our study where fall applications versus no fall applications were applied to control the dandelion. Now again, admittedly, the dandelion pressure in our block, because we use this for herbicide efficacy studies to develop our efficacy tables in our pest management guide, A3646, is maybe a heavier density of dandelion than most growers would observe, or at least I hope it’s a heavier dandelion density than most growers would observe, but it does show you that extreme and total crop failure can occur when this population gets out of control.
To summarize what I’ve talked about so far today, is that I didn’t give great specifics on weed control removal timing, nor did I give great specifics on herbicide recommendations, or what to do to this. What I wanted to point out, is the importance of weed management in years, and particularly stressful years, that we have encountered this year. We started with basically good systems where weeds were adequately controlled and progressed all the way to where I ended up here with total crop failure, because of poor weed management. What I want to recommend, in a year like this, is that this may be an excellent year to get out there, to scout your fields for weed densities and weed pressures and do it in the afternoon and see how that relates to visual crop stress for lack of moisture. Even in areas where you don’t see visual crop stress, having those detailed scouting report maps of weed species and weed densities may help you understand the variability in yield monitor maps at the end of the season and help you evaluate the control strategies of successes or failures of your weed management program, which in a year like this is obviously very critical.