Late-Season Weed Escapes in Wisconsin Corn and Soybean Fields
The potential increase of glyphosate-resistant weeds is a major threat to corn and soybean production across the Nation. Integrated Weed Management tactics, including diversified herbicide use, are important components of management to delay the onset of glyphosate resistance. Identifying geographies that may be most vulnerable to resistance development could help direct attention and pro-active resistance management tactics before wide-scale control failures occur. To help with this, the University of Wisconsin-Madison Field Crops Weed Science Extension program is asking for your participation in a research study investigating the weed species diversity in Wisconsin Corn and Soybean fields due to reduced atrazine use and subsequent increased use of glyphosate. The purpose of this research is to identify areas in the state where there may be a shift to weeds that are more difficult to control with glyphosate, or where weeds that are resistant to glyphosate may first appear.
This survey asks questions about target weed species and limited management history information relating to crop production fields. There are two levels of participation in this survey. The first level simply includes filling out an on-line survey with information from ONLY ONE CROP PRODUCTION FIELD per survey form. If you are willing to provide information about more than one field, please repeat the survey. The second level of participation, if you would please participate further, is to allow weed science research staff from the University of Wisconsin-Madison to survey your crop fields for weed escapes in late-summer months.
We expect the survey to take only 5 to 10 minutes of your time, and we don’t anticipate any risks to you. For fields we scout for weed escapes in the late summer, we will provide a detailed weed scouting report to participants.
You may ask questions about the research at any time by contacting Vince M. Davis at vmdavis@wisc.edu (608) 262-1392 or Ross Recker at rrecker@wisc.edu. Your participation is completely voluntary. By completing and electronically submitting this survey, you consent for participating in the first stage of the survey. If you would like to participate in the second stage, and allow UW weed science researcher to scout your production fields, please complete the last question of the survey by providing your contact information.
To complete the survey, please visit: http://www.zoomerang.com/Survey/WEB22FSESTMEKJ
We THANK YOU in advance!
Vince M. Davis, Extension Weed Scientist and Ross Recker, Graduate Research Assistant
Early Season Water Deficit Stress on Southern WI Soybeans
I went to bed last night hoping this article would not have to be written, but that whopping 0.05 hundredths (or less) of rain we received across much of Southern WI last night forced the issue. According to data from the 2012 Weather Summary for UW ARS – Arlington and Marshfield WI Locations (compiled by Dr. Joe Lauer) we are tracking over 4 inches behind the 30 year norm at Arlington (precipitation from April 1 to today). A similar trend was occurring at our Marshfield location until recent rainfalls brought us back to near 30 year norms. The implications of this water deficit on soybean are as follows.
In soybean there are two growth periods for which soil moisture is critical for optimum growth and development: at planting and during the reproductive stages from bloom through pod fill. The time period from stand establishment to bloom is not as critical. Drought stress during this time period will often shorten internodes; however yield loss rarely occurs. Luckily most of the WI soybean crop is in the vegetative growth phases though bloom is beginning. As stated above depleted soil moisture at planting can significantly impact the soybean crop. Therefore if this dry weather pattern continues growers should be very cautions about planting double cropping soybean into dry soil.
In Wisconsin the main reproductive growth in soybean occurs from early July to mid-September. Soybean in this stage use about 1/4 to 1/3 inches of water per day. Lack of sufficient water can cause flowers and young pods to abort reducing the number of seeds per plant (Image 1). Also, soybean plants reduce the size of their leaf pore openings to reduce the loss of water vapor. This also reduces the intake of carbon dioxide and the manufacturing of photosynthates which slows plant growth. When normal soil moisture returns, normal growth is resumed. This ability to reduce metabolic activity allows plants to tolerate dry spells without dying or harming their ability to resume growth when normal moisture returns.
Image 1. Pod abortion in soybean caused by drought stress.
If a drought does develop and severely affects podset and seed fill, and if livestock feed is needed, soybeans can be harvested as a forage for ensiling. Highest protein and yields are obtained from soybean harvested at the R6 to R7 growth stage. Harvesting soybeans for forage between the R1 and R5 stage will result in very high quality silage, but dry matter yields will be reduced significantly. Forage quality will be reduced from R5 soybean forward if a conditioning process is used during harvest. Conditioning will cause significant seed shattering.
References:
Managing Drought-Stressed Soybeans in the Southeast. North Carolina Cooperative Extension Service. 1999.
Virginia Soybean Update. Virginia Agricultural Experiment Station. Volume 2, No. 4, July 1999.
Cereal Leaf Beetle and Desiccated Soybean Seeds
Over the weekend two issues came to my attention:
1. It appears that cereal leaf beetle has hit threshold in a few fields. Dean Volenberg noted “Seeing high densities in some fields (5 per plant) and the flag leaf is about finished off. It is hit or miss as far as scouting, one field will have them and the next is void of any larvae and adults. Threshold at this stage of wheat is one Cereal Leaf Beetle per plant (NDSU Extension).
Image 1. Cereal leaf beetle larvae and crop injury on oat.
(Image from D. Volenberg)
(Image from D. Volenberg)
2. Also some late planted soybeans that were planted at the dry/wet soil threshold have imbibed water then desiccated. Please review my article entitled: Variable Germination and Emergence in Soybean: Which Seeds Are Still Viable? for recommendations.
Addendum from Jim Specht (UNL):
Thought I would let you know that some Nebraska soybean producers have experienced the problem of germinating seed not having enough soil moisture to complete either the germination and/or emergence process because of two reasons.
One reason is because they planted in dry soil and hoped for a rain, which is risky. Some producers did get a hoped-for rain, but the rain amount was only enough to wet the soil down to where the seed was placed and not enough to connect that wet layer with the moist soil another inch or two below that seed. As a result, the seeds germinated and the radicles emerged, but because roots will not penetrate a dry soil layer, the seedlings died because rooting systems were limited to using surface water, which ultimately dried out. This scenario forced a replanting. A second reason was because some producers have been using cover crops for some years now even though I warned them that cover crop use WILL be definitively detrimental in a dry spring. We have had wet springs to date, which led producers to not think about the fact that while cover crops offer all the great stuff that extension specialists have promoted, they have ONE GIANT PROBLEM – unlike fallow which can only surface dry out in dry years, cover crops put roots into the soil and act like putting blotting paper in the soil, meaning that cover crops can transpire away the stored soil water! Well, BINGO, we got a dry spring in Nebraska this year! Cover crop users discovered the problem this year that I warned them about every time they discussed the advantages of cover crops. One NE Soybean Board Member actually found out that his cover crop had dried out the soil to a depth of almost 10 inches, and when he only got sufficient rain to wet the seed, it was definitely not enough to connect the wet soil surface by wetting the soil down to a deeper down moister soil depth. Consequently, his entire field of soybeans germinated, and then died. What’s worse for him, is that he still needed a drenching rain to eliminate that dry soil layer before he could even begin to think about replanting!
Therefore, I have been re-urging all extension specialists in Nebraska to warn producers about this ever-so-often risky proposition of planting soybean seed into dry soil, or using cover crops temporally right up to the Round-Up burn-down before planting. Preventing erosion is a good thing, but transpiring off critical stored water is a definitely a BAD thing. There is no FREE LUNCH!
– Jim
Aster Yellows Was Confirmed in Oat
As a followup to last weeks article entitled Oat and Necrotic Leaf Tips and Margins Dr Russ Groves Lab PCR confirmed the presence of aster yellows in oat. We have also submitted wheat samples showing similar symptomology to Dr. Groves for analysis. Those should be done early next week. There are no known feeding issues related to this pathogen so heavily infected oat can be fed as a forage though tonnage and quality will likely be diminished.
Oat and Necrotic Leaf Tips and Margins
When I was out scouting early this week I noticed that many of my oat plots where showing necrosis on the leaf tips and margins (please see below image). I can honestly say I did not give it much thought as I had soybeans to spray. By Wednesday however my email, text, and phone where all buzzing about this consistent and widespread oat issue so I started to do some digging. If you look closely at the below picture you could easily write this crop injury off to our unpredictable spring environment and/or barley yellow dwarf virus (bydv). However after speaking with John Mochon who is the project manager in the oat breeding program and Scott Chapman in entomology they both vividly remember the tremendous influx of aster leaf hoppers (ALH) that arrived in early May. A follow-up conversation with Russ Groves in Entomology confirms that we experienced one the highest ALH influxes in the past decade. Furthermore, Randy Van Haren, with Pest Pros Inc., has performed qPCR assays on populations in the Central Sands in the past 3-4 weeks with infectivity rates as high as 10-12% which is very high for this pathogen. Since I have never dealt with ALH I found a good article written by Janet J. Knodel at NDSU. She wrote “Aster leaf hoppers feed on plant sap and vector aster yellows, a phytoplasma disease that presents like BYDV. Disease symptoms will appear in 2-3 weeks (which fits with our timeline). Plants infected earlier in crop development are more susceptible to yield loss than mature crops. For example, wheat infected with aster yellows at the seedling stage will not produce kernels due to stunting. A heavy infestation of aster leafhoppers in the field also will increase the incidence of aster yellows.” Limited information exists about the susceptibility of grain crops (e.g. oats and wheat) to infection of the aster yellows phytoplasma (AYp). Work includes oat susceptibility to AYp of Chiykowski and Wolynetz 1981, Can J. Plant Path. And most recently Hollingworth et al. 2008 (http://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-92-4-0623). Over the next few days I will be collecting samples and working with Russ Groves to confirm if this is the potential culprit. Stay tuned…
Article co-authored with Russ Groves, UW Entomology.
Fusarium Head Blight Risk Remains Low
The risk window for Fusarium Head Blight infection is rapidly closing as wheat across the state progresses through flowering. Lack of rainfall and low humidity has kept the risk level for infection low statewide (Image 1). A few pockets may still present themselves but for the most part if the model is accurate (which it has shown to be over the last few years) we should have a relatively scab free year.
Image 1. Fusarium Head Blight Assessment Tool Risk Map on 5/24/2012.
In scouting our Arlington wheat plots in preparation for this blog article I noted a few varieties showing significant stripe rust incidence and severity (Image 2). This pathogen has been prevalent in the southern U.S. and was expected at some point.
Image 2. Stripe rust on wheat in WI.
Fusarium Head Blight Risk Remains Low for WI
Wheat will begin flowering in the southern portion of Wisconsin over the next several days. This is a critical time to determine if the crop is at risk for Fusarium head blight (FHB). Following from our previous updates, a check of the risk map for today indicates a low risk of infection across the state. Weather over the next week is forecasted to range from overnight temperatures around 50F to daytime highs around 75-80F (Air Resources Laboratory, ready.arl.noaa.gov). A similar check for rainfall suggests an extended dry period, with isolated showers or thundershowers in the forecast. An examination of several weather stations in the main wheat production areas indicates low amounts of accumulated rainfall. Based on this, the risk for FHB this week appears to be low. Fungicide decisions should be based on a combination of this risk as well as active scouting of fields to determine if any foliar diseases pose a risk to the upper canopy.
A reminder, as the wheat crop moves into flowering, it is critical to understand the difference in harvest restrictions related to the different fungicide products. Primary compounds recommended for control of FHB have harvest restrictions of 30 days (Proline, Prosaro, and Caramba). These products also carry good to excellent ratings for control of several major foliar diseases (powdery mildew to the different rust diseases). However, as we earlier pointed out, it is important that you take the time to scout fields to determine if the level of disease warrants a fungicide application.
The most effective timing for FHB management is Feekes 10.5.1 Recent work has shown (Christine Cowger, USDA and NCSU) that post-flowering infection can occur. However, I would say that going in early doesn’t get you the best efficacy. There are still questions related to the early, pre-anthesis risk of infection however, because the greatest risk of infection is at that early flowering period, this is the optimal timing.
Joint contribution from Shawn Conley; State Soybean and Small Grain Specialist; University of Wisconsin, Madison and Dr Paul David Esker, University of Costa Rica.
WI 72 Hour Fusarium Head Blight Forecast
The prevalence of powdery mildew coupled with impending wheat flowering and risk of head scab many growers are considering holding off their fungicide application to target both pathogens. Based on our 24 to 72 hour prediction for Fusarium head scab using the Fusarium Head Blight Risk Assessment Tool the risk of Fusarium head scab for flowering wheat is low (May 10). However based on my observations and consultant and agronomist phone calls today we are still 5 to 7 days away from flowering in southern WI. I will rerun the model Sunday evening with and updated forecast.
Looking Ahead – Early Scab Forecast and Fungicide Labels
Winter wheat in southern Wisconsin is starting to head (Feekes 10.1) indicating we are ~ 7 days away from anthesis or flowering (weather dependent of course). Calendar wise this puts the WI wheat crop developmentally about 3 weeks ahead of normal. Anthesis is the last critical wheat management growth stage and accurate identification of this stage is important due to fungicide label restrictions as well as timing of fungicides for management of fusarium head scab. To better understand and identify the flowering growth stage, please check herefor an UWEX YouTube Video.
Most commercial fungicide products are only labeled through Feekes 10.5 (full heading) and others have restrictions based on days to harvest. A partial summary of these products as well as those labels for head scab please access them here. Not all products may be listed and not all products (especially some generic forms of tebuconazole) may be approved in WI. It is important to always check the label for specific use requirements.
Our prediction for Fusarium head scab is based on the Fusarium Head Blight Risk Assessment Tool (please see below). In terms of Fusarium head scab risk as of today (May 8), pockets of medium to high risk are showing up in the western portion of the state, as well as a small pocket in the eastern portion of Winnebago and Outagamie Counties. The current increase in risk is most likely a function of the weather events of the past several days. Interestingly, when we checked the May 7 forecast map and did a 24 hour prediction, it did pick up the areas in the western portion of the state, although today’s risk is somewhat higher than the forecast was. There is a chance for rain today around the state before some drying patterns move in. The risk for FHB may remain higher over the next several days. However, since we are approximately a week from flowering in the southern portion of WI, these conditions can, and will change, so we will continue to monitory and update the risk information, and management recommendations as we near flowering.
