C.O.R.N. Newsletter: 2016-14
Early postemergence plus residual in soybeans and other weed issuesAuthor(s): Mark Loux
It’s possible to find just about everything in this year’s weed control situation – cover crops that didn’t die, marestail that didn’t die, early burndown plus residual treatments that worked but are now breaking because soybeans haven’t been planted, PRE herbicides that did not or may not receive enough rain, and of course more cressleaf groundsel than in an average year. Some comments on a few of these:
1. Where burndown has yet to be applied for no-till soybeans, and the field has big marestail, we would suggest pulling out all the stops. Wait another week to plant soybeans, and apply a mix of glyphosate, 2,4-D, Sharpen, and metribuzin. Be sure to include MSO and higher spray volumes (20 gpa) are likely to be beneficial. Where it’s not possible to wait a week, omit the 2,4-D and ideally switch to Liberty Link soybeans so there is the option of applying glufosinate POST to try to control marestail escapes. It’s also possible to switch from glyphosate to glufosinate in the burndown mixture. This will definitely help with marestail, but there is the risk of less control on larger grasses and a few other weeds. Where glufosinate is used in both the burndown and POST treatments in LibertyLink soybeans, be sure to know the total amount that can be applied per season among all treatments. It’s also possible to till some fields that are in this situation of course – be sure tillage is thorough enough to completely uproot weeds and not just beat them up.
2. Where burndown plus residual treatments were applied early, and are now becoming reinfested with weeds, best strategy is to apply another burndown before soybeans are planted or emerged if possible. This is a mandatory step in fields with emerged marestail. Consider including a reduced rate of residual herbicide since much of the activity of residual applied a month or more ago has dissipated. Where the initial burndown consisted of glyphosate plus 2,4-D, something like glyphosate plus Shapren could be applied now. A mixture of metribuzin plus either Gramoxone or glufosinate could also work. There are various options depending upon what was used in the initial burndown and how long it will be until soybeans are planted.
3. We have also received questions about the possibility of early POST application of residual herbicides in soybeans, where it was not possible to apply residuals before soybeans emerged. Most residual herbicides cannot be applied once soybeans have emerged, due to risk of severe injury. Scepter always had a good fit in this situation, and apparently is likely to be sold again at some point by AMVAC. Pursuit has substantial activity on a range of grass and broadleaf weeds, as long as they are not resistant to ALS inhibitors (group 2). FirstRate has activity on broadleaf weeds that are not ALS-resistant, and products containing fomesafen (Flexstar, etc) have activity on certain broadleaf weeds. Some products that contain dimethanamid (Outlook), metolachlor, pyroxasulfone (Zidua), or acetochlor (Warrant) can be applied early POST for residual control of grasses, nightshade, and Amaranthus species (redroot pigweed, waterhemp, Palmer amaranth). Several newer premix products combine two of the individual herbicides just mentioned, and these are described and rated in the “Weed Control Guide for Ohio, Indiana, and Illinois”. These include Prefix and generic equivalents, Anthem, Torment, and Warrant Ultra among others. Most anything applied early POST for residual would still need to be mixed with glyphosate or glufosinate for control of emerged weeds. And a final caution is that many of these products have little or no residual activity on marestail and giant ragweed – check our ratings during the selection process to make sure the product addresses the weeds of concern.
Asiatic Garden Beetles in Northwest Ohio
We have been monitoring Asiatic garden beetle grubs (AGB, Maladera castanea) in Northwest Ohio since 2012. Typically known as a turf pest, the grub has caused varied economic damage to corn in Northwest Ohio since then. While 2014 remains the worst year for their damage to date, there were isolated outbreaks—including in soybeans--of the grub in 2015 but generally they had limited impact, perhaps due to weather related conditions. This year we noticed their presence as early as May 6th, after a period of warm weather in late April. Since then, limited root feeding and overall impacts on corn stand have not been seen like in previous years. What could be the cause? Most of Northern Ohio became cool and wet after the first full weekend in May when some corn was planted. However, the majority of corn was not planted until the 3rd or 4th weeks of May. Generally, we believe that the life cycle of the AGB was ahead of corn planting or growth to see negative impacts. We typically observe less AGB damage in later planted fields. Recent digs for the grub have turned up fewer, but more lethargic, grubs indicating possible earlier pupation or control from in furrow insecticidal treatments.
A dead AGB grub (left) next to a healthy grub in the same dig.
Identification and scouting: This beetle has four life stages: egg, larva (or grub), pupa and adult. The grubs that are present now represent the third instar larva. Damage appears to be most prevalent in sandier soils, which are concentrated in NW Ohio, but can also be found in isolated areas near sandy river beds. Dig around the plant and look for the presence of white grubs (see the video here:http://www.oardc.ohio-state.edu/ag/pageview3.asp?id=3787 ). AGBs are typically smaller and more active than other grubs and also have white, maxillary palps (bubble) near their mouth (CORN Newsletter 2013-15), see photo 1. If uncovered from the soil surface, the g+rubs try to move quickly back underneath the soil. Damaged fields often have gaps in rows, and affected corn often appears wilted and stressed.
Strategies for Control: While there are no perfect treatments for controlling AGBs, here are some thoughts to consider. The mis-matched timing of the AGB life cycle and later corn planting and emergence appears to be helpful this year. While there was no statistical difference in yield after using in-furrow insecticide in 2014 On Farm Research (https://agcrops.osu.edu/sites/agcrops/files/ofr_reports/2014%2520Fulton%2520AGBproducts.pdf), we can find dead or dying grubs when soil insecticides are used in furrow at planting (see yellowing AGB larva in photo 2). Fields with low to moderate pressure may benefit from an insecticidal seed treatment, although more data is needed for both control tactics. Finally, if stand loss occurs, consider replanting corn (See replant calculator: http://web.extension.illinois.edu/csrec/eb260/entry_6903/). If you have questions on this new pest, please contact Eric Richer (email@example.com), Andy Michel (firstname.lastname@example.org), or Kelley Tilmon (email@example.com).
Predicting leaf development in corn using accumulated heat unitsAuthor(s): Peter Thomison
When estimating yield losses in corn due to hail, frost, and other types of plant injury, it’s essential to establish the stage of plant growth at the time damage occurred. It’s also important to know corn stage of development in order to apply post-emergence chemicals effectively with minimum crop damage. Counting leaf collars to determine the vegetative stage is feasible until the lower leaves can no longer be identified. At about the V6 stage, increasing stalk and nodal growth combine to tear the smallest lower leaves from the plant. This results in degeneration and eventual loss of lower leaves which makes it difficult to locate the lower leaves (especially the first rounded leaf). When identification of specific leaf collars on plants is not possible how can the leaf stage of development of a field be estimated?
Given an understanding of corn leaf stage development and heat unit (growing degree day, GDD) calculation, a grower can estimate what leaf stage of development a particular field is at given its planting date and temperatures since planting.
Corn leaf developmental rates may be characterized by two phases. Purdue University research indicates that from VE to V10 (ten leaf collars), leaf emergence occurs approximately every 82 GDDs accumulated (Nielsen, 2014). From V10 to tasseling (VT) leaf collar emergence occurs more quickly at approximately one leaf every 50 GDDs accumulated. Iowa State University findings (Abendroth et al., 2011) relating leaf appearance to GDD accumulation are similar – from VE to V10 a new collared leaf appears every 84 GDDs accumulated and from V11 to VT, each leaf appears at approximately every 56 GDD accumulated.
Example: (from Nielsen, 2014): “A field was planted on April 28, but you do not know exactly when it emerged. Since planting, approximately 785 GDDs have accumulated. If you assume that the crop emerged in about 120 GDDs, then the estimated leaf stage for the crop would be about V8. This estimate is calculated by first subtracting 120 from 785 to account for the estimated thermal time to emergence, then dividing the result (665) by 82 (equal to V8.1).”
Growth-limiting stresses and conditions (soil moisture deficits, nutrient deficiencies, compaction, etc.) affect the accuracy of these predictions. Nevertheless, this method may be useful in timing when plants will reach an approximate stage of growth.
Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. 2011. Corn growth and development. PMR 1009. Iowa State University Extension, Ames, Iowa.
Nielsen, R.L. 2014. Use Thermal Time to Predict Leaf Stage Development in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/VStagePrediction.html (verified 5/31/2016)
Let It Grow, Let It GrowAuthor(s): Ryan FliehmanThe weather continues to be favorable for the majority of the state as mainly dry conditions prevail. While heat continues early this week, cooler and moister conditions are expected in the coming days and beyond. With the majority of planting completed, these conditions will be welcomed as the prime growing season comes into full swing.Looking over the past week we experienced dry conditions along with temperatures well above normal for late May. Temperatures soared into the double digits above normal while we also experienced the humid air from the Gulf region. The only notable precipitation came in the form of isolated, albeit heavy convection causing problems for a few, while leaving most others below normal in the moisture department.As our pattern shifts later this week from flow with a southerly component to one with a northerly one, the temperatures along with the humidity will be on the downhill. Weather systems look to ride along the steering flow which we anticipate will provide near normal precipitation for the later half of this week and into next. Looking at the 16 day rain outlook from the NOAA/NWS Ohio River Forecast Center we can see the more consistent and near normal rainfall pattern we can expect over the next couple of weeks. Moving to the middle of June we will see temperatures swing back to near normal or slightly above while precipitation is expected to remain near normal. July looks to continue the above normal temperature trend along with precipitation remaining near normal.Looking at the anticipated conditions, the initiation of the growing season looks promising for the entire state. Very heavy rain from convection along with hazards from severe weather look low as we transition to a more stable northwesterly flow pattern. In the anticipated flow pattern, more consistent and less intense rainfall will be expected. The main concern with the upcoming pattern will be finding the multi-day window necessary for the hay cutting process. Overall, the agriculture industry will welcome the upcoming pattern as we move into the front half of June.
Crop Observation and Recommendation Network
C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.
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