C.O.R.N. Newsletter: 2014-41

There are a bunch of residual herbicide premixes available now for use in soybeans.  Most of these are listed in the 2015 edition of the Weed Control Guide, but it seems like there’s always one or two that we don’t know about.  Many new premixes are essentially generic versions of products that had already been available.  Example – Boundary, Ledger, and Tailwind are premixes of metribuzin and metolachlor from different companies that are essentially identical in formulation and label.  Once there are more than a couple of trade names for the same herbicide or herbicide premix, we usually list them in the guide by active ingredient, with a list of trade names underneath.  So we now have a listing for “flumioxazin” instead of Valor, but show the trade names for flumioxazin underneath – Valor, Encompass, Outflank, and Panther. 

Many of the available premixes are broad-spectrum and take care of a lot of the basic broadleaf weeds.  This is evident in the effectiveness table in the Weed Control Guide, where there are is a plethora of “8”s and “9”s on lambsquarters, smartweed, pigweed, velvetleaf, and even nightshade with a few exceptions.  We have generally emphasized the need for residual broadleaf control more than grass control in Ohio, but a number of the premixes now also contain a grass herbicide such as metolachlor or pyroxasulfone, which provides early-season control.  So, when sorting through options, it’s possible to ignore these easier weeds somewhat and make sure that the herbicide handles the weeds that have developed herbicide resistance and are generally tougher to control – giant ragweed, marestail, common ragweed, and also waterhemp and Palmer amaranth if you are unlucky enough to have one of the few infestations of these in Ohio.  So it makes sense to key in on these weeds when using resources such the OSU weed control guide or in conversations with your supplier.  Be aware that with the current emphasis by manufacturers on developing herbicides for control of Palmer amaranth, some new premixes may not fit well in Ohio even if they are broad spectrum, due to deficiencies on marestail and ragweeds.  The basic principles on residual herbicides for the tougher weeds mentioned above:

Marestail – Many populations are resistant to both glyphosate and ALS inhibitors, and so the chlorimuron, cloransulam, or imazethapyr in many premixes fails to contribute residual marestail control.  The nonALS active ingredients that have residual activity are flumioxazin, sulfentrazone, metribuzin, and saflufenacil (primarily at rates higher than the base rates that are used for burndown).  While we rate the premixes containing some of these as an “8” on marestail, this can be optimistic, especially when applied a week or more ahead of planting.  Our research increasingly shows that combinations of two nonALS actives provide more consistent residual control than just increasing the rate of a single active.  Examples – using a mixture of Sonic + metribuzin rather than just Sonic; using a mixture of Canopy DF + metribuzin + Sharpen rather than just the Canopy DF + metribuzin.  For the latter example, the higher rate of Sharpen would have to be applied 2 weeks ahead of planting to use 1.5 oz of Sharpen and maximize residual.  Something else that’s important to keep in mind for marestail – where something has been applied the previous fall or early spring to control emerged marestail, it can be adequate to apply glyphosate+2,4-D closer to planting.  Any residual herbicide can be included with glyphosate and 2,4-D.  Where nothing was applied the previous fall or early spring, there can be a need for a more aggressive burndown such as glyphosate+2,4-D+Sharpen, and this can limit the ability to use flumioxazin and sulfentrazone or force earlier application.  The bottom line here is that if it appears that there will be a need for an application fairly close to planting that includes Sharpen, stick with products that contain metribuzin – Canopy DF, Matador, Boundary, etc – and add metribuzin as appropriate to bring the rate up to 8 to 12 oz where soil type allows.

Giant ragweed – residual control of giant ragweed comes primarily from two ALS inhibitors that are components of many premixes – chlorimuron (Classic) and cloransulam (FirstRate).  We rate these as “7” in the guide but they can be better or worse depending upon density of the population, rainfall etc.  The imazethapyr (Pursuit) in some premixes also provides some control, which we rate as a “6”.  None of these work on ALS-resistant giant ragweed, and nothing else provides much control either – maybe a little from fomesafen or the higher rates of Sharpen.  Populations resistant to ALS inhibitors are most effectively controlled by two POST applications of glyphosate or Liberty, or Flexstar followed by Cobra in nonGMO soybeans.

Common ragweed – A similar story to giant ragweed but a few more choices.  In addition to the ALS inhibitors mentioned above, the PPO inhibitors flumioxazin (Valor, etc) and fomesafen (Prefix, etc) have fair to good activity.  Pryroxasulfone (Zidua, Anthem, etc) has at least some activity, as does metribuzin.  In ALS-resistant common ragweed populations, premix products containing flumioxazin have the edge over those containing sulfentrazone, because the latter has no activity on ragweeds.  There are some populations of common ragweed in Ohio with resistance to both ALS and PPO inhibitors (sites 2 and 14), and it’s difficult to obtain even fair residual control of these with pyroxasulfone and metribuzin.  LibertyLink soybeans can be a good option for these multiple-resistant populations.

Waterhemp and Palmer amaranth – Both of these weeds are challenging because they can emerge well into the growing season.  ALS inhibitors are largely ineffective due to a high frequency of ALS resistance, but the following active ingredients provide fair to good residual control for the early part of the growing season (combinations or premixes that contains two of these can be more effective then single actives, especially for Palmer):  acetochlor, metolachlor, pyroxasulfone, dimethenamid, pendimethalin, flumioxazin, sulfentrazone, and metribuzin.  Some of these can be applied POST in combination with herbicides that control emerged Palmer amaranth and waterhemp, in order to extend the residual control and minimize the need for additional POST treatments.  This strategy, known as “overlapping residual”, does not replace the need for residual herbicides at or before planting.  It should therefore be implemented primarily where these two weeds are already a problem, since it is added cost and does not work for marestail or giant ragweed.  An exception might be if other fields in the area already have the problem, and the goal is to prevent the spread of waterhemp and Palmer amaranth.

This past growing season demonstrated that forage grasses are not created equal. Following one of the coldest winters on record in Ohio, there were large differences among forage grass species and varieties for winter injury and yield. We all remember the bitter cold days of last winter. Surprisingly enough, the temperatures at the two-inch soil depth never fell below 25 F all winter across most of Ohio. We had enough snow cover during the coldest days to moderate soil temperatures, but the cold air temperatures still had very damaging effects on some grass species and varieties.

The table below illustrates the differences we observed in 2014 in side-by-side forage grass trials at the Western Research Station of the Ohio Agricultural Research and Development Center near South Charleston, OH. We tested four to six varieties of each species. There was a strong relationship between winter injury score and total forage dry matter yield in 2014. Across all species having some level of winter injury (all except tall fescue and timothy), for each one unit increase in winter injury score the total season yield declined by 1.2 tons/acre.

* Winter injury rated from 1 = no injury to 5 = severe injury and mostly dead.
Byron Seeds, LLC provided support for the trials reported in the above table.

Orchardgrass, tall fescue, and timothy had little to no winter injury symptoms in early spring, and they yielded quite well. The festuloliums (fescue by ryegrass cross) also performed well and were much better than the perennial ryegrasses we had in the test. They have similar forage quality characteristics as perennial ryegrass, so they are a good alternative to perennial ryegrasses.

Meadow fescue is a cool-season grass native to northern and southern Europe that was introduced to USA in the early 1800s. It has recently received renewed interest among forage producers and scientists. It is generally lower yielding than orchardgrass and tall fescue, but it is more palatable to animals and has higher fiber digestibility resulting in higher animal performance than orchardgrass and tall fescue. It appears to be a good alternative to perennial ryegrass because of its high quality combined with better winter hardiness and higher forage yields than perennial ryegrass.

The perennial ryegrasses suffered the most winter injury overall and took a very long time to recover last spring. We delayed the first cutting of perennial ryegrass until June 12^th, similar to the normal later time of first cutting for timothy. We have observed large differences in winter injury among perennial ryegrass varieties in the past.

The Italian ryegrasses planted in spring 2013 did surprisingly well in 2014. They recovered well after moderate winter injury and yielded over 4 tons of dry matter in this second year of the stand. There are large differences in winter hardiness among Italian/annual ryegrasses. This can be seen from the data in the trial planted in September 2013 that is reported in the Ohio Forage Performance Trials (http://oardc.osu.edu/forage2014/). Of 32 varieties planted in September 2013 in that trial, only four survived reasonably well and could have produced forage this year.

These results emphasize the importance of carefully selecting varieties for forage production in Ohio. Grass is not grass! Not all grass varieties and species are created equal. Not all survive harsh winters the same, not all yield as well in dry years, and not all have the same forage quality and animal performance potential. Always ask the dealer for performance data from regions similar to your own to ensure you will have a productive forage stand year after year.

Many dates for agronomic educational programs being held in the upcoming months can be found at https://agcrops.osu.edu/calendar. A variety of Agronomy Update Programs, Intensive Crop Workshops, Webinars and programs which offer Pesticide Applicator License Recertification, Certified Crop Adviser or Agricultural Fertilizer Applicator Certification credits are listed. The calendar will be completed in the next couple of weeks with even more offers.

We would suggest bookmarking this page https://agcrops.osu.edu/calendar and visiting it often over the next month to know what is happen in your area.