Science for Success: Answering Soybean Questions

science for success

With funding from United Soybean Board, soybean agronomists across the U.S. are hosting a ‘Notes from the Field’ webinar series the first Friday of each month beginning May 7. Join research and extension specialists from Land Grant institutions for monthly informal discussion on production topics of timely relevance. Bring your questions!

When-  May 7, June 4, July 9, and August 6 at 9:00 AM eastern time

Want to plug in- Register to attend (via Zoom) for each monthly session and you will receive Zoom login information. Register at: https://ncsu.zoom.us/meeting/register/tJEkdeiqrTIqHNMYI3FuXRVPgsC87mavL6hs

If you have any questions, please contact Laura Lindsey (lindsey.233@osu.edu or 614-

Cressleaf Groundsel (Packera glabella)

Source: Marcelo Zimmer and Bill Johnson, Purdue University

Every spring we receive several calls and e-mails about a certain 3-foot tall weed with yellow flowers (Figure 1). The most common yellow flowered weeds we have in Indiana are cressleaf groundsel, the buttercup species, and dandelion.  Occasionally we have some fields of canola or rapeseed in the state. But, by far the most prevalent specie we see in no-till corn and soybean fields, and occasionally pastures, is cressleaf groundsel.  I have only rarely observed wild mustard in Indiana.  Wild mustard is more common in the northern tier of states near the Canadian border.  This year, due to recent cooler weather, cressleaf groundsel is flowering later than it did last year.  This article is intended to provide information on the biology and life cycle of cressleaf groundsel, as well as how to control it in fields and pastures.

Biology and Identification

Cressleaf Groundsel is a winter annual weed that has become more prevalent in Indiana pastures and agronomic crop ground over the past 20 years.  The small seeds produced by this weed allow it to thrive in reduced and no-till systems as well as poorly established pastures.  Cool and wet springs of the past few years have also favored cressleaf groundsel, as it is a weed that prefers moist soils and typically struggles in hot and dry weather.

Much like most winter annual weeds, cressleaf groundsel emerges as a rosette in the fall then bolts, flowers, and produces seed in the spring.  Basal rosette leaves are deep pinnate serrations with roundly lobed leaf margins.  Leaves are typically 2 to 10 inches in length (Britton and Brown 1970).  Bolting stems are hollow and can reach up to three feet in height with inflorescences that contain six to twelve yellow ray flowers that are often compared to the flowers of common dandelion.  When looking for cressleaf groundsel in older weed id or taxonomic guides be aware that it has traditionally been placed in the Senecio genus and only recently was placed into the Packera genus.

Toxic Properties

The competitiveness of cressleaf groundsel with agronomic crops has not been researched, though its presence as a winter annual in no-till fields will have the same implications of slowing soil warming and drying as other winter annual weeds.  The presence of this weed in pastures and hay fields should be of more concern as it does contain toxic properties when ingested by livestock.  Leaves, flowers, and seeds of cressleaf groundsel contain alkaloids that will cause liver damage in livestock that is termed seneciosis and typically occurs on a chronic level (Kingsbury 1964).  Symptoms of seneciosis are loss of appetite, sluggish depressed behavioral patterns, and in extreme cases aimless walking without regard to fences or structures.  Although cressleaf groundsel is not as toxic as many of its relatives in the Packera genus, livestock producers encountering this weed in pastures or hay should take steps to avoid prolonged ingestion by animals.

Control

Herbicide applications for control of cressleaf groundsel are most effective when applied to plants in the rosette stage.  Plants that are larger, or bolting are very difficult to control with herbicides.  Infestations in pastures can be controlled with 2,4-D or a combination of 2,4-D and dicamba applied to rosettes in the fall or early spring prior to bolting.  Producers should be aware that applications of these herbicides will also kill favorable broadleaves (legumes) that are present in pastures.

Control recommendations for cressleaf groundsel in no-till agronomic crop fields has typically been to apply 2,4-D @ 1 qt/A to actively growing rosettes in the fall.  In fact, just about any broadleaf herbicide commonly applied in the fall in the eastern cornbelt will work well on controlling this weed.  However, we have observed that control of cressleaf groundsel with spring burndowns can be challenging if the plants are large and spray applications are made in cool weather.  In situations like this, we often observe severe injury and necrosis of leaves, but new growth will appear from live buds on the plant.  In some instances, resprays are needed to finish off the cressleaf groundsel. The best herbicide programs for spring burndowns are 2,4-D + dicamba, atrazine + paraquat + 2,4-D, something with chlorimuron in it, and Elevore + 2,4-D. for more information on spring burndown information, consult the burndown section in the Weed Control Guide for Ohio, Indiana, and Illinois (publication WS-16).

 

Adapting Burndown Programs to Late-Planted Situations

Source: Mark Loux, OSU Extension

It’s déjà vu all over again.  We have run this article every few years, and it seems like maybe the frequency is increasing as we deal with wet and cold weather that delays planting.  The questions about this have not changed much, and neither have the suggestions we provide here.  One of the most common questions, predictably, is how to kill glyphosate-resistant marestail and giant ragweed and generally big weeds in soybeans when it’s not possible to delay planting long enough to use 2,4-D ester (Enlist soybeans excluded since there is no wait to plant).  Overwintered marestail plants become tougher to kill in May, so this is an issue primarily in fields not treated last fall.  The good news is that we have more effective herbicide/trait options for help with burndown compared with a few years ago.  The bad news is that nothing we suggest here is going to be infallible on large marestail.

A burndown of glyphosate and 2,4-D struggles to control marestail in the spring anyway, especially in the absence of fall herbicide treatments.  Our standard recommendation, regardless of when spring treatments are applied, is to either replace the 2,4-D with something more effective, or to add another herbicide to supplement the 2,4-D.  Sharpen has been the frequent replacement/supplement, and we now have the option to use dicamba in the Xtend soybean system instead of 2,4-D.  While it’s possible to use higher 2,4-D rates in the Enlist soybean without waiting to plant, higher rates do not necessarily solve this issue based on our research, although a follow up POST treatment that includes glufosinate or 2,4-D usually finishes off plants that survive burndown.  There’s a list of suitable soybean burndown treatments in our marestail fact sheet, and also below – these are for fields not treated the prior fall.

  • Glyphosate + saflufenacil + 2,4-D (+ metribuzin if possible)
  • Gramoxone (3-4 pt) + 2,4-D + metribuzin
  • Glyphosate + dicamba (Xtend soybeans)
  • Glyphosate + dicamba + saflufenacil (Xtend soybeans)
  • Glufosinate + Sharpen (+ metribuzin if possible)

Salfufenacil herbicides include Sharpen, Zidua PRO, and Verdict.  It is possible to use a mix of glyphosate, saflufenacil, and metribuzin, omitting the 2,4-D, but control can be more variable.  We have observed some weakness also with the glyphosate/saflufenacil combination on dandelion, purple deadnettle, and larger giant ragweed.  There is usually going to be a benefit to keeping 2,4-D in the burndown where possible, as part of a more comprehensive mixture.  We advise against using Gramoxone unless it can be mixed with both 2,4-D and a metribuzin-containing herbicide.  One strategy would be to plant corn first as soon fields are fit, and delay soybean planting so that 2,4-D could still be used.  And a reminder – deciding to include saflufenacil at the last minute can result in a need to alter the residual herbicide program.   Labels allow mixtures of Sharpen/Verdict with herbicides that contain flumioxazin (Valor), sulfentrazone (Authority), or fomesafen (Reflex) only if applied 2 or more weeks before planting.

Some other things to consider in a delayed burndown situation:

1.  Aside from glyphosate-resistant weeds, increasing glyphosate rates may be one of the most effective ways to maintain effective control.  We suggest a rate of at least 1.5 lb ae/A, and higher rates could be warranted.  This will not improve marestail control, but should help with most other weeds, especially under (presumably) warmer May conditions. Continue reading

Growing Degree Days vs. Calendar Days – How Long Will Emergence Take?

Source: Alexander Lindsey, Greg LaBarge, OSU Extension

When we examine crop emergence post-planting, two factors can impact speed of emergence – soil moisture content and soil temperatures. If soil temperatures are lower, it can take more calendar days for emergence to occur meaning rowing corn may take a little more time. In the Ohio Agronomy Guide, emergence should begin to occur after approximately 100 air GDDs.

A difference in 10 degrees in temperature can dramatically affect how quickly crops will emerge. For example, at a temperature of 60 degrees F heat unit accumulation per day would be 60 F – 50 (base temperature for growth) = 10 GDDs. If it takes 100 GDDs to start to see emergence, at this rate it would take 10 calendar days to see the crop start to emerge. If temperatures are 70 degrees F, heat unit accumulation per day would be 70 F – 50 = 20 GDDs. This would shorten the emergence window to 5 calendar days instead, resulting in more rapid emergence from planting.

Figure 1. Emerged corn on May 6, 2021 planted April 19 near London, OH.

In recent work from Nemergut et al. (2021), researchers from OSU observed emergence starting at 110 to 120 soil accumulated GDDs (base of 50 degrees F) for corn, which equated to first emergence observed in 4 or 5 days after planting. Some of the difference in calendar date for emergence (though GDD accumulation was similar) was because planting depth was changed, and the 1” planting accumulated GDDs faster than the 2” and 3” planting depths. These studies though were planted in May or early June (2019 wet spring delayed planting), and daily accumulated GDDs was higher than we might expect if planted in late April. Soil accumulated GDDs have been discussed above, and these could vary slightly compared to air accumulated GDDs (calculated using air temperatures). In the work referenced above, accumulated air GDDs in the first four days post-planting were 106-118 GDDs, slightly less than the soil accumulated GDDs.

If you want to predicate emergence on your farm, the GDD calculator found at https://mrcc.illinois.edu/U2U/gdd/ is a useful tool. It is a two-step process, first find your location on the map, then enter your planting date. The graph will display accumulated GDD’s for your location. Example output in Figure 2 shows GDD accumulation from an April 19, 2021 planting date near London, OH in Madison County. By May 6 the accumulated GDD was 138 and the emerging corn is shown in Figure 1. The GDD calculator can be used to predict growth stage throughout the growing season. This is a handy to time when scouting and management decisions should be made.

Figure 2. GDD accumulation from April 19 to May 6, 2021 near London, OH.

As the days turn cooler, don’t be surprised if the crops don’t pop out of the ground quickly due to lower soil temperatures. If emergence is still not observed after two weeks, it may be worth checking the field to see if other issues may be affecting emergence.