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
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.
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.
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.
Source: Jim Noel, NOAA
There are challenges ahead so we will break them into short-term and long-term.
The recent snow was a rare event for the amount that fell across Ohio. However, the minimum temperatures in the 20s and 30s was not that far off of normal for last freeze conditions for Ohio.
The strongest typhoon ever in the northern hemisphere occurred east of the Philippines last week and this energy will come across parts of North America over the next week. When that happens weather model performance often drops. Hence, if you see more bouncing around of forecasts the next 10-15 days that may be one reason why.
We have a big warm-up the first half of this week ahead of a strong storm that will move through Ohio the second half of the week with wind and rain. We could see anywhere from 0.50 inches to over 2 inches across Ohio later this week but placement is not certain and seems to favor central and southern Ohio with the highest amounts. Expect most places to see an inch or less given recent track record of events coming in lighter. Once the storm passes colder air will push in and some frost will be possible this weekend with lows in the 30s.
The rainfall the next 30-days is critical for the growing season as moderate drought over northern Ohio already has soil conditions in a shortage.
The latest drought monitor can be found here:
Also, some of the greatest evaporative demand in the country has been in parts of northern Ohio the last 30+ days and can be monitored as a leading indicator for drought development at this webpage via NOAA:
You can keep up on the Ohio River Forecast Center’s Water Resources Outlooks at:
May appears will see periods of well above and below normal temperatures but will average out close to normal or just slightly above normal. Precipitation continues to trend at or below normal but models suggest a normal May for precipitation. If we get timely rains that will help soil conditions for summer. If we miss critical rains in May, this could lead to summer issues.
The latest rainfall outlook for the next 16-days is viewable in the attached image. Normal rainfall is nearing 2 inches for the next 16-days. We expect 1-3 inches for most areas.
For summer, most climate models indicate above normal temperatures and medium to high confidence of above normal temperatures during typical peak temperatures from mid-June to mid-August. We will need to monitor this. Confidence in summer rainfall is low. Most outlooks and models suggest not too far from normal rainfall but the reality is since 30-50% of summer rainfall comes from local soils, the next 30-days will be a big player in our summer rainfall outcome.
Source: Dr. Laura Lindsey, OSU
After a (short) second round of winter last week, there has been some concern regarding winter wheat. As a reminder, the magnitude of freeze damage depends on: 1) temperature, 2) duration of temperature, and 3) wheat growth stage. During the cold snap last week, the majority of winter wheat in Ohio was at the Feekes 6 to 8 growth stage. In northern Ohio, temperatures were in the low 30s to upper 20s. In Southern Ohio, temperatures were mostly above 30°F with a dip to 26°F on April 23, recorded by the CFAES weather system in Pike County. Underneath the snow, temperatures were warmer (Figure 1 records the temperature under the snow on April 21).
A few years ago, we conducted a freeze chamber experiment to examine the effect of low temperature on winter wheat at several growth stages (Table 1). Keep in mind, actual yield reductions in the field can be quite variable depending on the weather for the remainder of the growing season. At Feekes 6 growth stage, temperatures >20°F caused no damage. However, by Feekes 8 growth stage, temperatures of 25°F to 28°F caused a 10 to 25% reduction in wheat yield. These temperatures were from the crown of the wheat plant, not air temperature.
What to look for: After a freeze event, wait one to two weeks after active growing conditions resume to check for visual signs of freeze injury. Make sure to examine several areas of the field as landscape features influence the micro-climates within fields. Small differences in temperatures can cause large differences in damage and grain yield.
At Feekes 6 growth stage, damage from freezing will cause discoloration of the leaf tissue, with leaf tips or edges exhibiting symptoms first (Figure 2). However, discoloration does not necessarily indicate a reduction in grain yield. At Feekes 6 growth stage, damage can also be assessed by carefully cutting the wheat stem lengthwise to expose the developing spike at the first node. Damaged spikes will appear discolored and shriveled. A healthy, developing spike should be rigid and whitish-green (Figure 3).
Figure 2. At Feekes 6 growth stage, freeze damage causes yellowing of browning (necrosis) of the leaf and stem tissue. Wheat plants pictured (left to right) were exposed to temperatures of 3, 14, 21, 28, and 39°F corresponding to death of 100%, 80%, 50%, 25%, and 0% death of the plant tissue.
Figure 3. At Feekes 6 growth stage, freeze injury causes damage to forming wheat spike within the stem. Wheat spikes pictured (left to right) were exposed to 39, 28, 21, 14, and 3°F temperature treatments. At 3°F, the wheat spike appears discolored and deformed.
At Feekes 8 growth stage, damage from freeze may include yellowing or browning of the flag leaf. The flag leaf may appear twisted or in a spiral (Figure 4). As the plant continues to grow, the wheat spike may get stuck in the leaf sheath, causing a crooked appearance at heading (Figure 5). (Although, this phenology can also be associated with spikes that emerge quickly due to warm temperatures.)
Overall, I think freeze damage should be minimal from this most recent cold snap. At Feekes 6 growth stage, wheat is still fairly tolerant of cold temperatures. In the southern portion of the state, where wheat stage was more advanced, temperatures tended to be warmer. However, the best way to assess for potential damage is to scout your field after active growing conditions resume this week. For more information, see our new ‘Freeze Symptoms and Associated Yield Loss in Soft Red Winter Wheat’ FactSheet: https://ohioline.osu.edu/factsheet/anr-93
Figure 4. Twisting or spiral appearance of the flag leaf can be caused by low temperatures. Photo credit: Greg LaBarge.
Figure 5. At Feekes 8 growth stage, damage may include yellowing or browning of the flag leaf. The wheat head may get stuck in the leaf sheath causing a crooked appearance at heading.
Source: Dr. Mark Loux, OSU
Current forecast is for fairly warm temperatures through late evening Tuesday evening, followed by a substantial drop in temperatures and chance of snow, followed by cold/cool temperatures through the weekend. Primary question concerning this scenario seems to be whether it is okay to apply wheat or burndown herbicides prior to this cold snap. Some things we know about herbicides and cold weather:
– Herbicides applied to an emerged crop just prior to or during cold weather may be more injurious compared with favorable weather conditions. During cold weather when plants are not actively growing or growing slowly, the rate of translocation and metabolism of herbicide by the plant slows down, which can mean an accumulation of herbicide that is not being metabolized. This can increase the risk of crop injury since metabolism of herbicide by the crop, or conversion to an inactive form, is what allows that herbicide to be safely used on the crop in the first place. For some herbicides, there is such a large margin of safety with regard to crop safety that this is all inconsequential. For others the margin is narrower and issues such as cold weather and sprayer overlaps are more important. The inclusion of safeners in herbicide formulations reduces the risk of injury, usually be increasing the rate of metabolism, but may not completely solve issues that arise because of adverse weather or too high a dose. So with regard to this week and risk of injury to wheat, we would recommend avoid applying herbicide once the cold weather starts (from Wednesday on), until warm weather resumes.
– There is less certainty in making a recommendation about whether to treat wheat on Tuesday prior to the cold weather. We have seen instances in corn where application just prior to cold weather has resulted in greater injury. Wheat is actively growing now under favorable weather, and should readily translocate and metabolize herbicides. Much of this process occurs within the first few hours of application. Temperatures do not really start to plunge until early Wednesday morning per the forecast. While it’s somewhat of a guess, it seems that application during the first part of Tuesday would be possibly safer to the crop than later in the day. Past experience has shown us that some wheat herbicides are just generally safer than others, so one option would be to omit the ones that have stricter growth stage guidelines or have more of a history of causing injury. Having said this, in our research we have really not experienced injury from small grain herbicides applied per label.
– With regard to efficacy of burndown herbicides and cold weather, some of the same principles apply. Applying herbicide from Wednesday through the weekend, when weeds are not actively growing, is not recommended due to the likely loss of activity. Susceptible weeds metabolize herbicide slowly anyway, so the issue is a lack of translocation within the plant and the inability of herbicide to do it’s thing at the active site when plant processes are shut down. This is the type of cold weather we referenced in the recent article about dandelions, when we have observed control of this weed to plummet. We have also observed extremely slow control of overwintered annual weeds during cold weather.
– We would recommend going ahead with burndown herbicide applications on Tuesday, prior to the cold. As with wheat, weeds are actively growing under favorable weather so we assume herbicides will work. It’s still a bit of a guess, but it could be a while before field conditions and weather are suitable for application again.
– This is the type of scenario that makes us want to remind everyone again that a few dollars of herbicide in the fall can help avoid some of the nasty burndown issues that develop when spring conditions are less than optimum. Just saying.
Source: Jim Noel, NOAA
The climate pattern is in a state of a flux. The La Nina pattern is weakening rapidly and will cause changes in weather patterns in the coming weeks and will result in lower confidence forecasting for a while during this change.
For April it looks like a warmer than normal month with normal or slightly below normal rainfall. However, there will still be big swings in temperatures so the last freeze will likely be in the normal range which is generally mid-April for southern Ohio to late April for northern Ohio. Evaporation rates will be above normal. This will all result in typical or earlier than normal planting. Beneficial rains will fall over most of the corn and soybean belts in April with the least rain likely in the eastern areas including Ohio. Over the next two weeks we expect 0.50 to 2 inches of rain with normal rainfall being 1.5 to just under 2 inches. Hence rainfall is forecast the next two weeks to be 50-100% of normal.
Soil moisture is in good shape in southern Ohio but is short in northern Ohio and needs to be watched carefully. Soil moisture will improve in most of the corn and soybean belts in April especially in the western half of the region which needs it. However, soil conditions in Ohio will likely stay the same or get a bit drier in April with above normal temperatures, above normal evapotranspiration rates and normal to below normal rainfall.
You can get all the latest information from the NOAA/NWS/Ohio River Forecast Center on drought risk here: https://www.weather.gov/ohrfc/DroughtBriefing
Seasonal information can be found here: https://www.weather.gov/ohrfc/SeasonalBriefing
The outlook during the growing season from May through summer looks like a warmer to hotter than normal summer. It is not clear whether this will be more of a consistent warm of whether it will be more of an impact to maximum temperatures above 95. We will keep you posted on that.
Rainfall confidence from May through summer is quite uncertain. With La Nina weakening that could offset some of the risk to the drier side. Hence, at this time the outlook supports normal to slightly drier than normal. In the summer 30-50% of rainfall comes from local soil moisture so it is important to watch your local soil moisture between now and Memorial Day as it will be a big driver in summer rains. Bottomline, we are aware there is some risk for growing drought risk into summer but confidence is still low in the outcome.
In summary, the tendency supports warmer weather overall through the planting and growing season with rainfall normal to below normal. There is some risk of expanding drought but confidence in that remains low at this time.
Source: Laura Lindsey, Alexander Lindsey, OSU Extension
Prior to the Feekes 6 growth stage, the growing point of wheat is below the soil surface, protected from freezing temperatures. Most of the wheat in Ohio is at the Feekes 4 (beginning of erect growth) or Feekes 5 (leaf sheaths strongly erect) growth stage and should be unaffected by the incoming cold temperatures, predicted to be mid- to low 20s on Wednesday and Thursday.
At Feekes 6 growth stage, our research has shown only a 5% reduction in wheat yield at a temperature of 20°F for 15-minute duration and 50% reduction in wheat yield at a temperature of 12°F for 15-minute duration. (Although, it should be noted, there is a great deal of variability in response due to environmental conditions for the remainder of the growing season. Additionally, greater soil moisture levels can help buffer against short-term temperature fluctuations.)
For more information on Freeze Symptoms and Associated Yield Loss in Soft Red Winter Wheat, please see our new FactSheet: https://ohioline.osu.edu/factsheet/anr-93