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C.O.R.N. Newsletter: 08-2021
Control of dandelion with spring/summer herbicide treatmentsAuthor(s): Mark Loux
Dandelion seems to be on the increase in some fields, as we noted in a video last summer and CORN article last fall. Fall is the optimum time of year to reduce dandelion populations with herbicides, so we expect them to become more of a problem in fields that are not treated in the fall at least occasionally. If history is any indicator, other causes can include oversimplification of herbicide programs in soybeans, omission of residual herbicides, and delaying burndown herbicides until later in spring. All of these occurred during the first few years of RoundupReady soybeans, and we had some dense stands of dandelions that developed in late 1990’s. We again have some very effective weed management platforms for soybeans, and the possibility of the same happening. In addition, while POST applications of glufosinate have broad-spectrum activity on annual weeds, they are not that effective on dandelion and other perennials, which can allow some of these weeds to get more of a foothold.
In the absence of fall herbicide treatments especially, control of established dandelions in corn and soybeans will require effective burndown and POST herbicides. Do not expect adequate control of established dandelions from just the burndown or just the POST. Where the burndown herbicides are relatively ineffective for whatever reason, the POST herbicides will also likely be less effective. It’s also necessary to include residual herbicides to help control the dandelion seedlings that can emerge after planting from seeds produced last fall and this spring. Some things to consider:
- Our experience with dandelion over the years has shown that the effectiveness of spring burndown herbicides on dandelion can be extremely variable. We conducted research with Purdue and Penn State back in about 2000, where we applied glyphosate and glyphosate + 2,4-D weekly from early April to early May. Control generally improved with the later applications. The glyphosate + 2,4-D was more effective, but under some colder than normal conditions in late April, control decreased considerably. We suggest avoiding applications during this type of weather.
- Most effective burndown will generally result from combinations of glyphosate with 2,4-D or dicamba. Increasing rates of these products can improve control, but will not overcome the negative effects of cold weather. The addition of a chlorimuron-containing product can help in soybeans. In corn, products or mixtures that contain higher rates of atrazine and mesotrione have also been effective for suppression well into the growing season (adding 2,4-D can help).
- The addition of herbicides with contact activity to the burndown can make it appear as though control has been improved, but can actually reduce the activity of the systemic herbicides, and plants regrow sooner in some cases. This includes sulfentrazone, flumioxazin, saflufenacil, and metribuzin, and glufosinate.
- POST followup in soybeans should include glyphosate, and as with burndown, mixing with 2,4-D (Enlist) or dicamba (Xtend/XtendiMax) will be most effective. We would suggest including glyphosate with glufosinate in LLGT27 soybeans (resistant to both of these herbicides). Some of these same options apply to corn, along with mixtures that contain mesotrione. Adding a high rate of Classic in soybeans may also help any of these.
- After doing battle with dandelion this coming season, make a plan to apply herbicides this fall, when a little money goes a long way.
Weather Update from NOAA/NWS/Ohio River Forecast CenterAuthor(s): Jim Noel
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.
Calibration for Rate Controlled SprayersAuthor(s): Erdal Ozkan
I had an article in last week’s CORN newsletter encouraging growers to fine tune and calibrate their sprayers. I had mentioned that the next couple of weeks may be the last best time period to do this since planting season is just about to start. There would not be any better time to do this than now. The next day I got an email from a grower asking me this question that I get often: “I have a rate controller in the cab that regulates the flow rate of the sprayer regardless of the changes in sprayer ground speed. So, should I still calibrate the sprayer to find out the application rate?”. The answer is, Yes, you should. Although the rate controllers do an excellent job with regulating the flow rate of nozzles to keep the application rate constant, a manual calibration at least once a year is needed to ensure the rate controller is functioning properly.
Here is why we should confirm the accuracy of rate controllers: Unfortunately, electronic controllers usually cannot detect flow rate changes on each nozzle on the boom, and none can detect changes in spray pattern. If a nozzle is plugged, or extremely worn out, the rate controller cannot tell us this is happening. It will still try to maintain the constant application rate by changing the system pressure and force other nozzles to spray less or more to overcome the problem in one or several nozzles. If the ground speed sensor works based on revolutions of the tractor wheels, the ground speed determined may not be accurate, because of the slippage that may occur under some ground conditions. Even the tire pressure being off just a few psi may change the tire revolutions per minute leading to erroneous travel speed readings. Finally, Controllers don’t show changes in spray patterns that may happen when a nozzle is defective, plugged, or worn-out. So, we will have to continue manually checking the flow rate of the nozzles, and visually observing the changes in spray patterns until the technology is developed to do these observations remotely, and on-the-go.
As I mentioned in the article in last week’s CORN newsletter, it usually doesn’t take more than 30 minutes to calibrate a sprayer, and only three things are needed: a watch or smart phone to record the time when measuring the nozzle flow rate or the travel speed, a measuring tape, and a jar graduated in ounces. Please take a look at the Ohio State University Extension publication FABE-520 for an easy method to calibrate a boom-type sprayer. Here is the URL for this publication: http:// ohioline.osu.edu/factsheet/fabe-520
Not knowing limitations of rate controllers may create serious problems. I already mentioned how smoothly the rate controllers keep the application rate the same regardless of changes in travel speed. However, this convenience comes at a cost if the controller is forced to make drastic changes in the application rate as a result of too high or too low of a travel speed. As you know, to achieve best results from pesticides, the application rate, as well as the droplet size must remain relatively unchanged during the entire spraying. When sprayer speed goes up, to maintain the pre-set application rate, the controller requires the system pressure to go up to increase the nozzle flow rate. This, unfortunately results in more drift-prone droplets coming out of the nozzle, especially if the nozzle used is designed for low application rates within the recommended pressure ranges. Conversely, when the sprayer slows down, the opposite happens: the controller forces the system to lower the pressure, in order to reduce flow rate of nozzles. This will result in production of larger than the desired size of droplets, leading to inadequate coverage. If you are spraying Dicamba or 2,4-D herbicides, you need to pay even more attention to operation of rate controllers. As you know, only a small number of nozzles at specific ranges of pressure can be used to spray these products. Significant changes in ground speed may force the rate controller to make significant changes in spray pressure that may be outside the allowable legal pressure range required to spray these herbicides. Without you realizing it, you may find yourself in violation of the label. Make sure the nozzle size selected will allow the controllers to make necessary changes in the flow rates while still staying within a safe, applicable and allowable pressure range.
CFAES Ag Weather System 2021 Near-Surface Air and Soil Temperatures/Moisture
We are once again providing a soil temperature overview in the C.O.R.N. Newsletter through April-May 2021. The College of Food, Agricultural, and Environmental Sciences (CFAES) Agricultural Research Stations located throughout the state have two- and four-inch soil temperatures monitored on an hourly basis.
1 shows that two- and four-inch soil temperatures have varied significantly in response to large swings in air temperature over the last seven days. Soil temperatures were approaching 50°F last weekend before this week’s cold snap had soil temperature retreating into the low to mid 40s. Our current warming trend is allowing soil temperatures to recover, with most sites across the state seeing daily averages in the mid to upper 40s (above 50°F at Western and Piketon). Warmer than average air temperatures this week should continue these soil trends.
Figure 2 (left) shows that most precipitation this week fell along and southeast of about I-71, with very light precipitation once again across northwestern counties. Dry conditions have lingered across northern Ohio all winter and have worsened of late, especially across northeast Ohio. Currently, 16% of the state is designated as having Moderate Drought Conditions according to the U.S. Drought Monitor. Column relative soil moisture compared to 2020 is down 8-20% across much of Ohio (Fig. 2 right), with the driest start to spring planting season since about 2016.
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.
The information presented here, along with any trade names used, is supplied with the understanding that no discrimination is intended and no endorsement is made by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
CFAES provides research and related educational programs to clientele on a nondiscriminatory basis. For more information, visit cfaesdiversity.osu.edu. For an accessible format of this publication, visit cfaes.osu.edu/accessibility.