Aug 16, 2021 Edition

 

“If you torture the numbers long enough, they’ll confess to anything!” – Ronald Coase, British economist and author

Over the past couple weeks, there has been a few common topics for agriculture agronomy questions in our region: corn growing degree days and development, wildfire smoke/haze, will rain now help the corn and soybeans, and late season insect pressure.  As usual, we’ll keep the torture to a minimum and let the data freely explain itself.

 

Corn Development and Growing Degree Day (heat unit) accumulation:

We’ll continue to reference the NDAWN (North Dakota Agricultural Weather Network) system for weather and GDD data with an average start date for corn planting this year of May 5th.  For the fields that were planted about 7-10 days earlier, we can add 30-50 GDD’s, and conversely for fields planted 7-10 days later we can subtract about 40-60 GDD’s.  The first figure below reveals GDD’s in our region to date.

Within Pioneer’s 70-75 RM zone of hybrids, we’ll typically need about 1800 to 1900 growing degree days to achieve physiological maturity, or black layer, from planting.  So, with most of the northern Red River Valley region ranging from 1600 to 1800 GDD’s currently in 2021, we are starting to see early season corn hybrids at full dent, and longer maturity products in the dough to early dent stages.  Of course, with the drought conditions in play, we can see maturity hastened somewhat where grain is present.  If you have 85 RM zone hybrids on the farm, they will typically need about 2050 to 2100 GDD’s to reach maturity from planting.  However, please realize that there is no industry standard for GDD ratings on corn hybrids and GDD numbers can drastically change from one seed brand to another for a certain CRM zone.

From the second figure, we can conclude that we are ahead on GDD pace in 2021 compared to the average of the prior five-years with a May 5^th start date.  However, if you remember the GDD calculation, it does not take into consideration temperatures above 86F.  The daily GDD calculation for corn is ((Temp_max + Temp_min)/2)-50, with a base of 50F minimum and 86F maximum.  So, even though we have had more days above 90F this summer than years past, the GDD accumulation totals are only 5-7 days above the 5-year pace (assuming an average of 20 GDD’s per day).  When evaluating 2021 compared to the 30-year normal (1991-2020), we can see that 2021 has been much warmer for the first three fourths of the season (third figure) – in many cases 10-12 days ahead of normal.

From here to the end of the season (I’ll call it Oct. 1^st), we should see about 500 GDD’s from a 30-year average (chart below) for our region.  If you add that to the approximate 1,700 GDD’s we have already gained for the growing season, we’ll forecast to around 2200 GDD’s for the 2021 season up to October 1st.  In other words, with average weather conditions from here on out to October 1^st, we should see a Pioneer 85 RM hybrid, planted back in the first week of May, around 25% grain moisture content range by Oct. 1^st.  Also, without any reprieve from the drought, we should not expect the crop to have very strong legs late into the autumn. 

 

 

Will the wildfire smoke/haze impact our crops? 

Over the past month or so, it’s been very rare to have a clear day here in northeastern North Dakota or northwestern Minnesota.  With the numerous fires in the western US and Canada, as well as to our north in Ontario, it’s been difficult to get a break from the smokey haze.  Regardless of the reasons why we are seeing more wildfire numbers these last several years, we do know that the smoke in the air does affect plants in a few various ways.

First and most obvious is the reduced intensity of sunlight.  As the smoke reflects a portion of the incoming sunlight, plants will receive less light to drive photosynthesis.  Plants with C₄ carbon pathways like corn naturally respond greater to higher light saturation points, while plants with C₃ pathways (soybeans, wheat and sugarbeets) are much less efficient in their process which involves photorespiration.  Therefore, C₃ plants will be less significantly influenced than C₄ plants to the reduced sunlight intensity. 

Second, is the fact that smoke will increase local ozone levels.  Typically, we think of ozone as the beneficial upper atmosphere layer that helps shield us from harmful ultraviolet radiation.  However, lower-level ozone can also occur when certain pollutants are present.  Wildfires emit nitrogen oxides and other organic compounds that react in the atmosphere and persist as a pollutant to emulate ozone.  Ozone is very harmful to plants as it enters stomata and oxidizes (burns) plant tissue within the respiration and photosynthesis process.

Lastly, the smokey haze will diffuse or refract sunlight.  This scattering of the sun’s rays could actually help plants with higher leaf area index and narrower row spacings to intercept more sunlight.  With light coming at the plant from more various angles, we should see increased photosynthesis output which will be a benefit to the plant.

If you remember back to our experience in 2019 – the year we had cool and very wet conditions during the latter half of August through the remainder of the autumn – we did see significantly below average solar radiation levels as well.  Some would argue that the below average heat unit accumulation that year is mostly to blame for our poor corn grain quality, but it’s hard to discredit solar radiation quantity or lack there of in the conversation as well.  Unfortunately, it’s very difficult to duplicate the natural variety of a smokey haze in a controlled environment, and thus quality research data is questionable at best.

Back to 2021, our hazy conditions have probably reduced the impact of the heat we have experienced (a benefit), but our current drought conditions are intense enough to trump all other factors.

The Pioneer Agronomy Sciences team has placed a couple of documents together explaining the significance that wildfire smoke can play in crop performance.

https://corteva.showpad.com/share/OUqawYGy93kP4v4p9IhpB https://corteva.showpad.com/share/KqAAqAkNrbbWDPsO7vSIN

 

Can Late August Rain Help Our Soybeans and Corn?

Considering how little rain has fallen this spring and summer to date, it’s surprising to see how well the wheat and early canola yields have been.  Yes, they are not at our typical levels, but many people were forecasting much lower productivity. 

For most of the corn and soybeans, any rain received at this point in the next week to 10 days is not going to increase seed or kernel numbers on a plant or acre basis.  However, what we’ll see is those plants able to maintain their kernel count (no further abortion), increase the size of the kernels that are present, and aid in some late season plant health, most notably standability and ear retention in the corn.  Even though we may not see big significant benefits, any rain received now will obviously help in building soil moisture content for next year’s crop.

Last month I provided some great resources on corn for responses to drought conditions, and here is a nice document on soybean water use along with some comments on drought impacts. https://corteva.showpad.com/share/7W5ads9JMasc42NKogVBH 

2021 Season Rainfall

Obviously, we don’t have to stress how dry the 2021 season has been to date, but I thought a couple of rainfall charts from NDAWN would place some quick perspective on the situation.  The first chart reveals total rainfall for the season since May 1^st, while the second chart shows the departure from the 30-year normal (1991-2020 with a May 1^st start date).  As you know, many of the rains/storms had quite dramatic variability so local geographies could have greater (or lesser) impact compared to what NDAWN is depicting.  Also, some of the locations with higher rainfall totals had some big rains that were not timely.  For example, Langdon had close to 4” of it’s 10.14” total in one night on Aug 9^th.

Late Season Insects – spidermites and grasshoppers

With the spring wheat harvest progress nearing completion and the dry conditions continuing, we are seeing numerous full season crops being impacted by spidermites and grasshoppers.

Spider mites and grasshoppers are usually pests that tend to stay on the edge of fields, and flourish in drought conditions.  However, this year they are moving deeper into fields.  Mites are a piercing/sucking pest that robs the plant of nutritious sap and can impact yields very significantly.  Look for leaf stippling (attached picture) as a key symptom of spidermite infestation.  The leaf stippling will start at the bottom of the plant and move up.   When there is enough stippling, the leaves will turn a yellowish and then copper-brown color. 

The grasshopper populations also continue as a concern while they migrate into greener fields.  As the soybean fields now start to drop leaves, there is less green material in those fields as well for the grasshoppers to feed on.  Grasshoppers can move to the pods and even eat the actual seeds, especially in places where the grasshopper populations are on the higher side.

For the most part, both soybeans and corn are far enough along in maturity where these pests are losing significance each day.  Of course, there are always exceptions to the norm, so keep a close eye on any late planted fields or fields with strong yield potential still remaining.  One additional note on any insecticide applications - pyrethroid insecticides (Warrior®, Mustang®, Baythroid®, Pounce®, etc.) which are common for grasshopper control will flare spidermites, making them more intense.

Thanks to fellow Pioneer Field Agronomist Sarah Lovas for the above pic and comments on spidermites and grasshoppers.