July 19, 2021 Edition
July 19, 2021
“The facts ma’am, only the facts.” – Dan Aykroyd imitating Sgt. Joe Friday from the TV series Dragnet
Over the past couple weeks, there has been a few common topics for agriculture agronomy questions in our region: corn heat units, drought stress, and soybean injury/cupping (in no particular order). Everyone has their opinion, but let’s try to keep it to the facts.
Corn Growing Degree Day (heat unit) accumulation:
I like to reference the NDAWN (North Dakota Agricultural Weather Network) system for GDD accumulation data. I’ll choose May 5th as the average start date for corn planting this year. 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.
From the second figure, we can conclude that we are slightly ahead on GDD pace in 2021 compared to the average of the prior five-years with a May 5th 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 ((Tempmax + Tempmin)/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 slightly above the 5-year pace. When evaluating 2021 compared to the 30-year normal (1991-2020), we can see that 2021 has started much warmer for the first half of the season (third figure).
Drought Stress:
Considering how little rain has fallen this spring and summer to date, it’s surprising how well some fields of full season row crops are performing in areas. Yes, they could be much better, and the stand establishment was below average (in general), but many fields are still hanging-on to some of their yield production goals. The rain has been very spotty over the season to date and thus there is a lot of variability in field productivity potential for mid-July as well. For many fields, it doesn’t matter how much it may rain from here on out, the yield potential is going to be way below average.
For drought tolerance in crops, the most detailed research has been conducted on maize (corn). Many maize genes have been identified that are consistently highly correlated to increased drought tolerance in hybrids and breeders have been working on the development of understanding these genes – along with other new discoveries – and ultimately improving drought tolerant maize hybrids for decades. In soybeans, from my understanding, drought tolerant genes have been identified in some varieties, but the responses have variable consistencies from some varieties and environments to others.
In corn, we have good confidence in estimating yield loss per day of drought stress. For instance, yield loss is much less during early vegetative growth stages (1-3% yield loss per day) than compared to the pollination stages where yield loss can range from 3-9% per day depending on the severity of drought. Under a “normal” pollination window of 7-8 days for an individual plant, you can see how critical it is to have some moisture reserves leading up to the pollination period.
For further insight on drought impacts within corn, please see this Crop Focus document: https://corteva.showpad.biz/CropFocus-corn-drought...
This week will be interesting with high temperatures (>90F) and little chances of significant rain as the majority of the corn crop will begin to start the reproductive stages. The key over the next week to 10 days is how well the corn will pollinate. Most of the fertilization of corn kernels occur in the morning hours when temperatures are the coolest for the day (5-10 am). Yes, corn pollen can sterilize under high temperatures, but with the early morning silk receptivity, pollen viability during these times is normally less of a concern.
The larger concern would be the severity of drought stress and how it may impact pollination overall. Under severe drought stress, silk elongation from the female is delayed due to the fact that silks are 98% water and she would prefer to wait for better conditions. Conversely, the male is not as water dependent and actually speeds up the timing of its pollen dispersal under stress versus without stress. This creates a scenario where a normal corn fertilization window of 8-12 days across a field, may be condensed into a handful of days where both viable pollen and receptive silks are in synchrony due to the severity of the drought. In these cases, pollination success is inconsistent and highly variable across a field.
The below link is a Pioneer Crop Focus article discussing the corn pollination process and methods to evaluate pollination success. https://corteva.showpad.biz/CropFocus-pollination-success...
Soybean Crop Injury (cupping/leaf injury):
With all the warm dry weather, it’s been very suitable conditions for herbicide volatility and carryover symptoms to arise. Not all herbicides are created equally in this regard with some compounds much more suitable to move off target than other compounds and/or carryover from last season’s applications. With that being said, there are very distinguishing characteristics or clues we can read from the soybean crop that can lead a good detective to the most likely causes of injury.
I could detail all the differences myself, but the following Pioneer® Crop Focus document highlights, describes, and visually shows the key differences that can lead to the common crop injury symptoms we are seeing on soybeans this summer. Give it a good look here: https://corteva.showpad.com/share/axWvRVlETznmo8QiknQ9L
Some additional facts to consider:
· Copyralid (Stinger®) injury can look similar to dicamba in the form of “cupped” or “cobra” leaves. However, copyralid injury will typically cause shorter internodes in the soybean crop, and show inconsistent injury across soil types within a field
· Greater volume of growth regulator herbicide (dicamba, 2,4-D, and copyralid) are being sprayed today (both in total number of acres as well as rate/ac) than prior years as farm managers continue to try and control herbicide resistant weed species and fully utilize the GM technology in their soybean seed purchase
· Some states were allowed to spray dicamba longer into the summer in 2021 versus the 2020 season. For instance, Minnesota soybean producers had an extra 10 days in 2021 versus 2020 (June 30th cut-off date this season versus a June 20th date last season).
· Pioneer® sold significantly more units of Enlist®-3 soybeans in 2021 than the prior year. Overall, the market share of Enlist®-3 genetics for the 2021 growing season across the USA is estimated at 30-35% and is near double the 2020 season. Therefore, there are many more acres of susceptible soybeans to dicamba across the country
· 2,4-D choline (the primary growth regulator formulation in both Enlist One® and Enlist Duo®) does not have soybeans (non E-3 GM trait) on the label as a sensitive crop. The dicamba label states non-Extend® soybeans are a sensitive crop and additional regulations are in-play for cases where a sensitive crop is near the intended field being sprayed
· 2,4-D choline is very much less volatile than dicamba. Every weed scientist and chemist will approve this statement. Just how much less volatile? I could not find a source on the internet to confirm for a reference, but scientists within Corteva® verbally state it is over 200 times less volatile
· Corteva’s® regional crop protection team has fielded very few complaints on the performance of Enlist One® and/or Enlist Duo®. Less than 1% of the acres sprayed with either formulation has resulted in an applicator complaint.
At the end of the day, the 2,4-D herbicides of Enlist One® and Enlist Duo® are performing as expected along with the Enlist-3 soybean genetics. The folks on the other side of the isle will have to determine if they can make that same statement to aid farm managers in minimizing soybean production risk.
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