Posted: Jul 12, 2017
Notes from Pennington and Olson
What causes pre-harvest sprouting in wheat?
By Dennis Pennington, MSU wheat specialist, and Dr. Eric Olson, MSU wheat breeder
The week of June 19-25 saw significant rainfall for most of the Lower Peninsula of Michigan, with some areas receiving over 6 inches in a 36-hour period. The central part of the state was hardest hit with major flooding of fields and roadways.
When wheat seeds break dormancy and begin to sprout in the head prior to harvest, quality of the seed can degrade quickly. When sprouting occurs, alpha amylase enzyme begins to break down the long chains of starch into simple sugars. This impacts the quality of bread, cookies and crackers made from sprouted wheat. The amount of alpha amylase enzyme fluctuates naturally, as the seed develops and matures.
Falling number is a test that helps to identify the structural integrity of the starch chains. To conduct the test, you must grind the grain into meal, add water, mix with a stirrer and add heat for 60 seconds.
The falling number is the number of seconds it takes for the stirrer to fall to the bottom of the test tube. The longer it takes the stirrer to fall, the higher the quality of starch (longer chains). If it falls quickly, that is an indicator that alpha amylase enzyme may be at high enough levels to start the starch degradation process for seed germination. In fact, the falling number of a sample is very closely related (r2=0.924)to the concentration of alpha amylase. (See Trend Chart.)
Alpha-amylase Chart: Relationship of alpha amylase to falling numbers. From Stebers, C. USDA-ARS, Washington State University, "Causes of low Falling Numbers in Wheat."
Late Maturity Alpha (LMA) amylase
Late Maturity Alpha amylase (LMA) is a developmental defect that occurs as the embryo in each seed matures and is triggered by “cold shock”. Cold shock can be described as a sudden decrease in overnight temperature. The degree of change in temperature that can cause LMA is not yet known.
Varieties with lower ratios of amylose to amylopectin tend to be at higher risk for LMA and preharvest sprouting. It has long been understood that rain and high humidity after wheat kernels reach maturity can cause sprouting. This study suggests that temperature can also play a role in triggering a low falling number test.
Wetting events at high temperatures usually are not a problem. However, a rain event after or during a sudden drop in temperature can stimulate the seed to produce alpha amylase enzyme (LMA) which triggers germination of the seed. Varieties are variable in the response to cold shock and expression of LMA. In the future, we may be able to rate varieties for risk of LMA.
Data from the Saginaw Valley Research and Extension Center (figure 2) reveals a likely cold shock preceded by rainfall that could have triggered an LMA event (June 21). This could explain why some early harvest wheat samples have been testing low for falling number.
More work needs to be done in this area to better understand how temperature fluctuations impact wheat development and perhaps in the future, we can make recommendations for varieties that have a lower risk of an LMA event.
Weather Summary Chart: Selected weather data from the Saginaw Valley Research and Extension Center. Data downloaded from enviroweather.com.
Looking for pre-harvest sprouting of wheat and falling numbers indicator
By Martin Nagelkirk, MSU wheat educator
As wheat matures in central Michigan, growers would do well to minimize the risk of sprouting (low falling numbers) this season as some early grain loads suggest some fields are testing moderately low.
Pre-harvest sprouting of wheat is always a potential risk, but this season there is some concern given the past and current weather pattern and some early test sample results. In any event, the following offers a few reminders regarding the issue.
Pre-harvest sprouting sometimes occurs when natural dormancy is broken, triggering the kernel to behave as a germinating seed rather than a starch-storing grain.
Grain may be subject to pre-harvest sprouting once wheat matures. Indicators of maturity include a browning of the stem immediately below the head. (See photo; note stem on right.)
The process begins well before there is any visual evidence of sprouting. That's why for decades the milling industry has relied on a Falling Number test. This test score is actually the number of seconds it takes a plunger to fall through a grain/water slurry under very controlled conditions. The industry generally prefers grain measuring 300 seconds. Depending on the end-user, there is often significant concern when the seconds slip below 250 or 275.
Pre-harvest sprouting is more likely when grain is exposed to moisture in the form of rain, fog or high relative humidity. While the process may be more likely to begin at lower grain moisture levels, its clear that the process can occur as soon as grain reaches physiological maturity (35 to 40 percent).
There are differences in susceptibility among varieties. Soft white and many soft red wheat varieties grown in Michigan are considered susceptible or moderately susceptible. Linda Brown (PhD candidate, MSU) has categorized many of Michigan’s commonly grown varieties relative to sprouting (Wheat Variety Comments, 2017, page 2, "sprout” column).
The grain sample pictured (see photo) tested 40 percent moisture at or near maturity. Note range of kernel development: A few kernels from the same head or adjacent heads were still slightly green and retained some inner husk.
The following are some recommendations:
1) Bring samples to your local elevator before or as soon as harvest begins to learn if grain has a marginal falling number score;
2) Harvest as soon as wheat can be reasonably threshed, especially where grain has marginal falling number scores and the variety is not resistant to sprouting. Click here to review Wheat Variety Comments handout;
3) Be prepared to segregate grain from different parts of the same field as there can be significant differences in falling number;
4) Never blend grain having low falling numbers with good grain. Blending grain with low and high falling numbers is not a simple average. For example, if one were to blend grain having a falling number of 150 with an equal amount of grain having a 250 score, the bulk load will not test 200, rather its score will be closer to the 150-second level.
Additional References on Falling Numbers
Pre-harvest Sprouting of Wheat, Alpha-Amylase Enzyme, and Falling Number; and
Understanding Pre-harvest Sprouting of Wheat, a bulletin of Virginia Cooperative Extension.
RMA crop insurance improvements may come into play this summer; a recap of improved coverage for falling numbers in white winer wheat.
One of the Michigan Wheat Program’s most significant accomplishments to date is the major falling numbers coverage adjustment made this past fall by the USDA Risk Management Agency (RMA).
The Michigan Wheat Program began seeking the change in RMA policy in 2012, shortly after the check-off was formed.
Farmers said that although they had purchased crop insurance to cover falling number discounts, when they had a claim what they received was not even close to the discount.
In some cases the discount received was more than $1 and the payment received through crop insurance was 25 cents or less. This problem was costing Michigan wheat farmers dearly and a solution was needed.
The Michigan Wheat Program partnered with several other organizations in working through this complex problem. Initially, RMA reviewed the numbers from Michigan and made slight modifications to the program. This did not prove to be a significant enough improvement, and the board went back to the drawing board.
“The board decided to hire the consulting firm Watts & Associates, which had experience with other crops and crop insurance,” said board chairman David Milligan. “We wanted Watts to help the Michigan Wheat Program build a case and get the major adjustment we needed from USDA.”
What followed was significant, statewide- and industry-wide cooperation between millers, elevators and farmers to gather actual settlement sheets, coordinated by Watts & Associates.
Over 41,000 observations covering 53 million bushels of wheat were submitted to Watts & Associates, allowing the firm to compare what a farmer received in payment from crop insurance to the falling numbers dock at the point of delivery.
Watts’ data clearly showed the discrepancy for Michigan white wheat growers, and was submitted to USDA-RMA by the Michigan Wheat Program. This time, RMA made a significant program adjustment!
Unfortunately, there was not enough data to make the change for red wheat.
Beginning with the 2016 crop, USDA-RMA is using a new county special provision for Michigan allowing a farmer to use the actual price received in valuing production for Michigan white wheat with falling numbers below 200. For falling numbers above 200, the updated published discounts will still be utilized.
The Michigan Wheat program board continues to monitor red wheat falling numbers, as well as DON/vomitoxin ratings to ensure the risk management programs are appropriate for Michigan wheat growers.