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August 21, 2009

HRSW Varieties with a Higher Risk of Preharvest Sprouting

The continued wet weather and harvest delays are increasing the potential for preharvest sprouting. Once the dormancy of the seed is broken and sprouting is initiated the quality of the grain deteriorates, grain elevators will check for this decline in quality using the Hagberg Falling Numbers test. The HRSW that are ranked moderately susceptible to pre-harvest sprouting are listed in Table 1. Understand that the potential for preharvest sprouting increases if you swath the grain or if you leave it stand too long while waiting for the grain to reach 13% moisture, all the while rain and heavy dews are forecasted. Rather, harvest the grain as quickly as possible and as soon as moisture content approaches 15% as HRSW can be readily stored up to three months at that moisture content.

Table 1 - HRSW varieties with a higher risk of preharvest sprouting

Variety Preharvest Sprouting Rating*

Bigg Red 4
Blade 5
Granger 4
Hat Trick 4
Sabin 4
Samson 4
Traverse 4

* 1=best, 9=worst

August 12, 2009

Preharvest Management Options for Wheat

There are two methods of pre-harvest management for wheat that can speed up harvest. Swathing or windrowing is one method. An application of glyphosate is a second option. Several brands of glyphosate are labeled for preharvest weed control. Research has shown that glyphosate can also quicken the dry down of the wheat crop if conditions for dry down are adverse. The preharvest interval for preharvest glyphosate is seven days and expects only to gain a couple of days at the most. More time can be gained with swathing.

The optimum time for either pre-harvest management tool is right at or just after physiological maturity of the crop. At physiological maturity, the crop has the maximum kernel dry weight and no additional dry matter will be deposited in the grain. The kernel moisture percentage at physiological maturity is relatively high and can vary from 20 to 40%. Research has shown that swathing just before physiological maturity does not harm the grain yield or quality. This practice, however, is not recommended when using glyphosate as a pre-harvest tool.

There are two visual indicators that can be used to determine whether the crop has reached physiological maturity. The first indicator is the loss of green in the kernel and the appearance of a dark layer of cells or pigment strand along the crease of the wheat kernel (Photos 1). Kernels in the same spike will reach physiological maturity at different times with the middle of the head maturing first.

pigment_strand.jpg Photo 1 - Wheat kernels before (above) and at (below) physiological maturity.

Another visual indicator is the loss of green from the peduncle and glumes. If the peduncle just below the head becomes straw-colored, transportation of water and nutrients to the head has been cut off and the crop has reached physiological maturity (Photo 2). The advantages and disadvantages of pre-harvest glyphosate and swathing are listed in Table 1.

Physiological Maturity.JPG Photo 2 - Wheat spikes before (left) and at (right) physiological maturity

Table 1 - Advantages and disadvantages of different methods of pre-harvest management.

09 Table 1 Preharvest Management.jpg

July 15, 2009

Final Words of Caution on Wheat Midge

by Phillip Glogoza, Extension Educator - Crops

A lot of wheat is now heading in NW Minnesota. In the northern most counties, degree day accumulations are just reaching the 1300 DD mark (see map), the point where 10% of female midge have emerged. Emergence will continue through 1600+ DD (90% female emergence).

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July 9, 2009

Understanding the Risk for a Fusarium Head Blight Epidemic in Wheat

by Dr. Charla Hollingsworth, U of MN Extension Plant Pathologist

Crop growth stages of spring wheat are rapidly approaching early flower in some locations. This is the time of year that managers must make a decision to apply a fungicide application targeted for Fusarium head blight (FHB) management.

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July 1, 2009

Watch for Midge as Wheat Approaches Heading Stage

by Phillip Glogoza, Extension Educator - Crops

There could be about 70% of the region's wheat acres at the heading stage when wheat midge are emerging, based on those acres being planted in the high risk window (Figure 1). Heading is the growth stage when wheat is attractive to female midge for egg laying, and the time the plant is most susceptible to injury from midge larval feeding. Though midge populations have been small in recent years, this will be the most wheat acres we have had that are susceptible to midge in many years.

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Aphids in Small Grains - June 29, 2009

by Dr. Ian MacRae, U of MN Extension Entomologist

There have been some reports of bird cherry-oat aphids (Figure 1 and Figure 2) in small grains in NW and WC MN over the last week. The populations I've seen are at very low numbers. Add to this, the recent rainy weekend will likely have had a significant impact on those aphid populations, but it's still a good idea to scout for aphids in small grains. The most damaging aphid populations are ones that reach threshold around flag leaf stage, if populations are at or near threshold at this time, delaying treatment until heading may cost you yield.

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Bacterial leaf stripe of wheat: Something to keep in mind

by Dr. Charla Hollingsworth, U of MN Extension Plant Pathologist

Bacterial leaf stripe is a disease that can usually be found on wheat in the Red River Valley (RRV) later as crop growth stages progress. The disease (caused by a Xanthomonas sp.) can develop and become severe rapidly after the crop reaches the heading growth stage. Bacterial leaf stripe (BLS) can cause significant yield losses on some varieties. Like other disease issues, development is dependent on weather conditions and the presence of susceptible plant hosts. Epidemics of BLS occurred in the RRV during 2005 and again in 2008.

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June 30, 2009

Losses in Wheat due to Flooding and Waterlogging

Northwest Minnesota continues to be plagued by excess precipitation. Consequently many field or lower lying portions of fields are repeatedly flooding or are - at a minimum - completely waterlogged. Flooding and water logging causes a rapid depletion of oxygen in the root zone. In turn, this oxygen deficiency affects several physiological processes such as the uptake of water, the uptake and transport of nutrients, and the root/shoot hormone relations.

Wheat can probably handle 3 to 4 days of flooding and/or water logged soils before grain yield is impacted negatively as long as some of the leaves are above water. Higher temperatures will hasten the depletion of oxygen and increase the risk of damage to the crop. Acute nitrogen deficiencies are most commonly observed with the crop yellowing quickly. The waterlogged soils not only impair nitrogen uptake, denitrification and leaching further exuberate the problem. Extended periods of water logging reduce leaf elongation, kernel number, and ultimately grain yield.

Yield losses than have been reported in the literature range between 20 to 50% when soils were water logged in excess of 10 days. One study in winter wheat reported a yield loss of about 2% for each day soils were waterlogged. Several study, however, have also noted differences in water-logging tolerance among wheat varieties.

One of the characteristics that were observed of varieties that handled water logging better than other varieties was the ability of varieties to initiate adventitious roots of the first node (Photo 1). I have observed this trait in some of our spring wheat varieties but neither I nor any of the breeding program in the region have dedicated screening or evaluation nursery for this trait.

09 Adventitious wheat roots.JPG
Photo 1. Adventitious roots on the first node of a wheat stem visible after three days of flooding near Crookston in 2002.

June 18, 2009

Wireworms in Small Grains

by Dr. Ian MacRae, Extension Entomologist

I've received reports of wireworms in small grains this season - not surprising this year given that wireworm tend to be more active in cooler conditions. There are several species of wireworms in the Red River Valley and although they're usually neither a frequent nor wide-spread problem in the RRV, when they do occur, damage can be quite significant even leading to a total field loss.

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June 16, 2009

Causes of Seedling Stand Losses in Spring Wheat

Seedling stand loss is defined as the percentage of viable seed that fails to become a healthy plant. In order to understand the causes of stand loss we need to also define seedling vigor. Seedling vigor is defined as those seed properties that determine the potential for rapid, uniform emergence and development of normal seedlings under a wide range of conditions. Causes of seedling stand losses can be categorized in three broad categories - intrinsic attributes, biotic stresses, and abiotic stresses.

Both seed size and grain protein content have been shown to improve seedling vigor in spring and winter wheat seed lots of the same cultivars that have higher seed weight and/or grain protein content will have more seedling vigor. Some of the research, however, suggested that there was no need to remove the smaller seed fraction from a seedlot as long as the seedlot had commercially cleaned as there often wasn't a yield difference at the end of the season despite differences in seedling vigor. Some of the same research, however, did shown that were significant differences in seedling vigor among spring wheat cultivars and the authors of the studies suggested that breeders use it as a selection criterion in their breeding programs.

A cold stress test in addition to the standard germination test is a method to test seedling vigor of a breeding line, variety or seedlot. Corn breeders routinely use this test as a selection criterion in their breeding programs. I am not aware of any spring wheat breeding programs that use the cold stress tests in their breeding program. This can probably be explained by the fact that corn is more often seeded in - for corn - cold soils resulting in protracted germination and seedling emergence.

The physiological age of the seed is also an important parameter that influences seedling vigor. A standard germination test is used to determine the percentage viable seed under ideal conditions. There is also the 'accelerated aging test' to discern seedlots with poor seed vigor and excellent seed vigor. This test is routinely conducted in soybeans and corn but again seldom used in wheat. This too can probably be explained by the fact that corn and soybeans are more often seeded for their species in cool soils, resulting in protracted germination and seeding emergence.

Biotic stresses that cause stand losses include whole host of fugal diseases. Saturated and/or cold soils can aggravate the incidence and severity of a number of fungal seeding diseases including Pythium damping off.

Abiotic stresses that cause stand losses are water, temperature, and/or distance to the soil surface. Excess moisture (anytime the soil water content is above field capacity) depletes the soil of oxygen and germinating seed will quickly die in these anaerobic conditions. High temperatures in excess of 90F can induce a dormancy that will prevent germination. This dormancy is not broken until temperatures drop below 50F. Seeding too deep will prevent to coleoptile to reach the surface, and consequently, the first leaf will not get above ground. The seedling will ultimately die although an etiolated and crinkled up first leaf can often be found just below the soil surface. Crusting of the soil can give a similar result. Seeding too shallow or in a seedbed that is very cloddy poses the risk of poor seed to soil contact. In either case, the seed can not in imbibe enough water for germination to start. This seed will stay viable until a rain improves seed to soil contact and adds water into the upper soil layer. A big risk, however, is that the seed will start to imbibe water but that wind and/or warmth desiccate the seed again. This almost always means the death of the germ.

Judging from some of the fields I have surveyed, the shallow seeding and the anaerobic conditions have contributed equally to the uneven emergence we see in many fields. A clue whether shallow seeding contributed to a delay in emergence is to dig up the seedling and measure the distance from the crown to the tip of the coleoptile. You also count the number of leaves of these seedlings and compare this to the better parts of the field. Given the fact that it takes about 180 GDD for each leaf to appear, you can use the difference in development to reconstruct whether the seed lay in dry dirt; the number of days needed to accumulate difference in GDD should be equal to the number of days between seeding and the first rain received after seeding.

June 12, 2009

Now is The Time to Evaluate Stands

The challenging spring in Northwest Minnesota has forced many to seed their wheat and barley under less than ideal conditions and into poor seedbeds. Now is the time to evaluate how well your seeding operation went and what the attained stands are. This is important as the decision about inputs further into the season will depend on the yield potential that is left.

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June 11, 2009

Orange Wheat Blossom Midge: Vigilance is in order

Orange wheat blossom midge (Figure 1) as a wheat pest has been off the front page as a major production problem in NW MN for many years. Populations in the region have been small enough that significant outbreaks and associated yield losses have been of small concern. However, we learned in the mid-90’s that given the right circumstances, this insect can increase its population rapidly and cause major yield losses in a very short time frame.

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June 2, 2009

Blending of Wheat Varieties – II

In a previous article that appeared in Prairie Grains Magazine and the Farm & Ranch Guide blog, I discussed the merits of blending different varieties of spring wheat. The harsh winter and spring have added another dimension to this discussion that demands some attention.

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March 30, 2009

Seeding Rates in Hard Red Spring Wheat

Jochum Wiersma, Small Grains Specialist, University of Minnesota Extension

Each year questions arise about the correct seeding rate for hard red spring wheat. ‘Is a bushel and a peck enough?’ is a question I have been asked more than once.  Research in the mid nineties demonstrated that - on average - an initial stand of 30-32 plants/ft2 maximized grain yield. As planting was delayed past the optimum, the initial stand needed to be increased by ~ 1 plant/ft2 for each week of delay to maximize grain yield. With this number in mind and assuming a stand loss between 10-15% one can calculate a seeding rate using the following formula.

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