White heads in wheat, could it be wheat stem maggot?

The following information is available in the Manitoba Insect and Disease Update for the week of July 27th & posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-update-2015-07-28.html
White heads of wheat (Figure 1) are noticeable in some fields of wheat that should otherwise have green heads still. One possible cause of this is wheat stem maggot.  If wheat stem maggot is the cause, most of the heads will easily slide out of the stem when you pull on them. And if you slit the stems you may be able to see the pale green maggots inside (Figure 2). They also tend to leave frass in the stem that looks like sawdust. In some of the wheat around Carman the white heads are noticeable, but at such low levels that yield loss would be negligible.

Figure 1. White head from wheat stem maggot.



Figure 2. Larva of wheat stem maggot.


This is something that can be very noticeable, because of the way the white heads stand out, but is rarely of economic significance. The are no insecticides registered for wheat stem maggot, nor guidelines for timing an insecticide. So it is worth checking out what is the cause of the white heads, but for wheat stem maggot it is not something to get too alarmed over.
Keep in mind too that there are diseases and environmental factors that can also cause white heads in wheat, so it is not always immediately obvious what the cause is.  More on other causes can be found in the Crop Chatter post “What’s Causing the Bleached Heads in my Wheat Crop?” at http://cropchatter.com/whats-causing-the-bleached-heads-in-my-wheat-crop/
By:  John Gavloski, Entomologist, & Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD
Visit the Insect Pages of our MAFRD website at: http://www.gov.mb.ca/agriculture/crops/insects/index.html


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Importance of Preharvest Glyphosate Timing

Modified from Post Originally Published July 30, 2014

Staging a crop for preharvest glyphosate application for weed control can be difficult when there is variability of crop staging within the targeted field.  To go back to the basics, for wheat you want to apply the preharvest glyphosate when grain moisture of the wheat crop is less than 30%.  In terms of visual assessment, the wheat crop must be in the hard dough stage.  This is when the kernel has become firm and hard and a thumbnail impression remains on the seed (see Figure 1).  Remember….you can’t rely on the color of the field as an indicator.  Walk the field and hand thresh heads to determine kernel staging.

Figure 1:  Kernels at various times during grain filling: a) kernel at watery ripe, b) kernel at late milk, c) kernel at soft dough, d) kernel at hard dough showing loss of green color, and e) kernel ripe for harvest.

Source:  Growth and development guide for spring wheat. 1995.  S.R. Simmons, E.A. Oekle & P.M. Anderson.  Photographer:  Dave Hansen.

So what is special about this 30% moisture content?  At the end of the hard dough stage, the kernel has reached its maximum dry weight and the wheat is therefore physiologically mature, i.e. no more weight is added to the grain.  Therefore, final yield has been determined.

If application of a preharvest glyphosate occurs prior to the 30% moisture content, yield can be reduced, along with quality factors such as kernel weight, test weight and protein.  In addition, early application prior to the recommended timing may result in grain with glyphosate levels above maximum residue limits.  This could have implications depending upon target market.

So in timing an application on a variable field, this will be difficult but remember its likely better to apply when majority of the field is at the recommended timing, or even on the later side, than too early.  Also remember that depending on weather conditions, glyphosate can take up to 2 weeks for optimal weed control. However, under hot, dry conditions harvest could commence is as little as 7 days after application.  So keep harvest timing and weather forecasts in mind as well when planning your preharvest application.

Notes: Do not apply to wheat, or any crops, grown for seed.  Not all glyphosate products are registered for preharvest application on all crop species – always refer to individual crop labels for a list of registered uses and crop species. Check with malt barley or milling oat buyers prior to application to confirm acceptance of glyphosate-treated grain.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist & Ingrid Kristjanson, MAFRD Farm Production Advisor, Morris, MAFRD

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Seeing Leaf Tip Necrosis in Your Wheat Fields?

Updated from Archived Crop Chatter post made June 28, 2013

I have received a few reports over the past couple of days where spring wheat are showing symptoms where flag leaf tips are yellowing and necrotic.  Amir Farooq, Farm Production Extension Specialist from Hamiota, submitted this photo from a field in his area.  He noted the symptoms appeared with the warmer temperatures.

Leaf Tip Necrosis in Spring Wheat, 2015 (A. Farooq)

Leaf Tip Necrosis in Spring Wheat, 2015 (A. Farooq)

Manitoba Agriculture’s Crop Diagnostic lab technician has seen similar symptoms in previous seasons when environmental conditions have caused rapid moisture loss from the leaves, i.e. windy weather combined with warm/hot temperatures.   The result is leaf tip burn or necrosis.

Wind and/or high temperature can result in injury of leaf tips of small grains
Credit: Photo Library of Manitoba Agriculture’s Crop Diagnostic Lab Reports (2009)

Leaf tip necrosis normally progresses from the margins of the flag leaf tip and lower leaves should show some signs of it as well. Note that leaf tip burn caused by wind and/or hot temperature injury can appear similar to the damage of contact herbicides, fungal diseases, viral diseases (BYDV), foliar fertilizer burn or soil salinity.  However, with wind and/or hot temperatures, damage is often limited to the newest, just emerging, leaf tips.  Most reports to date in Manitoba indicate symptoms are on the flag leaf.

Symptoms of leaf tip necrosis can also be observed to some extent in all wheat varieties containing the leaf rust resistance gene Lr34.  The leaf tip necrosis can be more pronounced after cooler weather, such as cooler evening temperatures.

The severity of the leaf tip necrosis is dependent on both the variety and the growing conditions during flag leaf emergence and early grainfill and thus some varieties have a tendency to show a lot more leaf tip necrosis than other.

Unfortunately, there is little information reported in the literature whether this type of damage causes any yield losses. However, the remainder of the canopy has a great ability to compensate for this type of physiological damage. In either case, there is nothing producers can do to avoid or alleviate the symptoms.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

Source: “Flag Leaf Burning: Hot Weather and Leaf Tip Necrosis in Wheat” by Jochum Wiersma, University of Minnesota


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2015 Fusarium Head Blight Risk Maps On-Line!

The Fusarium Head Blight Risk Map webpage will be available at http://www.gov.mb.ca/agriculture/crops/seasonal-reports/fusarium-head-blight-report.html
This website will be updated daily Monday to Friday with the current risk maps.
Please refer to the risk maps to help decide risk to your crop, based on heading and flowering stage of your crops.  Remember the disease triangle – the existence of a disease requires three factors: the interaction of a susceptible host, a virulent pathogen, and an environment favorable for disease development. Therefore, although a risk map may show High to Extreme risk levels due to environment, disease risk may be low if the wheat crop is not at the proper stage for infection.
Depending on the weather, wheat can move through the following stages of development below in as little as five days to more than a week.  So if a fungicide for FHB suppression is planned, scout your fields daily to ensure proper timing.
Wheat Development Stages
Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD & Holly Derksen, Plant Crop Pathologist, MAFRD
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Historical Seeding in Progress in Manitoba – First Week of May

Producers who participate in AgriInsurance provides seeding date information to Manitoba Agricultural Services Corporation (MASC).  This dataset provides us a historical perspective of when seeding has taken place in the past.  Seeding date data information is broken down into a week:month format, i.e. 1:05 is Week 1 in the 5th Month (May).  So 2:05 is Week 2 in May, and so on.

Each week is then categorized dependent on the day of the week in which the month starts.  So if Week 1 starts on a Sunday, there will be 7 days of seeding captured in Week 1.  However, if Week 1 starts on Friday (like we have in 2015), there are 9 days captured in Week 1.  Confused yet?  Essentially, each year will have a different number of days captured in each weekly timeframe, varying from 5 days up to 12 days.  However, the data still provides good reference points to seeding progress in Manitoba.

In Table 1, cumulative seeding progress to the end of Week 1 in May for six crop types is provided.  The last five year (2009-2013) average cumulative seeding progress is noted, along with what was seeded in the same timeframe in 2014.   Please note that data is for final insured crop in the ground.

Table 1:  Seeding progress (%) in Manitoba by end of Week 1 in May (1:05).

End of Week 1 May Seeding Progress

Based on the May 11th Manitoba Crop Report, overall seeding progress is estimated at 55% complete.  There isn’t a provincial breakdown provided of seeding progress by crop type, but in looking at each region, seeding of spring cereals is ahead of the 5-year average of 2009-2013, and well ahead of 2014!

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD 

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Should Manitoba growers be worried about the early reports of stripe rust in Alberta?

Submitted by Holly Derksen, MAFRD Field Crop Pathologist

Probably not.

Stripe rust has been reported in winter wheat fields in Alberta this spring (http://www.producer.com/2015/04/stripe-rust-in-alberta-winter-wheat/). This could indicate that the fungus overwintered on the crop. Overwintering of stripe rust in Canada also occurred in 2011, a year where there were measurable losses from stripe rust in both winter and spring wheat in Alberta and parts of Saskatchewan. That year a breakdown in resistance in the 2010 planted winter wheat crop led to higher infections leading into 2011. Persistent snow cover allowed for good overwintering conditions and a cool, wet spring favoured spread and infection of the stripe rust fungus. Growers in Alberta are being encouraged to vigilantly scout for the spread and proliferation of this disease this spring, especially in varieties that do not carry any resistance. Reports from Montana and Oregon have also indicated an early outbreak of stripe rust with fungicide applications being recommended in many cases.

In Manitoba, the majority of our inoculum blows in from the central US states by what is known as the “Puccinia Pathway”. Progress of this inoculum, as well as other cereal rusts, is documented on the USDA’s website (http://www.ars.usda.gov/News/docs.htm?docid=9757). To date, there have been a number of stripe rust detections with the furthest north located near Omaha, Nebraska. There have been no reports of stripe rust in Manitoba, however, inoculum can move quickly so growers should continue to scout their winter wheat and newly emerging spring wheat for early infections. The ideal timing for a fungicide application for protection against stripe rust in wheat is at the flag leaf stage. If rust infections are only noticed later in the year, especially past the flowering stage, a fungicide is likely unwarranted as the yield effect will be minimal.

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Why are my Wheat Heads Dark?

There have been a number of reports of ripe canola looking black or, in some cases, sooty. We are hearing the same thing in wheat.  So what is the cause?

wheat melanism 005

Wheat affected by melanosis (photo by MAFRD’s Crop Diagnostic Lab)

Holly Derksen, MAFRD’s Field Crops Pathologist, recently did an interview with RealAgriculture.com on the topic of “Black Chaff, Melanosis, Glume Blotch: The Causes of Darkness on Wheat Heads at Harvest“.  Learn more by listening to Holly’s interview with Kelvin Heppner of Real Agriculture.com: http://www.realagriculture.com/2014/08/black-chaff-melanosis-glume-blotch-darkness-wheat-heads-harvest/

Submitted by:  Pam de Rocquigy, Provincial Cereal Crops Specialist, MAFRD



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Manitoba Insect & Disease Update – Week of July 14th to 18th

A Manitoba Insect and Disease Update for the week of July 14-18, 2014 has been posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-update-2014-07-16.html

Highlights include:

  • Flowering canola crop needs to be protected against white mold since there have been many rain events lately.
  • Phytophthora root rot of soybean has started showing up, especially in flooded fields.
  • Early lesions of sunflower rust have been found in a 2nd location.
  • Alfalfa weevil levels were quite noticeable in some alfalfa fields, but they are now starting to pupate, so levels are declining.

Submitted by: John Gavloski, Entomologist & Vikram Bisht, Pathologist, MAFRD

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Seeding Date Relationship to Crop Yield

One of our most used extension messages is seed early!

In a year that is later, this may cause some concern that seeding into the second half of May is not going to have good crop yields. Typically seeding earlier does normally translate into higher yields, but good yield potential remains when seeding throughout the month of May, provided you don’t compromise the seeding operation.

Things Other than Seeding Date That Influence Yield:

  • Using clean seed with high %germination
  • Applying the appropriate fertilizer nutrients and rates to support yield goals
  • Seeding for a good plant stand – taking in account TKW, %germination and seed mortality!
  • Seeding into a firm seedbed
  • Seeding into soil warm enough to result in quick germination and emergence
  • Timely weed control
  • Timely fungicide application if needed
  • Appropriate harvest operation timing

2005-13 Seeding Date x Yield

Table 1: Crop Yield Response to Seeding Date (2005-2013)

Source: MASC – Harvested Acreage Report (2005-2013)

For more information see MAFRD website post “Crop Choice Considerations in a Delayed Year”  http://www.gov.mb.ca/agriculture/crops/production/crop-choice-in-delayed-year.html


 Contributed byAnastasia Kubinec, MAFRD Oilseed Crop Specialist



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What are minimum germination temperatures?

Soil temperature is a useful gauge for timing when crops are seeded.  Table 1 shows the minimum germination temperatures for various crops.  These values should be regarded as approximate since germination depends on several factors.  If the soil is too cool, germination can be delayed which can result in uneven or inadequate seedling emergence.

How do I measure soil temperature?

Determine how deep you will be seeding. Then place your soil thermometer at that targetted depth. Take two measurements throughout the day: one in the morning (8am) and one in the early evening (8pm) . Average the two readings to determine the average soil temperature.

MAFRD recommends that you take readings for two to three days to establish a multiple day average, and reminds you to measure temperature in a number of locations in the field, to account for field variability.  Still not sure, see soil temperature data for various locations across Manitoba is available from MAFRI’s Ag-Weather Program:  http://tgs.gov.mb.ca/climate/SoilTemp.aspx.  This can be used as a guideline for an area, but in-field measurements are going to tell you what is actually going on in your field!

Table 1: Minimum Germination Temperatures for Various Crops

Crop Temperature (°C)
Wheat 4
Barley 3
Oats 5
Corn 10
Canola 5
Flax 9
Sunflower 6
Edible Beans 10
Peas 4
Soybeans 10

Sources: North Dakota StateUniversity Extension Service, Alberta Agriculture & Rural Development and Canola Council of Canada

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