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.
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