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.
By: John Gavloski, Entomologist, & Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD
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Based on archived post from September 2014
In 2012 and 2014 bleached, white heads showed up in wheat, barley, and oat fields across Manitoba. It appears the bleached heads are making a reappearance in 2015.
White heads caused by root rot. (Image: Kansas State University)
There are a number of things that could be the cause:
- Insect damage – One of the tests to see if a white head is potentially wheat stem maggot is to try to pull the head out of the stem. If the head pulls out easily, it could be because a larva of wheat stem maggot has severed the stem, resulting in the head turning white. Larvae may be present above the top node. See Manitoba Agriculture’s website for more information on wheat stem maggot: http://www.gov.mb.ca/agriculture/crops/insects/wheat-stem-maggot.html
- Root rot – infected plants will generally pull free from the soil without much resistance. In years where the plants are under stress due to either lack of moisture or excess moisture, a loss of root tissue from root rots will have a much larger impact.
- Fusarium head blight – if seed is produced they are smaller, chalky, and can be shrivelled. Pink or orange mycelium may be visible at the base of the glumes.
- Aster yellows – infected plants show white heads, but green stems and seemingly healthy root systems.
- Environmental stress – high temperatures, bright sunlight, and hot winds can results in white, empty heads.
Additional information can be found in the July 27, 2012 issue of Manitoba Agriculture’s Manitoba Insect & Disease Report available at: http://www.gov.mb.ca/agriculture/crops/miu/2012/2012-07-27/report.pdf
Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture
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