By Sherri Roberts PAg Weyburn Crops Extension Specialist
Driving around the Province this year, you may see wheat fields that have random white wheat heads in them. What’s causing this phenomenon can usually be figured out through the process of elimination.
Fusarium Head Blight: If only the wheat head and not the stem below the head is white, fusarium head blight is likely the cause. Fusarium head blight hosts include wheat, barley, oat, corn, rye and wild grass species. Fusarium head blight will cause premature bleaching of one or many of the spikelets in a head. The infected spikelets are often sterile and depending on the Fusarium species causing the infection, the grain that is produced can contain high levels of toxins such as DON or deoxynivalenol that can cause health issues in livestock and humans. Grain from blighted heads is often shriveled, light-weight and chalky white or occasionally pink.
Wheat Stem Maggot: Pull on the affected wheat head; if the head comes off and the stem comes out of the leaf sheaf your cause is likely the wheat stem maggot. Use a hand lens to look at the tip of the stem, chew marks may be evident. You may also be able to see a white wiggly worm (wheat stem maggot larvae). Wheat stem maggot is found in wheat, rye, barley, oats, bluegrass, millet, timothy, and a range of other native and introduced grass species. The damage is fairly distinctive - white heads without kernels on a plant that is still green. Typically, only one to five per cent of the heads are affected and they are usually scattered randomly throughout the field. In cereal plants or grasses, wheat stem maggot larvae overwinter in the lower parts of the stems. The larvae pupate in the spring and the adults emerge in June. After mating, the female flies lay small, white eggs, one per stem, near the sheath of the flag leaf, over a period of two to three weeks. These eggs hatch into green-coloured maggots in about five days. There are no insecticides registered for wheat stem maggot or guidelines for timing an insecticide.
Root Rot Complex: If you pull on the affected head and multiple stems along with the head come off in your hand along with some roots, the probable cause is root rot. Root rot will affect the entire plant causing it to turn white.
If your plants are also exhibiting signs of stunting, reduced tillering, empty white heads and premature ripening or death, the cause may be take all (Gaeumannomyces graminis). The disease often occurs in patches and similar to root rots, plants with rotten roots pull easily from the ground. Unlike root rots, fungal growth may be visible on the lower stem of plants infected with take all and roots and culms may exhibit a shiny black appearance.
High temperatures and drought stress may also cause prematurely-whitened heads and the death of some spikelets.
Even though nothing can be done to fix the issue this year, knowing how to distinguish between these issues will assist you in making sound, economically viable decisions in your wheat management program in future years.