Fusarium head blight (Fusarium graminearumor scab) will be a serious problem if humidity and temperatures are high (25 to 30 C) from just prior to wheat head emergence through to head fill. Infection will occur at cooler temperatures, if high humidity persists for longer than 72 hours. Given the high moisture level throughout Manitoba and eastern Saskatchewan, the possibility of this disease being a larger problem than usual this coming season is significant.
Fusarium inoculum comes from two main sources — infected seed and infected cereal residue.
When an infected seed is planted or an untreated seed becomes infected they often die out either just prior to or just after breaking the soil surface. This can be a reason for patchy establishment in the field.
In some cases, seeds will germinate and be infected at the three to four leaf stage via fungal penetration of the crown roots. In many ways, this type of infection is more severe than seedling death because the fusarium fungus now has a host on which to grow and complete its life cycle. When the fungus develops within the plant the stems, the lower leaves of the plant often turn brown and die off. This provides the fusarium fungus with perfect conditions to form reproductive infective spores. Rain splash and air currents move these spores to the canopy where they can attack the exposed anthers, the major point of infection for FHB.
Crop residue is also a major source of inoculum. The overwintered fruiting bodies that survive on the crop residue produce copious spores capable of causing FHB. It is during periods of heavy rainfall and good moisture that the fruiting bodies swell and eject countless spores into the canopy. From there, air currents take the spores up the canopy on to the emerged anthers, again the major point of infection for FHB.
Rather than relying entirely on a foliar fungicide application as your only tool to man-a ge FHB, use preventative measures that will potentially reduce the incidence and severity of this disease. Fusarium can establish in the crop earlier in the season and needs to be managed preventatively. A preventative approach to FHB management includes the following strategies:
1.Get a toxin test done on harvested grain. Many fusarium species are of the non-toxin producing types; F. graminearum and
F. culmorum are the only species of concern in a seed sample.
2.Buy clean seed or seed with the lowest levels of F. graminearum infection possible or buy seed grown in fusarium-free areas. FHB is lowest to non-existent in western Saskatchewan, Alberta and the B.C. Peace region.
3.Treat seed with a fungicide registered to help control the seed borne phase of FHB.
4.Plant as far away as possible from last year’s grain corn. Grain corn stover is by far the biggest source of this fungus and is a particular problem in Quebec, Ontario and Manitoba.
5.Grow fusarium resistant varieties of wheat or barley. There are a several CWRS wheat varieties available, such as Carberry and Waskada and for barley: Cowboy and Dolly. Check your provincial seed guides.
6.Durum wheat is more susceptible to FHB than bread wheats. Some newer varieties of durum wheat could be available for this spring and should be grown in high-risk areas. Examples are Brigade, Eurostar and Enterprise.
7.Follow a strict crop rotation from infested cereal fields.
8.Prevent leaf diseases at flag with fungicides. Vigorously growing plants are more resilient than weaker stressed plants and may resist infection for longer periods.
9.Manage and balance plant nutrition. Again, vigorously growing plants are more resilient than weaker stressed plants and may resist infection for longer periods. In addition, evidence suggests that copper/zinc/phosphate deficiency can slow down the flowering process increasing the plants time at risk.
10.Avoid seeding cereals following a grain corn crop in Manitoba, Ontario and Quebec.
11.Incorporate straw on significantly infested fields.
12.Stagger cereal seeding dates so that fields head out at different times as a means of spreading out the risk of infection in high risk areas. Now only those fields whose flowering coincides with the conditions favourable to FHB infection will be affected while the others will not be affected significantly.
13.Some fields may get significant fusarium infection while others may not because now conditions are unfavourable for disease infection.
14.If risk evaluation indicates a fungicide application is necessary, apply Prosaro, Caramba or Proline (all triazoles), when 75 per cent of the main stem heads have emerged and/or are at 10 per cent flowering.
15.The LATEST effective stage for fungicide application is 50 per cent flowering. Because FHB control/suppression is about prevention, at 50 per cent flowering the plants have been “exposed” for a while. The fungicides have a small amount of “kickback” activity that can stop fungal growth but only to a point. Once significant infection has occurred, the fungicide response is minimal. The products work better by preventing infection by the fungus.
IeuanR.Evans,PhilParkerandMikeDolinski areallsenioragri-coacheswithAgri-Trend Agrology
For more on fusarium management, Alberta’s government offers the following fact sheets.
Fusarium Head Blight of Barley and Wheat: www.agriculture. alberta.ca/publications Agdex 110/632-1
Alberta Fusarium Graminearum Management Plan: www.agriculture.alberta.ca/publications Agdex 110/632-3