Be Alert for Frost Injury in Wheat!

A significant frost event occurred through much of southwestern Ontario during the evening of May 27 (morning of the 28th). Temperatures as low as minus 7oC were reported in Nairn but for most areas the temperatures were not as extreme but as seen in the overview map of southwestern Ontario by Weather Innovations Network (WIN) from Chatham, temperatures in the minus 1 to minus 3oC were widespread. The impact on the developing corn and soybean crop is expected to be minimal but there has been concern surrounding the winter wheat crop, in particular those early planted fields which are nearing heading/flowering. The winter barley crop however will most likely be at the highest risk, as it was headed and pollinating.

OMAFRA , agribusiness along with Dave Hooker (U of Guelph, Ridgetown Campus) have been assessing the situation and we have been unable to find any injury to date. While this is not a guarantee, it does bode well. The next thing growers/scouts should look for is pollen shed. Damaged plants/areas will not extrude anthers, thus no pollen will be seen on heads or the ground. If you remember last spring, this was the situation which occurred in the southern US. If you find this anywhere, please contact Peter Johnson: peter.johnson@ontario.ca

Figure 1. Minimum Air Temperature durng the Evening of May 27 - 28 in the southwest.

Although today's winter wheat varieties can tolerate very low temperatures during the winter, their ability to tolerate (hardiness) low temperatures decreases significantly when growth continues in the spring (Figure 2). When the frost (cold injury) occurs is very important (Table 1). Injury during the tillering stage does not normally impact yield since the growing point is protected (below ground).

Figure 2. Wheat Resistant to Freeze Injury.

Table 1. Temperatures that cause freeze injury to wheat at various growth stages.

As the wheat plant moves into the stem elongation (jointing), boot, flowering and filling growth stages, low temperatures can result in significant damage since the growing point (head) is no longer protected. It is in these most advanced wheat fields in the southwest which has us concerned. As mentioned earlier the early indications bode well but we need to keep scouting the heads and closely look for a normal pollen shed.