The temperature just before and right after spraying wheat with herbicides determines whether you damage wheat or not
If the temperature gets down to 3 to 5 C you may injure wheat. The extent of this injury depends on how good the wheat plant is growing after you spray. Most times the wheat looks poorly but grows out of it. The affect depends on the herbicide and can range from leaf burn to twisted plants. Again I don't think there is a real yield loss. But to be safe, wait for 48 hours after these low temperatures before your spray.
The wheat plant will try to break down the herbicide in the few hours after application. If it is sunny and warm, say 10 to 15 C, after spraying there is less chance of damage than if it is cool (5 to 10 C) and overcast. The addition of some fungicides can make the damage appear worse than it really is.
The final decision to spray will depend on weeds present. Winter wheat offers a unique opportunity to prevent weeds from setting seed and increasing the weed seed bank. Controlling weeds now should help harvest.
Currently many fields have the disease Septoria and Powdery Mildew. Rain decreases the damage from Powdery Mildew but increases the spread of Septoria. Many growers combine weed control with early disease control. Ask your inputs supplier for details. BF