Don’t assume because there is frost (or snow) on the ground, that your emerging crop is dead.
With the drop in temperatures in the past couple of days and the risk of frost on the May long weekend there are a few things to keep in mind if the mercury dips below 0 C. The temperature is the instigator for causing frost, but whether it is -0.1 C or -4 C the damage inflicted is highly influenced on these other factors.
A short frost of less than two hours might not cause much damage if frost is light (above -1 to -2 C) and depending on the crop type and if the staging is tolerant, conditions wet and crop has become acclimatized.
Crops like canola are more sensitive to a short but harder frost vs. cereals. Damage can be variable in field and across area.
Whether frost is light or hard the longer (more than two hours) the negative temperatures the more time for damage to happen. Tolerance by crop type varies.
Other Environmental Conditions
Cloudy and wet prior to a frost: Cool temperatures slow plant growth and ‘hardens’ plants off, which will help them tolerate a frost. Also wet soil helps buffer the cold air effects on the plants. Wet soils also change temperature slower than dry soils.
Sunny and dry: The combination of a dramatic drop in air temperatures when plants are actively growing then a brilliant sunny day after the frost event is where we have seen the most damage. Scouting after the frost (24 and 48 hours) is very important though to assess extent and percentage of field injury.
Field trash cover: Increased trash in fields was seen to increase frost damage on very susceptible crops in the 2009 June frost.
Spring Cereals: They are more tolerant than other crops types and can tolerant temperatures as low as -6 C as the growing point is below ground until the five leaf stage.
Winter Wheat: It can withstand very low temperatures for a short period of time (-11 C for less than 2 hours) up until the tillering stage.
Corn: When smaller then V5, it will recover from light frost as the growing point is below ground. Leaves will probably be killed, but plants will recover if the growing point all right.
Oilseeds: Environmental conditions impact frost severity on susceptible canola and flax cotyledons. Resiliency increases at the three to four leaf stage in canola or the second whorl flax. Sunflowers are fairly tolerant up to the V4 stage.
Pulses: Peas are most tolerant than soybean. Edibles bean are very susceptible even before emergence. Field pea crops are rarely lost to frost. Soybean are more sensitive, but the smaller the soybean plant the more tolerant they are. From emergence to cotyledon soybeans can withstand short light frosts.