• A killing frost occurs when temperatures reach 28⁰F or less for two hours or more.
• When corn is at physiological maturity, kernels typically have about 30-33% grain moisture.
• Corn that reaches 35% grain moisture when frost occurs, will have few problems with dry weight, yield or storage.
• Corn at half milk-line with frost damage to leaves loses approximately 5% yield potential, while frost damage to leaves and stalks at this time will result in 8-12 % yield loss.
• Frost damage that occurs on soybeans prior to physiological maturity (R7) can result in lower oil content, more elongated and smaller than normal seeds when dry.

Fields that were planted late this season as a result of the wet spring we experienced, are set to mature later than normal and could be subject to frost damage.In fact, isolated instances of frost have already occurred within our core geography of the Midwest and Ontario.So… what happens to the grain quality and yields of crops affected by frost?Whether a light frost or a killing frost occurs (where temperatures reach 28⁰F or less for two hours or more), yield can be impacted, and grain quality can be compromised.

Corn is physiologically mature at around 30-33% moisture (range 25 to 36%).Corn must be above 35% moisture before a killing frost can cause problems with dry weight, yield or storage conditions.Corn that is at half milk-line and experiences frost that damages only leaves, but not the stalk, can lose around 5% yield potential.If both leaves and stalks are damaged at this stage, the potential yield loss increases to 8-12%.Corn that is killed by frost before physiological maturity usually has scattered kernels on the ear that have light test weight and are subject to damage during harvest or handling.Assessment of frost damage is best done a few days after the freeze occurs. Damaged leaves and stalks will appear water soaked and feel soft at this time.

Soybeans are physiologically mature at the R7 growth stage (one mature color pod on the main stem), but some beans remain green at this stage of growth.Basically, if there is any green left in soybeans at the time the killing frost occurs, some quality and harvest issues may be experienced. Soybeans that have been damaged by frost usually dry slower in the field, and field drydown should be allowed when possible.Field drydown allows the green color to disappear and can result in fewer quality issues over rushing the harvest of these immature beans.Depending on the degree of greenness left when they were killed, frost-damaged soybean plants will be tougher to cut and thresh.Keep in mind that there are some other factors that may influence soybeans staying green and frost damage is not always to blame.

Moisture levels have been reported to sometimes be higher in frost-killed soybeans than portable moisture meters can detect.Oil content of immature, frost-killed soybeans is often significantly lower than in fully mature soybeans.Processors will sometimes reject these soybeans based on oil content.Perhaps the most noticeable effect of early kill of soybeans is that the beans are often more elongated and smaller than usual, and the beans will sometimes shrivel as they dry. Since green color often fades in immature soybeans over time, some producers will elect to store the beans for several weeks before marketing.It is important to remember that immature soybeans could have quality issues in storage.These soybeans should be checked often for moisture and condition.