NDSU Crop and Pest Report

Plant Science

ISSUE 15   August 19, 2004


The 2004 growing season will no doubt go down in the record books as one of the coldest in recent years. Due to the unusually cold weather, the development of the 1.85 million acres (also a record) of corn planted this year is way behind average. The question of the day is, "will corn mature this year?" The answer to that question depends on a number of factors such as when and where the crop was planted, the RM of the hybrid used and how many growing degree days we accumulate between now and the first killing frost. Given that the high today (Aug 10th) will probably be about the same as the long-term average low for the month, the prospects of a delayed crop being pushed by warm weather to the finish are rapidly diminishing. So what are the prospects for the current corn crop in ND?

As I reviewed the available literature, it became apparent that given the diversity of environments and hybrids used in the state, developing a broadly applicable prognosis on how corn will finish this season would not be possible. So in this article I will describe some principles and provide some numbers that will hopefully allow you to make a reasonable predication as to how your corn might fair this year.

Corn growth and development can be fairly closely predicted using growing degree day accumulations. A 75 RM hybrid, for example needs about 1900 GDD from planting to reach physiological maturity, while a 95 RM hybrid requires about 2300 GDD. Much of the difference in GDD requirements between early and late maturing hybrids is related to the number of days from planting to silking and less so in the number of days from silking to physiological maturity. Therefore, the silking date is a useful reference point to start from when evaluating how your current crop might finish.

In general terms, corn hybrids adapted to ND require between 900-1100 GDDs from silking to reach physiological maturity (black layer) or about 55 to 60 calendar days. Some data suggest that the number of calendar days and not just GDDs play an important role in correctly predicting grain development (Lauer, 2004), so both GDD and calendar days will be considered here. Table 1 summarizes the GGD accumulations and date of first killing frost (30 degrees or less) for selected locations in the state for the past five years assuming a August 1 silking date (about half of the corn in ND was reported to have silked by 1 August). I should also point out that we have to be a bit caution in using these data to predict how things will happen this year as GDD accumulations this year to date are significantly less than those of the past five year. Having said that, these GDD accumulations for the past five years suggest that only corn that flowered on or before August 1 in locations with GDD like Fargo (i.e. those further south) has a reasonable chance of reaching physiological maturity. Days from August 1 to the first killing frost varied over the past 5 years and locations from about 50 to 65, suggesting a slightly more optimistic scenario for corn development than GDDs alone (i.e. in most locations and season there are at least 55 days from 1 August to the first killing frost).

For corn crops that will not reach physiological maturity based on the analysis described in the previous paragraph, Table 2 summarizes the GDDs needed to reach various stages of kernel development and the associated moisture content of those stages. As an example of how you might use this table, if we use just GDDs, a corn crop that silked on August 1st in Langdon will receive on average (average of the 5 most recent growing season) only 713 GDDs from August 1 until the first killing frost. This is less than the 900 GDDs needed for the crop to reach physiological maturity and just slightly more than the 700 required for the crop to reach the early dent stage. At this stage(early dent), the moisture content in the grain will be about 50% and the yield potential will be reduced by about 40% (Table 2). Hopefully combining the information on the likely number of GDDs (in Table 1) that will accumulate near your farm with the information on the number of GDDs needed for kernels to develop (Table 2) will allow you to make a fairly good prediction of how your crop might finish.

Summary and recommendations:

Due to the unusually cool growing season, corn development in most of the state is far behind the average for this time of the year. Based on the available data it appears probable that fields that were planted early with an adapted hybrid in the southeastern part of the state (that silked on or before August 1) will likely reach physiological maturity, but will have higher than average moisture at harvest. Fields that silked on or before August 1 in the central region of the state and those that silked after 1 August in the southeastern region of the state will probably not reach physiological maturity by the first frost and will probably be difficult to combine without exceptionally favorable field drying conditions. Yield losses will be modest and test weights will be light. Corn in the central and northern regions of the state that silked after August 1st (particularly those that silked after the first week of August) will likely only reach the dent stage of development. Corn in the early dent stage at the time of the first frost will produce light grain that may be difficult to harvest even after several weeks of field drying. If it appears that your corn crop will only make the early dent stage, you should carefully consider some of the alternative uses of corn that are discussed elsewhere in this report.

Table 1. Corn growing degree day (GDD) accumulations from August 1st to the first killing frost (30B or less) and date of the first killing frost for selected locations in North Dakota, 1999-2003.









Frost Date


Frost Date


Frost Date


Frost Date


Frost Date


















































Table 2. Growing degree or calendar days required from silking for the corn plant to reach the indicated stage, moisture content of the grain and potential yield loss after a killing frost at the indicated growth stage (adapted from Jones and Andersen, 1997; and Lauer, 2004,).



Calendar days

% Grain moisture

% loss after a killing frost

Early dent





Half milk





Black layer





1This range of values applies to hybrids between 75 and 95 RM with the smaller number corresponding to the earliest hybrids and the larger number to later maturing hybrids. Since earlier maturing hybrids tend to be grown in regions of the state where GDDs are accumulated more slowly than regions where later hybrids are grown, the calendar day requirements for early and late hybrids grown in locations of the state where they are adapted are about the same.


Jones, M. And J. Anderson. 1997. Delayed maturity in 1997 - Potential frost damage and other effects in corn. (http://www.ipm.msu.edu/delayed.htm)

Lauer, J. 2004 projected 2004 corn harvest dates for silage and grain.Wisconsin Crop Manager 11(20):132_133. (http://corn.agronomy.wisc.edu/WCM/2004/W154.htm)

Joel Ransom
Extension Agronomist - Cereal Crops



Many of our row crops such as corn, soybean, drybean and sunflower are slow to develop this season due to the cool summer growing season. In many places of the state the growing degree heat units for corn are from 250 to 350 heat units behind normal. The "F word" or frost is on everyones mind these days.

A killing frost is a temperature which kills the plant tissue. If your crops have frost (low temperature) damage it is the result of tissue death.

Critical stages and temperatures for various major crops are described as follows:

Wheat, durum and other small grains: Temperatures below 32 degrees will cause sterile spiklets if the plant is in the late boot through the flowering stage. In the milk stage it will create shriveled kernels. Frozen immature spikes will turn white. After mid-dough stage, temperatures as low as 25 degrees will result in bran damage, some kernel shriveling and possible germination reduction. The bran damage will change test weight and probably will be discounted in the market. Grain that may be saved for conditioning and seed should be tested for germination and vigor.

Flax: is most susceptible during flowering and early boll stage. Immature seeds can be killed by temperatures from 28-32 degrees. After flax reaches dough stage it is more resistant to frost.

Sunflower: is most susceptible at bud and flowering. Temperatures of 28 degrees to 30 degrees can result in damaged buds and sterile sections or rings in the flowering head. After pollination and petal wilting and drying (late R-6) sunflower can withstand temperatures as low as 25 degrees F with only minor damage. If 25 F temperatures occur at the bud stage this will often damage stalk tissue below the bud and seeds will not develop.

Soybean: Easily damaged by light frosts in the 28-32 degree range. Stalks rapidly turn dark green to brown and will not recover. Beans in pods that have turned yellow will mature normally. Green beans in pods that are still green and soft will shrivel. Studies have shown that "yellow pods" sprinkled with some brown are the best clue to physiological maturity. It is also suggested to open pods and check if the beans are shrinking and also look for separation of the beans from the white membrane inside the pod. This further indicates that the soybeans are near physiological maturity. Some green beans will turn yellow after 30-40 days of storage.

Pinto & navy beans: are very sensitive to frost (30-32 degree range). Earlier pods with yellow to brown color are sufficiently mature to escape damage. Late green pods or flowers are easily damaged by frost. Green beans will shrivel but should be left in field until dry in order to separate from mature beans.

Corn: usually is damaged by temperatures in 30 F degree range or less. Corn is usually physiologically mature 50-55 days after the 50 percent silking date. Colder temperatures < 29 F will kill entire stalk. If only leaves above the ear are frosted by a light frost, then kernel development will continue. If entire stalk, ear shank and leaves are frozen, kernel development will cease and soft shriveled corn will result. If corn is at around 35 percent moisture or if a black layer has formed at the base of the kernel the plant is physiologically mature and kernels will develop normally despite frost. Frosted immature corn is best used for silage or fodder.

Other crops:

Most other crops such as buckwheat and proso millet are easily damaged in flower to milk stage. Buckwheat is reported by the Canadians to be very sensitive to frost prior to the mid-dough stage.

Potato tops: will turn black but tubers are not usually damaged by light frosts.

Sugarbeets: are very resistant to frost.

Alfalfa: can withstand light damage to tops but if frozen to ground level will not recover and should be harvested as soon as possible.

Remember temperatures of 32 F degrees at weather stations or farmsteads may result in temperatures of 28 F to 29 F degrees in low lying areas of fields. Also, time of exposure to freezing temperatures will influence degree of damage done. Usually 2 to 4 hours duration of a critical low temperature will cause damage. Two other factors which may influence critical frost temperatures are soil moisture and wind velocity. When soil moisture is higher, frost injury is somewhat reduced due to heat slowly released from the stored heat in the soil within a plant canopy. Wind movement also helps reduce freezing to some degree and is better that a still cold night with no air movement. Cloudy nights are also better than clear nights.

Duane Berglund
Extension Agronomist

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