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ISSUE  3  May 20, 1999


    The recent heavy rains have resulted in heavy weed infestations and it is obviously time to apply
post-emergent herbicides. Monitoring crop development and correct staging is crucial to insure proper
application timing of these herbicides and pesticides in general.

    Staging small grains, and wild oat, is based on both vegetative and reproductive development. Vegetative
stages are defined by the number of leaves produced on the main stem and the number of tillers on a plant.
All leaves must be counted even if missing.

    Leaf stage is are defined by the number of leaves on the main stem only and can be described in multiple
ways. When using the Haun scale count all fully developed leaves and the next leaf as a fraction of the last
completely developed leaf; using this system the plant in Figure 1 would be in the 4.5 leaf stage. When using
the Feekes scale a new leaf is counted when it reaches one-half the length of the leaf below it; using this
method the plant in Figure 1 would be in the 5 leaf stage.

Insert Figure 1...


    Each tiller produced in addition to the main stem is numbered when it becomes visible. There are two
types of tillers: those arising from a crown leaf axis and those arising from the coleoptiler node. Only tillers
arising from a crown leaf axis are counted when staging. These tillers are also surrounded by a small
membranous structure, called a prophyll, that is useful to distinguish axillary tillers from main stem tillers.
When present there will only be one coleoptiler tiller. Following this system the plant in Figure 1 is in the
two tiller 4.5 leaf stage.

    The flag leaf stage is reached when the last leaf on a tiller has emerged. This is followed by jointing which
begins when stem elongation occurs and the growing point emerges from the soil surface. Boot stage occurs
when the flag leaf sheath becomes visible and continues until head emergence, or flowering.

    A small grain plant enters its reproductive stage when flowering starts. In wheat this is generally 3 days
after heading; whereas in barley flowering occurs just before heading while still in late boot stage.

    There are six developmental stages that occur after flowering in small grains: watery stage, milk stage,
soft dough stage, hard dough stage, kernel hard stage, and harvest ripe. Hard dough is the stage in small
grains when physiological maturity (PM) is reached, and occurs at 30 - 35 percent moisture. Once PM
has been reached the crop will not assimilate additional dry matter into the kernel. Swathing to facilitate
drying and hasten harvest, it should be done at or after this stage.



    Growing Degree Days (GDD) correlates plant development with heat units (daily temperature extremes).
Based on plant emergence and historic temperature trends GDD can be used to predict the time when a
crop will reach a certain developmental stage, however, the actual stage is best determined by visual

    Using heat units to predict plant development functions on the premises that the actual number of GDD
for a crop to reach maturity remains relatively constant across environments even though calendar days
change. Growing degree days are based on daily high and low temperatures and are calculated for one
day as follows: (high temp. + low temp.)/2 - minimum base temp = GDD in degrees Fahrenheit.

    When calculating GDD there are minimum and maximum base temperatures for each crop that are
used when temperatures reach extremes. When the temperature falls below the minimum base temperature
or exceeds the maximum base temperature for the crop in question then the minimum or maximum base
temperature is used in the calculation. For example if you are calculating the GDD for corn when the high
temperature was 78o F and the low temperature was 45o F then the GDD would be (50 + 78)/2 - 50 = 14.
The low temperature of 45o is not used because it is below the minimum base temperature of 50o F for corn.
Table 1. gives minimum optimum and maximum base temperatures for several cereal crops.

    In small grains early growth is the most sensitive to high temperatures and 70o F should always be
used as the maximum temperature until the crop has reached the two leaf stage. Following the two leaf
stage the maximum temperature will be higher.

    Table 1. Minimum base, optimum and maximum growth temperatures in Fahrenheit of several crops
for use when calculating growing degree days.


Growth Temperatures (F)





















    There is good agreement of what minimum base temperatures should be used when calculating GDD
for the cereal crops, however, there is often disagreement of what maximum base temperatures are
appropriate. Use of GDD is based on a model that assumes developmental rate increases linearly to
a maximum temperature and then remains constant. In reality, developmental rate in any crop does
not increase linearly and remain constant but will increase to an optimum rate and then decrease.
Disagreement occurs over the question, should the optimum temperature for development be used
as the maximum temperature when calculating GDD or should the temperature at which development
rate falls to near zero. I prefer to use optimum growth rates as the maximum when calculating GDD,
as is commonly done with corn at 86o F as the maximum temp.

    When calculating GDD in North Dakota the maximum temperature will make little difference in
many years. If the daily temperature rises above 90o F three or four days during the entire growing
season and does not significantly exceed the optimum temperature the rest of the season the total
accumulated GDD will differ little with method of calculation.

    When using GDD to determine crop growth stage accumulation should start the day after planting.
Small grains require about 180 GDD for germination and emergence. A wheat plant requires about
140 GDD for each leaf whether accumulated in four days or ten days, and about 2400 GDD to reach
maturity, which can range from 83-100 calendar days.

    This is important since the number of GDD that have accumulated for your crop will be different
from the total accumulation for the growing season. The North Dakota Agricultural Weather Network (http://www.ext.nodak.edu/weather) provides daily temperatures that can be used to determine the
accumulated GDD. GDD listed for wheat are for the entire season and should be adjusted for planting
date. The maximum temp used by NDAWN is 95o F for wheat and 86o F for corn.

    Growing degree days calculated for crops should not be confused with insect degree days (DD or IDD).
Insect degree days start accumulating when the minimum temperature for the insect in question is reached.

Michael D. Peel
NDSU Extension Agronomist, Small Grains



    Statewide average starting for fieldwork was April 23, while the normal starting date is April 15.
Some seeding was accomplished in many regions of the state but very little in some east central,
eastern and northern regions by mid-May. Looking back in history, the North Dakota Agricultural
Statistics Service - USDA, reported 1979 (twenty years ago) was a wet spring with below average
temperatures and was the latest start on May 13, of recent times.

    Checking back however, yields were fairly good that year, as favorable weather followed and
good soil moisture was present statewide to help crops reach above average potential.

1999 could be a similar year if some sunshine and warm weather soon come our way.

Here are the state-wide results of that late year.

Crop Performances



1979 1994-1998
(5 yr avg.)


26.5 bu

30 bu

Durum Wheat

26.0 bu

28 bu


44.0 bu

55 bu


46.0 bu

50 bu


13.0 bu

17 bu


16.1 ton

18.8 ton


160 cwt

211 cwt


27.0 bu

28 bu

Dry Edible Beans

13.5 cwt

12 cwt

Grain Corn

76.0 bu

85 bu

Silage Corn

6.7 ton

6.6 ton

Sunflower (all)

1357 lbs

1275 lbs


1050 lbs

1282 lbs



    Wet soils and recent rains have led to questions of whether soil crusting will be a problem in area
small grain fields. It’s always best to wait at least 5 days to a week after a crop is beginning to
emerge to determine what percentage of the stand will be established
. If a heavy crust does
occur, a harrow or rotary hoe will be the best option. Before deciding to harrow, be sure that seedlings
are unable to emerge through the crust. Harrowing can break off an emerging coleoptile resulting in more
damage than good.

    If the plant is leafing out under the crust layer and the stand is poor, then breaking the crust
layer is recommended
. A harrow, rotary hoe or any empty press drill has been used successfully to break
up a crust.

    Harrows should be set shallow (1/2 inch deep) and angled back to reduce the potential of going too
deep. Harrowing at a right angle to the rows and driving as slow as possible will also reduce the injury
potential to the crop that has emerged.



    Crops will compensate for stand reduction through tillering, branching or increased head or kernel
size. Listed below is the minimum stand of several crops to avoid major yield reductions when
making decisions on tearing up the field.


Minimum Stand

% of
Normal Stand

Small Grains

8-10 plants/sq.ft.



12-15 plants/sq.ft.



2-2.5 plants/sq.ft.


Canola, Mustard

4 plants/sq.ft.



11-13,000 plants/a


    Even stands below 12 plants per square foot of barley and oats have yielded near normal because
they typically tiller more than spring wheat which typically tillers more than durum. Refer to NDSU
Extension Circular A_934, "Replanting after EarlySeason Crop Injury" for further information.

Duane R. Berglund
Extension Agronomist



    Unexpected stand losses from flooding, late spring frosts, hail, insect or disease damage, herbicide
or fertilizer injury or other causes can put corn and soybean producers in the position of evaluating the
crop for possible replanting. Growers should assess the need to replant carefully and not make a quick
or uninformed decision.

    Especially with low crop prices making it important to hold production costs down, careful consideration
of the replant decision is essential.

    Growers faced with a thin stand should first scout the field thoroughly to determine the plant population
and compare the actual stand to the desired population. Requirements of a crop insurance plan may be a
consideration when considering replanting. Another major point is to compare the original planting date to
the likely replanting date.

    Besides considering crop losses from a planting made at a later date, add in the cost of the replant seed
and other replanting and pest control costs. This information along with yield loss or gain from a later
planting can be used to determine if replanting is worth the time, money and effort.

    Estimating plant population involves counting the number of viable plants in a length of row that equals
1/1000 of an acre in several spots across the field—six to eight spots across every 20 acres is a good
sample. Average these counts and multiply by 1000 to get the plant population.

    Length of row needed to equal 1/1000 acre varies with planting width. In 22-inch rows the length
will be 23.8 feet; in 30-inch rows it is 17.4 feet.

    Actual stand counts will give a good estimate of plant population. Guessing at the population remaining
in the field is more difficult, but the National Crop Insurance Service corn loss instruction book shows that
a 75 percent stand will result in a 10 percent yield loss, a 50 percent stand in 26 percent loss, and a
25 percent stand in a 43 percent yield loss. Yield losses may increase with uneven distribution or large
gaps or skips in the stand.

    Actual stand counts are important in soybeans, as guessing at the remaining population is even more
difficult. Length of row to equal 1/1000 of an acre goes from 87 feet in 6-inch rows, to 52.3 feet in
10-inch rows, and 17.4 feet in 30-inch rows. Yield loss in soybeans may increase if seedlings are
unevenly distributed.

    After determining the plant population, the next step is to compare that population to the target
population of the original planting and determine the cost of the loss field by field.

    Growers need to consider the yield loss incurred from replanting at a later date. Yield losses from
adapted corn hybrids in North Dakota and northwestern Minnesota are negligible until after May 15,
when later planting will result in a shorter than normal growing season. In this northern area yield losses
accumulate rapidly, from 7 percent or more through May 20, 13 percent or more to May 25, and
24 percent or more to June 1.

    With soybeans, yield losses of adapted varieties in the Red River Valley are usually negligible
until May 20. Depending on weather, possible yield loss can be around 13 percent from May 26
until June 9, when late planting losses can be around 24 percent. Soybeans planted as late as mid
June can have a 43 percent or more yield loss compared to more timely plantings.

    Replant considerations vary across farms and locations. Growers need to carefully weigh
potential yields from a replanted crop against current plant stands, and base decisions on
current crop pricing.

Denise A. McWilliams
Extension Crop Production Specialist

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