2 Common Agronomic Problems
Although small grains are adapted to a wide range
of climates and soils, they are sensitive to various agronomic and environmental
conditions. Among factors to consider when evaluating small grains are
temperature, rainfall, humidity, sunlight, fertility, herbicide carryover,
insects, and diseases. Most of these factors cause the same kinds of reaction
and general appearance in small grains. Under stress, the leaves of small
grains will generally turn yellow, brown, red, or purple. It is very important
to be able to eliminate certain factors in order to pinpoint others as
the real cause of observed problems.
Different varieties and kinds of small grains may
respond in different ways to agronomic and environmental conditions. In
general, early maturing varieties tend to be more susceptible to problems,
while mid- to late-maturing varieties tend to be more winterhardy and benefit
from late-season showers. However, late varieties may not be as suitable
for double cropping.
Since small grains display similar symptoms in reaction
to many different problems, careful attention is needed to identify the
causes of any problems. A general knowledge of how small grains grow is
essential (See the Feekes Scale of Wheat Development, Figure
1). Keep records on temperature and rainfall; maintain field histories
with crop rotation and pesticide applications. Always have soil tested
before planting any crop and use results from soil tests and tissue analysis
to provide adequate nutrition. Remember, no one can identify a problem
without scouting thoroughly.
Environmental Conditions
Temperature. Small grains grow well between 50' and
75' Fahrenheit (F.). High temperatures can slow growth, reduce yields,
and cause insect problems. Depending upon the status of certain agronomic
factors, temperatures below freezing (32' F.) can cause some damage, and
temperatures below 15' F. can kill. A sudden change in temperature, from
75' F. during the day to 30' F. at night, for example, can cause more damage
than gradual change. Symptoms of cold damage will vary depending upon the
type of grain, variety, fertility level, and the growth stage of the small
grain (Figure 2 and Figure
3). Generally, more damage will occur in the later growing stages.
For example, the heading stage (G.S. 10. 1 to 10.5) would suffer more damage
than the boot stage (G.S. 10) and the boot stage would suffer more damage
than the jointing stage (G.S. 6 to 8). Symptoms of cold damage include
dark brown to black discolorations on the lower stems. Leaves will show
a burning effect similar to nitrogen bum and may have brown tips that begin
to twist. Split the stems open and look for dark areas around the nodes.
Damage to the heads will cause a bleached or white-colored appearance over
the entire head or just the tips. It will take about four or five days
for conclusive visible symptoms to appear. Rye is the most winterhardy
small grain followed by wheat, triticale, barley, and oats.
Rainfall and Humidity. Small grains (except oats) do not require much
water for good growth and high yields. Rainfall of 25 to 30 inches will
produce adequate yields. However, 70 percent of the water is needed in
the actively growing stages (jointing through dough, stages 7 to 10.5).
Too much water early in the season will cause leaves to turn yellow, stunt
growth, and, in severe cases, reduce yields. Too much rain and high humidity
will also contribute to a high incidence of diseases such as powdery mildew
and glume blotch. Small grains very seldom show signs of drought. When
water is needed, leaves will begin to turn yellow or reddish purple and
twist or fold as in corn.
Sunlight. Fields of small grain often change appearance for better
or worse. Small grains will appear normal when sunlight is adequate
for photosyntheses. During long cloudy periods, however, small grains
sometimes grow poorly or develop off colors.
|
|
|
| Too Wet - Precipitation of 20 to 30 inches is adequate if well distributed. More than that can cause problems. | Severe diseases; slow growth; late planting, topdressing and weed control; poor test weights |
| Dry (but not droughty) | Little or no disease; good yields. Management usually on schedule. |
| Too cold -(below 20o F. in winter or below 40oF. in April and May) | Reduces disease development; crop injury may occur if at wrong stage of growth; alters some pesticide results. |
| Too Hot - (above 60o F in fall and winter; above 80o F in April and May) | Rapid growth and respiration resulting in low yields; optimum for leaf rust, but reduces mildew and growth of winter annual weeds; poor test weights. |
| Cool and Wet - (40o to 50o F. fall/winter;60o to 70o F. April/May) | Moderate diseases; some delay of management practices; slightly better than average yields. |
|
Cool and Dry - (38o to 48o F. in fall and |
Ideal conditions for excellent crop and high yields. winter; 60o to 70oF. in April/May) |
| Hot and Wet - (over 30 inches of precipitation; temperatures above 50o F in fall/ winter; above 80o F. in April and May) | Severe insect and disease problems, poor yields, Disaster for small grains. |
Agronomic Conditions
Fertility. Small grains need adequate nutrients
to produce good yields. Most nutritional problems in small grains will
be caused by low pH, high pH, or nutrient deficiencies of copper, manganese,
or sulfur (See Figures 4 to 9; links at bottom of page). In general, nutrient
deficiency problems can be corrected by applying the nutrient before or
at planting or during the growing season as a foliar spray. For more information
on fertility refer to: Small Grain Production Guide; Soil Fertility
Management, AG 419-4.
Herbicide Carryover. Several classes of herbicides
such as dinitroanihnes, triazines, and some amides can kill or cause damage
to small grains when residues remain from a previous crop.
If the plants live, conditions should improve with each rain. Of the small
grains, oats are most likely to be susceptible to herbicide injury, followed
by barley, wheat, and rye. Triticale, when showing symptoms of herbicide
injury, should react in a manner similar to other small grains.
| Agronomic Problem | Most frequently occurs | Symptoms |
| Low pH | Stunted plants; poor root system | |
| Copper deficiency | In coastal plain and organic soils | Yellowing on leaf edges; twisted leaf tips; grayish-green or yellow color; "burning" of leaf tips; death. |
| Manganese deficiency | When pH is high | Light yellow-greenish color; localized spots; circular patterns in field. |
| Sulfur deficiency | In sandy soils | Similar to manganese symptoms. Growth retarded because plant cannot use nitrogen. |
| Herbicide injury | Following dinitroanilines, triazines, and some amides. | Yellowing; stunted growth; poor root system; roots stubby, not fibrous. |
Figure 4 Copper deficiency
symptoms are similar to those of cold injury.
Figure 5 Plants with moderate
and severe copper deficiency.
Figure 6 Manganese deficiency,
field view.
Figure 7 Manganese deficiency;
normal leaf
Figure 8 Sulfur deficient
plants and normal plants
Figure 9 Sulfur deficient
plants are light green, whereas those with normal sulfur are dark green