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ISSUE 10  July 5, 2001

 

OILSEED SUNFLOWER DEVELOPMENT

Sunflower growth and development responds to heat units similar to corn and several other crops. The base temperature of 44E F is used to determine Growing Degree Days (GDD). GDD formula = [(daily maximum temperature + daily minimum temperature)/2] - 44 degrees F.

In the table below research data was collected at the Carrington Research and Extension Center over a number of years on sunflower stage of development and heat units.

Oil sunflower development by days and growing degree day (GDD) units, 1994-95, Carrington Research Extension Center*

Sunflower stage

Average days and GDD units increase from previous stage

Average days and GDD units accumulated from planting

 

days

units

days

units

VE

10

167

10

167

V4

10

182

20

349

V8

8

196

28

545

V12

6

145

34

690

V16

5

82

38

772

V20

6

99

44

871

R1

2

49

46

919

R2

15

333

61

1252

R3

6

142

67

1394

R4

4

99

71

1492

R5.1

3

54

73

1546

R5.5

4

77

77

1623

R6

8

158

84

1780

R7

12

272

96

2052

R8

9

159

104

2211

R9

15

259

119

2470

Planted on May 25 in 1994 and May 23 in 1995. Growing Degree Days were averaged over 5 hybrids each year and 5 plants per hybrid per plot were observed.

GDD units/data for 2001 can be found on NDSU’s Extension Web site under Ag weather (NDAWN). Just click on The Daily Observation tables and maps section.

 

TILLERS IN CORN

When farmers see extensive tillering in their corn hybrids, they often express concern that the tillering will have a detrimental effect on crop performance. This was the prevailing view in the early 1950's when it was widely believed that tillers if allowed to develop would "suck" nutrients from the main plant and thereby reduce yields. As a result, tillers were more frequently referred to as "suckers" and many farmers actually walked their corn fields to remove tillers. However, since then research has shown that tillers usually have little influence on grain yields and the effects they do have are generally beneficial. So what causes tillers to appear?

Tillers are lateral branches that form at lower, below ground nodes. Although tiller buds form at each below ground node, the number of tillers that develop is determined by plant population and spacing, soil fertility, early season growing conditions, and the genetic background of the hybrid. Nearly all hybrids will take advantage of available soil nutrients and moisture by forming one or more tillers where stands are thin in the row or at ends of rows. Tillers are most likely to develop when soil fertility and moisture supplies are ample during the first few weeks of the growing season. They are usually visible by the 6-leaf stage of development. Hybrids with a strong tillering trait may form one or more tillers on every plant even at relatively high populations if the environment is favorable early in the growing season.

One often asked question is: Do tillers deprive the main plant of nutrients?

A number of research studies have been conducted to determine "tiller-main plant relationships." Defoliation experiments in the 1930's revealed that defoliated plants that had tillers yielded nearly twice as much grain as defoliated plants that had no tillers. These results suggested that a connection existed between the tiller leaves and the main plant that allowed sugars produced in the tiller leaves to be moved to the ears on the main plants.

More recent research reports have found that there is little movement of plant sugars between the main plant and tillers before tasseling. However, after silking and during grainfill, a substantial amount of plant sugars may move from earless tillers to ears on the main plant. When there are ears on both the tiller and the main plant, little movement of plant sugars occurs. In this case the main plant and tiller act independently, each receiving sugars from their own leaves. The nubbin ears, which tillers may produce, therefore have no impact on the ear development of the main plant as was once thought.

Should tillering be ignored?

If a particular hybrid shows excellent yield potential and also produces extensive tillers under some growing conditions, it should not be avoided. However, excessive tillering may indicate problems with stand density and plant distribution within the row. If tillering is associated with row gaps and less than optimal plant populations, these are the conditions which need to be corrected to ensure optimal yields rather than selection of the hybrid. Tillering is also caused by the fungal disease "crazy top", which also produces a range of other symptoms. Such tillering is a disease symptom and not beneficial to plant performance.

Duane R. Berglund
Extension Agronomist
 
dberglun@ndsuext.nodak.edu

 

SCOUT CORN FIELDS TO ELIMINATE WORRY

Corn is now entering the rapid-growth phase that can weaken the corn stalk even more than was seen in the early vegetative growth stages. Also, the number of kernels per row on each ear will be determined from V12 through V14 with rapid dry matter accumulation setting the yield potential for each plant. Herbicide applications should be over for most fields, unless corn is behind due to late planting. Scout weekly for disease, insect or physical plant damage up through tasseling (less intense scouting can commence after tasseling - every two weeks).

Common corn rust thus far has been minor. The cinnamon-brown circular-to-elongated pustules (blister-like growths) can occur on any above-ground plant tissue. Rust thrives in moderate to cool temperatures and high humidity. Luckily, this disease rarely causes economic loss.

Northern corn leaf blight will develop with long, elliptical, gray-green lesions on the leaves that will become tan-brown. Infection spreads from the lower leaves, up the plant. High humidity and moderate temperatures favor the disease.

High winds and hail in some locations earlier this season may also spell head smut trouble. The corn seedling was infected when damaged and the disease systemically developed with the plant growth. Tassels of affected plants often show the affects. Tassels may not develop (in a sporadically pattern) across the field, being replaced instead with a mass of leaves or the tassel may be replaced by a black, smutty mass which will rupture and release spores (to provide more spores to be harbored in the soil for later years when conditions are ideal). In some cases, ears may be completely replaced by similar smut masses or an ear may only produce a few kernels. Hot, dry soil at corn seedling stage favors infection so perhaps this problem will be low in prevalence as it usually is low.

However, crazy top or corn plants with excessive tillering or rolling/twisting of newer leaves often is more prevalent when young plants were under flooded conditions (often appearing in low areas). In this systemic (but usually small incidence) disease, the tassel can also become a mass of leaves, as can the ears. However, these leaves are often narrow, thick and appear "strap-like." Sometimes with crazy top over-sized plants will develop and can be easily spotted in fields. This disease is actually only one of numerous downy mildews that may attack corn.

Many of the stalk rots that may be harbored in corn are not expressed until the plants reach maturity. However, stalk rots caused by several fungi and sometimes bacteria organisms can contribute to weaken stalk strength. Visual identification without destroying plants in the field in order to split stalks to observe early, interior signs is very difficult. Often only a wilting of plants (sometimes very minor) may be seen. Later, infected plants may show leaves that are just barely "frosted" with a gray color and may then progress to definite ears drooping and the outer rind of the corn plant's lower stalks may turn brown. Any fields with stalk rot will have to be harvested early to reduce grain losses.

Also while scouting, watch for late-appearing herbicide injury symptoms. Observe surrounding fields as well as your field's conditions and the season's problems with other probable causes in mind above and beyond herbicides before making a hasty guess on the problem. Many environmental conditions as well as environmental by hybrid interactions can mimic drift or post-application injury conditions. Also, review and analyze any symptoms against any previous herbicides used prior to the current cropping season. Corn plants frequently outgrow the effects of herbicide injury and final yields may not be reduced, so carefully evaluate each situation in your fields.

Insects must also be scouted for now in corn. Often damage from insects is difficult to define and identify. It is not unusual to find insect damage but then to not find any of the suspected insects! Carefully consider economic thresholds of damage before treating and definitely consider if timing is appropriate to give control by spraying. Watch corn for aphids this year, as number have been large in other crops in many areas. Armyworms have also made an appearance in locations. Corn borer numbers appear down this year, but more time is needed to determine if the recent surge in moth flights will result in any larvae that are detrimental. Flea beetles can feed on corn and while often only leaving a "scratch mark" on corn can also be the primary vector of bacterial wilt of corn. Many other insects can contribute to problems in corn.

Nutrient deficiency can be accentuated by poor root development and unfavorable soil conditions (such as water-logged or compacted soil). Nutrient deficiencies are very difficult to diagnose. Soil and plant analysis can help in identification and determination of the cause of these problems.

Scout your corn fields regularly in order to eliminate worry about the crop. Check various regions of individual fields so that you periodically see most of each field.

 

SOYBEAN DIAGNOSTICS FROM V5 TO R1

Many of the soybeans across the Valley are beginning to bloom; however, if the beans are just into this stage or have not yet initiated flowering consider the following symptoms to determine problems in the field.

A. Soybean plants have leaf or stem damage:

1. leaf and/or stem damage

a. leaves are physically torn but show no insect, disease or herbicide injury · hail damage · wind damage · wildlife or livestock feeding

b. leaves show insect feeding/damage· foliage feeding insects present--compare damage to probable insect· leaves with narrow silver to light brown areas along the major veins or over the whole leaf--thrips · leaves yellow, may wilt, some plants may die but insect damage is definite--white grubs, wireworms, nematodes (not prevalent in ND), lesser cornstalk borer · leaves yellow speckled, plants may be stunted with webbing and/or mites under leaves--spider mites · leaves may or may not show damage, plants may be broken off at ground level-three-cornered alfalfa hopper, lesser cornstalk borer · leaf petioles collapsed and leaves hanging-three-cornered alfalfa hopper · terminal of the stem showing feeding damage and hanging from the plant-corn earworm, cutworms· stem girdled or having a dark ring at or above the soil line--three-cornered alfalfa hopper (also check for hail damage or dinitroaniline herbicide damage) · stem tunneled into at or below the soil line--lesser cornstalk borer ·stem snaps off at base when plant is bent or blown over--three-cornered alfalfa hopper, lesser cornstalk borer (also check for hail damage and dinitroaniline herbicide damage) · leaves wilted, dead or dropped--lesser cornstalk borer, white grubs, wireworms · top or leaves or underside of leaves appear silvered or speckled (plants may also be stunted)--thrips (silver streaks), spider mites (yellow mottling) · narrow yellowing along the leaf margins with leaf curling--potato leafhopper

c. leaves show yellowing, followed by browning of leaf margins and possibly plant death--triazine injury

d. leaves wilted, dead or dropped (particularly in a circular pattern in the field)--lightning

e. stems or leaves show discoloration or other disease symptoms · leaves have a dead, ragged appearance after a hard rain or wind but appears more than weather related--bacterial blight · white fungal growth and sclerotia (large, black, irregular structures inside the stem)--Sclerotinia blight (white mold) · lower stem discolored--Phytophthora rot, Rhizoctonia, Fusarium, black root rot (will show discolored stem with reddish fruiting bodies present) · dead spots on leaves with raised areas on under-leaf surface--bacterial blight · brown spots on upper leaf surfaces and gray to purple fungal growth on underside of leaves--downy mildew ·leaves with leafspots with light-colored centers and dark margins--frogeye leafspot · brown spots and/or yellowing on lower leaves--brown spot disease · leaves crinkled and/or disfigured--soybean viruses (also check if the plants are also stunted for glyphosate injury, manganese toxicity, phenoxy injury, benzoic acid injury, boron toxicity)

f. stem is discolored and may be burned at the soil line--high soil temperature, herbicide injury from post_directed sprays, including shielded contact herbicides such as paraquat

g. leaves are speckled or burned, new growth is generally unaffected--diphenyl ether herbicide injury, sunburn, air pollution

h. yellowing along the leaf margins, followed by browning and later necrosis of the leaf but without leaf curl--potassium deficiency, triazine injury

i. interveinal yellowing of young leaves while veins remain green--manganese deficiency, iron chlorosis, chlorimuron, clomazone (may turn white) herbicide injury

j. yellowing of both old and young leaves--sulfur deficiency, nitrogen deficiency, molybdenum deficiency, nematode (usually not a problem in ND), water damage, zinc deficiency, magnesium deficiency

k. possible yellowing and some distortion of young leaves, plants may be stunted with shortened internodes--imazaquin, imazethapyr, imazamox herbicide injury

l. scorching of leaves along the leaf margins--chlorine toxicity, boron toxicity

B. Roots show damage on the soybean plants

1. root damage

a. roots are stunted or showing abnormal growth · little or no nodule development--molybdenum deficiency, nitrogen deficiency, nematodes (usually not a problem in ND), low soil pH, calcium deficiency, soil compaction · little or no secondary root development--nematodes (usually not a problem in ND) · secondary or lateral roots swollen--dinitroaniline herbicide injury · proliferation of secondary roots beyond normal growth--nematodes (usually not a problem in ND), phenoxy herbicide injury

· secondary roots showing bottle-brush symptoms--imazaquin, imazethapyr, imazamox herbicide injury, nematodes (usually not a problem in ND) · roots are irregular or "L-shaped"--soil compaction · roots showing insect feeding--wireworms, white grubs

 

DOG DAYS AND SOIL SIGNS

As the dog days, a time of hot and sultry weather, commence around July 3 and last for the next 40 days or so crops will be in rapid growth and will proceed into flowering. With spraying finishing up on corn and soybeans, a quick look at your qualitative soil health indicators is pertinent. Taking a look at fields through a twelve-step soil evaluation will help you quantify which fields are your best, before harvest yields give yet another indication. One indicator is the presents of earthworms. Best assessed in the spring or fall, you can still take a shovel full of earth from the top foot of soil and do a quick count. In the Sustainable Agriculture Network's book on "Building Soils for Better Crops," over 10 earthworms per shovel-full is a good soil health indicator. Other signs of soil condition are birds that follow behind tillage in the spring looking for worms. A second indicator is organic matter, sometimes seen by color. A topsoil that is clearly defined and darker than the subsoil usually shows excellent soil health. Organic residues on most of the soil surface are another indicator. A fourth review point is subsurface compaction. Can you place wire flags easily into the ground down to the plow layer with only your fingers? If so, you have the fifth soil health indicator, soil tilth or mellowness or friability. If the soil crumbles well, is easily sliced and even spongy (but not wet!) when you walk on it, you have stewarded the land well. No gullies are rills should be evident on fields with no runoff apparent. Eighth, the soil should hold water for long periods without signs of drought-usually evident during our dog days. There should be no ponding, no runoff and water moves through the soil steadily. Tenth, crop condition should have normal, healthy dark green color, across fields, throughout the season. The pH should fit the crop grown as best as possible. And twelfth, your nutrient holding capacity should be indicated by soil tests showing a trending up in relation to fertilizer applied and crop harvested but not into the "very high" nutrient category. It is difficult on any piece of land to hit all twelve soil signs perfectly for that ultimate season, but that is the dynamic and desirous destination that has drawn many into farming.

 

BURN, CUT, FERMENT: WEED SEEDS STILL SURVIVE

Weed seed have an amazing ability to survive, no matter what nature or you throw at them. Even burning fields after weed seed mature will give only erratic control. Field bindweed with 36% germination before burning can consistently still have 7% that can germinate, according to very early studies compiled by the Bureau of Reclamation (Mercer, 1940). Thus, weed species that may have been absent for many years may suddenly appear after a burn. Likewise, cutting or shredding the weeds may or may not decrease your weed seed bank on your farm unless you eliminate the weeds before the bud stage. Common sowthistle still has 100% germination of seed if the weed is cut in flower. Even Meadow barley (90%), soft brome (81%), curly dock (88%), shepherdspurse (82%) and common chickweed (56%) seed are largely viable when the weed is cut with the seed only medium ripe. Some weed seed will even germinate after being stored in a silo for up to four years while others may lose their germinating ability in 10 to 20 days depending on silage moisture content, temperature and organic acids present. Some weed seed may even survive in manure, even during the heating and decomposition processes. Field bindweed still had 22% viability after stored in manure for two months and velvetleaf had a 2% viability after one month.

Denise McWilliams
Crop Production Specialist
 
dmcwilli@ndsuext.nodak.edu

 

MELANISM VS BLACK CHAFF

While looking at some plots yesterday evening I noticed melanism on wheat heads that had emerged from the boot several days ago. Melanism, a genetically controlled discoloration, can be confused with black chaff.

Black chaff is a bacterial disease. Symptoms consist of dark lines or patches on glumes and dark lesions on the awns. The lesions often result in alternating green and brown areas on the awns which aids in identifying the disease. Black strips are also diagnostic of black chaff. Leaf symptoms are dark water soaked longitudinal streaks that result in tan or brown dead tissue.

Melanism, or false black chaff, produces dark purple to black streaks or blotches on the glumes. This dark discoloration is usually more uniform black than black chaff. The awns and peduncle show no symptoms. A dark purple to purple brown ring forms at the each joint; it is often necessary to peel away the leaf sheath to see this symptom. These purple rings are diagnostic of melanism.

Melanism is not thought to reduce yield in currently grown varieties. Development of melanism usually occurs with hot humid weather; consequently, the recent hot weather may result in substantial amounts of melanism showing up.

 

ESTIMATING YIELD POTENTIAL OF WHEAT/DURUM

Even though included in past pest reports, the requests for information on estimating yield keep pouring in.

Estimating yield in wheat, or any crop, is done based on the components that compose yield and only determines potential; crop yield is determined after harvest. Small errors in counting the components that contribute to yield can result in large errors in the yield estimate.

Yield in small grains is the sum of three components: i) the number of heads in a unit area; ii) the number of kernels that are produced on a head; and iii) the weight of each of those kernels. Kernel weight can not be determined until harvest so a historical average must be used.

Formula:

(heads/3 ft X spikelets/head X kernels/spikelet X 0.142*)
                            row spacing (inches)

* Conversion factor that incorporates area, kernel weight and volume.

Using the formula:

1. Determine the number of heads in three feet of row. Small heads with two or three kernels should not be counted; they will result in biased high yield estimate.

2. Determine the number of spikelets per head. This should be an average of six or more randomly selected heads. Top and bottom spikelets contribute little to overall yield and should not be counted (Figure 1).

3. Determine the average number of kernels per spikelet. Small errors in this number result unrealistically high yield estimates; consequently, using a fixed number that accurately reflects long term yield trends best. Usually 2.3 gives the most accurate results, or 2.1 when the crop has been stressed.

4. Finally determine the drill row width. When unknown simply measure the distance between several rows of plants and use the average. Most double disc drills are set at 6, 7, or 8 inch row spacings. Air seeders place seed in bands that can range from three to five inches wide; in this case the band width plus distance between bands is used. Measure several rows from the left side of the band to the left side to determine the width.

wpe2.gif (8360 bytes)

Figure 1. Wheat spike, arrows indicate which spikelets do not contribute significantly to yield and should not be included in number of spikelets per head when calculating yield.

As illustrated yield estimates are subjective. The correlation between an estimate and the final yield is related to how close head and kernel counts are to the real numbers and crop development during the remainder of the growing season. Keep in mind that no field is uniform and yield potential varies tremendously within a single field. To get accurate counts the process should be repeated several times, not less than eight per field.

Happy counting!

Michael Peel
Small Grains Extension Agronomist

mpeel@ndsuext.nodak.edu


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