NDSU Crop and Pest Report

Plant Science


ISSUE 13   July 29, 2004

ESTABLISHING A "RESIDUE" CROP PRIOR TO WINTER WHEAT PLANTING

There is increasing interest in planting winter wheat this fall in areas of the state that were not cropped this year due to excessive moisture or to drought. Successful winter wheat survival is largely dependant on good snow cover in the winter. Therefore, for fields that were tilled or that have little or short stubble it is recommended that special management options be implemented in order to reduce the risk of winter kill. The most effective of these option is the establishment of a flax "residue" crop in early August. Flax can be established as a lightly seeded solid stand, in wide rows (i.e. 3-4 feet spacing) or as strips. Strips of flax 3 to 5 feet wide and 15 feet apart have been found to effectively trap snow while minimally depleting soil moisture. When seeding flax in strips or in wide row spacings, the drill should be set at a high seeding rate (40-60 pounds per acre) and drill spouts should be taped shut to obtain the desired spacing. Strips of flax more than 20 feet apart can be risky as they do not catch sufficient snow in most years. Flax should be seeded on or about August 1 and no later than August 15, depending on the region of the state. Establishment of flax can be difficult if moisture is limiting, but in the regions of the state that have been dealing with excess moisture this year, that should not be a serious concern.

Other management practices that can help increase the winter survival of winter wheat are:

Joel Ransom
NDSU Extension Agronomist - Cereal Crops
joel.ransom@ndsu.nodak.edu

 

CRITICAL STAGES IN SOYBEAN DEVELOPMENT

Moisture is critical at this time in North Dakota and Minnesota. Below lists the various reproductive (R) stages of the crop and what is happening at each stage of growth and development. The flowering and pod filling stages are the most critical with yield being greatly reduced if water shortages occur during that time.

Soybeans

Stage

Description

Stage

Description

Beginning Bloom
(R1)

At least one flower on the plant. If flower is showing on Ĺ the plants then soybean field is 50% bloom.

Beginning Seed  (R5)

Seed is at least 1/8 inch long in one of the pods on the four upper nodes. Half-way through this stage the plant attains itís maximum height, node number and leaf area. Critical stage not to have water stress.

Full Bloom
(R2)

At least one of the two upper nodes has an open flower and the soybean has about 50% of its full height - No Stress is best.

Full Seed
(R6)

The green bean or beginning full seed stage - Pods with green seeds fills the pod cavity on at least one of the 4 top nodes. Root growth is complete. Lower leaves can start to yellow at the end of this stage. This stage is vulnerable to frost injury.

Beginning Pod
(R3)

A pod on the upper four nodes is 3/16 inch long - No water or high temperature stress at this time.

Beginning Maturity
(R7)

One pod on the main stem obtains mature color such as tan or brown. Seeds are nearing physiological maturity and are relative safe from a killing or injurious frost. Lower leaves are rapidly turning yellow and some dropping off the plant.

Full Pod
(R4)

Beginning seed development - Pods 3/4 inch long on one of the four uppermost nodes. Most crucial period for seed yield. No water or heat stress at this time to insure maximum yields.

Full Maturity
(R8 or PM)

Crop is physiologically mature. 95% of the pods have reached mature color. Moisture will drop to 15% within five or ten days with good drying weather. Seed required to drop to 13% for long term storage. Usually all leaves are dropped at the start of R8.

 

SWATHING AND HARVESTING CANOLA

The warm and sunny weather the past week and caused canola to come on fast and mature to the point that time for swathing is fast approaching. Swathing canola at the optimum stage of ripening reduces green seed problems and seed shatter losses, and ensures the quality required for top grades and prices. Field inspections should be made every "2 to 3 days" when there is some color change in the first formed pods on the bottom of main stem. Canola seeds within the pod will change color an average of 10 percent every 2 to 3 days. Under hot conditions, seed color changes can be very rapid.

Examine only those pods on the main stem. Seeds in pods on the "bottom third" of the main stem were formed earlier and will turn color much sooner than seeds in the pods on the top third of the plant. Optimum time to swath is when overall moisture content of seed from the total plant averages 30 to 35 percent, about 30 to 40 percent of the seeds in pods on the main stem only will have changed color or have started to change color. Seeds with only small patches of color should be counted as color changed. Remember, the color of the seed is more important than the overall color of the field in determining the stage of maturity.

Most of the seeds that have changed color will be from the bottom third of the stem. When seeds in the bottom pods slightly turn color, seeds in the top, last-formed pods are filled or nearly filled. At this time, most of the seeds will be firm and roll, as opposed to break, when pressed between the forefinger and thumb.

Seeds in all pods on a plant complete filling (physiological maturity) at about 40 percent moisture and then slowly turn from green to light yellow, or reddish brown to brown depending of variety. Once filled the seeds rapidly lose moisture at about 2 to 3 percent or more per day, depending on the weather.

Green Seed Problems

Cutting too early with high temperatures and rapid drying can lead to excessive green seed count. Two percent or less green seed is currently the allowable limit. Any higher than the 2 percent and market discounts can occur. The key to curing the crop is moisture. The enzyme responsible for clearing the chlorophyll requires moisture. Therefore, seed moisture is critical. If the stems and seeds dry too rapidly after swathing, then chlorophyll can be fixed.

Leaving canola in the swath longer can help eliminate some green seed problems or potential. A rain will also help reduce green count in canola. Once the moisture content of seed is 20 percent, chlorophyll will begin to be moved out. In some cases however, when swathed too green in hot weather the chlorophyll will not be reduced to any great extent. Cool temperatures and light frosts in August and September slow the enzyme activity that breaks down chlorophyll. Frosts from 32 to 33 degrees F disrupts that system, more specifically it can reverse it and restart the synthesis process. This is very sensitive in the seed development stage, and the window is very narrow. This can cause differences between adjacent fields that are only days apart in maturity, or differ in uniformity of maturity. Even canola swathed four to six days before a frost will retain relatively high levels of chlorophyll. Thin stand counts can result in plants with more branching and more variability in seed maturity and are more likely to have immature seed at swathing. Late seeded canola may be impacted by all these situations.

Uneven Stands-mixed maturity

When looking at uneven stands, its suggested that one do a count early on the ratio of early emerged canola which is bolting or starting to flower and the late emerged flush of young more immature plants.

If one knows the ratio of "early to late" emerged canola plants, a better decision can be made as to how soon to swath or wait until the later crop catches up. If the stand is on 20-25% early and 75-80% late, then waiting to cut later may be the best strategy to reduce the amount of green seed. One would take the chance of shatter in the early maturing canola but would avoid the problem of green seed count and market discount. One could also swath at night or in the early morning hours to avoid shattering in the fields where portions of the canola are ahead in maturity and development.

Two years of NDSU research has shown that at 0-5 seed color at swathing time resulted in 3.5 percent green seed content which is higher than the 2% allowed in the market place before a discount will occur. Approximately 180 lbs/A of yield gain was noted when swathing was delayed to the 15-20 percent seed color change.

Another sign of canola being very near the swathing stage is the natural yellowing and senescence of leaves and leaf drop. When canola plants consist only of stems, stem branches and pods, it is probably very near the optimum time for swathing.

Canola should be allowed to cure and ripen from ten to 14 days in the swath before combining. If combined too early, the chance if increased green seed in the harvested crop is much greater. "Be in a hurry to swath on time and prevent shattering, but take your time in moving the combine in the field to ensure maximum drying, maturation and quality of your harvested canola."

Duane R. Berglund
Extension Agronomist
duane.berglund@ndsu.nodak.edu


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