ISSUE 9   June 29, 2006

FLOPPY CORN SYNDROME

This past week I visited a corn field in southeastern ND where a large percentage of the plants in the headlands were stunted, purpled and lodged. Upon close inspection, it was noted that few if any nodal roots had developed on these plants. The stubby and darkened stumps of nodal roots that tried to develop had the appearance of having been injured by a herbicide or infected by some disease (see accompanying figure). In this case, however, the problem was most likely caused by inadequate soil moisture for nodal root development. This malady is generally referred to as the floppy corn syndrome and is usually associated with the surface layer of the soil becoming so dry that nodal roots are not able to develop during the V1-V6 stages. Not surprisingly, floppy corn syndrome is most commonly observed in the southwestern region of the state. Shallow seeding (less than an inch deep) can increase the likelihood of this problem because the crown, where the first nodal roots arise, cannot become established deeper than the depth of the seed. At this particular site it was suggested that the problem may have been induced by pheasants digging around the seedling in an attempt to get the corn kernel as a large number of pheasants were seen in this field. Although confirmation of this is not possible at this time, it is reasonable that digging by the pheasants could have broken contact between the emerging roots and moist soil, similar to if the soil surface had been dried out before nodal roots, thus resulting in the observed symptoms.

Nodal root development
Normal nodal root development on left,
restricted root nodal root development on the right
resulting in a "floppy" plant.

USE CAUTION WITH FLOWERING DATE PREDICTION FROM NDAWN

The NDAWN prediction for flowering date of small grains is lagging behind what is actually being observed in the field at some locations in North Dakota. For example, the actual heading date of medium-maturing spring wheat varieties I planted in late April at Prosper, ND was about 5 days earlier than that predicted using NDAWN. Therefore, if you are using NDAWN to help you plan for a flowering date application of fungicide, be sure to begin scouting fields when NDAWN indicates fields are approaching boot stage. It likely this year that your crop will be approaching flowering at this time. The NDAWN growth model uses growing degree accumulations to predict plant development and is fairly robust over a range of temperatures. Perhaps the temperatures this spring were beyond the range of temperatures used to develop and validate the model. The warmer temperatures of 2006 could have "pushed" development faster than predicted.

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

 

CHECKING PLANT POPULATIONS - ROW CROPS

Use the following table to estimate plant populations.

1. Count number of plants in the length of row equal to 1/1000 of an acre.

2. Make several checks within a field and average the stand counts.

3. Multiply the average by 1000 to get population per acre estimate.

 

Row width

Row length for 1/1000 acre

Row width spacing

Row length for 1/1000 acre

7"

74' 8"

30"

17' 5"

14"

37' 4"

32"

16' 4"

20"

26' 2"

34"

15' 4"

22"

23' 9"

36"

14' 6"

24"

21' 9"

38"

13' 9"

28"

18' 8"

40"

13' 1"

Hint: Use a small diameter rope, cord or a tape measure for the correct distance.

 

HAIL DAMAGE IN OILSEED & ROW CROPS

Hail damage to crops occurs somewhere in the state every year. Reports of hail damage have already been received from some areas of the state during the past couple of weeks. When hail damage occurs on corn, soybean, dry bean and sunflower early in the growing season, replanting is possible; however, deciding whether to replant can be difficult. Stand reduction, leaf loss, stem injury, weed control, and calendar date are important factors to consider when making this decision. At this time (late-June) it is too late to replant.

Corn: The growing point remains below ground 2-3 weeks after the plant emerges (5-leaf). If the growing point is not damaged, corn will recover and perform better than replanted corn. To inspect a plant, split the stalk down the center and examine the growing point. If normal, it will appear white in color and firm in texture. Injured growing points will appear brown or discolored 2-3 days following the hail. Early complete loss of leaves in small corn plants usually does not significantly affect grain or silage yields. Hail can result in severe yield losses when corn is in silking or tasseling stage.

Soybean and Dry Bean: Growing points of bean plants are located in the top of the plant and in leaf axils. Growing points of beans are easily damaged by hail soon after emergence. Regrowth will not occur if hail stones cut the stem off below the cotyledonary node. If the tip of the plant is damaged, regrowth can occur from one or more axillary buds. Bean stems may be bruised or broken. Although damage may not be severe enough to kill the plant, it may lodge later because the callus tissue is weakened and cannot support the pod weight. Soybean stands reduced to four plants per linear foot of row in 30-inch row spacing can still produce fair yields. Soybean fields with populations of >120,000 plants remaining will suffer very little yield loss due to stand reduction. Dry bean fields can get down to two plants per foot of row and still produce fair yields.

Sunflower: Sunflower may be more tolerant to hail damage than beans, but the degree of hail tolerance depends on the intensity of the hailstorm and growth stage of the crop. Sunflower is least tolerant during the seedling and budding stages and most tolerant after flowering. Hail damage may be direct or indirect. Direct damage results from stand reduction, loss of recoverable heads because of severely bruised or broken stems, and head shatter at later stages. Indirect damage results from defoliation and disease infestation to injured plant tissue.

Research conducted on simulated hail losses in sunflower indicated that a one-to-one relationship does not exist between stand reduction and yield loss. A 50% stand reduction resulted in only a 28% yield reduction. Defoliation of sunflower by hail was reported to be most damaging during the bud stage. Defoliation of 80% at the bud stage resulted in yield reduction of 53%. Whereas 80% defoliation at the 50% mature stage resulted in only a 12% yield loss.

Canola: Seedling stages of canola can have stands reduced by 50% and still produce acceptable yields. An average stand of 11-12 plants/ft2 can be reduced to 4/ft2 before yield losses exceed 10 percent. Prior to bolting and flower development, canola can withstand hail without much economic loss. Canola with leaves that are torn and shredded suffer only partial loss, while leaves bruised on the main vein or torn and broken will be lost. Leaf area destroyed will result in seed yield loss. Seed yield loss in canola is approximately 25 percent of leaf area lost. For example, if leaf defoliation is 50 percent, then yield loss would be about 12.5 percent.

Canola plants injured in late bolting to early flowering stages seldom die. Well-developed root systems and the ability to rebranch and develop secondary flower clusters help plants recover. When buds or flowers are destroyed, canola recovers rapidly by development of flowers that normally would have aborted. New branches also develop from growth buds lower down on the plant. Seed yield loss will depend on both percent leaves and branches lost. For example, if canola has 60 percent lost branches 7 days into flowering, seed yield loss would be about 18 percent, whereas yield loss would be about 60 percent if the same injury occurred 21 days into flowering. If hail strikes late, such as during pod filling or ripening, plant recovery is not possible. The time needed to develop new growth, flower, and mature is limited before a killing frost. Canola seed yield loss following injury at the ripening stage depends directly on the loss of branches and individual pods, as well as and seed knocked out of pods. Severe hail damage to canola swaths has also resulted in major yield losses.

 

CANOLA TEMPERATURES AND SOIL MOISTURE

The canola crop in North Dakota presently varies from 4 leaf stage to early blooming. What do warm temperatures and low soil moisture do to potential canola yields? Heat injury to canola occasionally occurs on hot (90-95 F), sunny days with soil temperatures of 120 F. Heat injury is commonly associated with drought injury.

Heat blasting and flower abortion are strong possibilities when canola in the blooming stages is subjected to temperatures in the 90s and higher. This can vary from field to field and is very dependent on stage of flowering, soil moisture, and humidity during hot periods. One would normally see limited or zero pod growth under these conditions. Thus, no seed set would occur. It will usually be seen in sections of the main stem and branches as related to time of flowers pollinating and the heat stress. Canola flower abortion will usually be minimized under good soil moisture conditions.

Both low and high temperatures can adversely affect development prior to and during flowering. Low but non-freezing temperatures, just prior to flowering, will slow the rate of plant development. This can result in delayed onset of flowering, slowed rates of flower opening, and reduced pollen shed. High temperatures at flowering will hasten plant development and reduce the time from flowering to maturity. High temperatures during flowering shorten the time the flower is receptive to pollen, as well as the duration of pollen release and its viability. This can decrease the number of pods which develop and the number of seeds per pod, resulting in lower yields. It appears that Brassica rapa (Polish) is more susceptible to this type of damage than Brassica napus (Argentine). Very hot weather combined with drought may cause bud blasting wherein the flower clusters turn brown and die, resulting in serious yield losses.

Canola is more tolerant to high temperatures once pods are formed than at flowering. Cool night temperatures at this time also help the plant recover from extreme heat or dry weather. However, during this stage, a combination of heat and extreme drought will severely affect pod and seed formation, seed size, and oil content. Seed oil content is highest when seeds mature under lower temperatures (50 to 70 F). High temperatures during seed maturation result in reduced oil content. High temperatures, drought, and long days hasten maturity and in combination, can reduce yield through fewer pods which also contain fewer and lighter seeds.

Duane R. Berglund
Extension Agronomist
Duane.Berglund@ndsu.edu


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