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ISSUE 3  May 21, 1998

 

HARROWING FOR WEED CONTROL

    Populations of shallow emerging weed seedlings such as pigeongrass, kochia, Russian thistle, pigweed and cutleaf nightshade can be severely reduced by timely harrowing. Harrowing won’t reduce wild oat and volunteer sunflower populations that much due to their deeper emergence, however control will be higher if they have not yet emerged and are near the soil surface.

    Harrows should be set shallow ( inch deep) and angled back to reduce the potential of crop injury.

    It’s best to harrow wheat and barley at the two leaf stage and no later than the three leaf stage to minimize injury potential. Wheat can be harrowed twice while barley should be harrowed only once. Corn can be harrowed between the one and four leaf stage, and sunflower, 2 to 6 leaf stage. Soybeans and dry beans can be harrowed between the 1 to 2 trifoliolate stage. It’s advised not to harrow canola, mustard, crambe or flax seedlings.

 

CRUSTING PROBLEMS WITH FLAX, CRAMBE, MUSTARD, CANOLA, SAFFLOWER

    Some parts of the state received a hard rain a week ago that caused some crusting problems. One question that is being asked is, "How can I break a crust when I’ve seeded a crop such as flax, crambe, canola, mustard or safflower?"

    A light harrowing at a inch depth can be safely done only if the crop has been seeded deeper than 1 inch. Three days afer the crops has been seeded, harrowing should not be considered because if the seedling is within inch of the surface, the seedling probably will be killed.

    If the crop is trying to emerge through a heavy crust layer and the stand is in jeopardy, the best rescue treatment would be to run an empty press drill at a right angle across the field. Keep the pressure off the drill; this will reduce the injury potential.

Source: Duane R. Berglund
NDSU Extension Agronomist

 

HYBRID SUNFLOWER MATURITY CLASSES

    The U.S. sunflower industry along with the National Sunflower Association (NSA) recently revealed a new system of sunflower maturity ratings.

    What’s the days-to-physiological maturity (DPM) rating for that new "Hybrid X" you’re planting this spring? Is it 100 days? Ninety-five days? Perhaps 104 days?

    All three answers could be correct, depending upon where your farm is located. If planted in central South Dakota versus northern North Dakota, the same hybrid can differ by a week or more in terms of the number of days required for it to progress from emergence to physiological maturity.

    Given this variability, farmers and crop insurers have, to a degree, been comparing "apples and oranges" when it comes to physiological maturity comparisons among sunflower hybrids. If one company bases its ratings upon tests conducted in South Dakota and another upon tests in North Dakota, the comparisons really are not accurate. The gap grows even wider if the High Plains is brought into the picture.

    Discussions initiated two years ago by the National Sunflower Association Research Committee culminated in the establishment of a 1997 study to address this concern.

    Twelve commercial hybrids were chosen to represent the full range of sunflower maturities currently available in the North American market. These 12 hybrids were planted at 28 locations in seven states. Each cooperator was asked to collect data on (1) date of planting; (2) days from planting to emergence; (3) days from emergence to flowering; and (4) days from emergence to physiological maturity. Harvest moisture percentages were an optional measurement.

    Complete sets of data were received from 15 of the 28 locations (seven in North Dakota, four in Nebraska, three in Minnesota and one in South Dakota).

    The standardized grouping system is a voluntary effort by seed companies to provide better methods of comparison among hybrids. The system likely will be refined in the future (e.g., the addition of sub-groupings).

    Based on the 1997 study, the NSA Research Committee came up with a recommendation of four maturity groups incorporating four current hybrids as standards. This classification system - which has been endorsed by the NSA Board of Directors - is indicated below. The system accommodates any current or future hybrids which may be earlier than the earliest hybrid in this study (Hysun 311).

 

SUNFLOWER HYBRID GROUPING INTO MATURITY CLASSES

GROUP 1 (early)    DPM < Hysun 311
GROUP 2   DPM > Hysun 311 & < Cargill 270
GROUP 3     DPM > Cargill 270 & < Pioneer 6451
GROUP 4 (late)     DPM > Pioneer 6451

 DPM = Days to Physiological Maturity Rated from date of emergence

Source: The Sunflower, April/May 1998

 

GROWTH STAGING SMALL GRAINS

    Small grains are planted and it will soon be time to apply pesticides especially post-emergent herbicides. Monitoring the development of these crops is crucial to insure proper timing for pesticide applications.

    When staging a field, 10 to 12 plants per field should be chosen at random for staging. The average growth stage of these plants is the stage of the crop in that field.

    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 stages are defined by the number of leaves on the main stem only. Leaf stages can be described in multiple ways. One way is to 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. Another common way is to count a new leaf as complete 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.

    Each tiller produced in addition to the main stem is numbered when it becomes visible. There are two types of tillers: those arising from the crown and those arising from the coleoptiler node. Only tillers arising from the crown are counted. When present there will only be one coleoptiler tiller and it will appear separate from the other tillers (Figure 1).

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    All tillers originating from the crown are surrounded by a small membranous structure called a prophyll.  These tillers arise from the axis of main stem leaves and are sometimes called axillary tillers.  The leaf sheath of leaves from the main stem surround the prophyll and thus can be distinguished.

    The flag leaf is the last leaf produced on a tiller. Once the flag leaf on the main has emerged jointing begins; which is the time when stem elongation begins and the growing point emerges from the soil surface.

    The plant enters its reproductive stage when flowering starts. In wheat this is generally 3 days after heading where as 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. The names of each of these stages are sufficiently descriptive that they need not be described.

    Hard dough is the stage in small grains when physiological maturity is reached, and occurs at 30 - 35 percent moisture. Once physiological maturity has been reached the crop will not assimilate additional dry matter into the kernel. When swathing wheat or barley to facilitate drying and hasten harvest, it should be done at or after the hard dough stage. Swathing before this stage will reduce yield and result in shriveled kernels.

 

PLANT STANDS AND YIELD LOSS

    Following up on last weeks article on replanting decisions Table 1 shows minimum plant stands that provide acceptable yields. Only when stands fall below these levels should replanting be considered.

    Historic yield reductions that can be expected when planting is delayed past May 15, are shown in Table 2. Taking into consideration historic yield reductions and low plant populations that can produce an acceptable yield there are probably very few incidences where replanting would be advisable.

Table 1. Minimum stands of several crops that produce acceptable yields; only when stands fall below these levels should replanting be considered.

Crop

Percent of Normal Stand

Minimum Stand

Small Grains

30 - 40

8 - 14 plants/ft2

Flax

20 - 40

10 - 20 plants/ft2

Soybean

25 - 50

37,500 - 75,000 plants/A

Sunflower

50 - 60

8,000 - 11,000 plants/A

Safflower

40 - 50

2 - 2.5 plants/ft2

Dry Bean:

   Navy

50 - 60

45,000-60,000 plants/A

   Pinto

40 - 50

28,000 - 35,000 plants/A

Field pea

40 - 70

3 - 5 plants/ft2

Corn:

   Irrigated

70 - 75

See A-1130 †

   Dryland

60 - 70

See A-1130 †

Crambe

15 - 20

4 plants/ft2

Canola

25 - 50

4 plants/ft2

† Varies with region, see NDSU Extension bulletin A-1130.

Table 2. Expected yield reductions when planting after May 15.

Crop

Percent Yield Loss/Day

Wheat

1.5

Barley

1.7

Oat

1.2

Soybean

0.8

Irrigated Corn

1.2

Dryland Corn

1.0

Flax

2.3

Dry Bean

0.3

Crambe

0.9

Canola

1.9

 

    Replanting will be necessary in areas with excessive rainfall resulting in a drowned out crop, particularly in the southern part of the Red River Valley where flooding occurred. If small grains are planted back in these areas it is critical to remember that most days between now and flowering are probably going to be much warmer than optimum for plant growth and development. Consequently; development of the small grains will proceed more rapidly, tillering will typically be less and heads will be smaller. To some degree increased seeding rate can compensate for fewer tillers and smaller heads. Seeding rates should be increased 5 to 10% for every 10 days planting is delayed past May 15.

    Optimum Yield of small grains is achieved at 1.3 million plants per acre. Seeding rates should be increased to compensate for percent germination and seedling mortality. A simple formula that can be used is: (plants/acre seeds/lb) % germination X (1 + expected % mortality) = seeding rate in lbs/acre.

Michael Peel
Extension Small Grains Agronomist

 

SUPERVISING AND TRAINING NON-CERTIFIED PESTICIDE APPLICATORS

    In North Dakota all restricted use pesticides (RUP) must be applied by a certified applicator. This applies to both commercial and private situations. However, people who are not certified to apply RUP may legally apply them IF they are properly supervised by an individual who is certified.

    What is proper supervision? Generally, the availability of the certified applicator (supervisor) must be directly related to the hazard of the situation. In many situations, where the certified applicator is not required to be physically present , "direct supervision" shall include verifiable instructions to the actual person, as follows:

1.  Detailed guidance for applying the pesticide according to the label instructions.

2.  Provisions for contacting the certified applicator in the event needed. In this situation a reasonableness test should apply. Is        the certified applicator available by radio or phone within minutes of the site of application? Or is the applicator several        hours away chasing parts for machinery? Certainly the first situation is reasonable, the second clearly is not.

    If the situation is particularly hazardous, the certified applicator may need to be physically present. This is a judgement call based on the supervisor's confidence in the individual applying the product and in the degree of difficulty involved in applying the product correctly. However, if the label clearly states that a certified applicator must be physically present, then HE MUST BE ON SITE, SUPERVISING THE OPERATION.

    Finally, any person whether actively applying pesticides or simply being casually exposed to pesticides must be trained to a minimum standard of competence. This is the Worker Protection Standard (WPS). This training must be conducted by a certified applicator and should include:

1.    Basic instructions which are found on the pesticide label.

2.    A discussion of the risks associated with the application of the pesticide and how to minimize those risks.

3.    Basic safety training.

4.    Instructions on how to properly use personal protective equipment.

5.    Instructions on obtaining emergency assistance.

    The WPS requires additional measures too numerous to cover here, but if you would like additional information, the NDSU Pesticide Program would be happy to forward on additional resource materials. We have an excellent video library in both English and Spanish language as well as numerous publications and posters. They are available upon request.

Andrew A. Thostenson
Pesticide Program Specialist


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