NDSU Crop and Pest Report

Plant Science

ISSUE 2  May 8, 2003



As we get later into the planting season, its suggested that canola (a heat sensitive crop) be seeded first and then complete small grains, sunflower and soybeans. Research has shown that canola yields drop quickly if planted late.

For canola planted acreage south of U.S. Highway 2, its suggested canola always be planted before small grains and, if possible, before May 15. For the NE and areas and growing areas north of Highway 2, canola should be planted no later than May 25.

The optimum planting date for canola is late April to mid-May. Canola yields have decreased sharply across most of the state (except the northeast) when canola is planted beyond mid-May.

Canola is more sensitive to heat stress than all small grains, flax, and other cool season broadleaf crops, thus the utmost importance to seed canola early. Canola is also quite tolerant to spring frosts.

Seed canola at a rate of 5 lbs/A under most conditions. An optimum seedling plant population is 16 plants per square foot or 600,000 plants per acre. A good stand is 10 to 12 plants per square foot whereas, a minimum stand of canola is 4 plants per square foot. The recent rains in the state should allow for shallow seeding of ½ to 1 inch for rapid emergence. It is not recommended to broadcast seed canola and cover by harrowing or other forms of tillage. Stands and emergence of seedlings have been erratic. For additional information on Canola Production, see NDSU Extension Cir. A-686. Also available on the web at:




Current high soybean prices and good loan support have many farmers considering planting a second or even a third year of soybeans in some fields. This may appear to be a good option after the initial pencil pushing but should be examined more closely. Although production costs may be lower, there is a good chance that yields may be lower as well. Additionally, producers may be setting themselves up for long term management headaches.

The two major concerns with planting soybeans on soybeans are: disease problems and weed specie shifts.

First what about yield potential?

It is not a certainty that a second year of soybeans will yield poorly, although this behavior does tempt fate. Organisms that attack soybeans are a major concern. Problems that immediately come to mind are certain root rots, white mold, brown stem rot and soybean cyst nematode (SCN which has not been identified or reported in ND yet!). They are well documented to be greater problems in continuous soybean and we already have enough problems to go around. White mold, root rots and soybean cyst nematode persist in the soil. Brown stem rot overwinters and can also live as saphrophyte on soybean residue. A few other organisms that survive the winter on residue include those causing bacterial blight, stem canker, pod and stem blight, brown spot, etc. Soybeans on soybeans benefit these organisms as follows: the first year of soybeans allows reproduction and buildup of disease inoculum and nematode populations. The third or fourth year of soybeans planted into the elevated disease or nematode levels can bring about drastic results and low yields if conditions are right for disease buildup.

If we have a dry 2003 summer and somewhat droughty conditions, disease incidence could be down.

The higher the pathogen levels, however, the greater the potential for yield loss. A piece of good news is that some root rot causing pathogens (Phytophthora, Fusarium, Pythium, and others) are already prevalent in the soil and a few more probably won't make a major difference. Also there are a number of cultivars of soybean which are resistant or tolerant to Phytophthora root rot. It mainly depends on the race and if you have the correct resistant gene in your variety.

Weed species shifts, or the increase of a particular weed species in the population of a field because it escapes by herbicide tolerance or time of emergence, have been known to occur. The increase of certain nightshades, biennial wormwood, ALS resistant Kochia and waterhemp are examples. By planting the second or third year of soybeans and applying the same herbicide or cultural practices you are helping speed the selection process along. From a natural ecological perspective your field wants to have weeds growing in it. The objective is to prevent a buildup of those weeds that are hard to control.

Some suggestions if you have no other choice - Maximize the disease defensive characteristics in the varieties planted. Varieties with lower susceptibility to white mold should be selected. Go to wide rows (30 inches) as this planting pattern is less susceptible to white mold problems. Planting shorter season varieties and delayed planting may in some years help reduce white mold pressure.

Try to use a different weed control program in 2003 than in 2002 if certain weeds are starting to become a major problem. Rotate chem. families/modes of action of herbicides.

Condition and test any saved seed if that is what you will be planting. A seed treatment may be appropriate, depending on the disease, if you suspect that the seed may be infected. Remember that Roundup Ready soybean cannot be saved and replanted. Its against the law!!

Moldboard plowing may help control some (but not all) of the fungi and bacteria that survive on residue. Unfortunately, heavy tillage of soybean residue has other negative impacts and spring moldboard plowing is not

advisable. Soil tilth can be destroyed and this increases erosion potential.

Reduce or eliminate any nitrogen application, and no need to inoculate seed unless you had poor nodule formation in last years crop. Phosphorous fertilization maybe required depending on soil tests and crop yield removed last year.



Soybeans respond to day length so the actual calendar date is highly influenced by latitude location. Each variety therefore has a narrow range of north to south adaptation. Soybean yield and quality are affected if a season ending freeze occurs before a variety reaches its physiological maturity. Dates of maturity are listed in NDSU performance tables and indicate when the plants in a variety are observed and estimated to be physiologically mature. Usually harvest will commence approximately 7 to 14 days after the soybeans are physiological mature.

Relative maturity ratings are also provided for many of the varieties entered in the trials at various locations. These ratings consist of a number for the maturity group designation such as: (000, 00, 0 or 1) and followed by a decimal and another number, ranging from .0 to .9, which indicates maturity rankings within each maturity group.

For example the variety Jim is indicated as 00.6, making it a medium maturing variety in the 00 group. Walsh would be a 0.0 making it one of the earliest varieties in the 0 group whereas Sargent is a 0.8 making it one of the later varieties in the 0 group. Few if any group 1 soybeans are currently planted in North Dakota except in the extreme SE part of the state.

Group maturity rankings of public varieties were developed after observing them for a number of years and sites. Relative maturity ratings for private varieties are usually provided by owners and were developed in a similar manner.

Soybean Maturity Groups



(Very few available)













For each 0.1 change in group rating this represents approximately 0.75 to 1 day later maturity!

See NDSU web site below for 2002 Soybean Performance and maturity data:


Duane R. Berglund
NDSU Extension Agronomist




The earliest date soybeans should be planted in the northern and western regions of the state is May 10. Soybeans have "hypocotyl" emergence; which is similar to sunflower. Once the cotyledons emerge, the growing point is above ground. The cotyledon "cracking stage" can handle temperatures of 29° F for a short time; however, if they are killed by frost the plant will die. Soybeans are more tolerant to an early frost than dry bean, but, not as tolerant as sunflower. The optimum plant date for soybeans in the north central and west. regions of the state is May 12 to May 25.

An important consideration when planting soybeans is seedbed temperature. The minimum soil temperature for germination is 50° F. At that temperature soybeans will take 17 to 21 days to emerge. Soil temps of 56 to 60° F, emergence will only take approximately 10 days.

Plant Population/Row Spacing:

The optimum seeding rate is from 180,000 to 200,00 PLS per acre. Research studies at Carrington, Minot, and Hettinger indicate only a 10% higher yield with narrow (6 inch) rows vs 30 inch rows. There is no specific row spacing that is recommended and growers should select a row spacing that works best for them. There is no need to buy specific equipment for the ideal row spacing. Both narrow and 30 inch row spacings have their advantages and there are no distinct advantages between narrow and 30 inch rows.

Direct Seeding:

Direct seeding or no-till planted soybeans is highly suggested in the northern and western regions of the state. Research studies at Minot, Washburn, and Hettinger indicate a consistent 24% yield advantage with no-till soybeans compared to convention tilled (one spring till or one fall till plus one spring till) soybeans. The 24% increase in soybean yield is averaged across many location years and is one of the highest yield increases for all crops. The are many herbicide options to consider with conventional soybeans to allow for successful no-till production. There are many early maturing Roundup Ready soybean varieties that are adapted to the northern regions that would work under a no–till program.

Kent McKay
Area Extension Agronomist
North Central Research/Extension Center



Prior to the most recent rains, cereal planting was ahead of schedule for most of the state. The small grains that were planted early have emerged and the early planted corn is just poking through the soil. Reports from throughout the state suggest that most of the winter wheat crop survived the winter and is now starting to develop rapidly. For the crops that have emerged it is now time to assess your plant stand. Poor plant stands can result from a number of factors. Limited soil moisture in parts of the state may have caused poor germination and uneven emergence. Poor quality seed can be the source of poor stands. Diseases, insects and waterlogging can also take a toll on emerging seedlings. For plant stand losses early in the growing season, replanting can be a viable option. The following guidelines should help you decide whether replanting will be more profitable than continuing to manage your "not so good looking crop" (if that is the case).

Factors to consider before replanting.

1. Make an accurate assessment of your stand. A first glance plant stands or early season damage can look much worse than it really is. Moreover, there are times when things are actually worse than they might appear at a distance. If poor emergence or damage is not uniform, focus only on those areas of the field that will likely need to be replanted. For small grains take plant counts from 4 or 5 randomly selected areas (use a 1 square yard quadrant or something similar). For corn, count several randomly selected rows (a 17' 5" in row of corn equals 1/1000 of an acre if 30" rows are used).

Within the range of zero to the optimum number of plants per acre, plant population is highly correlated with yield. If stands are not too low, however, cereal crops do have a remarkable ability to compensate for reductions in plant numbers. Under low population densities, small grains will put on more tillers and produce larger heads. Corn will produce larger cobs and on occasion produce two cobs when densities are less than optimum. Table 1 describes the minimum plant stand that is needed for a "poor stand crop" to produce as much or more than a replanted crop.

Table 1. Stand reduction level at which replanting of cereals should be considered in ND.


Percent stand

Plant numbers

Winter Wheat


5-11 plants/ft2

Spring Small grains


8-14 plants/ft2



Dependant on the area of the state*

* Recommended plant populations vary from region to region in the state. As an example, if the target population is 28,000, when populations fall below 16,000 you should consider replanting.

2. Estimate the yield potential of the replanted crop and the costs associated with replanting. Bear in mind that late planted crops will yield less, sometimes substantially less, than those that are planted in a timely manner. Table 2 provides a rough guide as to the yield reductions that will occur with later plantings.

Table 2. Expected yield reduction when planting after May 15 in North Dakota



Yield loss (%/Day)













Notes for small grains

As indicated in Table 1, fairly large reductions in the "optimum" plant density can be tolerated before it becomes more profitable to replant small grains. For sparse stands, care must be taken to ensure that weeds are adequately controlled. If you do decide to replant, consider the following: When planting after May 20 replant with a higher seeding rate to compensate for the reduced tillering of the later planted crop. After June 1, consider growing the earliest varieties that are available in addition to the higher seeding rate, or consider growing an alternative crop with shorter maturity. Planting small grains after June 21 is not recommended.

Notes for corn

Corn, when compared to small grains, is much more sensitive to reductions in plant populations as can be noted from Table 1. The timing of replanting is also critical with corn, so that decisions on replanting should be made as soon as it is practical to fully assess the plant stand of your crop. For corn when replanting after May 20th earlier maturing hybrids should be planted (how much earlier will depend on the actual date that you will replant). After June 1 corn for grain should probably not be planted except in the southeastern corner of the state where the latest date of planting should be June 10th. In the northern areas of the state, corn replanting should be avoided after May 25th.

Additional information on replanting can be obtained from the NDSU Extension Service bulletin, "Replanting after Early Season Crop Injury (A-934)" which is also available through the internet at:


An additional resource for corn, "Estimating Yield and Dollar Returns From Corn Replanting", is published by Purdue University Cooperative Extension Service can be found at:


Joel Ransom
NDSU Extension Agronomist - Cereal Crops



The following is an approximate number of planted acres at the sugar cooperatives. American Crystal Sugar Company (ACSC) - 375,000 acres (75%), Minn-Dak Farmers Cooperative - 104,000 acres (92%), Southern Minnesota Beet Sugar Cooperative - 102,000 acres (85%), and growers in western North Dakota - 15,000 acres (100%).

At ACSC, the Moorhead, Crookston, and Drayton factory districts have completed 88-90% of their planting. However, Hillsboro and East Grand Forks factory districts, because of wet fields, have completed just about 55% of their planting.



In the seedling growth stage, death of plants may occur after 48 to 72 hours of standing water in the field. Flooding of sugarbeet fields results in oxygen depletion that may cause plant death or crop damage. Flooding may result in sprangling of sugarbeet roots. Root sprangling increases the amount of tare dirt hauled to the factory. Plant damage is usually more severe if flooding is accompanied by high temperatures and bright sunshine compared to low temperatures and cloudy conditions. Seedlings that survive a flood may become susceptible to seedling diseases and root rots. Good seedbed preparation, proper land leveling, and an approved drainage system are the best ways to prevent a flood or facilitate drainage after a flood.

Mohamed Khan
Extension Sugarbeet Specialist

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