NDSU Crop and Pest Report

Plant Science

ISSUE 1  May 2, 2002



Below is a listing of NDSU Field Day Tours and other crop-related special events. Exact starting times will be given at a later date via this newsletter or other media releases.

June 25 at the Central Grasslands Research Extension Center, Streeter (701) 424-3606.

June 27 at the ARS-USDA Northern Great Plains Research Laboratory, Mandan, ND (701) 663-6445.

July 9 at the Hettinger Research Extension Center, Hettinger (701) 567-4323.

July 10 at the Dickinson Research Extension Center, Dickinson (701) 227-2348.

July 11 at the Williston Research Extension Center, Williston (701) 774-4315.

July 16 at the Carrington Research Extension Center, Carrington (701) 652-2951.

July 17 at the North Central Research Extension Center, Minot (701) 857-7677.

July 18 at the Langdon Research Extension Center, Langdon (701) 256-2582.

August 20 Field day at the Garrison Diversion Conservancy District site, Oakes (701) 652-2951.



It is important to plant canola early because it is more sensitive to heat stress during flowering and seed fill than small grains, flax, and other cool season broadleaf crops. Once weather conditions are favorable to preparing a good seedbed, canola should be planted prior to small grains to avoid the potential of decreased yields due to late planting. A combination of low moisture and high temperatures during flowering and pod set can substantially reduce yields.

Research has shown that yields drop quickly with delayed planting. Results in North Dakota and NW Minnesota have shown that about 1% decrease in yield per day will occur when canola planting is delayed after the first possible planting dates of late April or early May.

For canola planted acreage south of U.S. Highway 2, its suggested canola always be planted before small grains and, if possible, before May 10. 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-early May. Canola yields have decreased sharply across most of the state (except the northeast) when canola is planted beyond mid-May.



Cool spring soils have brought questions on crop and weed seed germination. Below are minimum temperatures for a number of major North Dakota grown crops and for common weeds. Some will germinate at lower temperatures but germinate very slowly and would result in non-uniform emergence and poor stand establishment.







Dry beans



Min. soil temp: 35-40 F

Min. soil temp: 50 F or higher

Wild mustard
Wild buckwheat
Russian thistle
Absinth wormwood
Canada thistle
Common lambsquarters
Wild oats
Frenchweed (pennycress)
Tansy mustard

Redroot pigweed
Wild sunflower
Vol. sunflower
Field bindweed
Foxtail (pigeongrass)
Cutleaf nightshade
Lanceleaf sage

Duane R. Berglund
NDSU, Extension Agronomist



Allelopathy is when a plant gives off a chemical that influences another plant. Plants like oats and rye are known to give off chemicals that reduce or prevent the growth of weeds in the community. Alfalfa is known to have an allelopathic chemical also, but the chemical is not known to affect other plants. The chemical, believe to be ethylene and possibly medicarpin (not known for sure), affects alfalfa germination and seedling growth. Therefore, it is said to be autotoxic or toxic to itself.

Autotoxicity in alfalfa was demonstrated in the field in the mid 1980s by researchers at the University of Illinois. They seeded alfalfa in the spring without a companion crop, took two harvests in the seeding year, plowed out the stand in the fall, and reseeded the stand the next spring for 7 years. The first couple of years stands were very good and yielded greater than 4 tons/acre. By the third year, plant establishment was less and productivity was decreasing. By the seventh year, very poor stands were established and forage yields were less than 1.1 tons/acre. These data suggest that the autotoxin was accumulating in the soil.

Jennings in Arkansas seeded alfalfa in a wagon-wheel design with an old plant at the hub. Alfalfa seedlings rarely emerged in the 0 to 8 inches of the hub and plants that did were weak and spindly generally. Seedlings generally emerged in the next 8 inches but productivity was about 75% of maximum. These data suggest that even if alfalfa seedlings established, productivity may be reduced greatly.

In 2001, we evaluated autotoxic effects in alfalfa. Alfalfa established in 1996 was tilled during the 2000 fall and again as early as possible in spring 2001. Alfalfa was seeded the same day as spring tillage and 1, 2, and 3 weeks latter. Nearly 1.2 inches of rain occurred two days after the first seeding date, which created a good seedbed and removed concerns about a poor seedbed, especially for the 1 week after seeding. Plant density was about 10 plants/ft2 for the first and second seeding date in the spring- tilled plots but greater than 40 plants/ft2 in fall-tilled plots. Plant density in spring-tilled plots improved with delay in seeding but never obtained the level in fall-tilled plots. The lower plant density in spring vs. fall-tilled plots was due to the autotoxic chemical found in alfalfa.

Forage yield at 10% bloom was only 0.4 tons/acre for the spring-tilled first seeding date but 0.9 tons/acre for the fall seeding. Forage yield increased as the seeding date was delayed in both tillage treatments, but the spring-tillage increased more. Obviously, the first-harvest forage yield was impacted by the autotoxic chemical. Forage yield in the second harvest was the same for both the spring and fall tillage and all seeding dates. To have equal productivity from 10 to 40 plants/ft2 in the second harvest of the seeding year is similar to earlier work at Fargo.

Seasonal forage yield in this experiment was 2.3 tons/acre in the fall-tilled plots. What is not clear is how much the yield was lowered by seeding on the fall-tilled area since we did not have an area without alfalfa to be used as a check. However, the seeding-year yield of a new variety trial seeded on fallow was greater than 3.5 tons/acre. Was the lower yield in the fall-tilled plots due to allelopathic effects? An experiment was initiated last year to test this, but it will take at least 4 years before we have a complete answer, stay tuned.

At present, the best recommendation is to NEVER seed alfalfa on alfalfa! We know that adequate stands can be obtained by waiting at least 3 to 4 weeks after tillage, but we donít know if the chemical persists in the soil. Remember the early Illinois data where the autotoxin was accumulating in the soil and reducing productivity. Does seeding alfalfa one year after alfalfa also decrease yield?

If winter kill occurs, which is a possibility with the past open winter, I would not reseed alfalfa on the field without at least one grass crop intervening. Seed the alfalfa on a new field to stay away from the possibility of reduced yield due to the autotoxic effect.

Dwain Meyer
Forage Management Research/Extension




Soybean has the ability to fix nitrogen from the atmosphere if the root system is properly nodulated. Inoculation of seed or placing inoculant in the seed furrow is highly recommended for North Dakota soils with no previous history of soybean planting. Inoculant with seed also should be considered for fields having prior soybean history to insure the bacteria is present in the soil and to introduce improved strains of bacteria. The primary objective is to place viable soybean inoculant (Bradyrhizobium japonicum) uniformly on or with the seed and rapidly place in the soil. The viability of the soybean inoculum depends on environmental conditions during storage through soil placement. Inoculum is easily killed by direct sunlight, desiccation, or high temperatures. Good nodulation usually will not occur in fields under extremely dry, wet, or high nitrogen conditions. Soil N should be about 50 pounds per acre. Inoculants formulations include peat-based, liquid, and granular. Formulation selection depends primarily on price and application method. Advantages and disadvantages exist with each inoculant formulation. If properly used, all formulations should perform well. Recent NDSU research at Carrington generally indicates similar soybean yield among inoculant formulations.

Greg Endres
Area Extension Specialist



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