ISSUE 6   June 8, 2006

EVALUATING CROP PROBLEMS

Persons working in crop production are often called upon to trouble-shoot in situations involving suspected crop injury or problems. These situations require careful analysis and scouting before judgment is formulated. For purposes of this discussion, I would like to define "injury" as stunting, delayed development or malformation of plant tissues which may or may not affect yields. Herbicide injury may result from applications to the crop, from residues in the soil or from drift.

When evaluating crops involved in suspected herbicide injury, keep in mind that some other factors may have caused the observed effects or the herbicide may be only one of a combination of several casual factors. Look for other possible causes. Are there holes in the leaves or stems or pruned roots from insect damage? Has there been severe weather - wind, drought, hail, flooding, earlier frost, high temperatures, etc. - that could have caused damage, Flooding damage in crops in some areas which recently occurred, greatly compounds the diagnosis. Could a disease be involved? Could it be excessive or misplaced row fertilizer or a nutrient deficiency? Or is the effect resulting from a combination of causes?

Look for patterns of injury in the field. Herbicide injury is often in a pattern associated with soil types or movement of application or incorporation equipment. Observe other susceptible crops or weeds in the area for herbicide effects. For comparison, try to find a check area where no herbicide was applied in the same field.

If you conclude that herbicides are the probable cause of crop injury, try to determine why the injury occurred. Limited crop tolerance to certain herbicides is sometimes a problem especially under heavy rainfall or sandy soils or on dry, loose soil. Miss-use such as high rates, wrong chemical, improper method of application, non-uniform application, overlaps, improper applicator adjustments and tillage operations that concentrate the chemical - are some reasons for herbicide injury. Some varieties/hybrids are more susceptible than others. Weather and soil conditions that cause plant stress may make the crop more susceptible to herbicide injury.

Donít be too hasty to evaluate the effects of herbicide injury. Give the plants a chance to grow and recover. Check growing points to see if the plants have potential for recovery. Compare injury effects and weed control benefits. Stand counts and injured plant counts are important considerations. Unbiased yield checks in affected and unaffected similar areas of the same field are the best estimates.

 

NODULES ON SOYBEANS

Nodulation, the symbiotic relationship of bacteria on the soybean roots, can be seen shortly after emergence (VE), but the plant is not actively fixing nitrogen until the V2 to V3 stages. Soybean plants that are 5 to 6 inches tall should have their second unfolded trifoliolate leaflets (V2 stage) totally unrolled. The number and nodules formed on the soybean roots along with the amount of nitrogen fixed increases until the R5.5 stage. Nodules actively fixing nitrogen for the plant are pink or red inside. White, brown or green nodules indicate that nitrogen-fixation is not occurring. Nitrogen fertilization after planting is not recommended as nitrogen fertilizer applied to active nodules will render these nodules inactive or inefficient, depending on the amount of nitrogen applied.

Soil nitrogen is utilized over fixed nitrogen, if available in large amounts. Check the health of your soybean nodules and check root proliferation. At V2, soybeans should be rooting down six inches into the soil and by V5 will completely reach between 30-inch rows, making any cultivation at V5 needing to be very shallow.

When checking soybean seedlings for nodules, donít pull the roots directly from the soil since that process will slough off the nodules and result in an inaccurate count. Its best to use a small shovel, spade or trowel and dig the soybean roots carefully and shake gently or place in a bucket of water to wash soil off the roots. Nodules then can be counted and examined for viability. Itís suggested to check at a minimum of five sample sites in a field to make a good assessment.

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

 

TEMPERATURES FOR 2006 GROWING SEASON COMPARED

Temperature regulates the rate of crop development and indirectly impacts yield potential. So how do temperatures this spring compare to other growing seasons? In the following table I have listed the growing degree day (GDD) accumulations for small grains (wheat and barley) and corn for this year and the averages for the last five years.

Through June 5th this year we have accumulated about 200 more small grain GDDs than the running 5 year average (see following table). Similarly corn GDDs are running about 100 greater than the average. What does this mean in terms of crop development? Small grains require ~143 GDDs for the appearance of a new leaf. Therefore, the crop this year is about 1 to 1.5 leaves ahead of the average. Unfortunately, faster development usually means less yield potential. Nevertheless, many crop physiologist believe that the most critical period for "fixing" yield potential is from jointing until anthesis, so we could still achieve excellent yields if temperatures (and moisture) are favorable in the coming weeks.

Corn requires 85 GDDs for the appearance of a new leaf. This year we are, therefore, just over 1 leaf ahead of the average. It also means that the corn crop is on track to finish a week earlier than average. That is good news as it means less drying will be needed in the fall. Though many weeks of unpredictable weather remain of this growing season, the data to date suggest that we are on track for a warmer than average season and that crops will likely finish earlier than "average".

Use the North Dakota Agricultural Weather Network (NDAWN) to continue monitoring growing degree accumulations for the season (http://ndawn.ndsu.nodak.edu/applications.html).

Small grain and corn GDD accumulations through June 5th for selected locations in North Dakota for 2006 and the average of the last five growing seasons. GDDs are calculated based on planting dates of April 15 and May 1 for small grains and corn, respectively.

 

Small Grain GDDs

Corn GDDs

Location

2006

Ave 2002-06

2006

Ave 2002-06

Carrington

1230

995

416

305

Dickinson

1143

984

388

297

Fargo

1302

1095

426

340

Minot

1228

1003

401

297

Average of locations

1225

1019

408

310

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


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