NDSU Crop and Pest Report

Plant Science


ISSUE 8   June 24, 2004

ANALYZING AND EVALUATING CROP PROBLEMS

Persons working in crop production are often called upon to trouble-shoot in situations involving suspected crop injury from herbicides. These situations require careful analysis and scouting before judgements are formulated. For purposes of this article, 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, frost, high temperatures, etc. - that could have caused damage. Flooding damage in crops 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 problem 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, certain soil pH’s, sandy soils or on dry, loose soil. Miss-use, high rates, wrong chemical, improper method of application, nonuniform 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.

Don’t be too hasty to evaluate the effects of herbicide injury. Give the plants a chance to recover. Check growing points to see if the plants have potential for recover. 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.

GROWTH STAGING OF CANOLA

Determining the growth stages of canola is relatively simple using a scale developed in Canada. This scale uses five principal stage designations and subdivides these into secondary stages. These stages are described below:

Stage

Description of main Raceme

0

Pre-emergence

1

Seedling - cotyledons showing

2

Rosette

 

2.1 First true leaf expanded
2.2 Second true leaf expanded
2.3 Etc. for each additional leaf

3

Bud (Bolting)

 

3.1 Flower cluster visible at center of rosette
3.2 Flower cluster raised above level of rosette
3.3 Lower buds yellowing

4

Flower

 

4.1 First flower open
4.2 Many flowers opened, lower pods elongating
4.3 Lower pods starting to fill
4.4 Flowering complete, seed enlarging in lower pods

5

Ripening

 

5.1 Seeds in lower pods full size, translucent
5.2 Seeds in lower pods green
5.3 Seeds in lower pods green-brown or green-yellow, mottled yellow
5.4 Seeds in lower pods yellow or brown
5.5 Seeds in all pods brown, plant dead

With the new herbicide tolerant canola’s one has to pay special attention to plant stage for last application. For the Roundup Ready canola, application can be made from seedling emergence to bolting (5 - 6 leaf). For Liberty Resistant canola, the application can be made from seedling stage up until early bolting stage (3.2). For Clearfield canola varieties, Beyond application can be made up to just prior to bloom.

Canola in the 5.3 to early 5.4 stage should be near or at swathing stage. These stages change very rapidly during the ripening period if temperatures are warm and under dry conditions.

 

GROWING DEGREE DAYS: SUNFLOWER GROWTH AND DEVELOPMENT

Sunflower plants are starting to grow and develop at a fairly rapid pace. The growing degree days formula uses 44EF as the base temperature and the 86EF temperature as the maximum for calculation. The high temperatures ans low temperatures are used each day to obtain a cumulative number of GDD’s. See table below for approximate growth stages of sunflower as related to relative heat units.

Sunflower Stage

Plant Description

GDD* units

Days*

VE
V4
V8
V12
V16
V20
R1
R2
R3
R4

R5.1
R5.5
R6
R7
R8
R9

Emergence
4 True Leaves
8 True Leaves
12 True Leaves
16 True Leaves
20 True Leaves
Miniature Terminal
Bud
Bud <1.0" from leaf
Bud >1.0" from leaf
Bud open Ray flowers visible
Early flower (Start Pollination)
50% flowered (50% pollinated)
Flowering Complete
Back of head - pale yellow
Bracts green - head back yellow
Bracts yellow - head back brown

167
349
545
690
772
871
919
1252
1394
1492
1546

1623
1780
2052
2211
2470

10
20
28
34
38
44
46
61
67
71
73

77
84
96
104
119

*Average number of Days and GDD units accumulated from planting

Source: NDSU Carrington Research Extension Center: 2 yrs. Data average over five sunflower hybrids.

Note: Check the NDSU NDAWN web site for the 2004 Growing Degree Units in various locations in North Dakota. Just enter in the planting date and the current date for your location.

Web site for Growing degree days:

http://ndawn.ndsu.nodak.edu/sunflowerdd-form.html

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


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