ISSUE 6    June 9, 2005

GROWTH STAGING OF CANOLA

Canola planted this spring is now 84 per cent emerged. There have been a few reports of very early plantings now starting to bolt and flower. 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 - cotyletons showing

2

Rosette

 

2.1 First true leaf

 

2.2 Second true leaf expanded

 

2.3 Etc. For each additional leaf

3

Bud

 

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 herbicide tolerant canola varieties, one has to pay special attention to plant stage for last application. For the Roundup Ready canola, glyphosate application can be made from seedling emergence to start of bolting (3.1 to 3.2). For Liberty Resistant canola, the Liberty 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. Watch the blooming stages closely also when spraying fungicides to prevent white mold or sclerotina stem rot. This would be between the 4.1 and 4.2 stages. Check NDSU Extension Cir. A-1208 entitled Canola Flowering and Fungicide Application Timing. It is also available on the NDSU Extension web site at: http://www.ext.nodak.edu/extpubs/plantsci/crops/a1208w.htm

Later in the summer, 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.

 

WET, SATURATED SOILS AND CROP GROWTH

Recent heavy rains in some eastern and east central production areas have caused some real concerns. Not only has the wet conditions prevented farmers from completing planting but can be very damaging to emerged seedlings. Prolonged soil saturation affects crop growth and yield. In early growth stages, corn or soybeans can survive for only two to four days under water in anaerobic conditions. Most dry bean classes or types are extremely sensitive to flooding. One or two days can completely destroy bean plants. Corn is also somewhat sensitive to flooding in the early vegetative stages (especially prior to the fifth or sixth leaf stage). It appears that soybean are more tolerant to flooding that either corn or dry beans. Moderate water movement can reduce flood damage by allowing some oxygen to get to the plants, keeping them respiring and alive. Drainage within one to two days increases the chance of survival.

The injury extent to seedlings is determined by the plant stage of development at ponding, duration of flooding and the air/soil temperatures as well as if axillary buds are present on damaged plants. If temperatures are warm during flooding (greater than 77 F), plants may not survive 24 hours. Cool temperatures and cloudy conditions may prolong survival. However, wet weather favors disease development. Seed treatments are effective, but limited in protection. Seedling development slowed or delayed two to three weeks allow soil-borne pathogens a greater opportunity to cause damage. Seed rots, seedling blight, corn smut and crazy top affect corn plant development later even though ponding occurred earlier. Delayed soybean growth allows diseases such as Fusarium root rot, Phytophthora rot and Pythium rot to establish and weaken or destroy seedlings. Carefully assess damage before tearing up or abandoning an existing stand.

Rotted seed or damped-off seedlings will reveal probable crop losses. On surviving stands, remember that favorable weather for plants after ponding is important. Cultivation, once soils are dry enough, will open and aerate surface soil and promote root growth. Be careful working the soil. Working wet soil causes compaction that impacts crop growth. One must be patient in waiting for the soils to dry.

An additional nitrogen application in corn may be necessary in fields that show signs of yellowing or uneven growth. A late test for nitrate when corn plants are still six to twelve inches tall can determine if more nitrogen is needed. Maintain a good weed control program so that crop plants are not robbed of nutrients and moisture later in the season.

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

 

CORN GROWTH AND DEVELOPMENT: ROOTS

Corn growth is beginning to pick up pace with the warmer weather of recent weeks. Though this spring has been cooler than normal, corn growing degree day accumulations for most stations this year are actually running ahead of accumulations for the same period for the three previous years. Due to cool wet soils this spring, corn generally lacks the deep green color that characterizes corn plants later in the summer. Constraints to early growth under typical North Dakota spring conditions can be attributed to sub-optimal root growth. Hence the need to consider roots, the unseen half of the plant, when evaluating plant health and growth potential.

Corn has two rather distinct rooting systems. The first is comprised of the seminal roots that arise from the seed at germination. The seminal root system is limited in size and function but provides a mechanism for the emerging plant to access nutrients and water. The nodal roots develop at about1 inch below the soil surface beginning at about the first collar leaf stage. Nodal roots (2-10 per node) generally develop from all of the subterranean nodes (typically 5). They quickly supplant the seminal roots as the primary source of nutrients and water by the three leaf stage. It is also common for roots to arise from nodes that are above the surface of the soil. These roots are called brace roots and if conditions are favorable are able to penetrate into the soil and effectively extract water and nutrient from the top layer of the soil.

Factors that affect root growth to consider and manage when possible:

  • Soil temperature - the optimum soil temperature for corn root development is 79; there is little or no growth below 50. The cool temperatures this spring have generally limited root development causing plants to be pale green or show symptoms of P deficiency. No-till soils with high residue tend to be a few degree colder than soils that are tilled. Furthermore, well drained soils warm up faster than wet soils.
  • Inadequate soil moisture - Roots will not develop or grow through soil that is below the permanent wilting point. They will follow water in the soil, however, in that they will branch and develop in regions of the soil that have favorable soil moisture even if surface layers are depleted of moisture. If the soil surface is dry, hot or compacted during nodal root development, nodal roots may be limited resulting in young plants that easily lodge. This has been referred to as the 'rootless corn syndrome'. There were a few reports of this problem last year in North Dakota.
  • Excess soil moisture - Excess moisture this spring is a much bigger problem for corn root development than inadequate soil moisture. When soils become saturated, the amount of oxygen available to the roots decreases rapidly as plants and microorganisms deplete available sources. Corn roots need oxygen for respiration, cell division and nutrient uptake. Water-logged conditions can also predispose plants to root rots later in the season, so the ultimate effect of excess moisture may not be known until late in the season. Promoting rapid field drainage can directly benefit root development in wet seasons like this year.
  • Nutrient status - Root growth is favored by phosphorous. Roots will not preferentially grow towards a band of fertilizer but if they grow into one, they will develop more profusely there if nutrients are otherwise limiting. Pop-up fertilizers are recommended in North Dakota in order to enhance P uptake by corn seedlings that typically have restricted root growth due to cold soil temperatures. Mycorrhizae fungi also aids corn roots in extracting P from the soil. Add additional P when corn follows a black fallow, canola or sugar beets as these crops/practices reduce the amount of Mycorrhizae fungi in the soil.
  • Compaction and chemical barriers - Roots are not able to penetrate very compacted layers of soil or grow into layers that are high in salts or calcareous hardpans. For fields with soils known to be prone to compaction, check for compaction layers by digging a root pit.
  • Insect damage - the most common root damaging insects in ND are white grubs, wireworms and corn root worm larvae (there are currently only a few areas known to have a problem of corn rootworm). As part of your scouting program examine the roots for damage from insects. I am aware of at least one report of serious white grub damage to corn this year. Most root-feeding insects are best controlled with insecticides applied on the seed or at the time of planting.
  • Joel Ransom
    NDSU Extension Agronomist
    Cereal Crops
    joel.ransom@ndsu.edu


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