Section 2 - Crop Development

Relative Maturity of Field Crops Following is average days to physiological maturity of many crops grown in the Northern Plains. Early killing frost plus extreme high temperatures at flowering stages are the two factors most limiting yields of late planted crops. Time required for maturity varies with variety or hybrid, seeding

date, geographic region, and available growing degree days. A shortage of growing degree days can increase days required for maturity. Corn, soybean, sunflower and milletare especially sensitive.

Tracking Growth Stages, Growing Degree Days All grain plants follow the same general pattern of development, although the specific time interval between stages, the number of leaves and nodes on the main stem and the number of tillers will vary by variety, season, planting date and location. As well, the amount of growth for any variety is directly related to nutrient and moisture availability. .Still, the rate of growth development for any wheat variety is directly related to temperature (accumulated heat units), except under extremely dry conditions. Thus, by knowing the planting date for wheat, and by tracking weather data, one can predict growth development and plant stage. This helps growers make timely treatments to control weeds, top dress fertilizer, control diseases, and other management decisions. The North Dakota Agricultural Weather Network (NDAWN) can help growers keep track of weather and growing degree days. On NDAWN’s Internet home page (http://ndawn. .ndsu. .nodak. .edu) click on the “applications” link. There, you will find a number of applications for using NDAWN, including

:• Predicting Sclerotinia risk in canola •  Corn degree days  • Potato late blight severity  • Sugarbeet degree days, growth stages, cercospora   •   Sunflower degree days   •   Wheat degree days,growth stages, disease forecasting, midge forecasting   •   Crop water use  •  Insect degree days   •   Heating/cooling degree days

For wheat, the GDD informationcan be used for determining date of emergence and current growth stage. Current leaf stage provides information, for example, on when herbicides are needed and when the crop is too advanced for certain herbicides.  If frost or wind damage causes loss of leaves, the GDD information provided by NDAWN would allow correct leaf staging in absence of some leaves. Correct growth staging also is important for fungicide decisions. 

Consult with an agronomist, certified crop adviser, or county extension agent/educator for more background on growing staging crops, or about how to apply NDAWN information.  NDSU has a publication online, “Identifying Leaf Stages in Small Grains,” at www.ag.ndsu.edu/pubs/plantsci/weeds/w564w.htm. The University of Minnesota publication “Growth and Development Guide for Spring Wheat” can be found online at www..extension.umn.edu/distribution/cropsystems/DC2547.html.

Effect of Environment on Growth,Development and Yield of Small Grains The following describes how temperature and water stress impacts small grain development and yield at key growth stages. 

Emergence to Four-Leaf Stage -- During the vegetative phase of development, from emergence to about the four-leaf stage, growth is directed towards new leaves and tillers.   All leaves that will emerge on the main stem are initiated during this stage. Tillering begins at about the 2-leaf stage but tillers do not become visible until the 3rd to 4th leaf stage . The total number of leaves (typically 8) that will develop is primarily determined by the genetics of the variety and is rarely altered by the environment . The only yield component that is fixed at this stage of development is plants ft-2 . Yield potential is generally not adversely affected during this phase except by severe moisture stress or very high temperatures .

Four-Leaf to Jointing -- At the four-leaf stage, the plant switches from vegetative to reproductive development as the growing point begins forming the spike. Shortly after the six-leaf stage the main stem begins to elongate (begins jointing). Spikelet numbers are fixed in this relatively short period of about 10 days between the four-leaf stage and jointing. Though tiller development can continue beyond this stage, most tillers that produce spikes that contribute to yield will form by the beginning of jointing. Drought stress and elevated temperatures can reduce the number of spikelets that develop and induce tiller mortality.

Jointing to Anthesis -- During the period from jointing to anthesis, tillers that cannot be supported by the plant die and the number of spikes per plant and the number of florets per spikelet become fixed. Most physiologists seem to agree that yield is most affected by stress during this phase. Any stress that will reduce the rate of photosynthesis (i.e. high temperatures, drought, foliar diseases, competition from weeds) will impact yield potential by reducing the number of tillers that survive and the number of florets that will be fertile. It is in the previous growth stage that most of the potential components of yield are developed, but it is during this growth stage the components that will actually contribute to yield are fixed.

Anthesis to Physiological Maturity -- After anthesis the number of kernels per plant is fairly well established, though some kernel abortion can occur early in the grain filling process. Any stress that will reduce the rate of photosynthesis can impact the weight of the kernel. High temperature and drought during this stage typically produces kernels with low seed and test weight.

Soybean Growth Stages Soybean plant development is divided into vegetative (V) and reproductive (R) stages . With the exception of the first two stages, the (V) stages are designated numerically as V1, V2, V3, etc . through V(n), where (n) represents the number for the last node stage of a specific variety . The (n) will fluctuate with variety and environmental differences . The eight R stages are simply designated numerically .

The V stages following VC are numbered according to the uppermost fully developed leaf node. Start with the unifoliolate leaf node when counting the number of fully developed leaf nodes. A leaf node is fully developed when the leaf above it has leaflets which are fully unrolled. That is, the leaflet edges are no longer touching.

Vegetative Stages - Stage Description

VE Emergence

VC Cotyledon

V1 Unifoliolate and first trifoliolate leaves are fully developed

V2 Unifoliolate and first two trifoliolate leaves are fully developed

V3 Unifoliolate and first three trifoliolate leaves are fully developed

V(n) Unifoliolate and (n) trifoliolate leaves are fully developed

Reproductive Stages Stage Description

R1 Open flower at any node on the main stem

R2 Open flower at one of the two uppermost nodes on the main stem with a fully developed leaf

R3 Pod is 3/16 inch long at one of the four upper- most nodes on the main stem with a fully developed leaf

R4 Pod is 3/4 inch long at one of the four upper- most nodes on the main stem with a fully developed leaf

R5 Seed is 1/8 inch long in the pod at one of the four uppermost nodes on the main stem with a fully developed leaf

R6 Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf

R7 One normal pod on the main stem that has reached its mature pod color

R8 95% of the pods have reached their mature pod color

Sources: Iowa State University, Purdue

Soybean Growth Stages Online

• http://weedsoft.unl.edu/documents/GrowthStagesModule/Soybean/Soy.htm

• www.planthealth.info/pdf_docs/soy_growthstages_msu.pdf

• http://extension.agron.iastate.edu/soybean/production_growthstages.html

• www.ag.ndsu.edu/pubs/plantsci/rowcrops/a1174/a1174w.htm

Bloom Key Soybean Development Stage The beginning bloom stage or R1 stage in soybeans is marked by the plants having at least one flower on any node of the main stem.  If there is still a need to spray for weeds, check the label carefully for spraying after flowering begins. There are a number of herbicides that can be used after flowering begins.  Always read and follow label guidelines when using pesticides.  Soybeans are at 50% bloom when an open flower can be found on every other plant in a row. Flowering, unlike maturity on soybeans, begins toward the bottom of the plant (at the third to sixth node) and then progresses upward and back downward. Branches off of the main stem will flower a few days later than the main stem. While flowering begins at the base of the plant and proceeds to the top of the plant, physiological maturity of the beans will progress anywhere on the plant stem.  Normally, soybean pods will be mature in the middle or top of the plant and down. Thus, remember to check pods toward the bottom of the plant when determining if harvest time has come. Flowering of soybeans is an important time in bean growth and development.   At stage R2, full bloom, each plant has accumulated about 25% of its total dry weight and nutrients; it has attained about 50% of its mature height; and, it has produced 50% of its total mature node number.  This later flowering stage begins the period of very rapid N-P-K and dry matter accumulation that will continue through R6. Also, during flowering, the soybean plant gears up on its nitrogen fixation in order to provide for the demands of the plant.  Scout for disease and insect problems (aphids) during this critical early time period of flowering. 

Corn Growth Stages Corn plant development can be divided into vegetative (V) and reproductive (R) stages. The (V) stages are designated numerically as V1, V2, V3, etc.  through V(n) where (n) representsthe number of leaves with visible collars. The first and last (V) stages are designated as VE (emergence) and VT (tasseling). The six reproductive stages are simply designated numerically. Each leaf stage is defined according to the uppermost leaf whose leaf collar is visible. Loss of the lower leaves will begin about V6 due to increased stalk size and nodal root growth.  To determine the proper leaf stage after lower leaf loss, split the stalk lengthwise and inspect for internode elongation.  The first node above the first elongated internode is generally the fifth leaf node.  This fifth leaf node can be used as a reference point for counting the top leaf collar.

Vegetative Stages Stage Description

VE Emergence

V1 One leaf with collar visible

V2 Two leaves with collars visible

V(n) (n) leaves with collars visible

VT Last branch of tassel is completely visible

Reproductive Stages Stage Description

R1 Silking - silks visible outside the husks

R2 Blister - kernels are white and resemble a blister in shape R3 Milk - kernels are yellow on the outside with a milky inner fluid

R4 Dough - milky inner fluid thickens to a pasty consistency

R5 Dent - nearly all kernels are denting

R6 Physiological maturity - the black abscission layer has formed

Sources: Iowa State University, Purdue

Evaluating Corn Growth Stages The growth and development of corn is largely regulated by temperature accumulations and not calendar days.  In fact, corn development can accurately be predicted from corn growing degree day accumulations.  Corn growing degree days are calculated using a base temperature of 50 degrees and can readily be obtained from the NDAWN web site (http://ndawn.ndsu.nodak.edu) by going to “corn degree days” under the “applications” section on the left hand section of the home page.

At the five leaf stage, the corn plant switches from vegetative growth to reproductive growth as the growing point stops initiating leaves and begins initiating the tassel.  At the 6 leaf stage, ear shoots begin to form. The number of kernel rows on the developing ear is determined relatively soon after it begins development and is largely determined by genetics, and less so by the environment. The length of the kernel row and therefore the total number of potential kernels, however, is determined during a longer period of time (6 leaf stage through one to two weeks before tasseling). Severe stress during this stage can shorten the length of the cob and reduce yield potential. Nevertheless, stress during ear development is far less damaging to yield potential than stress during and shortly after pollination, as the potential number of kernels developed typically exceeds the number that can be pollinated filled.  Certain management practices are growth stage dependent; therefore, properly identifying the growth stage of your corn crop will be important to ensuring that management practices are applied at the appropriate time.  This is particularly true of the application of herbicides. When growth staging a crop you should begin by obtaining a representative sample of plants from the field or part of the field of interest. Remove any soil attached to the plants so that you are able to observe the roots and crown.

Vegetative growth stages of corn are defined by the number of leaves . Counting leaves in corn is fairly straight forward as the process is not encumbered with tillers and leaves on tillers as is the case in small grains.  However, care must be taken to ensure that the earliest leaves are included when counting leaf numbers.  The first leaf is small and often dies and is torn from the plant early in the growth of the plant. The first leaf has a blunt tip.  Look for sheath remnants at the crown of the plant if you suspect that the first leaf (or second for that matter) is missing. Include only those leaves that have a collar. Include all leaves, even those that have been damaged by hail or frost.  The total number of leaves that a plant will develop is more or less fixed for a given hybrid; leaves that are stripped from the plant will not be replaced by additional new leaves.

In order to determine the growth stage of older plants that have lost their lower leaves, uproot the plant and split the stem with a knife through the root ball. At the very base of the stem, identify the first visible internode. Internodes are the white area between the more yellow bands of the nodes. The first obviously visible internode should about ½ to 3/4 inch in length . The node directly above this internode will be the fifth node, and the leaf arising from this node will be the 5th leaf.  Find that leaf and continuing counting leaves from that point.

In corn, management recommendations can also refer to the height of the plant, rather than leaf stage.  For example, certain herbicides can only be applied to corn less than 12 inches tall. The plant height in this case is measure from the base of the plant to where the upper most leaf reaches without stretching it out.

Canola Growth Stages

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 in the following growth chart. With herbicide tolerant canola, one has to pay special attention to plant stage for last application. For 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.

Diagnosing plant problems

Local agronomists and county extension agents/educators are an excellent resource for diagnosis; the following plant labs can also help diagnose plant pests and problems.  Contact the lab or see lab web site for instructions before submitting plant samples. Digital photos can help provide clues and missing information to aid in diagnosing a problem.

NDSU – NDSU Plant Diagnostic Lab, NDSU Dept 7660, PO Box 6050, Fargo ND 58108-6050, ph 701-231-7854, email: diaglab@ndsuext .nodak .edu, web site: www.ag.ndsu.nodak.edu/diaglab.  Fee-based services include insect, weed, disease identification and control recommendations, herbicide injury diagnosis, and soybean cyst nematode screening.

UM - Plant Disease Clinic, 495 Borlaug Hall, 1991 Upper buford Circle, University of Minnesota, St.  Paul, MN 55108 ph. 612-625-1275.  Web site: http://pdc.umn.edu. Fee-based services include plant disease, virus ID, nematode analysis, as well as seed quality testing. .SDSU – Oscar E. Olson Biochemistry Labs, Brookings, ph 605-688-6171, web site: http://anserv.sdstate.edu.

 SDSU Plant Disease Clinic: http://plantsci.sdstate.edu/planthealth (click on Plant Diagnostic Clinic). Ph 605-688-5545Agvise Labs – www.agvise.com, Northwood, N.D. ph 701-587-6010; Benson, MN, ph 320-843-4109. Midwest Labs – www.midwestlabs.com. These labs (as well as professional crop consultants/certified crop advisers) can help determine key factors that affect crop productivity, such as:

Soil organic matter tests – Knowledge of the organic matter level will serve as a guide in selecting an effective herbicide and rate of application, as well as helping to assure crop safety. Testing once every five years should be adequate.

Herbicide spray water analysis – High salt levels in spray water can reduce weed control in nearly all situations. Calcium, and to a lesser degree, magnesium, are antagonistic to 2,4-D and MCPA amine, dicamba, and glyphosate.

Plant tissue analysis – This indicates the nutrient status of plants at the time of sampling, serving as a monitoring tool for determining the adequacy of current fertilization practices . Plant tissue analysis will also detect unseen nutrient deficiencies and may confirm visual symptoms of deficiencies. Toxic levels also may be detected. Combined with soil test information, a plant analysis report can help a producer tailor fertilization practices to specific soil-plant needs.

IPM Surveys Track Growing Season Field Pests

Crop scouting results from North Dakota field surveys are posted on the NDSU IPM web page at: www.ag.ndsu.nodak.edu/aginfo/ndipm. This site provides maps and updates indicating weekly survey results for diseases and insect pests of various field crops. Links to additional information about these pests and other IPM (integrated pest management) resources are provided as well. The Minnesota Department of Agriculture Plant Pest Survey and Crop Pest Fact Sheets can be found online at www.mda.state.mn.us/plants – a wealth of timely pest information – what’s happening where – can be found during the growing season here as well .