NDSU Crop Pest Reports

Issue #3, May 14, 2009

• Effect on Corn Yields Due to Late Planting

• Cold Soils and Soybean Emergence

• NDAWN to Determine GGD for Field Crops

Effect on Corn Yields Due to Late Planting

       The optimum planting dates for corn for southeastern North Dakota are from April 25 to May 30.  Data from University of Minnesota has shown yield reductions of 1.2% per day after May 30.  U of M Extension Corn Agronomist Jeff Coulter, has recommended the latest planting dates for corn in central and northern Minnesota to be harvested for grain to be June 5.  If corn is to be planted from June 1 to 10, plant hybrids that are 8 to 15 maturity units earlier than full season.  Planting depths should remain the same and be planted into adequate moisture to ensure germination.  Shallow planting is not encouraged due to the increased risk of poor establishment of nodal roots.  Plant at depths of 1.75 to 2 inches for is considered optimal.  To read all of Jeff Coulter's newsrelease, visit  "Considerations for Late-Planted Corn in Minnesota".

Cold Soils and Soybean Emergence

    Current weather conditions have not been favorable for soybean emergence.  As a result, several diseases may affect emergence and stand establishment.  Diseases of concern include; Phytophthora root rot, Rhizoctonia root rot, Pythium and Fusarium root rot.  The best defense against these diseases is a good fungicide seed treatment and Phytophthora resist varieties.  Nothing can be done to protect the seed once it's been planted.
Phytophthora root rot: Is a common soil fungus that survives from growing season to season as spores or mycelium in soil or in crop refuse buried in soil.  Soybeans may be infected at any stage of development.  This disease is associated with cool temperatures and high soil moisture.  The best diagnostic symptom is a brown discoloration of the stem and lower branches that extends from below the soil line upward several inches above the soil line.  The tap root is dark brown and the entire root system may be rotted. The disease pattern varies within a field.  Control is to plant resistant varieties.
Rhizoctonia root rot: This disease produces no spores and survives in the soil as sclerotia.  It will grow as a saprophyte on dead plant material in the absence of soybeans.  This disease occurs when conditions are unfavorable for germination and emergence.  Disease symptoms appear as brown, dark brown, or reddish discoloration at the base of seedlings or on roots just below the soil surface.  Use fungicide seed treatments for control.
Pythium: Is a fungi that are found in most cultivated soils and survive in soil or crop refuse as oospores and mycelium.  This disease is found under cool, moist conditions and is associated with seedlings and young plants.  Infected plants develop a "wet rot" which results in pre- and post emergence damping-off.  Cortical tissues may "slip off" when infected seedlings are pulled up.  Control is to use recommended seed treatments.
Fusarium root rot: Is a common soil fungus that survives in the soil as chlamydospores and as mycelium or chlamydospores in crop refuse.  This disease develops on seedlings and young plants under cool, moist conditions throughout a field.  A dry rot of upper roots and lower stems is associated with delayed emergence, and stunted and weak plants.  Under droughty conditions, seedlings may wilt and later develop adventitious roots is moisture is available.  Control is to use recommended seed treatments.

NDAWN to Determine GDD for Field Crops

    The North Dakota Agricultural Weather Network (NDAWN) system can be used to determine growing degree days (GDD's) to estimate crop growth for field crops throughout the growing season.  This can be used to determine when to scout for various crop pests or for the correct growth stage for herbicide and fungicide applications.

    How are GDD determined?   GDD are calculated using the following formula.

                     Min. daily temp + Max daily temp  minus Base Temperature = Daily GDD
                                                2

    Base Temperatures vary from cool season and warm season crops.  When the temperature falls below the minimum base temperature or exceeds the maximum base temperature for the crop in question, then the minimum or maximum base temperature is used in the calculation.  The following table lists the minimum and maximum temperatures for three crops.

    It is important to be sure to use the correct base temperature for the crop.  When comparing GDD's between wheat and corn, will be totally different for the same amount of days due to the different base temperatures used.   For example, Small grains require about 180 GDD"s for germination and emergence.  While corn requires 120 GDD's for germination and emergence.  Wheat will requires 140 GDD's for each leaf whether accumulated in four days or ten days and about 2400 GDD's to reach maturity, which can range from 83 to 100 calendar days.  Corn leaf development is described be two response curves.  Emergence to leaf stage V10 (ten visible collars) takes 80 GDD's per leaf.  From V10 to the final leaf is faster and is approximately on leaf every 50 GDD's.

    The NDAWN system has other features that measures rainfall, wind speed, wind direction, solar radiation, dew point, wind chill, soil temps and relative humidity.  Us the following link for the NDAWN system. 

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