Traill County Ag Alert Newsletter

July 17, 2008

RAINFALL & GROWING DEGREE DAYS (GDD)

 Location                                 Mayville                      Hillsboro                    Galesburg
Corn GDD                                953                               964                               951
Compared to 2007                   -214                               -209                              -211
5 Year Average                        -114                               -105                                -77

 Wheat GDD                           2120                              2125                             2130
Compared to 2007                   -324                               -325                              -303
5 Year Average                        -197                               -193                             -133 

Rainfall Since June 1                 5.58 inches                   6.46 inches                   7.04 inches

SOYBEAN APHIDS
Soybean aphids made an early appearance this year and numerous fields have been treated and more fields are scheduled to be treated. Please refer back to last weeks Ag Alert for more information on scouting and thresholds for these pests. Last weeks Ag Alert can also be accessed via the Traill County web page at: www.ext.nodak.edu/county/traill/ 

SOYBEAN PLANT DEVELOPMENT
At this time of the year the soybean plants are starting to flower. Soybean plant development has two distinct growth phases. The first is the vegetative stage (V) that covers emergence and leaf development. The second phase in the development is the reproductive (R) stage which starts with flowering and ends at the time the seed is mature. Plant stages are determined by the leaf, flower, pod, and seed development within the pods.  

A leaf is considered fully developed when the leaf at the node directly above it (the next younger leaf) has expanded enough so that the three leaflets, which make up the “trifoliate leaf”, are fully visible. A node is a part of the stem where a leaf is attached. Although the plant will change from the vegetative stage to the reproductive stage, leaf development will continue and plant stature will still increase. Growth stages can overlap. On a field level a growth stage begins when 50% or more of the plants are in or beyond that stage.

Growth stages of Soybean

VE Emergence (Plant is emerging)
VC Cotyledon (Unifoliate leaves fully developed)
V1 First true leaf (The first trifoliate leaves are fully developed)
V(n) Leaf development (Additional trifoliates are fully developed)
R1 Beginning bloom (One open flower at any node on the main stem.)
R2 Full bloom  (Open flower at one of the two uppermost nodes on the main stem with fully developed leaf).
R3 Beginning pod  (Pod is 3/16 inch long at one of the four uppermost nodes on the main stem with a fully developed leaf.)
R4 Full pod  (Pod is 3/4 inch long at one of the four uppermost nodes on the main stem with a fully developed leaf.)
R5 Beginning seed (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 Full seed  (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 Beginning maturity (One normal pod on the main stem that has reached its mature pod color) (normally brown or tan, depending on variety).
R8 Full maturity (Ninety-five percent of the pods have reached their mature pod color.) 

Flowering of the soybean plant is initiated on the third to sixth main stem node and continues upward and downward from there. Pollination and fertilization are usually accomplished before the soybean flower opens.

The critical growth stage in soybean for water stress is from flowering to seed fill. Any stress from the R4-R6 (late pod development to early seed fill) will cause more yield reduction than if the stress takes place at another time in the plant’s development.

SUNFLOWER BUD MOTH
As I was scouting sunflower fields I have noticed a black granular material on the top of the developing head, at the base of the head, or on the stalk.  It's frass (bug poop). We have to wait and see what this problem will be like though, generally, even high populations of sunflower bud moth do not cause serious economic loss.  The exception is when they attack the head, preventing normal head and seed development.  Unfortunately, there's little to be done about this particular insect problem, mostly because of where it's located.  Like sunflower midge, these insects are inside the plant making it extremely difficult to get insecticide to them, and even long residual insecticides might not be that effective as we don't have good information on their developmental rate.

Sunflower bud moth have two generations in the northern plains, I suspect we're seeing generation 1, generation 2 is not generally economically important because the plant has outgrown it's susceptibility to yield loss (head is already developed).  Most of the plants I have seen have older larvae in them, indicating the damage has already been done in these cases.  Generally, sunflower bud moth feeds on the backs of developing heads in later planted sunflowers.  (Source Dr. Ian MacRae U of M)

EARLY APPEARANCE OF SUNFLOWER RUST
Sunflower rust is a disease that is capable of causing significant yield loss to sunflowers. Sunflower rust appears most years in North Dakota, but isn’t usually observed until late July or early August. However, the presence of sunflower rust in North Dakota was recently found by crop consultant Mike Hutter (Renville County), and the disease has since been observed in other counties. 

Symptoms. Rust will often appear initially on the lower leaves and spread upward as new leaves are produced. The disease produces small (approximately 1/16 inch) dusty cinnamon-brown pustules full of brown spores. Brushing your thumb across rust pustules will leave a dusty brown streak on it. Rust can also infect the stems, bracts and head.

Disease Cycle. Once pustules are observed, they each are capable of producing many more spores and many cycles of infection. These spores can be dispersed long distances by wind, which may rapidly spread the disease to other fields. Spores need a minimum of 2-3 hours of free water (either dew or rainfall) to germinate, but 6-10 hours of free moisture will produce higher levels of germination and infection. Optimal temperature for infection ranges from 60-75 F, but can occur between 39 and 86 F. At temperatures above 90 F, rust spores do not germinate on sunflowers. Once infection occurs, temperature is the only environmental factor that will determine how fast the disease progresses. During cool conditions (65 F day/55 F night) it may take up to 14 days for new pustules to form, but at warm conditions (85 F/75 F) new pustules can form in as few as 8 days. Thus, warm temperatures will often speed disease development.

Fungicides. We have almost no fungicide data from early rust epidemics, simply because they are rare. However, after conversations with colleagues in other sunflower growing states and provinces, the state is recommending being aggressive controlling this disease. We have a long growing season in front of us, the disease is well-known to cause yield and quality losses, and the price of sunflowers is high enough to justify managing the disease.

FIELD SCOUTS RESULTS
Spring wheat fields in Traill County are showing some leaf diseases on the lower leaves but the upper leaves are clean. I did not find any rust in the fields. I did find some symptoms of scab in one field but it was not a lot. As the wheat matures during the next week we will be better able to assess scab severity. 

Field scouts are noticing more bacterial blight (stripe) symptoms in fields now, with 8% of wheat fields and 18% of barley fields with symptoms. High winds with rain result in more leaf wounds, which allow for bacterial infection and spread. Symptoms are brownish, necrotic streaks on the leaves, often with dried, shiny bacterial colonies still evident on the leaf surface.

NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating, Duane Hauck, Director, Fargo, North Dakota. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. We offer our programs and facilities to all persons regardless of race, color, national origin, religion, sex, handicap, age, Vietnam era veteran status, or sexual orientation; and are an equal opportunity employer.
 

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Traill County Extension Office

P.O. Box 730

Hillsboro, ND 58045

701-636-5665 or toll-free1-877-843-6383

Contact us at:  NDSU.Traill.Extension@ndsu.edu