Issue #7, July 24, 2000

• Wheat Diseases and Identification
• Scab (Fusairium Head Blight)
• Root Rots
• Wheat Stem Maggot
• Sclerotinia in Canola
• Staging Canola For Swathing
• There's a Buzzzz Around the Griggs County Courthouse

Wheat Diseases and Identification

    Several questions concerning how effective fungicide applications have been coming into the office this week.  I have looked at some fields and the leaf diseases were heavy in untreated fields.  Scab suppression could also be seen in treated fields.  But with fungicides, the best way to determine effectiveness is with a combine.  There are several other diseases that are being observed this year and what may look like scab may not be.  To determine whether fungicides were effective we first we must identify what disease or insect caused the damage.  The fungicide applications were targeting head scab and leaf diseases but have no effect on root rots and wheat stem maggot damage.  The following paragraphs and pictures will try and help you identify these diseases or insect damage.

Scab (Fusarium Head Blight)

    This disease has become a major problem in our small grains since 1993.  Scab is still with us this year.  We have become very familiar with the symptoms and the yield and quality decreases it causes.  To look at the symptoms, survival and management goto NDSU Extension Publication PP-804 "Fusarium Head Blight (Scab) in Small Grains".

Root Rots

    The following information is from the NDSU Extension Publication PP-785 "Root and Crown Rots of Small Grains".  For more information, goto this publication.
    The "common root rot" of spring wheat and barley in North Dakota is caused primarily by the fungus Cochliobolus sativus.  Other fungi, such as Fusarium or Pythium, may follow initial C. sativus infection and increase the severity of the disease, but these secondary infections are infrequent and often are associated with unusual conditions such as excessive rainfall or high soil temperatures. Outbreaks of root rot caused by Fusarium, Pythium, or other fungi which act as the primary pathogens may occur in localized areas in some years. In very wet years, take-all root rot may also appear on spring wheat.

Symptoms 

    C. sativus infects roots, crowns and other below-ground parts of the plant. Such infections appear as discrete elongate brown spots or lesions. Infections are especially noticeable on the sub-crown internode and coleoptile but are also found on crowns and roots. When root rot is very severe, the entire crown, sub-crown internode and root system will be dark brown and killed. The stem base also may be discolored dark brown. If such severely diseased plants are pulled from the soil, many of the roots break off because they are decayed. 
    When root rot is very severe, the destruction of the root and crown tissue may be so great that plants are killed outright, usually during heading and early filling stages. Killing of plants may be severe when hot weather follows cool wet weather. Such killed plants exhibit "early maturity" or "prematurity blight" and the heads frequently appear almost white. Any seed in these heads is shriveled; many heads contain no grain at all. This severe symptom may appear as scattered plants or as patches in the field.  When the root rot patches are small (a few yards across) and scattered, they resemble the appearance of salt spots or subsoil sand lenses, with which they are sometimes confused. Examination of the roots and crown of a few plants pulled from such a
spot show if root rot is the cause of the problem. Prematurity blight of scattered individual plants also is often found when other root-rot fungi such as Fusarium or Pythium are involved in the complex or when take-all root rot is the cause. 
    In most fields and in most seasons, the severe root rot symptoms of prematurity blight are not present. This does not mean that root rot is absent, but only that the peculiar combination of weather and soil conditions which promote this very severe disease expression have not occurred. Crops which do not show killed individual plants or patches may still be suffering a reduced yield from root rot. 
    Where root rot does not kill, it weakens the plant so that it produces fewer tillers and fewer heads, and there is less grain in each head. Grain from root-rotted plants may be shriveled or have a low test weight. Root and crown rot is most severe when wheat or barley are planted continuously without rotation to other crops. Under these conditions, the root rot fungi can build up to very high levels in the soil. 

Wheat Stem Maggot

    This insect is usually a minor problem but can be found every year in our area.  The Wheat Stem Maggot causes heads be turn bright white while the rest of the plant remains green.  To determine if the head was damaged by wheat stem maggot, pull on head and remove it from the leaf sheath.  Look at the lower part of the stem for any chewing or tunneling.  This is the type of damage done to the plant.

.Note the white head and damaged bottom of the stem.  (click on photo to enlarge)

    The insect overwinters in the larval stage.  The maggot being hidden away inside the lower part of the stem of plants.  The adults appear in June, lay their eggs on the leaves of plants.  Upon hatching the young maggots crawl down behind the leaf sheaths to the tender part of the stems and tunnel into them, reach maturity about mid-summer, pupate and the adults emerge.  This time the adults lay their eggs on grasses or volunteer grain.  These maggots mature although they do not pupate and emerge as adults until the following season.  The adult flies are yellowish-white in color and about 1/5 inch long.  The maggots are slender, pale green in color and about 1/4 inch long.

Sclerotinia in Canola

    Sclerotinia is beginning to show up in canola fields.  This disease can resemble field maturity.  The wet conditions during late June and early July was ideal for sclerotinia infections.  Infections usually occur in the upper part of the plant.  Yield losses occur because the disease will destroy the stem and interrupt  nutrient transfer.  The stem will become bleached in color and will break or lodge.  The following pictures will show the bleached color and breakage.

Note the stem breakage and bleached appearance.  (click on photo to enlarge)

Staging Canola For Swathing

    This is one of the most critical operations in the raising of canola.  Staging the correct time to swath will have a major effect on the quality of canola.  To stage canola we must use the main stem.  Do not stage by using any of the branches.  The correct time is when 30 to 40% of the bottom one third of the pods on the main stem have started to change color.  An easy way to determine this is to measure the length of the main stem bearing pods.  For example the main stem is 18 inches in length.  So one third of the length would be 6 inches.  Measure out the bottom six inches and remove the pods from this section.  Then check the pods for color change and determine what percentage of the pods have changed color.  If levels of 30 to 40 % have color changes in the seed, then the crop is ready to swath.  Take samples from several parts of the field to get a good representative sample.  Another staging indicator is that all the leaves have dropped and the top pods will have a yellow green color.  Besure to use plants that are not infected with sclerotinia when staging.  For more information goto NDSU Extension Publication A-1171 "Swathing and Harvesting Canola".

There's a Buzzzz Around the Griggs County Courthouse

    The Griggs County Courthouse has a new bee swarm over the front entrance.  The bees moved in this past week and have began to form a new hive.  Efforts are on the way to try and eliminate this hive.  Recommendations from Phil Glogoza, NDSU Extension Entomologist, is to use of mixture of Dawn Dishwashing Detergent and water at a rate of 1 cup of Dawn for every gallon of water.  The soap will immobilize the bees and it also has some insecticidal qualities as well as help drown the bees.  I will give you an update as to our success.

Bees on the front entrance of the Griggs County Courthouse (click on photo to enlarge)

Close up of the bee swarm

Wasps and Hornets

    This week I have received several call concerning wasps or hornets building nests around homes or yards. for more information on getting rid of these pests goto and article by Phil Glogoza "Whats The Buzz" 

Please Contact Our Office For Additional Information
E-mail: griggs@ndsuext.nodak.edu
Go to the 2000 AgAlert Index Page