May 23, 2006

Manitoba Insect and Disease Update

Compiled by:    

John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives, Phone: (204) 745-5668; Fax: (204) 745-5690; and David Kaminski, Plant Pathologist, Manitoba Agriculture, Food and Rural Initiatives, Phone: (204) 745-5656; Fax: (204) 745-5690;

To report observations of insect and disease activity or control that may be of interest or importance to others in Manitoba, please send messages to the above contact addresses.

To be placed on an E-mail list to be notified when new Manitoba Insect and Disease Updates are posted, please contact John Gavloski at the address or numbers listed above.

Winter Cereals

Leaf Rust in Winter Cereals:

More carryover disease in winter cereals – leaf rust!

Last week Thursday, I had a call from a grower north of Carman who had discovered rust pustules on fall rye that was very close to shot blade.  By Friday, we had a sample in hand and determined that it was indeed leaf rust (stripe rust was another possibility prior to examining fine symptoms).

Figure 1. Leaf rust in cereals
Click on image to enlarge

The source of infection is believed to be overwintering uredospores, the same infection that we observed on some winter wheat crops in the fall of 2005.  This same phenomenon is described on winter wheat in Minnesota in the latest (May 16) edition of the USDA’s Cereal Rust Bulletin.  This is not a normal situation.  Overwintering survival on winter cereals is rare and it is difficult to estimate how serious a loss such infection might cause.  According to label information, there is only one fungicide that is registered on rye against leaf rust and that is Headline (pyraclostrobin).

We also had reports from agronomists east of the Red River that they have seen the odd pustule of leaf rust on winter wheat.  If an above average crop is expected and there are signs that other fungal diseases (tan spot and powdery mildew) are also present, a fungicide application may be warranted.  If so, the list of registered products includes propiconazole-based fungicides (Tilt, Bumper, Pivot), Stratego (propiconazole + trifloxystrobin) and Folicur (tebuconazole).  Consult the 2006 Guide to Crop Protection for details and remember that, with the amount of leaf material now present, sufficient water volume for coverage is critical to success.  It may be tempting to go after broadleaf weeds at the same time but it will be very difficult to adequately penetrate the canopy.  It may be best to rely on crop competition to suppress the weed growth.

Protection of the uppermost leaves prior to infection is another key to success with a foliar fungicide in a cereal crop.  The rye was beginning to show the tips of the awns already this week.  It may surprise you how far advanced many winter cereals are already until you look at the heat units that have been accumulated already this spring.  Check the back page of the Manitoba Crop Report (Crop Weather Report tab) for conditions in your vicinity.  Most locations have had more than 50% above normal heat units since the beginning of April.

General Insect Concerns

Seedcorn Maggot: Seedcorn maggots populations were noted to be quite high in a field of germinating corn near Shilo. The small, white larvae of seedcorn maggots are easy to tell from cutworms and wireworms because they have no legs and lack a well-developed head; characteristics that are typical for fly larvae. You will see legs on both cutworm and wireworm larvae.

Insects and Diseases in vegetable crops