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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

June 21, 2010                   

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives
                    Phone: (204) 745-5668; Fax: (204) 745-5690, and
                    Vikram Bisht, Plant Pathologist, Manitoba Agriculture, Food and Rural Initiatives
                    Phone: (204) 745-0260; Fax: (204) 745-5690

To report observations on insects or plant pathogens that may be of interest or importance to farmers and agronomists in Manitoba, please send messages to the above contact address.

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

Summary

• Leaf rust and tan spot have been found on wheat in southern Manitoba
• Barley yellow dwarf has been found in rye in western Manitoba
• The early stages of sunflower rust have been found on sunflowers in Manitoba.
• Cutworms feeding seems to be tapering off

Recent Insect and Plant Pathogen Activity

Leaf Rust on wheat: A wheat sample from near Winkler was found to contain many spots of leaf rust. It could become a serious issue in the coming few days, if the moist condition persists.

Tan Spot in wheat: Volunteer wheat in a ryegrass field near Carman was found to have tan spots.

Wheat Streak Mosaic: Winter wheat (2010 crop) in the Minto / Boissevain area tested positive for wheat streak mosaic. If this leads to volunteer winter wheat in 2011 and 2012, it could be a source of inoculum, thus when appropriate efforts to break the green bridge are recommended.

Spring wheat fields near Boissevain, Pilot Mound and La Rivierre were found to have wheat streak mosaic virus and all had in-field volunteer wheat plants (spring or winter wheat) as the source of inoculum and probably wheat curl mites.

Barley Yellow Dwarf: Some fall rye from the Boissevain area tested positive for barley yellow dwarf virus. ELISA testing was performed by Dr. Steve Haber’s lab at the Cereal Research Centre in Winnipeg.

Brown Spot and Net Blotch on Ryegrass: Perennial ryegrass near Carman had leaf spots that were visually identified as leaf spots caused by Drechslera spp. This is being confirmed by sporulating the pathogen, and results should be known in a few days.

On Ryegrass, the first symptoms of brown spot caused by Drechslera siccans are small, circular brown spots on the leaves. As they enlarge, these spots develop tan centers and brown margins. Brown
streaks may also appear between the leaf veins. Once the spots become numerous, the
leaves typically will wither and die, starting at the leaf tips.

Net blotch is also reported on perennial ryegrass. Several other Drechslera species are known to cause leaf spot diseases of ryegrass but are of minor importance. Usually occurs in late fall or early spring.

Sunflower Rust: Through the work of the Manitoba Sunflower Surveillance Survey (run by the National Sunflower Association of Canada), the early stages of sunflower rust have been detected in Manitoba sunflower crops. The first signs of rust infection were found on June 9th, which is two weeks earlier than last year (June 23). The fields in which rust was found were located near Portage la Prairie and Elgin, Manitoba and both fields did not have a history of sunflowers. Samples were taken to the Crop Diagnostics lab in Winnipeg and were confirmed to be the aecial stages of sunflower rust. More monitoring is needed to keep updated information on this. Rust on sunflower can be quite damaging.

Cutworms and Seedcorn maggots: Some cutworm feeding was noted on soybeans in the Dugald area, and minor damage to dry beans by seedcorn maggots was noted in the Westbourne area. One of the first signs of seedcorn maggot feeding is often plants that start to look like they are wilting, or bare patches in a field. Seedcorn maggots are a legless fly larva and can often be found in the seeds or tunneling in the lower stem.

 

Seedcorn maggot larvae

 

Surveys and Forecasts

Alfalfa weevil: Weekly monitoring of alfalfa weevil levels is being conducted by Brent Elliott (MAFRI’s horticulture and forage crop entomologist). Brent reports that so far larvae are still small, mainly first and second instars, and damage to alfalfa remains fairly minimal. Updates on alfalfa weevil and other insects in forage crops are posted weekly at: https://www.gov.mb.ca/agriculture/crops/mfsr/

Diamondback moth: Highest counts of adults in pheromone baited traps are from the eastern part of the province:

Location of trap

Recent Count

Total count since early-May

Landmark

40

393

Beausejour

35

291

Morris

64

243

Carey

78

220

Dugald

28

216

Kleefeld

25

216

Dufrost

28

209

The highest single week count is still the 137 near Dugald 2 weeks ago.
The highest count from Central Manitoba is 135 from a trap near Oakville.
The highest count from western Manitoba is 107 from as trap near Griswold.

So far no high populations of diamondback moth larvae have been found or reported. It is not a given that because trap counts detect a lot of adults have blown into an area that there will also be a lot of larvae to follow. We have had years before where high counts of adults did not result in significant numbers of larvae.

Factors such as weather and natural enemies can regulate the population. A parasitic wasp known as Diadegma is one the natural enemies can be quite effective at regulating diamondback moth numbers. Collections of diamondback from Alberta this year also included Diadegma. We will try to get some measure of Diadegma levels in Manitoba as well.

It is important that monitoring for diamondback moth larvae be an important part of canola crop scouting this summer, particularly in eastern Manitoba. But do not make assumptions on larval levels or plan management options based on the trap counts for adults. The best course of action for now is to keep monitoring and let the management occur for free if possible. If any fields are found to contain high levels of diamondback moth larvae, please alert myself or a nearby Farm Production Advisor so we can provide alert in future Manitoba Insect and Disease Updates of any regions where high larval counts are starting to appear.

A reminder that traps for monitoring adults of diamondback moth can now be removed. We now have the information that we need from these traps.

Data for the diamondback moth monitoring program is updated at the beginning of every week on the MAFRI website at: Diamondback Moth Forecasting Program

Bertha Armyworm Monitoring: Counts for bertha armyworm adults are still very low. The highest counts so far are 8 in Morris and 6 in Dominion City. We are likely still in the early stages of emergence.

Data for the bertha armyworm monitoring program is updated at the beginning of every week on the MAFRI website at: Bertha Armyworm Monitoring Program