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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

June 27, 2011                   

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives
Phone: (204) 745-5668; Fax: (204) 745-5690
Holly Derksen, Plant Pathologist, Manitoba Agriculture, Food and Rural Initiatives
Phone: (204) 750-4248; 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.


 

Recent Insect and Plant Pathogen Activity

Cereals

Aphids: Both English grain aphids (Sitobion avenae) and oat-birdcherry aphids (Rhopalosiphum padi) were found while scouting cereal fields in the Central region of Manitoba over the past week. Both of these species blow into Manitoba. Oat-birdcherry aphid is known to be a good vector of barley yellow dwarf in cereals. Although both species can vary somewhat in colour, oat-birdcherry aphid is generally darker than English grain aphid and has a reddish-orange patch at the back of its abdomen. Sometimes it is easy to see this patch, other times magnification is needed.

Oat-birdcherry aphid English grain aphid
Fig. 1. Oat-birdcherry aphid Fig. 2. English grain aphid

If out scouting for aphids in cereal crops, note that we were also finding some lygus bug nymphs while sweeping the crop. Although not regarded as a major pest of cereals, this is something that can easily be confused with aphids. Note that aphids have a pair of tube-like structures called cornicle projecting from the end of the abdomen, and aphids move relatively slow. When Lygus bug nymphs are small they are green and the same size as aphids, but do not have cornicles and move relatively quickly.

Barley Yellow Dwarf: Be on the lookout for symptoms of barley yellow dwarf which can include yellowing of leaves, stunting, and changes in tillering. This virus can infect cereal crops and a wide range of grasses. Of the crop species, oat is the most severely affected. At this point, there have been no reported cases of BYDV in the province, but with the presence of the aphids that can vector the virus it is important to scout for this disease.

Bacterial Blight: There have been a few cereal samples come into the Crop Diagnostic Lab that were identified as showing symptoms of bacterial blight. Symptoms of this disease begin as water-soaked spots or streaks on the leaves that progress to yellow or light brown. This disease prefers rainy, damp weather and therefore may be present in a number of fields this year. However, warm, dry weather will stop the spread of this disease to new tissue.

Aster leafhoppers: While scouting cereal crops in the central region of Manitoba, we were also finding aster leafhoppers (Macrosteles quadrilineatus) in many of the fields. Although they can potentially overwinter in Manitoba, it is felt that most of our population blows in. This is another potential disease vectors, transferring a disease to crops known as aster yellows. Although many field crops can be affected by this disease, it is horticultural crops that suffer the highest impact. At this point we do not know to what level the aster leafhoppers would be infected and transmitting the disease.

Aster leafhopper
Fig. 3. Aster leafhoper

Note that there are many species of leafhoppers; about 800 species in Canada. Only are few species can be harmful to crops. One of the things that is distinctive about aster leafhoppers is the markings on the front of the head. There are six markings; 3 pairs of either dots or dashes. There is a pair at the top that look like spots, and then two pair of markings below these that look like dashes. See if you can see these in figure 3. To identify leafhoppers in the field, you would have to catch some and look at the head under magnification to see the markings.

Canola

Sclerotinia: In some areas of the province, canola is nearing or has begun flowering. This is the stage at which is most susceptible to infection by Sclerotinia. Apothecia (fruiting bodies) of Sclerotinia have been spotted amongst canola stubble in winter wheat fields and these structures produce the ascospores that can infect nearby canola fields. The timing for optimum control of this disease using a fungicide application is fast approaching and growers must consider the cost-effectiveness of this approach before deciding to spray.

Apothecia of sclerotinia
Fig. 4. Apothecia of sclerotinia

 

Surveys and Forecasts

Diamondback moth monitoring: Diamondback moth (Plutella xylostella) was first reported this year in a trap near Carman during the week of May 2-8, then more generally during the week of May 9-15th. There has been an increase in the number of moths caught in some of the traps in the eastern region over the past few weeks. Higher catches of note are 108 from a trap near Beausejour for the week of June 6-12th, and 94 and 77 from a trap near Sewell (southwest of Morris)) over the last 2 weeks.

Table 2. Highest cumulative trap counts for diamondback moth in Manitoba as of June 27, 2011

Location

Cumulative
Trap count

Sewell

239

Beausejour

175

Plum Coulee

71

Carman

55

Thalberg

55

St. Adolphe

55

The full data set for adult counts of diamondback moth can be viewed at: https://www.gov.mb.ca/agriculture/crops/insects/db/pdf/2011diamondbackdata.pdf

Bertha armyworm monitoring: Data continues to come in from the bertha armyworm traps that have been set up. Emergence of adults is just starting and numbers so far are very low. Data from the bertha armyworm monitoring program and a chart on how to interpret the data are available at:
https://www.gov.mb.ca/agriculture/crops/insects/bertha/index.html