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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

July 4, 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

We are in that period where some of the early-season concerns, such as flea beetles on canola and cutworms, become less of a concern and our crop scouting shifts to a different set of potential pests. In this update we will look at what the top scouting concerns are as we move into July.

Cereals

Pathogens in cereals: Cereal crops around the province are advancing and may be near the flag leaf stage. Protection of the flag leaf against leaf disease is important to protect yield potential. Rust diseases may begin showing up in Manitoba in July as wheat leaf rust symptoms have recently been observed in southern North Dakota. In addition, as the spring wheat crops continue to progress fusarium head blight risk becomes more important. FHB forecasting maps are currently being produced and will continue to be produced as long as cereal crops in the province remain in a susceptible stage. Visit the FHB forecasting webpage to subscribe to the map updates:
https://www.gov.mb.ca/agriculture/crops/fhb/index.html

Insects in cereals: Armyworms blew in and seemed to establish early this year. So when scouting cereal fields, remember to look for defoliation and check for armyworms under debris on the ground.

Both English grain aphid and oat-birdcherry aphid have blown in and are present in many cereal fields. With a lot of late seeding this year, aphids will be something that should be scouted for the next few weeks, at least until the soft-dough stage. The economic threshold for aphids in cereals is 12-15 aphids per stem prior to the soft dough stage. But one additional factor to consider is that young cereal plants are more susceptible to barley yellow dwarf than older plants, so if high levels of oat-birdcherry aphid are found in younger fields, using a lower threshold may be appropriate.

Oat-birdcherry aphid
Fig. 1. Oat-birdcherry aphid

Some thrips feeding has been noted on barley in the eastern region. Fields with the flag leaf emerged should be scouted for barley thrips or their feeding until the head is completely emerged. It is feeding to the flag leaf, or the head while it is still in the boot and not fully emerged, that can be economical if thrips levels are high. Once the head is fully emerged, it is too late to be controlling barley thrips. There can be a heavy edge effect with barley thrips, so the distribution of feeding within the field would be something to assess if barley thrips are noticed.

Canola

Insects in canola: Adult flea beetles are starting to decline in numbers and canola in many areas is beyond the stage where feeding by the remaining beetles would be of concern.

Now that canola is getting taller, it is at the stage in many fields where we can begin using a sweep net to assess insect levels. Note that is most canola fields, on a hot day you will get a lot of insects in a set of 10 sweeps. This may or may not be a concern. There will often be a lot of beneficial insects in the net, as well as some that are present in the field but are not feeding on the crop. The insects to currently pay close attention to when assessing what is in the net are diamondback moth and Lygus bugs. If you start seeing lots of diamondback moth larvae in the net while doing the sweeps, you may want to additionally assess what levels on some individual randomly selected plants are like. Economic thresholds for diamondback moth are based on levels per plant, not per sweep, so this extra step is needed if they are present in the net. Although there have been no reports yet of high levels of diamondback moth larvae, results from the adult monitoring program (see below) indicate that diamondback moth populations should be something we watch, particularly in Eastern Manitoba. Note also that young larvae can be killed by heavy rains.

Diamondback moth pupa & larva
Fig. 2. Diamondback moth pupa (left) and larva (right)

General crop scouting

Sclerotinia: Some canola in the Carman area has entered the flowering stage of its life cycle; this becomes an important stage to look for and protect against sclerotinia infection. Sclerotinia may also begin to affect other crops such as sunflowers, soybeans, and dry beans.

Cutworms: Cutworms larvae have or are turning into pupae; a few large larvae can still be found but the period where we would be worried over controlling cutworms is done.

 

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)) recently.

Table 1. Highest cumulative trap counts for diamondback moth in Manitoba as of July 4, 2011

Location

Cumulative
Trap count

Sewell

239

Beausejour

175

Plum Coulee

74

Carman

63

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: Counts from the bertha armyworm traps are starting to rise, but all areas of the province are still in the low risk category based on adult counts. Highest counts so far are:

Table 2. Highest cumulative trap counts for bertha armyworm in Manitoba as of July 4, 2011

Location

Cumulative
Trap count

Glenboro

85

Neepawa

35

Durban

18

Altona

17

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