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Manitoba Insect & Disease Update – Issue 10: July 20, 2016

The Manitoba Insect and Disease Update is now posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2016-07-20.html

Some highlights from the update:

Insects:

  • Pea aphid levels are still a concern in some pea fields, although many fields will be getting to the stage where management would no longer be economical.
  • Aphid levels have dropped in many cereal fields where previously levels had been increasing. High levels of natural enemies have been noted in some of these fields, and some intense rains may have also contributed.
  • In some areas of Central and Southwest Manitoba, greater than 90% of the wheat midge are expected to have emerged. In many areas of Manitoba about 50 to 90% of wheat midge are expected to have emerged. A reminder that wheat that has already produced anthers is no longer susceptible to feeding by wheat midge. Even if adults are still active in these more advanced fields, the larvae will not feed on the grain.
  • Egg masses of European corn corer are starting to be noted in some fields of corn. So far there are no reports of high levels, but now is the time to be checking fields for the egg masses.
european-corn-borer-egg-masses

Figure 1. Egg masses of European corn borer.

Plant Pathogens:

  • Some infections of blackleg in canola and fusarium head blight in cereals have been reported.
  • A few cases of loose smut in barley were also reported.
  • Two positive identifications of Goss’s Wilt in corn were made. The positive identifications were made based on immunostrips and/or polymerase chain reaction (PCR) assays.

Submitted by: John Gavloski, Entomologist & Pratisara Bajracharya, Field Crop Pathologist, Manitoba Agriculture

Manitoba Agriculture website: www.manitoba.ca/agriculture
Manitoba Agriculture on Twitter: @MBGovAg
Manitoba Agriculture on YouTube: www.youtube.com/ManitobaAgriculture

 

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Aphids in Cereals

Information provided is from the Manitoba Insect and Disease Update for the week of July 13th at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2016-07-13.html

You will often find aphids clustered on some plants; adults with the young nymphs nearby. Aphids develop through their stages very rapidly, so when monitoring all aphids are counted, not just larger ones. Parasitized aphids (Fig. 2), known as aphid mummies will look swollen and discoloured and are not counted.

aphids-on-wheat

Fig. 1. Aphids on wheat

Fig. 2. Aphid mummy

The economic threshold on cereals is 10-15 aphids /stem prior to the soft dough stage. Research has found that after the early-dough stage insecticide treatments were not cost-effective.
Scouting tips: It is quite normal to find some plants with 10-15 or more per stem, but if there are a lot of plants around these with none or very few per stem, than the field would be below the economic threshold. If you can randomly pick plants (not looking specifically for plant with aphids to do counts on), and on average be above 10-15 per stem, and not yet at the soft dough stage, that is the point when insecticides become economical. Aim to sample at least 20 stems for aphids; selecting 5 stems from each of at least 4 areas of the field is a good sampling plan.
Factors regulating aphid populations: Sometimes aphid populations will increase, but other times populations will stabilize or decrease due to predators and parasites, diseases, or heavy rains which can reduce a population. So if a heavy rain goes through, sometimes it is good to reassess a population. And if natural enemy levels are high, it is good to assess whether levels of aphids are possibly declining.
Soil moisture levels and aphids in cereals: As another consideration, research on English grain aphid in winter wheat found that there was a greater yield reduction for a given aphid density when plants were grown under water stress versus nonstress conditions. They concluded that “therefore, the water status of the plant should be considered to determine an economic injury level for S. avenae infesting winter wheat” (Environmental Entomology. 1988. Pp. 596-602). This may be difficult to do, but does show that a given level of aphid feeding on cereals is likely to reduce yields more when plants are growing under water deficits, which is generally not the case this year.
Submitted by: John Gavloski, Entomologist, Manitoba Agriculture

 

Visit the Insect Pages of Manitoba Agriculture’s website at:http://www.gov.mb.ca/agriculture/crops/insects/index.html

 

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Manitoba Insect & Disease Update – Issue 6: June 22, 2016

The Manitoba Insect and Disease Update is now posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2016-06-22.html

Some highlights from the update:

Insects:

  • Cutworm and flea beetle levels and damage continues to decline.
  • Alfalfa weevil is being noted at high levels in some alfalfa fields
  • Barley thrips are quite noticeable in some barley fields in Eastern Manitoba.
  • Low levels of English gain aphid and oat-birdcherry aphid are being found in some cereal fields.
  • Pea aphid is showing up in some pea crops.

Plant Pathogens:

  • Cereal rust diseases continue to develop and spread.
  • Bacterial blight symptoms in winter wheat and oats were also reported.
  • Root rot pathogens continue to cause problems in soybean fields.

Submitted by: John Gavloski, Entomologist & Pratisara Bajracharya, Field Crop Pathologist, Manitoba Agriculture

Manitoba Agriculture website: www.manitoba.ca/agriculture
Manitoba Agriculture on Twitter: @MBGovAg
Manitoba Agriculture on YouTube: www.youtube.com/ManitobaAgriculture

 

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Manitoba Insect & Disease Update – Issue 3: June 1, 2016

The Manitoba Insect and Disease Update for June 1, 2016 is now posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2016-06-01.html

SUMMARY

Insects: Cutworms and flea beetles on canola continue to be the insects of greatest concern. The cool, damp weather from the last few days would have slowed cutworm feeding, and the soil moisture, where not excessive, may help the plants compensate for feeding. Cutworm levels are quite variable, hard to find in some fields, more noticeable in others. So scout for potential cutworm feeding on emerging plants and dig for the larvae if you find an area that is showing signs of cutworm feeding. Precautionary insecticide applications, if cutworm levels are not economical, is not encouraged because of the potential damage to beneficial invertebrates.

Plant Pathogens: Rain has not only provided enough moisture for crops, but also for pathogens causing various crop diseases. Look for early signs and symptoms of diseases in crops. Scout! Scout! Scout!

Submitted by: John Gavloski, Entomologist & Pratisara Bajracharya, Field Crop Pathologist, Manitoba Agriculture

Visit the Insect Pages of our Manitoba Agriculture website at http://www.gov.mb.ca/agriculture/crops/insects/index.html
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