Root, bulb, leafy and brassica vegetable pest report – 28 August 2012

The thresholds for emergence of third generation onion maggot flies and third generation cabbage maggot have been reached in Wellington.

The presence of carrot leaf blights have been reported since mid-July in the Holland Marsh, perhaps seen earlier in other areas. Warm, humid conditions favour the development of both Cercospora and Alternaria leaf blights. For example, Alternaria infection is favoured by warm temperatures (16-25C) and prolonged leaf wetness. Cercospora infection requires a minimum of 12 hours of leaf wetness at 20-30C. Rain, irrigation, high humidity and/or dew promote ‘humid’ conditions in the carrot canopy. Obviously as the canopy grows larger, less air movement is occurring within the canopy also creating a ‘humid’ environment.

Fungicides can be used to manage these diseases. Usually the first fungicide application is timed when 25% of randomly sampled mid-age leaves have one or more leaf blight lesions (i.e. 13 out of 50 leaves, 25 out of 100 leaves). Spray intervals of 7-10 days, depending on the fungicides applied, after the initial fungicide application can help manage these diseases, especially after the leaves have closed over the rows. The intervals can sometimes be extended if the weather in unfavourable for blight development. Please see Pub. 838 Vegetable Crop Protection Guide for more information on fungicides registered for this use.

Here are the degree days accumulated from April 1st until August 28th, 2012.

(These values are provided as guidelines only. Local environments, soil type, field history, etc. may influence activity of these pests.)

Area

Onion Maggot (base 4)

Cabbage Maggot (base 6)

Carrot Rust Fly (base 3)

Carrot Weevil (base 7)

As of

Bradford/Holland Marsh*

1922.1

n/a

2067.8

n/a

28/08/2012

London

1995.2

1710.7

2143

1578.5

28/08/2012

Wellington

1762.1

1498.6

1901.6

1373.3

28/08/2012

Windsor

2292.5

1996.6

2442.4

1852.4

28/08/2012

Thedford

1989.3

1712.8

2134.9

1580.3

28/08/2012

Delhi

1867.9

1598.1

2012

1473.8

28/08/2012

Ridgetown

Data not updated since 28 May 2012

Area

Tarnished Plant Bug (base 12)

Leafhopper (base 9)

GDD (base 5)

As of

Bradford/Holland Marsh*

919.6

1278.2

1786.5

28/08/2012

London

964.5

1327.9

1850.9

28/08/2012

Wellington

772.3

1128.0

1627.6

28/08/2012

Windsor

1192.1

1576.6

2143.7

28/08/2012

Thedford

969.6

1329.8

1848.6

28/08/2012

Delhi

883

1233.2

1728.9

28/08/2012

Ridgetown

Data not updated since 28 May 2012

*Data provided by Muck Crops Research Station, University of Guelph.

Degree day model information for pests 

Degree Days

1st Generation

2nd Generation

3rd Generation

Onion Maggot

210

1025

1772

Cabbage Maggot

314-398

847-960

1446-1604

Carrot Rust Fly

329 – 395

1399-1711

n/a

Carrot Weevil

138 – 156
455 (90% oviposition)

No model available

n/a

Tarnished Plant Bug

40

n/a

n/a

Aster Leafhopper

128 (overwintering egg hatch)

390 (local adult emergence)

n/a

n/a

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