State of LDD moth in 2021


The MLA received the following information regarding the 2021 season with respect to LDD from the Ministry of Northern Development, Mines, Natural Resources and Forestry





Report from the Ministry of Northern Development, Mines, Natural Resources and Forestry

Aerial forest health surveys began in early July with flight lines based on:

  • public reports of potentially infested areas

  • 2020 survey data

  • knowledge of previously infested areas

After the aerial surveys, ground verification surveys were undertaken. This included collecting LDD moth specimen samples to confirm species identification in the laboratory.


Areas affected by LDD moth defoliation in 2021
  • Defoliation caused by LDD moth in Ontario increased from 586,385 hectares in 2020 to almost 1.8 million hectares in 2021.

  • This area included both light and moderate to severe defoliation mapped mainly in the southern region but also north to Sault Ste. Marie, Sudbury, North Bay and Temiskaming Shores.

  • All affected districts reported an increase in area defoliated from 2020.

  • Defoliation caused by LDD moth was most severe in forest stands containing species of:

  • oak

  • maple

  • poplar

  • willow

  • other broadleaf trees

  • In some areas, LDD moth defoliated conifer species including eastern white pine and spruce species.

Southern region

  • In the southern region, we recorded most of the moderate to severe defoliation in the eastern districts including Peterborough, Bancroft and Kemptville.

  • The Peterborough District had the largest area of moderate to severe defoliation of 374,268 hectares, an increase from 159,578 hectares in 2020.

  • This concentrated area of defoliation extended north to Pembroke District, where we mapped smaller areas of defoliation.

Southwestern Ontario

  • In Southwestern Ontario, areas of moderate to severe defoliation were more fragmented. Defoliation in the Aylmer District totaled 119,586 hectares and Guelph District totaled 113,877 hectares; both increased from 2020.

  • We also recorded increased areas of defoliation in the Midhurst and Aurora districts (176,264 and 97,164 hectares, respectively) that extended to the Parry Sound District where we mapped 75,349 hectares.

Northeast region

  • In the northeast region, the Sudbury District had the largest area of moderate to severe defoliation of 68,874 hectares.

  • In the North Bay and Sault Ste. Marie districts, we recorded smaller areas of moderate to severe defoliation, but in both cases the total area was higher than in 2020.

  • A small area of defoliation, totaling 52 hectares, was recorded in the Kirkland Lake District. This was a record high for this area.



Map of areas defoliated by LDD moth in 2021 across Ontario



enlarge photo


Forecasting defoliation: Egg mass survey protocol

To predict LDD moth defoliation, we use a Modified Kaladar Plot (MKP) protocol at select locations across the defoliated area. This protocol considers:

  • egg mass location in the stand

  • the proportion of new egg masses relative to old ones

The total number of egg masses per hectare is used to forecast LDD moth defoliation for the following year:

  • severe defoliation (more than 75% of forest stand) is projected in areas with more than 6,175 egg masses per hectare

  • moderate defoliation (40% to 75% of forest stand) is projected in areas with 1,236 to 6,175 egg masses per hectare

  • light defoliation (1% to 40% of forest stand) is projected in areas with 1 to 1,235 egg masses per hectare