California Cotton: Silverleaf Whitefly, Aphid Numbers Low

Photo: Ron Smith, Auburn University

Introduction

The third round of sampling for the silverleaf whitefly (SLWF) surveys began on Monday, July 30, 2018. Program personnel collected samples from designated sites at 10% of all cotton fields in each county of the San Joaquin Valley. The Program has a total of 204 SLWF sampling sites with 19 sites in Kern County, 40 sites in Kings County, 21 sites in Tulare County, 60 sites in Fresno County, 2 sites in Madera County, and 62 sites in Merced County. At each site 1 leaf sample from 10 different cotton plants was collected for a total of 10 leaves/site.

Kern County:

Five of the nineteen sample sites (26%) had at least one leaf containing SLWF nymphs during the third survey round. Thirteen of the nineteen sites (68%) had at least one leaf containing aphids. A total of 190 leaves were collected, of which thirteen leaves (7%) contained SLWF nymphs, and thirty-six leaves (19%) contained aphids.

All five of the sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while one site (20%) had leaves in the 6-49 nymphs/leaf range, and no sites contained leaves in the 50 or more nymphs/leaf range.

All thirteen of the sites positive for aphids (100%) had leaves in the 1-5 aphids/leaf range, five of the sites (38%) had leaves in the 6-49 aphids/leaf range, and none of the sites had leaves in the 50 or more aphids/leaf range. Two of the nineteen sites (11%) had leaves with honeydew and two of the sites (11%) had leaves with sooty mold.

Mites were found at two sites (11%), and armyworm and other whitefly species were not found at any of the sites.

Kings County:

Fifteen of the forty sample sites (38%) had at least one leaf containing SLWF nymphs and twenty-three of the sites (58%) had at least one leaf containing aphids. A total of 400 leaves were collected, of which thirty-nine leaves (10%) contained SLWF nymphs and fifty-one leaves (13%) contained aphids.

All fifteen of the sites positive for SLWF (100%) had leaves in the 1-5 nymph/leaf range, while four of the sites (27%) had leaves in the 6-49 nymphs/leaf range, and one of the sites (7%) had leaves in the 50 or more nymphs/leaf range.

All twenty-three of the sites positive for aphids (100%) had leaves in the 1-5 aphids/leaf range, while seven of the sites (30%) had leaves in the 6-49 aphids/leaf range, and none of the sites had leaves in the 50 or more aphids/leaf range. Six of the forty sample sites (15%) had leaves with honeydew and two of the sites (5%) had leaves with sooty mold.

Mites were found at thirteen sites (33%), and none of the sites had leaves with armyworm or other whitefly species.

Tulare County:

Seven of the twenty-one sample sites (33%) had at least one leaf containing SLWF nymphs and thirteen of the sites (62%) had at least one leaf containing aphids. A total of 210 leaves were collected, of which sixteen leaves (8%) contained SLWF nymphs and thirty leaves (15%) were infested with aphids.

All seven sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while one of the sites (14%) had any leaves in the 6-49 nymphs/leaf range, and none of the sites had leaves in the 50 or more nymphs/leaf range.

All thirteen of the sites positive for aphids (100%) had leaves in the 1-5 aphids/leaf range, three of the sites (23%) had leaves in the 6-49 aphids/leaf range, and none of the sites had leaves in the 50 or more aphids/leaf range. Five of the twentyone sample sites (24%) had leaves with honeydew and none of the sites had leaves with sooty mold.

Mites were found at four of the sites (19%), while none of the sites had armyworm or other whitefly species.

Fresno County:

Twenty-two of the sixty sample sites (37%) had at least one leaf containing SLWF nymphs and twenty-six of the sites (43%) had at least one leaf containing aphids. A total of 600 leaves were collected, of which fifty-three leaves (9%) contained SLWF nymphs and eighty-six leaves (14%) were infested with aphids.

All twenty-two of the sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while three of the sites (14%) had leaves in the 6-49 nymphs/leaf range, and none of the sites had leaves in the 50 or more nymphs/leaf range.

All twenty-six of the sites positive for aphids (100%) had leaves in the 1-5 aphids/leaf range, while six of the sites (23%) had leaves in the 6-49 aphids/leaf range, and none of the sites had leaves in the 50 or more aphids/leaf range. Seven of the sixty sample sites (12%) had leaves with honeydew and five of the sites (8%) had leaves with sooty mold.

Mites and armyworm were found at none of the sites, while two of the sites (3%) had leaves with other whitefly species.

Madera County:

Neither of the two sample sites contained any leaves with SLWF nymphs or aphids. A total of 20 leaves were collected. Neither of the two sample sites had leaves with honeydew or sooty mold. None of the sites had leaves with mites, armyworms, or other whitefly species.

Merced County:

One of the sixty-two sample sites (2%) had leaves containing SLWF nymphs and five of the sites (8%) had at least one leaf containing aphids. A total of 620 leaves were collected, of which three leaves (<1%) contained SLWF nymphs and sixteen leaves (3%) contained aphids.

The one site positive for SLWF only had leaves in the 1-5 nymphs/leaf range.

Four of the sites positive for aphids (80%) had leaves in the 1-5 aphids/leaf range, while two of the sites (40%) had leaves in the 6-49 aphids/leaf range, and none of the sites had leaves in the 50 or more aphids/leaf range. Twelve of the sixty-two sample sites (19%) had leaves with honeydew and eleven of the sites (18%) had leaves with sooty mold.

Mites were found at three of the sites (5%), while armyworm was found at two of the sites (3%), and one of the sites (2%) had leaves with other whitefly species.


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