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California Cotton: Pest Surveys Show Limited Whitefly Infestations, Abundant Aphids

Ernst Undesser
By Lauren Murphy, University of California Cooperative Extension September 6, 2017

California Cotton: Pest Surveys Show Limited Whitefly Infestations, Abundant Aphids

Photo: James Castner, University of Florida

Introduction

Sampling for the silverleaf whitefly (SLWF) surveys began on Tuesday, July 11, 2017. Program personnel collected samples from pink bollworm (PBW) trap sites at 5% of all cotton fields in each county.

The Program has a total of 109 SLWF sampling sites with 29 sites in Fresno County, 13 sites in Kern County, 24 sites in Kings County, 1 site in Madera County, 31 sites in Merced County, and 11 sites in Tulare County. At each site 1 leaf sample from 10 different cotton plants was collected for a total of 10 leaves/site.

Kern County

Nine of the thirteen sample sites (69%) were positive for SLWF during the first survey round. All of the thirteen sites (100%) were positive for aphids. A total of 130 leaves were collected, of which thirty-eight leaves (29%) were infested with SLWF, and 107 leaves (82%) were infested with aphids.

All nine of the sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while six sites (67%) had leaves in the 6-49 nymphs/leaf range, and none of the sites infested with SLWF contained leaves in the 50 or more nymphs/leaf range.

Eleven of the sites positive for aphids (85%) had leaves in the 1-5 aphids/leaf range, ten of the sites (77%) had leaves in the 6-49 aphids/leaf range, and five of the sites (38%) had leaves in the 50 or more aphids/leaf range. Eleven of the thirteen sites (85%) had leaves with honeydew and five sites (38%) had leaves with sooty mold.

Mites were found at eight sites (62%), armyworm at one site (8%), and two of the sample sites (15%) had leaves with other whitefly species.

Kings County

Six of the twenty-four sample sites (25%) were positive for SLWF and twenty-two of the twenty-four sites (92%) were positive for aphids. A total of 420 leaves were collected, of which twenty leaves (5%) were infested with SLWF and 241 leaves (57%) were infested with aphids.

All six of the sites positive for SLWF (100%) had leaves in the 1-5  nymph/leaf range, while two of the sites (33%) had leaves in the 6-49 nymphs/leaf range, and one site (17%) had leaves in the 50 or more nymphs/leaf range.

Twenty of the sites positive for aphids (91%) had leaves in the 1-5 aphids/leaf range, while thirteen of the sites (59%) had leaves in the 6-49 aphids/leaf range, and nine of the sites (41%) had leaves in the 50 or more aphids/leaf range. Fifteen of the twenty-four sample sites (63%) had leaves with honeydew and seven of the sites (29%) had leaves with sooty mold.

Mites were found at fifteen sites (63%), armyworm at one of the sites (4%), and four sites (17%) had leaves with other whitefly species.

Tulare County

One of the eleven sample sites (9%) were positive for SLWF and nine of the eleven sites (82%) were positive for aphids. A total of 130 leaves were collected, of which one leaf (0.8%) was infested with SLWF, and thirty-seven leaves (28%) were infested with aphids.

The only site that was positive for SLWF had one leaf in the 1-5 nymphs/leaf range; no other leafs contained SLWF.

All nine of the sites positive for aphids (100%) had leaves in the 1-5 aphids/leaf range, while two of the sites (22%) had leaves in the 649 aphids/leaf range, and none of the sites had leaves in the 50 or more aphids/leaf range. Three of the eleven sample sites (27%) had leaves with honeydew and two of the sites (18%) had leaves with sooty mold.

Mites were found at six of the sites (55%), while none of the sites had armyworm or other whitefly species.

Fresno County

Eight of the twenty-nine sample sites (28%) were positive for SLWF and twenty-five of the twenty-nine sites (86%) were positive for aphids. A total of 590 leaves were collected, of which sixteen leaves (3%) were infested with SLWF, and 257 leaves (44%) were infested with aphids.

All eight of the sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while one site (13%) had a leaf in the 6-49 nymphs/leaf range, and none of the leaves were in the 50 or more nymphs/leaf range.

Twenty-four of the sites positive for aphids (96%) had leaves in the 1-5 aphids/leaf range, while nineteen of the sites (76%) had leaves in the 6-49 aphids/leaf range, and nine of the sites (36%) had leaves in the 50 or more aphids/leaf range. Nine of the twenty-nine  sample sites (31%) had leaves with honeydew and only one of the sites (3%) had leaves with sooty mold.

Mites were found at eight of the sites (28%), armyworms at two sites (7%), and only one site (3%) had leaves with other whitefly species.

Madera County

The one sample site was not positive for SLWF, but was positive for aphids. A total of 20 leaves were collected, of which zero leaves were infested with SLWF, and two leaves (20%) were infested with aphids.

The two sites that were positive for aphids had leaves in the 1-5 aphids/leaf range only. There were zero leaves with honeydew, sooty mold, mites, armyworms, or other whitefly species found at this site.

Merced County

Two of the thirty-one sample sites (6%) were positive for SLWF, and eighteen of the thirty-one sites (58%) were positive for aphids. A total of 460 leaves were collected, of which two leaves (0.4%) were infested with SLWF, and eighty-eight leaves (19%) were infested with aphids.

The two sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range only.

All eighteen of the sites positive for aphids (100%) had leaves in the 1-5 aphids/leaf range, while seven of the sites (39%) had leaves in the 6-49 aphids/leaf range, and five of the sites (28%) had leaves in the 50 or more aphids/leaf range. Three of the thirty-one sample sites (10%) had leaves with honeydew, and two of the sites (6%) had leaves with sooty mold.

Mites were found at seven sites (23%), armyworms at two sites (6%), and there were zero sites that had leaves with other whitefly species.

Ernst Undesser
By Lauren Murphy, University of California Cooperative Extension September 6, 2017