Introduction
This period of sampling for the silverleaf whitefly (SLWF) surveys began on Monday, August 14, 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:
All thirteen sample sites (100%) were positive for both SLWF and aphids during this survey round. A total of 390 leaves were collected, of which 227 leaves (58%) were infested with SLWF, and 198 leaves (51%) were infested with aphids.
All thirteen of the sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while ten sites (77%) had leaves in the 6-49 nymphs/leaf range, and three sites (23%) 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, while 10 sites (77%) had leaves in the 6-49 aphids/leaf range, and four sites (31%) had leaves in the 50 or more aphids/leaf range. All thirteen of the sites (100%) had leaves with honeydew and eleven sites (85%) had leaves with sooty mold.
Mites were found at eleven sites (85%), armyworm at two sites (15%), and three of the sample sites (23%) had leaves with other whitefly species.
Kings County:
Twenty-two of the twenty-four samples sites (92%) were positive for SLWF and twenty-three of the twenty-four sites (96%) were positive for aphids. A total of 520 leaves were collected, of which 123 leaves (24%) were infested with SLWF and 253 leaves (49%) were infested with aphids.
All twenty-two of the sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while seven of the sites (29%) had leaves in the 6-49 nymphs/leaf range, and none of the sites (0%) had leaves in the 50 or more nymphs/leaf range.
Twenty-two of the sites positive for aphids (96%) had leaves in the 1-5 aphids/leaf range, while seventeen of the sites (74%) had leaves in the 6-49 aphids/per leaf range, and eight of the sites (35%) had leaves in the 50 or more aphids/leaf range. Fourteen on the twenty-four sample sites (58%) had leaves with honeydew and eighteen of the sites (75%) had leaves with sooty mold.
Mites were found at twenty-one sites (88%), armyworm at three of the sites (13%), and two of the sites (8%) had leaves with other whitefly species.
Tulare County:
All eleven of the sample sites (100%) were positive for SLWF and aphids. A total of 300 leaves were collected, of which 111 leaves (37%) were infested with SLWF, and 178 leaves (59%) were infested with aphids.
All eleven sites (100%) that were positive for SLWF had leaves in the 1-5 nymphs/leaf range, while five of the sites (45%) had leaves in the 6-49 nymphs/leaf range, and one of the sites (9%) had a leaf in the 50 or more nymphs/leaf range.
All eleven of the sites positive for aphids (100%) had leaves in the 1-5 aphids/leaf range, while nine of the sites (82%) had leaves in the 6-49 aphids/leaf range, and two of the sites (18%) had leaves in the 50 or more aphids/leaf range. Seven of the eleven sample sites (64%) had leaves with honeydew and ten of the sites (91%) had leaves with sooty mold.
Mites were found at seven of the sites (64%), armyworm at three of the sites (27%), and two of the sites (18%) had leaves with other whitefly species.
Fresno County:
Twenty-two of the twenty-nine sample sites (76%) were positive for SLWF and all twenty-nine sites (100%) were positive for aphids. A total of 780 leaves were collected, of which 180 leaves (23%) were infested with SLWF, and 359 leaves (46%) were infested with aphids.
All Twenty-two of the sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while nine of the sites (41%) had leaves in the 6-49 nymphs/leaf range, and four of the sites (18%) had leaves in the 50 or more nymphs/leaf range.
All twenty-nine of the sites positive for aphids (100%) had leaves in the 1-5 aphids/leaf range, while twenty-five of the sites (86%) had leaves in the 6-49 aphids/leaf range, and nine of the sites (31%) had leaves in the 50 or more aphids/leaf range. Four of the twenty-nine sample sites (14%) had leaves with honeydew and seven of the sites (24%) had leaves with sooty mold.
Mites were found at twenty-four of the sites (83%), armyworm at four sites (14%), and seven of the sites (24%) had leaves with other whitefly species.
Madera County:
The one sample site (100%) was positive for both SLWF and aphids. A total of 20 leaves were collected, of which three leaves (15%) were infested with SLWF, and six leaves (30%) were infested with aphids.
All three leaves from this site that were infested with SLWF were in the 1-5 nymphs/leaf range.
Of the six leaves from this site that were infested with aphids, four of the leaves were in the 1-5 aphids/leaf range and two of the leaves were in the 6-49 aphids/leaf range.
This site did contain leaves with mites and other whitefly species, but had zero leaves with armyworm, honeydew, and sooty mold.
Merced County:
Twenty of the thirty-one samples sites (65%) were positive for SLWF, and twenty-eight of the sites (90%) were positive for aphids. A total of 880 leaves were collected, of which 125 leaves (14%) were infested with SLWF, and 302 leaves (34%) were infested with aphids.
All twenty sites positive for SLWF (100%) had leaves in the 1-5 nymphs/leaf range, while four of the sites (20%) had leaves in the 6-49 nymphs/leaf range, and zero of the leaves (0%) had leaves in the 50 or more nymphs/leaf range.
Twenty-seven of the sites positive for aphids (96%) had leaves in the 1-5 aphids/leaf range, while sixteen of the sites (57%) had leaves in the 6-49 aphids/leaf range, and eight of the sites (29%) had leaves in the 50 or more aphids/leaf range. Eight of the thirty-one sample sites (26%) had leaves with honeydew, and nineteen of the sites (61%) had leaves with sooty mold.
Mites were found at twenty-six sites (84%), armyworm at two sites (6%), and six of the sites (19%) had leaves with other species of whitefly.
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