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California Cotton: Whitefly, Aphid Numbers Rising

Ernst Undesser
By Lauren Murphy, University of California Cooperative Extension Specialist October 5, 2017

California Cotton: Whitefly, Aphid Numbers Rising

White flies on cotton leaf.

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.

Click Image to Enlarge

Ernst Undesser
By Lauren Murphy, University of California Cooperative Extension Specialist October 5, 2017