California Cotton: Latest County-Level Whitefly Survey Results

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The second 2019 round of sampling for the silverleaf whitefly (SLWF) surveys began on July 15 and ended on July 26. Program personnel collected samples from designated sites at 10 percent of all cotton fields in each county of the San Joaquin Valley.

The Program has a total of 192 SLWF sampling sites with 15 sites in Kern County, 42 sites in Kings County, 17 sites in Tulare County, 59 sites in Fresno County, 2 sites in Madera County, and 57 sites in Merced County. At each site one leaf sample from 10 different cotton plants was collected for a total of 10 leaves/site.

Kern County:

Leaves in two of the 15 sample sites in Kern County contained SLWF nymphs during the second survey round. A total of 150 leaves were collected, of which two leaves contained SLWF nymphs. Both sites positive for SLWF nymphs contained one leaf in the 1-5 nymphs/leaf range, and none of the sites contained leaves in the 6-49 nymphs/leaf range or the 50 or more nymphs/leaf range. Thirteen of the 15 sites had at least one leaf containing aphids.

Out of the 150 leaves collected, 45 contained aphids. All 13 of the sites positive for aphids had leaves in the 1-5 aphids/leaf range, while 6 of the sites had leaves in the 6-49 aphids/leaf range, and 1 of the sites had leaves in the 50 or more aphids/leaf range.

Three of the 15 sites had leaves with honeydew and none of the sites had leaves with sooty mold. Mites were found at four sites, and armyworm and other whitefly species were not found at any of the sites.

Kings County:

Two of the 42 sample sites had leaves containing SLWF nymphs during the second survey round. A total of 420 leaves were collected, of which two leaves contained SLWF nymphs. Both sites positive for SLWF nymphs contained one leaf in the 1-5 nymphs/leaf range, and none of the sites contained leaves in the 6-49 nymphs/leaf range or the 50 or more nymphs/leaf range. Thirty of the sites had at least one leaf containing aphids.

Out of the 420 leaves collected, 114 leaves contained aphids. All 30 of the sites positive for aphids had leaves in the 1-5 aphids/leaf range, while seventeen of the sites had leaves in the 6-49 aphids/leaf range, and four of the sites had leaves in the 50 or more aphids/leaf range.

One of the 42 sample sites had leaves with honeydew and none of the sites had leaves with sooty mold. Mites were found at eight of the sites, and none of the sites had leaves with armyworm or other whitefly species.

Tulare County:

None of the 17 sample sites had any leaves containing SLWF nymphs during the second survey round. Twelve of the sites had at least one leaf containing aphids. A total of 170 leaves were collected, of which 30 leaves contained aphids.

All twelve of the sites positive for aphids had leaves in the 1-5 aphids/leaf range, three of the sites had leaves in the 6-49 aphids/leaf range, and none of the sites had leaves in the 50 or more aphids/leaf range. None of the 17 sample sites had leaves with honeydew or sooty mold. Mites were found at three of the sites, while none of the sites had armyworm or other whitefly species.

Fresno County:

Three of the 59 sample sites had at least one leaf containing SLWF nymphs during the second survey round. A total of 590 leaves were collected, of which four leaves contained SLWF nymphs. All three sites positive for SLWF had leaves in the 1-5 nymphs/leaf range, none of the sites had leaves in the 6-49 nymphs/leaf range or the 50 or more nymphs/leaf range.

Forty-eight of the sites had at least one leaf containing aphids. Out of the 590 leaves collected, 245 leaves contained aphids. Forty-three of the sites positive for aphids had leaves in the 1-5 aphids/leaf range, while 21 of the sites had leaves in the 6-49 aphids/leaf range, and six of the sites had leaves in the 50 or more aphids/leaf range.

Nineteen of the 59 sample sites had leaves with honeydew and none of the sites had leaves with sooty mold. Mites were found at 25 of the sites, armyworms at one of the sites, and nine of the sites had leaves with other whitefly species.

 

Madera County:

Neither of the two sample sites contained any leaves with SLWF nymphs. One of the sites contained two leaves with aphids. A total of 20 leaves were collected. Both of the leaves that contained aphids were in the 1-5 aphids/leaf range.

Neither of the two sample sites had leaves with honeydew or sooty mold. Both the sites had leaves with mites, while neither of the sites had leaves with armyworm, and one of the sites had leaves with other whitefly species.

Merced County:

Eleven of the 57 sample sites had at least one leaf containing SLWF nymphs. A total of 570 leaves were collected, of which 14 leaves contained SLWF nymphs in the 1-5 nymphs/leaf range, and none of the sites had leaves in the 6-49 nymphs/leaf range or the 50 or more nymphs per leaf range.

Thirty-three of the sites had at least one leaf containing aphids. Out of the 570 leaves collected, 93 leaves contained aphids. All 33 of the sites positive for aphids had leaves in the 1-5 aphids/leaf range, while four of the sites had leaves in the 6-49 aphids/leaf range, and none of the sites had leaves in the 50 or more aphids/leaf range.

Fifteen of the 57 sample sites had leaves with honeydew and none of the sites had leaves with sooty mold. Mites were found at 23 sites, armyworms at 1 site, and 21 sites had leaves with other whitefly species.


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