“Welcome to the Hotel California
Such a lovely place
Plenty of room at the Hotel California
Any time of year”
Proprietor: Kent Daane. Fittingly, Black Widow Spiders are the only guests of this Hotel California...”such a lovely place...such a lovely place.”
No need for a desk register. Desk clerk Daane knows all his guests. He personally reared all 3,000 of them for a stay in this special place that ... “could be heaven or this could be hell.”
California Table Grape Commission is the mortgage holder of this particular lovely place....”You can checkout any time you like. But you can never leave!”
Daane’s real job is University of California Extension specialist, biological control. His charge is to make sure his guests in this vineyard established to study the habits of black widows never reach the upper floor where there are table grape clusters.
One black widow spider in a bunch of table grapes is definitely an unwanted guest. One is one too many, and the California Table Grape Commission is funding an aggressive research effort by University of California entomologists to help growers to turn ones into zeros.
Hotel California for Black Widows is just one element of the research Daane and others are conducting on how to find and control black widow spiders, which have been found in table grape clusters in supermarket produce departments here and overseas.
A definite no-no in this country, but even more so in critical markets overseas. One-third of California table grapes are exported each season and if enough black widows are found in bunches shipped overseas, hard earned markets could be lost. This is especially true in countries where there are no black widow spiders. There these evil doers are considered invasive species to never become established.
Black widows are certainly not invasive in America where Daane estimates one-third of all households have black widows in backyards, basements or other places.
One of the big reasons homeowners and table grape growers alike do not see them is that they are nocturnal.
“The black widow spiders always come out at night in vineyards, typically starting after dusk and remaining until just before sunrise,” Daane told the annual San Joaquin Valley table grape seminar in Visalia recently.
Treat early, late
Daane told 300 growers and PCAs there they could use that little bit of research information to ensure that black widows do not get a one-way ticket out of a vineyard on a table grape bunch. Early morning or late evening may be the best time to treat with insecticides.
Fortunately, said Daane, there is an array of effective insecticides for control of black widows.
In direct contact studies, Danitol, Lorsban and Lannate “provided excellent control of adult black widows with 100 percent mortality one day after treatment.”
However, Applaud, Provado, Agrimek and Omite had little or no impact.
Of the effective material, only Danitol and Lorsban provided “residual control,” said Daane. This is where spiders died after contact with treated bark. Danitol was also “very effective” against immature black widows, while Lorsban had less impact.
Most black widows (40-60 percent) in vineyards with known black widow problems were found near the trunk base with fewer than 8 percent found in the canopy and clusters. Fewer than 1 percent were actually found in clusters, according to Daane.
Black widows like to spin webs in areas between grapestakes and the vine and in irrigation standpipes. They love milk cartons used to protect young vines. Daane suggests removing the protective milk cartons as soon as practical. In one vineyard where the cartons were removed, spider populations quickly declined.
Finding black widow webs is easier than finding spiders. Daane suggests destroying webs around the base and other areas of the vine where they are found before applying an insecticide. Three to five days after treatment return to those sites — he suggests 50 webs -- and see if the webs have been rebuilt. If the black widows are still alive, the webs will be built back in three to five days.
Black widows are active year-round, even in when temperatures are freezing or near freezing. Nighttime applications in the winter when they are slow moving may be the best time to reduce the problem with pesticide applications.
Both mature and immature black widow stages are present year-round. Spiderlings are most common from May through October, typically peaking in May and June. Spiderlings were always found on webs at the base of the vine. Adult female black widows produce egg sacs from April through September.
Found at harvest
“Unfortunately, the largest number of black widows are found during the harvest months of August through November,” Daane noted. Fall is also when 50 percent of the state’s table grapes move to market.
Daane says the late season movement into canopy and clusters could be spiders looking for prey. “This will be especially true in vineyard systems with dense overhead canopies that block growth of plant materials on the vineyard floor, which also reduces the potential prey near the ground and away from the grape clusters,” he said.
As a biological control specialist, Daane is always looking for beneficial insects/predators. The best biological control for black widow spiders is black widow spiders. They eat their young.
Welcome to Hotel California.
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