Curly Top Virus Updates
Beet Leafhopper Status, April 4, 2003
December rains germinated
a bumper crop of Plantago this spring throughout the historical BLH
breeding grounds. There was sufficient rain to germinate rangeland host
plants but not enough to develop a heavy grass cover. This condition has
left south- facing slopes with favorable vegetation for BLH development.
In almost every case, Plantago is the preferred host this spring
over the peppergrass and filaree developing in the same areas. We
anticipate this year’s BLH population to be above average. BLH’s are
emerging from Plantago in higher numbers than has been seen in
quite a few years. The bulk of the BLH population ranges from the
Kettleman Hills north, to Big Panoche Canyon. There are also some
populations developing in Kern County on the south side of the Elk and
Buena Vista Hills. A few of the more advanced BLH populations now contain
30% to 40% spring adults and will begin a full migration as the
Plantago completely dries.
Current (CTVCP) Treatment Activities
The Curly Top Virus Control Program (CTVCP) is
currently conducting the spring treatment campaign. Due to below normal
winter/spring rainfall, treatment activities were initiated about 10 days
earlier than normal. Winds have reduced the treatment times each day from
sun-up to about 9:30 in the morning. This has made progress slow at
times. Since March 20, 2003, the CTVCP has treated approximately 56,000
acres from Kettleman City, north to Big Panoche Canyon.
If BLH’s find suitable host
plants, they can reproduce quite rapidly and pose a later season threat of
BCTV infection in susceptible crops. Currently, the highest risk area is
along the Interstate 5 corridor between Kettleman City and Big Panoche
Creek, to about five miles east of the hills.
Growers Can Help
Beet leafhopper (BLH) populations are beginning to
migrate from the overwintering rangeland habitat on the west side
of the San Joaquin Valley. Of concern are the thousands of acres of
fallow fields containing London rocket and mustards. There is sufficient
moisture for these weed hosts to sustain another generation of BLH’s. The
mustards are an excellent virus reservoir for beet curly top virus (BCTV).
DO NOT REMOVE WEEDS
WITHOUT CHECKING FOR BLH’S AND ELIMINATING THE BLH’S, IF NECESSARY.
April 10, 2002
4-2002
Curly top virus (CTV),
spread by the sugar beet leafhopper (BLH), is a severe threat to susceptible
crops this year. In 2001, severe CTV was experienced in some fields of
transplant tomatoes and sugar beets. This year, the BLH population is at
least 50%larger and covering a much bigger area.
Being a very warm, dry winter, the BLH
survival rate was high and propensity for migration was earlier than we
would normally expect. The bulk of the BLH population in the San Joaquin
Valley is centered between the Kings/Kern County line south of Kettleman
City and Los Banos.
To date this winter/spring, the Curly Top
Virus Control Program (CTVCP) has treated over 100,000 acres:
Winter Treatment = 20,850 acres
Spring Treatment = 79,650 acres
An excellent kill was achieved where we had
concentrations.
Even though the CTVCP treated large areas, there are
still high levels of BLH’s moving out of the hills and on to roadside weeds
and into fallow fields. Just in the past week, the numbers of spring BLH’s
migrating into fallow fields along the west side of the San Joaquin Valley
has caused the numbers of BLH’s to increase ten fold, particularly between
Cantua Creek and Little Panoche Canyon (Shields Avenue).
The BLH’s that are
migrating are mated females and they will deposit eggs in the weed hosts
within a few days of arrival, producing another generation of BLH’s.
DO NOT REMOVE WEEDS
WITHOUT CHECKING FOR BLH’S AND ELIMINATING THE BLH’S, IF NECESSARY.
If BLH’s are allowed to reproduce on these
weedy areas, they will migrate in higher numbers when the weeds dry
spreading later season CTV.
Monterey County
We have detected a large concentration of BLH’s
along the east side of the Salinas Valley between Kings City and Soledad.
These BLH’s cover an area of between 6,000
and 7,000 acres of drying rangeland. We expect to initiate control
operations on or about April 10, 2002. Though there are not the high
numbers of BLH’s throughout the area, there are a few to be found just about
anywhere there are host weeds. Clean up the weedy areas around susceptible
crops now to avoid major problems later in the season.
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March 18, 2002
3-2002
Growers of crops susceptible to curly top virus (CTV),
including sugar beets, tomatoes, melons, pumpkins, squash, beans, and
spinach, should take special precautions against the sugar beet leafhopper
(BLH). The BLH is the only known vector of CTV.
Dry conditions this year created conditions in
the hills along the west side of the San Joaquin Valley that are ideal for
overwintering and reproduction of BLH’s over an extremely wide area. The
warm, dry winter encouraged the emergence of the spring generation of BLH
nymphs nearly a month earlier than usual this year. The Curly Top Virus
Control Program (CTVCP) was delayed in starting control operations due to
windy conditions, which not only held up the spraying operations, but also
changed the timing of the spring migration of the spring BLH population.
The dry winds desiccated much of the rangeland host plant base that could
have held some of the adult BLH’s; therefore, many of the hoppers, as
they reach adulthood, were leaving and starting to move toward cultivated
areas searching for host weeds.
In an earlier update, I predicted this BLH
movement would begin in mid-March rather than April, which was correct.
However, the numbers of BLH’s that are beginning to move is much smaller
than predicted. The dry winds desiccated the rangeland so fast that many
nymphs did not hatch or did not have time to mature before their hosts
were lost. The greatest amount of drying occurred on rangeland on the west
side of Kern County.
After extensive survey, the CTVCP staff targeted
over 60,000 acres in western Kings, Fresno and Merced as requiring control
operations.
Windy weather delayed aerial spraying until
Friday, March 15, 2002. We couldn’t spray on the 16th because
of wind and only treated a little over 5,000 acres on the 17th
before we were shut down by both wind and rain. In my opinion, rain at
this time, is the last thing we need. On one hand, it could delay further
movement of adult BLH’s, but there appears to be enough moisture to both
revive much of the rangeland hosts and possibly germinate more roadside
weeds.
The adult BLH’s, who stay in the hills, could
produce another generation similar to what occurred last year, spread over
a wider area. New weed germination could undo the excellent weed control
that has been done by growers. BE ALERT FOR
ANY NEW WEED GERMINATION. THIS DOES NOT HAVE TO BE BIG WEEDS; BLH’s ARE
ATTRACTED TO VERY SMALL, SPARSE GROWTH. The few BLH’s that
have moved into cultivated areas at this date are of little concern
compared to what could happen if we allow another generation to develop on
fallow fields and roadsides.
This rain event has crippled the CTVCP control
operations and will require re-survey of much of the rangeland and an
increased expenditure of the Program’s dwindling resources. On the other
hand, the cooler temperatures will slow BLH development.
As this is written, late in the evening of March 17th,
the CTVCP staff is in the process of re-allocating resources and survey to
try to find any advantage this turn in the weather has given. We will
continue stepped up control operations, but it will be several days before
we have a clear picture of where the biggest threat of CTV infection will
come from.
We do know that the largest BLH populations
remain in western Fresno County, from the county line on the north tip of
the Kettleman Hills, north to Little Panoche Canyon.
As soon as the weather warms, there will be
continued movement of BLH’s from the hills, at least to a limited
extent.
PLEASE DON’T TAKE THIS
WARNING LIGHTLY AS THE BLH POPULATIONS HAVE AN ASTOUNDING ABILITY TO
REBOUND AND STRIKE WITH CTV WHERE WE LEAST EXPECT.
Please call the office at (559) 445-5472,if you have
questions.
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February 27, 2002
2-2002
CURLY TOP VIRUS (CTV) COULD BE EVEN MORE SERIOUS THAN
2001 .
The
weather pattern and beet leafhopper (BLH) population development is
beginning to match conditions that preceded the disastrous CTV outbreak in
1977. It is too early to tell, until we start seeing infection in
susceptible crops.
In 2001, besides the migration out of the hills, we had
BLH coming out of fallow fields where they carried CTV from infected weeds
to crops. We had BLH’s coming out of sugar beet fields being harvested
and carrying CTV into young sugar beets. We even had some growers plowing
down weeds infested with BLH right next to newly transplanted tomatoes and
peppers.
Let’s not take any chances this year. It
looks like we are all working together, but clearing weeds at the wrong
time can put your neighbor out of business. Most of the beet growers
are using a good systemic on their newly planted beets that will help
reduce the buildup of BLH and CTV. Since BLH’s are so fond of young
sugar beets, the Curly Top Virus Control Program (CTVCP) staff will be
checking as many beet fields as they can as an early warning of BLH
population buildup. The sugar company has furnished the Program maps of
beet field locations. Staff will also be checking fallow fields throughout
the west side of the San Joaquin Valley in an attempt to head off any BLH
buildup and movement from that quarter. We have found BLH’s, in low
numbers, in fallow fields checked last week. As we all know, if nothing
happens, we could have a couple hundred offspring from each BLH adult. So
far, we are not seeing a hatch of spring nymphs on the Valley floor.
Our staff is seeing a sporadic hatch in the hills along
the west side from Utica Ave. south of Kettleman City to Little Panoche
Canyon in the north. Rainfall has been
just sparse enough to create ideal BLH conditions from
Highway 46 north to about Los Banos. South of Highway 46 through western
Kern County, the rain has been even less, limiting BLH’s mostly to the
flats where water has accumulated enough to establish winter hosts.
We know there’s a large BLH population this year.
We also know there will be BLH’s impacting susceptible crops, because no
matter how effective the CTVCP is in areas treated, there will always be
holes left in endangered species habitat, vernal pool buffers, crews
working in oil wells or other sensitive areas the CTVCP cannot treat.
Even though the overall population is substantially
reduced when the BLH’s exit the hills, if they find suitable hosts, they
can reproduce quite rapidly and pose a later season threat of CTV spread.
ELIMINATE THE WEEDS EARLY AND KEEP THEM DOWN THROUGHOUT
THE GROWING SEASON .
Last year the Program had difficulty getting
serological diagnosis of CTV and other plant diseases in a timely manner.
To speed up diagnosis of plant disease and ease some of the burden on the
University of California and other laboratories, the growers can send
plant samples directly to the California Department of Food and
Agriculture, Plant Pest Diagnostics Branch in Sacramento at no cost to the
grower.
A pamphlet has been put together illustrating how to
take, prepare and ship samples. All you need to do is give the Program’s
Fresno office a call and we will mail, fax or drop one off in person. All
CTVCP staff will have extra copies in their vehicles; if we don’t offer
you a copy, please ask for one.
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