Santa Barbara County
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Santa Barbara County

Grower Notes and Pest News

Japanese dodder, an exotic and noxious weed found in Santa Barbara County

Japanese dodder, Cuscuta japonica recently found in Lompoc, Santa Barbara Co. 
(Photo by: Matt Victoria, Santa Barbara Ag Commissioner's Office)


Japanese dodder is an exotic parasitic weed which is a high priority noxious weed in California.  It was recently detected in a natural wooded area in Lompoc.  It is the first time it is reported in Santa Barbara Co and the Ag Commissioner's office is taking an immediate action.

Biology:
Japanese dodder, Cuscuta japonica is a parasitic plant that belongs to Convolvulaceae family (note that older literature refers to it as a member of Cuscutaceae family).  It is a parasitic annual plant that has a slender, yellow stem with red spots and striations, and scale-like leaves.  It produces haustoria (singular hostorium), which are root-like structures that penetrate the vascular tissue of the host and absorb nutrients and water.   It can reproduce by seed and by vegetative means through fragments of the plant.  Seed can germinate in soil, but the plant has to come in contact with a host to for the young shoot to survive beyond a few days.  It appears that Japanese dodder seed produced in California is not viable and vegetative reproduction is the main source of propagation.

Host range: Japanese dodder has a wide host range that includes herbaceous annuals to woody shrubs and trees.  Crop plants like corn, cucumber, egg plant, pea, pumpkins, soybean, and tomato, and ornamental shrubs, fruit and other trees are among the hosts that are parasitized by this weed.

Damage: Depending on the extent of infestation, damage can range from stunted growth to death.  Japanese dodder growers faster and spreads to larger areas than the other dodders.

Dissemination: It is spread by equipment, birds, animals and people as seed and fragments of plant material.  Gardening activities and improper composting and infested plant material can spread the weed.  Intentional planting for medicinal purposes is thought to be a significant factor for the dissemination of this weed.

Management: Prevention of the infestation is the best way to manage Japanese dodder.  Due to its current status a high priority regulated pest, one should not attempt to control or remove Japanese dodder if detected.  It should be immediately reported to the local Ag Commissioner's office (805-681-5600 for Santa Barbara Co and 805-781-5910 for San Luis Obispo Co).

Detailed information on Japanese dodder biology, identification, and reporting the infestation can be found at the following sources.

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References:

Santa Barbara Co Ag Commissioner's Office: http://www.countyofsb.org/agcomm/wma.aspx?id=29344

UC IPM: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7496.html

CDFA Noxious Weed Information Project: http://www.cdfa.ca.gov/plant/ipc/noxweedinfo/noxweedinfo_jdodder.htm

Center for Invasive Species and Ecosystem Health: http://www.invasive.org/eastern/other/DicCusCjO01.pdf

Posted on Thursday, September 1, 2011 at 3:17 PM

Downy mildew of basil

Basil plants that originated from a central coast nursery were recently found infected with downy mildew pathogen, Peronospora belbahri in a home and garden store in California.  This is a new pathogen that can cause serious damage to culinary and ornamental basil plants.

Symptoms include yellowing of the area between the veins on the upper leaf surface and growth of fungal mycelia and purplish grey spores on the lower surface.  Yellowing on the upper leaf surface can be confused with nutritional deficiency, so careful examination of the lower side is important.

Fungal spores on the lowerside of the basil leaf (Photo by: Heather Scheck, Santa Barbara County Ag Commissioner Pathologist)


Basil downy mildew was first reported in the United States in 2007 in Florida and in several eastern states by 2008.  It was also found in California by 2009.  Infected seeds and plants are main sources of infection.  Growers should try to obtain clean seeds.  Spores can be dispersed by wind and close spacing and overhead irrigation can also aid in the dispersal of the inoculum.

Regular monitoring of the fields for early detection of the infection and timely application of the fungicides is important for managing this disease.  Proper ventilation and temperature control in the greenhouses is also critical as prolonged leaf wetness, high humidity, and cool weather promote the disease development.

Additional information about the disease and management
guidelines can be found at: http://vegetablemdonline.ppath.cornell.edu/NewsArticles/BasilDowny.html

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Posted on Sunday, June 5, 2011 at 11:08 PM

Casebearer moth infestation on manzanita

Manzanita leaves showing blotch mines and cases made by Coleophora sp. 
(Photo by: Surendra Dara)

Manzanita (Arctostaphylos sp.) leaf samples that were recently brought from the San Luis Obispo area appear to have casebearer infestation. 
Casebearer adults are small, narrow moths that belong to the family of
Coleophoridae in the order Lepidoptera. Young larvae are leaf miners.  Their name comes from the casing they make with silk, frass and plant material as older larva.  Pupation takes place inside the casing.

The specimens in hand appear to be Coleophora sp.  It has a selnder, shiny dark brown or black casing that is about 0.4 inches (10 mm) and is attached to the leaf lamina near the mined area.  The type of mine is blotch mine where larva turns around (unlike the unidirectional serpentine mines) causing irregularly shaped mine.

Blotch mine and pupal case (Photo by: Surendra Dara and Rodney Cooper, USDA-ARS).

Pupa is located towards the end attached to the leaf.  The other end of the case is flat. (Photo by: Surendra Dara and Rodney Cooper, USDA-ARS)

Empty pupal case after the adult emergence, above and below (Photo by: Surendra Dara and Rodney Cooper, USDA-ARS)

Reference

Borror, D. J.,  C. A. Triplehorn, and N. F. Johnson. 1989.  An introduction to the study of insects, 6th edition. Saunders College Publishing.

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Posted on Monday, May 16, 2011 at 5:43 PM

Lewis mite: A potential pest of strawberries and raspberries

Lewis mite, Eotetranychus lewisi (Photo courtesy: Daniel Gilrein, Cornell University)

Lewis spider mite or Lewis mite, Eotetranychus lewisi (McGregor) (Phylum Arachnida, sub-class Acarina, family Tetranychidae) is a pest of many host plants.  In the US, it has been reported on citrus and greenhouse poinsettias.  Lewis mites have been seen on strawberries and raspberries in the Ventura area for some time, but growers appear to be noticing increased infestations in the recent years.  Some growers have also seen them in Santa Maria in the recent years, but they have so far not been reported from the Watsonville area.  Considering the recent trend, growers might keep them in mind while scouting for pests.  Environment, natural enemies, cropping patterns, pesticide usage and other agronomic practices are among the factors that influence the status of pests.  It is not yet clear why infestations are increasing, but here is some information on Lewis mite.

Host range and distribution: According to an earlier report (Bolland et al, 1998), Lewis mite is distributed mostly in the western hemisphere and some parts of Africa infesting 65 species of plants including food and multipurpose plants like Erythrinia edulis, Citrus spp., Prunus sp., papaya, fig, ornamentals like Cleome sp., Bauhinia spp., Rosa sp., Euphorbia spp. (poinsettia, snow-on-the-mountain, fire-on-the-mountain), weeds like silverleaf nightshade, and various other hosts.  It has later spread to parts of Europe and East Asia.  Lewis mite infestation on strawberries was reported from Philippines nearly a decade ago (Raros, 2001).

Biology: Males are about 0.25 mm and females are about 0.36 mm long.  Species identification is tricky and requires both sexes to be examined microscopically.  They can be confused with twospotted spider mite (TSSM), Tetranychus urticae in their general appearance.  But, comparing adult females, Lewis mites are smaller than TSSM and have several small spots on their body while TSSM have a single dark spot on either side of the body.  Lewis mite has five life stages – egg, larva, protonymph, deutonymph and adult.  Eggs are round, whitish to light orange.  Females lay 60-90 eggs over a period of about a month.  It takes about 12-14 days from egg to adult stage at 21oC (70oF).

Twospotted spider mite (right, UC IPM)

Damage: Symptoms of damage vary according to the host plant.  On poinsettia, Lewis mite feeds on the underside of the leaves and causes very fine stippling or flecking on foliage, which can be initially mistaken for nutrient deficiency.  Infestations can build to high levels in poinsettia before mites and their webbing are noticed.  Since their infestation in strawberries currently coincides with TSSM infestations, exclusive Lewis mite damage symptoms in strawberries are yet to be determined.  In some hosts like papaya, damage resembles symptoms of viral infection and may cause distortion and yellowing of young leaves.  According to Daniel Gilrein, an extension entomologist from Cornell University, fine flecking from Lewis mite feeding almost resembles nitrogen deficiency and can delay detection until populations build up.  Leaves turn brown and webbing can be seen as the damage advances.

Management: In research on greenhouse poinsettias (D. Gilrein, pers. comm.), abamectin (Avid for ornamentals, Agri-Mek and generics for food crops), acequinocyl (Kanemite and Shuttle-O), bifenazate (Acramite and Floramite), fenpyroximate (Akari and Fujimite), spiromesifen (Judo and Oberon) were found effective in controlling Lewis mite.  These are also among the miticides recommended by UC IPM for spider mites on strawberries.   However, there have been some suspected resistance issues in some populations of Lewis mite in strawberry growing areas of California, but some of these materials act primarily as contact miticides and issues of coverage cannot be ruled out in all cases.

What to do: Look for Lewis mites while scouting for TSSM especially in fields close to infested ornamentals.  Keep in mind that there could be resistance or efficacy problems with some miticides in certain areas with TSSM or Lewis mites.  It is always a good practice to rotate miticides with different modes of action for better management and reducing the risk of resistance development.   The mode of action is indicated on most lables (e.g. Agri-Mek is a Group 6 Insecticide) If you suspect resistance in TSSM or Lewispopulations in your area, perform a simple test to evaluate the effectiveness of the intended miticides.  Dip several mite-infested leaves in a cup of miticide solution (concentration similar to the field application rate), let them dry and then cover (to keep foliage from drying out completely) and place in a cool area away from direct sun.  Check to see if any mites have survived 24 and 48 hours after dipping.  The effectiveness of the miticide will be indicated by the number of mites alive or dead.  For comparison, dip several similar mite-infested leaves in normal water and treat similarly, observing the survival of mites on those leaves as well.  This can be a useful comparison for new, untested miticides as well as for older products where miticide resistance is suspected.

UC researchers are working on this issue and will have some more information in the near future.  If you suspect or find Lewis mites in your fields, please contact me at skdara@ucdavis.edu or 805-788-2321.

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References

Bolland H. R., J. Gutierrez and C.H.W. Fletchtmann.  1998.  World Catalogue of the Spider Mite Family (Acari: Tetranychidae.) Brill, Leiden (NL).

European and Mediterranean Plant Protection Organization.  2006.  Eotetranychus lewisi.  OEPP/EPPO Bulletin 36: 161-163.

Gilrein, D.  2011.  Cornell Cooperative Extension of Suffolk County, LIHREC, Riverhead, NY.

Raros, L.A.C.  2001.  New mite pests and new host records of phytophagous mites (Acari) from the Philippines.  Philippine Agricultural Scientist 84: 341-351.

Posted on Friday, March 11, 2011 at 7:03 PM

Degree-days for timing treatment decisions for lygus in strawberries

Lygus bug (Lygus spp.) is a major strawberry pest in California affecting the yield and quality of berries.  Although strawberry is not a preferred host for lygus bug compared to other hosts like alfalfa, as the strawberry crop is available almost throughout the year, it seems to serve as a permanent habitat for this pest.  Flowering weed hosts like wild radish and wild mustard also harbor lygus bug populations.

Regular monitoring to make treatment decisions, managing weeds or alternative hosts to limit the spread of lygus bug to strawberry fields, using flowering hosts as trap crops, conserving natural enemies, vacuuming, and chemical control are common techniques used for lygus bug management.  Calculating degree-days is an approach that can help estimate when immature or adult stages of lygus bug will be seen in the fields so that appropriate treatment decision can be made.

Lygus degree-day model for strawberries (Photo illustration by Surendra Dara)

Degree-day is the unit of measurement for physiological time for insect maturity.  In other words, it is the time an insect takes from one point to another point in its life cycle depending on the temperature.  The amount of heat accumulated in 24 hours when the temperature is one degree above the lower developmental threshold is a degree-day (oD).  The lower developmental threshold for lygus bug is 54 oF and it requires 252 oD (in Fahrenheit) for egg stage and 371 oD for nymphal stages to complete.  Adults require 176 oD before they start laying eggs.  So, it takes a total of 799 oD from egg to next generation egg.  By monitoring the presence of lygus bug and daily temperatures, degree-days can be calculated to make treatment decisions against nymphal stages following UC IPM guidelines.

For example, if lygus nymphs are first seen in March on weed hosts or adults are first seen in strawberries in April, degree-day model predicts that first generation nymphs from adults can be seen in strawberries around May-June after accumulating 252 oD.  Second generation nymphs, from the nymphs on weeds, can be seen in July in strawberries after accumulating 799 oD.  The third generation nymphs from first generation can also be seen after 799 oD in August.

California Strawberry Commission, in collaboration with growers in the Watsonville and the Santa Maria areas, is working on monitoring lygus populations and calculating degree days.  Data loggers that record temperatures and calculate degree-days were recently set up in about 35 strawberry fields in these two areas.  Growers periodically monitor the fields and once the adult lygus bug is found, calculation will begin until 252 oD are accumulated.  This indicates the time when the first generation nymphs emerge so that appropriate management decisions can be made.  Although lygus bugs can move into the strawberry fields and deposit eggs several times during the growing season, resulting in the emergence of nymphs at different times, degree-day model can still help tackling the first generation nymphs.

Andrew Kramer from California Strawberry Commission explaining the functioning of the unit to Dave Peck, Manzanita Farms, Santa Maria

One degree-day (01 at the extreme right) was accumulated one day after installing the data logger in one of the Santa Maria fields

Visit UC IPM web resources to find out more information about degree-days (www.ipm.ucdavis.edu/PHENOLOGY/ma-lygus_bug.html) or to calculate degree-days by uploading your own temperature data (http://www.ipm.ucdavis.edu/WEATHER/ddretrieve.html).

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Posted on Tuesday, March 8, 2011 at 8:53 AM

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