Strawberry plants suffering from salt toxicity.  Symptoms include brown and brittle leaf margins (above, photo by Albert Ulrich, UC) and stunted plant growth (below, photo by Stuart Styles, CalPoly). 

Strawberry is among the crops that are very sensitive to salinity.  In addition to the drip irrigation system that caters to the water needs throughout the crop season, overhead aluminum sprinklers are used during the first few weeks after transplantation to leach out salts from the root zone.  Lack of rains earlier during this season has caused some concern about the impact of salinity on young strawberry plants.  However, with the recent rains the total amount of precipitation in Santa Maria area for January, 2012 was about 2 inches (~50 mm) easing some of  the concerns.

Symptoms of salt injury include dry and brown leaf margins, brittle leaves, stunted plant growth, dead roots and plants.  When salt toxicity is seen in localized areas in a field, it could be due to poor drainage.  Symptoms can be seen throughout the field when salinity of the irrigation water is high.  Excessive fertilization or application to wet foliage can also result in salt toxicity.  More than 0.2% of sodium or more than 0.5% of chloride in plant tissue indicate salt toxicity.

Salinity of the irrigation water depends on the amount of sodium, calcium and magnesium salts.  Salinity is measured either as total dissolved solids (TDS) or the electrical conductivity (EC) imparted by the salts.  The latter is often considered a better measure of salinity and is expressed as the EC of the irrigation water (EC_w) or the EC of the saturated soil extract (EC_e).  Units of measurement for are milligrams/liter (mg/L) for TDS and decisiemens/meter (dS/m) for EC.  Other parameters for soil salinity are pH and the sodium absorption ratio (SAR).  SAR is a measurement of sodium absorption compared to calcium and magnesium absorption and is used as an infiltration index.

Insufficient leaching of irrigation water in the soil is a major cause of salt accumulation in the root zone.  When irrigation is made just to meet the plant needs, salts gradually build up in the root zone.  It is important to provide sufficient irrigation so that water will wash the salts away from the root zone.  The proportion of water that leaches below the root zone after meeting the crop needs is known as leaching factor (LF).  The amount and frequency of irrigation should be calculated appropriately to allow sufficient leaching at the same time avoiding excessive soil moisture which could cause other problems.

Compared to the crops grown in hot and dry areas, crops grown in milder climatic areas such as California Central Coast are likely to tolerate higher salinities.  Salts in the Central Coast area waters are gypsiferous with calcium and sulfate ions.  Waters with such salts do not cause the same level of detrimental effects compared to water with chloride even when they have same EC_w. 

According to Dr. Stuart Styles, Professor of BioResource and Ag Engineering at Cal Poly, EC_w (salinity of the irrigation water) is a better indicator than EC_e (salinity of the soil) to measure the impact of salinity on strawberry or other crop yields in the Central Coast.  There can be up to a 50% reduction in the yield potential of strawberries when the salinity increases from 0.7 to 1.7 EC_w (dS/M) with a leaching factor of 15-20%.

It is important to look at the type of salt and kind of test being done to determine the salinity.  It is also necessary to consider the leaching factor when scheduling irrigation.  Sampling the irrigation water two or more times a year to test is recommended if salinity is suspected.  The following are ideal properties of irrigation water for strawberries:

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Reference:

Grattan, S. R. 2002.  Irrigation water salinity and crop production.  UCANR publication 8066 (http://anrcatalog.ucdavis.edu/pdf/8066.pdf)

Hanson, B. R. and W. Bendixen.  2004.  Drip irrigation evaluated in Santa Maria Valley strawberries.  California Agriculture 58:48-53 (http://ucanr.org/repository/cao/landingpage.cfm?article=ca.v058n01p48&fulltext=yes#bib5)

Maas, E. V. and S. R. Grattan.  1999.  Crop yields as affected by salinity.  In R. W. Skaggs and J. van Schilfgaarde, eds., Agricultural Drainage.  Agron. Monograph 38. ASA, CSSA, SSSA, Madison, WI.

Martínez, M. C. and C. E. Alvarez.  1997.  Toxicity symptoms and tolerance of strawberry to salinity in the irrigation water.  Scientia Horticulturae 71: 177-188.

2008.  IPM for strawberries. UCANR publication 3351.

Light brown apple moth (LBAM), Epiphyas postvittana (Walker) was recently found in Santa Barbara County for the sixth time.  LBAM is a quarantine pest on the United States mainland and can cause serious damage to various crops, nurseries, fruit trees, landscapes, and native plants.

Light brown apple moth (Epiphyas postvittana) male (above, from California Agriculture 2008, vol 62: 57-61) and female (below, photo by Jack Kelly Clark). 

Origin and distribution: It is an invasive pest native of Australia, but has been present in Hawaii for more than a century.  It was first found in Alameda County in 2007.  It is now frequently found in Alameda, Contra Costa, Marin, Monterey, Napa, San Benito, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, and Sonoma counties in California.  It has also been detected in San Diego, San Luis Obispo, and Santa Barbara counties.

Host range: LBAM feeds on a variety of host plants, but prefers members of Asteraceae (aster), Fabaceae (legumes), Polygonaceae (knot-weed) and Rosaceae (rose).  It is a pest of apples, apricots, peaches, pear, grapes, strawberries, cane berries, cole crops, ornamental shrubs, trees and many other hosts.  Nurseries near urban areas are especially sensitive to LBAM infestation in California.  If it spreads and establishes as a pest, many agricultural crops can be at risk.

Damage: Damage to foliage and other parts by rolling and webbing, loss of inflorescence, feeding on or boring into the buds, fruit, or stems, fruit drop or damage to the surface, and exposing the damaged areas to plant pathogens typical of LBAM larval feeding.

Light brown apple moth larva and damage to the foliage.  You can also see the silken webbing that attaches the leaves together.  Photo by Jack Kelly Clark.

Biology: LBAM belongs to a large lepidopteran family of Tortricidae.  It is a large family containing many of the common months including important pests such as codling moth (Cydia pomonella), oriental fruit moth (Grapholitha molesta), spurce budworms (Choristoneura spp.), and the western black-headed budworm (Acleris gloverana).  Mexican jumping-bean moth (Cydia deshaisiana) also belongs to this family. There are 1200 species of tortricids in North America.

 

Eggs deposited in batches and covered with transparent material.  (From California Agriculture 2008, vol 62: 57-61)

LBAM eggs are laid in groups of 20-50 in overlapping manner and are covered with greenish transparent material.  On average, females lay a total of 120-500 eggs in its life time.  Eggs turn dark as they mature and hatch in 1-2 weeks.  Larvae are pale to medium green with a yellowish to tan colored head capsule.  Younger larvae roll the leaves and form webbings of leaves as they mature.  Mature larvae may also bore into fruits.  Mature larvae are about 10-18 mm long.  During winter, larvae can survive for two months without feeding.  Pupae are formed in a silken cocoon among the leaf webbings.  They turn from green to brown as they mature in 1-3 weeks.  Adults mate right after they emerge and females lay eggs within 2-3 days after emergence.  Adults are small, light brown with darker markings and have a wing span of 16-25 mm.  They hold their wings in a roof-like pattern at rest.  Markings on their wings can be highly variable and identification based on external features can be very difficult.  Positive identification of LBAM adults often requires examination of reproductive organs.  Females are lighter colored and larger than males.  They rest in sheltered parts of the plant canopy during the day time and fly during the night time.  They are not powerful flyers, so stay close to the infested areas within a 100 m (330 feet) range.  Adults survive for 2-3 weeks.  Depending on temperature, there can be two (Central and Noth Coast areas) or three to four (Central Valley and Southern California) generations per year in California.

Female (A) and male (B-H) moths.  Notice the variation in the wing pattern in males.  Similarity of these moths to other tortricid moths makes it difficult to distinguish them based on external characters.  (From California Agriculture 2008, vol 62: 57-61.  Photos A and B by David Williams, State of Victoria Department of Primary Industries, C to H by Jack Kelly Clark)

LBAM eggs are laid in groups of 20-50 in overlapping manner and are covered with greenish transparent material.  On average, females lay a total of 120-500 eggs in its life time.  Eggs turn dark as they mature and hatch in 1-2 weeks.  Larvae are pale to medium green with a yellowish to tan colored head capsule.  Younger larvae roll the leaves and form webbings of leaves as they mature.  Mature larvae may also bore into fruits.  Mature larvae are about 10-18 mm long.  During winter, larvae can survive for two months without feeding.  Pupae are formed in a silken cocoon among the leaf webbings.  They turn from green to brown as they mature in 1-3 weeks.  Adults mate right after they emerge and females lay eggs within 2-3 days after emergence.  Adults are small, light brown with darker markings and have a wing span of 16-25 mm.  They hold their wings in a roof-like pattern at rest.  Markings on their wings can be highly variable and identification based on external features can be very difficult.  Positive identification of LBAM adults often requires examination of reproductive organs.  Females are lighter colored and larger than males.  They rest in sheltered parts of the plant canopy during the day time and fly during the night time.  They are not powerful flyers, so stay close to the infested areas within a 100 m (330 feet) range.  Adults survive for 2-3 weeks.  Depending on temperature, there can be two (Central and Noth Coast areas) or three to four (Central Valley and Southern California) generations per year in California.

Management: Insecticides like insect growth regulators and spinosyns, biopesticides like Bacillus thuringiensis-based products, natural enemies that include predators and parasitoids are some management options.  However, due to its current status in California, use of pheromone traps to cause mating disruption and quarantine practices to restrict movement are important components of current LBAM management.  According to Guy Tingos, Deputy Ag Commissioner, Santa Barbara County, movement of nursery stock into Santa Barbara County from areas where LBAM is established must have a thorough inspection and LBAM certification to ensure the material is free of the pest.  Movement of nursery stock, cut flowers, fruit or other plant material that can host LBAM out of quarantine area is highly regulated.  Tingos also said that commercial farm operations in infested areas  should be under compliance agreement for plant movement and public in quarantine areas should not move the host plants out of their property.

For insect identification and information on quarantine regulations contact your local Ag Commissioner's office.

Additional information can be found at the following sources:

CDFA website for photos, videos and other information: http://www.cdfa.ca.gov/plant/PDEP/lbam/lbam_main.html

National Invasive Species Information Center: http://www.invasivespeciesinfo.gov/animals/applemoth.shtml

UC IPM website: http://www.ipm.ucdavis.edu/PMG/r302303011.

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References:

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

Varela L. G., M. W. Johnson, L. L. Strand, C. A. Wilen and C. Pickel.  2008. Light brown apple moth's arrival in California worries commodity groups.  California Agric. 62: 57-61. (http://ucanr.org/repository/cao/landingpage.cfm?article=ca.v062n02p57&fulltext=yes)

Two species of dipteran larva (maggots) were found feeding on strawberry fruits in the Santa Maria area recently.  Last year, there was a minor issue of fungus gnat larvae and another species (probably Delia sp.) damaging young strawberry plants, but the recent observations are isolated incidents of damage to the fruit.  Specimens brought to the Santa Barbara Ag Commissioner's office were identified by the county entomologist, Dr. Brian Cabrera.

Strawberries from a greenhouse in the Santa Maria area were infested with dark-winged fungus gnat larvae (Family: Sciaridae).  These maggots have a dark head capsule and a worm-like body.

Dark-winged fungus gnat larva feeding on a strawberry (above).  Larvae have dark, shiny head capsule with a whitish, slender, worm-like body (below).  Photos by: Brian Cabrera

The second incident was where some field strawberries were heavily infested with the larvae of the fruit fly, Drosophila simulans Sturtevant.  It is a species very closely related to the common fruit fly, D. melanogaster.  Both fruit fly species are very similar, but can be distinguished based on the characters of external male genitalia.

Fruit fly, Drosophila simulans larva in damaged strawberry (above) and adult female (below).  Photo by: Brian Cabrera

Fungus gnats or fruit flies are normally not considered as pests of strawberries.  Ripe fruit left on the plants could have attracted resulting in the damage we noticed.  With good sanitation practices and timely harvesting, these insects are not expected to damage strawberry fruits.

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Reference:

Sturtevant, A. H.  1920.  Genetic studies on Drosophila simulans.  I. Introduction.  Hybrids with Drosophila melanogaster.  Genetics 5: 488-500.  (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1200491/pdf/488.pdf)

20100701 Spotted snake millipede-Blaniulus guttulatus damage in zucchini-SLO (14)-small 2

Spotted snake millipede infestation on zucchini (Photo by: Surendra Dara)

Phylum: Arthropoda
Subphylum: Atelocerata
Class: Diplopoda
Order: Julida
Family: Blaniulidae
Scientific name: Blaniulus guttulatus (Bosc, 1792)

The snake like slender body and brownish or pinkish spots on the lateral sides give them the name spotted snake millipede (SSM).  SSM are soil inhabitants that feed on decaying plant material.  When disturbed, they curl into a coil.

Biology: They are about 15 mm long and have approximately 60 body segments.  Eggs are deposited in the soil.  Juveniles have three pairs of legs.  Number of body segments increases with each molt and it takes about a year to reach adult stage.

Feeding of millipedes on the root system causes plant collapse and death.  See the root system completely disconnected from the plant. (Photo by: Surendra Dara)

Damage: Although they primarily feed on decomposing organic matter, they can become serious pests of cultivated crops in certain conditions.  They are capable of causing both primary and secondary damage.  During prolonged dry conditions SSM can be attracted to the crop plants for their moisture needs. Damage to the plant tissue due to other pests and diseases can also attract SSM.  Infestation is severe in soils rich in organic matter.  Rainfall can also activate their infestation.

Strawberries, potatoes, sugar beets, turnips, beans, squash and other vegetables are susceptible to SSM infestation.  Feeding damage to the root system can cause rapid death of the plant.

Zucchini field in San Luis Obispo with severe spotted snake millipede infestation.  Crop loss can be seen in large parts of the field. (Photo by: Surendra Dara)

Management: Proper disposal of crop residue, avoiding fields with decaying plant material, removal of old mulch or decomposing leaves can minimize the chances of infestation.  Proper water management will also reduce the attractiveness of soil for SSM infestation.  Reports indicate mixed results with various chemicals, but certain thiocarbamate, carbamate, organophosphate, neonicotinoid, and pyrethroid chemicals were found effective.  Entomopathogenic nematodes like Steinernema feltiae are also effective in managing SSM.

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