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Grower Notes and Pest News

Reporting downy mildew of ice plants in California


Healthy red apple ice plant, Aptenia cordifolia.  Photo by Heather Scheck, Santa Barbara Ag Commissioner's Office

A downy mildew caused by the oomycetous fungus, Peronospora mesembryanthemi Verwoerd has recently been confirmed by the USDA -APHIS from a red apple ice plant sample collected in San Diego.  Since its first finding in San Diego County last summer, the disease has spread to Orange, San Bernardino, and Ventura counties and is now found in the Goleta area in Santa Barbara County.  Peronospora mesembryanthemi was first reported from South Africa (Verwoerd, 1924) and later in the United Kingdom (Francis and Waterhouse, 1988) and New Zealand (McKenzie and Dingley, 1996), but has never been reported in North America.  The host range of P. mesembryanthemi is thought to be limited to ice plants and it is currently found infecting the red apple ice plant, Aptenia cordifolia, the trailing ice plant or the pink carpet, Delosperma (syn. Mesembryanthemum) cooperi, and Lampranthus sp. in California.  Both these ice plant species are native to southern Africa.  Because of their environmental hardiness, ease of growing, and bright, colorful flowers, ice plants are grown as ornamental plants or found as groundcovers.  However, the red apple ice plant is listed as an invasive plant by the California Exotic Pest Plant Council.  It can sometimes grow like a weed.

Red apple ice plant overwhelming yucca plants.  Photo by Heather Scheck, Santa Barbara Ag Commissioner's Office

Pathogen: Downy mildew appears as a mat of grey, blue, or brown fungal growth on the lower or both sides of leaves and other infected plant parts.  Fungal growth consists of the asexual fruiting structures known as sporangia that are produced on sporangiophores, which are specialized hyphae.  Downy mildew fungi cause systemic infection and grow internally in all plant parts.  Infection rapidly spreads under cool and wet conditions.  Windblown rain or sprinkler splashing spreads disperse sporangia and aid in the disease spread.  Downy mildew fungi are obligate parasites of plants and most of them have narrow host range of one or just a few hosts.

Greyish sporulation of Peronospora mesembryanthemi on an ice plant.  Photo by Jose Rodriguez, Soil and Plant Laboratory, Inc

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Downy mildew-infected red apple ice plant.  Photo by Heather Scheck, Santa Barbara Ag Commissioner's Office


Severe downy mildew damage to an ice plant.  Photo by Heather Scheck, Santa Barbara Ag Commissioner's Office

Damage: The rapid spread of P. mesembryanthemi through southern California could be from accidental movement of infected nursery stock.  Severe damage with heavy or total loss of plantings is becoming common in southern California counties where the disease is currently found. 

Management: There are relatively few fungicides effective against oomycetous fungi and control can be very difficult.  Since most of the fungicides are fungistatic (inhibit the fungal growth) rather than fungicidal (kill the fungus) against P. mesembryanthemi, fungicidal treatments only suppress the fungus, but systemic infections cannot be cured.  Downy mildew fungi evolve very quickly to form new races and can rapidly develop fungicide resistance.  (Is this sentence necessary?  It is scary.)

Good cultural practices and sanitation can prevent or minimize downy mildew of ice plants.  Some management options include:

  • Prune plants regularly and remove weeds to improve air circulation and reduce fungal growth.
  • Avoid overhead irrigation during cool weather.
  • Consider watering in the morning hours so that plants dry during the day.
  • Do not over- or under-fertilize as it may increase the chances of infection.
  • Monitor highly susceptible species like the red apple ice plant and remove and destroy plants with symptoms of infection.
  • Consider other host plants as groundcovers when replacing diseased ice plants.


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References:

Chitambar, J. 2016.  Peronospora mesembryanthemi. (http://blogs.cdfa.ca.gov/Section3162/?tag=peronospora-mesembryanthemi)

Francis, S. and G. Waterhouse.  1988.  List of Peronosporaceae reported from the British Isles. Trans. Brit. Mycol. Soc. 91: 1-62.

McKenzie, E.H.C. and J. M. Dingley.  1996.  New plant disease records in New Zealand: miscellaneous fungal pathogens III. New Zealand J. Bot. 34: 263-272.

Verwoerd, L.  1924.  Peronospora mesembryanthemi n. sp., die oorsaak van ‘n donsige skimmelsiekte van Mesembryanthemum-soorte. Ann. Univ. Stellenbosch 2A: 13-23.

 

Posted on Tuesday, March 22, 2016 at 8:06 AM

Lygus bug management during and at the end of the strawberry production


Lygus bug (Lygus hesperus) adult (above) and young nymph (below).  (Photos by Rodney Cooper, USDA-ARS and Surendra Dara)

Lygus bug or the western tarnished plant bug, Lygus hesperus is a major pest of strawberries in California (Zalom et al. 2014).  Lygus bug has a wide host range that includes more than 100 species of cultivated crops and wild host plants (Scott, 1977; Fye, 1980 and 1982; Mueller et al., 2005) that include cultivated crops such as alfalfa, broccoli, celery, cauliflower, grapes, strawberries, and tomatoes on the California Central Coast.  Additionally, ornamental and vegetable crops in greenhouses or home gardens along with weedy hosts from Chenopodiacae, Compositae, and Cruciferae in vast uncultivated landscapes offer a continuous food supply for lygus bug throughout the year.  Warmer and dryer conditions as experienced in the recent years can also contribute to increased lygus bug problems.  Milder winters fail to bring down overwintering populations and drought conditions dry out wild hosts early in spring forcing lygus bugs to migrate to cultivated crops.  Under these circumstances, timely monitoring and implementation of appropriate management practices is necessary to limit damage and spread of lygus bugs to other crops.  Vegetable crops such as celery are reported to have an increased risk of lygus bug damage in recent years (Dara, 2015a).

Damage

Lygus bugs primarily feed on inflorescence and developing seeds.  They can also feed on foliage by sucking plant sap, but seeds which are rich in protein and lipids are important for the reproductive success of lygus bugs.  Depending on the crop and crop stage, lygus damage can result in bud and flower loss, blemishes on seeds, necrotic spots on stems, or deformity of the fruit.  In strawberries, fruit deformity caused by lygus bug renders fresh berries unmarketable.  However, nearly 1/3 of the fruit deformity in strawberries is caused by factors other than lygus bug (Dara, 2015b). 

Strawberry fruit deformity likely from lygus bug feeding (Photo by Surendra Dara)

Management

Lygus bugs typically move into strawberry or other cultivated crops from weedy hosts in the wild habitats in April.  However, seasonal weather conditions can alter these typical patterns.  In a typical fall planting of strawberries, three generations of lygus bugs can be seen.  But summer-plantings, extended season for fall-plantings, or early planting of fall strawberries make the crop available almost throughout the year.  Improper management of lygus or any pest can lead to increased problems in crops where the pest is not usually a problem.

While UC IPM guidelines provide details of lygus bug management in strawberries and celery, here are some important points for managing lygus bug in strawberries during and at the end of the fruit production season:

Biological control:

  • Several species of predatory and parasitic arthropods provide natural control of lygus bug.  Big-eyed bug (Geocoris spp.), damsel bug (Nabis spp.), minute pirate bug (Orius tristicolor), and multiple species of spiders are among the predacious arthropods.  Parasitic wasps that attach eggs (Anaphes iole) and nymphs (Peristenus relictus) are commonly found in strawberries.  Conserving natural enemies by providing flowering hosts as refuges and selecting chemicals that are less harmful can contribute to biological control.

Cultural control:

  • Manage weeds near and around strawberry fields that serve as sources of lygus bug infestations.
  • Some studies suggest growing strips of alfalfa or flowering hosts that attract lygus bugs and managing them with pesticides or vacuuming.  This practice requires close monitoring to prevent dispersal of lygus bugs to strawberries.

Chemical control and biopesticides:

  • A variety of chemicals that belong to different mode of action groups are registered for lygus bug in strawberries.  Select appropriate label rates to obtain desired control.  Using surfactants and proper application techniques can improve control efficacy.
  • Rotate chemicals from different mode of action groups to reduce the risk of resistance development.
  • Use appropriate materials for appropriate life stages of the pest.  For example, an insect growth regulator like novaluron (Rimon) is effective against nymphal stages.  To control a mixed population of nymphs and adults, novaluron can be used with other insecticides.  Botanical insect growth regulator like azadirachtin (e.g., AzaGuard, Debug Turbo, Molt-X, and Neemix), which also has insecticidal properties, can be used with chemical pesticides.  Microbial pesticides based on insect pathogenic fungi such as Beauveria bassiana (BotaniGard), Isaria fumosorosea (Pfr-97), and Metarhizium brunneum (Met52) in combination with azadirachtin or chemical pesticides can also be used as a part of the lygus IPM program.

Mechanical control:

  • Bug vacuums can help remove lygus bugs from strawberry plants.  They are typically run twice a week at a speed of 2 mph.  Improved design and increased number of passes each time can enhance the control efficacy.  Vacuums may not be effective in removing all life stages of lygus bugs and may also remove beneficial arthropods.

Control specific to end of the season:

  • Do not neglect managing lygus until the end of the fruit production.  Negligence can lead to the spread of the pest to neighboring fields requiring aggressive management practices.  Such a situation that demands additional pesticide applications can lead to insecticide resistance in the long run.
  • Some growers indicated that sulfuric acid applied as soil amendment at the end of the season helped in controlling lygus bugs.  This practice is, however, not recommended for lygus management.

IPM strategies:

Several IPM studies in the Santa Maria area with a focus on lygus bug management provide information on effective chemical and non-chemical options.

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References

Dara, S. K.  2015a.  Increasing risk of lygus bug damage to celery on the Central Coast.  (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19221)

Dara, S. K.  2015b. Role of lygus bug and other factors in strawberry fruit deformity. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19630)

Fye, R. E.  1980.  Weed sources of lygus bugs in the Yakima Valley and Columbia Basin in Washington.  J. Econ. Entomol. 73: 469-473.

Fye, R. E.  1982.  Weed hosts of the lygus (Heteroptera: Miridae) bug complex in Central Washington.  J. Econ. Entomol. 75: 724-727.

Mueller, S. C., C. G. Summers, and P. B. Goodell.  2005.  Composition of Lygus species found in selected agronomic crops and weeds in the San Joaquin Valley, California.  Southwest. Entomlo. 30: 121-127.

Scott, D. R.  1977. An annotated list of host plants for L. hesperus Knight.  Bulletin of the Entomological Society of America 23: 19-22.

Zalom, F. G., M. P. Bolda, S.K. Dara, and S. Joseph., 2014.  UC IPM pest management guidelines: strawberry.  University of Californi a Statewide Integrated Pest Management Program.  Oakland:  UC ANR Publication 3468.

 

Posted on Friday, February 19, 2016 at 10:38 AM

Erythrina stem or twig borer: a new and potentially devastating pest of coral trees in California


Erythrina caffra is a spring-flowering landscape tree.  (Photo by Don Hodel)

The Erythrina stem borer (ESB) (sometimes known as the Erythrina twig borer) (Terastia meticulosalis), a potentially devastating pest of Erythrina spp. (coral trees), has been sighted numerous times in southern California in the latter half of 2015 from San Diego to Ventura. Erythrina, a member of the Fabaceae (formerly Leguminosae, bean family) encompasses about 112 species (Bruneau 1996) and includes some of our most useful, valuable, well adapted, and spectacular flowering trees, adorning landscapes along the coast and adjacent plains and valleys in southern California. Indeed, a famous planting of E. caffra adorning the broad median of San Vicente Boulevard in Santa Monica and West Los Angeles was designated an exceptional planting (Hodel 1988). The plethora of sightings suggests a more recent introduction but the ESB was recorded as early as 1973 at Fort Piute in the California desert north of Needles near the southern tip of Nevada (CMSD 2016).

The ESB is of special concern for us because so little is known about its management and it appears to be especially destructive on coral trees, infesting seeds, destroying branch tips, and even killing whole plants. In Florida where it is native, it is a serious pest of naturally occurring and exotic coral trees, which are valued for agriculture, medicine, and landscape ornament (Powell and Westley 1993). Indeed, the cultivation of exotic coral trees in Florida is essentially impossible because of the ESB (Raven 1974); the only coral tree that can be cultivated reliably there is the native Erythrina herbacea, which likely co-evolved with and is found over most of the range of the ESB. In California the ESB has been observed so far on E. × bidwillii, E. chiapasana, E. coralloides, E. crista-galli, and E. falcata; other species will likely be added in the future. Although much remains to be know about the ESB in California, at least at this early stage, the ESB seems to prefer species of coral trees with more lender stems and slender regrowth of larger-stemmed species.

Fortunately, another serious pest of coral trees that is sympatric and co-evolved with the ESB, the Erythrina leaf roller (Agathodes designalis), has not yet been detected in California. The Erythrina leaf roller and the ESB are in closely related genera that have tended to niche-partition the coral tree resource to reduce inter-species competition (Armstrong and McGehee 1980, Sourakov 2011).

Much remains to be known about the natural history of the ESB, and the summary we provide here of its taxonomy, identification, distribution, and life cycle and damage it inflicts on coral trees is mostly from Arakelian (2016), Sourakov (2011, 2012, 2013), Sourakov et al. (2015), and our observations of infested coral trees here.

Taxonomy

The ESB is one of five species in the largely tropical moth genus Terastia, which ranges from the Americas to Africa, Asia, and the western Pacific (Sourakov et al. 2015). The ESB is the only species of the genus native to the Americas. The other four species are T. africana, T. egialealis (Africa), T. margaritis (India), and T. subjectalis (Asia and western Pacific).

Identification

The adult ESB is a small-sized, brownish moth with mottled forewings and whitish hindwings with dark margins. Varying in size, adult forewing wingspans range from 2.5 to 4.6 cm, and the mottled body from 1.5 to 2.5 cm long, the latter with conspicuous knobs toward the posterior (Sourakov et al. 2015).  In Florida the ESB varies greatly in size, which largely depends on the seasonal generation and diet. The spring generation, which feeds mostly on seeds, is larger than the fall and summer generation that feeds inside of stems. For example, wingspans of the spring generation average about 3.7 cm while those of the summer and fall generations average about 3cm and 2.5 cm respectively (Sourakov 2011). When at rest, the mottled- or marble-brown forewings are effective at camouflaging the ESB but when the wings are spread the white hind wings are conspicuous.  Males and females are similar but the latter has more beige-brown forewing markings. In live specimens, the knobby abdomen is held in a curved, upright position, mimicking a praying mantis head, which is possibly a deterrent to predators (Sourakov et al. 2015).  Eggs of the ESB, typically laid singly in the axil of leaves near stem tips, are translucent, white, delicate, dome-shaped with a reticulated surface, and about 0.8 mm long (Sourakov 2012). Young larvae are minute, about 0.5 mm long, and probably burrow directly into the flower, stem, or sometimes even a leaf petiole and then follow it to the stem.  Larvae of the ESB are translucent and brownish white or cream-colored with a black sclerotized head and a dark sclerotized prothoracic plate that becomes lighter as the larva matures. Mature larvae are about 4 cm long. Larvae turn pinkish before pupation, especially when they complete their development on seeds. Pupae are cigar-shaped, light brown, and enclosed in a loose, double-layered cocoon (Sourakov 2011). 

Distribution

Endemic to the Americas, the ESB occurs from South Carolina to Florida and west to Arizona (and now California) in the United States and south to Argentina. Although recorded from Hawaii (Swezey1923, Zimmerman 1958), this report is now thought to be misidentification. Numerous publications list it as part of African or Asian faunas, but that misconception has been recently clarified (Sourakov et al. 2015), and it seems to be a strictly New World species, with superficially similar but genetically distant relatives in other tropical regions.

Life Cycle and Damage

Larvae of the ESB likely emerge through the ventral surface of the egg and tunnel directly into the plant (Sourakov2012). The downward-boring larvae feed on stem tissues as they go, hollowing out the stem and causing a characteristic dying-off of stem tips, which turn black and sometimes collapse. The entire upper and lateral sides of the plant canopy can be killed. This damage acts like pruning, forcing out new lateral shoots below the damaged area; these, in turn, can become infested and killed. Entire plants can be killed although this can take up to several years.  In Florida after killing off stem tips in the spring, the last instar larvae move into seed pods, a condition which appears to be less common in California so far. Feeding on the red seeds typically causes larvae to accumulate reddish pigments, changing their color to pink before they pupate. In contrast, summer and fall generations feed inside the stem and do not feed on the hardened seeds; thus, they are typically paler in color and do not take on the pinkish hue. Larvae typically purge the hollowed out stem of frass by crawling backwards to the entry hole to defecate (Sourakov 2013).  Full grown larvae descend from a silk thread to the ground and construct their cocoons in leaf litter to pupate. They have also been found in cocoons in old dead flowers at the ends of dead stems or inside folded up living leaves on the plant (Sourakov 2012). Adult ESBs are good fliers and can hover in flight similar to that of the Sphingidae (sphinx moths) (Sourakov 2012). This flight ability, along with larval endophagous feeding habits that provide some protection from predators, parasites, and abiotic mortality factors, largely explains why the ESB has been so successful in infesting Erythrina plants (Sourakov 2012).

Management

Unfortunately, next to nothing is known about the management of the ESB. Nearly all attempts at post-infestation eradication in Florida have failed. Virtually nothing is known about resident natural enemies although they must be present; until they are identified biological control holds little promise. Perhaps vigilant scouting, judicious and immediate removal, bagging, and disposal of infested shoot tips, and ground and foliar treatment with systemic pesticides might be effective and justified for rare, exceptional, and/or noteworthy and valuable coral tree specimens. Because the ESB pupates in leaf litter on the ground, thorough raking and disposal of fallen leaves might reduce regeneration and provide some control. Cover/barrier insecticides, like pyrethroids (permethrin, cyfluthrin, bifenthrin) or emulsifiable concentrate formulation of carbaryl, might work well in killing of newly hatched larvae when they attempt to bore into the stems; although not yet tested for ESB, they have relatively long residual effects and might be effective. Further work is needed on this pest that poses a serious threat to California's ornamental landscape coral trees.

Acknowledgements

We thank Andrei Sourakov of the University of Florida for reviewing this paper and providing some of the images. Readers interested in supporting his important work can contact Andrei directly (asourakov@flmnh.ufl.edu).

Literature Cited

Arakelian, G. 2016. Erythrina Stem Borer (Terastia meticulosalis). L. A. County Dept. Agri.Comm. /Weights Measures Pest Note.

Armstrong, R. A. and R. McGehee. 1980. Competitive exclusion. Amer. Naturalist 115: 151-170. Bruneau, A. 1996. Phylogenetics and biogeographical patterns in Erythrina (Leguminosae: Phaseoleae) as inferred from morphological and chloroplast DNA characters. Syst. Bot. 21(4): 587-605.

CMSD. 2016. California Moth Specimens Database. On-line: https://essigdb.berkeley.edu/cgi// calmoth_query?stat=BROWSE&query_src=eme_BrowseCalmothNames&where- genus=Terastia. Accessed 5 January 2016.

Hodel, D. R. 1988. Exceptional Trees of Los Angeles. California Arboretum Foundation, Arcadia.

Powell, M. H. and S. B. Westley. 1993. Erythrina Production and Use: A Field Manual. Nitrogen Fixing Tree Association, Paia, HI.

Raven, P. H. 1974. Erythrina (Fabaceae): achievements and opportunities. Lloydia 35: 321-331.

Sourakov, S. 2011. Niche-partitioning, co-evolution and life histories of erythrina moths, Terastia meticulosalis and Agathodes designalis (Lepidoptera: Crambidae). Trop. Lepid. Res. 21(2): 89-94.

Sourakov, A. 2012. On the biology of moths that feed on Erythrina in Florida. Trop. Lepid. Res. 22(2): 110-118.

Sourakov, A. 2013. Erythrina moths Terastia meticulosalis Guenée and Agathodes designalis Guenée. Department of Entomology, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Publ. EENY 516. Available on- line: http://edis.ifas.ufl.edu/in921.

Sourakov, A., D. Plotkin, A. Y. Kawahara, L. Xiao, W. Hallswachs, and D. Janzen. 2015. On the taxonomy of the erythrina moths Agathodes and Terastia (Crambidae: Spilomelinae): Two different patterns of haplotype divergence and a new species of Terastia. Trop. Lepid. Res. 25(2): 80-97.

Swezey, O. H. 1923. The Erythrina twig borer (Terastia meticulosalis) in Hawaii (Pyralidae, Lepidoptera. Proc. Hawaiian Ent. Soc. 5(2): 297-298.

Zimmerman, E. L. 1958. Insects of Hawaii. Vol. 8 (Lepidoptera: Pyraloidea). University of Hawaii Press, Honolulu.

Authors:

Donald R. Hodel is landscape horticulture advisor for the University of California Cooperative Extension in Los Angeles. drhodel@ucanr.edu.

James E. Henrich is curator of living collections at the Los Angeles County Arboretum & Botanic Garden in Arcadia, CA. jim.henrich@arboretum.org.

Kenneth J. Greby is an arborist with ArborPro in Yorba Linda, CA. fastfeat@gmail.com.

Gevork Arakelian is the entomologist with the Los Angeles County Agricultural Commissioner/ Weights & Measures in South Gate, CA. GArakelian@acwm.lacounty.gov.

Linda M. Ohara is a biology sciences lab technician at El Camino College in Torrance, CA, a horticulturist, and a former nurserywoman. lohara@elcamino.edu.

Surendra K. Dara is Strawberry and Vegetable Crops Advisor and Affiliated IPM Advisor for the University of California Cooperative Extension, San Luis Obispo, Santa Barbara, and Ventura Counties, skdara@ucanr.edu.

This article is a reprint of the original article published in the eJournal, PalmArbor.

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Posted on Wednesday, February 17, 2016 at 8:35 AM
  • Author: Donald R. Hodel
  • Author: James E. Henrich
  • Author: Kenneth J. Greby
  • Author: Gevork Arakelian
  • Author: Linda M. Ohara
  • Author: Surendra K. Dara

The UC Pest Management Guidelines Just Got Spicier!

Whether or not your favorite team is playing in Sunday's big game, the Super Bowl is often a great excuse to gather with friends and family and enjoy some tasty treats!  Maybe your favorite snack involves chips with salsa or guacamole, or perhaps you prefer shrimp with a delicious avocado dip.  Whatever your snack of choice, chances are that you might spice it up with a little cilantro or parsley.

Cilantro and parsley growers have something else to be happy about – The UC Statewide IPM Program just released new Pest Management Guidelines for Cilantro and Parsley.  

Cilantro and parsley are herbs used both fresh and dry for preparation of many popular dishes in almost all parts of the world including California.  Apart from their pleasant flavor, both plants are also known for a number of nutritional and health benefits. 

In California, cilantro and parsley are grown commercially on more than 7,000 acres, primarily along the southern and central coast.  Cilantro (also known as Chinese or Mexican parsley) and parsley are examples of specialty vegetable crops important in crop rotations and in contributing to California's overall agricultural diversity.

Although pest problems aren't too common for home gardeners growing cilantro or parsley, for commercial growers, crop damage due to insect pests and diseases may be devastating and cause important economic losses.  The new UC IPM Pest Management Guidelines for cilantro and parsley provide pest and management information for insects pests (including beet armyworm, cabbage looper, and aphids), diseases (including apium virus Y, bacterial leaf spot, carrot motley dwarf, cilantro yellow blotch, Fusarium wilt, and septoria leaf spot), and nematodes.  Because weed management costs can be very high in cilantro and parsley unless weed control programs are carefully planned and implemented, a comprehensive weed management section is also included.

Check out the new guidelines and other pest management information on the UC IPM website.

Posted on Monday, February 1, 2016 at 5:37 PM

Producing with the seal of IPM is a practical and sustainable strategy for agriculture

Seal of IPM - a practical and sustainable crop production system

Arthropod pests or diseases cause a variety of damages to crops.  Some by reducing plant vigor resulting in lesser yields and some by causing direct damage to the produce which can be unmarketable due to deformity, unpleasant taste, damaged tissue due to insect feeding, presence of insects and/or frass, decay due to secondary infections, and other factors.  It is quite understandable when the produce is not accepted because of the taste or potential health risk.  For example, citrus fruit with huanglongbing or citrus greening disease transmitted by Asian citrus psyllid gives a bitter taste to citrus juice.  Navel orangeworm larvae bore into almonds and feed on the nut causing complete or partial damage and leave frass and cause fungal infections.  Brown marmorated stink bug damage on fruits and vegetables change the texture and taste of the damaged area.  Such damage certainly makes the produce unmarketable and applying pesticides or administering other control measures to prevent the damage is warranted. 


Brown marmorated stink bug damage to apple (above - Photo by Chris Bergh, Virginia Tech) and navel orangeworm damage to almond (below - Photo by Jack Kelly Clark, UC IPM)

On the other hand, certain damage is only cosmetic with no reported change in taste or quality of the produce.  One example would be fruit deformity caused by the lygus bug in strawberries.  Strawberry is a high value fruit appreciated for its taste, shape, color, and flavor.  Lygus bug feeding on young green berries results in uneven growth and deformity of mature berries.  While there is no record of the impact of lygus damage on strawberry fruit quality, millions of pounds of pesticides are applied to control lygus bug or similar pests that cause cosmetic damage in strawberries and other crops.


Cosmetic damage to strawberry by lygus bug (Photo by Surendra Dara)

The preference of consumers for perfectly shaped fruits and vegetables creates a need for intensive pest management practices and results in associated financial and environmental costs.  Since chemical pesticides are generally economical and effective tools to manage pests, they are widely used.  The overuse of certain effective pesticides causes development of resistance in pest populations. This, in turn, leads to increased use of the same or other pesticides.  Excessive use of chemical pesticides can have a harmful effect on beneficial arthropods resulting in secondary pest outbreaks.  Organic agriculture is gaining popularity due to environmental and human health concerns from chemical pesticide use.    “Organic agriculture produces products using methods that preserve the environment and avoid most synthetic materials, such as pesticides and antibiotics” according to USDA.  But organic agriculture is not necessarily the only sustainable solution.

Before agricultural industrialization, there was a better balance between pests and their natural enemies (beneficial arthropods such as predators and parasitoids that attack pests).  Once agriculture was industrialized, thousands of acres of monoculture now provide an unlimited supply of food for a variety of pests.  When the natural balance is disrupted, natural enemies alone are not sufficient to manage pest populations.  This is where an Integrated Pest Management (IPM) strategy plays an important role in bringing a sense of balance into pest management.  IPM employs multiple tools that include selecting resistant varieties, modifying planting dates, changing irrigation and nutrient management practices, conserving or releasing natural enemies, applying chemical, botanical, and microbial pesticides, or using mechanical tools.  Each of these tools contribute to reducing pest numbers, complement each other, and result in pest management in an environmentally sustainable manner.

Organic agriculture, on the other hand, relies on biopesticides instead of chemical pesticides, which can sometimes be less effective or slow in achieving desired control.  For example, an effective chemical pesticide with a specific mode of action could kill pest populations within a few hours of application.  However, using a biopesticide based on an insect-pathogenic microorganism like the bacterium Bacillus thuringiensis or the fungus Beauveria bassiana, can take a few days to allow the microorganism to infect and kill the pest.  When pest numbers are low, non-chemical solutions may provide required control to minimize damage. However, with heavy pest infestations, chemical pesticides are often needed to provide timely control that prevents further buildup of pest populations and the resulting damage to crops.

Organic agriculture is expensive because of generally higher losses due to pests and higher cost of agronomic and pest management practices.  Sometimes, ineffective control of pests on organic farms may result in their spread to neighboring fields and increase the risk of pest damage.  Organic agriculture does not mean pesticide-free farming, and biopesticides used on organic farms also require safety guidelines similar to chemical pesticides used on conventional farms.  Organic agriculture may require a higher number of pesticide sprays increasing the risk of exposure for workers.  In some pest and disease situations in certain crops, organically registered products are not available and yield losses could be higher.  Exporting organic produce, in light of exotic and invasive pests spreading to other areas, is also a challenge due to limited options for shipping organically produced pest-free fruits and vegetables.

Using cultural practices to reduce the risk of pest infestations and applying biopesticides when pest populations are low and chemical pesticides when populations are high can be components of an IPM strategy where multiple tools are exploited in a balanced manner.  Combining and rotating chemical pesticides with non-chemical alternatives strengthens the effectiveness of IPM by providing desired control without the excessive use of chemicals.  Chemical pesticides can be used during early stages of the crop growth while biopesticides can be used closer to harvest.

Considering the challenges and risks associated with organic agriculture and the practicality of IPM-based agriculture, a couple of ideas could be worth pursuing to maintain environmental and human health, reduce harmful chemicals, and ensure food security for the growing world population.

Acceptance of imperfect produce: When consumers are tolerant of imperfectly shaped fruits and vegetables with no health risk from pathogens or arthropod pests, a significant amount of pesticides of all kinds could be avoided.  This would translate into saving millions of dollars otherwise spent on pesticides and their application costs, and money earned on selling otherwise unmarketable produce.  This may also reduce the disposal of unpicked produce at the grocery stores.  When consumers accept imperfect fruits or vegetables, the cost of produce, both to produce and purchase, could come down.  I recently came across Imperfect Produce, a company that sells imperfect produce and End Food Waste, an organization that started the Ugly Fruit And Veg Campaign.

IPM: Considering the difficulty in ensuring food security exclusively through non-chemical agriculture for the growing world population (projected to be 9.6 billion by 2050), IPM is an effective, practical, and sustainable tool that uses a balanced approach. While organic agriculture is encouraged and supported, and there are several organizations that certify organic production around the world, IPM hasn't caught the attention of marketers yet. Perhaps a seal of IPM should be considered and promoted in the near future.

Organic certification agencies from around the world.  Source organicguidemalaysia.com

Opinions expressed in this article are my own and based on my experience in IPM, microbial control, biological control, and from discussions with several growers and scientists.

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Posted on Saturday, December 12, 2015 at 11:51 AM

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