- Author: Surendra Dara
Bagrada bugs on peppers (Photo by Brendan Kreute, PCA in Ventura Co)
It was in last January when I first wrote about the invasive pest Bagrada bug (Bagrada hilaris). It was only reported in Imperial, Riverside, and Orange Counties at that time. In the past two months or so, I have received several phone calls and emails from various places outside Santa Barbara County about Bagrada bug infestations in the home gardens and fields on arugula, broccoli, kale, Monterey pine, mustard, peppers, radish, and strawberries. In some cases, they were also seen inside the homes.
Early this week, Santa Barbara County Ag Commissioner Entomologist, Brian Cabrera received specimens from Solvang and found infestations of Bagrada bug on mustard in other areas making an official record of this pest in the county. This pest currently has a B rating by CDFA.
Like lygus bug, Bagrada bug can also migrate to crop plants from alternate hosts such as wild mustard. So, proximity to such wild hosts can lead to possible infestations when wild plants dry out.
Bagrada bug adult in Santa Barbara Co (Photo by Brian Cabrera, Santa Barbara County Ag Commissioner Entomologist)
Management options: There are varying reports on the effectiveness of various products especially for organic crops. Someone reported effective control with mechanical exclusion and azadirachtin. However, University Arizona Entomologist, John Palumbo did not see effective control by organically approved products when compared to the combination of dinotefuran and bifenthrin in his studies.
Cultural control through pest monitoring and early detection, removal of weed hosts, mechanical removal through handpicking or vacuuming, cultivation to destroy eggs in the soil, and overhead irrigation to dislodge nymphs and adults from the plants are some of the options suggested in the literature.
Please read my earlier article for more details on this pest at http://ucanr.org/blogs/strawberries-vegetables/index.cfm?tagname=Bagrada%20bug
If you see Bagrada bug, please contact me or your local Ag Commissioner's office.
/h4>/h4>- Author: Surendra Dara
Spotted wing drosophila (SWD), Drosophila suzukii has become a potential concern for strawberries following its damage to cherries, blackberries, raspberries, and blueberries in coastal California. Other species of Drosophila are morphologically not equipped to attack ripening strawberries. Their ovipositors or egg laying parts are not strong enough to penetrate unripe or ripening berries. They may damage overripe strawberries left on the crop, but since such berries are not marketed, they have not been an issue for growers. However, SWD has a heavily sclerotized, serrated ovipositor that enables it to lay eggs in fruits that are not fully ripe.
In response to the concern that SWD could be a potential pest to strawberries, I monitored some fields in Santa Maria last year. Five fields – four conventional and one organic – in various parts of Santa Maria were monitored for five months from March to July, 2011. Two kinds of traps, one with apple cider vinegar and the other with yeast-sugar extract were used in each location and were observed every week. During this monitoring there were no signs of SWD in any of these traps. However, I recently received some specimens from a Santa Maria grower in which I found what seemed to be the females of SWD among other Drosophila sp. There were no males with their obvious characteristic of spotted wings, but the following and other characters of the females suggest these were SWD:
- Hard and dark (sclerotized) ovipositor with prominent serrations or saw-teeth that enable the fly to lay eggs in intact ripening fruit.
- Antennae with branched bristle-like part called arista.
According to Dr. Brian Cabrera, Santa Barbara County Ag Commissioner Entomologist, there haven't been any SWD infestations that were brought to his attention. So, it appears to be the first report of SWD in Santa Maria strawberries. Sanitation, trapping, and chemical control are among the available options to manage SWD. Close monitoring is necessary in vulnerable areas. More details about identifying and managing SWD can be found in the listed references. Here is a brief note about this pest.
SWD belongs to the group of flies that are generally known as vinegar flies or lesser fruit flies. It was initially known as cherry fruit fly in 1930s and is now referred to as spotted wing drosophila.
Origin and distribution: It is traditionally known to be a pest in Asia, but it is now reported in Neo Tropics, North America, and Europe. In the US, it has been found in Hawaii, Washington, Oregon, California, and Florida.
Host range: They generally infest thin-skinned fruit and prefer temperate climate. Host range includes apple, blackberry, blueberry, cherry, dogwood, grape, mulberry, peach, persimmons, plum, raspberry, and strawberry.
Biology: SWD prefer 68-86 oF and overwinter as adults. Various sources suggested 5-10 generations per year. According to Kanzawa (1939) egg laying starts in spring and can last for 10-59 days. Females lay an average of 384 eggs at 7-16 per day. Eggs hatch in 2-72 hours and larval stage lasts for 3-13 days. Pupation takes place inside the fruit or in the soil and lasts for 3-15 days. Life cycle takes anywhere from 21-25 days at 59 oF to 7 days at 82 oF.
Damage: Other fruit flies usually infest overripe and fallen fruit, but SWD infests fresh fruit because of its powerful ovipositor. Adults feed on fallen fruit but lay their eggs under the skin of intact fruit. Softening and collapse of the tissue results from larval feeding inside the fruit. Oviposition holes can be seen on the fruit with close observation. In addition to the direct damage, SWD makes the infested fruit vulnerable to other pests and diseases. Monitoring SWD is very important to avoid harvesting and marketing infested berries.
Maggots (of unknown species) in infested fruits showing up in processed strawberry container. Photo by Surendra Dara
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References
Calabria G., J. Máca, G. Bächli, L. Serra and M. Pascual. 2012. First records of the potential pest species Drosophila suzukii (Diptera: Drosophilidae) in Europe. J. Appl. Entomol. 136:139-147.
Kanzawa, T. 1939. Studies on Drosophila suzukii Mats. 49 pp. (http://www.cabdirect.org/abstracts/19410501073.html;jsessionid=81E9221496390100F7C13052E18F8079)
http://www.agf.gov.bc.ca/cropprot/swd_identification.pdf
http://www.al.gov.bc.ca/cropprot/swd.htm
http://entnemdept.ufl.edu/creatures/fruit/flies/drosophila_suzukii.htm
http://www.freshfromflorida.com/pi/pest-alerts/drosophila-suzukii.html
http://www.ipm.ucdavis.edu/EXOTIC/drosophila.html
- Author: Surendra Dara
False chinch bug (Nysius sp.) infestation on strawberries (Photo by Sal Ponce, Pacific Coast Produce.
False chinch bugs migrated to new strawberry field (above) from dried weeds in an old strawberry field (Photo by Surendra Dara)
There was an isolated incident of heavy infestation in a Santa Maria strawberry field with false chinch bug, Nysius sp. (very likely N. raphanus). False chinch bug is normally not a pest of strawberries or cultivated crops. They usually multiply on herbaceous weeds during spring time and move on the nearby cultivated crops when the weed hosts dry out. In the current incident, an old, leftover strawberry field with severe weed growth right next to the cultivated strawberry field harbored false chinch bug populations which moved to the new strawberry field. The grower immediately treated the field with malathion and bifenthrin (Brigade) that effectively controlled the migrating pest. This is a classic example of weeds and alternate hosts serving as a source of pest populations. It emphasizes the importance of cultural practices such as managing weeds and alternate hosts of pests and good agronomic practices for controlling pests without pesticide application. Such cultural practices are also important for avoiding early infestations of lygus bug, a major pest of strawberries in California's Central Coast.
If you notice false chinch bugs in strawberries or other crops this article should help you in identifying and taking appropriate action.
False chinch bugs are true bugs belonging to the order Hemiptera and family Lygaèidae. Members of Lygaèidae are generally known as seed bugs. Crops pests like lygus bug (Lygus spp. - family Miridae) and chinch bug (Blissus spp. - family Blissidae), and beneficial predator, big-eyed bug (Geocoris spp. - family Geocoridae) are some other commonly known lygaeids.
Host range: False chinch bugs are usually found on grassy and cruciferous weeds in spring and move in large numbers to nearby vegetation when the weed hosts dry out. They can be a nuisance to farms, orchards, landscapes, and gardens.
Damage: Nymphs and adults feed on foliage, stems, fruit, and seeds using their piercing and sucking mouthparts. Feeding causes discoloration, scorched appearance, wilting, and in severe cases death of the plant.
Biology: Eggs are laid in loose soil and hatch in 4-7 days. Nymphs have brownish gray bodies with orange or reddish markings. Developing wing pads are dark brown. The abdomen has a transverse white page in the middle and an alternating brown and grey pattern in the margins. Nymphs molt a few times and mature into adults in about three weeks. Adults are 3-5 mm long, grayish brown, with a slender body and silvery gray wings. Margins of the folded wings appear like an X. Note that true chinch bugs have a triangular black marking near the middle of the outer wing margin.
False chinch bug nymphs with gray brown mottling and dark developing wing pads and adult (bottom right) with silvery grey wings (Photo by Surendra Dara)
Management: Mass migration of false chinch bugs lasts for a short period and many plants can with stand minor damage. Chinch bug infestations usually do not require any treatment, unless plants are at a vulnerable stage or there is a serious damage. Some of the common pesticides can be effective, but it is important to refer to the product label and pest management guidelines specific to the crop.
- Author: Surendra Dara
The combination of 1,3 dichloropropene (1,3-D)and cholorpicrin is a popular choice for fumigating strawberry fields after methyl bromide. It is very effective and convenient to administer through the drip irrigation system. However, 1,3-D can result in phytotoxicity if transplanting takes place before the fumigant completely dissipates.
Phytotoxicity from 1,3-D
Symptoms of phytotoxicity from 1,3-D include yellowing of leaves purple coloration and stunted plant growth. Newly emerged leaves will look normal and plants appear to recover to some extent, but subsequent growth and yield potential can be affected.
Strawberry plants (variety Albion) about 85 days after transplanting (above and below). Stunted plant growth, discoloration of the foliage with purple tinge indicated injury from 1,3-D. Transplanting took place 16 days after fumigation. (Photos by Surendra Dara)
Purple coloration on older leaves can still be seen even up to 110 days after transplanting as a result of 1,3-D injury (Photo by Surendra Dara)
A typical plant from 1,3-D injured field 110 days after transplanting (left) is smaller than a typical plant from a neighboring field which was transplanted about 3 weeks later and not subjected to 1,3-D injury (right) (Photos by Surendra Dara)
Avoiding fumigant injury
Proper planting interval after fumigation is very important to avoid phytotoxicity and subsequent crop losses. It usually takes two or more weeks for the fumigant to dissipate depending on the type of soil, method of application, plastic mulch, and soil temperature and moisture conditions. Use of virtually impermeable film (VIF) or totally impermeable film (VIF) increase the effectiveness of fumigation, but retain the fumigant for a longer period in the soil requiring additional time before planting. Chloropicrin and 1,3-D usually are ideal for dryer soils and require longer planting interval in moist soils. In drip fumigation, adequate amount of water to apply fumigants is important. Excessive water can dilute the fumigant concentration and reduce its effectiveness. Insufficient water limits the distribution and may increase the volatilization of the fumigant and thus reduces its effectiveness. A minimum of three weeks of plant-back time is recommended for drip applied 1,3-D products. It is important to refer to the product label for proper fumigation procedures and planting interval. A healthy start is essential for the season long performance of the strawberry plant and realizing the maximum yield potential.
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References
2008. IPM for strawberries. UCANR publication 3351.
Santos, B. M. 2007. Life after methyl bromide: research on 1,3-dichloropropene plus chloropicrin in Florida. University of Florida Cooperative Extension Service publication HS1119.
- Author: Surendra K. Dara
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 (ECw) or the EC of the saturated soil extract (ECe). 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 ECw.
According to Dr. Stuart Styles, Professor of BioResource and Ag Engineering at Cal Poly, ECw (salinity of the irrigation water) is a better indicator than ECe (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 ECw (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:
Characteristic |
Ideal level |
Electrical conductivity (ECw) |
0.7 dS/m |
Total dissolved salts (TDS) |
450 mg/L |
Sodium |
3 SAR |
Chloride |
4 meq/L (milliequivalent/L) |
Boron |
0.7 mg/L |
Nitrate |
5 mg/L |
Bicarbonate |
1.5 meq/L |
Acidity |
6.5-8.5 pH |
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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.
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