- Author: Surendra K. Dara
Some Santa Maria strawberry growers experienced heavy infestations of whiteflies last year and there are already reports of infestations in some fields this year. Greenhouse whitefly, Trialeurodes vaporariorum has been a common strawberry pest in California for the past few years occasionally reaching high infestation levels that require targeted treatments. It used to be a concern mainly in the Oxnard area. Presence of the cut-back strawberries for second year production aid prolonged presence of whiteflies in the area and contribute to the early season infestations in new plantings.
Life stages of the greenhouse whitefly: Eggs darken when they are close to hatching. First instar nymphs are mobile and called crawlers. Later instars are immobile. Fourth instar nymphs are called pupae and characterized by long, waxy filaments. Adults have waxy, white wings. Black sooty mold grows on the honeydew secreted by whiteflies. (Photos by Jack Kelly Clark, Frank Zalom, and Surendra Dara)
Direct and indirect damage: Whitefly feeding affects plant growth and reduces yield and fruit quality. As they consume large quantities of plant sap, whiteflies excrete sticky honeydew deposited on the plant. Fungi of a few genera develop as black sooty mold on the honeydew covered surfaces. Sooty mold interferes with photosynthesis and affects plant growth. It also reduces the quality of the fruit.
Disease transmission: Greenhouse whiteflies are also important as vectors of pallidosis-related decline of strawberries. So, growers should be watching for symptoms of the disease which can be mistaken for nutritional deficiencies or abiotic disorders.
Pallidosis-related decline of strawberry is a viral disease caused by Strawberry pallidosis associated virus(SPaV) or Beet pseudo yellow virus(BPYV) along with non-whitefly transmitted viruses. Disease is not caused by SPaV or BPYV alone, but by the infection of SPaV or BPYV along with any of several non-whitefly transmitted viruses.
Symptoms of the disease include stunted plant growth, purple to red foliage, and brittle roots with reduced rootlets. Disease causes severe yield loss.
Whiteflies can cause a significant reduction in strawberry yield through direct feeding and indirectly through sooty mold and as viral disease vectors.
Biology: Greenhouse whitefly is about 1 mm long and has four membranous wings with white, powdery wax coating. Wings are held parallel to the top of the body. Eggs are small, elongated and attached to the lower leaf surface with a short pedicel. They are pale yellowish green to brown and turn dark with maturity. Eggs hatch and go through four nymphal instars before becoming adults. Immatures are oval, flat and often semitransparent. First instars are called crawlers which move around in search of ideal feeding sites on the underside of leaves. Later nymphal stages are immobile. Fourth instar nymphs are called pupa and have long, waxy lateral filaments and red eyes.
Management: Low population densities of whiteflies are usually controlled by the natural enemy complex in strawberries and pesticide treatments for other pests. Heavy infestations require timely treatments to prevent population build up. Monitor whitefly populations by using yellow sticky cards (1 per 10 acres) and counting their numbers on 20 mid-tier leaflets per each quarter of the field.
Refer to http://www.ipm.ucdavis.edu/PMG/r734301011.html for additional details on greenhouse whiteflies and their management.
My field trials: Among the control options that I evaluated, spiromesifen (Oberon) provided good control in a 2009 trial. In my 2012 large plot field trial, acetamiprid (Assail) alone at full label rate and acetamiprid at half the label rate along with the entomopathogenic fungus, Beauveria bassiana (BotaniGard 22 WP) provided a better control than other treatments.
2009 Trial: Percent change in whitefly populations two weeks after the treatment. *Note that spirotetramat is not registered for strawberries.
2012 Trial: Average percent change in whitefly populations after three applications. There was a general decline in their numbers throughout the experiment.
- Author: Surendra Dara
Petals, sepals, and developing fruit damaged and darkened from freezing temperatures (Photos by Surendra Dara)
Fruit deformation as a result of low temperatures which affect pollination. Smaller achenes are formed and uneven development of the tissue around them results in misshapen fruit. Notice larger achenes in unaffected areas (Photo by Surendra Dara)
Unusual cold weather during the past few days is a concern for the strawberry growers. Second year crop and cultivars that produce early or late can influence the extent of impact experienced by the growers because injury depends on the stage of development.
Damage: Low temperatures could completely damage the flowers or injure developing fruit tissue resulting in misshapen fruit. Pollination is also affected if temperature drops below 60 oF (15 oC) during flowering. As a result, some achenes do not have a seed, remain small, and cause fruit distortion. Cold injury can also cause fruit with multiple tips. Distorted fruit from lygus bug damage have uniform sized achenes, but the achenes affected by cold injury are much smaller than those on unaffected parts of the fruit.
Protection: Sprinkler irrigation can protect the fruits from cold injury when there is no or low wind. Freezing water releases heat and protects the flowers and fruits as long as temperatures do not fall below 23 oF (-5 oC) on still nights or 25 oF (-4 oC) when wind speed is no more than 2 mph. If wind speed is more than 4 mph, sprinkler irrigation is not recommended. Sprinklers must be started before the temperatures drop to freezing levels and continued throughout that period.
The time to start irrigation for frost protection depends on the dew point. If the dew point is low, irrigation has to be started before the freezing temperature. The following table shows when irrigation should be commenced depending on the dew point.
Dew Point |
Temperature at which irrigation should start |
Dew Point |
Temperature at which irrigation should start |
32 oF (0.0 oC) |
32 oF (0.0 oC) |
23 oF (-5.0 oC) |
38 oF (3.3 oC) |
31 oF (-0.6 oC) |
33 oF (0.6 oC) |
22 oF (-5.6 oC) |
38 oF (3.3 oC) |
30 oF (-1.1 oC) |
34 oF (1.1 oC) |
21 oF (-6.1 oC) |
39 oF (3.9 oC) |
29 oF (-1.7 oC) |
34 oF (1.1 oC) |
20 oF (-6.7 oC) |
39 oF (3.9 oC) |
28 oF (-2.2 oC) |
35 oF (1.7 oC) |
19 oF (-7.2 oC) |
39 oF (3.9 oC) |
27 oF (-2.8 oC) |
35 oF (1.7 oC) |
18 oF (-7.8 oC) |
40 oF (4.4 oC) |
26 oF (-3.3 oC) |
36 oF (2.2 oC) |
17 oF (-8.3 oC) |
40 oF (4.4 oC) |
25 oF (-3.9 oC) |
37 oF (2.8 oC) |
16 oF (-8.9 oC) |
41 oF (5.0 oC) |
24 oF (-4.4 oC) |
37 oF (2.8 oC) |
15 oF (-9.4 oC) |
41 oF (5.0 oC) |
Water should be applied at 0.10-0.15 (0.25-0.4 cm) inches per hour through sprinklers to provide adequate protection. Discontinuing sprinkler irrigation during the frost period can cause more damage. If sprinkler equipment is in shortage, limit the area to be irrigated. Sprinkler irrigation to an upwind or uphill field may provide some protection to an adjacent field downwind or downhill.
Drip irrigation can also provide some protection by wetting 6-12 inch (15-30 cm) of soil before the frost period. Wet soil stores and releases more heat than the dry soil.
Reference
2008. Integrated pest management for strawberries. Second Edition. UC ANR Publication 3351.
- Author: Surendra Dara
Novaluron (Rimon 0.83 EC, Chemtura USA Corp, Middlebury, CT) is a popular insecticide used by the strawberry growers for managing nymphal stages of the lygus bug. It is an insect growth regulator that inhibits chitin synthesis and thus interferes with the growth and development of the immature stages. It is effective against egg, nymphal or larval stages. According to some earlier studies, Chemtura restricted the use of adjuvants with novaluron. This has been a concern for the growers especially when novaluron has to be tank mixed with other pesticides and adjuvants. Chemtura's request to amend the label to remove the adjuvant/surfactant statement has been approved by the Environmental Protection Agency (EPA). Growers will soon be able to use adjuvants with novaluron when the new label is ready.
Background about EPA's requirement of adjuvant studies
Unless an adjuvant is not supposed to be used with a pesticide, EPA' s Office of Pesticide Programs (OPP) requires inclusion of adjuvants in the field trials for registering pesticides. This is mainly because of the impact of adjuvants on the pesticide residue levels. Because of this impact, there was a concern in EPA to require new studies with adjuvants for products that were previously registered without the adjuvant data. Crop Life America, Chemical Distributors and Producers Association analyzed historical data from OPP and concluded that adjuvants increase the pesticide residues, but the inherent variability in pesticide residues is more than what is caused by the adjuvants. Based on these analyses, Health Effects Division and Chemistry Science Advisory Council decided not to require new studies with adjuvants for products previously registered without them. As a result when registrants ask for label amendments related to the adjuvant use, EPA would use the fast track process.
What is an agricultural adjuvant?
Adjuvants are substances used with pesticides to improve their efficacy by improving the formulation, atomization, or biological action. Adjuvants act as spreading or wetting agents which reduce foaming, drift, and droplet size and increase the pesticide deposition, retention, and absorption. Agricultural adjuvants are categorized based on the chemical class into surfactants, oils, acidifiers and buffers, fertilizer adjuvants, and others. There are some green adjuvants that are safe to the environment.
Based on how an adjuvant is produced and its impact on the environment, Beck et al (2012) provided a definition for green adjuvants. “According to the production-based approach, adjuvants are defined as green if they are manufactured using renewable raw materials as much as possible while making efficient use of energy, preferably renewable energy. According to the environmental impact approach, adjuvants are defined as green (1) if they have a low human and environmental impact, (2) if they do not increase active ingredient environmental mobility and/or toxicity to humans and non-target organisms, (3) if they do not increase the exposure to these active substances and (4) if they lower the impact of formulated pesticides by enhancing the performance of active ingredients, thus potentially lowering the required dosage of active ingredients.”
References
Beck, B., W. Steurbaut, and P. Spanoghe. 2012. How to define green adjuvants. Pest. Manag. Sci. 68: 1107-1110.
Grains Research and Development Corporation. 2012. Adjuvants – oils, surfactants and other additives for farm chemicals – revised 2012 edition. Australian Government.
Ishaaya, I., S. Yablonski, Z. Mendelson, Y. Mansour , and A. R. Horowitz. 1996. Novaluron (MCW-275), a novel benzoyl urea, suppressing developing stages of Lepidopteran, whitefly and leafminer pests. pp. 1013-1020. In: Brighton Crop Protection Conf., Pests & Diseases, The British Crop Protection Council.
Martin, D. E., J. D. Lopez, Jr., Y. Lan, B. K. Fritz., W. C. Hoffmann, and S. E. Duke. 2010. Novaluron as an ovicide for bollworm on cotton: deposition and efficacy of field-scale aerial applications. J. Cotton Sci. 14: 99-106.
Spanoghe P, M. De Schampheleire, P. Van derMeeren, W. Steurbaut. 2007. Influence of agricultural adjuvants on droplet spectra. Pest. Manag. Sci. 63: 4–16.
- Author: Surendra Dara
Small, but damaging pest. Female (top), male and female in copulation (middle), and mature nymph (bottom) of Bagrada bug. Photo by Surendra Dara
In the third week of September, nearly two weeks after they were first reported in Santa Barbara County, Bagrada bugs were found in the Arroyo Grande area in San Luis Obispo County. Organic growers are especially worried due to limited management options. Conventional growers are also concerned at the sudden appearance of overwhelming numbers of Bagrada bugs in some cases, but good control with insecticides such as dinotefuran has been reported.
Feeding damage on broccoli. Photo by Surendra Dara
Even death does not separate some of them. Photo by Surendra Dara
Here is some more information in addition to what I have written in my previous articles:
- Adults can survive for nearly four months under optimal conditions.
- Since it is a new pest, we do not know its overwintering efficiency in Santa Barbara and San Luis Obispo Counties. Bagrada bugs overwinter as adults, but periods of winter in our area could be very cold for them.
- Although brassicas are known to be preferred hosts, they can feed on a variety of other hosts.
- In Ventura County, they were reported on strawberries in large numbers, but it was not clear if they were feeding and causing damage to the crop. Because this pest is multiplying in large numbers and spreading around, they can be seen on atypical host plants in their way. If they happen to stay on these hosts for a long period, it is quite possible the bugs explore feeding on them.
- Bagrada bugs seem to be aggregating in weed hosts like wild mustard and alyssum even when crop plants such as broccoli and kale are nearby. So, using the wild hosts as trap crops can be a strategy as long as they do not serve as a source of infestation for crop plants.
- They seem to be responding well to synthetic pyrethroids, neonicotinoids, and organophosphate compounds. Since we do not know the future status of this pest, rotating chemicals with different modes of action is very important to minimize potential resistance problems.
- For organic growers, mechanical removal and use of pyrethrins and azadirachtin (for immature stages) seem to be available options at this moment. Azadirachtin is a natural growth regulator and should be used mainly against immature stages. Other organically approved materials do not seem to be effective based on available information.
- Careful monitoring, especially in sensitive areas such as those close to wild hosts, removal of wild or weed hosts, and rotating crops with non-host plants, can reduce the risk of infestation.
- New infestations can occur from infested nursery plants. So, care must be taken to prevent spread through the movement of plant material.
Bagrada bugs on strawberries during their migration to a more suitable host. Feeding damage has not been reported. Photo by Lane Stoeckle
- 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.
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