Doug O'Brien, Doug O'Brien Agricultural Consulting
Phil Foster, Phil Foster Ranches
Alex Stone, Oregon State University
Helen Atthowe, Oregon State University
This article is part of the Phil Foster Ranches Farm System Description
- Critical Tools
- Insect Pests
- Cucumber beetle
- Flea Beetle
- Cabbage aphid
- Onion Thrips
- References and Citations
- Tables and Figures
The goal for managing arthropods at Phil Foster Ranches (PFR) is to design a system with optimal ecology, economy, effectiveness, and few external inputs. Phil Foster has 25 years (1989-2014) of yield and supplemental input records. Doug O’Brien (PhD) has scouted PFR’s fields 2-3 times per week for 18 years (1997-2014). They monitor pests and beneficial organisms, develop thresholds for applying supplemental inputs, and keep good records. All of these data are archived, and the records are used to inform management decisions. These farm-collected data sets and the experiences and opinions of Phil and Doug form the foundation of this insect system description.
Rare sighting of an assassin bug (Reduviidae) feeding on cucumber beetle. Row of insectary plants (green) in red lettuce. Photo credits: Doug O’Brien
Goals Related to Ecologically-Based Insect Pest Management and the Tools and Strategies Used to Achieve Them
PFR’s ecologically-based insect management system goals include landscape-level design, soil building, habitat building, identification and monitoring of pests and beneficials, and supplemental inputs (Table 1).
IMPORTANT: Before using any pest control product in your organic farming system:
- Read the label to be sure that the product is labeled for the crop and pest you intend to control, and make sure it is legal to use in the state, county, or other location where it will be applied.
- Read and understand the safety precautions and application restrictions.
- Make sure that the brand name product is listed in your Organic System Plan and approved by your USDA-approved certifier. If you are trying to deal with an unanticipated pest problem, get approval from your certifier before using a product that is not listed in your plan—doing otherwise may put your certification at risk.
Note that, although OMRI and WSDA lists are good places to identify potentially useful products, all products that you use must be approved by your certifier. For more information on how to determine whether a pest control product can be used on your farm, see the related article, Can I Use This Input On My Organic Farm?
Critical Tools in PFR’s Insect Management Toolbox
PFR uses a toolbox of tools and strategies (Table 2) to meet the system management goals articulated in Table 1. For each arthropod pest, Phil chooses items from this list. Tools or strategies are added as useful ones emerge, and those shown to be ineffective are discarded. Tools and strategies may be adapted for specific crop situations.
Insect Pests for Which the PFR System is Working and Not Working
The arthropod management system is mostly working. According to Phil, Doug, and the scouting, yield, and spray records, many insect pests problematic at PFR in the early years (and typically problematic on vegetable farms in the Monterey Bay area) are no longer considered problematic.
Infrequently seen and cause no damage: Tomato hornworm (Manduca quinquemaculata)
Frequently seen but cause no economic damage: Diamondback moth (Plutella xylostella)
Insects not actively managed—damage significant in past but no longer significant:
- Wireworm (Family Elateridae)
- Root maggots (Delia spp.)
- Squash bugs (Anasa tristis)
- Turnip aphid (Lipaphis erysimi)
- Potato aphid (Macrosiphum euphorbiae)
Insects actively managed:—damage significant in past but no longer significant due to management (the effective management strategy is listed after scientific name):
- Lettuce aphid (Nasonovia ribis-nigri, resistant varieties)
Insects for which damage is almost never significant due to management, and successful management strategies (listed after scientific name) are known:
- Corn earworm (Helicoverpa zea; no longer grow crops that mature after August 7)
- Tuber moth (Phthorimaea operculella; early block grown in Santa Ana/late block grown in San Juan, high hilling)
- Onion thrips (Thrips tabaci; Entrust® [Dow AgroSciences] applications)
- Bagrada bug (Bagrada hilaris; tightly sealed row cover until 6 leaf stage)
Insects for which damage is almost never significant. Insects suppressed by farming system; specific strategies that contribute to suppression unknown:
- Armyworms (Spodoptera spp.)
- Imported cabbageworm (Pieris rapae)
- Cabbage looper (Trichoplusia ni)
- Garden symphylan (Scutigerella immaculate)
- Two spotted spider mite (Tetranychus urticae)
- Tarnished plant bug (Lygus Hesperus)
- Honeysuckle aphid (Hyadaphis foeniculi)
- Black bean aphid (Aphis fabae)
- Melon aphid (Aphis gossypii)
- Green peach aphid (Myzus persicae)
Insects for which damage is significant most years, occasionally very significant, despite active management:
- Spotted cucumber beetle (Diabrotica undecimpunctata) and striped cucumber beetle (Acalymma vitatum), see description below
- Brassica flea beetles (Phyllotreta spp. and/or Systena blanda), see description below
- Cabbage aphid (Brevicoryne brassicae), see description below
Crops that are no longer grown entirely or in part because of inability to control an insect pest:
- Sweet potato (cucumber beetle larvae)
- Peanuts (two-spotted spider mite)
- Napa and bok choy in Santa Ana (lygus bug, beet western yellow virus vectored by aphid; cucumber beetle)
- Summer direct-seed broccoli and cabbage (flea beetle)
- Late spring and fall lettuce in Santa Ana (spotted cucumber beetle adults)
- Late summer specialty melons: Galia, honeydew, orange flesh, Piel de Sapo (striped cucumber beetle)
Management System Descriptions for Five Important Insect Pests
(summarized in Table 3)
The management systems of five important insect pests are described in detail below. The goals of these detailed descriptions are to:
- Illustrate the diversity of tools and strategies used for each pest-specific management system
- Identify which management tools and strategies are working and which are not
- Identify critical research needs
Striped and Spotted Cucumber Beetle on Watermelon
Damage: Striped and spotted cucumber beetles cause yield losses, primarily by adults feeding on foliage, resulting in sunburn and scarring (melons and cucurbits) or general leaf and stem damage (all crops). Root feeding by larvae is commonly observed.
Crops: Melons of all varieties are the crop most affected, but many other crops, such as all other cucurbits, lettuce, bean, sweet corn, napa, bok choy, chard, and beet may be damaged. Striped cucumber beetle adults feed moderately on a wide variety of crops, but larvae feed only on cucurbits. Spotted cucumber beetle has a very wide host range.
Trend: Watermelon scouting data reveal that the occurrence of severe cucumber beetle damage is highly variable (0-14% of scouting observations), but overall, there is no trend in the incidence of severe damage. (Fig. 1). Doug thinks that outbreaks may be worse in warm and dry years. Yields of watermelon have been steadily declining. Although this decrease is mostly attributed to Verticillium wilt, cucumber beetles have reduced marketable yield by scarring fruit and damaging leaves since watermelons were first grown, according to Phil and Doug.
Effective management strategies:
- Crop diversity
- Spatial crop rotation, including not planting watermelon immediately after a host crop, so pupae will not emerge directly into the watermelons
- Row covers (physical protection) until female flowers open
- High tunnels (physical protection)—delays damage onset
- Handheld propane burner for killing large groups of beetles on field edges
- Tractor-mounted flamer to kill beetles in field after harvest, reducing the number of beetles moving to adjacent fields
- Yellow sticky tape barriers across ends of high tunnels to capture entering beetles
- Surround® (Novasource)—single backpack treatment targeting only the fruit at 10-14 days before harvest. Surround® may make the fruit less attractive to the beetles than the untreated leaves, thus reducing fruit scarring. Severe leaf damage may occur, but is late enough to allow some of the fruit to mature. This practice is expensive, because Surround® must be washed off fruit before sale.
Ineffective management strategies:
- Conservation biological control: Biological control of cucumber beetles most likely occurs when the pest is overwintering underground in field margins, and therefore is not detected by the PFR scouting program. Cucumber beetles can fly long distances, so can come in from off-farm. Biological control is likely occurring at some level but is insufficient. Natural enemies are not reported to be helpful in California (Natwick et al., 2012).
- Vacuuming is ineffective for insect pests of vine crops.
- Yellow sticky tape suspended in field (no high tunnel) blocks catches large but insignificant numbers of beetles.
- Varietal resistance: Although melon types and varieties vary in susceptibility (cantaloupe is damaged the least, according to Phil and Doug), strong/useful varietal resistance is not available.
- Applying Surround® to both leaves and fruit: does not reduce fruit scarring (and may increase it).
- Pyganic® (Valent) applications: Dead beetles have been observed after Pyganic® sprays, but at very low numbers. A mixture of Cide-trac® (Trece) (a cucumber beetle-feeding attractant) and Pyganic® was trialed but was marginally effective; it was then discontinued when researchers documented its inefficacy (Pedersen et al., 2011). The number of pesticide spray days targeting cucumber beetle in watermelon varied over time with no trend until very recently (4-12 days per year, 2002-2013, Fig. 2). Cide-Trac®/Pyganic® applications ceased in 2014.
Flea Beetle on Broccoli and Cabbage
Damage: Flea beetles cause yield losses in brassica crops, including broccoli and cabbage, primarily by adults feeding on foliage. Emerging seedlings can be completely killed. Older plants can be severely stunted, producing small or unmarketable yield.
Crops: Broccoli, cabbage, and other brassicas are affected; varieties vary in susceptibility, reflected in differences in the percent of scouting observations with flea beetles between broccoli and cabbage (Figs.3a-d).
Trend: Scouting reports for broccoli and cabbage at San Juan and Santa Ana show that flea beetle is more of a problem in broccoli than cabbage, and most severe in broccoli grown in Santa Ana (likely due to the higher temperatures in Santa Ana compared to San Juan, and the brief mid-day irrigations in San Juan). In addition, the data indicate that overall, there is no trend in flea beetle severity except for a recent increase (since 2009) in broccoli grown in San Juan (Figs.3a-d). Doug thinks that outbreaks may be worse during warm and dry years.
Yields of broccoli and cabbage vary, perhaps partially from years with heavier flea beetle infestations, but we don’t have sufficiently fine yield data to confirm this (Fig.4, broccoli and cabbage yields). According to Phil and Doug and the scouting reports, while the increasing flea beetle severity could be a contributor, the lower yields of broccoli starting in 2012 are most likely attributable to bagrada bug. This new pest did considerable fall damage in 2012-14 before losses declined in 2015 when tightly-sealed row covers were deployed.
Effective management strategies: Crop diversity, spatial/temporal/environment-based crop rotation (lower temperatures in San Juan results in lower flea beetle damage), row covers, and transplants (very young plants are most susceptible) are helpful but do not provide complete control. Row covers exclude flea beetles but also aphid predators, so cabbage aphids arriving on transplants or through cover tears can become a problem. Mid-day brief overhead irrigations reduce damage (mechanism unknown; PFR’s hypothesis is that the water washes the beetles off the crop during prime feeding time). Row covers, irrigations, and transplants are expensive. Daily overhead irrigation is not feasible at Santa Ana due to water scarcity and the irrigation system design.
Ineffective management strategies: Biological control of flea beetles most likely occurs when the pest is underground and therefore not detected by the PFR scouting program. Biological control is likely occurring at some level, but is insufficient. Natural enemies are not reported to be helpful in California (Natwick, 2009). Although crop species vary widely in susceptibility, useful varietal resistance is not available. Vacuums cannot pick up small insects like flea beetles.
According to Doug and Phil, PFR experimented with pesticides (Pyganic®, Valent; and soaps) before 2001 and found them to be mostly ineffective (pesticide records not available quantitatively before 2001). Almost no pesticides with activity against flea beetles have been used since that time (Fig.5), except during unusually heavy aphid pressure in 2009, and unusually heavy flea beetle pressure in 2014 (Pyganic® has activity against aphids and flea beetles); these pesticide (Pyganic®) applications were considered ineffective.
Cabbage Aphid on Broccoli and Cabbage
Damage: Cabbage aphids cause yield losses primarily by contaminating harvestable portions, although very high populations can cause stunting.
Crops: All brassicas can be affected, but susceptibility varies. According to Phil and Doug, kale and romanesco broccoli seem to be the most affected, and green cabbage seems to be the least affected. PFR’s two green cabbage varieties appear to have different susceptibility as well (Fast Vantage is more susceptible than Green Vantage).
Trend: Scouting reports show that in general, cabbage aphid is more of a problem on broccoli grown at Santa Ana than broccoli grown at San Juan, likely due to higher temperatures in Santa Ana. In addition, the aphid severity index declined on both crops and at both ranches over time (Fig.6a-d), while the percent of observations in which no aphids were observed increased (Fig.7a-d). Doug thinks that outbreaks may be worse in warm and dry years. Yields of broccoli and cabbage vary, perhaps partially from years with heavier aphid infestations, but we don’t have enough data to confirm this (Fig.4). The lower yields of broccoli starting in 2012 are most likely attributable to bagrada bug, a new pest that did considerable fall damage in 2012-14; this pest is now successfully controlled with row covers.
Effective management strategies: Crop diversity, conservation biological control (insectary plants, cover crops, hedgerows), temporal rotation, spatial rotation (planting succession plantings upwind, widely separating blocks), mowing of field margins, and environment-based rotation (avoiding planting brassicas for spring harvest at San Juan, as at that time aphid pressure is higher at San Juan than Santa Ana) are considered useful. Conservation biological control is occurring: natural enemies (syrphid flies, lacewings, lady beetles, parasitoid wasps, Pandora neoaphidis) have been observed interacting with cabbage aphids during scouting events. Foliar compost tea applications (begun in 2005) seem effective when field conditions allow regular application, although the mechanism for control is not known.
Ineffective management strategies: Almost no pesticides with activity against aphids have been used since 2001 (Fig.8a and 8b; pesticide activity vs. aphid), except during unusually heavy aphid pressure in 2009 and unusually heavy flea beetle pressure in 2014. The applied pesticides were some combination of PyGanic® (Valent), M-Pede® (Gowan), and/or Aza-Direct® (Gowan). Doug and Phil do not consider these pesticide applications to be particularly effective, although other growers apply them regularly and efficacy has been reported elsewhere (Levy and Sideman, 2016). Although species vary in susceptibility, useful varietal resistance is not available.
Lepidopterans (Cabbageworms) on Broccoli and Cabbage
Damage: Cabbageworms eat all portions of the aboveground plant and contaminate edible portions.
Crops affected: All brassicas can be affected, but susceptibility varies. According to Phil and Doug and the scouting reports, cauliflower, broccoli and green cabbage seem to be most affected, and red cabbage and kales are the least affected. PFR’s two green cabbages appear to have different susceptibility as well (Fast Vantage is more susceptible than Blue Vantage green cabbage).
Trend: Scouting reports for broccoli and cabbage at the Santa Ana ranch show a general decrease in the cabbageworm severity index (Figs. 9a and 9b) over time, while the trend at San Juan is not clear (Figs.9c and 9d). Doug thinks that outbreaks may be worse during warm years. Yields of broccoli and cabbage vary, but variations in yield are likely due more to flea beetle, cabbage aphids, and bagrada bug damage (see above) than cabbageworm damage as cabbageworms are controlled by the management system (Fig. 4).
Effective management strategies: Crop diversity, conservation biological control, spatial rotation, scouting, and threshold-based applications of commercial formulations of Bacillus thuringiensis (Fig. 10) all contribute to cabbageworm management. Conservation biological control (insectary plants and hedgerows) appears to be contributing to cabbageworm management at PFR; birds, lady beetles, lacewings, damsel bugs, carabid beetles, minute pirate bugs, and spiders, as well as granulosis virus, have been observed interacting with cabbageworms at PFR during scouting events.
Damage: Onion thrips suppress yield in onions, primarily the result of adult and larval feeding on foliage, resulting in smaller onions.
Crops affected: According to Phil and Doug, red onions, shallots, leeks, and garlic are more susceptible than yellow and white onions. Doug thinks that outbreaks may be worse in warm and dry years.
Trend: Yields of red onions increased from 2002 to 2009 and then declined (Fig.11); this decline is mostly attributed to Fusarium basal rot. Onion thrips may have suppressed onion yields in some years before Entrust® was available and used regularly (starting around 2010) (Fig.11), but there is insufficient yield data to confirm this.
Effective management strategies: Mowing of field margins (to remove thrip habitat), spatial crop rotation (planting succession crops upwind), scouting, and Entrust® (Valent) applications. Conservation biological control occurs at some level but is insufficient for control. Six-spotted thrips (onion thrip predators) are frequently observed in the spring, and may be quite helpful with early thrips infestations, but as temperatures warm, thrips populations steadily increase and six-spotted thrips observations decrease.
The effectiveness of Entrust® has resulted in increasing insecticide applications (Fig.11) and better control, according to Phil and Doug. In the early years, high action thresholds were used to reduce the impact of the pesticides on biological control organisms. These concerns diminished because of the apparent ineffectiveness of biological control organisms (chiefly 6-spotted thrips), the lack of other important arthropod pests on onions, and the more effective control from more frequent Entrust® sprays. For these reasons, action thresholds have been lowered (fewer thrips per plant trigger an Entrust® application). A few thrips per plant when plants are small and >20 when plants are large will trigger an Entrust® application. Entrust® must be applied frequently when thrips populations are increasing rapidly and when they are migrating into a field after nearby hay or cover crop fields are mowed. Grandevo® is less effective against thrips, but is softer on natural enemies. As natural enemies do not seem to be very important contributors to thrip control at PFR, Entrust® is used rather than Grandevo®.
Ineffective management strategies: Although onion varieties and colors vary in susceptibility, economically important varietal resistance is not available. Insectary plants are not planted in onion fields, as biological control organisms supported by those insectary plants are not observed interacting with thrips, and the insectary plants (and hedgerows) also support thrips.
This farm system description shows that many years of farmer observations plus scouting, supplemental input, and yield records can generate valuable information on organic farming system function. Farm-collected records are useful in documenting both practices and outcomes. Trends observed over many years make it possible to perceive overarching trends despite year-to-year variability in environmental factors and insect populations. While PFR practices and outcomes are not necessarily directly transferable to other farms and regions, farmers and researchers may use PFR’s experiences and data to develop insect management systems and prioritize research needs.
Conservation Biological Control
Conservation biological control of insect pests is generated at many scales, from habitat in the broader landscape far beyond the borders of the farm (largely out of the control of the farmer), to habitat on field margins and within the field and crop (within the control of the farmer). PFR is located in a region with little habitat and habitat diversity at the broader landscape level (see map), and much of this landscape consists of unmanaged non-native trees, shrubs, and weeds. PFR has no direct control over the management and use of these lands. Development of habitat for beneficial organisms in the broader landscape would require community effort and/or changes in government policies for the management of public and private land next to organic farms.
On the other hand, and to compensate in part for the lack of broader landscape habitat and complexity, PFR has invested in field border habitat development (hedgerows) and annually invests heavily in developing in-field habitat, through its soil building practices, cover crops, and in-field insectary plantings.
What is Working, What is Not
The overall economic success of PFR indicates that most of its 60+ crops and multiple plantings per year are not significantly affected by insect pests. PFR’s management system of techniques and practices (Table 2) has resulted in a decline in damage caused by several insect pests both with and without the use of pesticides. Many arthropods that might be problems in PFR’s region (University of California Integrated Pest Management Program) are not problems at PFR. PFR’s supplemental input records show this is not because of the application of pesticides/supplemental inputs, but because of integrated management systems comprised of resistant germplasm (essential for lettuce aphid), crop diversity, habitat for biological control organisms, and cultural practices. PFR’s soil building practices likely contribute, particularly for insect larva susceptible to soil-dwelling natural enemies such as cabbage maggots, wireworms, and symphylans. However, we have no evidence that soil building has helped with some other insects with a soilborne stage, notably cucumber beetles and flea beetles.
Creating habitat for biological control organisms has been effective, but is costly in terms of inputs and management time. Coordinating in-field insectaries with many individual plantings is management intensive, particularly with transplanted insectaries because of timing and spacing requirements. PFR’s twenty-year experience with hedgerows shows that they require knowledge and intensive management. The incorrect choice of species, and lack of proper and regular pruning and weed management, resulted in the removal of most of the hedgerows at the Santa Ana ranch in 2017. Invasive saltbush plants had overgrown many species and were sheltering vertebrate pests. New native species will be installed. Doug thinks that the new hedgerows should be regularly pruned to no more than eight feet high and five feet wide, with all low branches removed.
Of the cultural practices, crop rotation (temporal and spatial) and diversity may be among the most important. Spatial crop rotation has probably been important for controlling insects that are weak fliers, chiefly aphids; upwind sequential planting makes it harder for aphids to move from old plantings to young. The diversity of PFR’s crops and cover cropping provide longer spatial rotations than less diverse farms. The two geographically separated farm areas (Hollister and San Juan Bautista, 15 miles apart) provide significant temporal rotation, and Phil has a precise schedule to avoid planting particular crops at each area when they are most susceptible to some insects. This crop rotation and crop diversity is not free. Managing so many different crops and two widely separated farms is expensive and requires exceptional management skills. Some crops are not well adapted to PFR’s climate and soils and need expensive inputs (such as high plastic tunnels and polyester row covers) to achieve adequate yields and acceptable quality. PFR needed to develop markets for non-shipping grade produce, which increased management and infrastructure costs.
The vast majority of Phil’s crops receive no supplemental inputs/pesticides for insect control. Organic insecticides are used regularly only for cabbageworms and armyworms (Bt), and thrips (Enrust®). Phil has experimented with some commercially available, organically-acceptable materials (soaps, oils, plant extracts, PyGanic®, neem materials), but uses only Seduce® (Certis, for earwig), Surround® (NovaSource), commercial formulations of Bacillus thuringiensis, and Entrust® (Dow AgroSciences). Compost tea is applied for the management of cabbage aphid.
Crop scouting records and farmer observations led to the economic control of several arthropods using insect-suppressive materials. Most notable was control of thrips with Entrust® (diverse crops including onions, garlic, pepper, kale, cabbage). Entrust® is not compatible with some beneficial insects (e.g. syrphids), so an effective alternative would be preferable. Grandevo® (Marrone Bio Innovations) has shown some efficacy if applied early and often on smooth-textured leaves such as leeks. Doug thinks Entrust® kills significantly more thrips regardless of leaf texture.
Unlike many organic farmers in the area, PFR does not apply a tank mix of soaps, neem-derived materials, and Pyganic® for the management of cabbage aphid. Phil does not have equipment that can deliver 200 gallons per acre, and this high volume is considered necessary for control by the soap mix; in addition, Phil thinks he achieves adequate control with insectary plantings and compost tea.
As a group, brassicas are PFR’s most important crops, so sporadic losses from cabbage aphids and flea beetles and the high costs associated with the management of these pests are a threat to PFR’s long-term sustainability. More effective strategies would be helpful.
The only insect management system that is truly not working is that for cucumber beetles (both striped and spotted). Effective natural enemies, resistant varieties, cultural strategies, and/or insecticides are urgently needed.
Abandoning crops when insect pests are uncontrollable (e.g., some varieties of melon because of cucumber beetle; romanesco and kales because of cabbage aphid and flea beetle) is always an option, but has significant negative economic and farm system design implications.
Development of resistant germplasm, imported natural enemies, or other effective strategies for the control of cucumber beetle, cabbage aphid, and brassica flea beetles are critical research priorities for Phil Foster Ranches and other organic farms in California and the United States.
Scouting records indicate that some pest populations fluctuate widely from year to year (e.g., cucumber beetles, flea beetles, cabbage aphids, cabbageworms). Records also indicate that some pests occur at very low populations for years and then occur at very high populations (e.g., flea beetle, lygus). This variability is one reason that research on insect management may be more conclusive if conducted over several to many years on organic farms. Farmers can expect an occasional year of very heavy insect pest pressure despite integrated whole system management that is successful overall. The risk of infrequent yet serious arthropod infestations may discourage otherwise willing farmers from converting acreage to organic. Research to understand and reduce this risk would be helpful.
References and Citations
- Levy, T. and B. Sideman. 2016. Managing cabbage aphid in Brussels sprout [Online]. Research Report. University of New Hampshire. Available at: https://extension.unh.edu/resources/files/Resource006332_Rep9072.pdf (verified 26 Jan 2021).
- Natwick, E. T., J. J. Stapleton, and C. S. Stoddard. 2012. Cucumber beetles. University of California Agriculture and Natural Resources (UCANR) Publication 3445. (Available online at: http://ipm.ucanr.edu/PMG/r116300511.html) (verified 26 Jan 2021).
- Natwick, E. T. 2009. Flea beetles. University of California Agriculture and Natural Resources (UCANR) Publication 3442. (Available online at: http://ipm.ucanr.edu/PMG/r108300511.html) (verified 26 Jan 2021).
- Pedersen, A. B., and L. D. Godfrey. 2011. Evaluation of cucurbitacin-based gustatory stimulant to facilitate cucumber beetle (Coleoptera: Chrysomelidae) management with foliar insecticides in melons. Journal of Economic Entomology 104:1294—1300. (Available online at: https://doi.org/10.1603/EC10213) (verified 26 Jan 2021).
- University of California Integrated Pest Management Program. Agricultural pests [Online]. Available at http://ipm.ucanr.edu/PMG/crops-agriculture.html (verified 26 Jan 2021).
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