Phytophthora is the genus name given to a group of fungus-like organisms that have tremendous impacts on plants. Recent research indicates Phytophthora is closely related to brown algae and diatoms. Of the many documented Phytophthoras, a few dozen species cause disease on vegetable, fruit, ornamental and forest plants grown worldwide.

Phytophthora has a notorious record for damaging crops. One of the earliest notable cases involved Phytophthora infestans, which caused epidemics of late blight on potato in Europe in the 1840s to 1850s. Devastating losses of potato crops resulted in famines, human suffering and death, and forced migrations. Another species, P. cinnamomi, caused the loss of hundreds of plant species in Australia. Such widespread decline threatens the plant and animal ecosystems in this region. And even closer to home, in coastal California and southern Oregon, P. ramorum (sudden oak death) has killed millions of tanoak and coast live oak trees, and imposed the destruction of millions of ornamental nursery plants due to state and federal regulatory measures. This article will focus on Phytophthora problems of annually grown row crops.

Types of Phytophthora Diseases
Phytophthora is a plant pathogen that resides in the soil. However, this soilborne pathogen can cause both belowground and aboveground diseases.

Root and crown rot
The majority of Phytophthora diseases involve tissues in contact with infested soil (Table 1). Roots are directly infected by Phytophthora in the soil; such roots become gray, brown or black in color. Roots later decay, with outer layers of the root sloughing off, leaving intact only the central wiry xylem core. While the stems and crowns of annual crops can be directly infected by Phytophthora present in the rhizosphere, it is common to have root infections progress up the root and into the crown. Diseased crown tissues likewise become discolored and decayed. More fibrous row crops like strawberry will also manifest discolored roots and crowns. However, these roots and crowns usually retain their structure and do not have the soft decay symptom.

All row crops having root and crown infections can appear delayed in development, stunted and deficient in nutrients due to non-functional roots. With time, these plants wilt, collapse and die. Fruit-bearing row crops can develop a gray to brown rot on fruit if such fruits are in contact with soil or puddled water. Fruit diseases can be seen on cucumber, melon, squash, pepper, tomato and strawberry. Postharvest decay can occur if fruits are infected in the field prior to harvesting.

Foliar blights
Some Phytophthora species can produce airborne or splash-dispersed spores that can infect leaves, stems and fruit that are not touching the ground (Table 1, see page 14). Initial symptoms include small, brown or gray lesions. Such lesions rapidly expand to affect large areas of the foliage, causing it to collapse. Fruits can also be infected by these aerial spores, resulting in fruit rot. Collectively, such diseased foliage and fruit are called blights. As previously mentioned, one of the best known foliar Phytophthora diseases is late blight of potato and tomato caused by P. infestans. Phytophthora capsici causes both root and crown rot diseases as well as foliar blights on cucurbits and other vegetables. While not formally called a “blight,” P. ramorum causes aboveground diseases on foliage, twigs, branches and trunks of many woody trees and shrubs.

Biology and Disease Development
Phytophthora species are labeled with the common name “water molds.” This is an appropriate name because these organisms are closely connected to water. If sufficient soil moisture is present, Phytophthora will grow mycelium like fungi. If host roots and favorable soil water conditions are present, Phytophthora will produce asexual reproductive structures called sporangia. Sporangia are flask- or oval-shaped structures within which are made zoospores. Zoospores released from these sporangia will swim in the soil water in the direction corresponding to increasing gradients of root exudates, land on roots and initiate infections. Sporangia and zoospores are short-lived structures; if a host root is not found or if soil conditions become too dry, these structures shrivel up and die.

In addition, Phytophthora forms a second type of structure that is spherical, with a thick resilient cell wall, that is called an oospore. Oospores are sexual structures that allow Phytophthora to recombine genetically and form diverse genotypes and strains. With their thick walls, oospores enable the pathogen to survive periods when the soil is dry and host plants are absent. Oospores are the likely means by which these pathogens are spread when contaminated soil is moved from field to field.

Detection and Diagnostics
Confirmation that Phytophthora is causing a disease requires laboratory testing. Traditional culturing methods, in which pieces of diseased plant tissue are placed into Petri dishes containing selective agar media, are still very useful. More advanced and rapid detection tools include serological methods (such as lateral flow devices or ELISA) in which specifically designed antibodies detect the antigens of Phytophthora and molecular methods (such as qPCR or RPA) in which molecular markers target the Phytophthora DNA. In seeking confirmation of Phytophthora diseases, make sure the diagnostic lab has experience with Phytophthora and uses the appropriate tests.

Diagnostic precision is needed because several soilborne pathogens including Phytophthora cause similar symptoms on row crops. Plant pathogenic species of Pythium and Phytophthora in particular cause very similar root rots, crown infections, foliage yellowing, leaf wilting, poor overall growth and death of the plant (Table 2). Even systemic vascular wilt pathogens such as Fusarium and Verticillium can cause aboveground symptoms that resemble Phytophthora root and crown diseases (Table 2). With so much economic capital committed to the growing of high-value row crops, guessing which pathogen is responsible for losses is too risky. Knowing which pathogen is causing plant loss will help the grower optimize disease management strategies.

Managing Phytophthora Managing soilborne Phytophthora diseases uses strategies like those deployed against other soilborne pathogens. However, unlike many other soilborne pathogens, post-plant chemical control is a viable option against Phytophthora.

Diagnosis
Have qualified professionals confirm that Phytophthora is the issue; in some cases, it is useful to also know which species of Phytophthora is involved.

Site selection
Choose fields that do not have a history of Phytophthora problems and that have well-draining soils. Soils higher in clay content have been associated with increased risk of Phytophthora.

Crop rotation
If Phytophthora is a concern, avoid back-to-back plantings of the same susceptible crop. Rotate with crops that are not known to be susceptible to the Phytophthora present at that location. Selection of non-susceptible crops will depend on the identification of the Phytophthora species (Table 1).

Irrigation management
Because Phytophthora is dependent on wet soil conditions, carefully schedule irrigations to prevent over watered, saturated soils. Low-flow irrigation systems such as drip irrigation for strawberry and microsprinklers for tree crops, can help discourage Phytophthora outbreaks. When possible, route excess or ponding water away from the production area with the use of ditches, raised beds or slopes.

Sanitation
Sanitation refers to measures used to prevent the introduction or spread of the pathogen in the growing location. Because Phytophthora resides in soil, avoid moving mud-encrusted farm implements from infested areas to clean fields. Avoid using transplants, cuttings and other vegetatively propagated materials that show disease symptoms and are infected with Phytophthora.

Fungicides
For some crops, applying fungicides to the crop may provide some protection. Because Phytophthora is not a true fungus, fungicides with modes of action effective against oomycete diseases are necessary. The repeated use of products having the same mode of action can result in Phytophthora populations that are insensitive (=resistant) to those products; therefore, fungicide applications should include products having different modes of action.

Resistant or tolerant cultivars
There appear to be relatively few row crop cultivars that are genetically resistant to Phytophthora; on the other hand, some cultivars (e.g., the strawberry cultivar Radiance) are known for their increased susceptibility to Phytophthora diseases.

The IPM components for managing soilborne Phytophthora diseases are also relevant for foliar Phytophthora problems and include proper diagnosis, site selection, crop rotation and genetic resistance. For foliar Phytophthora, the mode of irrigation can be extremely critical; the use of overhead sprinkler irrigation can exacerbate Phytophthora blights on cucurbits, tomato, potato and pepper, for example. Sanitation is a key factor for the prevention of epidemics of late blight since P. infestans can over-season on infected plant material. For example, diseased potato tubers, left in old fields or lying in cull piles near production areas, are a source of airborne spores that can infect new plantings. Managing foliar Phytophthora diseases relies more heavily on protectant fungicide sprays than control programs targeting soilborne Phytophthoras. For this reason, careful field scouting plays a critical role for early detection of symptoms and deployment of fungicide tools.

Fungal canker diseases of sweet cherry trees can be devastating to an orchard’s productivity and longevity and thus constitute a major threat to the cherry industry in California. Managing canker diseases has been challenging for growers as no control strategy alone suffices to manage these diseases. With funding from the California Cherry Board, the Trouillas Lab at UC Davis has worked during the past several years to improve management of canker diseases.

Main Fungal Canker Diseases of Sweet Cherry
Main fungal canker diseases of sweet cherry in California include Calosphaeria canker, Cytospora canker and Eutypa dieback, with Calosphaeria canker being the most widespread canker disease in the state. These diseases affect cherry trees in all cherry-producing areas worldwide, including Australia, Chile, France and Turkey. Canker diseases are caused by the plant-pathogenic fungi Calosphaeria pulchella, Eutypa lata and Cytospora sorbicola. These fungi infect and colonize the wood of cherry trees, killing branches, scaffolds and trunks, and causing important yield losses. Fungal cankers are to be distinguished from bacterial canker caused by the bacterium Pseudomonas syringae, which mostly affect the bark of cherry trees but also can lead to the killing of branches and entire trees.

Symptoms of Fungal Canker Diseases
A canker in woody plants usually refers to a lesion produced in the bark of twigs and branches. However, most fungal canker diseases colonize both the bark and internal wood tissues causing canker rots or wood cankers that persist for years. The dead area can block water and nutrient transport thus causing the dieback of affected branches. Wood cankers typically consist of reddish-brown to dark-brown discoloration of xylem tissues and may vary in shape from wedge-shaped to round, or irregular. Typically, if you cut through a disease branch on a cherry tree, canker infection will appear as vascular (wood) discoloration (Figure 1), which indicates a disruption in the flow of water and nutrients through the tree vascular system. It is also common for canker diseases to produce gumming near the infected area.

Biology of Fungal Canker Diseases
Calosphaeria pulchella and Cytospora sorbicola commonly produce fruiting bodies in sweet cherry trees. These can be observed easily beneath the periderm of dead or infected branches after peeling the external bark tissue with a knife. This method is a great way to diagnose canker diseases in the field. Calosphaeria pulchella produces fruiting bodies or perithecia occurring in groups with long cylindrical necks that emerged together through the bark at lenticel openings (Figure 2). Spores of Calosphaeria pulchella are primarily dispersed via rain and wind and infect open wounds such as pruning wounds. Sprinkler irrigation that wets the tree trunks also can contribute to spore release in cherry orchards, particularly during summer months. Cytospora sorbicola can be recognized as it forms pinhead-sized pimples pushing through the bark of cherry trees (Figure 3).

These pimples are the reproductive structures of Cytospora. Under humid conditions, masses of spores may ooze out of the fruiting bodies in long, brownish, coiled, thread-like spore tendrils. These spore masses are then rain-splashed to fresh pruning wounds and other openings where infections initiate. Perithecia (the reproductive structures) of Eutypa lata are rarely observed on cherry trees in California. These mostly form on riparian trees such as willow or ornamental tree such as oleander as well as in apricot trees and eventually grapevine. Eutypa canker disease is more common in the Northern San Joaquin and Sacramento valleys as well as in Contra Costa and San Benito counties, and rarely occurs south of Merced County. During rainfalls, spores of fungal canker pathogens are air-dispersed or rain-splashed onto fresh wounds such as fresh pruning wounds where they germinate and initiate infection. Fungal mycelium then colonizes the heartwood before expanding into the sapwood, causing wood discoloration and the typical canker.

Management of Canker Diseases
To best manage canker diseases, we propose an integrated, preventive approach that minimizes risks of infection of sweet cherry trees by fungal pathogens. This integrated approach involves disease avoidance and prevention, combining cultural, chemical and biological control practices. First, pruning should be performed to avoid rain and when dry weather is predicted for at least two weeks. Pruning of sweet cherry trees may be done after harvest during late spring and summer when conditions are warm and dry and when no rain is forecasted. Canker pathogen populations will be at their lowest during this period and the risk for infection is reduced. However, spore release and infection of pruning wounds can occur during late spring if rain occurs and during summer if sprinkler irrigation that wets trees is used in the orchard.

Overall, cold winter temperatures are unfavorable to pruning wound infection by Calosphaeria, and winter pruning may be considered particularly in orchards and regions where Calosphaeria canker represent the main canker disease. Indeed, spores of Calosphaeria pulchella will not germinate at temperatures below 15 degrees C (60 degrees F), and pruning during cold winter period can prevent infection of pruning wounds by Calosphaeria pulchella. Infection of pruning wounds by Cytospora sorbicola can be avoided also by pruning sweet cherry trees in the coldest parts of winter when temperature is below 10 degrees C (50 degrees F). Winter pruning, however, generally will not prevent infection of cherry trees by Eutypa if rain is present at the time of pruning. So, winter pruning is best done during cold and dry weather conditions, with no rain in the forecast.

Because pruning wounds serve as the main entry sites for canker pathogens, these must be protected following pruning of trees, especially if pruning occurs during the wet winter and spring months or during summer in orchards that receive sprinkler irrigation that wet the trees. Water from rain and sprinkler irrigation combined with wind are important factors for aerial dissemination of canker pathogens. Our laboratory recently evaluated the efficacy of different compounds to protect pruning wounds from infection by canker pathogens. Of the different fungicidal compounds tested, Topsin M (Thiophanate-methyl) and Quilt Xcel (Azoxystrobin + Propiconazole) performed best against Cytospora and Eutypa pathogens of sweet cherry, allowing significant disease reduction. Biological, Trichoderma-based products (e.g. Vintec®, RootShield® Plus) provided significant protection of pruning wounds against all canker pathogens, and performed best at reducing infection by Calosphaeria pulchella. Fungicide or biocontrol products should be applied immediately after pruning to avoid infection at pruning wounds.

When orchards are seriously infected with canker diseases and branch dieback occurs, remove diseased branches/limbs at least 4 to 6 inches below any sign of wood discoloration. The pruning cut should be made into healthy wood to ensure that all the disease has been removed. Incomplete canker removal wastes time and money with little to no benefit in disease management. Dead branches left in the orchard or adjacent to living trees provide inoculum for further infection and should be removed and destroyed.

It is also advised to regularly disinfect pruning shears, particularly after cutting through dead wood, using common sanitizers or a flaming torch. Note that wood grinding or wood chipping potentially could release an important number of spores in orchards that could infect pruning wounds. Accordingly, the grinding or chipping of dead cherry wood should be avoided until at least several weeks following pruning. Although burning of cherry wood is restricted, it is often the best option to get rid of fruiting bodies from cherry canker pathogens that have developed on dead wood. Storing dead wood near orchards also will have no effect at reducing inoculum sources unless the wood is thoroughly covered and protected from rain and irrigation water.

Topping cherry trees to encourage new vegetative growth also has been linked to severe sunburn damage in cherry orchards. Branches with sunburn damage then become highly susceptible to both fungal and bacterial canker pathogens. Techniques that help limit sunburn in cherry trees are encouraged to avoid canker disease outbreak in orchards. These may include proper pruning and training to promote adequate branch and tree structures as well as whitewashing, which consist of applying white paint to the interior of scaffold branches to reflect light and reduce bark heating from exposition to direct sunlight.

Management of canker diseases of sweet cherry is difficult due to the diversity of canker pathogens affecting sweet cherry trees in California. However, disease management may be achieved when considering multiple factors linked to disease spread and infection timing. These include the weather and weather forecast at the time of pruning and irrigation practices in the orchards as well as the orchard location and history of canker diseases. An integrated approach that combines disease avoidance and prevention is critical to achieve best control as no curative practices are available. While pruning must be conducted outside of the high-risk periods for infection, it is strongly advised also to protect pruning wounds with a fungicide or biological control agents.

Disclaimer: Mentioning of any active ingredients or products is not an endorsement or recommendation. All chemicals must be applied following the chemical label, local and federal regulations. Please check with your pest control adviser to confirm rates and site-specific restrictions. The author is not liable for any damage from use or misuse.

Leafroll is the most widespread and devastating viral disease of grapevine worldwide. It reduces yield, delays fruit ripening, increases titratable acidity, lowers sugar content in fruit juices, modifies aromatic profiles of wines and shortens the productive lifespan of vineyards. The economic cost of leafroll is estimated to range from $12,000 to $92,000 per acre of ‘Cabernet Sauvignon’ in California (Ricketts et al. 2015).

Grapevine leafroll-associated virus 3 (GLRaV 3) is the most dominant virus in leafroll-diseased vineyards. This virus is phloem-limited and transmitted by vegetative propagation and grafting as well as by several species of mealybugs. Mealybugs are sap-sucking insects and pests of grapes. At high densities, mealybugs can cause complete crop losses, rejection of fruit loads at wineries and death of spurs, although small infestations may not inflict significant direct damage. Several mealybug species feed on grapevines in California vineyards, including vine mealybug (Planococcus ficus), grape mealybug (Pseudococcus maritimus), obscure mealybug (Pseudococcus viburni) and longtailed mealybug (Pseudococcus longispinus) (Daane et al. 2012). Vine mealybug is an invasive species and the most damaging of the mealybugs that occur in California vineyards. Unassisted, mealybugs have limited mobility, but immature instars (crawlers) can be dispersed over long distances by wind and other means.

GLRaV-3 is acquired within one hour or less when instar mealybugs feed on infected grapevines. The virus is transmitted in a similar short time to healthy grapevines (Tsai et al. 2008). Following inoculation of healthy grapevines, it takes at least three months for GLRaV-3 to be detected in inoculated grapevines using laboratory-based diagnostic assays and one year for inoculated vines to exhibit typical leafroll disease symptoms in the vineyard (Blaisdell et al. 2016). In most diseased vineyards, the dynamics of leafroll spread is influenced by virus incidence and mealybug population density (Arnold et al. 2017, Cooper et al. 2018). In addition, the two adjacent vines to an infected vine are more likely to become infected over time than their counterparts located across the row, suggesting a predominant within-row virus spread and a spatial dependence for secondary spread (Bell et al. 2018).

Current Management Options
There is no cure for leafroll in diseased vineyards. However, the disease can be managed by reducing the number of infected vines and by controlling mealybug vector populations. For example, the elimination of diseased vines (a strategy known as roguing) and their replacement with clean vines derived from virus-tested nursery stocks that test negative for economically relevant viruses, including leafroll-associated viruses, reduce the incidence of GLRaV-3 and limit its secondary spread in vineyards (Bell et al. 2018, MacDonald et al. 2021).

Spatial Roguing, a New Response to Leafroll
Modelling leafroll disease spread in relation to economic factors predicted when roguing diseased vines, if disease prevalence is less than 25% (Ricketts et al. 2015) and two immediate within-row neighboring vines on each side, regardless of their disease status (for a total of five vines in the case of one infected vine), a strategy referred to as spatial roguing is more effective at reducing the level of virus inoculum in a diseased vineyard than roguing only diseased vines (Atallah et al. 2015). This strategy was inspired by the fact that 1) mealybug crawlers are more efficient vectors of leafroll viruses than adults; 2) crawlers are more likely to move along rows than between rows; 3) leafroll spread predominantly occurs at a short spatial scale; 4) a healthy-looking vine that is adjacent to a diseased vine may be infected without exhibiting disease symptoms; and 5) disease symptoms are only apparent at least one year after inoculation by viruliferous mealybugs (Blaisdell et al. 2016). Predictive models suggested that spatial roguing targeting symptomatic vines and their four immediate neighbor vines, two on each side, would be of statistically significant greater economic value than spatial roguing targeting symptomatic vines and their two immediate neighbor vines, one on each side. Simulations further predicted that a nonspatial strategy targeting only diseased vines is less effective and more costly than spatial roguing (Atallah et al. 2015).

We applied spatial roguing in a ‘Cabernet franc’ vineyard with overall low leafroll virus prevalence (5%) and a low grape mealybug population density in New York and tested its effectiveness at reducing the incidence of leafroll disease and slowing virus spread (Hesler et al. 2022). Four treatments were applied to select vine panels from 2016 to 2021: (1) spatial roguing only, (2) spatial roguing in combination with insecticide applications targeting grape mealybugs, (3) insecticide applications only (no spatial roguing), and (4) no spatial roguing and no insecticide intervention (the untreated control). Results showed that virus incidence was reduced from 5% in 2016 to less than 1% in 2020 to 2021 in both spatial roguing treatments. Among vines in the insecticide-free, non-rogued control treatment, virus incidence increased from 5 to 16% from 2016 to 2021 (Hesler et al. 2022). Insecticides applied in 2016 to 2021 helped significantly reduce grape mealybug populations to near zero annually, while populations in the untreated control vines were 57- to 257-fold higher during the same period (Hesler et al. 2022). This work validated spatial roguing as a leafroll disease management response in a vineyard with low disease incidence and low grape mealybug abundance.

Spatial roguing adds to the overall cost of vineyard maintenance. Revenue losses directly related to spatial roguing were estimated in our study at $5,565 per acre over six years (Hesler et al. 2022). These estimates agreed with earlier predictions and underscored the economic value of spatial roguing, despite added costs relative to the costs of maintaining a healthy vineyard, particularly when considering a scenario of no intervention, for which $10,000 to $15,750 losses per acre were calculated over a 25-year lifespan of a ‘Cabernet franc’ vineyard in New York (Atallah et al. 2012). The cost/benefit analysis of roguing may need to be evaluated by individual vineyard owners who are willing to adopt this leafroll disease management strategy. Critical to the success of roguing is the health status of the replants. Replants should be sourced from nursery vine stocks (scions and rootstocks) that have been extensively tested for viruses, including leafroll viruses, and shown to be clean (Bolton 2020).

In the future, it would be interesting to test the effectiveness of spatial roguing in California vineyards where mealybug population densities are consistently higher than in New York vineyards. Similarly, it would be interesting to compare the efficacy of spatial and nonspatial roguing approaches as a response to leafroll disease management. Of equal interest would be a study to test whether a sequential roguing strategy based first, for instance, on spatial roguing to drastically reduce sources of virus inoculum, and then on nonspatial roguing to limit secondary spread would be of value. If carried out in different vineyards with distinct disease prevalence, rate of spread and mealybug species and abundance, such research would inform the best approach for leafroll disease management both from a biological and economical perspective.

A six-year experiment in a commercial ‘Cabernet franc’ vineyard with low disease prevalence and low-density grape mealybug populations in New York showed that spatial roguing and the combination of spatial roguing and insecticides significantly reduced the percentage of infected vines. By comparison, virus incidence among vines in the untreated control vine panels where roguing was not implemented and no insecticides were applied increased from 5% to 16% during the same period. This study was the first to demonstrate the effectiveness of spatial roguing at reducing the incidence of leafroll disease and limiting its spread. It will be interesting to see whether our results on spatial roguing are reproducible in other vineyards of New York, and in vineyards of other grape growing regions of the world, including in California, where many more mealybug species, including the vine mealybug, are of concern and reside at higher populations.

References
Arnold K, Golino DA and McRoberts N. 2017. A synoptic analysis of the temporal and spatial aspects of grapevine leafroll disease in a historic Napa vineyard and experimental vine blocks. Plant Dis 107:418-426.

Atallah S, Gómez M, Fuchs M and Martinson T. 2012. Economic impact of grapevine leafroll disease on Vitis vinifera cv. Cabernet franc in Finger Lakes vineyards of New York. Am J Enol Vitic 63:73-79.

Atallah S, Gómez M, Conrad JM and Nyrop JP. 2015. A plant-level, spatial, bioeconomic model pf plant disease diffusion and control: grapevine leafroll disease. Am J Agri Econ 97:199-218.

Bell VA, Hedderley DI, Pietersen G and Lester PJ. 2018. Vineyard-wide control of grapevine leafroll-associated virus 3 requires an integrated response. J Plant Pathol 100:399-408.
Blaisdell GK, Cooper ML, Kuhn EJ, Taylor KA, Daane KM and Almeida RPP. 2016. Disease progression of vector-mediated Grapevine leafroll-associated virus 3 infection of mature plants under commercial vineyard conditions. Eur J Plant Pathol 146-105-116.

Bolton SL. 2020. What every winegrower should know: viruses. Lodi Winegrape Commission. pp. 138.

Cooper ML, Daugherty MP, Jeske DR, Almeida RPP and Daane KM. 2018. Incidence of grapevine leafroll disease: effects of grape mealybug abundance and pathogen supply. J Econ Ent 111:1542-1550.

Daane KM, Almeida RPP, Bell VA, Walker JTS, Botton M, Falladzadeh M, Mani M, Miano JL, Sforza R, Walton WM and Zaviezo T. 2012. Biology and management of mealybugs in vineyards. In Arthropod Management in Vineyards: Pests, Approaches, and Future Directions, N.J. Bostanian, ed. (Springer), pp. 271-307.

Hesler S, Cox R, Loeb G, Bhandari R, Martinson T and Fuchs, M. 2022. Spatial roguing reduces the incidence of leafroll disease and curtails its spread in a ‘Cabernet franc’ vineyard in the Finger Lakes region of New York. Am J Enol Vit 73:227-236.

MacDonald, SL, Schartel TE and Cooper ML. 2021. Exploring grower-sourced data to understand spatiotemporal trends in the occurrence of a vector, Pseudodoccus maritimus (Hemiptera: Pseudococcidae) and improve grapevine leafroll disease management.

Ricketts KD, Gómez MI, Atallah SS, Fuchs MF, Martinson T, Smith RJ, Verdegaal PS, Cooper ML, Bettiga LJ and Battany MC. 2015. Reducing the economic impact of grapevine leafroll disease in California: identifying optimal management practices. Am J Enol Vit 66:138-147.

Tsai C-T, Chau J, Fernandez L, Bosco D, Daane KM and Almeida RPP. 2008. Transmission of grapevine leafroll-associated virus 3 by the vine mealybug (Planococcus ficus). Phytopathol 98:1093-1098.