Editors: Alexander Purcell, University of California, Berkeley
Rhonda J. Smith, Viticulture Advisor, Sonoma County
NOTE: There are important additions to these guidelines because of the recent establishment of a new vector, the glassy-winged sharpshooter.
A new Pierce’s disease vector, the glassy-winged sharpshooter, has recently become established in California. This new vector is a serious new threat to California vineyards because of its faster and longer distance movements into vineyards. It inhabits in unusually high numbers citrus and avocado groves and some woody ornamentals that until now have not been sources of Pierce’s disease vectors. It has been seen in high numbers in citrus along the coast of southern California since the early 1990s. During the past few years it has become locally abundant further inland in Riverside and San Diego counties. In 1998 and 1999 high populations on citrus and adjacent vineyards were seen in southern Kern County. The glassy-winged sharpshooter will spread north into the citrus belt of the Central Valley and probably will become a permanent part of various habitats throughout northern California. There is no reason to believe it will not become established along the coast and inland at least as far north as southern Mendocino County.
Because the glassy-winged sharpshooter feeds much lower on the cane than other sharpshooters in California, late season (after May-June) infections introduced by the glassy-winged sharpshooter may survive the winter to cause chronic Pierce’s disease. This would enable vine-to-vine spread of Pierce’s disease, which has not been the case in California. Vine-to-vine spread can be expected to increase the incidence of Pierce’s disease exponentially rather than linearly over time, as has been normal for California vineyards affected by Pierce’s disease. The glassy-winged sharpshooter also feeds on dormant grapevines during the winter. Until more information about this aspect of glassy-winged sharpshooter’s role in spreading Pierce’s disease is available, growers should try to reduce numbers of glassy-winged sharpshooter present in vineyards at any time. Additionally, removing diseased vines as soon as possible when Pierce’s disease first appears in a vineyard may help reduce the infection rate.
Causal agent: Pierce’s disease (PD) is caused by the bacterium Xylella fastidiosa.
Mode of action
The bacterium lives in the water-conducting system of plants (the xylem) and is spread from plant to plant by xylem-feeding insects. The chief function of xylem tissue is to transport water and minerals from the soil to above-ground plant organs. Bacterial cells taken up by insect vectors from diseased plants attach to the mouthparts and multiply, forming a bacterial plaque. During subsequent feeding, bacteria dislodged from the insect’s mouth enter the host’s xylem tissues. In infected grapevines the bacteria multiply for several months and spread throughout the xylem system, eventually blocking the movement of water. Symptoms appear when a significant amount of xylem is blocked.
Insect Vectors
Insect vectors capable of transmitting PD belong to the sharpshooter (Cicadellidae) and spittlebug (Cercopidae) families. The blue-green sharpshooter (Graphocephala atropunctata) is the most important vector in the North Coast. The green (Draeculacephala Minerva) and red-headed sharpshooters (Carneocephala fulgida) are also present in the North Coast and are vectors under some circumstances.
Since the xylem fluid is under negative pressure, insect vectors able to tap into it must have strong muscles that operate the sucking pump in their mouthparts. These bulky muscles give the face a swollen appearance which differentiates them from other sucking insects.
Other sucking insects, such as grape leafhoppers are not vectors; they feed on mesophyll cells and phloem tissue. Recently a large leafhopper, Thamnotettix zeleri, which is not a PD vector but which is similar in appearance to some sharpshooter vectors, has been found in the North Coast. To be able to differentiate between sharpshooters and this look-alike non-vector, please contact your local UC Cooperative Extension Office for a key of distinguishing characteristics.
Vector capability and efficiency of bacteria transmission
Bacterial transmission to grape is extremely efficient for some vectors. Insects are able to transmit the bacteria immediately after acquiring it from an infected plant. Less than 100 bacteria per insect are required for efficient transmission. An infectious blue-green sharpshooter has more than a 90% chance of transmitting the bacteria.
Once the adult acquires the bacteria the insect remains capable of transmitting it throughout its life. Immature insects are able to transmit until they molt, shedding the lining of the mouth along with the outer skin. Every time immatures molt they must reacquire the bacteria by feeding on an infested plant to be capable of transmitting the disease.
Vector Habitat
Xylem-feeding insects require succulent plant tissue or rapidly growing plants as food sources. They are found primarily in habitats where soil moisture promotes vigorous plant growth. Grapes are a good feeding host for the vectors because they are pruned every year, thus producing succulent new growth annually.
In coastal areas, riparian (riverbank) vegetation is the principal breeding habitat for blue-green sharpshooters, which have been collected from over 150 species of plants. These insects shift their feeding preferences as the season progresses always preferring succulent growth. Blue-green sharpshooters can also be found in ornamental landscapes in residential areas or parks. Woody ornamentals when pruned, especially in the winter, will produce spring growth that is very vigorous and succulent. This growth is often very attractive to the insect, even when the same plants would otherwise be minor feeding hosts. For example, live oaks that are heavily pruned produce suckers that the blue-green sharpshooter finds highly attractive for laying eggs. Otherwise oaks are a transient feeding host for this insect in the spring.
In the Central Valley, irrigated pastures, hay fields, or grasses on ditch banks are the principal breeding habitats for the green and red-headed sharpshooters, which prefer grasses and certain annual weeds for breeding and feeding. Grapes are only accidental hosts of grass feeding sharpshooters.
Even though the blue-green sharpshooter is the most important vector in the North Coast, all three vectors are present in this region and the green and red-headed sharpshooter can be a source of the disease in vineyards near irrigated pastures or ditches.
Vector Life Cycle
- Blue-green sharpshooter
There is only one generation per year in most areas. Adults overwinter mainly in riparian habitats, but also may be distributed at low density in areas with trees and shrubs. Eggs are laid singly in green tissues of leaves and stems beginning in April, depending on temperature. Most adults (80-90%) breed in riparian areas, hence the majority of the eggs are laid within riparian plants. Adults that have started to migrate will lay their eggs in vines at the edge of the vineyard. Their dispersal into the vineyard increases as natural vegetation dries up. Most overwintered adults die out by the end of June.
The flightless immatures (nymphs) emerge from late April or early May through July and remain on the same plant where they had emerged from the eggs, thus the majority of the nymphs are found on riparian plants. Nymphs become adults between late June and the end of August. As adults begin to emerge in late June they move deeper into the vineyard. At the beginning of September, when grape foliage is less succulent, sharpshooters begin to move back into nearby natural habitats.
Blue-green sharpshooter breeding host plants (plants on which the insect will lay eggs):
| Woody Perennials | Perennial Herbaceous Plant | Ornamentals in Residential Settings |
| Wild grapes | California Mugwort | Ivy |
| Himalayan blackberries | Stinging nettles | Virginia creeper |
| California blackberries | Roses | |
| Elderberry | Fuchsia | |
| Sandbar willows | Periwinkle | |
| Snowberry | Geranium | |
| Wild rose | Liquid amber | |
| Woody shrubs |
- Green and Red-headed Sharpshooters
The green and red-headed sharpshooters have three generations per year. They feed primarily on grasses. The green sharpshooter breeds and feeds on water grass (Echinochloa crusgalli) Bermuda grass (Cynodon dactylon), perennial rye (Lolium perennae), and fescue grass (Festuca spp.). The red-headed sharpshooter breeds and feeds primarily on Bermuda grass. They are found on grasses in wet spots, sump ponds, irrigation ditches, irrigated pastures or where the growth of grasses is lush and continuous all year. They overwinter as adults and lay eggs from late February to early March. The overwintering adults do not live long (no later than March or April). Thus it is probably the second generation that migrates to the vineyard.
Vector characteristics and relationships to grapevines are presented in a Table at the end of this document.
Geographic distribution of PD
One consistent requirement of PD appears to be mild winters. PD is present across the southern US from Florida west through southern Texas to California. In the eastern US it extends up to Virginia. In the West it has not been found north of California or equivalent latitudes. In general, the disease is rarer and less severe in areas that are further north, more inland from the ocean or at higher altitudes. The geographical distribution of PD on grapevines appears to be related to the ability of the bacteria to survive winter temperatures. The effects of low winter temperatures on bacterial survival are not well understood.
Spread of the disease in vineyards
In the North Coast, the distinctive spatial patterns of the disease (a border effect with high mortality of vines adjacent to native vegetation) match the early season spatial distribution of the blue-green sharpshooter vector entering vineyards from their nearby overwintering habitat. Chronic vine infections are found in the first 200 to 300 feet from the blue-green sharpshooter breeding habitat receiving the initial adult migration. When vines are infected early in the growing season there is a long period of time for the bacteria to reproduce and spread throughout the vine. A high bacterial population present in the vine by autumn increases the chance the infection will survive through the following winter. This implies that eliminating vectors for disease control should be done very early in the season to most effectively prevent new chronic infections.
After June, the blue-green sharpshooter can be found throughout the vineyard even in sections where symptomatic vines are rare. Infective sharpshooters can establish infections of X. fastidiosa in grapevines throughout the growing season. Most vines (depending upon variety and vine age) infected late in the growing season “recover” during the winter, and are non-infected the following spring. For this reason vine-to-vine spread during the same growing season is not considered significant. Note that late-season infections usually have mild or no symptoms. It takes approximately five months for vines to show symptoms in the field. Thus, you will not be aware that overwinter recovery occurs unless vines are tested for the bacteria before and after the winter.
While vine-to-vine spread is not significant, vine-to-insect-to-alternate host may be a significant factor in reinfection from one year to the next. As feeding continues on an increasing number of infected vines during the season, the number of insects carrying the disease also increases. In the late summer and fall sharpshooters migrate to the riparian habitat carrying the bacteria to the alternate hosts where they overwinter. Since infected adults remain capable of spreading the disease throughout their lives, these overwintering insects are a source of infection the following spring.
Irrigated pastures, sump ponds, irrigation ditches or areas where Bermuda grass and other perennial grasses or sedges flourish and remain lush year-round are major sources of the green and red-headed sharpshooters. Although spread from these sources is not the most common, it has been documented in the North Coast. Cleaning up grasses and sedges growing along ditches and roads prior to bud break in grapes should prevent the green or red-headed sharpshooters from being a source of infection for PD.
Annual cover crops are not important vector sources unless the cover is allowed to grow throughout the year. Summer cover crops that result from repeated mowing and irrigation generally do not provide the kind of weeds or the permanent habitats needed to build up sharpshooter populations.
Ornamentals such as ivy, small periwinkle, rose, fuchsia and other woody plants support populations of the blue-green sharpshooter in residential or commercial landscape and can create ‘hot spots’ of PD in adjacent vineyards.
PD does not spread by way of contaminated pruning shears. Graft transmission does not appear to be a major factor in commercial vineyards. Hot water treatment of dormant cuttings (immersion at 45° C for three hours or at 50° C for 20 minutes) will destroy X. fastidiosa. If fall budding is done with fresh budwood make sure the buds come from a non-infected vine. Late-season infections in vines are symptomless. To ensure that a vine is free of bacteria, collect wood samples and test for the presence of bacteria.
Susceptibility of the disease in grapevines
Some vines infected during the season appear to recover from PD the first winter following infection. Recovery from PD depends on variety. In Cabernet recovery is high while in Barbera, Chardonnay and Pinot Noir it is low. In more tolerant cultivars, the bacterium spreads more slowly within the plant than in more susceptible cultivars. Once the vine has been infected for over a year (i.e. bacteria survive the first winter) recovery is much less likely. Young vines are more susceptible than mature vines, possibly because the bacteria can move more quickly through younger vines that through older vines.
Rootstock species and hybrids vary greatly in susceptibility. Testing of rootstock plants show that V. riparia is rather susceptible; V. rupestris (St. George) and 420A are very tolerant. Rootstock does not confer resistance to susceptible vinifera varieties grafted on to it.
Climate, variety and age determine how long a vine with PD can survive. One-year old Pinot Noir or Chardonnay can die the year they become infected, whereas chronically infected 10-year-old Chenin Blanc or Ruby Cabernet can live for more than five years. Long before that, however, these chronically infested vines will cease to bear a crop.
All vinifera cultivars are susceptible to PD but cultivars can vary markedly in
levels of field resistance and tolerance:
| Most susceptible | Less susceptible | Most tolerant |
| Barbera | Cabernet Sauvignon | Chenin Blanc |
| Gray Riesling | Gray Riesling | Sylvaner |
| Mission | Merlot | Ruby Cabernet |
| Pinot Noir | Napa Gamay | White Riesling |
| Petite Sirah | ||
| Sauvignon Blanc |
Alternate hosts of Xylella fastidiosa:
Many plants harbor the bacterium without having symptoms of disease. Of 100 plants tested by placing infective sharpshooters on them, 75 harbored the bacteria but only a few species developed disease symptoms. Natural vegetation near vineyards and wild plants distant from agricultural areas can harbor the bacteria.
Plant species vary in their role as reservoirs of Xylella fastidiosa for disease spread. Plant species are highly variable in how easily the PD bacterium infects the plant, how rapidly it will spread and the maximum population size it will reach within the plant. X. fastidiosa does not move systemically in all its plant hosts and must multiply in the plant for the vector to acquire bacteria.
In Vitis vinifera and in wild grape, the bacteria multiply, spread systemically and build up to concentrations of ten million to one billion bacteria per gram of plant tissue. The more the bacteria multiply and move within the plant, the greater the probability that a vector can pick it up by feeding on the plant. Blackberry is a systemic host like grape but has many fewer bacteria (1/100 to 1/1000 fewer), and these move more slowly than in grapevines. Mugwort is a propagative host (bacteria multiply) but not a systemic host. Thus sharpshooters can only acquire the bacterium from mugwort by feeding on the limited portions of the plant where the bacterium has multiplied after being introduced by the previous feeding of infectious vectors.
The PD strain of Xylella fastidiosa causes alfalfa dwarf disease and almond leaf scorch in California. In eastern U.S. various strains of X. fastidiosa cause phony peach disease and leaf scorch diseases in oak, elm, maple, mulberry, plum and sycamore. In South America strains of X. fastidiosa cause citrus variegated chlorosis and plum leaf scald. The relationship among the different strains is presently under investigation.
The role plants play as hosts of Xylella fastidiosa is presented in a Table at the end of this document.
Symptoms
Symptoms are caused by blockage of the water-conducting system by the bacteria. Water stress begins in midsummer and increases through fall. Summer and fall symptoms are more reliable for positive identification of the disease than spring symptoms.
First symptoms mid- to late summer
The combination of these three symptoms is a definitive indication that PD is present:
1) Leaves become slightly yellow or red along margins in white and red varieties respectively. As the disease advance leaf margins progressively dry or die (turn brown) in concentric zones.
2) Scorched leaves dry down and the blade falls, leaving the petiole attached to the cane.
3) Wood on new canes matures irregularly, producing patches of green, surrounded by mature brown bark.
Leaf symptoms vary among grape varieties. Pinot Noir and Cabernet Sauvignon have highly regular zones of progressive marginal discoloration and drying on blades. In Thompson seedless, Sylvaner and Chenin Blanc the discoloration and scorching may occur in sectors of the leaf rather than along the margins.
Usually only one or two canes will show PD symptoms late in the first season of infection. Symptoms gradually spread along the cane from the point of infection out towards the end and more slowly towards the base. By mid-season some or all fruit clusters may wilt and dry up. Tips of canes may die back, roots may also die back. Climatic differences between regions can affect the timing and the severity, but not the type of PD symptoms. Hot climates accelerate symptoms due to moisture stress even when there is more than adequate soil moisture. Vines deteriorate rapidly after appearance of symptoms. Shoot growth of infected plants becomes progressively weaker as symptoms become more pronounced.
Spring symptoms of vines infected the previous year (chronically affected vines)
Infected vines exhibit delayed and stunted growth. Some canes or spurs may fail to bud out. New leaves (first 4 to 8 leaves) become chlorotic (yellow) between leaf veins. Scorching appears first in leaves at the cane’s base (oldest leaves). Leaves are stunted and distorted with shortened ‘zig-zag’ intemodes.
From late April through summer PD infected vines may grow at normal rates, but the total new growth will be less than in healthy vines. In late summer leaf burning symptoms reappear.
The symptoms of PD can be easily confused with other diseases or phenomena that cause water stress, such as insufficient soil moisture or excessive salt concentrations.
| Agent | Similar sypmtoms | Distinguish by: |
| Eutypa | Stunted shoots and small chlorotic, distorted leaves. | Associated pruning wounds cankers (wedge-shaped discoloration in cross section). |
| Oak root fungus (Armillaria root fungus) | Wilting along with discoloration and drying of fruit and foliage. | Examine roots for white, threadlike fungal growth with ‘mushroom’ odor beneath the bark. |
| Measles | Some similar foliar symptoms | No irregular maturing of bark on cane. ‘Measles’ berries with round dark spots. |
| Phylloxera | Decline of vines. | Examine roots for galls, and bark that sloughs off easily. Leaf blades remain attached. |
| Drought-induced early Spring boron deficiency | Delayed bud break, slow shoot growth, distorted shoots with short internodes. Lower leaves may be fan shaped. | Shoot growth becomes normal by late spring. No leaf scorching occurs in the fall. |
| Late Spring boron deficiency | Irregular fruit set, numerous, distinctly shaped shot berries. Yellow mottling between leaf veins that may turn necrotic. | Fruit ripens to full maturity. Shoot growth becomes normal by midsummer without symptomatic leaves. |
| Salt in soil | Leaf scorching. | No irregular maturing of bark on cane. Leaves fall off normally in autumn. |
| Zinc deficiency | Small or stunted leaves with interveinal chlorosis, shortened “zig-zag” internodes | PD infected vines will test positively for zinc deficiency, but will not respond to zinc fertilization. |
Identification of X. fastidiosa
Positive identification of X. fastidiosa can be obtained by three methods: culturing the bacterium on selective media, serological test such as ELISA (Enzyme linked immunosorbent assay) or PCR (Polymerase chain reaction).
For cultural diagnosis a specialized media has been developed for isolating and growing the PD bacterium. Petioles are used to isolate the bacteria. An advantage of this technique is that it does not give false positives and it is a comparatively inexpensive diagnostic test. The disadvantages are that it is time consuming, colonies may require one to three weeks to develop, microbial contaminants cloud or obscure results and the bacteria can only be isolated from petioles during the summer and early fall.
ELISA is based on using antiserum to detect the presence of the bacteria. This technique is fast and relatively inexpensive. It is useful to confirm the presence of X. fastidiosa in symptomatic plants after June. The disadvantage is that it does not provide as sensitive detection of the bacterium as PCR.
PCR enzymatically amplifies specific parts of the bacterium’s DNA. This is the most sensitive technique to detect small numbers of bacteria in plants. It is specific for X. fastidiosa but has the disadvantages that it is expensive, cannot determine if the bacteria are dead or alive or how many bacteria are present in the sample.
Commercial Identification of the bacteria
Using ELISA, commercial laboratories can confirm if vines harbor X. fastidiosa. Make arrangements with the diagnostic laboratory for taking samples and shipping. Samples taken from August through October of symptomatic leaves which are still attached to green portions of canes (live tissue) generally give the most reliable test results. Tag the samples and the plant from which they were taken in order to later identify the infected and non-infected plants.
Management of the disease
Studies have shown that insecticide treatments of vector habitats adjacent to vineyards reduced PD incidence, but the degree of control was not promising for very susceptible varieties such as Chardonnay and Pinot Noir.
For establishing or replanting vineyards near a known or suspected PD ‘hot spot’ one should plant varieties that are less susceptible to PD.
When infection is coming from well irrigated grasses, check this area for presence of green or red-headed sharpshooters. If they are present prevent these vectors from breeding by weed control rather than by insecticide treatments.
Early Spring Vector Monitoring
- Place traps adjacent to “blue-green sharpshooter source areas” (e.g. riparian habitat, best on both sides of the river or creek and next to ornamental landscapes) and 50 feet into the vineyard. Place a minimum of six traps per vineyard block 100 to 200 feet apart. Start trapping in early March.
- Minimum size of yellow sticky traps is 4 X 7 inches.
- When the populations are low it is important to have many traps.
- Check traps once a week early in season and more frequently after two or three days of warm weather. Remove insects from trap after counting them. Replace traps every 2 weeks or if they become excessively dirty or discolored by moisture.
- When you catch more than three sharpshooters/trap/week, calculated in per week average (see example of trap catch calculations below), begin direct observations on vegetation around the trap and at the edge of the vineyard.
- As you begin to detect sharpshooters in the traps you may want to place a continuous yellow-sticky tape to detect ‘hot spots’. The tape will allow you to determine where the greatest concentration of blue-green sharpshooters enter a vineyard from surrounding vegetation. Tapes are not effective for mass-trapping of sharpshooters for control purposes. Support tape every 10 to 15 feet with a grape stake, fence post or sturdy tree trunk. Replace tape every two weeks to a month depending on wetness and debris.
Note: green and red-headed sharpshooters are not attracted to yellow traps. Use sweep net to monitor for these pests along pastures and ditches.
After catching three sharpshooters/trap/ week:
- Look for sharpshooters on host plants and on grapevines early in the morning when it is cool and sharpshooters don’t fly. To be able to see the vector on both sides of the leaf, squat down so that the leaves are backlit.
- Ideally, vector control should be done when warm weather increases foraging activity by the blue-green sharpshooter but before bud break. This is usually possible only when warm weather precedes bud break. In practice, most applications will be made after bud break.
Treat:
1) If after several successive warm days (above 70°F) there is a sharp increase, or more than an average of 7 sharpshooters/trap/week
- Treat those plants where you observe the vectors and the edges of the vineyard if new shoot growth is longer than a few inches (see instructions on vector control with insecticide below).
- Replace traps after spray.
- Keep monitoring traps and vegetation to make sure the vector population is down and stays down. Respray if trap catches exceed 7/week/trap. It is important to eliminate more than 95% of the vector population.
- Keep monitoring until late April or for a month after treatment.
- Monitor during May to July with a sweep net and visual search to see where sharpshooters are reproducing.
Example on how to calculate average blue-green sharpshooter (BGSS) trap catches per week:
| Trap # | Date set out or last checked | Date counted | # of days | # BGSS | #BGSSa/week |
| 1 | 3/17/95 | 3/22/95 | 5 | 1 | 1.40 |
| 2 | 3/17/95 | 3/22/95 | 5 | 0 | 0.00 |
| 3 | 3/17/95 | 3/22/95 | 5 | 1 | 1.40 |
| 4 | 3/17/95 | 3/22/95 | 5 | 2 | 2.80 |
| 5 | 3/17/95 | 3/22/95 | 5 | 0 | 0.00 |
| 6 | 3/17/95 | 3/22/95 | 5 | 1 | 1.40 |
| TOTAL | 3/17/95 | 3/22/95 | 5 | 5 | 1.17b |
G
Average # BGSS/trap/week
a # of BGSS/week = Divide the number of BGSS caught in that trap by the number of days the trap was up and multiply by 7.
b The Average # BGSS/trap/week is the sum of the # of BGSS/week of all trap divided by the number of traps.
Vector Control with Insecticide
- Monitor to determine appropriate timing (see monitoring).
- On vines use a systemic insecticide which will move in the xylem system. In the riparian area the only insecticide currently allowed under a Special Local Need label is Dimethoate 400.
- In the riparian area apply insecticide only with a ground rig- handgun sprayer.
- Coverage is critical. Apply onto a band of natural vegetation approximately 50- 100 feet wide along the vineyard edge. Apply especially to blackberry, elderberry, mugwort, peri-winkle, stinging nettle, snowberry, wild grape, and willows.
- Be extremely careful to AVOID DRIFT into water. In practice, this means spraying as soon as possible in the morning before winds increase.
- If sharpshooters have migrated to the vineyard and there are a couple of inches of new shoot growth, treat the first 200 to 300 feet in from the edge of the vineyard.
- It is best to treat during warm weather because sharpshooters need to move and feed in order to ingest the insecticide.
- In the lab, Dimethoate persists for about three to four weeks. In the field, persistence will depend on plant vigor, temperature, and rainfall. It is important to continue monitoring for sharpshooter activity after treatment.
- A maximum of two applications per year is allowed in the riparian area.
Vine Removal
- Remove vines that have had PD symptoms for more than one year; they are chronically infected and are unlikely to recover or continue to produce a significant crop. They may also provide a source of infection for sharpshooters that will overwinter nearby and might reenter vineyards the next spring.
- Remove vines with extensive foliar symptoms and severe die back of canes even if it is the first year you have seen it.
- Mark slightly symptomatic vines in the fall; reexamine for symptoms the following late summer or fall and remove vines that have PD symptoms for a second year.
Riparian Vegetation Management
In an effort to reduce PD infections in vineyards adjacent to riparian vegetation, long term University of California experiments are underway to assess the effect of vegetation management on disease incidence and severity. Understanding the role that each plant species in the riparian system plays in this disease will take time. The practice of removing blue-green sharpshooter breeding hosts and systemic hosts of Xylella fastidiosa is often prohibited or restricted. Several agencies from federal, state and local government have permit or similar authority over activities in or adjacent to the riparian area. In addition to addressing PD related concerns, any vegetation management plan must be acceptable or beneficial for wildlife and water quality and maintain other important values provided by the riparian habitat.
Pierce’s Disease Vectors and the Impact of their Habitat Proximity to Vineyards
| VECTOR | Blue-green sharpshooter | Green sharpshooter | Red-headed sharpshooter | Spittlebugs |
| Breeding Habitat | Riparian | Grasses in wet spots | Grasses in wet spots | Riparian |
| Breeding Host | Woody perennials | Sedges, nutgrass, water grass, rye and fescue grass | Bermuda grass | Grasses & herbaceous plants |
| Transmission Efficiency | High | Low | High | High |
| Occurrence in breeding habitat | Frequent | Frequent | Sporadic | Frequent |
| Movement into vineyard | Along riparian edge | Along pastures & ditches | Along pastures & ditches | Only adults along riparian edge, carried by wind beginning in May |
| Monitor | Yellow sticky traps | Sweep net. (Not attracted to yellow sticky traps) | Sweep net. (Not attracted to yellow sticky traps) | Yellow sticky traps and check vines visually |
The information contained in this document is current as of April 1997. Research continuing in both the field and lab addresses several of the issues summarized in this document. As a result, some aspects of what is discussed herein will change as our knowledge base increases. This should be thought of as a work in progress. Updated information, if it significantly modifies or contradicts what is presented, will be available from North Coast farm advisors — although perhaps not in written form. Call your local UC Cooperative Extension office to ask for current information.
Confine chemicals to the property being treated. Avoid drift onto neighboring properties especially gardens containing fruits and/or vegetables ready to be picked.
Dispose of empty containers carefully. Follow label instructions for disposal. Never reuse the containers. Make sure empty containers are not accessible to children or animals. Never dispose of containers where they may contaminate water supplies or natural waterways. Do not pour down sink or toilet. Consult your county agricultural commissioner for correct ways of disposing of excess pesticides. Never burn pesticide containers.
To simplify information, trade names of products have been used. No endorsement of named products is intended, nor is criticism implied of similar products which are not mentioned.
Blue-green sharpshooter feeding and breeding hosts and alternate host status of Xylella fastidiosa, 1996
Blue-green sharpshooter X. fastidiosa hosts
| Breeding | Feeding | Propagative | Systemic | Comments | |
| Alder, red and white | no | rare | no | no | non-host |
| Ash, Oregon | no? | occasional | yes | no | |
| Bay laurel, California | no? | occasional | yes | no | |
| Blackberry, California | major | major | yes | yes | Occurs in riparian habitat in shaded areas. Major propagative and systemic host of the bacteria. |
| Blackberry, Himalayan | major | major | yes | yes | Major propagative and systemic host of the bacteria. Occurs in riparian habitat and in drier locations such as along fenced rows, ornamental landscapes, along roads and railroads. These drier locations are not as important, because the growth is not very succulent for very long. |
| Broom, French | no? | rare | yes | yes | Major propagative and systemic host of the bacteria. |
| Brush, Coyote | no? | rare | yes | no | |
| Buckeye, California | no? | rare | yes | slight | |
| Coffeeberry | major | major | yes | ? | Not common near vineyards in Sonoma and Napa Counties, it is only attractive for the BGSS in moist and sunny or partially sunny locations. |
| Cottonwood | no | no | no | Non-host | |
| Elder, Box | no | rare | yes | no data? | |
| Elderberry | major | major | yes | yes | Major propagative and systemic host of the bacteria. |
| Grape, wild | major | major | yes | yes | No. 1 host for the BGSS and the bacteria. Find high levels of infection in nature, bacteria achieves highest number per gram of tissue, and multiplies and spreads faster than in other hosts. |
| Hemlock, Poison | no | minor | yes | yes | BGSS winter feeding host, not a significant host in the spring and summer. Very susceptible to Pierce’s Disease, gets very severe disease symptoms. Because it is an annual plant it is not a reservoir of the bacteria year round. |
| Ivy | minor | minor | yes | no | |
| Maple, Big leaf | no | rare | yes | sporadic | |
| Mugwort | major | major | yes | no | Common in the riparian area. It is attractive to BGSS as a feeding host as long as it remains succulent which is well into the summer. Because it is a propagative host of the bacteria but not a systemic host, insects can pick up the bacteria only at the site where a previous feeding insect has infected the plant. |
| Nettle, stinging | major | major | no? | no | Under the right conditions an excellent breeding host for the BGSS but a poor host of the bacteria. |
| Oak, Coast live and Valley | rare | minor | yes | slight | |
| Periwinkle ground cover | minor | major | yes | yes | BGSS breeding and feeding host at the end of winter and occasional feeding and breeding will continue where periwinkle is grown in shade with high moisture, e.g. riparian areas. Major propagative and systemic host of the bacteria and it survives the winter. |
| Plums, wild | minor | minor | yes | no? | |
| Poison oak | no | no | yes | no? | |
| Rose, Wild | minor | minor | yes | no data | Major feeding host when the plant is succulent. |
| Snowberry | minor | minor | yes | no data | |
| Sedge, Umbrella | no | minor/rare | yes | yes | Green SS feeding host, problem in ditches. Excellent propagative and systemic host of the bacteria, the plant gets a disease from the bacteria evident at the end of the summer. |
| Spice bush | no | no | no | no | Non-host |
| Walnut, Black | no | rare | no | no | Non-host |
| Willows, arroyo (yellow), red and sandbar | minor | minor | yes | no | In the case of red and arroyo (yellow) willows the bacteria multiplies but survives only for a few weeks. Willows when removed will tend to resprout and succulent sprouts are good BGSS feeding sites. |
? = insufficient data