Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Help Desk Request: I'm delighted you're available to help diagnose garden problems! Below are four pictures of a grape leaf problem. I have four old vines - Flame and Thompson seedless - that grow against a south-facing solid fence. The vines are close enough that they are co-mingled across the fence. The problem currently is located in one area of the vines and was not visually noticeable three weeks ago. All the vines are vigorous and seem healthy except for the affected leaves. I have cut most of the leaves and vines that are visibly distressed and placed them in my green waste bin. In the 15+ years I've had the grapes I have never had this problem; however, this year I was VERY, VERY late in pruning back the vines, and did not complete the pruning until the new vines had grown a couple feet long. Perhaps the evil villain over-wintered because of my tardy pruning?
Any idea what the problem is - fungus, bug or insect critter, bacteria? I have not seen anything crawling on either side of the leaves. And, what is your recommended approach and treatment? Thanks in advance for your help!
Submitted Representative Images of Affected Grape Leaves (below)
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Help Desk with your issue of ‘bumps and holes' on your grape leaves.
Thank you for the pictures and note that the blister is on the top of the leaf and the bottom shows fuzzy white. We were able to diagnose simply from the damage itself. The bumps are the result of mites – specifically grape erineum mites. The good news here is that even though the mites infest the leaves, no management is necessary as they rarely lead to any crop losses.
Erinium mites are wormlike, light yellowish white and microscope so you really would need magnification to see the actual mites themselves.
Young leaves show bright pinkish or reddish swellings on upper surfaces. Corresponding areas on lower surfaces are concave and densely lined with a felty mass of plant hairs
The mites overwinter under outer bud scales and move to unfolding leaves in spring. They associate in small groups to feed on lower leaf surfaces; the result is production of masses of enlarged leaf hairs inside a blisterlike area on the leaf. On the undersides of the leaves, beneath the swellings, are concave, densely lined, felty masses of oversized leaf hairs in which the mite populations develop. As the population increases, some move to new areas or to other leaves. From mid-August to leaf drop, there is a movement back to the overwintering site underneath the bud scales.
You indicated that this is new to you and that you were a bit late pruning. I cannot explain for sure why this year and not prior years and I cannot be sure the late pruning added to this situation.
Following is a link to a UC Pest Management website on the subject but it does not really add to the information I have provided above. http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/PESTS/grerineummte.html
Good luck and enjoy those grapes, and do not hesitate to contact us again with garden problems.
Help Desk of the UC Master Gardener Program of Contra Costa County (EDC)
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Biog.
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
MGCC's Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your questions about grape culture.
Based upon the information you have provided, here are several reasons your grapevines may not flower and produce grapes:
- Grapevines need full sun to activate the flower blossoms. Without sufficient sunlight, the flower buds won't develop properly.
- Pruning the vines incorrectly may affect the blossoms. Most wine grapes are pruned severely in the winter, leaving only short spurs on the woody trunk and main branches. However, some grape varieties, such as "Concord," "Crimson Seedless" and "Thompson Seedless" are cane pruned. These varieties require longer branches, or canes, because the lowest buds may not produce fruitful vines. The non-productive vines should be trimmed back in spring and early summer to prevent them from shading the developing flower buds and blocking the sunlight, thus reducing the number of flowers produced that season.
- Grapevines thrive in well-drained, rich soil. However, if the soil contains too much nitrogen, or if you've over-fertilized, the grapevine may put all of its energy into foliage instead of flowers and fruit.
- Grapevines harbor a variety of pests that can affect the development of flowers and fruit.
- Grape blossoms are mostly wind pollinated, however, varieties that require both a male and female plant require cross pollination to produce fruit. This may be accomplished by wind or insects
Following are several links from UC leading to further useful information about grape culture and pests. These links also cover and expand on the reasons for lack of flowering and production listed above:
Hope that information helps. Please do not hesitate to contact the Help Desk again if you have further questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (SLH)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer our gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523, although we will be moving this spring. We will notify you if/when that occurs. We can also be reached via telephone: (925)646-6586, email: firstname.lastname@example.org, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/)/table>
Client's Request: (via earlier phone call) I have Zinfandel grapes in my backyard garden. Looking at them now it appears that they aren't providing me with a good harvest. I'm concerned about pruning them this winter to get the best harvest. Would you please provide me with the appropriate information about pruning Zinfandel grape vines.
MGCC's Help Desk Response: Thank you for contacting Master Gardeners with your Zinfandel grape pruning question. I understand that when you phoned our offices, the Master Gardener with whom you spoke mentioned that we occasionally have presentations on growing and caring for grapes. Right now, we have only one such presentation on the calendar. It will occur at “Our Garden” on Saturday, October 3, beginning at 10 a.m (click for more info). Our Garden is a demonstration garden that is maintained by our Master Gardener program. It is located at the corner of Wiget Lane and Shadelands Drive in Walnut Creek. This link will take you to a map where you can download driving directions: http://ccmg.ucanr.edu/?mapd=&calnum=267082
I believe that the presenter at Our Garden will demonstrate grape pruning on table grapes that grow in the garden. However, he is quite knowledgeable about grapes and will probably reserve some time to answer questions that attendees may have after seeing the demonstration.
Now for some general information about pruning Zinfandel grapes. As you may know, there are two primary systems of pruning for grapes. The system you use is based on the variety of grapes you are growing. Zinfadel grapes are typically spur pruned. (The other pruning system is called cane pruning.)
Pruning of grape vines typically occurs in the dormant season (any time after the leaves have fallen from the plants and before new growth begins the following spring… usually mid to late winter.)
In the first year the grapes are pruned, start by cutting each plant back to a single two bud spur. Page 11 of the PowerPoint presentation slides at this link shows a photograph of a two bud spur: http://afghanag.ucdavis.edu/a_horticulture/fruits-trees/grapes/presentations-powerpoint/PPT_Grape_Pruning_Systems.ppt. Keep in mind that the photo was taken after the buds had begun growing. When you do your pruning, the buds will not yet have begun growing.
When the plants start growing, you'll need to decide whether you are going to train them as bilateral cordons attached to a trellis or “head train” them which uses stakes to support the plants but does not require a trellis system.
This publication on growing Zinfadel from the University of California indicates that either cordon training or head training can be used for Zinfandel grapes: http://iv.ucdavis.edu/files/24366.pdf As you'll see in the article, the author indicates that many Zinfandel growers prefer to use head training. The reason is that Zinfandel tends to overcrop easily, and if the fruit is not thinned, it will ripen with difficulty or not at all. Because head training produces fewer fruiting spurs than cordon training, using head training will reduce the chance that you will accidentally allow too many grape clusters to remain on the plant.
Here is a UC diagram that illustrates how a bilatereal cordon trained spur pruned grapevine will look:
The best illustration I located of what head pruned grapevines look like appears on page 16 of this Oregon State University publication: http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/21285/ec1639.pdf The OSU publication focuses on table grapes, but the pruning principles would apply equally well for wine grapes.
Finally, keep in mind that once your vines are mature and fully trained, you'll need to do annual pruning to prompt development of new grapes and to keep them producing well. The OSU publication as well as the UC article on head-pruning also contain good information about pruning of mature, fully trained vines.
I hope that this information is helpful and that you have an opportunity to attend the presentation at Our Garden on October 3. You are welcome to contact us again if you have additional questions.
Help Desk of the Master Gardeners of Contra Costa County
Note: The Master Gardeners of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us//span>/span>
Client's Question and Request:
I'm in central county and growing Zinfindel Grapes in my backyard garden. The vines are now several years old and producing fruit this year. The grape leaves have now developed “blotches” and the grapes look “cloudy” and not very healthy. What's the problem and what can I do about it? The pictures below show the leaf damage and what the grape bunches look like.
MGCC Help Desk Response and Advice:
Based on the grape samples and the photos you provided, the problem with the grapes appears to be powdery mildew.
Powdery mildew is a common fungal disease on grapes. It first shows up as faint white powder on the grapes but later can progress to cause brown russeting on the developing grapes. That russeting was somewhat apparent on the grape samples you brought in. Affected fruit cannot ripen normally and may crack as it grows.
Shady conditions and lack of good air circulation favors the development of the disease on grapes. When the vines are pruned iduring dormancy so that shoots are positioned in the next growing season, try to prune so that the plants will allow exposure of the developing fruit to sunlight and good air circulation. Avoid overhead watering of the vines which can spread the fungal spores to new locations.
Next growing season, watch closely for the appearance of powdery mildew. Early signs of a developing problem include young emerging leaves being deformed or showing a puckered condition. Prune out such areas as soon as they appear and it may help to prevent new infections.
If you lose a large percentage of the grapes this season, you may also want to consider the use of fungicides to prevent a recurrence next year. Take a close look at this UC website which gives detailed information about different types of fungicide that can be used and includes directions on how and when they should be applied: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7494.html
We hope this information is helpful. You're welcome to contact us again with any further questions
Help Desk of the Master Gardeners of Contra Costa
Note: The Master Gardeners of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: firstname.lastname@example.org, or on the web at http://ccmg.ucanr.edu/Ask_Us/
Help for the Home Gardener from the Contra Costa Master Gardener Help Desk
Client's Questions and Problems:
Client lives in a condominium/town house complex in central Contra Costa County that permits individual gardens. The client grows both roses and grapes. Immediately adjacent, the Homeowners Association (HOA) maintains a privacy/sound wall covered in ivy (maybe English or Boston ivy). Client brought samples of the plants into the CCMG Help Desk for assistance identifying the plants' problems and what could be done about correcting them. All the plants look distressed with maybe a fungus or possible insect activity, the roses looking somewhat the same and also with black spots on the leaves, and the grape showing signs of distress including discolored leaves and withering. Several days after the client brought samples of the plant problems, and before CCMG could analyze plants for the problems, the client contacted the CCMG Help Desk again to inform HD that after reading an article in California Agriculture (2014, Jan-June, volume 68, page 20), it appeared that the grape leaves may be infected with Pierce's Disease (PD). Based upon the article, the client was concerned that all the grape vines should be removed.
Pierce's disease is caused by a strain of the bacteria Xylella fastidiosa, which blocks the water-conducting system of a grapevine, leading to vine death 1 to 5 years after the plant becomes diseased.
CCMG Help Desk Response:
This is a follow-up to your recent discussion with our MG volunteer, and a follow-up voicemail regarding the discoloration and die-back of your grape leaves and roses.
You are correct that it looks like your grapes have contracted Pierces' Disease. The photographs you viewed on line and the photos we have viewed in our library certainly seem to confirm the presence of the disease.
I don't know how many grape vines you have, but in case you have more than the one infected plant, here are some of the symptoms to look for:
According to our Pest Management resources:
“In vines that are infected in spring, symptoms of Pierce's disease first appear as water stress in midsummer, caused by blockage of the water-conducting system by the bacteria. The occurrence of the following four symptoms in mid- to late summer indicates the presence of Pierce's disease: (1) leaves become slightly yellow or red along margins in white and red varieties, respectively, and eventually leaf margins dry or die in concentric zones; (2) fruit clusters shrivel or raisin; (3) dried leaves fall leaving the petiole (leaf stem) attached to the cane; and (4) wood on new canes matures irregularly, producing patches of green, surrounded by mature brown bark. Delayed and stunted shoot growth occurs in spring following infection even in vines that did not have obvious symptoms the preceding year.
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 Pierce's disease symptoms late in the first season of infection, and these may be difficult to notice. 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 on the infected cane of susceptible varieties may wilt and dry. Tips of canes may die back; roots may also die back. Vines of susceptible varieties deteriorate rapidly after appearance of symptoms. Shoot growth of infected plants becomes progressively weaker as symptoms become more pronounced.
Climatic differences between regions can affect the timing and severity of symptoms, but not the type of symptoms. Hot climates accelerate symptoms because moisture stress is more severe even with adequate soil moisture.
A year after the vines are infected some canes or spurs may fail to bud out, and shoot growth is stunted. New leaves become chlorotic (yellow) between leaf veins, and scorching appears on older leaves. From late April through summer infected vines may grow at a normal rate, but the total new growth is less than that of healthy vines. In late summer leaf burning symptoms reappear.”
Management and Control
Control of sharpshooters is not effective, although removal of alternate hosts might help. Some alternate hosts are Bermuda grass, blackberry, and willow. There are many hosts though, so removal of these might not be effective either.
Removing diseased vines as soon as possible when Pierce's disease first appears is critical to help reduce infection of other vines. I would not recommend putting them into your own personal compost bin. If there is a large volume, you might want to consider burning it.
Remove the grapevines as they become unproductive. You could replant with less susceptible cultivars such as 'Sylvaner', 'Thompson Seedless', and 'Ruby Cabernet'.
Certain plants have been identified as preferred breeding hosts for the blue-green sharpshooter (places they will lay eggs). These plants should be avoided if possible.
|Blue-green Sharpshooter Breeding Plants|
As you can see, roses are one of the preferred breeding plants. Although Pierce's Disease doesn't infect roses, it is quite possible given that the sharpshooter prefers roses, and you mentioned that your rose is close to your grapes, that the plant is showing the effects from sharpshooter feeding.
Currently, the only other recommendations with respect to plant selection are to plant conifers, or to establish a non-irrigated xeriphytic (i.e., dry) landscape. These plants should not be attractive to blue-green sharpshooters.
Further information on identifying Pierce's Disease can be found at http://www.ipm.ucdavis.edu/PMG/C302/mt302sppiercedis.html
From the sample you gave us, and a search of other photos we have, it appears that your rose might be suffering from a couple of things – black spot and the effects of the sharpshooters.
Black Spot Symptoms
According to our resources, “Black spot causes black spots to develop on the upper surface of leaves and succulent stems. The spots have feathery or fiber like margins and no powdery growth on the undersides of leaves. Small black fruiting bodies are often present in spots on upper sides of leaves. Yellow areas develop around the spots. Leaves may drop.”
The black spot fungus requires free water to reproduce and grow, so leaves should never be allowed to remain wet for more than 7 hours. (When hosing off aphids, do so in the morning so leaves have a chance to dry by midday.) Provide good air circulation around bushes. Remove fallen leaves and other infected material and prune out infected stems during the dormant season. Black spot is usually not a problem during California's dry summers unless overhead sprinklers are used, but the disease can be serious where rainy summers prevail or in cooler areas. Miniature roses are more susceptible than other types, although a few varieties are reliably resistant to all strains of black spot. A combination of bicarbonate of soda plus light horticultural oil can be used to manage black spot (as well as powdery mildew). Use about 4 teaspoons of baking soda per gallon of water with a 1% solution of narrow-range oil. Avoid getting on open blossoms. Neem oil can also be effective. Preventive sprays of fungicides such as triforine or chlorothalonil may also be effective.
A UC IPM Pest Note (free), that will give you some more information on rose pest management can be found on the web at http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7463.html
I hope this helps. Thank you again for bringing this problem to us. It was a lot of fun to research.
Follow-up: Further Questions and CCMG Help Desk Response:
From the Client:
Thanks for all the helpful information. I see that I'll have my work cut out for me in taking out all the vines, cutting back the roses, and trying not to spread this further. I'll let my HOA know also, because I believe there is an extensive outbreak of something that has affected most of the ivy in the HOA's 30 acres. The ivy within a foot of my grape vines has all died off—and within 10 feet is a Liquidamber tree, and of course geraniums – all of the plants you listed as being breeding plants for the insects. My last question is should I be notifying the county ag department or vector control about this infection?
Follow-up Response: from CCMG Help Desk:
We did some checking and Pierce's disease is not a reportable problem in Contra Costa County, so you don't need to notify anyone.
We also don't think your HOA's ivy dieback is caused by PD, even though ivy is considered a host plant. There are also other insects and diseases that affect ivy, as well as cultural problems. I've been seeing many patches of ivy in the area that appear sunburned and water-stressed and even many drought-adapted plants are having serious problems this year. Here is information from UC that covers pest and diseases in ivy: http://www.ucdavis.edu/PMG/GARDEN/PLANTS/ivy.html. This may help your HOA trouble shoot the ivy problem.
Please feel free to call again if you have more questions.
Contra Costa Master Gardeners' Help Desk
Editor's Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523.