Posts Tagged: Verticillium
Gardening Confusions
By Susanne von Rosenberg, UC Master Gardener of Napa County Some gardening advice...
Not all wilted leaves are caused by lack of water. (gardeningknowhow.com)
Waterlogged soil could be a cause for wilted leaves. (greenmylife.in)
Fusarium wilt in strawberry. Known to affect tomatoes, too. (ucanr.edu)
Verticillium wilt on tomatoes. Caused by a soil fungus. (ucanr.edu)
Vertebrate pests damage roots, leading to loss of water to leaves. (ucanr.edu)
Using tree chips instead of bark chips conserves water. (sonorantreesvc.com)
Read the label. Follow directions exactly. (bgi-usa.com)
Woven landscape fabric is water and air permeable. (flowerarmor.com)
Weeds -do- grow through landscape fabric, and mulch. You might have fewer weeds, but they'll still need to be removed! (homeguides.sfgate.com)
Blog, Linda Chalker-Scott Horticultural Myths (pinterest.com)
Broccoli Rotations Lower Pathogen Populations and Reduce Disease Incidence of Verticillium Wilt
SUMMARY Two broccoli plantings immediately prior to growing the verticillium-susceptible crop is...
UCANR banner
Avocado Collapse!
It's that time of year to see some drama in avocado orchards. Once healthy-looking trees can suddenly turn brown in a weekend and all the surrounding trees still look fine. And it can be quite common in some years along the coast. The winter weather will have mild, cool even rainy days and then suddenly there's one of those 97 deg days and the tree goes down,
The entire tree or only one or several branches wilt suddenly when affected by Verticillium wilt. Leaves turn brown and die, but the dead leaves usually remain on the tree for several months. Brown to gray-brown streaks are visible in the xylem of the branches or roots when the bark is removed. Sometimes the streaking is visible in the branches, but often it is found at the base of the trunk.
Trees with Verticillium wilt often send out new, vigorous shoots within a few months after the initial wilting. If well cared for, affected trees often recover completely with no reoccurrence of the disease. However, not all trees survive an infection and disease symptoms sometimes reoccur after an apparent recovery.
The fungal pathogen Verticillium dahliae infects many hosts, including various berry and flower crops, cotton, eggplant, olive, pepper, stone fruit trees, strawberry, and tomato. Verticillium wilt is present throughout the state but is less common in avocado than root rot and canker diseases. Verticillium dahliae persists for years as microsclerotia in soil. Microsclerotia spread in infested organic matter and soil that is moved. The fungus infects through feeder roots, and then moves up in the water-conducting xylem system, restricting or preventing water movement to foliage from the roots.
No known methods are effective in curing infected trees. Trees often recover completely and display no further symptoms, even though they are still infected. After dieback ceases and new growth begins, prune off dead branches. Provide optimal irrigation and modest fertilization to promote new growth. If a tree dies from Verticillium, remove it. But give it a chance, there's a good chance it will recover.
In areas where V. dahliae is known to occur, plant Mexican rootstocks instead of the more Verticillium-susceptible Guatemalan rootstocks. Do not plant avocado on land where crops susceptible to Verticillium wilt have previously grown. Do not interplant avocado with other hosts of Verticillium, which are listed in publications such as Plants Resistant or Susceptible to Verticillium Wilt (PDF). Even if they have recovered, do not use trees infected with Verticillium wilt as a source of budwood or seed.
avocado verticillium
Verticillium Wilt (Try Saying That Three Times Fast): Managing VW
In the garden, Verticillium Wilt (VW) can affect potatoes, peppers, tomatoes, eggplant, some cole crops, tomatoes, lettuce, strawberries, cucurbits, artichokes, avocados, peaches, nectarines, caneberries, and apricots. It can also affect landscape plants and flowers. In fact, there are over 400 plant species that are affected by the Verticillium wilt disease (VW). Given the wide range of hosts that succumbs to VW, it is important to prevent, or at least manage, the disease.
The fungus persists in soil for long periods. Although infection is favored by cool weather, because the fungus interferes with water transport in the stems, crop damage is most severe during periods of hot weather when plants are stressed for water. This is one of those diseases that can “crop” up on you (har har snort, pun intended), but with some forethought, can be avoided or at least minimized. If you suspect that your soil is infected with VW, the best way to know for sure is to have your soil tested by a plant & soil diagnostic laboratory.
Use Resistant Cultivars. If you don't have a problem with VW, then a great way to avoid it is to try to select resistant cultivars when choosing your starts. Some cultivars are more tolerant than others. Practice proper cultural practices in order to avoid stressing plants. For example, if growing artichokes, don't take crowns to be used for propagation from where the disease has occurred (plant only pathogen-free plants). Likewise, don't plant annual artichokes in an area with a history of V. dahliae. All annual artichoke varieties are more susceptible to VW than the perennial Green Globe variety so consider planting only perennial artichokes.
Crop Rotation. Another way to manage VW is to rotate your crops. Don't plant the same crop/similarly susceptible crop in the same area/bed in consecutive years. Ideally, rotate out susceptible crops for 2 to 3 years. For example, rotate the tomatoes and peppers with non-host crops such as beans, corn or broccoli. Cereals, grasses, and legumes are good rotation crops.
Biofumigation. Planting broccoli, a non-host of VW, may also help reduce pathogen levels through a process called biofumigation: decaying broccoli residue, when disced into the soil, either gives off natural chemicals that can kill VW or alters the soil microflora so that VW survival is reduced. You can also use cauliflower too, but only in winter or early spring.
Soil solarization. In warmer areas of the state, solarization is an effective control of soilborne pathogens and weeds. Solarization is carried out after the beds are formed and when the weather conditions are ideal (30-45 days of hot weather that promotes soil temperatures of at least 122°F). The effectiveness of solarization can be increased by solarizing after incorporating the residue of a cruciferous crop, in particular broccoli or mustards, into the soil.
(all information courtesy of UC Davis ANR, Integrated Pest Management Program) For more information, see the links below:
Wilting Tomatoes
Help for the Home Gardener from the Contra Costa Master Gardener Help Desk
Client's Problem and Questions:
Client called (early September) and left a phone message that the her community garden colleague's tomatoes, although now 4 feet tall, set some fruit, but that the plant had suddenly started to turn yellow and appears that the plants won't surive. CCMG Help Desk responded with both a phone call and an email.
CCMG Help Desk Response:
As I mentioned in the phone message that I left for you this morning, the information in your phone message about the tomato problem your community garden colleague has experienced wasn't sufficiently detailed to allow us to diagnose the problem. You mentioned that the tomato had grown about four feet tall and had set some fruit, but that the leaves on the plant suddenly started turning yellow and it now appears that the plant won't survive.
Yellow leaves on tomatoes is associated with many different problems, including lack of nutrients, excess salts in the soil or in irrigation water, toxicity in the soil from nearby walnut trees, and many different plant diseases. You report that the plant had been growing well and producing fruit and declined very rapidly leads me to suspect that the cause may have been a vascular wilt disease.
There is nothing that can be done for plants that have Verticillium or Fusarium wilts. Plants that die should be removed and destroyed. Put the diseased plant refuse in the garbage. Don't compost it since doing so could contaminate the compost with the fungal spores. Crop rotation is of limited value as the vascular wilt fungi may survive in the soil for several years.
You can learn more about Verticillium and Fusarium wilts at these websites: http://www.ipm.ucdavis.edu/PMG/r783100911.html and http://www.ipm.ucdavis.edu/PMG/r783101011.html.
One other word of caution about something you mentioned in your phone message. You indicated that you are using free wood chip mulch from a tree service company in your community garden plot. You said that your plants are growing well and look beautiful, but you didn't mention whether you are growing vegetables or ornamental plants. We don't recommend the use of wood chip mulch in vegetable gardens. Using such mulches for vegetables leads to two different problems. One is that wood chips, if dug in, and as they haven't been fully decomposed, will rob much of the nitrogen from the soils. This depletion of a critical nutrient can affect some ornamentals. It is particularly a challenge for heavy feeders such as tomatoes. If your colleague was using wood chips as compost for her tomatoes, it's possible that one of the problems for her tomatoes was a lack of nitrogen which would also lead to yellowing of the leaves.
The other problem with using wood chip mulch in vegetable gardens is that such gardens need to be replanted after each growing season. The wood chips really get in the way when you're trying to prepare the planting beds, add compost, etc. It is not a good idea to simply work them into the soil since they will continue to decompose, using up the available nitrogen in the process.
A better mulch to use for vegetable gardens would be weed free straw or dried leaves.
Hope that this information is helpful to you and your colleague.
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.
We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/