Posts Tagged: Verticillium wilt
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...
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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:
Verticillium wilt and Compost Amendments
Verticillium dahliae is the cause of Verticillium wilt, a disease that affects strawberries and many other plant species, including annual vegetables, fruit trees, nut trees and fiber crops, as well as weeds and native plants in California. Once a susceptible plant is infected, V. dahliae can produce large numbers of survival structures (called microsclerotia) (Vallad and Subbarao, 2008), which can survive in the soil for more than 14 years (Wilhelm, 1955). In addition, V. dahliae can colonize the roots of many crops that are not susceptible to disease and may show no symptoms (Lloyd and Gordon, 2011). This provides another means by which the fungus can produce survival structures. Verticillium dahliae is easily spread between fields with soil on farming equipment. It can also be introduced with seed (Wu and Subbarao, 2014) or infected transplants. Owing to the ease of dispersal, a wide host range and production of long-lived survival structures, V. dahliae is resident in agricultural soils throughout the state. Whether or not Verticillium wilt occurs in a particular situation is determined by the susceptibility of the crop variety being grown and the abundance of inoculum in soil. Consequently, the absence of disease does not mean the pathogen is not present. In fact, it is likely that V. dahliae occurs at some level in most fields in coastal California. Good management practices aim to keep the inoculum level below a damaging threshold (Gordon and Subbarao, 2007).
Many growers use compost amendments to improve the physical and chemical properties of soil. Compost can also enhance the activity of microorganisms that are inhibitory to plant pathogenic fungi (Mazzola, 2004). However, compost made from crop residue may include plants that were infected with V. dahliae, and because microsclerotia can survive in animal guts (Markakis, 2014), manure may be contaminated as well. Proper composting is required to ensure that no viable microsclerotia remain in the final product. The California Composting Council and CalRecycle have established regulations that require materials reach 55 °C (131°F) or higher for 15 days or longer with a minimum of five turnings of the windrow during this time (Cal Recycle, Title 14, Chapter 3.1), which should be sufficient to kill V. dahliae microsclerotia in manure or crop residue (Baker, 1957). All state permitted composting facilities are visited monthly by the local enforcement authority (LEA) to ensure compliance with these regulations. Consequently, if your supplier is operating under a state permit, the compost you purchase is unlikely to be a source of inoculum of V. dahliae, and it would not be advisable to forego the benefits of compost amendments out of concern that this will increase the risk of damage from Verticillium wilt.
REFERENCES
Cal Recycle. Title 14, Chapter 3.1. Composting Operations Regulatory Requirements, Article 5. Composting Operation and Facility Siting and Design Standards, Section 17868. 3. Pathogen Reduction. http://www.calrecycle.ca.gov/Laws/Regulations/title14/ch31a5.htm
Baker, KF and Roistacher, CN. 1957. Heat treatment of soil. In K.F. Baker [ed]. The U.C. system for producing healthy container-grown plants. Calif. Agr. Exp. Sta. Manual 23:123-137.
Gordon, TR and Subbarao, KV. 2007. Production Guidelines: Verticillium wilt of Strawberry. California Strawberry Commission, Issue 1: 1-4.
Lloyd, M and Gordon, TR. 2011. Evaluation of ten leguminous cover crops as cryptic hosts for Verticillium dahliae. Phytopathology 101: S109-S109.
Markakis, EA. et al. 2014. Survival, persistence and infection efficiency of Verticillium dahliae passed through the digestive system of sheep.Plant Disease, (ja).
Mazzola, M. 2004. Assessment and management of soil microbial community structure for disease suppression. Annual Review of Phytopathology 42: 35-59.
Vallad, GE and Subbarao, KV. 2008. Colonization of resistant and susceptible lettuce cultivars by a green fluorescent protein-tagged isolate of Verticillium dahliae. Phytopathology 98:871-885.
Wilhelm, S. 1955. Longevity of the Verticillium wilt fungus in the laboratory and field. Phytopathology 45:180-181.
Wu, B and Subbarao, KV. 2014. A model for multi-seasonal spread of Verticillium wilt of lettuce. Phytopathology 104:908-917.
Windrows of compost. Photo courtesy Margaret Lloyd, UC Davis
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