Tackling Verticillium Wilt

Tackling Verticillium Wilt

I visited an almond orchard last summer in Manteca, CA, with second-leaf trees showing Verticillium wilt. Cool, wet spring conditions favor Verticillium wilt on young almond trees, and we certainly had that this year in the San Joaquin Valley. Leaves on one or more branches, often on only one side of the tree, will turn yellow and wilt early in the growing season.

Affected young shoots typically resemble a shepherd’s hook. When shoot, branch, or trunk tissue of infected trees is cut, the vascular tissue and often much of the heartwood will display dark discoloration. Foliar symptoms usually appear only on young trees (first to fifth or sixth leaf). Older infected trees do not normally exhibit symptoms of Verticillium wilt, though yields may be reduced as a result.

Verticillium dahlia, the causal fungus, can survive many years as hardened spores called microsclerotia, either in soil, in the debris of previous susceptible crops, or in roots of infected trees. The soilborne fungus invades tree roots and then grows up the xylem, or water-conducting tissues. The fungus eventually plugs up the xylem and the shoots wilt because they are not getting enough water. Hot summer temperatures eventually cause the fungus to dieback in scaffolds, but it can continue to live on tree roots. Do not immediately cut out diseased branches, for they often grow back nicely with the summer heat. Wait until winter to prune when you can accurately assess the damage.

Fungus Among Us

Verticillium naturally occurs in low populations in the San Joaquin Valley, but years of farming susceptible crops (tomatoes, cotton, cucurbits, strawberries, etc.) have dramatically increased microsclerotia populations in our soils. When replanting in an area where susceptible perennials were previously grown, try to remove as many roots of the previous crop as possible, and have soil samples taken to determine inoculum levels. Soil samples should be taken from the top 12 inches, where populations will most likely range from 0 to 60 microsclerotia per gram. Wilt can occur with as little as 1 to 3 microsclerotia per gram and the ideal environmental conditions (cool, wet soil).

Pre-plant fumigation with chloropicrin or combinations of methyl bromide and Telone (1,3-Dichloropropene, Dow AgroSciences) have reduced Verticillium populations. Solarization with clear plastic is also effective pre-plant, while black plastic can be used post-plant. To solarize soil before planting, cover moistened soil with clear UV-inhibited plastic in late spring, and leave the plastic in place during the hot summer months. To solarize soil after tree planting, cover the soil around the trees with black plastic and leave in place for one to two growing seasons.

When it comes to choosing rootstocks, Mariana 2624 has been shown to be somewhat more resistant to Verticillium wilt than peach or peach/almond hybrid rootstocks. Avoid interplanting young orchards with susceptible cover plants, such as cotton and tomatoes.

Leave a Reply

Featured Stories
Photo of New Guinea flatworm found near Coral Gables, FL
CitrusSouth Florida’s Newest Pest Has Significant Ooze Factor
July 2, 2015
The infamous New Guinea flatworm, one of the ‘world's worst invasive alien species,’ might have found a new home. Read More
Farm ManagementPMA Advocates For Improvements To Proposed FSMA Mandatory Food Recall Guidance
July 2, 2015
This week the Produce Marketing Association (PMA) submitted comments on behalf of its membership to FDA regarding the proposed Mandatory Read More
VegetablesUnited Fresh Leadership Program’s Class 20 Donates 28 Salad Bars To Schools
July 2, 2015
Over the past year, the twelve members of United Fresh Produce Industry Leadership Program’s Class 20 raised funds to support Read More
CitrusFlorida’s Young Farmers Working To Bridge Generation Gap
July 2, 2015
Leadership conference to give GenNext Growers tools to become better agvocates. Read More
ProductionUse Broccoli Rotations To Reduce Disease And Minimize Leaching
July 1, 2015
Crop rotations are a key production practice utilized by every grower. You recognize the importance of rotations to break insect Read More
CitrusIndustry Stakeholders Rip Report Linking Citrus Consumption With Skin Cancer
July 1, 2015
Associations react swiftly; call out flaws in study released by the Journal of Clinical Oncology. Read More
Cucurbits11 Pumpkin And Squash Varieties
July 1, 2015
This month’s variety specs feature focuses on pumpkin and squash varieties. Features highlighted include great disease resistance packages, excellent yield potential, Read More
VegetablesInterview With Hazera Global Onion Product Manager
July 1, 2015
Onion is one of the most produced vegetable crops in the world. A lot of expertise is required to develop Read More
EquipmentHarvest Trends: More Mechanization Needed For Vegetable Growers
July 1, 2015
As the labor supply declines, industry experts and growers say investing in the latest harvesting technology will be necessary. Read More
healthy piece of citrus
Citrus Achievement AwardNeglected Research, Future Growers Top Of Mind For 2015 Citrus Achievement Award Winner
July 1, 2015
Orie Lee advises young up-and-comers to supplement production knowledge with business acumen; calls for more focus on blight. Read More
The Latest
Photo of New Guinea flatworm found near Coral Gables, FL
CitrusSouth Florida’s Newest Pest Has Significant Ooze Factor
July 2, 2015
The infamous New Guinea flatworm, one of the ‘world's worst invasive alien species,’ might have found a new home. Read More
Farm ManagementPMA Advocates For Improvements To Proposed FSMA Mandato…
July 2, 2015
This week the Produce Marketing Association (PMA) submitted comments on behalf of its membership to FDA regarding the proposed Mandatory Read More
VegetablesUnited Fresh Leadership Program’s Class 20 Donates 28 S…
July 2, 2015
Over the past year, the twelve members of United Fresh Produce Industry Leadership Program’s Class 20 raised funds to support Read More
CitrusFlorida’s Young Farmers Working To Bridge Generation Ga…
July 2, 2015
Leadership conference to give GenNext Growers tools to become better agvocates. Read More
ProductionUse Broccoli Rotations To Reduce Disease And Minimize L…
July 1, 2015
Crop rotations are a key production practice utilized by every grower. You recognize the importance of rotations to break insect Read More
CitrusIndustry Stakeholders Rip Report Linking Citrus Consump…
July 1, 2015
Associations react swiftly; call out flaws in study released by the Journal of Clinical Oncology. Read More
Cucurbits11 Pumpkin And Squash Varieties
July 1, 2015
This month’s variety specs feature focuses on pumpkin and squash varieties. Features highlighted include great disease resistance packages, excellent yield potential, Read More
VegetablesInterview With Hazera Global Onion Product Manager
July 1, 2015
Onion is one of the most produced vegetable crops in the world. A lot of expertise is required to develop Read More
EquipmentHarvest Trends: More Mechanization Needed For Vegetable…
July 1, 2015
As the labor supply declines, industry experts and growers say investing in the latest harvesting technology will be necessary. Read More
healthy piece of citrus
Citrus Achievement AwardNeglected Research, Future Growers Top Of Mind For 2015…
July 1, 2015
Orie Lee advises young up-and-comers to supplement production knowledge with business acumen; calls for more focus on blight. Read More
Business PlanningTake Climate Change — Please [Opinion]
June 30, 2015
It’s a difficult issue because people tend to think of it in terms of something tangible — like the weather. Read More
NutsWalnut Nitrogen Budgeting Critical
June 30, 2015
Applying the right amount of N is not easy because walnuts take a lot, but these days you don’t want to apply too much. Read More
FruitsHighlights From The Ohio Produce Growers And Marketers …
June 30, 2015
American Vegetable Grower magazine made its way to the Ohio Produce Growers and Marketers Association (OPGMA) Summer Tour & Field Read More
Insect ControlAlabama Insect Scouting Report Indicates Armyworm Numbe…
June 30, 2015
Report discusses caterpillars, sucking pests, and cowpea curculio activity and management. Read More
Nutrient ManagementResearchers Say Cover Crops May Help Save Soil In Flood…
June 30, 2015
According to experts, planting cover crops may help preserve healthy soil in fields in fields left empty this year thanks to flooding. Read More
TomatoesGSPP Accreditation Enables Sakata Seed America To Offer…
June 30, 2015
The seed company is now authorized to store, treat, process, package, and distribute GSPP-certified tomato seed for the NAFTA market. Read More
MarketingThe Power Of Local Food [Opinion]
June 30, 2015
Summer is now in full swing and we have entered what I like to call “the season of farmers markets.” Read More
PotatoesInnovative Technology Is Necessary For Potato Growers T…
June 30, 2015
Historically, there has often been opposition or fear of new agricultural technologies and today is no different, but it is critical that growers have access to technologies that meet consumer demand while using less land and conserving soil, water, and energy. Read More