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

Farm ManagementIndustry Organizations Sound Off On President’s Immigration Plan
November 21, 2014
Agriculture is not given the attention it so sorely deserves when it comes to the immigration debate. Read More
Insect ControlDon’t Turn Your Back On Striped Blister Beetles
November 21, 2014
Learn how to ID, the survival and spread, as well as management methods of this vegetable pest. Read More
CitrusRamped-Up Predatory Mite Production To Benefit Growers
November 21, 2014
Biologics company Beneficial Insectary now rearing two species in its California facility. Read More
NutsArizona Pistachio And Pecan Growers Benefiting From High Prices
November 21, 2014
Pecan production alone is expected to double in the next 10 years. Read More
Apples & PearsOn The Road With The International Fruit Tree Association Study Tour To Italy Part 2 [Slideshow]
November 21, 2014
Attention to detail is evident in the production of high quality feathered apple trees at GRIBA’s nursery. Read More
Fruits2014 California Winegrape Harvest: Outstanding
November 21, 2014
It’s the earliest crop of the decade, but still a third in a string of great vintages. Read More
FruitsFetzer Vineyards Pioneers Zero Waste
November 21, 2014
Company achieves top sustainability certification by diverting 98% of its waste from the landfill. Read More
VegetablesFormer Harris Seeds Co. CEO, Per Jensen, Passes At 85
November 21, 2014
A passion for plants defined longtime industry influencer. Read More
GrapesPerfect Storm Hurts New York Concord Grape Growers
November 21, 2014
More than 10,000 tons of juice grapes are abandoned because of too much production and no market. Read More
FruitsClassic Turkey Day Dinner Costing Consumers More This Year
November 20, 2014
Despite increase, a family of 10 can still get stuffed for less than $50. Read More

The Latest

Farm ManagementIndustry Organizations Sound Off On President’s Immig…
November 21, 2014
Agriculture is not given the attention it so sorely deserves when it comes to the immigration debate. Read More
Insect ControlDon’t Turn Your Back On Striped Blister Beetles
November 21, 2014
Learn how to ID, the survival and spread, as well as management methods of this vegetable pest. Read More
CitrusRamped-Up Predatory Mite Production To Benefit Growers
November 21, 2014
Biologics company Beneficial Insectary now rearing two species in its California facility. Read More
NutsArizona Pistachio And Pecan Growers Benefiting From Hig…
November 21, 2014
Pecan production alone is expected to double in the next 10 years. Read More
Apples & PearsOn The Road With The International Fruit Tree Associati…
November 21, 2014
Attention to detail is evident in the production of high quality feathered apple trees at GRIBA’s nursery. Read More
Fruits2014 California Winegrape Harvest: Outstanding
November 21, 2014
It’s the earliest crop of the decade, but still a third in a string of great vintages. Read More
FruitsFetzer Vineyards Pioneers Zero Waste
November 21, 2014
Company achieves top sustainability certification by diverting 98% of its waste from the landfill. Read More
VegetablesFormer Harris Seeds Co. CEO, Per Jensen, Passes At 85
November 21, 2014
A passion for plants defined longtime industry influencer. Read More
GrapesPerfect Storm Hurts New York Concord Grape Growers
November 21, 2014
More than 10,000 tons of juice grapes are abandoned because of too much production and no market. Read More
FruitsClassic Turkey Day Dinner Costing Consumers More This Y…
November 20, 2014
Despite increase, a family of 10 can still get stuffed for less than $50. Read More
Insect ControlFlorida Vegetable Growers Gain Access To New Nematicide
November 20, 2014
Methyl bromide alternative Nimitz approved for use on tomatoes, peppers, okra, eggplant, cucumber, watermelon, cantaloupe, and squash. Read More
EquipmentHighlights From EIMA International In Italy [Slideshow]
November 19, 2014
The 2014 edition of the International Agricultural and Gardening Machinery Exhibition (EIMA) boasted a record number of attendees from 124 countries. Read More
Farm ManagementVegetableGrowerConnect Delivers Results For Growers And…
November 19, 2014
Suppliers and growers got down to business in San Diego discussing current needs, solutions, and ways to increase efficiencies on the farm. Browse this slideshow for VegetableGrowerConnect highlights. Read More
FruitsFixing Farm Labor Woes Worth The Extra Effort [Opinion]
November 19, 2014
40th annual Ag Labor Relations Forum encourages outreach and action. Read More
BerriesPackaging Company’s Campaign To Benefit Future Organi…
November 19, 2014
Sambrailo Packaging of Watsonville, CA, has partnered with California Certified Organic Farmers and will donate a portion of the sales of clamshells made from plastic bottles. Read More
Apples & PearsOn The Road With The International Fruit Tree Associati…
November 19, 2014
Win Cowgill of Rutgers University details a trip through the one of the most concentrated fruit growing areas in the world, the South Tyrol region of Italy. Read More
IrrigationAlmond Grower Honored For Water Efficiency
November 18, 2014
Ongoing drought highlights the efforts of third-generation Madera County grower Tom Rogers. Read More
CitrusWomen’s Impact On Agriculture Impressive [Opinion…
November 18, 2014
Florida Agriculture Commissioner Adam Putnam says the long-term sustainability of farming depends on our youth. Read More