Tackling Verticillium Wilt In Almonds

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

Nuts Stories
Citrus
August 17, 2017
How Wicked Will Winter 2018 Be in the U.S.?
The 200th edition of the Farmers’ Almanac reveals wide-ranging weather patterns and events that would require everything from shovels to shorts. Read More
Nuts
July 30, 2017
The New Normal of Almond Orchard Canopies
Just because an almond orchard has no live lower limbs doesn’t mean it’s not extraordinarily productive. Read More
Nuts
July 29, 2017
New Orchard Systems Advisor Returns Home
Luke Milliron, who’s back in the Butte County area, is ready to help growers, especially improving irrigation. Read More
Nuts
July 28, 2017
Self-Fertile Almond Dominates New Plantings
‘Independence’ almond — which cuts pollination and other cultural costs — now represents one-quarter of all plantings. Read More
Citrus
July 23, 2017
USDA Invests $7.6 Million toward Beneficial Insect Research
Projects to promote beneficial organisms as part of a pest control strategy. Read More
Fruits
July 14, 2017
Brown Marmorated Stink Bug Predator Egg Mass Found
Samuri wasp parasitized egg mass found in Southern New Jersey peach orchard. Read More
Mobile technology farming
Citrus
July 10, 2017
Practical Solutions Are Bringing Precision Agriculture Closer to Earth
Growing the budding ag-tech sector to maturity likely will require a deeper meeting of the minds between technologists and agriculturists. Read More
Nuts
July 7, 2017
Lab Opens to Test for Pistachio Problem
AgExperts Inc. is now testing for Rhodococcus bacteria, which has plagued growers for the past few years. Read More
Nuts
July 7, 2017
California Almond Crop Projected to Increase 5%
This year’s California almond crop is forecasted to exceed 2 billion pounds, according to the California Almond Objective Measurement Report Read More
Closeup of a managed bee hive next to a blueberry field
Citrus
June 28, 2017
Felony Charges in Beehive Thefts
The men accused of heading up an operation to steal and re-sell beehives, Pavel Tveretinov and Vitaliy Yeroshenko, 48, have Read More
Citrus
June 21, 2017
Storm Runoff May Recharge Aquifers and Your Crops
A new study hints that tapping into storm water during dry years does more than increase water table levels. Read More
honeybees
Fruits
June 6, 2017
Survey: Bee Loss Drops Last Season
Bee Informed Partnership says preliminary analysis of results show second-lowest loss rate recorded in last seven years. Read More
Nuts
June 3, 2017
Have Flooded Orchards? Keep an Eye out for Damage
While the damage from waterlogging or Phytophthora may not be immediately known, there are some warning signs to be on the lookout for. Read More
Managed bee hive boxes around a blueberry field
Nuts
May 25, 2017
Stolen Hives Recovered in Nearly $1M Heist
Man likely stole hives from across the state of California in the last three years. Read More
Nuts
May 16, 2017
Another Record California Almond Crop Forecast
Bearing acreage officially hits the million mark, though per-acre yields are off from 2016. Read More
The Latest
Nuts
September 12, 2017
Walnut Crop Expected to be Down 5%
While wet California winter was welcome to growers, some orchards were flooded, compromising root systems. Read More
Nuts
September 3, 2017
Codling Moth Monitoring Tips in Walnuts
Mating disruption doesn’t just affect those orchards directly involved; you need to consider the potential impact on nearby orchards. Read More
Insect Control
August 22, 2017
Stink Bug Threatens High-Dollar Crops in…
While populations are low, it appears invasive pest has recently stumbled upon the state’s peaches and almonds. Read More
Citrus
August 17, 2017
How Wicked Will Winter 2018 Be in the U.…
The 200th edition of the Farmers’ Almanac reveals wide-ranging weather patterns and events that would require everything from shovels to shorts. Read More
Nuts
July 30, 2017
The New Normal of Almond Orchard Canopie…
Just because an almond orchard has no live lower limbs doesn’t mean it’s not extraordinarily productive. Read More
Nuts
July 29, 2017
New Orchard Systems Advisor Returns Home
Luke Milliron, who’s back in the Butte County area, is ready to help growers, especially improving irrigation. Read More
Nuts
July 28, 2017
Self-Fertile Almond Dominates New Planti…
‘Independence’ almond — which cuts pollination and other cultural costs — now represents one-quarter of all plantings. Read More
Citrus
July 23, 2017
USDA Invests $7.6 Million toward Benefic…
Projects to promote beneficial organisms as part of a pest control strategy. Read More
Fruits
July 14, 2017
Brown Marmorated Stink Bug Predator Egg …
Samuri wasp parasitized egg mass found in Southern New Jersey peach orchard. Read More
Citrus
July 10, 2017
Practical Solutions Are Bringing Precisi…
Growing the budding ag-tech sector to maturity likely will require a deeper meeting of the minds between technologists and agriculturists. Read More
Nuts
July 7, 2017
Lab Opens to Test for Pistachio Problem
AgExperts Inc. is now testing for Rhodococcus bacteria, which has plagued growers for the past few years. Read More
Nuts
July 7, 2017
California Almond Crop Projected to Incr…
This year’s California almond crop is forecasted to exceed 2 billion pounds, according to the California Almond Objective Measurement Report Read More
Citrus
June 28, 2017
Felony Charges in Beehive Thefts
The men accused of heading up an operation to steal and re-sell beehives, Pavel Tveretinov and Vitaliy Yeroshenko, 48, have Read More
Citrus
June 21, 2017
Storm Runoff May Recharge Aquifers and Y…
A new study hints that tapping into storm water during dry years does more than increase water table levels. Read More
Fruits
June 6, 2017
Survey: Bee Loss Drops Last Season
Bee Informed Partnership says preliminary analysis of results show second-lowest loss rate recorded in last seven years. Read More
Nuts
June 3, 2017
Have Flooded Orchards? Keep an Eye out f…
While the damage from waterlogging or Phytophthora may not be immediately known, there are some warning signs to be on the lookout for. Read More
Nuts
May 25, 2017
Stolen Hives Recovered in Nearly $1M Hei…
Man likely stole hives from across the state of California in the last three years. Read More
Nuts
May 16, 2017
Another Record California Almond Crop Fo…
Bearing acreage officially hits the million mark, though per-acre yields are off from 2016. Read More