Pest Of The Month: Alternaria Leaf Spot of Cabbage

Alternaria Leaf Spot of Cabbage

Identification

In addition to cabbage, cauliflower, broccoli, collards, mustards, and other brassicas are commonly infected. Alternaria also  can affect the edible flower parts of broccoli and cauliflower. Symptoms on broccoli and cauliflower appears as brown-black discolorations on the heads (sometimes referred to as brown rot). Spots on leaf blades vary in size from small dark circular spots to large black, brown, or tan spots 2 to 3 inches in size as infections progress. Leaf-spotting on margins of leaf blades can be confused with black rot symptoms. Old leaf spots become papery in texture and may tear and display a shot-hole effect.

Affected leaves may have a purplish cast. Larger spots often have a dark green-black coloration of fuzzy growth in the spots, usually concentrated in the center. This dark, fuzzy growth consists of the fungus spores (conidia) and spore stalks (conidiophores). The spore masses may be interrupted, forming concentric rings within the leaf spot as the result of interruptions in weather favorable for spore production.

Survival And Spread

The fungus can survive on or in crop debris, seed, and possibly cruciferous weeds. Spores are produced on old crop debris and leaf spots. In culture, the optimum temperatures for spore production are between 75°F to 82°F. If leaf wetness is prolonged, spore production may occur outside the optimum range of temperatures.

Spores are released during the day as the relative humidity diminishes. Movement of equipment or work crews in the field and wind aid in spore release and disease spread. Spores can blow more than one mile downwind from infected crops.

After landing on susceptible plant tissue, spores germinate in the presence of free moisture in the form of dew, rain, or irrigation water.

With longer periods of leaf wetting due to prolonged dew periods or heavy or frequent rains, the number of infections increases drastically and lesion size increases.

The fungus also may be seedborne.

Management Methods

An integrated approach is most effective in managing Alternaria leaf spot of cabbage.

• Purchase quality seed, preferably hot water-treated.

• Seed treatment with a broad spectrum fungicide will help reduce any inocula carried on the seed.

• Rotate crops and avoid planting crucifers on the same land in succession or in successive years.

• Purchase disease-free transplants.

• Begin a preventative fungicide spray program during transplant production and after plants are set in the field. More frequent applications may be necessary if wet conditions prevail. If control efforts are started after symptoms are widespread, control will be difficult.

Harvested fields should be disked in shortly after harvest to bury old crop debris.

Leave a Reply

One comment on “Pest Of The Month: Alternaria Leaf Spot of Cabbage

  1. H i am very much happy about our all work associated with that of Organic and its production…………………..which is very important for the Agriculture ………..

Featured Stories

CitrusForecast: South Florida Dry Season May See Fair Share Of Damp Days
October 31, 2014
Outlook calls for possible above-normal precipitation around region for fall and winter months. Read More
ProductionDrought Forcing California Growers To Rely On Groundwater
October 31, 2014
While the state issues curtailments to those with junior rights, growers are increasingly relying on groundwater to irrigate their crop. Read More
Crop ProtectionThe Unlikely Parallel Between Human And Plant Health
October 31, 2014
One of the notable national developments in the summer of 2014 was the unexpected occurrence of serious respiratory infections in Read More
VegetablesWhy You Should Be Trialing New Vegetable Varieties
October 31, 2014
Selecting high-performing selections is no easy task. Read More
FruitsCalifornia Growers Sue State Over Drought
October 30, 2014
They claim the State Water Resources Control Board illegally denied water deliveries. Read More
CucurbitsNew Watermelon Planting Program For The Southeast U.S.
October 30, 2014
Sakata seeking to make regional impact by providing in-demand material through several local producers. Read More
Leafy Vegetables3 Can’t-Miss Cabbage Varieties For Florida Growers
October 30, 2014
Reed's Seeds highlights a trio of high-performance selections for Sunshine State producers. Read More
Insect ControlTake Control Of Thrips In Your Greenhouse
October 30, 2014
Why such a foreboding title? Thrips, one of the tiniest pests of greenhouse crops, are the carrier of one of Read More
BerriesManage Black Root Rot Of Strawberry
October 30, 2014
Controls include preplant nematode analysis, three-to-five year crop rotations, and more. Read More
FruitsSexual Evolution May Bear More Fruit In The Orchard
October 30, 2014
Scientists take a closer look at genes and find new plant breeding possibilities. Read More

The Latest

CitrusForecast: South Florida Dry Season May See Fair Share O…
October 31, 2014
Outlook calls for possible above-normal precipitation around region for fall and winter months. Read More
ProductionDrought Forcing California Growers To Rely On Groundwat…
October 31, 2014
While the state issues curtailments to those with junior rights, growers are increasingly relying on groundwater to irrigate their crop. Read More
Crop ProtectionThe Unlikely Parallel Between Human And Plant Health
October 31, 2014
One of the notable national developments in the summer of 2014 was the unexpected occurrence of serious respiratory infections in Read More
VegetablesWhy You Should Be Trialing New Vegetable Varieties
October 31, 2014
Selecting high-performing selections is no easy task. Read More
FruitsCalifornia Growers Sue State Over Drought
October 30, 2014
They claim the State Water Resources Control Board illegally denied water deliveries. Read More
CucurbitsNew Watermelon Planting Program For The Southeast U.S.
October 30, 2014
Sakata seeking to make regional impact by providing in-demand material through several local producers. Read More
Leafy Vegetables3 Can’t-Miss Cabbage Varieties For Florida Grower…
October 30, 2014
Reed's Seeds highlights a trio of high-performance selections for Sunshine State producers. Read More
Insect ControlTake Control Of Thrips In Your Greenhouse
October 30, 2014
Why such a foreboding title? Thrips, one of the tiniest pests of greenhouse crops, are the carrier of one of Read More
BerriesManage Black Root Rot Of Strawberry
October 30, 2014
Controls include preplant nematode analysis, three-to-five year crop rotations, and more. Read More
FruitsSexual Evolution May Bear More Fruit In The Orchard
October 30, 2014
Scientists take a closer look at genes and find new plant breeding possibilities. Read More
Apples & PearsWashington Apples To Restart Shipments To China
October 29, 2014
Agreement reached between U.S. and Chinese governments to reinstate market access after two-year absence. Read More
EquipmentEnter To Win A Kubota At The Washington State Horticult…
October 29, 2014
Attendees have a chance to take home a new utility vehicle courtesy of Wilbur-Ellis and Western Fruit Grower. Read More
CitrusUSDA To Provide $4 Million For Honey Bee Habitat
October 29, 2014
The funds will go toward helping growers implement conservation practices to improve honey bee health. Read More
FruitsHuge California Drought Meeting Planned
October 29, 2014
State, federal officials to meet as forecasts for the coming year look bleak. Read More
PotatoesNew CEO At Black Gold Farms, A Top 100 Grower
October 28, 2014
Eric Halverson takes the reins at the potato operation, while his father Gregg will remain president of the farm’s board of directors. Read More
FruitsValent U.S.A., MGK Enter Into Marketing Agreement
October 28, 2014
Valent U.S.A. to manage the marketing and sales of MGK’s crop protection line of insect control products beginning in April 2015. Read More
VegetablesMultistate Land-Grant University Research Project Contr…
October 28, 2014
The project began in the 1970s as a Regional Initiative and has since expanded Internationally. Read More
FruitsMichigan State Offers Online Database Of Tree Fruit Dis…
October 28, 2014
Search engine helps growers identify several issues in the orchard. Read More