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Brassicaceae

General Disease Management in Brassicas

Production of Brassica Seed Crops in Washington State: A Case Study on the Complexities of Coexistence, Washington State University Extension Bulletin No. EM062E.

Crucifer Disease Guide - A Practical Guide for Seedsmen, Growers and Agricultural Advisors. Published by Seminis Vegetable Seeds, Inc.’s Plant Health Department and Seed Health Departments.

Small-Scale Cost-Effective Hot Water Seed Treatment
By Frank Morton (Wild Garden Seed), Tom Stearns (High Mowing Seeds), Nick Andrews (OSU Small Farms Extension)

Hot water seed treatment is an important way of reducing the risk of seed-borne diseases, especially for organic Brassica growers (seed, fresh market or processed market) now that Pacific Northwest growers are dealing with black leg and potential light leaf spot epidemics. Hot water treatment can improve our defense against diseases like blackleg, light leaf spot, Verticillium, Fusarium, Xanthomonas, Alternaria, Botrytis and many seed-bourne viruses.

The authors have put together some slides with some practical ideas for low-cost and efficient hot water treatment.
Download the Hot Water Treatment Slideshow.

 

Diseases Common to Brassica Vegetables

Disease: Black leg
Pathogens: Phoma lingam (sexual stage = Leptosphaeria maculans)
Host crops: Most members of the Brassicaceae (Cruciferae) = cabbage family, including broccoli, Brussels sprouts, cabbage, canola, cauliflower, various Chinese brassica vegetables, collard, kale, mizuna, mustard, oilseed rape, oilseed turnip rape, rutabaga, turnip, etc.), Sinapis (white and yellow mustard), and Raphanus (daikon and radish). Several wild species exist that may be infected by P. lingam including Descurainia (tansymustard), Sisymbrium (hedge mustard), and Thlaspi (penny-cress). This is a quarantine disease in six counties in northwestern WA and all counties east of the Cascade Mountains because of the risk of this pathogen to the brassica vegetable seed industry.

Black leg symptoms on a cabbage seedling grown from an infested seed lot. Note the small, black fruiting bodies (pycnidia) on the hypocotyl of the seedling.	Black leg infection of the cotyledon of a cabbage seedling grown from an infested seed lot. Note the small, black fruiting bodies (pycnidia) on the cotyledon.	Pycnidia of Phoma lingam on the base of the stem of a Brassica rapa plant, showing pink cirrhi oozing out of each pycnidium, containing thousands of conidia. The conidia are readily splash-dispersed.
Photo Source: Lindsey du Toit, Washington State University.

Black leg lesion at the base of the stem of an infected plant from a Brassica rapa seed crop. Note the small, black pycnidia embedded in the lesion.	Phoma leaf spot lesion with tiny, black pycnidia present in the necrotic, circular lesion, surrounded by a narrow, chlorotic (yellow) halo.	Black pycnidia of the black leg fungus, Phoma lingam, on an infected cauliflower seed. Note the amethyst-colored cirrhi (gelatinous matrix) oozing from the pycnidia, which indicates the strain of the pathogen is virulent (able to cause Phoma leaf spot or black leg of brassicas)
Photo Source: Cynthia Ocamb, Oregon State University.	Photo Source: Lindsey du Toit, Washington State University.

 

Disease: Clubroot
Pathogen: Plasmodiophora brassicae
Host crops: Broccoli, cabbage, cauliflower, brassicaceae (cruciferous) weeds, and radish.

Stunting from clubroot.	Below-ground symptoms of clubroot.
Photo Source: Lindsey du Toit

Disease: Downy mildew
Pathogens: Hyaloperonospora parasitica = Peronospora parasitica
Host crops: Most members of the Brassicaceae (Cruciferae) = cabbage family, including cabbage and cauliflower.

Downy mildew sporulation on cabbage leaves.			Sporulation of downy mildew on a cabbage seed pod in a cabbage seed crop.
Photo Source: Lindsey du Toit

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Cabbage and Cauliflower (Brassica sp.) – Downy Mildew {Staghead}

Pacific Northwest Plant Disease Management Handbook: Mustard Greens (Brassica juncea) – Downy Mildew {Staghead}

Downy Mildew of Crucifers. Plant Pathology Fact Sheet. Florida Cooperative Extension Service.

Brassica Downy Mildew. University of Massachusetts Amherst.

 

Disease: Light leaf spot
Pathogens: Cylindrosporium concentricum (sexual stage: Pyrenopeziza brassicae)
Host crops: Light leaf spot has been observed causing disease in canola (oilseed rape can be very susceptible), forage Brassica species, “field” turnip, other Brassica members including wild mustard, volunteer black mustard, vegetable Brassica seed fields, and Brassica species used as cover crops. It is likely that all brassicas crops grown in the Pacific Northwest are susceptible with a range of susceptibility within each crop species.

Light leaf spot on mustard.	Light leaf spot on Brassica.	Light leaf spot on Brassica.
Photo Source: Oregon State University Plant Clinic	Photo Source: Oregon State University Plant Clinic	Photo Source: Cynthia Ocamb, Oregon State University-Corvallis	Photo Source: Cynthia Ocamb, Oregon State University-Corvallis

Online Resources:

Light leaf spot OSU Disease Alert in crucifers 17 June, 2014 (pdf)

Disease: Ring spot
Pathogen: Mycosphaerella brassicicola

Photo Source: D.A. Inglis

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Cabbage and Cauliflower (Brassica) – Ring spot (Black Blight) 

Disease: White leaf spot
Pathogens: Pseudocercosporella capsellae (sexual stage: Mycosphaerella capsellae)
Host crops: White leaf spot and gray stem were observed during 2014 in canola research fields as well as in commercial seed fields of forage Brassicas and “field” turnip. White leaf spot was also detected in volunteer black mustard and forage fields. Susceptible hosts reportedly include species of Brassica (broccoli, cabbage, canola, cauliflower, Chinese cabbage, mustard, turnip, etc.) as well as radish and horseradish. Weedy types such as wild radish, wild mustard, and shepherd's purse are susceptible to white leaf spot and gray stem.

Late stage white leaf spot (yellowish spots) and Phoma leaf spot (grayish spots) on turnip.	Earlier stage of white leaf spot.	Gray stem of turnip.	Close-up of white leaf spot showing white conidia.
Photo Source: Cynthia Ocamb, Oregon State University-Corvallis

Online Resources:

White leaf spot OSU Disease Alert in Brassiceae (pdf)

Disease: White mold
Pathogens: Sclerotinia sclerotiorum
Host crops: Most members of the Brassicaceae (Cruciferae = cabbage family) and many other vegetables (see Diseases, pests, and other problems common to many vegetables: White mold )

White mold symptoms on a cabbage head.	Severe white mold in an overwintering cabbage seed crop.	Stem canker in a brassica seed crop caused by Sclerotinia sclerotiorum.
Photo Source: Lindsey du Toit

Black sclerotia of the white mold pathogen, Sclerotinia sclerotiorum, and remnant veins of a cabbage leaf following decomposition of the leaf by the pathogen.	A salmon-colored apothecium of the white mold pathogen produced in spring adjacent to a cabbage plant. The apothecium releases thousands of sexual spores (ascospores) into the air, which serve as a primary source of inoculum.
Photo Source: Lindsey du Toit

Online Resources:

Management of Sclerotinia in Turnip Seed Crops - A Clinic Close-up, Oregon State University Extension Service

Pacific Northwest Plant Disease Management Handbook: Cabbage and Cauliflower (Brassica sp.) – Sclerotinia Stem Rot and Watery Soft Rot

See Diseases, pests, and other problems common to many vegetables: White mold.

Insects/Mites

Common name: Root maggots (cabbage maggot and seedcorn maggot)
Latin binomial: Delia brassicae = Delia radicum (cabbage maggot), and Delia platura (seedcorn maggot)
Host crops: Cabbage maggot can damage and destroy root systems of all cole (crucifer or Brassicaceae) crops. Tunnels from the feeding maggots can become numerous in roots in crops with severe infestations. The tunnels provide wound sites for pathogens, particularly bacteria that can cause bacterial soft rot. The seedcorn maggot can affect many vegetable crops including snap, kidney, and lima beans, onion, corn, turnip, pea, cabbage, and cucurbits. They cause the most damage in spring to newly emerging seedlings, and can cause severe losses in plant stand.

Severe damage to a radish seed crop from cabbage maggots feeding on the roots, followed by development of bacterial soft rot.	Small holes where the cabbage maggot fed and tunneled inside a radish root, followed by colonization of the wound sites by soft rot bacteria that caused the lower 75% of the root to discolor and rot.	Holes inside a radish root where cabbage maggots fed and tunneled through the root, with early symptoms of secondary bacterial colonization (discolored, softened tissue) around the wound sites.
Photo Source: Lindsey du Toit, Washington State University

Online Resources:

 PNW Insect Management Handbook section on cabbage maggot affecting radish

Abiotic Problems Common to Brassica Vegetables

Problem: Boron (B) deficiency
Crops affected: Most crops can develop symptoms of boron (B) deficiency. Brassica or cole crops have moderate to high B requirements. B deficient cole crops can develop cracked, corky stems, as well as petioles and midribs. Broccoli, cabbage and cauliflower stems may become hollow and discolored. Cauliflower curds may turn brown and leaves roll and curl. Cabbage heads may be smaller than normal and discolored yellow. Cauliflower is the most sensitive of cole crops to B deficiency.

Boron deficiency in broccoli can cause external corkiness and scarring of the main stem, and hollowing of the stem internally.
Photo Source: Gail Ruhl, Purdue University Plant and Pest Diagnostic Lab		Photo Source: Lindsey du Toit, Washington State University

Online Resources:

Boron Deficiencies in Cole Crops, University of Delaware Extension

https://customers.hbci.com/~wenonah/min-def/cauliflr.htm

https://www.ipmimages.org/browse/subimages.cfm?sub=18132

https://www.spectrumanalytic.com/support/library/ff/B_Basics.htm

Boron mobility in plants. Chapter 7 from the book Plant and Soil by Patrick H. Brown, Department of Pomology, University of California, Davis and Barry J. Shelp, Department of Horticultural
Science, University of Guelph, Guelph, Ontario.

Boron Deficiency Symptoms U.S. Borax Corp.

Boron in vegetables U.S. Borax Corp.

 

Problem: Edema
Cause: A physiological problem prominent when air is cooler than the soil, soil moisture is high, and relative humidity is high. The low plant transpiration rates combined with an increase in water absorption by roots from the soil leads to increased cell turgor pressure, resulting in eruption of epidermal cells as the inner cells enlarge. Protrusion of the inner cells causes epidermal cells to die and discolor, resulting in a ’warty’ appearance that can be misidentified as a disease. Symptoms are usually worse on the lower leaf surface and on older (lower) leaves.
Host Crops: Numerous vegetables including spinach, brassicas, tomato, etc. Vegetables with waxy leaves, e.g., brassicas, tend to be most susceptible.
Photo Source: Pop Vriend Seed Co.

Symptoms of edema on the lower (abaxial) surface of a cabbage leaf, including calloused/warty protruberances from bursting of epidermal cells.

Online Resources:
Pacific Northwest Handbooks: Cabbage and Cauliflower Brassica SP Oedema Edema

What are these bumps on my vegetables? Edema or oedema: It doesn’t matter how you spell it, it still doesn’t look good. What is it, what causes it and how can I prevent it? Michigan State University Extension

Problem: Redheart
Cause: Freeze damage to inner leaves of a brassica head as a result of an extended period (>24 hours) of freezing in the field or in storage. Damage is often irreversible. Leaves several layers inside the head become watersoaked/glassy while outer leaves of the head appear normal. Internal affected leaves become tan or red in color, and may dry to a papery texture. A bad odor may develop. A dark zone may delimit the affected vs. healthy areas. Similar symptoms can be caused by exposure of cabbage heads to low oxygen levels or high carbon dioxide levels in controlled atmosphere storage.

Crops affected: Brassica vegetable crops with heads, e.g., cabbage. Some cultivars are more sensitive to redheart than others.

Photo Source: Osborne International Seed Co.

Harvest crops before extended periods of severe frost. If freezing conditions occur, allow heads to thaw completely before they are harvested. Monitor the heads at harvest for glassiness of the internal leaves. For longer-term storage, only store cabbage heads that have not been exposed to frost. Ventilate storage rooms adequately at temperatures just above freezing and high humidity.

Online Resources:
University of California Postharvest Technology. Cabbage (Round and Chinese types): Recommendations for Maintaining Postharvest Quality

Problem: Stem splitting
Crops affected: Any brassica crop grown for seed can develop stem splitting under conditions that promote very rapid growth (high soil moisture and warm temperatures).

Stem splitting in a winter canola crop in central Washington in spring (early May) resulting from very rapid growth under conditions of high soil moisture and sudden warm spring temperatures, following a supplementary nitrogen fertilizer application.				Stem splitting in a radish seed crop in central Washington.
Photo Source: Karen Sowers, Washington State University Dept. of Crop & Soil Sciences				Photo Source: Carrie Wohleb, Washington State University Extension Educator

Online Resources: