Growing Healthy Cruciferous Vegetables
Avoiding Pests and Diseases in Brassica and Raphanus Cultivars
Mar 22, 2009
The genus Brassica includes a wide variety of familiar plants that don’t all appear to be related to one another. Cabbages, Brussels sprouts, cauliflower, turnips, kale, broccoli, kohlrabi, Chinese cabbage, pac choi, and mustard are all members of this heterogeneous group.
A related genus, Raphanus, includes radishes and their relatives.
The very diversity of this popular vegetable family may increase the likelihood of insect damage and disease in a family garden: Many gardeners might not appreciate the close genetic kinship of some of these crops, and this could contribute to a breakdown in normally fastidious gardening practices.
Cruciferous vegetables, like nearly all plants, have their own host of diseases and pests. Once they are established, it is sometimes difficult to eradicate problems without resorting to extreme measures.
Bacterial Diseases of Cruciferous Vegetables
- Bacterial leaf spot: Pseudomonas syringae
- Bacterial soft rot: Pseudomonas marginalis and Erwinia carotovora
- Black rot: Xanthomonas campestris
- Crown gall: Agrobacterium tumefaciens
- Xanthomonas leaf spot: Xanthomonas campestris
Fungal Diseases of Cruciferous Vegetables
- Alternaria black spot: Alternaria species
- Anthracnose: Colletotrichum higginsianum
- Black leg and Phoma root rot: Leptosphaeria maculans and Phoma lingam
- Black mold rot: Rhizopus stolonifer
- Black root: Aphanomyces raphani
- Bottom rot, damping-off, head rot, seedling root rot, basal stem rot, and wire stem: Rhizoctonia solani, and Thanatephorus cucumeris
- Clubroot: Plasmodiophora brassicae
- Damping-off: Fusarium and Pythium species
- Downy mildew/staghead: Peronospora parasitica
- Graymold: Botrytis cinerea
- Leaf spot: Cercospora brassicicola and Pyrenopeziza brassicae
- Phymatotrichum root rot (cotton root rot): Phymatotrichopsis omnivore
- Phytophthora root rot: Phytophthora megasperma
- Powdery mildew: Erysiphe polygoni
- Ring spot: Mycosphaerella brassicicola and Asteromella brasicae
- Southern blight: Sclerotium rolfsii
- Stem rot and watery soft rot: Sclerotinia sclerotiorum
- Verticillium wilt: Verticillium albo-atrum
- White leaf spot/gray stem: Pseudocercosporella capsellae
- White rust/staghead: Albugo candida
- Yellows: Fusarium oxysporum
Viral Diseases of Cruciferous Vegetables
- Cauliflower mosaic virus
- Radish mosaic virus
- Turnip mosaic virus
- Yellows: Beet western yellows virus
Parasitic Nematodes that Affect Cruciferous Vegetables
- Dolichodorus species (Awl)
- Heterodera schachtii and H. cruciferae (Cyst)
- Pratylenchus pratensis (Lesion)
- Paratylenchus species (Pin)
- Meloidogyne species (Root-knot)
- Belonolaimus species (Sting)
Common Insect Pests of Cruciferous Vegetables
In addition to causing physical damage to plants, insects often carry plant diseases.
(The following chew holes in foliage or bore into stems and leaf veins)
- Beet armyworm
- Cabbage looper
- Cabbage webworm
- Corn earworm
- Cross-striped cabbageworm
- Cutworm
- Diamondback moth larva
- Imported cabbageworm
- Striped flea beetle
- Vegetable weevil, adult and larva
(The following either pierce or “file” plant tissue, causing foliage to become yellow or distorted)
- Aphid
- Harlequin bug
- Onion thrips
(The following attack plants from beneath the soil surface)
- Cabbage maggot
- Cutworm
- Vegetable weevil larva
- Symphylan (soil-dwelling, centipede-like arthropods)
Control of Insects and Diseases that Affect Cruciferous Vegetables
- Most diseases can be controlled by practicing long crop rotations (three to four years between planting crucifers in the same space), avoiding interplanting of related cultivars, using sterile starting mixes when transplanting, and cleaning up plant debris at season’s end. When composting, make sure internal temperature of pile reaches 140-150º. Remove obviously diseased plants and exclude them from composting.
- Early recognition of insect infestation is crucial to successful control; inspect plants frequently, including stems, undersides of leaves, and soil line.
- Control insects with forceful sprays of water, insecticidal soaps, pepper-wax sprays, or rotenone/pyrethrin. Late-maturing plant varieties help to avoid aphid damage, as these pests tend to decline later in the season.
- Floating row covers help to discourage mobile insects like flea beetles and moths.
- Bacillus thuringiensis (BT) will minimize caterpillar damage.
(From Insect and Related Pests of Vegetables, Ag-295,The North Carolina Cooperative Extension Service, and APSnet, Common Names of Plant Diseases, Diseases of Crucifers (Brassica andRaphanus spp.), Paul H. Williams, primary collator, 1993)
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