Downy Mildew Of Cole Crops – Managing Cole Crops With Downy Mildew


By: Mary Ellen Ellis

If your favorite cole crops, like broccoli and cabbage, come down with a case of downy mildew, you may lose your harvest, or at least see it greatly reduced. Downy mildew of cole vegetables is a fungal infection, but there are steps you can take to prevent it, manage it, and treat it.

Cole Crop Downy Mildew

Downy mildew can affect any cole vegetable, besides broccoli and cabbage, such as Brussels sprouts, kale, collard greens, kohlrabi, and cauliflower. It is caused by a fungus, Peronospora parasitica. The fungus may start an infection during any point in a plant’s life cycle.

Cole crops with downy mildew will show symptoms beginning with irregular yellow patches on leaves. These will then change to a light brown color. Under the right conditions, fluffy white fungus will start to grow on the undersides of leaves. This is the origin of the name downy mildew. Cabbage, cauliflower, and broccoli may develop dark spots as well. Severe infections in young plants can kill them.

Treating Downy Mildew on Cole Crops

Conditions that favor cole crop downy mildew are moist and cool. An important way to prevent the disease is to manage moisture. Plant these vegetables with enough space between them to allow for air flow and for them to dry out between watering. Avoid overwatering and overhead watering.

The spores of the fungus overwinter in plant debris, so good garden hygiene practices can help prevent infections. Clean up and destroy old plant debris each year. The main times for infection are in the spring on seedlings and in the fall on mature plants, so be especially cautious about moisture and keeping debris out of the garden during these times.

You can also treat downy mildew with fungicides, which may be necessary to save damaged seedlings. Copper sprays are available for organic gardening, but there are also several other fungicides that can be applied to treat downy mildew. Most will successfully control the infection if applied as directed.

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Growing Cabbage: How to Plant, Grow, and Harvest Cabbage Successfully

Jennifer is a full-time homesteader who started her journey in the foothills of North Carolina in 2010. Currently, she spends her days gardening, caring for her orchard and vineyard, raising chickens, ducks, goats, and bees. Jennifer is an avid canner who provides almost all food for her family needs. She enjoys working on DIY remodeling projects to bring beauty to her homestead in her spare times.

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Brassicas are my absolute favorite plant family. After all, the group includes cabbages, which are a delight to try growing.

Harvesting a glorious head of cabbage at the end of a long season is one of my most cherished garden rewards. I’m always astounded to watch a tiny seed grow into a dense, round cabbage.

While they’re fun to grow and provide a tasty end-of-season reward, cabbages—like other members of the brassica family—pose several important challenges, including annoying pests.

Keep reading to find out how to grow your very own heads of cabbage right in your front or backyard garden patch.

If you’re looking to expand your nutritious options while cooking, an excellent place to start is by growing cabbage. Cabbage is full of vitamin B, calcium, iron, protein, and niacin.


Program Areas

Targeted Pest

Labeled Crops

(Cuprofix Ultra 40 Disperss)

Various blights, leaf spots, downy mildew, bacterial blight, late blight on tomatoes, bacterial spot (depending upon the crop, see label).

Many including cucumbers, eggplant, peppers, tomatoes.

Preventative, contact fungicide. Crops grown in the greenhouse may be more sensitive to copper injury so the user should determine plant sensitivity. Observe for 7 to 10 days for symptoms of injury.

Bacillus amyloliquefaciens D 747

Various leaf spots (bacterial or fungal), downy mildew, powdery mildew, botrytis blight damping off seedling blights, root and crown diseases. (Depending upon the crop, see label).

Many including Brassica vegetables, curcurbits, fruiting vegetables, leafy vegetables.

Broad spectrum, preventative biological fungicide. Use before disease occurs with proper cultural practices.

Downy mildew, powdery mildew on many different crops (see label)

Early blight, late blight on tomatoes

Many including Cole crops, curcurbits, fruiting, and leafy vegetables

Broad spectrum, preventative biological fungicide. Use before disease occurs with proper cultural practices. Begin applications when conditions in the greenhouse favor disease development.

Bacillus subtilis QST 713

Fungal and bacterial leaf spots, powdery mildew, Botrytis blight, downy mildew (see label)

Many including Cole crops, curcurbits, fruiting vegetables, leafy vegetables, bulb vegetables

Broad spectrum, preventative biological fungicide. Use before disease occurs with proper cultural practices. Begin applications when conditions in the greenhouse favor disease development. Thorough coverage is essential.

(Companion Liquid Biological Fungicide)

Damping off fungi, root rots (Fusarium, Pythium, Phytophthora, Rhizoctonia)

Botrytis, leaf spots, (fungal and bacterial), late blight, powdery mildew

Many including Cole crops, cucurbits, fruiting vegetables, leafy vegetables, bulb vegetables

Preventative biological fungicide for control and suppression of soil and foliar diseases. Activates ISR (induced systemic resistance). Use before disease occurs with proper cultural practices.

Rhizoctonia, Pythium, Fusarium (suppression), Powdery Mildew

Curcurbits, fruiting vegetables

(see label for specific types)

Preventative biological fungicide. Growing media or foliar applications to greenhouse- grown crops. Use before disease occurs with proper cultural practices.

Leaf spots, Anthracnose, Bacterial spots, late blight, downy mildew and other diseases (see label)

See labels for specific crops.

Protectant, contact fungicide. See labels for specific usage instructions. Several Kocide products are available.

Copper hydroxide & Copper oxychloride

Downy mildew, alternaria blight, phomopsis, bacterial spot, bacterial speck, early blight, grey leaf mold, late blight, septoria leaf spot

Cucumber, eggplant, pepper, tomato

Protectant, contact fungicide. The sensitivity of crops grown in greenhouses differs from field conditions. Test a small area and observe for 7 to 10 days to determine safety before application.

Bacterial and fungal leaf spots

(many), powdery mildew, downy mildew, early blight, late blight and others (depending upon crop)

Greenhouse Vegetable Crops: Cole crops, lettuce, onion, tomato, potato, eggplant, pepper

Works by contact. See label for specific usage instructions, precautions and limits.

Downy mildew, alternaria blight, phomopsis, bacterial spot, bacterial speck, early blight, botrytis blight, late blight, septoria leaf spot (depending upon crop)

Cucumber, eggplant, pepper and tomato

Protectant, contact fungicide. The sensitivity of crops grown in greenhouses differs from field conditions. Test a small area and observe for 7 to 10 days to determine safety before application.

Copper Sulfate Pentahydrate

Fungal and bacterial leaf spots (see label for specific crops/pests), downy mildews, powdery mildews, Botrytis

Blight, and late blight on tomatoes

Crucifer crops, curcurbits, eggplant, pepper, tomato

Systemic bactericide and fungicide.

Alternaria blight, bacterial spot, bacterial speck, early & late blight, gray leaf mold, septoria leaf spot (depending upon crop)

Protectant, contact fungicide. The sensitivity of crops grown in greenhouses differs from field conditions. Test a small area and observe for 7 to 10 days to determine safety before application.

Pythium damping off on tomato, Downy mildew on basil

Tomato Greenhouse Transplant Production, Basil

Locally systemic fungicide. Apply as a drench for Pythium damping off.

Cottonseed oil, corn oil, garlic oil

Vegetables such as melons, squash, tomatoes, cucumbers

Contact fungicide. Thorough coverage needed. Spot test before widespread use.

Fruiting vegetables, tomatoes, cucumber and certain leafy greens

Preventative translaminar fungicide. Resistant populations of Botrytis have been documented. Do not apply in the field.

Botrytis, damping off and root rot diseases (Pythium, Rhizoctonia, Fusarium)

Many vegetables such as tomato, pepper, cucumber and lettuce

Preventive biological fungicide that contains naturally occurring fungus. Use before disease occurs with proper cultural practices. Available as WP and G formulations.

Peroxyacetic acid (Oxidate 2.0)

Downy mildew, powdery mildew, leaf spots and blights, root rots (see label)

Tomatoes, peppers, leafy and Cole crops, cucurbits, bulb crops and others

Works by contact. Strong oxidizing agent.

Potassium salts of fatty acids

Curcurbits, fruiting vegetables, leafy vegetables, greenhouse cucumber

Works by contact. See label for usage instructions.

Mandipropamid

Downy Mildews, Late Blight on Tomatoes

Leafy and vegetable transplants grown in an enclosed greenhouse with permanent flooring for resale to consumers (see label)

Contact, protectant and translaminar fungicide. Begin applications prior to disease development. See label for specific usage instructions.

Pentachloronitrobenzene PCNB

(Terraclor 400, Terraclor 75% WP)

Root and stem rot, damping off (Rhizoctonia solani)

Vegetable bedding plants see label for more information.

Protectant, contact fungicide.

Alternaria, Botrytis, powdery mildew and various leaf spots and blights (see label)

Tomatoes, peppers, and edible peel curcurbits

Broad spectrum fungicide with preventative, curative, and locally systemic activity. Test for plant safety.

Greenhouse vegetables crops (see label for specific types.

Works by contact. Thorough coverage of all plant parts is important. Foliar injury may occur if applied during humid conditions. See labels for information on plant safety. All applications should be preceded by a phytotoxicity check to ensure that the material is safe for that particular plant variety.

Downy mildew, Phytophtora spp., Pythium spp., Late blight and others

Brassicas, curcurbits, fruiting and leafy vegetables

Systemic fungicide. See label for plant safety precautions and use directions.

Downy mildew, powdery mildew, Phytophthora, Pythium, Fusarium, Rhizoctonia

Many vegetables (see label)

Systemic fungicide. Make applications prior to disease development in conjunction with good cultural practices.

Downy mildew, Phytophthora, Pythium

Curcurbit vegetables: powdery mildew, gummy stem blight, botrytis, Corynespora leaf spot, scab, early blight

Fruiting vegetables: powdery mildew, Botrytis blight, early blight, suppression of anthracnose

Curcurbit vegetables, fruiting vegetables

Preventative and curative fungicide. Active ingredient (Polyxin) is a natural antibiotic and fermentation product of a soil bacterium.

Powdery mildew and others

(see labels for more information)

Many vegetables (see labels)

Contact fungicide. Through coverage essential. Potassium bicarbonate disrupts the potassium ion balance in the fungus cell, causing the cell walls to collapse. See labels for precautions.

Root rot and damping off caused by Pythium, Phytophthora

Tomatoes, cucurbits, peppers, leaf lettuce

Systemic fungicide. Apply in the evening Phytotoxicity (brown, necrotic spots) may occur if applied directly to dry growing media, especially in intense sunlight.

Pyraclostrobin & boscalid (Pageant Intrinsic brand fungicide)

Crown and basal rot (Fusarium, Rhizoctonia, Sclerotinia), Damping off, Downy mildew, spots and blights, Phytopthora blight, Powdery mildew, rots and blights

Tomato transplants for the home consumer market. (Not agricultural fields).

Broad spectrum fungicides. Use preventatively. See label for usage instructions. Provides improved plant health in the form of stress management of cold, heat, drought and shipping stresses.

Gray mold (Botrytis), Early Blight (Alternaria)

Preventative fungicide. Apply only in well ventilated greenhouses and ventilate for at least 2 hours after application. Phytotoxicity may occur in unventilated greenhouses with relative humidity above 80%.

extract of Reynoutria sachalinsis

Powdery mildew, downy mildew, bacterial leaf spot, early and late blight (depends upon crop). Soil drenches for Pythium, Phytophthora, Rhizoctonia, Verticillium

Curcurbits, peppers, leafy vegetable crops, and tomato

Formulation of an extract from the giant knotweed. Use preventatively to increase the natural defense system of plants. Activates ISR (induced systemic resistance). Translaminar fungicide.

Streptomyces griseoviridis strain K 61

For control of seed rot, root and stem rot (Fusarium, Alternaria, and Phomopsis).

Suppression of Botrytis, and root rots of Pythium, Phytophthora and Rhizoctonia (damping off)

Many vegetable transplants in the greenhouse

Preventative biological fungicide. Contains a beneficial bacterium. Repeat applications may be needed. Use as a soil spray or drench. Use before disease occurs with proper cultural practices.

Suppression of soil borne fungi such as Fusarium, Rhizoctonia, Pythium, Phytophthora, and foliar diseases such as downy mildew, powdery mildew, Botrytis, blight Alternaria and others

All greenhouse vegetables

Preventative biological fungicide for suppression of root rots diseases and some foliar pathogens. Use before disease occurs with proper cultural practices.

Suppression of Fusarium, Pythium, Rhizoctonia, Phytophthora, and others

Preventive biological fungicide that suppresses certain diseases. Also, contains iron, molybdenum and humic acid. Use before disease occurs with proper cultural practices.

Xylem mobile fungicide. Repeated applications can result in resistant bacteria.

Sulfur

Many vegetable transplants (see labels

Contact fungicide. Crops grown in greenhouses may be more sensitive to sulfur injury, so the lowest label right should be tried initially. Do not use within two weeks of oil spray treatment.

Trichoderma harzianum

Root rots such as Pythium, Rhizoctonia, Fusarium, Cylindrocladium and Thielaviopsis

Many vegetables, see label

Preventative biological fungicide. It will not cure diseased plants. Use before disease occurs with proper cultural practices.

Trichoderma harzianum and Trichoderm virens

RootShield Plus+ WP

4 hr. REI

Rootshield Plus= G

Root rots such as Pythium, Phytophthora, Rhizoctonia, Fusarium, Cylindrocladium and Thielaviopsis

Many vegetables, see label

Preventative biological fungicide. . It will not cure diseased plants. Use before disease occurs with proper cultural practices. Rootshield Plus WP- greenhouse soil drench only.

Triflumizole

Curcurbit greenhouse transplants

Protectant and eradicant fungicide. Thorough coverage needed. Begin applications at first sign of disease.

This information is supplied with the understanding that no discrimination is intended and no endorsement implied. Due to constantly changing regulations, we assume no liability for suggestions. If any information in these tables is inconsistent with the label, follow the label. Always follow label instructions regarding registered uses and note cautions. To avoid any phytotoxicity problems, spot test first before widespread use.

* Fungicides are grouped by their mode of action (MoA) and each MoA group is assigned a Fungicide Resistance Action Committee (FRAC) code. Most systemic fungicides (that are absorbed into plant tissues) are specific in their mode of action. Protectant fungicides are less likely to develop resistance problems as they have multi-site modes of action (M). To prevent the development of resistance, alternative applications among different FRAC codes and incorporate biological fungicides into your disease management plan. See www.frac.info/frac/indes.htm

By Leanne Pundt, Extension Educator University of Connecticut and Tina Smith, Extension Educator University of Massachusetts 2007. Updated 2013, 2015

The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.


Disease Management

Chemical

Maneb is a fungicide primarily used to manage downy mildew and is applied every seven to 10 days. Florida lettuce growers also use copper (hydroxide or sulfate) to manage downy mildew as well as bacterial diseases. Growers can also use sulfur to control several lettuce diseases.

Cultural

Scouting is the main cultural practice used by lettuce growers. Growers also plow in residue, remove perimeter and field vegetation, and use mulches. Flooding can also be used if water management districts allow the practice.

Biological

Phage use has become increasingly successful at reducing bacterial diseases. While this is an active area of disease management, more research has to be done to determine the best environmental condition for phage and the best time to apply it during the disease cycle.

For more information on growing crops in the state, please view the 2012-2013 Vegetable Production Handbook for Florida, which includes the chapter Lettuce, Endive, Escarole Production in Florida.


Reports on Plant Diseases

Downy mildew or crazy top of wheat, oats, barley, and rye (also of corn, sorghum, rice, and a large number [about 140] of annual and perennial cultivated and wild grasses) is caused by the fungus Sclerophthora macrospora. Among perennial grasses, species of bentgrasses (Agrostis spp), bluegrasses (Poa spp), bromegrasses Bromus spp), canarygrasses (Pharis spp), St. Augustinegrasses (Stenotaphrum spp), and wheatgrasses (Agropyron spp) are likely reservoirs for the downy mildew fungus. The disease occurs all over the world. It is widespread but sporadic in Illinois.

Downy mildew occurs only in localized areas of fields where seedlings have been growing in waterlogged soil. Infected plants are most common in flooded areas near ditches and lowlands where the Sclerophthora fungus commonly occurs on other host plants.

Downy mildew is not a major disease of cereal plants in Illinois. However, it may become destructive in individual fields when the soil is saturated for 24 hours or longer within several weeks after planting. Spots within a field may have dead plants in the center, surrounded by plants with a variety of symptoms.

Figure 1. Oat panicle deformed by downy mildew (T.H. Bowyer photo).

Symptoms

Downy mildew produces various symptoms, depending on the severity of the disease. The symptoms may closely resemble those produced by an excessive concentration of 2,4-D or other phenoxy herbicide.

Affected small-grain or grass plants often tiller excessively. Many of the tillers grow only a few inches before they wither, turn brown, and die. Such plants appear as dense, dead clumps. Diseased plants may appear somewhat stunted to severely dwarfed and deformed with short, thickened or warty leaves that need to be stiff and upright. The upper leaves also may be twisted and curled. Some leaves will have yellow stripes, or will turn almost completely yellow and fleshy. Such affected plants rarely head-out. Some may die prematurely others may remain green a few days longer than healthy plants.

The most characteristic symptoms are the proliferation of florets and the development of distorted, twisted, and abnormally large panicles (Figures 1 and 2) or heads (Figure 3). When downy mildew infects wheat, the heads have a more open appearance than healthy heads, and the chaff may be fleshy and green. The beards of bearded wheats are distorted and abnormally long (Figure 3, left). Diseased heads yield no viable grain. The stems (culms) below the affected heads are often thick and deformed. A virus carried by the fungus may influence the expression of symptoms in host plants.

Figure 2. Oat plants variously distorted by downy mildew

Disease Cycle

The downy mildew fungus produces a large number of round, pale yellow, smooth-walled resting spores (oospores) within infected, senescing leaf, glume, and culm tissue (Figure 4). Thee fungal structures are best seen with a light microscope in decolorized leaf tissues stained with acid fuchsin. The thick-walled oospores may persist in dead host tissue for several years and are released into the soil when diseased tissues decay. Oospores are carried from one field to another in diseased plant residues and soil, in seed grain, and by the wind, surface runoff water, and tillage equipment.

The oospores germinate in water or saturated soil to produce lemon-shaped sporangia (conidia). Within an hour or two of formation the sporangia usually liberate 30 to 90 motile zoospores.

The zoospores are capable of swimming short distances in water before settling down and forming slender germ tubes that penetrate the host tissues of mostly seedling plants.

Following infection, the downy mildew fungus develops systemically within the plant, becoming most abundant in actively growing tissue. Sporangia are formed and infection occurs over a wide range of soil temperatures (44 to 88 F or 6 to 31 C optimum 50 to 77 F or 10 to 25 C).

The causal fungus is incapable of reproducing in the absence of a host plant. The fungus must infect living plants each season–small grains, grasses, corn, sorghums, or rice however, oospores persist and remain viable for several years.

Figure 3. Wheat heads abnormally enlarged and deformed by downy mildew (University of Wisconsin photo).

Control

Downy mildew is seldom severe enough in Illinois to warrant special control measures. However, the following steps may be taken.

1. Where possible, provide for proper surface and subsurface soil drainage. Plant in well-prepared soil. Rotation with noncereal crops is beneficial.

2. Control all grassy weeds since they may serve as host plants.

3. Avoid low areas of fields that are likely to be flooded.

4. Grain to be used for seed should be thoroughly cleaned by fanning to remove all fragments of diseased tissue and lightweight kernels.

5. Whenever possible, select seed from fields known to be disease-free.

Very little is known about the relative resistance of small-grain varieties to downy mildew. Seed treatment has no effect.

Figure 4. Oospores of the downy mildew fungus, Sclerophthora macrospora, embedded in oat leaf tissue.

For further information concerning diseases of crucifers and other vegetables, contact Mohammad Babadoost, Extension Specialist in Fruit and Vegetable Pathology, Department of Crop Sciences, University of Illinois at Urbana-Champaign.

University of Illinois Extension provides equal opportunities in programs and employment.


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