Northern Gardening hosts Diane Booth and Joan Farnam talk with the experts about container gardening and early diseases in the garden. Click to listen.
The hosts were joined by Ilena Berg, local container gardener, Michelle Grabowski, U of M Extension Educator in Horticulture and Plant Pathology and Jane Horn, U of M Master Gardener, who will be teaching a workshop on container gardening at the Community Center June 2.
Michelle Grabowski talked about plant diseases and prevention and control. Here is a summary of a few of the points she made. (Listen to the broadcast to hear all her advice.)
• Starting seeds indoors: Use a soil-starting medium, not dirt from your garden. Keep it moist but not too wet. It is very important to have enough drainage.
• Different seeds need different soil temperatures to germinate. Radishes, for example, can germinate in 50 degree soil, while tomatoes and peppers need 70 degrees to germinate.
• Soil thermometers are useful for garden soils as well as indoor pots.
How to have healthy plants
• Clean up your garden in the fall to eliminate habitats and overwintering sites for pathogens and pests
• Rotate where you put your plants in the garden each year for fertility and to deprive the pathogen of a suitable host
• Healthy soils with good drainage
• Proper plant nutrition
• Environmental management -- use physical controls like floating row covers to keep out pests and/or warm soils,
• Use cultural techniques such as proper timing or practices to avoid a pathogen
• Use disease resistant varieties and treated seeds
IPM (Integrated Pest Management) At what point do we decide to intervene and decide we have a pathogen we need to take action against? It’s important to understand the pathogen and under what conditions it can become a problem where damage & economic loss is not tolerable.
Here are some of the specific issues with pathogens that we might encounter in Cook County.
1. Anthracnose: Caused by the fungus Colletotrichum lindemthianum, primarily infects snap beans and dry beans such as pinto, kidney, and navy beans. It survives the winter in infected plant debris and produces spores in the spring that are rain splashed or windblown to healthy plants. It may also be introduced into the garden on infected seed. Develops quickly during cool, wet conditions. Small, reddish brown spots on leaves and pods that enlarge. Remove plant material as soon as noticed.
2. Bean rust: Caused by the fungus Uromyces appendiculatus, survives winter in infected plant material and produces spores in the spring that are wind blown. It is not seed-borne. Appears as rust-colored pustules on the bottom of leaves and on pods surrounded by a yellow halo. Remove plant material as soon as noticed.
3. Bacterial diseases on garden beans: Bacteria can be from the seed or infected plant material from the previous year. Common blight, halo blight and brown spot infect the leaves and pods of many different beans. Not all beans are susceptible. The disease starts as a watersoaked spot that usually become brown surrounded by a yellow halo.
Don’t save seed from infected plants and remove infected plants from the area.
4. Mosaic: Virus that overwinters in perennial weeds. It is transmitted to beans and vine crops by aphids. Yellow and green mottling of leaves, plants are stunted, yields reduced, infected fruit is mottled, bumpy and misshapen. Rogue out infected plants.
1. Black Rot: Light brown to yellow ‘V’ shaped lesion on the leaf caused by the bacteria Xanthomonas campestris. When leaf veins are cut in half – they will be black. Seed-borne, water splash. Moves very quickly under warm, moist conditions.
2. Fungal diseases: Black leg (Leptosphaeria maculans)light brown lesions with purplish outline often containing pinhead-sized black dots. Favored by wet, windy conditions.
Seed-borne, water splash, crop residues, equipment.
Club root (Plasmodiophora brassicae) causes galls to form on the roots of infected planats. First sign is wilted plants in warm weather because plant can’t pick up water due to galls. Dig up plant and check for disease.
1. Aster Yellows: Plant disease which affects a wide range of plants: aster, chrysanthemum, cosmos, daisy Echinacea, gladiolus, marigold, petunia, carrots, onions, potatoes, tomatoes. Caused by a microscopic organism called a phytoplasma. Aster yellows is transmitted by leafhoppers and grafting. The phytoplasma survives winter in perennial and biennial plants. Symptoms include: stunting with outer leaves rust colored to purple; roots are bitter, stunted and deformed with tiny hair-like roots. Flowers are often irregular, deformed, green. Once infected, there is no cure. Remove infected plants.
1. Corn smut: Common disease of sweet corn caused by the fungus Ustilago mayclis. Disease rarely kills corn plants, but results in smaller ears. Fungus survives winter in corn debris or in the soil. Spores are windblown or rain-splashed on healthy plants. When the galls formed are small and silver or white you can eat them and they are considered to be a delicacy. Remove before they turn brown and the spores erupt. Some corn varieties are more susceptible than others.
2. Purple leaves: Low pH can cause purpling of leaves with yellow leaf edges. Plants will be uneven in height if the pH is low. Low phosphorus can also be seen in the spring with cold, wet soils. Plants will be uniform in height and not have the yellow leaf margin.
1. Bottom rot: Caused by the fungus Rhizoctonia solani. Favored by warm, wet weather. Plants are usually affected when they are nearly mature. First symptom is usually wilting of the outer leaves. The fungus enters the plants where leaves are touching the soil. If conditions are favorable, the fungus continues to grow until the entire head becomes a slimy brown mass that soon dries and becomes darker.
2. Sclerotina Drop: Fungi Sclerotina sclerotium and S. minor do well under cool, moist conditions. Wilting of the outermost leaves is preceded by a water soaked area that appears on the stem near the soil. As the fungus grows into each leaf, the leaf tips droop and wither with their tips touching the soil.
3. Gray mold, lettuce mosaic, aster yellows, etc.
Onions, Garlic, Leeks
1. Yellow Streak virus: This is carried by the wheat curl mites that can be found inside of garlic cloves. Leaves are yellow streaked, stunted. Loosen up the clove covers and soak the cloves for a few minutes in alcohol to kill the adult mites at planting time.
2. Fusarium basal rot: Bulbs may become infected at any point during their time in the field. Yellowing and browning of leaves begins at the tip and moves downward. Red brown rot appears where the roots are attached to the basal plate. Rot may happen in storage.
3. Botrytis neck rot: Outer leaves yellow and die back. Stem appears water soaked at the soil line. Small, hard black fungal structures form in the decayed stem tissue. Disease is common in cool wet weather or in heavy wet soils.
4. Bacterial soft rot: Softening and water soaking of one or more of the inner fleshy scales of the onion bulb. Shows up just before or at the time of harvest or when in storage. Pathogens are soil borne.
1. Ascochyta blight: Disease involving three different fungi. All survive winter in plant debris or enter the garden on infected pea seeds. Plants generally show blackening of the stem from the soil line to about 7” tall. Plants have yellow foliage, brown spots on leaves and stems and bud drop. Pods and seeds can be infected. Remove infected plants.
2. Bacterial blight: Disease caused by Pseudomonas syringae that initially appears as shiny dark green (water-soaked) spots on the upper and lower leaf surfaces. Older spots may appear brown, papery and translucent with the center of the lesion lighter in color. Remove and discard all infected material.
3. Seed decay, Damping off, and Root rot: These are caused by a number of fungi with cool, wet soils favoring seed decay and damping off. Infected seedlings may fail to emerge or collapse after they emerge. Older seedlings may also fail as they develop a root rot. Root rot is more common in heavier wet soils. Plants infected by root rot fungi may appear yellow, stunted. Symptoms may not show up in cooler weather but as soon as the weather becomes hot and dry, plants die quickly.
Peppers (Diseases are similar to tomatoes)
1. Common scab: Disease caused by bacteria Streptomyces scabies is most severe in soils with a pH greater than 5.2 or under drought conditions. Tubers are most susceptible but stems and roots may also be infected. Scab does not adversely affect potato tubers in storage. Scab tolerant: Norland, Norgold, Russet, Superior. Scab can also infect beets, carrots, parsnips, turnips and radishes.
2. Verticillium wilt: Soil-borne fungi that can affect tomatoes, potatoes, cucumber, eggplant, pepper, rhubarb, watermelon, beet, etc. Wilting is the characteristic symptom during the warmest part of the day in August and then recover at night. Leaf edges and areas between the veins appear yellow and then brown. Vascular brown streaking can be found in stems near the ground. Cool weather disease 65-83 degrees. Plant resistant varieties; remove and destroy plant material so it doesn’t overwinter. Enters through wounds in roots – nematodes, etc. Resistant: Gold Rush, Itasca, Century Russet, Ranger Russet.
1. Aschochyta leaf spot: Leaf infection with Aschochyta rhei appears as small, green-yellow irregular spots less than ? “ in diameter on the upper leaf surface. The infected spots turn brown, die and fall out – producing a ‘shot-hole’ appearance. Stalks are not affected.
2. Phytophthora ‘root rot’: Serious disease of rhubarb. Slight, sunken lesions at the base of the stalks enlarge rapidly, resulting in wilted leaves and collapse of the entire stalk. The crown & roots turn brown or black and disintegrate. Control by setting out disease-free plants and plant in well-drained soil.
3. Ramularia leaf spot: Ramularia rhei shows up as small red dots that enlarge to form circular lesions a ?” or larger in diameter. Stalk infections appear later and white fungus develops in the centers of spots on both leaves and stalks.
1. Blossom end rot: A disease most often found on summer squash under wet conditions. Also may be found on pumpkins, etc. Flowers are covered with white then purplish black fungal growth. The blossom end of the squash is soft, rotted and covered in fluffy purplish black growth. The fungus can survive in crop debris and spread by insects, splashing water, wind. Good air circulation helps.
1. Anthracnose: Symptoms do not appear until the fruit is ripening. The fungus is between the cuticle and epidermis of the fruit and is activated by low temperatures, fruit maturation or plant stress. Small, depressed lesions appear circular in shape. Lesions enlarge, become more shrunken, and eventually turn tan with black fruiting bodies. Cut off as soon as you see the shrunken areas. This fungus can persist in the soils.
2. Early blight: Target spot of tomato, potato, eggplant, pepper is caused by the fungus Alternaria solani. Symptoms usually appear at the end of the season. Brown lesions first appear on older, lower leaves and spread up toward new growth. Lesions are small, dry and papery and may develop dark concentric rings of raised and necrotic tissue. Leaf tissue turns yellow at the edge of the lesion. Lesions on stems begin as small dark slightly sunken areas. Fungus overwinters in the soil. Under cool, moist conditions, the fungus can produce numerous spores that are wind blown. Nitrogen and phosphorus deficiencies increase susceptibility to early blight.
3. Late blight: Caused by the fungus Phytophthora infestans this can occur any time during the growing season but is more likely to be seen in late summer and early autumn. Disease spreads rapidly during cool, rainy weather, killing plants within a few days. Daytime temps between 60 – 70 degrees and night time temps between 50 – 60 degrees and high humidity create ideal conditions for infection and spread of disease. Fungus becomes inactive during dry periods. Fungus survives in potatoes and perennial weeds like nightshade. Late blight starts out as irregularly shaped, dark-green (water-soaked) lesions on the lower leaves of the plant. Lesions enlarge, entire leaves turn grown, shrivel and die. The entire plant collapses. Rotate potatoes and tomatoes; don’t plant potatoes next to tomatoes; ensure good airflow; remove and dispose of any volunteer potato or tomato plants; apply chlorothalonil or mancozeb at the first sign of the disease.
4. Septoria Leaf Spot: Caused by the fungus Septoria lycopersici. The fungus can survive winter on diseased plant materials. Spores are wind blown or rain splashed to healthy leaves. Symptoms usually begin to appear on the lower leaves after fruit set. Initially round, yellow spots develop. Later, these spots enlarge and turn brown to gray. Tiny black fruiting bodies form in the center of the leaf spots. Exposed fruit may be damaged by overexposure of the sun.
Vine Crops: Cucumbers, Pumpkins, Watermelon, Squash
1. Alternaria leaf blight: Caused by the fungus Alternaria cucumberina is most problematic on melons but can also occur on cucumber, pumpkin, squash. Does not infect fruit but can reduce yields and fruit quality due to reduced plant vigor. Brown leaf spots that can cause leaves to turn brown, curl up, wither and die.
2. Angular leaf spot: Bacterial disease caused by Pseudomonas syringae with cucumbers less affected due to resistant varieties. Leaves develop small, angular brown or straw-colored spots with a yellow halo. Leaf spots dry out, leaving irregular shaped holes in the leaves. Water soaked to tan small circular spots on fruit. Thrives in warm humid conditions. When fruits are infected, the seed also becomes infected. White sticky bacterial ooze can form. Pathogen can survive on plant debris.
3. Anthracnose: Caused by fungus Colletotrichum orbiculare that can attack all cucurbits but especially cucumbers, muskmelons and watermelons. Irregular brown leaf spots form on squash, melon and cucumber. The center of the leaf may drop out resulting in shot hole or ragged appearance. Very common on cucumbers. May have sunken elongate lesions on stems. Disease is favored by warm, moist environments. First seen in mid to late season. Purchase clean seed; some resistant varieties are available for cucumbers.
4. Bacterial wilt: Caused by bacteria Erwinia tracheiphila. This can cause severe losses in cucumbers, muskmelons. Squash and pumpkins are less severely affected. Watermelons are not affected. Does not occur in Minnesota every year. Leaves first appear dull green, wilt during the day, and then recover at night. Leaves eventually yellow and brown at margins, completely wither and die. Striped and spotted cucumber beetles carry bacteria in their gut.
5. Powdery mildew: Primarily caused by fungus Podosphaera xanthii that infects vine crops. First shows up as pale yellow leaf spots. White powdery spots can form on both upper and lower leaf surfaces rapidly covering entire leaf, stem, etc. When majority of plant is infected, plant is weakened and fruit ripens prematurely. Humid conditions with temperatures 68-81 degrees and usually noticed in mid-late summer. Older leaves are most susceptible. Fruit has poor flavor, doesn’t store well, etc.
Sulfur applied when first noticed can slow spread. Good air circulation, not over applying nitrogen, planting less susceptible varieties.
6. Viruses: Infection with virus is common on all cucurbits. It is very difficult to identify individual viruses by symptoms. Virus infected leaves often have a mottling or mosaic pattern in shades of green and yellow. Leaves may be distorted or deformed. Early infections result in no fruit production. If you see symptoms, remove plants. Keep tools and hands clean.
1. Botrytis blight: The fungus Botrytis cinerea attacks stems, buds and leaves. It begins early in the spring, most common during cloudy, rainy weather. Young stalks discolor at the base, wilt and fall over. Gray, fuzzy fungal spores are usually characteristic of this infection.
2. Phytophthora blight: The fungus Phytophthora cactorum is similar to Botrytis however doesn’t have the felty growth. Infected parts become dark brown or black and somewhat leathery. The entire shoot my turn black and die. Cankers can infect the stem, crown, etc. Remove and destroy along with adjacent soil.
1. Black spot: Caused by the fungus Diplocarpon rosae it can cause almost complete defoliation by early Fall. Circular black spots that are surrounded by a yellow halo. Yellow leaves fall prematurely.
2. Powdery mildew: Caused by the fungus Sphaerotheca pannosa. Young leaves can curl and turn purple. Young canes can become distorted and dwarfed. Leaves, buds, and stems are covered with a white powdery coating.
A few botanical and biological controls
• Fermented nettle tea (preventative spray for fungus + nutrient boost)
• Equisetum tea (root dip during transplanting against fungal attack – dessication silica)
• Chamomile tea (preplanting seed soak to kill seed borne pathogens)
• Liquid seaweed (strawberries foliar treatment for nutrients / disease)
• Watery compost extract (suppression of soil borne plant pathogens?)
• 1% chlorine bleach solution for 10 minutes for some tomato or brassica seeds to reduce pathogens on seeds
• Baking soda /milk for powdery mildew
Container gardening is becoming more popular with people living in rentals and/or downsizing their outdoor space.
Ilena Berg talked to us about what containers she uses to grow plants, what kind of plants she grows, and her successes and failures.
• Small containers (1-2 gallons) lettuce, spinach, peppers, radishes, carrots, beets, beans, patio tomatoes
• Medium containers (3-10 gallons) eggplant, broccoli, cauliflower, determinate tomatoes, gourmet potatoes
• Large containers (greater than 10 gallons) cabbage, indeterminate tomatoes, high yielding potatoes, vine crops including cucumbers, melon, squash
• Full sun 8 -12 hours daily
Jane Horn was also a guest and talked to us about her experiences with container gardening. She began gardening 14 years ago when she moved into her first house and for five years has been a University of Minnesota extension Master Gardener. Her garden was showcased as one of the Star Tribune's Beautiful Gardens and has been featured on the Better Homes and Gardens web site. Her experimental garden planted in a pile of dirt on asphalt was the focus of an article on www.Learn2Grow.com.
Container design is one of Jane’s strengths and she has placed in the top 10in Fine Gardening magazine's Container Design Challenge.
Jane is also going to be teaching a Container Gardening Workshop on Saturday, June 2 at the Community Center hosted by the U of M Cok County Master Gardeners.
Here’s the schedule for that day.
• 7:30 a.m. Eleanor Hoffman teaching Yoga for Gardeners (Please wear loose clothing and bring a beach towel or mat.)
Following our yoga start to the day, refreshments will be available.
• 8:30 a.m. Container gardening workshop begins.
Topics will include:
Growing Vegetables in Containers with Diane Booth;
Spicing up Your Garden by Planting in Containers with Jane Horn
Hands-on Container Planting Demonstrations with Nancy Carlson, Max Linehan, and Emma Bradley.
Cost for the entire morning is $20 that includes handouts, etc. Call 387-3015 to reserve your splot.
Also, the Art Colony Potters are making a bunch of flower pots, containers and garden art as a fundraiser for the ceramics studio. They will hold a silent auction of the items during the workshop.
• A Container Gardening Contest is being sponsored by the U of M Cook County Master Gardeners with sign-up information becoming available in May. Categories will include: Best Miniature Garden, Best Hanging Garden, Most Unusual Garden, Best Edible Garden, and Best Window Box Garden. Prizes will be $25 for each category. You need to sign up by Friday, July 13. Watch for the sign-up information or stop by the Cook County Extension office to pick up entry forms.
Gardens will be judged on Aug. 18 in conjunction with the container garden tour on that Saturday, Aug. 18 from 1- 3 p.m. as well. If you are interested in being on the garden tour, please contact Diane in the Extension office at 387-3015.
Cook County Extension office located in the CC Community Center building in Grand Marais does have soil testing available through the University. We do recommend a soil test before you start adding amendments to your soil. We also have an animal husbandry and gardening library available for folks who would like to check out more specific information on topics we discuss on Northern Gardening.