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I’ve been gardening for a long time and I don’t think there’s been a year where a new disease or insect hasn’t shown up in my lawn or garden. In this first of a series I’ll give you my top 10 plant diseases that you’re most likely to see.
INumber 10. Fire Blight on Ornamentals.
Blossoms and leaves will suddenly turn brown or black, but will usually stay attached to the plant. Cankers on branches are usually dark brown or purplish in color.( A canker is a dead or dying area usually found on branches.) The terminal branch will usually bend and look like a shepard’s crook.
Control
Prune and dispose of any infected branches as soon as you notice them. Pruning tools should be sterilized with alcohol or bleach during pruning to avoid spreading the disease to other parts of the plant.
Remove water sprouts (water sprouts are fast growing branches that grow staight up from established branches) as soon as they appear, they are very susceptible to this disease.
Chemical control is not recommended for homeowners.
Crabapple and pears are prone to Fire Blight, when purchasing these choose a variety that is resistant to this disease.
Number 9 Nuisance and Detrimental Molds.
Organic mulches are a valuable asset to the gardener. They control weeds and retain moisture. They add valuable beneficial microorganisms to the soil.
However every now and then undesirable microorganisms find their way into our soil. The result is molds and fungi. How many of us have discovered slime or mushrooms appearing overnight in our mulch? The fungal growth is caused by a lack of oxygen.
Control
If you have a reoccurring fungus problem, sprinkle and rake in a little high nitrogen lawn fertilizer, for example a 24-0-0 into the affected areas.
Number 8 Damping Off
This is a bacterial disease which attacks seedlings as they emerge. It thrives in wet, poorly drained and cool soils.
To avoid this problem, when starting seeds follow sanitary practices. If reusing containers make sure they are clean. Sterilize in a 10% bleach solution. Allowing the soil surface to dry out will go a long way in preventing this problem. If, for some reason, your seed starting mix remains wet for an extended period of time, look to your kitchen cabinet to help prevent the disease.
Contrpl
Cinnamon powder is a natural fungicide and has been shown to be particularly effective against damping-off. In addition, Weak chamomile tea ( 4 tea bags per quart of water) is another natural fungicide.Spray seedlings every week.
Number 7 Rust
This is a fungal disease that usually attacks ornamentals and fruit trees. Dry, reddish orange, spores are usually found on the under side of leaves. Moderate amounts will usually not harm plants. Severely infected plants can die from rust.
Control Rust is extremely difficult to control. The most effective means is to identify the fungus early and remove affected leaves, including fallen leaf debris. The leaves should be placed in a sealed bag for disposal or burnt. Never place infected debris in the compost bin. Rust can also be controlled with sulphur and homemade sprays made from Chamomile tea.
Number 6 Downy Mildew
A fungal disease usually causing the most damage on cucurbits (curbits are plants in the cucumber, squash gouard and melon family) than any other crop. In 2006 in southern Michigan this disease destroyed 90% of the pickling cucumber crop and cost farmers millions of dollars.
Yellowish in color it eventually turns the entire leaf yellow. Spots appear between veins on the leaves; the plant dies very quickly once attacked.
Control
Proper spacing of plants to allow adequate air circulation is important. Yellowish in color it eventually turn the entire leaf yellow . Avoid overhead watering to keep the leaves as dry as possible.Foliar fungicides such as Daconil or Maneb can be used as a preventive. They must be applied every 7 days.This disease also attacks watermelons and cantaloupes.
Choose resistant varieties.
Number 5 Dollar Spot on Turf Grass
Dollar Spot is a fungal disease that is present worldwide. It is usually found on bluegrass and fescues. It usually appears during cooler weather throughout the year.
It first appears as tiny yellow spots on the grass blades. As the blades begin to die the area enlarges until you have dead circles 2-3 inches in diameter.
Control
A healthy lawn is the beat way to resist fungal diseases. Fertilize on a regular basis. Do not water late in the day to avoid the turf being wet for long periods. Select resistant varieties.
Chemical controls are difficult.
Number 4 Powdery Mildew
This is a fungal disease that appears in all gardens at one time or another. It appears as a whitish or gray powder on the leaves. Severe cases will turn the leaves yellow.
Most often seen on lilac, roses, zinnias, phlox and viburniumns
Control
Buy only top quality healthy plants; provide adequate spacing to allow for air circulation. Do not water late in the day.
Several fungicides are available for chemical control.
Number 3 Clematis Wilt
The most devastating disease to attack clematis. It is a fungal disease. The disease appears as a sudden stem collapse just as the flowers begin to open.
One or several stems on the plant may discolor and collapse.
Control
Remove affected stems below the discolored areas. Safer Garden Fungicide or Thiolux are recommended chemical controls.
Number 2 Black Spot
Fungal disease appearing on rose leaves as small dark circles 1/16 -1/2 inch in diameter. Entire leaves that are affected turn yellow and fall from the plant. If left untreated, the plant will weaken and die.
Control
Follow good sanitary practices. Clean up beds, remove diseased leaves and place in trash, do not add to compost.
A regular spray program of fungicides is critical to prevent this disease. Switch between several brands to avoid the plant building up an immunity to a specific brand.
I spray my roses every 4-6 weeks during the growing season.
Buy resistant varieties.
Number 1 Blossom End Rot
A physiological disease most usually seen on tomatoes but can also attack peppers and egg plant.
Usually seen on plants grown under favorable conditions early in the season then subjected to a long period of drought.
Calcium deficiency can also contribute to this disease.
Appears as a dark spot at the blossom end of the fruit (opposite the stem end). The skin of the affected area becomes black and leathery.
Control
Maintain an even supply of moisture.
Mulch plants to conserve moisture
Avoid over fertilizing during fruit development
Try to maintain soil pH around 6.5
Sprinkle ½ cup non fat dry milk around base of plant. (This adds calcium.)
There you have it. There are other diseases that will attack your plants but I feel these are the ones that you are most likely to see.
Check your plants often and take action as soon at you see a disease.
References:
Ohio State University Plant Pathology Bullentin
Virginia Tech Cooperative Extension
Oregon State University Extension
Photos courtesy of Ohio State, Virginia Tech and Oregon State University
About Paul Rodman
Paul Rodman has been gardening for over 40 years. He is an Advanced Master Gardener, and American Rose Society Consulting Rosarian. He is currently president of the Western Wayne County Master Gardener Association in Wayne County, Michigan.
Rodman is the garden columnist for The News Herald newspaper, in Southgate, Michigan. He has also written for the OrganicGardening.com web site.
He has lectured on various gardening topics throughout southeastern Michigan.
His favorite pastime is teaching children about gardening. For the past several years he has conducted classes for second grade students teaching them about subjects ranging from vermi-composting to propagation.
Posted by carrkathy1313 (from Charlotte, NC) on April 29, 2008 at 10:02 AM:
I've spent $600.00 to plant a southern magnolia tree which is approx. 6-7ft tall. It was planted last fall.. Today, after two days of torrential rain I see that many leaves are yellow and the tree itself appears to be getting sparse. Can someone tell me what the problem might be and how to fix it? My family could not believe that I would spend that much for a tree but I just moved south to North Carolina and I truly wanted this beautiful symbol of the south in my yard to enjoy. I just hope the tree is not dying. Any information on this problem will be appreciated.
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Posted by paulgrow (from Allen Park, MI) on April 29, 2008 at 12:52 PM:
After spending that much I would get a certified arborist out to look at it.
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Subject: Great pics!
Posted by greenbrain (from Madison, IL) on April 25, 2008 at 9:34 AM:
I like the nice large pics that'll be helpful identifying these diseases. Most of them I recognized, but didn't know what was going on at the time these symptoms appeared because I couldn't match them to any photos.
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Subject: Fantastic Article
Posted by wrightie (from Metro DC, MD) on April 25, 2008 at 8:34 AM:
Thanks for writing this - the photos are especially handy!
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Posted by cathy4 (from St. Louis County, MO) on April 25, 2008 at 10:06 AM:
I found 3 kinds of mushrooms in my lasagna garden yesterday and was going to start a hunt as to why and how to get rid of it. Perfect timing, now I know what to do. Thanks Paul!
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Posted by rain2shine (from Glen Ellyn, IL) on April 28, 2008 at 10:27 AM:
Great article! I have had my share of most of these. it really helps to have pictures and the descriptions together with how to control them. Thank you!
