Diseases of Flowers, Vegetables & Lawn
Powdery Mildew
Powdery mildew looks like a dusting of icing sugar on the upper surface of leaves of susceptible annuals, perennials and roses. It is common in wet, cool weather.
Powdery mildew can be controlled somewhat by keeping plants well spaced apart, watering in the morning, and avoiding getting water on the leaves. Systemic fungicides can also help, but are expensive to use routinely.
Black Spot
Black spot is a fungal infection that causes black spots on the leaves of roses. It is spread in wet weather. Leaves eventually turn yellow and fall off. Many new rose varieties are resistant to black spot but some older ones are very susceptible.
Black spot can be controlled with systemic fungicides. It is also important to plant roses in the sun, water early in the day and avoid getting the foliage wet if possible.
Hollyhock Rust
Hollyhock rust causes numerous black spots on the undersides of hollyhock leaves, causing large yellow spots with red centres on the upper sides.
Hollyhock rust can be controlled somewhat by removing infected leaves as soon as they appear and cutting the plant down to the ground as soon as flowering is finished. It is much more prevalent in wet weather.
Botrytis
Botrytis is a fungus that affects peonies particularly, causing a black rot at the base of the stems, which wilt and fall over. Flower buds shrivel and young leaves have black spots. Be sure peonies are planted just barely below the soil surface.
Botrytis All infected parts should be cut away and destroyed. Systemic fungicides applied to the soil as soon as damage is seen and again in two weeks will keep it under control.
Aster Yellows
Aster yellows is caused by a virus-like organism that affects many plants such as delphiniums, asters, and carrots. It causes stunting, leaf yellowing and a witches' broom appearance, and softening of the roots.
Aster yellows is spread by leafhoppers, so keeping insects under control can prevent it from spreading. There areno chemical controls for viruses.
Mosaic Virus
Mosaic virus causes yellow lines and swirls in leaves of roses, tomatoes, and peppers. It weakens the plants and makes them less winter tolerant, but doesn't kill them.
There is no controlfor mosaic virus. It doesn't spread to other plants so they do not necessarily have to be removed immediately but they will not be good flower or fruit producers.
Blossom End Rot
Blossom end rot is a blackening on the end of tomatoes, caused by the plants' inability to absorb calcium when the soil is too dry.
We have ample calcium in our soil, so keeping the soil moist (not soggy) helps prevent the problem. Some varieties are very susceptible, while others are quite resistant, so choose varieties carefully if it has been a problem.
Physiological Leaf Roll
Physiological leaf roll of tomatoes is a curling and crisping of tomato leaves caused by inconsistent temperatures and watering, not a disease or insect.
Our nights are cool, so planting tomatoes in sheltered places and watering in the morning can help not in the evening. Watering in the evening is sometimes essential, but does mean that moisture on the leaves during our very cool nights stresses the plants. If you have a rain barrell with water warmed by the sun in it, so much the better!
Bacterial Spot of Tomatoes
Bacterial spot of tomatoes causes irregular black spots on the skin that do not penetrate very deeply. Stems and fruit may also be affected. It spreads during heavy rain. It is seed borne.
Remove affected plants immediately and do not plant tomatoes or peppers in the soil for at least two years.
Catfacing of Tomatoes
Catfacing of tomatoes creates lobes and scaly areas instead of the regular tomato shape. It is caused by fluctuating temperatures, and does not harm the tomatoes, although they are unsightly.
Catfacing of tomatoes does no harm to the plants and cannot be controlled. We can't do much about inconsistent weather! Planting in protected spot lessen the chances of catfacing.
Red Leaf of Rhubarb
Red leaf of rhubarb is a bacterial disease which causes a crown rot in the plants. As the root dies, spindly side shoots grow but die quickly and leaves turn a dull red.
Remove affected plant and do not plant rhubarb in that area. It can be spread by foliage feeding insects, particularly aphids, so control of insects can help prevent its spread.
Scab
Scab on potatoes is caused by a bacteria which is carried by manure. The skin appears rough and 'scabby'. The potatoes are safe to eat, although unsightly.
It is important not to use manure in the soil where potatoes will be grown. Compost made from decomposed plants is a good substitute. Alkali soil also encourages scab. Do not add lime to soil in Calgary.
Mushrooms
Mushrooms in lawns grow on decomposing plant material. The most common cause is roots of trees previously removed. The roots take many years to decompose and mushrooms will grow along the root when the soil is wet for long periods of time.
It is important to water your lawn thoroughly and then let it become dry well below the surface before watering again. A good rule of is to water for an hour every 7-10 days. Mushrooms will be much more of a problem in wet, rainy weather. There is no chemical control.
Fairy Ring
Fairy ring is a fungal infection of lawns that causes circles of darker green grass that enlarge over time. Mushrooms often appear in the ring, and a mat of white threads develops below the surface of the soil that water cannot penetrate.
There is no chemical control. Aerating the area will allow water to penetrate the fungal mat and water to reach the roots of the lawn. Use a pitchfork to aerate the area, starting at the outside edge and working inwards, to prevent spreading the infection from soil on tools. Sterilize tools with one part bleach to ten parts water after using. Water well and allow to become dry. Fertilize with a slow release fertilizer regularly. Fairy rings will disappear as they reach a sidewalk, driveway, flower bed, etc.
Snow Mold
Snow mold is a fungal infection that is most prevalent after winters with heavy snowfall. The fungus lives under snow that stays the longest - on the north side of buildings, where snow has been packed because of traffic or has been thrown when shovelling. It causes grey, fuzzy mold on the grass blades, which often turn yellow or brown.
Packed snow that remains longer than usual should broken up to allow air to reach the grass. Shovel snow to a place where it will disappear sooner, if possible. Use a broom to break up the patches of mold. The grass roots are rarely affected and new grass will usually grow in again.
Slime Mold
Slime mold is a fungus that causes patches of sticky, jelly-like masses on lawns. It is more prevalent in wet weather, when the soil-borne fungus can reproduce.
Slime mold is unsightly but causes no harm. When it dries it can be swept off with a broom. No chemical control is necessary.