Disease Control

Plant diseases are often linked to a few simple issues.

Most common is a plant living in the wrong environment; how often does that plant from the nursery fall into poor health in a matter of weeks.
Read the plant tag before buying any gorgeous flower from the nursery and make sure you have a space at your home that fits its lifestyle.

Second most common problem is too much water or to infrequent a watering schedule.
Plants prefer a regular schedule for watering and fertilizing.
The further you get from that ideal situation the more stress it causes on the plant. Diseases, like pests, prefer a stressed plant.

And the third most common reason for disease problems is plant litter.
Many diseases overwinter on infected leaves and petals scattered about underneath the plant.
Remove any diseased plant material and do not add it to your compost.
This is very true of petal blight in camellias and black spot on roses.

Also check out the links page for links to fruit tree care and organic pest and disease management.

Baking soda makes an inexpensive control for powdery mildew on plants and helps on treating black spot and other foliar problems.

The baking soda fungicide is mostly effective as a preventative, the active component is a change in pH on the leaf which inhibits fungus.
Weekly spraying of susceptible plants during humid or damp weather can greatly reduce the incidence of powdery mildew in your garden.

Mix together:
• 1 tablespoon of baking soda
• 1 tablespoon of white vinegar
• 1 tablespoon of canola oil or similiar cooking oil
• 1 gallon of water
Add to a spray bottle and spray liberally on top and bottom of all leaves.
Apply in shady conditions, full sun will cause burning and leaf drop.
After effect will be a whitish residue on the leaves that is less uniform than powdery mildew.

Powdery mildew thrives in temperatures between 60 and 80 degrees. Dry, shady conditions are ideal, as are areas with poor air circulation. Planting disease resistant cultivars and making sure you allow for good air flow are two ways to guard against powdery mildew. Inspect plants regularly during warm, dry conditions, and remove any leaves that show signs of infection. Destroy (do not compost!) infected plant parts. A spray made with baking soda, if applied weekly at the first signs of infection, can protect plants against further damage. Plants that are badly infected should be ripped out and destroyed to prevent the disease from spreading further.

Interestingly enough, the most effective measure in preventing and treating powdery mildew is to spray the foliage of your plants daily with plain water from the hose. Powdery mildew hates water! The only caveat with this method is to be sure you do it early in the day so that the foliage completely dries before cooler evening temperatures arrive, otherwise you may invite other fungal diseases, such as black spot, into your garden.

Black spot spores overwinter on infected foliage and canes, including infected foliage that has fallen and been left on the ground. In spring, spores are splashed up onto newly emerging foliage during rains or irrigation. Once the weather begins to stay consistently warm and humid, the spores germinate and infect the plant within one day. Visible symptoms (black spot and some yellowing) will be evident within five days, and it will produce and spread new spores within ten days. The new spores will infect other parts of the plant, or be carried on the wind to any other nearby rose bushes.

Black spot is easy to recognize in its latter stages, but might not be noticeable in the beginning. In fact, by the time black spot starts showing signs, as few as 3 to as many as 10 days have already passed since the fungus first germinated. The first visible symptom is black-colored spots on the leaves. As the disease progresses, a yellow ring forms around the black spots and the spots spread through to the underside of the leaves. Spore-producing spots will be visible upon close examination. The black spots will continue to grow and soon the entire leaf may turn yellow. Many of the yellowed leaves will begin falling off the bush.

Black spot is a fungus and as such, it spreads. It’ll easily jump from one bush to another for as long as it’s left untreated. Like most fungi, black spot thrives in warm, moist environments. Spores will germinate after 7 hours of being wet and when the ambient temperature is between 65 F (18 C) and 75 F (24 C). The warmer the weather, the quicker the disease spreads.

Seeing red pustules on the underside of rose leaves? That is Rose Rust and is usually more of a problem in our Fall weather. For some reason we are seeing some Rust in the garden earlier than usual. Rust is another problem caused by a fungus; there are nine species of the rust fungus Phargmidium that attack roses. Spores that are carried by the wind spread funguses and when conditions are optimal, they infest our roses. Wet leaves for two hours or more and temperatures between 64° and 70° are enough to get Rust established on our roses.

If the infestation is light simply pick off the infected leaves and dispose in the trash. Again, planting with full sun and spacing bushes so that they are not crowded will help but if a particular bush seems to be infested year after year then prune with the shovel and dispose of your ‘Typhoid Mary’! The home remedy mentioned under Powdery Mildew will help, but again, if you must resort to chemicals then check with your Agricultural Advisor or a nursery for their recommendations.