Troubleshooting Specific Problems
Fungi When you live in a climate with high humidity, fungal problems abound. Black Spot and Powdery Mildew are the two most frequent problems with roses. Optimal conditions for Black Spot are 64° - 75°F with relative humidities around 95%, and the spores must be wetted continuously for several hours. For Powdery Mildew, optimal conditions are 81°F during the day and 61°F during the night with relative humidities anywhere from 40% - 70% during the day and 95% - 99% during the night. Although these are optimal conditions, most experienced gardeners know that fungi is seen here in Texas in less than optimal conditions.
Before describing some treatments, let's review the recommended environmental conditions for roses to reduce infections. The fungal pathogens need wet leaves to grow. So, keep the leaves as dry as possible. Plant your roses where they will get plenty of sunshine and good air circulations. The sun and wind will dry the leaves quickly. Since we have fog and morning dew occasionally, morning sun is best if you have the option. Instead of overhead irrigation, use dripper lines. If irrigation spray heads must be used, time them for just before sun-up. Once infected, the fungal spores will rapidly spread. Removing the infected leaves reduces the outbreak providing for a quicker control. We use a leaf blower in our gardens. On a low setting, it will blow infected leaves off the plant without disturbing the blooms. Higher settings remove the fallen leaves from the garden beds. This one cultural practice works wonders.
There are some excellent organic tools for control of fungi, including Serenade, Compost Tea, and Neem Oil.
Serenade provides protection against a broad spectrum of the most common fungal and bacterial garden diseases, yet is completely non-toxic to bees and beneficial insects. It is certified for use in organic gardening and can be used on your roses, fruits and vegetables, including tomatoes and peppers.
Diseases controlled include Bacterial Leaf Blight, Bacterial Speck, Bacterial Spot, Black Mold, Black Root Rot, Black Spot, Downy Mildew, Early Blight, Fire Blight, Gray Mold, Late Blight, Leaf Spots & Rusts, Powdery Mildew and Scab.
Serenade is available in a 24 oz ready-to-use spray bottle.
Compost Tea should be used as a preventive during the heavy growing seasons (Spring and Fall). As a foliar application, the beneficial organisms eat the food (exudates) disease-causing organisms require. Apply twice a month with a pump sprayer. As needed the rest of the year to control any noticeable disease.
Neem Oil is an extract from the Neem Tree. is an effective preventative control of most common garden fungus diseases like black spot on roses, rusts, powdery mildew, leafspot, blight and others. It is completely non-toxic to humans, pets, birds and other animals, and is harmless to beneficial predator insects that visit treated plants. It is gentle on the environment, too, biodegrading into harmless components in 2-3 weeks.
As a preventative fungicide, apply once every 7 to 14 days until the potential for disease development is no longer present. Spray to run off. Complete coverage of all plant tissue is necessary for control. We have not found it too effective once a bush is infected. In that situation, use Serenade.
Neem Oil comes in 24 oz. ready-to-use spray bottles, and in concentrate form for larger gardens.
Insects There are so many bugs in our gardens they cannot be counted. Even though most are beneficial and useful, the remaining few are unbearable at times. There are many options in the organic gardeners toolbox.
The long-term approach to controlling insects is to use beneficial insects. Click on the link to learn about those readily available solutions.
There are a few organic sprays available for a more direct and immediate control of problem insects. These are to be used when a problem insect (or symptoms thereof) are detected.
Neem Oil. Yes, this is the same Neem Oil product that controls fungal problems. Neem is actually a three-in-one solution, acting as a fungicide, insecticide and miticide. As an insecticide, Neem is quite selective in that it will not kill or repel you beneficial insects. It will kill any insect that ingests it. By applying to the foliage, any insect that chews and eats your foliage will die. Since beneficial insects (such as Lady Bugs or Praying Mantis) eat insects rather than leaves, they are not affected.
Neem Oil is labeled for aphids, whiteflies, spider mites, scale and many other insect pests. It is safe to apply to vegetables, fruits, nuts and herbs.
BT or Bacillus Thuringiensis is a biological control of leaf chewing worms and caterpillars on vegetables, fruits, shade trees and ornamentals. It will not harm bees and other beneficial insects.
Insecticidal Soap works best on soft-bodied insects such as aphids, mealybugs, spider mites, thrips, and whiteflies. Insecticidal soaps should be applied when conditions favor slow drying to maximize effectiveness, i.e., in the early morning hours with dew coverage or in the early evening. Avoid treating with soaps on hot sunny afternoons which promote rapid drying of the material. Soaps must come into contact with the insect. This may require spraying the under side of the leaves.