Common Disease Problems
Botrytis Blight: This causes the older leaves and the center of the plant to rot. It can start with a yellowish brown irregular spots on the leaves or water soaked spots on the stems. The fungus turns a fuzzy gray and emits a cloud of spores when touched. Burpee Recommends: Remove infected plants and plant debris to avoid the spread of the disease and make sure plants have good air circulation. Keep organic mulches away from the plants as spores can live in the organic matter. Use pea gravel as mulches they will help decrease humidity around the plants.
Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation; if you plant in containers, thoroughly wash them in soapy water and rinse in a ten per cent bleach solution after use.
Downy Mildew: This fungus causes whitish gray patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.
Powdery Mildew: This is a fungus disease that causes a white powdery look on the foliage and is often a problem when growing rosemary indoors. This disease weakens plants as it inhibits their ability to make carbohydrates for themselves using sunlight. Burpee Recommends: You can remove infected plant areas, increase air circulation, and try to reduce the humidity in the room. Check with your Cooperative Extension Service for fungicide recommendations.
Root and Crown Rot: A number of diseases can cause root and stem rots in rosemary. Symptoms include yellowing of the leaves, drying of the leaves and leaf tips, and whole branches may become brown and die. Burpee Recommends: Make sure the soil is very well drained and that the plant does not sit in water. Replace the soil with fresh potting mix for potted plants, after thoroughly cleaning the pot with a 10% bleach solution. Check with your Cooperative Extension Service for fungicide recommendations.
Common Pest and Cultural Problems
Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Leaves turn yellow or brown and may drop off: When the lower leaves turn yellow and the growth slows down this can indicate that the plant needs to be fertilized, or that it is rootbound. Burpee Recommends: If the roots are circling around in the pot (rootbound), clip them and repot the plant. For a nutrient deficiency, use Garden-tone as directed on the packaging.
Mealybugs: Flat wingless insects with a white waxy shell that form cottony looking masses on stems, branches and leaves. They suck the juices from leaves and stems and cause weak growth. They also attract ants with the honeydew they excrete, and the honeydew can grow a black sooty mold on it as well. Burpee Recommends: Wash infected plant parts under the faucet and try to rub the bugs off. They may also be controlled by predator insects such as lacewings, ladybugs and parasitic wasps. Check with your Cooperative Extension Service for pesticide recommendations.
Scale: Insects similar to mealybugs, they feature a waxy outer shell and suck the juices from plant stems and leaves. They weaken the plants and make them more susceptible to other pests and diseases and environmental stress. Burpee Recommends: If they are in the crawler stage (moving insects) they may be controlled with a cotton swab dipped in rubbing alcohol, or you may be able to scraping them off with your fingernail. Young plant parts that are infested may be removed. Check with your Cooperative Extension Service for pesticide recommendations such as horticultural oils.
Spider mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recomends: They may be able to be controlled with a forceful spray every other day. Check with your Cooperative Extension Service for miticide recommendations.
Every year I bring a rosemary plant inside in the fall and every year it dies in a few weeks. What am I doing wrong? Rosemary often has a tough time adapting to indoor growing conditions after being outside. It is often much drier indoors than people realize when they start heating their homes in fall, and the plants also require full sun. Rosemary can benefit from a light misting when grown in doors, and be sure that the pot has excellent drainage. Also, do not allow the plant to dry out, but also do not allow it to sit in water. Place the pot on a tray of moistened pebbles.
I harvested rosemary leaves and tried cooking with them but they were all woody. What did I do wrong? Always chop up your rosemary leaves before using them as flavoring or they will taste woody.
Are rosemary flowers edible? Yes they are! Remove the flower and you can scatter the petals on salads or appetizers.
When should I add rosemary to my cooking? Rosemary can be added early in the cooking process, at least twenty minutes before the food is ready.
How can I turn my rosemary into a topiary plant? Prune the side shoots to encourage vertical growth. Stake the plant and hold it to the stake with soft ties. Let it grow in full sun with plenty of water and when the plant is about 2 feet tall, snip the tops to encourage side shoots. Strip the bottom two thirds of the stem of the branches and leave the top third for shaping. Continue to pinch off the growing tips to maintain a full dense top.