Common Disease Problems
Bacterial Leaf Spot: First signs are small translucent spots with a broad yellowish edge that slowly enlarge and become angular or irregularly circular with a reddish center. It thrives in cooler temperatures. Burpee Recommends: Remove infected plants. Avoid overhead watering. Do not work around plants when they are wet.
Edema (Oedema): Leaves become distorted due to excess moisture in the soil. Plants absorb more water than they can use. Burpee Recommends: Do not overwater plants, keep the soil moist but not wet. If drainage is poor add compost or peat moss to improve drainage.
Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.
Rust: A number of fungus diseases that cause rust colored spots on foliage and stalks. Burpee Recommends: Remove infected plants. Contact your Cooperative Extension Service for recommendations.
Smut: This fungus attacks mostly young seedlings as the new leaves emerge. It causes blister-like lesions near the base of the plant and streaks on leaves. The streaks mature into black powdery spores. The fungus stunts the growth of the plants. More mature plants are not as susceptible. It is most prevalent in temperatures under 75 degrees F. The disease lives in the soil for several years. Burpee Recommends: Some fungicides are effective, Check with your Cooperative Extension Service for 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.
Mealybugs: Mealybugs are 1/8 to ¼ inch long flat wingless insects that secrete a white powder that forms a waxy shell that protects them. They 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 affected plant parts and try to rub the bugs off.
Rabbits: Chew on plant leaves. Damage is similar to deer damage but not usually as extensive. Burpee Recommends: Use a hot pepper wax spray or rabbit repellent.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
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 Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.
Ornamental Grass FAQs
Can I grow ornamental grasses in containers? Yes for smaller types, such as carex or hakonechloa, but not larger types such as cortaderia or panicum.
Are ornamental grasses deer resistant? Yes, most ornamental grasses are deer resistant.
Do ornamental grasses bloom? Yes, some have very showy plumes, such as eragrostis and cortaderia, while others bloom but are grown primarily for the foliage, such as carex and hakonechloa.
When should I divide my ornamental grass? The best time to divide them is usually in early spring just as the new foliage is coming up.
Do ornamental grasses attract pollinators to the garden? The ones that bloom attract birds and butterflies to the garden.