Leaves Drop; Stems Woody Due To Watering Problems
Overwatering: Shasta daisies growing in poorly drained or heavy soil, or soil that gets too much water, start to drop their leaves because their roots are drowning. Move the plants to a better-drained site and improve the original soil by mixing in lots of sand, peat moss and other organic materials to increase its ability to drain excess water.
Underwatering: If shasta daisy plants are consistently underwatered, they’ll develop woody stems and lose many of their lower leaves. Water more frequently, and insure that the water soaks through the mulch layer instead of running off bare soil. Water more frequently during droughts.
Lanky, Flopping Stems Are Caused By Too Much Shade
Shasta daisies need at least 5 hours of sun daily; even more is better. If they do not receive this, either clear away the plants or prune off branches which are shading the maturing shasta daisies, or move the plants to a sunnier location. If sun is scarce in your yard, plant them in containers that can be moved into the sun.
Leaves Are Curled And Distorted By Aphids
Aphids, also called “plant lice,” are soft-bodied, pear-shaped sucking insects about the size of the head of a pin. They often gather in large, visible groups on tender tips of stems and buds of shasta daisies. Their feeding distorts plant growth. Leaves may turn yellow or brown. They wilt under bright sunlight, or sometimes curl and pucker. Often this problem most easily eliminated by simply pinching off the infested tender tips and discarding them, aphids and all, in a plastic bag in the trash. Since shasta daisies respond well to pinching of their tips anyway, this does them no harm. If aphids return, then spray them with an insecticidal soap product according to label directions. Check to see if the plant is stressed in some way that makes it vulnerable to insect infestation.
For more information see file on Dealing with Aphids.
Plant Grows Poorly Because of Mealybugs
Mealybugs are 1/5 to 1/3 inch long, oval, flattened, covered with white waxy powder and adorned with short, soft spines around their margins. They suck plant sap, then the honeydew secretions from their feeding encourage mold growth on the shasta daisy leaves and attract ants. Mealybug-infested plants look unsightly and grow poorly. They may die if severely attacked. Control mealybugs by spraying them directly with insecticidal soap according to the product label.
For more information see file on Dealing with Mealybugs.
Ragged Holes In Leaves Are Chewed By Slugs Or Snails
Slugs are essentially snails without protective shells. They are usually 1 to 2 inches long (some species grow up to 8 inches). They may be white, gray, yellow, brown or black. Shasta daisies attacked by slugs and snails suffer large ragged holes in their leaves and stems. Slugs and snails are attracted to moist, well-mulched gardens and acidic soil. They are active at night, rasping holes with their file-like tongues in leaf and stem surfaces. They hide under boards or leaf litter during the day. Trap them in either a commercial slug trap or a shallow plate baited with beer and set in the garden. The pests are attracted to the yeast in the beer, climb in, and drown. Begin trapping within the first three to four weeks after the last frost. The more you catch early, the fewer there will be to reproduce over the season. If your trap has no cover, renew the beer or yeast bait after it rains. For more information see file on Dealing with Slugs and Snails.
Leaves Are Mottled, Blotched By Botrytis Gray Mold
This fungus attacks shasta daisy leaves in cool, damp environments or if they have too much shade. Control it by thinning plants to improve air circulation, moving them to a sunnier location, or improving soil drainage. Pick off damaged leaves and dust uninfected leaves with a garden sulfur fungicide to prevent the spread of the fungus. Dig up and discard individual plants that seem to catch this disease year after year.
For more information see file on Dealing with Fungal Disease.
Leaves Covered With White Powder Have Powdery Mildew
Powdery mildews are caused by fungi that live on the surface cells of the plant, not inside them. Infected leaves are coated with a white or ash-gray powdery mold. Badly infected shasta daisy leaves become discolored and distorted, then drop off. Powdery mildews thrive in both very humid or very dry weather. They are not life threatening, but they are unsightly. If it is not possible to ignore the mildew, spray healthy leaves on affected plants and healthy neighboring plants thoroughly with a garden sulfur fungicide to prevent the spread of the fungus. Follow the instructions on the product label. Allow ample spacing between plants to promote air circulation and collect and discard all aboveground refuse in the fall. For more information see file on Dealing with Fungal Disease.