I have large patches of periwinkle (vinca) ground cover around my house, it...
I have large patches of periwinkle (vinca) ground cover around my house, it is well established and has thrived for years. Suddenly this year a large patch that grows outside the slider door and up to the cement wall is rapidly dying off. The plants get brown and dry and then are gone. The die off started at the wall and is moving outward from the wall. The cement wall is not the problem because most of the vinca around the house grows up to the wall without any problem. We have done nothing new or different in this area, no animals visit there, no drainage problem, no apparent fungus (until they die, the leaves are healthy and glossy the same as all the other vinca around the house.) It gets the same sun, water, etc., as all the other vinca areas. We will get a soil sample, but any ideas? It is heartbreaking to see beautiful ground cover disappearing at a fairly rapid rate. Since it started in early summer, an area approximately 6 ft by 2 ft has died off. Thanks very much.
It would be helpful to submit photos of the vinca foliage that is declining - going from good to bad. Some possibilities of the decline of your vinca may be phomopsis blight, a fungal disease, or voles. You did not mention the site that they are growing in. Vinca grows best in light shade in moist, well drained soil. If located in too much sun they will be stressed.
Vinca is susceptible to fungal diseases, Phomopsis and Phoma Dieback of Vinca which are prevalent during rainy seasons ( which we experienced earlier in the season). Stressed plants are more prone to infection and dieback.
These fungal diseases attack through wounds, spread by water, and are favored by high levels of moisture. If the groundcover is located under mature shade trees and if leaves accumulate and are not removed they can trap moisture which promote the above fungal diseases. Remove fallen leaves and old debris. Unfortunately, the only way to deal with it is to thin the groundcover out severely. You could even try mowing high in the spring. See our Plant Diagnostic website http://plantdiagnostics.umd.edu/level3.cfm?causeID=627
Also, look around the base of the plants for silver dollar sized holes. If you see these holes, you may be dealing with voles, a type of meadow mouse. They feed on the roots of herbaceous plants, trees, and shrubs and cause dieback. Voles use the groundcover to hide in. See our Plant Diagnostic website for more information http://plantdiagnostics.umd.edu/level3.cfm?causeID=641