1 - Vinca and other plants may have diseases, but good samples are needed to properly diagnose problems.
Q. I am a novice gardener and have a sick vinca plant that I enclosed in this letter. A local seed store said it has "rust", but the product that they sold me last year did not work. The flower bed this plant is in is under a Russian olive tree and once upon a time the vinca thrived there. It was tall and green. Last year it never did grow and the flower bed looked very sparse.
My questions are; Should I dig out the infected plants and if I replace them with healthy plants alongside the others, will the new plants also get the "rust"? I am also seeing aphids on the plants.
A. It is possible that the sample you sent has rust fungus, but the sample arrived in very poor condition because it was sent in a plastic bag. The sample rotted under those conditions, but there appear to be spores of the rust fungus in the bag (and I see one of the aphids you mentioned).
From your description I wonder if the problem is more than rust fungus. The rust will be present and cause defoliation during periods of high humidity, but should disappear when the weather is drier. Because of your description, I am concerned that there is more than rust fungus involved. I suggest you take some sample foliage and twigs (pressed and in paper, not plastic) to your local Extension Service County Agent. Also, take some samples of the injured (not dead) plants by digging a sample of stem and attached roots. The Agent will look at this for signs of root disease and perhaps send the sample to the Plant Disease Diagnostic Laboratory in Las Cruces. Put these plant/root samples in a paper bag after wrapping them in paper. If these samples are kept in plastic, the sample may be contaminated by fungi that grow in the moist environment in the plastic.
If you dig up the old plants and replace them with new, healthy plants, there is a possibility that they too will develop the disease. It is important to determine what is happening to the plants before replacing them. It may become necessary to replace the plants with a different plant that is not susceptible to the specific disease if there is disease discovered in the roots. The spores of the rust fungus will remain in the local environment and under the proper conditions they are very likely to infect new vinca plants, but other species may not become infected.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: email@example.com, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!