Crown Gall, Azalea Leaf Gall & Dog Vomit Slime Mold

Christy, a regular contributor to RSFF, sent an image and an email message, “[I] found this gaillardia [or blanket flower] double-dipped in ugly sauce the other day and could not yank it out and dispose of it fast enough. [I]Almost missed it as the flowers and buds did not show the typical aster yellows symptoms that trigger the yankout.

I did not find any similar root blob symptoms when searching. Do you think this is aster yellows or some different issue I need to deal with? Thanks so much!”

Dr. Raj Singh, the AgCenter’s “Plant Doctor” made this diagnosis, “[It] Looks like crown gall caused by Agrobacterium tumefaciens.” Crown gall can appear on a wide range of host plants: Achillea, Anemone, Artemisia, Aster, Campanula, Coreopsis, Delphinium, Dianthus, Gaillardia, Geranium, Gypsophilia, Helianthus, Heuchera, Lathyrus, Nepeta, Oenothera, Penstemon, Phlox, Platycodon, Primula, Rudbeckia, Salvia, Scabiosa, Sedum, andStachys.Plant pathologists from the AgCenter make these recommendations for managing crown gall, “Disease management with crown gall is extremely important. Use only disease-free plants. Avoid injury to roots and crown during planting and cultivation. Plant only in properly fumigated or sterilized soil. Remove entire infected plants as soon as symptoms appear. Use only clean, disinfected pruning tools that have been dipped in a 10% bleach solution before each cut.”

Dennis also sent an email with a clear image of a fungal growth on his azaleas, “These are…pictures of something growing on wild azalea bush in front yard. I have found these on this bush for 3-4 years now. These are small [compared] to some I have removed in past. Can you tell me any information concerning this growth, if [it is] good or bad?”

Dennis has azalea leaf gall, a fungal disease that develops during cool, damp weather that we had earlier this year.

Dr. Raj Singh says, “This is primarily a leaf disease, but occasionally it may occur on stems, flowers and seed pods.”

Singh also adds, “Leaf gall can be managed primarily by adopting good cultural practices in the landscapes. Proper pruning and discarding of galled leaves are especially important in reducing the spread of the disease.

Cut galled leaves a couple of inches below the symptoms, and before discarding them, put them in plastic bags. Remove and destroy affected leaves with galls that have fallen on the ground.

Selectively thin the canopy of established plantings to improve air circulation and promote rapid drying of foliage and maintain adequate spacing when establishing new plantings to avoid creating favorable conditions for disease development.

Fungicides may help avoid infection when applied beginning at bud break, he said. Repeated applications may be required every 10 days if the conducive weather conditions persist for disease development.”

Mike in DeRidder asked, “I have this on one of my squash plants. Is this a concern?”

Mike has “dog vomit slime mold” and it is of little concern. Chris Dunaway, an Area Horticulture Agent in the New Orleans area, wrote about this strange life form, “Yet for having such an un-flattering name, dog vomit slime molds are fascinating and harmless creatures that provide a useful service. As they creep along, yes, they move, they ingulf and ingest bacteria, yeasts, spores, and decaying organic matter. In other words, they are nature’s cleaning crew. But because their favorite home is in decaying plant material and compost piles are made up of decaying plant material, these molds will frequently start residence in our gardens. Do not worry because they are not harmful to the growing plants and in fact, their presence can be an indicator of low fertility in the garden. This is because unfinished compost has more of the wood digesting bacteria and fungi which are the slime mold’s primary food source. These fungi lock up essential nutrients, especially nitrogen, as they work to break down the cellulosic material. This is common in new gardens made with garden soil from dealers that add undigested wood chips to their mix. If you see dog vomit slime molds in your garden, fertilize with a water-soluble fertilizer that is readily available to the plants.”

If you want to contact Roots, Shoots, Fruits, and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337.284.5188 or khawkins@agcenter. lsu.edu.

“Before you buy or use an insecticide product, first read the label, and strictly follow label recommendations. Mention of trade names or commercial products in this article is for informational purposes only and does not constitute endorsement by Louisiana State University AgCenter.”

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”