Roots, Shoots, Fruits & Flowers: More Slime Mold, Toxic Beans, Black Rot in Grapes and Walnut Caterpillar.

dog vomit slime mold.

Fig. 1 Dog vomit slime mold.

Castor bean plant.

Fig 2. Castor bean plant.

Black spot on grape.

Fig. 3. Black spot on grape.

Fourth stage of the walnut caterpillar.

Fig. 4. Fourth stage of the walnut caterpillar.

Amanda, a vegetable gardener, sent her message and an image, “We have a small raised bed and have started noticing what seems to be a fungus on our cherry tomatoes. I would appreciate any info you have on this and any solutions you may have to clear this up. I have included a photo.”

Amanda has “dog vomit slime mold” on her tomato plant. The good news is that it is harmless and can be rinsed off with a hosepipe. Dr. Raj Singh, the AgCenter’s “Plant Doctor” wrote this article “Slime mold showing up in Louisiana gardens” and he advised, “Slime molds are non-parasitic organisms…. Slime molds feed primarily on bacteria and other microorganisms.”

A homeowner from Alexandria called the AgCenter and had concerns about a “castor tree”. A neighbor advised that this tree is toxic, and our homeowners wanted to confirm this statement.

The short answer to the question of toxicity is “yes”. Dan Gill, retired horticulturist made this very clear point in an article, “Remember the seeds are highly toxic.” Dr. Christine Navarre, Extension Veterinarian, wrote about toxic plants to livestock, “Horses are easily poisoned by castor beans, the seeds being more of a hazard than the leaves and stem.” NC State Extension adds that cats, dogs, children, and adults can become painfully ill and even suffer mortality. The reason for this severe toxicity is a chemical called ricin. Based on all this information, why would anyone want a dangerous ornamental like castor bean plant?

Christy wanted to know, “What’s up with my white grapes???”, and she added, “These bunches were closest to the bottom of the vine. Some bunches farther along look unaffected or less affected.”

Dr. Stephen Vann, a plant pathologist with the University of Arkansas made this observation, “Although black rot can produce symptoms on any green portion of the vine, the most dramatic damage occurs to the berries. Infected berries turn dark blue-black and shrivel. Infected berries often cling to the cluster and resemble ‘raisins’”.

Dr. Vann discussed the control of the disease, “Disease management is most effective early in the season before the fruit rot phase has developed. For small home garden plantings, removal, and destruction of infected fruit clusters (mummies) and leaves during the late fall or winter can minimize disease incidence and severity the following growing season. Infected clusters and leaves may also be disposed of by burying in the soil. Weed control around plants encourages good air movement helping to keep leaves dry, reducing disease. Although many grape cultivars have some level of resistance to black rot, fungicide applications may be necessary, especially during rainy periods in the spring.

Chemical control options for the homeowner include fungicides containing the active ingredients of copper, lime sulfur, Bordeaux mixture, Captan or myclobutanil. To be effective, fungicide applications should begin early in the spring when young shoots are developing. Sprays may also be timed to anticipate rain events.”

Finally, here is a follow up note regarding the Tred Not slippery tape mentioned in the last RSFF. Marge writes, “[Here is] just a note on the slippery tape. My pecan trees are fairly old. The bark is so rough I could not get the tape to stay on and there were definitely spaces underneath that worms could crawl under. [I] had only one tree that it is successful on.... Thankfully, the worms do not seem to be such a menace this year! Unless they are still coming😳.”

If you want to contact , please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or Also, you can be on the “green thumbs” email list by emailing your request to the address above.

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

6/23/2020 7:00:41 PM
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