Question: We have patches of a weird growth on our St. Augustine lawn that seemed to have appeared overnight. The growth is bluish-black in color and can be easily rubbed off leaf blades. What is it and what should we do about it?
Answer: A few days after the multiple rounds of rainfall ended last week, I started receiving multiple e-mails describing unusual growths suddenly appearing in St. Augustine lawns. The blades of St. Augustine grass have a slime mold and it is commonly found in area lawns when heavy rainfall occurs after an extended period of dry weather conditions.
Slime molds are primitive organisms that feed on bacteria, fungi and decaying organic matter. They often cause concern to homeowners because the growth is colorful and quite noticeable on plant parts.
This is actually the reproductive phase of the slime mold. On turf, large numbers of small gray, white, or purple fruiting structures (called sporangia) form on the leaf blades during rainy, humid weather throughout spring, summer, and fall. Generally, these fruiting or reproductive structures, ranging in size from small pinhead-size flecks to lumps several inches in diameter, form in small patches in the lawn but may reach a diameter of 12 inches or more. In these patches, turfgrass foliage may be dotted with the fine specks of the slime mold or in other cases completely covered by the fungal mass whereas it can be very noticeable.
During wet weather, the fruiting structures may appear slimy in the early stage. As the structures dry out in hot weather, they become powdery, and break up easily upon touching or being walked upon. Although unsightly, the slime molds do not parasitize or infect living plants. Plant structures, such as leaves and stems, serve only as a means of support for the development of the slime mold fruiting structures. Heavy infestations of slime mold may cause a slight leaf yellowing resulting from partial shading of the photosynthetic area. Nevertheless, slime molds rarely, if ever, cause permanent damage to plants.
Chemical control of slime mold is not necessary. Frequent mowing and removal of the fruiting structures from plant parts by raking or even sweeping with a broom are generally sufficient to improve the appearance of the plant. Hosing the affected area down with a forceful stream of water will also break up colonies and removes the visible growth. Excessive thatch or accumulation of organic matter may increase the incidence of slime mold. Therefore, thatch control may help alleviate this problem.
Q: I have an ugly blob growing on the surface of the mulch in my flower beds at my home. While visiting the fruit orchard in the Discovery Garden last week, I saw a similar type of growth growing on the mulch. What is it and is it harmful?
A: The inquiring gardener was amazed (and a bit relieved) to come across blobs growing on top of the mulch around fruit trees in the orchard. Those blobs looked just like the blobs growing on top of the layer of mulch in her flowers beds back home.
The growth is produced by organisms known as slime molds. Slime molds must have been the inspiration for many “B” grade monster movies—bewildered homeowners would title this one “The Texas-size Blob from the Back Lawn.”
The brightly colored blobs usually spread across mulched beds when weather conditions are favorable (i.e., high rainfall, high humidity and warm temperatures). Needless to say that weather conditions over the past few weeks have provided an ideal growing environment to stimulate growth of slime molds.
This slime mold is similar to the one discussed in the first question above; however, this type of growth is produced by a different species of fungus. Fuligo septica is the species of slime mold that produces this type growth pattern in our growing area; this species is typically brightly colored (ranging from yellow, pink to red, depending the stage of growth). These growths can expand to the size of a medium size pizza and then hardens. As they begin to dry out, the bright colors fade to brown and tan. Breaking up the dried blob will reveal a dark brown to black inner core which contains the spores.
Slime molds play a beneficial role in nature by breaking down plant matter, which aids the microorganisms essential to recycling plant nutrients and supporting healthy growth of plants. Like several other critters found in home gardens and landscapes that creep people out, slime molds are actually good for the garden.
Q: I have a pecan tree in my back yard that I planted several years ago. It has leafed out every spring except for this spring. June is nearly over and the tree has not produced any new leaves. Is there a chance that the tree might produce new leaves?
A: I know to never say never on things horticulture-related.
However, given your description and since July is only a few days away, I think it is very, very unlikely that the pecan tree will put on any new growth this year since it has not done so thus far. Pecan trees are deciduous (a term meaning “falling off at maturity” and typically used in reference to trees or shrubs that lose their leaves seasonally– most commonly during autumn). While pecans are typically among the last trees to establish new leaves in the spring, they should have put on some new growth by now.
William Johnson is a horticulturist with the Galveston County office of Texas A&M AgriLife Extension Service. Visit his website at aggie-horticulture.tamu.edu/galveston/index.htm.
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