Fungal Issues in the South Central Texas Landscape: A Basic Primer

Fungal issues arise in our landscapes for a variety of reasons and cause any number of unsightly conditions, and worse, demise in our plant material. Some of the fungal diseases we experience in the South Central Texas Region are:

  • Powdery Mildew,
  • Black Spot,
  • Cotton Root Rot, and
  • Oak Wilt fungus.

We approach these issues by understanding ‘the disease triangle’ – the connection between the plant, the disease-causing organism, and the environment.

Many fungal issues arise from foliage remaining wet for long periods of time and in extended periods of temperatures in a certain range. Careful consideration of irrigation settings, especially during an odd bought of drought or intense seasonal rains, is crucial to successful landscape management. Watering in the early morning is best, to allow foliage to completely dry before nightfall. Leaves are the plant and tree’s lungs. They do not “drink”, they merely breathe.

Proper pruning techniques will save many a fungal issue from arising. Roses are very similar to Crape Myrtles in structure and pruning requirements. They both require excellent internal air circulation. Crossing branches and heavy foliage on the interior of roses and crape myrtles can lead to wet foliage and powdery mildew, which appears grey and crystalline, folding and contorting leaves. Roses will develop Black Spot when foliage is kept wet by improper irrigation rotor heads rather than the preferred drip irrigation. (See diagram for proper pruning techniques to avoid fungal issues in roses and crape myrtles).

041105308_pruning_lagerstroemia_xlg pruningdiagram


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Proper spacing of plant material, based on mature size, will also save many fungal issues. Overcrowded foliage is more susceptible to wet conditions by nature of the foliage density.  Shrubs can be pruned to achieve ideal branch configuration and to eliminate overcrowding and tangled branches. Planting a variety of cultivars, rather than wide swaths of monoculture, help create a well-integrated, multi-faceted garden that encourages beneficial inhabitants.

Powdery mildew and black spot can both be treated organically, with many recipes and opinions available online. Organic controls include neem oil, made from the neem tree in India. Neem has been found to be nominally effective for powdery mildew, and more effective as a broad spectrum, natural insecticide. Baking soda and a dormant oil or liquid soap mixture can be sprayed early on at first detection. Spraying every two weeks will usually deter further development of powdery mildew. Vinegar and even common mouthwash can be used to deter fungal disease. 1 part to 3 parts water is a good rule, but always test foliage to check any particular sensitivities and dilute mixture accordingly. 1 part milk and 2 parts water have been discovered to combat disease while also boosting a plant’s immune system. In any spraying task, wear good rubber gloves and if windy, wear eye and nose protection for any mixtures containing mint, citrus, alcohol or peppers.

Good hygiene in the garden is a very effective tool to combat disease. Keep the base of all plant material clear and free of mulch. Expose the flare root of all trees. In rose gardens, keep foliage exhibiting Black Spot, off the ground, or it will merely keep a cycle of disease going. Dispose of diseased plant matter carefully and do not add to your compost pile.  3-5% organic matter in landscape soils and under turf grass will keep a healthy ecosystem that will feed on organic applications of “biologicals”. We flip the ‘disease triangle’ on its back by building proper, balanced soil biology, planting a variety of cultivars and knowing the early signs of any fungal issue. Set your landscape up for success and know that there are many completely safe, non-toxic methods of help available, should your garden succumb to weather and a “fungus amongus”.

Stay tuned. In our next blog post, we will address Cotton Root Rot and Oak Wilt, A Basic Primer.