White powdery mold

White powdery mold can be seen on this Mondarda plant, pictured.

Summer arrived in true form this week with heat and humidity. The dry weather and hot temperatures have been replaced with cooler temperatures and rain along with a few heavy downpours and storms. The garden, both flower and vegetable gardens, look considerably better this week than 10 days ago, but the dampness is likely to create a great environment for molds and fungus issues to thrive in.

Molds and fungus can affect multiple species or be specific to just one plant. There are those that like warm, damp weather and others that prefer cooler damp weather. The most common garden issues in summer are those that thrive above 70/80 degrees. For any fungal disease to take hold, you need a host, a pathogen and the right environment. We cannot control the weather, but we can help avoid some issues by picking disease resistant plants and practicing good garden maintenance to keep the worst of the problems away.

Powdery mildew is a common issue on many plants including squash, roses and bee balm and it shows as a covering of white dust. Lack of good circulation is a prime cause of this mildew on large squash leaves that tend to crowd each other out. For a squash plant that has lots of healthy leaves, just remove the infected one promptly and discard the leaf in the trash rather than the compost.

Roses do get powdery mildew, sooty mold (a black covering) and black spots which can all occur on the leaves leading to overall yellowing of the leaves and eventually defoliating the plant. Early detection and treatment is the key to keeping roses healthy. Also try one of the new range of roses that were developed after the Knockout rose such as the ‘Oso Easy’ range of garden roses. These new roses are compact, easy to care for and generally disease free.

On tomatoes the most common issue is general rotting and blossom end rot, a condition that caused many gardeners to give up on tomatoes last year. Some more resistant varieties are out there, and last year I had great success with Garden Gem which is a new variety, developed in Florida for the Proven Winners line.

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Tomatoes also have two soil born issues – the fusarium wilt and verticillium wilt. Verticillium wilt is seen as browning of the lower leaves and stems. Fusarium wilt on the other hand starts closer to the top where the ‘starved’ new growth is affected. Look for disease resistant tomato varieties and clear all tomato debris from the garden, including dropped cherry tomatoes, during and after the season. Rotate the tomatoes each year to minimize the impact of soil borne problems or use a container with fresh potting mix each year.

For treatment of fungal issues, I prefer to use an organic spray such as Neem which helps minimize the spread of above ground issues, and always disinfect your clippers and tools both between gardening areas and gardening sessions to minimize transferring the fungal issues from one garden to the next.

Always ensure that you identify the issue as fungus or insect and it’s preferred habitat before you treat a plant.

A good comprehensive guide to common garden fungal issues can be found at wia.unl.edu/documents/4113987/vegdiseases.pdf

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