Guess what it is doing outside while I write this on Monday? Raining, of course. I can’t think of the last time I have seen so much rain over an eight-day period of time. Since Sunday night, June 2, I have gotten 9.4 inches of rain – and that doesn’t count Monday’s deluge!
We desperately needed the rain when it came because we were bone dry, but since we have gotten so much of it, certain problems could be showing up in the lawn and landscape.
One particular problem is slime mold on turfgrass, mainly on St. Augustine and zoysia. Monday I was e-mailed pictures from two people who had this mold on their grass.
Many fruiting bodies of these fungi may suddenly appear on the blades of turfgrass in small patches. They can be purplish, gray or other colors. These fungi grow on the surface of leaves and do not kill the leaves, but if it remains on there long enough, it may cause some yellowing by shading the affected leaves. There is no need to use a fungicide on this; just take a water hose and wash it off.
If we get back to drier times and it shows up on your grass, it means you are watering too often.
Another turfgrass disease that might have developed is dollar spot, mainly on Bermuda and zoysia lawns. It will occasionally show up on centipede too. Dollar spot appears as small tan-to-brown patches in the lawn. The best way you can tell if your grass has dollar spot is to go out in the morning when dew is on the ground and see if there is a white, cobwebby growth on the infected patches. Then look at the blades of grass up close and you should see small, gray or light tan lesions with reddish-brown margins.
This disease is a little different than the other ones we deal with around here. It usually occurs when the nitrogen levels available to the grass are inadequate and when there are heavy dews, particularly in May and June, then again in September and October. Last year it persisted all summer long on zoysia because of the cooler summer temperatures, coupled with excessive rain and cloudy days.
With all the rain, much of the nitrogen fertilizer put out a couple of months ago is gone, so adding more fertilizer is generally sufficient control and usually allows the turf to outgrow the problem.
This is a leaf blight disease and the use of fungicides is rarely necessary. If you think you have fertilized sufficiently and still have dollar spot, some fungicides you can use are myclobutanil (Fertilome F-Stop, Immunox), thiophanate methyl (Scotts Lawn Fungus Control), or maneb (Hi-Yield Maneb Lawn and Garden).
Shoes, garden hoses, mowers and other lawn equipment spread the fungus organisms.
Those with St. Augustine may also see gray leaf spot. Gray leaf spot lesions resemble dollar spot. They are straw colored with purple to brown margins. Severely infected blades wither and turn brown.
To help in control, do not over fertilize the St. Augustine. Fungicides can be helpful but it is very rare that the disease gets bad enough to warrant applying them. Most, if not all, of it will go away on its own once it gets drier again. If you feel a fungicide is warranted, choose between propiconazole (Ortho Lawn Disease Control, Fertilome Liquid Systemic Fungicide) or the above-mentioned thiophanate methyl.
A lot of annual flowers such as vinca, petunias, geraniums, and begonias may get root rot fungus due to saturated soils.
Symptoms of a plant with root rot are stunted growth, marginal leaf burn, wilting, yellowing, and general decline. These symptoms can be caused by other root problems such as nematodes, drought, low fertility, and/or improper planting, so a plant will have to be removed from the soil and examined to diagnose the problem.
The root system of affected plants is usually smaller than normal. Roots are fragile; they break apart easily when touched. Often, the outer portion of the root will strip away easily from the inner portion. Depending on the pathogen involved, the color of the roots may also show you something. Roots are usually a pale gray or honey color if infected with a disease called pythium. They are tan to brown if infected with Rhizoctonia, or streaked with black if infected by one we call black root rot. These are all root rot diseases. Once plants are displaying advanced symptoms, remove them because they cannot be cured.
Control for root rots should be preventive. Proper planting (breaking up the root ball and planting in well-prepared soil) reduces the likelihood of root rot diseases. Incorporating compost can improve drainage in wet areas and reduce the incidence of root rot diseases.
Elevating the grade of the bed by adding additional soil is also helpful.