ASK WENDY

Viburnums are susceptible to downy mildew disease


Published: Saturday, July 13, 2013 at 6:01 a.m.
Last Modified: Friday, July 12, 2013 at 10:21 a.m.

Q: My mirror leaf viburnum plants are losing their leaves. This is an established privacy hedge, and I don't want to lose this green wall between me and the neighbors. The leaves get spots and then fall off. Is there anything I can do?

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Awabuki viburnum is an evergreen hedge plant that has an upright growth habit.

Courtesy of Wendy Wilber

A: Mirror leaf viburnum, or Awabuki viburnum, is a gorgeous evergreen hedge plant. Many folks are familiar with the normal viburnums such as the Sandankwa viburnum, sweet viburnum, or our native type, but the Awabuki viburnum is just a little more attractive with its 5-inch-long glossy leaves and upright growth habit.

They can be susceptible to a downy mildew disease that is favored by high humidity and cool nights. Downy mildew blight first starts as large brown spots that merge together. The leaf then takes on a bronze color, curls up and drops to the ground. The spots are on the upper and lower sides of the leaves and the disease progresses quickly. Soon you will see large gaps in the hedge.

As soon as you notice the problem, rake up the diseased leaves from the bottom of the plant and remove them from the landscape. This will help to prevent the spread of the disease back into the hedge. Also, notice where your irrigation is hitting the plants. If your sprinkler is hitting the foliage, redirect the spray so it does not come in contact with the leaves. Downy mildew is a water mold and will be spread by irrigation water. Then you will need to treat it with a fungicide like Heritage or Insignia. Repeat applications will be necessary to bring back the leaves to the hedge. Next spring, watch the Awabuki viburnum carefully, and at the first sign of trouble, treat it with the fungicide.

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Q: My St. Augustine grass is in trouble again. This time the leaf blades have spots and the grass seems to melt down and die.

A: With all the wonderful rain we have been receiving, it is normal to see some disease problems. The spots you are seeing on the St. Augustine grass are more than likely caused by a disease known as gray leaf spot. It is the most common fungal disease, and mid-summer is the perfect time for it to rear its gray, ugly head. You first notice a thinning of an area of turf normally in the shade, and on closer inspection of the blade of grass, you'll notice elongated gray spots, often with a reddish margin.

Current UF/IFAS Extension recommend a fungicide treatment. Banner Maxx and Heritage products will be effective. Spot spray where you are seeing the problems. Beyond chemical treatment you also need to look at the growing conditions of the grass. A few cultural changes can make a big difference in preventing gray leaf spot in the future.

Irrigate early in the morning instead of in the evening. Evening waterings allow the grass blades to stay wet for a long period of time, and this encourages fungal growth. Avoid rapid flushes of growth that can occur with over-fertilization. Follow the IFAS guidelines for turf fertilization to prevent diseases and nitrogen run-off. Brighten the area, if possible, by lifting the tree canopy. Growing grass in heavily shaded areas can make the turf weak and more susceptible to problems. For more information on gray leaf spot, fertilizing grass and proper irrigation, visit the UF/IFAS Extension website www.solutionsforyourlife.com.

Wendy Wilber is an extension agent with UF/IFAS. Email her at wlwilber@ifas.ufl.edu.

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