15 Minutes of Fame for Leaf Spot

After looking back through prior alerts and posts, I discovered that leaf spot diseases have never made the cut, until now.  Recent weather patterns of cloudy and rainy weather across much of North Carolina have been perfect for foliar diseases such as Bipolaris leaf spot and gray leaf spot.

Bipolaris Leaf Spot on Bermudagrass

We have received several samples of bermudagrass in the past week that were devastated by the fungus Bipolaris cynodontis. Bipolaris leaf spot is most severe on turf that is growing slowly due to adverse weather conditions or improper management practices.  Shaded areas with little or no air movement result in weak turf and extended periods of leaf wetness that favor disease development. Deficient or excessive nitrogen, excessive thatch, extended periods of leaf wetness, drought stress, and low mowing heights are factors that encourage the development of leaf spot diseases.  These fungi may spread to the crowns and roots and cause melting out, which is most severe during periods of hot weather.  For more information about leaf spot, including control recommendations, click here.

Gray Leaf Spot on St. Augustinegrass

We have also received several samples of gray leaf spot on St. Augustinegrass here at the NC State TDL. Proper mowing practices are most important for gray leaf spot management in St. Augustinegrass. This grass must be mowed frequently during the summer months to remove excess leaf tissue, keep the canopy open and dry, and remove developing gray leaf spot lesions. Collecting clippings reduces spread of the disease when gray leaf spot symptoms are evident. Apply nitrogen and other nutrients as recommended to maintain vigorous foliar growth during the summer months. Excessive shade, in addition to promoting leaf wetness, slows St. Augustinegrass growth and enhances gray leaf spot problems. For more information about leaf spot, including control recommendations, click here.

Summer Solstice Welcomes Brown Patch

June is in full swing and so is brown patch in tall fescue lawns and landscapes.  Brown patch, caused by the fungus Rhizoctonia solani, is the most common disease in tall fescue during late spring and throughout the summer months in North Carolina.  Brown patch infections can start as early as April in some years with full blown outbreaks occurring by late May and early June in most years.  As the name implies, symptoms are brown to tan areas of turf that are roughly circular patches that range from a few inches to several feet in diameter.

Brown Patch Lesion on Tall Fescue Leaf

The two most common mistakes managers of tall fescue make are fertilizing too late or too much in late spring and over watering.  Tall fescue should not be fertilized after the first of May, unless you are using ultra low rates (< 0.25 lb N/M) with iron for a color effect.  The recommended amount of nitrogen on tall fescue per year is 3-4 pounds per 1,000 square feet.  Most people will apply a pound or two in the fall and a pound or two in the spring.  When in doubt, submit a soil test to ensure you're feeding your lawn the right nutrients at the correct amounts.

Watering should be done only as needed to prevent drought stress.  When you do apply irrigation, do it deep and infrequent instead of watering every day.  It is a common mistake for homeowners to set their irrigation system on a schedule and forget about it.  Remember, fungi love water and if you over water, you're giving the advantage to the fungi, not the turfgrass.  The ideal time to water your lawn is in the early morning hours before sunrise.  Irrigating during late afternoon or early evening is the worst thing you can do because this extends the leaf wetness period, however brown patch will love you for it!

Symptoms of Brown Patch in Tall Fescue

Need help knowing when and how much to water your lawn?  Try out our online water management tool at the following link.

http://turf-ims.ncsu.edu/

For more information about brown patch, including control recommendations, please visit the following link.

http://www.turffiles.ncsu.edu/Diseases/Brown_Patch.aspx

Severe Large Patch Outbreaks in NC

You know it's officially spring in North Carolina when there are giant patches of brown grass in bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. These giant patches of brown grass are better known as large patch, caused by the fungus Rhizoctonia solani, and if you've ever had an outbreak of this disease, you now know why the disease was coined large patch.

What you may not know however, is what your control options are this time of year. You shouldn't worry too much if you have this disease on bermudagrass. Bermudagrass tends to grow out of the damage once the temperatures are consistently warmer and the daylight longer.

As for our other warm-season friends, damage tends to be most severe on centipedegrass and recovery may take all summer in extreme cases. Unfortunately, there isn't much you can do to make for a magical recovery. We rarely recommend fungicides for large patch in the spring of the year, however in worst case scenarios, a fungicide application might help prevent the disease from spreading further. Fungicide applications are best when they are applied preventatively in the fall. If you choose to spray a fungicide this spring, don't expect a miracle to happen overnight. Also, remember that recovery will be even slower and tougher if you've applied a DNA type of herbicide as your pre-emerge for summer weeds.

In most cases, the best thing is to stay the course with management practices that will encourage each type of grass to do well. In severe cases, treating damaged areas like a new establishment with light and frequent fertilizer and water inputs may help encourage faster lateral spread. This doesn't mean you should apply more fertilizer, just smaller doses more often. Applying too much fertilizer will make the disease worse this fall!

Finally, be sure to map the affected areas now while they are clearly visible. You will save yourself some money this fall by spot treating these areas instead of having to make a whole property application, since the disease tends to reappear in the same areas.

For more information about large patch, click here.

For more information about warm-season grass maintenance, click here.

Nitrogen source impacts spring dead spot of bermudagrass

Most turf managers in the southeast and midwest are all too familiar with spring dead spot. However, in light of the results presented below, it is important to realize that the disease is caused by three different species: Ophiosphaerella herpotricha, O. korrae, and O. narmari. The most common species in the southeastern US is O. korrae, whereas O. herpotricha is prevalent in the midwestern US. If you are unsure of which species you have, ask your friendly neighborhood turf pathologist to find out which species is most common in your area.

We initiated this research in 2004 to determine how fertilization programs influence these different spring dead spot species. Each plot was inoculated with O. korrae and O. herpotricha in Fall 2004, fertilization treatments were initiated in May 2006, and were continued through 2007 and 2008.

Some of the main findings of this research are as follows:

1. Spring dead spot caused by O. herpotricha was suppressed very effectively in all 3 years by fertilization with ammonium sulfate. Sulfur coated urea provided some control in 2008, and calcium nitrate provided moderate suppression in 2009.
2. Ammonium sulfate had no effect whatsoever on spring dead spot caused by O. korrae. Instead, calcium nitrate provided almost complete control of this species in all 3 years.
3. Fall applications of potassium, dolomitic lime, gypsum, or elemental sulfur had no effect on either spring dead spot pathogen.

What does this mean? We are unsure at this time if the observed spring dead spot suppression is due to changes in soil pH or other nutritional effects. For example, suppression of O. korrae by caclium nitrate may be due to higher soil pH or increased calcium availability. Regardless, if you have struggled with spring dead spot in the past, take a look at the nitrogen source you've been using and consider a change to either calcium nitrate or ammonium sulfate.

Many turf managers apply potassium in the fall, as this has been thought to help reduce spring dead spot development. During the three years of this study, we saw no benefit from fall applications of potassium or other nutrients. It is important to point out, however, that we applied 2.7 lbs K/1000 sq ft from potassium chloride (0-0-60) during the summer in conjunction with our nitrogen applications. Therefore, as long as adequate amounts of potassium are applied during the season, additional fall applications do not appear to influence spring dead spot development.