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Tropical Storm Brings Rain But What About Gray Leaf Spot?

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The passing of tropical storm, Fay brought some needed precipitation to the region, albeit too much at once in many places. Relatively dry soils (assumes not being over-irrigated) and the long, warm days of summer should allow turfs to dry out reasonably fast.

But what about gray leaf spot? Spores of the pathogen are thought to be blown up from southern regions to the north on the winds of tropical systems. With the recent passing of Fay, Dr. Bruce Clarke recommends being on the watch for early symptoms and signs of gray leaf spot outbreaks. Gray leaf spot can be severe on older, non-tolerant cultivars of perennial ryegrass while new, improved cultivars will be much less sensitive although not immune. Over the last couple years, we have also experienced some strong outbreaks of gray leaf spot on tall fescue across the region. So don’t ignore the tall fescue turfs if you have some.

For more information, see the fact sheet, Integrated Control of Gray Leaf Spot on Perennial Ryegrass.

Gray leaf spot control with fungicides on perennial ryegrass.
Fungicide plots on a perennial ryegrass cultivar that is highly susceptible to gray leaf spot.

Green-up Started

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Soil temperatures have been warming and reached the mid-40s °F last week at Rutgers Hort Farm No. 2 in North Brunswick NJ and are creeping into the upper-40s °F early this week. Dr. Clarke recommends that treatment of turf with a history of take-all patch be initiated when soil temperature averages 40 to 60 °F. Treatment of fairy ring should be initiated when average temperature is in the range of 50 to 55 °F. Waiting to treat beyond these soil temperature thresholds will increase the risk that control strategies are not as effective.

Table 1. Soil Temperature Data under Bentgrass Turf Mowed at 0.375-inch in North Brunswick, NJ on 17 March 2020 at 2:00 PM.

 3-inch DepthThatch-Soil Interface
Current48 °F50 °F
24-hour Average45 °F44 °F
5-day Average47 °F47 °F

Additionally, the Forsythia bloom started last week in central New Jersey, which Dr. Matthew Elmore recommends as a traditional phenological indicator for preemergence herbicide programs on turf.

Initial forsythia bloom in a home lawn.
Initial forsythia bloom in a home lawn in central NJ last week.

Summer Patch on Hard Fescue

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Hot weather in early July brought on some severe summer patch (root disease) symptoms in hard fescue. This disease on fine fescues hasn’t been as thoroughly studied as it has been on other grasses.  So recommendations are based on knowledge learned in Kentucky bluegrass (Poa pratensis) and annual bluegrass (Poa annua) turfs. We are establishing plots this summer and fall to learn more about this disease on hard fescue.

Symptoms of summer patch disease on a 4-year-old hard fescue turf in New Brunswick NJ.

Fine fescues are better adapted to dry and infertile soils. Summer performance of fine fescue will generally be better in moderate to light shade than full sun.

To limit damage from summer patch on fine fescues, do not apply more than 2 lbs. of N per 1,000 sq. ft. per year. An acidifying form of N such as ammonium sulfate is thought to be the best choice when fertilizing fine fescues affected by summer patch. Caution is needed when irrigation fine fescue turf, especially on heavy (loamy) soils. Summer patch disease tends to be more severe on soil that retains water. Irrigation should be applied in a manner that moistens the soil after some time of drying but does not keep the soil excessively wet for many days. Mow fine fescue turf no lower than 2.5 to 3 inches and stop mowing when the turf shows symptoms of heat and drought stress in the summer. Fine fescue turf grows more slowly than other cool-season turfgrasses especially when air temperatures approach and exceed 90 °F.

See Dr. Bruce Clarke’s PowerPoint slides for more details on summer patch disease.

 

Soil Temperatures

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Soil temperatures have been steadily warming since late March at Hort Farm No. 2 (North Brunswick). Temperatures consistently ran above 50 degree Fahrenheit in early April, and between 50 and 60 degrees from 10 to 27 April.

May 1st was the fifth consecutive day of the maximum soil temperature reaching at least 65 degrees. Thus, soil temperatures are essentially entering into an ‘ideal’ period for the growth of cool-season turfgrasses.

Those experienced with managing summer patch may recall that 5 consecutive days with a soil temperature maximum of 65 degrees is the threshold for initiating a preventive summer patch control program. Isn’t it ironic that ideal growth of the fungus that causes summer patch is synchronized with ideal growth temperatures for cool-season turfgrasses.

Damage from summer patch disease, however, typically is not seen until later in the summer when heat and drought stresses make it challenging for plants with a compromised root system to survive.

summer patch disease on hard fescue
Severe summer patch disease on hard fesuce at Hort Farm No. 2 in July 2013.

Some Early Disease Activity

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Sorry no pictures for this post, but thought I would share some recent observations. The recent rains and warm night on Friday/Saturday brought out two diseases on annual bluegrass earlier than we typically experience at the research farm in North Brunswick NJ (Hort Farm No. 2).

Saturday morning, our graduate student found nickel- to quarter-sized spots of foliar Pythium on his annual bluegrass plots. Tended to be more spots on his plots with greater N fertility but the disease was also on low N plots. This is the earliest I have experienced foliar Pythium, but the Friday/Saturday nighttime temperature didn’t get much below 65 degrees F, ‘good’ for Pythium.

Also on annual bluegrass, was a slight outbreak of dollar spot on Saturday morning. Dollar spot in April is early but not unheard of in NJ.

You might notice that the pests mentioned have shown up first on annual bluegrass.

Weather Ideal for Pythium and Brown Patch

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The weather this summer has been very conducive for brown patch and Pythium blight diseases. I have received number requests this summer to address turf problems related to one or both of these diseases in lawns, sports fields, sod and now my own plots.

A brown spot on grass with a knife to provide scale.
Suspected initial outbreak of Pythium on velvet bentgrass maintained at a 0.110-inch height that occurred over the weekend (August 7) in a cultivation trial at Hort Farm No. 2 in North Brunswick NJ.

The weather forecast for the rest of this week indicates

[Read more…] about Weather Ideal for Pythium and Brown Patch

Killing Freezes… Finally

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Many people are pleased that typical winter temperatures have taken so long to show up. Below are some interesting observations from early- to mid-winter in New Brunswick.

Relatively warm soil temperatures (as high as mid-60s °F) stimulated growth late into December.

Dandelion bloom on 15 December 2015 in New Brunswick.
Dandelion bloom on 15 December 2015 in New Brunswick.

Had to remove cover (folded up in behind Kyle Genova) from our K-Microdochium Patch trial so that it could be mowed on 16 December 2016!
Removed the permeable growth cover (folded up behind Kyle Genova) from our K-Microdochium Patch trial to mow it on 16 December 2016!

 

 

 

 

 

 

 

Winter flush of seedheads on annual bluegrass
Annual bluegrass can go to seed about anytime of the year but this is a first for me — lots of annual bluegrass seedheads on 28 December 2015 in New Brunswick.

 

 

 

 

 

Kyle Genova pulled back permeable turf cover to inspect annual bluegrass growth and progress of the Microdochium Patch inoculation on 28 December 2015. Turf is still growing and disease is expanding.
Kyle Genova pulled back the permeable turf cover from the K-Microdochium Patch trial on 28 December 2015. The annual bluegrass was still growing enough to schedule another mowing. And the progress of the Microdochium Patch inoculation was expanding (good for the research but ugly!). No disease response to potassium at this point.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Odd to find weed species that are normally gone by this time of the year. Killing frosts/freezes are finally here and frost sensitive plants should be damaged and won’t persist much longer. Cool-season turfgrasses will transition into dormancy if freezing temperatures linger for a while. But it won’t be too long (66 days until spring, 20 March) before annuals like prostrate knotweed will germinate and start to emerge from bare soil areas.

Freeze Injury on Weeds
Don’t recall prostrate knotweed (annual) persisting into January. But freezing temperatures have finally killed the knotweed. Also note that the leaves of broadleaf plantain (perennial) have just now been frost damaged.

 

Right On Cue: Dollar Spot Disease

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Exactly like Dr. Bruce Clarke teaches, Memorial Day arrives and so does dollar spot disease.

Symptoms appear as round, brown to straw-colored spots approximately the size of a silver dollar. On short cut turf, the spots with advanced damage can become somewhat sunken. At taller cutting heights (greater than 1 inch), the damaged spots are larger and more diffuse.

Highly susceptible grasses will be the first to exhibit symptoms including annual bluegrass, creeping bentgrass (depending on cultivar), and perennial ryegrass. Tall fescue and most Kentucky bluegrasses will be more tolerant of this disease.

Cultural techniques that can suppress dollar spot disease include disruption of dew and guttation water in the morning and increasing N fertility (if it is low). Mowing early in the morning (disruption of dew) should also be helpful.

Creeping bentgrass.
Creeping bentgrass entries in Dr. Stacy Bonos’ evaluation trials that are highly susceptible to dollar spot disease appear in the image foreground.

Brown Ring Patch Spotted in New Jersey

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Brown Ring Patch (aka Waitea patch) is starting to show up on golf course putting greens at this time.  This disease is caused by the fungus Rhizoctonia circinata var circinata and typically develops during warm weather from April through June.  Symptoms start as small yellow rings (0.25-2 inches wide) with green grass in the center and can ultimately reach a foot or more in diameter. The yellow rings can turn an orange or brown color as the disease progresses.  Although the disease rarely kills turf, affected areas are extremely slow to heal.  For best results, apply Medallion, polyoxin-D (e.g., Affirm or Endorse), ProStar, one of the QoI fungicides (e.g., Heritage or Insignia), Trinity, Triton Flo, or Torque now and repeat in two to three weeks to limit disease development later this spring.   Unlike yellow patch, the brown ring patch fungus can degrade the thatch in infected areas so several fungicide applications are typically required to prevent significant damage.  Seedhead suppressants (e.g., Proxy + Primo) may enhance disease severity.  Therefore, be sure to initiate a preventive brown ring spot fungicide program in areas where this disease has been troublesome and seedhead suppressants have been applied.  For more information on brown ring patch, click here.

Brown ring patch on a golf green (Photo courtesy of S. McDonald)
Brown ring patch on a golf green (Photo courtesy of S. McDonald)

 

Leaf Spot and Melting-Out is Active

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Leaf Spot of Kentucky bluegrass.
Leaf Spot of Kentucky bluegrass.

The leaf spot phase of this disease, caused by the fungus Drechslera poae, is apparent on susceptible Kentucky bluegrass turf at this time.

Melting-Out of Kentucky bluegrass. A resistant cultivar (left) compared to a susceptible cultivar (right).
Melting-Out of Kentucky bluegrass. A resistant cultivar (left) compared to a susceptible cultivar (right).

To prevent severe damage from the melting-out stage of this disease during the next six weeks, avoid heavy applications of nitrogen in the spring (not more than 0.5 lb N / 1,000 sq. ft. / application of quick-release, water soluble formulations such as urea or ammonium nitrate), maintain the cutting height at or above 2 to 2-1/2 inches, remove excess thatch, and apply Armada, Compass, Disarm, Headway, Heritage, Insignia, mancozeb, Medallion, Tartan, or Velista now, per manufacturer’s recommendations.  Avoid the use of certain acropetal penetrant fungicides (e.g., benzimidazoles) this spring in areas with a history of leaf spot and melting-out, since these fungicides may intensify symptom expression.