Tropical Storm Brings Rain But What About Gray Leaf Spot?

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

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 Depth Thatch-Soil Interface
Current 48 °F 50 °F
24-hour Average 45 °F 44 °F
5-day Average 47 °F 47 °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 in central NJ last week.

 

Summer Aeration/Cultivation/Venting

Aeration during the summer can be a helpful practice but does need some caution. Many turf managers performing mid-season aeration on putting greens will be using needle tines, which are less disruptive. But the key words are [Read more…]

Glyphosate Alternatives

Recent news about glyphosate has many thinking about alternatives.

Joe Neal (Professor of Weed Science, Extension Specialist & Department Extension Leader Horticultural Science) and Andrew Senesac (Extension Weed Scientist Cornell Cooperative Extension, Suffolk Co., NY) have published a thorough summary of alternatives and the associated pros and cons through NC State Extension at https://content.ces.ncsu.edu/are-there-alternatives-to-glyphosate-for-weed-control-in-landscapes

Soil Health

Soil that has been severely compacted often breaks into large massive plates.

For those interested in soil health – we all should be – the Soil Health Institute has release a 60-minute documentary featuring innovative farmers and soil health experts from throughout the U.S.

You can view the film at https://livingsoilfilm.com/

 

Dog Days and Cool-Season Grass

 

Cool-season lawn struggling to grow in shallow soil on a south-facing slope during dog days.

According to Merriam-Webster, dog days is the period between early July and early September when the hot sultry weather of summer usually occurs in the northern hemisphere; a period of stagnation or inactivity.

The dog is actually the Dog Star – also called Sirius – which rises simultaneously with the sun during the hottest days of summer in the northern hemisphere. Plutarch (Greek writer, 46-120 AD) referred to the hot days of summer as hēmerai kynades (literally, “dog days”); the Latin translation dies caniculares is the source of our English phrase. But I digress…

You most likely have noticed that cool-season grasses have recently entered a period of stagnation or inactivity (dog days) and, in some cases, are spent. The hot summer days have steadily increased soil temperatures to the point that the soil is now warmer than air temperature for much of the daylight hours and all of the night. During the last 10 days at Hort Farm No. 2, soil temperature at 3-inches has oscillated between 76 and 90 °F and at 2-inches 78 and 92 °F. These soil temperatures are well above the optimum temperatures for root growth and clearly explain why cool-season grasses are lethargic at this time.

What to do? Be patient and do not “push” the grass. This is not the time of year to stress out turf – the grass has very little resiliency and will not tolerate much abuse or recovery quickly. I recently witnessed utility vehicle traffic on subtly drought stressed turf during the hottest part of the day result in classic tire-track damage. Root systems of cool-season grasses are weakest and shallowest at this time of year. Thus, localized drought stress can develop rapidly – within a couple hot, sunny days – during the dog days.

These cultural practices can be helpful in getting high value turf to survive dog days. Once the turf has drained after drenching thunderstorms (2-3 days), program daily, very-light (50-65% of reference ET), deficit irrigation using a rainhold setting (such as 0.2-inch rain) to stop irrigation from adding to over-wetting from storms. Deficit irrigation assures that thunderstorms will be the reason for excess wetness, not the irrigation schedule. This irrigation plan should encourage the turf the dry without over-drying between irrigations (or thunderstorms). If excess drying does occur with this irrigation plan, it probably will start in highly localized (small) areas, which can be effectively managed with well-timed syringing to re-hydrate dry leaves and prevent crispy thatch during the heat of the day. Crispy thatch means that surface adventitious roots either are or will soon be crispy as well. Moist to dry thatch is good, whereas crispy and crunchy thatch in the heat is bad. Weekly, low-rate fertilization (N and possibly P, K and micronutrients) is crucial on sand-topdressed and sand-based rootzones commonly found on golf course putting greens and some sports turfs. These rootzones have very little mineralization capacity to supply essential nutrients during dog days. Weekly low-rate fertilization provides a steady, consistent slow-growth and avoids the “surge-crash” cycle of growth that results from less-frequent and higher application rates. Typically, low-rate N is no more than a 0.1-lbs. per 1,000-sq. ft.

Managing Thatch

Recently received a couple of questions about managing thatch.

One question was concerning the recent trend in the industry to not core putting greens and only use solid tines. 

Non-coring programs rely on topdressing to dilute the organic matter (thatch) that accumulates, thus forming a mat layer as opposed to a thatch layer. Turgeon defines mat as a tightly intermingled layer composed of [Read more…]

Cadmium and Phosphate Fertilizer Debated in EU

Fertilizer derived from phosphate rock, which naturally contains cadmium, is being debated in the European Union. More than half the cadmium, a toxic heavy metal, in some agricultural soils originated from phosphate rock derived fertilizer. Sedimentary phosphate rock mined in northern Africa contains naturally high cadmium levels. Phosphate from mines of igneous rock in Russia has much lower levels.  Read more…

Rectangles of Melting Snow

Made an interesting observation while inspecting this trial for geese damage last December; rectangular plots of snow melting faster than other plots. Not sure of ramifications, but snow cover on some treatments was melted or melting faster compared to other treatments. This trial has numerous combinations of topdressing sands and rates as well as hollow tine cultivation. The treatments with a drier surface were retaining snow cover longer than treatments that tend to retain more water in the surface 0- to 3-inches.

Rectangular areas of melted/melting snow on this research (putting green) trial are treatments that have greater water retention in the surface 0- to 3-inches.

Goosegrass

Goosegrass is a summer annual weed of cool-season turfgrass that has become more problematic in recent years. My conversations with turfgrass managers suggest that goosegrass is firmly entrenched as a top 5 turfgrass weed issue of highly managed systems in the Northeast region. Crabgrass is more prevalent than goosegrass, but is less problematic in highly managed systems because it is effectively controlled with pre-emergence herbicide programs.

Goosegrass is easily identified by its prostrate growth habit and white, compressed sheaths. Photo: E. Reasor

Goosegrass and crabgrass are both summer annual grassy weeds. So why do pre-emergence herbicides typically used in cool-season turfgrass (dithiopyr, prodiamine, and pendimethalin) often provide inconsistent goosegrass control? It should be noted that the pre-emergence herbicide oxadiazon often provides excellent goosegrass control but is not widely used in cool-season turfgrass.

One reason is that goosegrass seedlings are thought to emerge 2 to 3 weeks later than crabgrass and continue germinating later in the summer. Indeed, the research we conducted this summer to evaluate seasonal goosegrass germination patterns found that the first goosegrass seedlings emerged in mid May, about 3-4 weeks after the first crabgrass seedlings. Interestingly, when we calculated the time it took 90% of the plants to emerge, there was a big difference between our two locations. Ninety percent of the goosegrass seedlings had emerged by early July at the golf course location, but at the research farm location just a few miles away (soil temperatures were similar) 90% emergence occurred in mid to late August. But I digress…

If goosegrass germinates later than crabgrass, making split applications of pre-emergence herbicides should provide more consistent control than single applications. However, my conversations with many in the turfgrass industry suggest is that goosegrass has become more problematic only in the last 5 to 15 years regardless of application strategy and mitotic-inhibiting pre-emergence herbicides have been used widely for over 25 years. So this would suggest some other factors are in play.

On the same golf course where we found 90% of the total goosegrass seedlings had emerged by early July, we evaluated several pre-emergence herbicide programs for goosegrass control in 2017. Treatments were applied in early May. By mid June we noticed that plots treated mitotic-inhibiting herbicides had as much goosegrass as non-treated plots. Meanwhile, plots treated with oxadiazon (a different mode of action) had almost no goosegrass. For reasons mentioned earlier, I would not expect these mitotic-inhibiting herbicides to provide excellent goosegrass control, but they should be providing some control, especially in mid-June.

We collected seed from the site in December 2016 and we compared this seed to a population collected from our turfgrass research farm using a controlled experiment in the greenhouse. We found that the golf course population was not controlled by a mitotic-inhibiting herbicide, but the research farm population was 100% controlled (figure below). Both populations were 100% controlled by an herbicide with a different mode of action.

Pots treated with a mitotic-inhibiting pre-emergence herbicide on the day of seeding. The wild type population was collected from our turfgrass research farm. The golf course population was collected from a golf course with a history of mitotic-inhibiting herbicide use.

In the Southeast, herbicide resistance to mitotic-inhibiting pre-emergence herbicides (dithiopyr, prodiamine, and pendimethalin) and oxadiazon has been implicated as the cause of goosegrass issues on many golf courses and was first reported over 30 years ago in 1984 (by Mudge et al.). However, I’m not aware of resistance to mitotic-inhibiting herbicides in the Northeast despite heavy reliance on these herbicides for annual grassy weed control.

Goosegrass resistance to pre-emergence herbicides typically begins with one plant surviving the application due to a genetic mutation. The goosegrass plants with the mutation probably goes unnoticed and sets seed, which leads to a small patch of plants the next year when the same pre-emergence herbicide is used again and does not control plants with the mutation. The patch may become larger each year as that population is spread throughout the property via seed eventually becoming problematic.

At the recent NJ Green Expo in Atlantic City in December, I briefly discussed the topic of goosegrass resistance to pre-emergence herbicides during a panel discussion. Responses suggested this is an issue that deserves more investigation.

If you suspect that resistance to pre-emergence herbicides is an issue on your property, please contact me via email (matthew.elmore@rutgers.edu) or Twitter (@RUturfweeds). Your will be extremely helpful to help determine if this is a widespread issue and potentially collect plants/seed samples for further testing.. All correspondence will be kept confidential.