As the wet
rainy summer continues, disease pressure continues to be high. As noted in a
May 15th blog post, dollar spot has been extremely active this year. Leaf Spot has
also been lingering across the state for 2 months. Leaf spot is an ascomycete fungi caused
by Bipolaris spp. and/or Dreschslera spp. A majority of the
damage recorded to this point has been on Kentucky bluegrass lawns, athletic
fields and golf course rough, but symptoms on bentgrass fairways/greens have also
been seen. Please refer to earlier posts for symptoms, pictures, and control
options.
In addition to the leaf
spot calls, I have received several regarding Rust (Puccinia spp.). I first noticed rust at a Kentucky bluegrass sod
field in the Des Moines metro about two weeks ago. It usually begins to show up about the first of August – mid
September, however, in the last two years rust has showed up in early to
mid-July. While several fungicides control rust, I usually do not recommend
chemical treatment unless it is on high-maintenance areas. Furthermore, rust is
usually a sign of relatively low nitrogen, and the addition of nitrogen and
regular mowing will help in the removal of the disease. The yellow to orange
flecks on the leaves and stems can be used to easily identify rust. As the
disease progresses, orange and cinnamon colored blisters and pustules form.
Clouds of spores can turn your shoes orange (as seen below in the pictures from
Larry Ginger) when walking through perennial ryegrass or Kentucky bluegrass
heavily infested with rust.
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Figure 1: Picture courtesy of Larry
Ginger showing a close-up of rust on perennial ryegrass
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Figure 2: Additional picture from Larry
Ginger showing rust on shoes
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| Figure 3: The brown colored area on the
left side is experimental plots that will be highlighted in future blog. A
little tough to see, but the entire top portion is rust on Kentucky bluegrass
along with small spots in the forefront. |
As mentioned in the previous post by Nick Christians, summer
patch (SP) reports are also coming in. A majority of the SP damage occurs
between June and September on Kentucky bluegrass/annual bluegrass.
It is known as one of the “frog-eyed”
diseases.
In mixed stands of grass, the symptom
patter is more irregular. The best way to identify SP is by the sparse, dark
colored runner hyphae on the outer surface of the roots. The infected roots are
unable to supply adequate water to the turf causing the appearance of moisture
stress.
Furthermore, SP survives winter as mycelium, and
begins colonizing roots between 68-90
oF. The fungi spread along
roots and rhizomes from plant to plant. Summer patch damage is often large
because it can spread long distances through aerification and infected sod.
Often recovery is slow, since new roots are inhibited by high soil
temperatures. Hot, wet weather, compaction, high pH soils, low mowing heights,
south facing slopes, and the use of soluble fertilizers increase the risk of SP.
Summer patch is most severe in 2-5 year old turf established from sod.
Severity can also increase when “muck soil
sod” is placed on native Iowa soil.
Several curative and preventative fungicides are labeled for
control. Applications need to begin early in the spring, when soil temperatures
reach approximately 64 oF. Repeat application 2-3 times in 21-28 day
intervals through mid-August. Once symptoms of SP appear, it is often too late
for fungicides. Curative fungicides have proven to be inconsistent and cultural
controls are the most effective option. Summer patch research has observed the
best control using combination products containing DMI’s and strobilurins.
DisarmTM, HeadwayTM, and ArmadaTM are a few of
the chemical trade names that fall into this category. Other products such as
fluxapyroxad, propiconazole, myclobutanil, thiophanate-methyl, trifloxystrobin,
and triadimefon are labeled for summer patch control.
When summer patch symptoms appear, it is most cost effective
to control culturally. Foliar spoon-feed applications of ammonium sulfate at
0.1 -0.3lbs./N/1000 sq. ft. can briefly reduce severity. If foliar feeding is
not an option, use slow release products rather than high rate applications of
soluble nitrogen fertilizers. An annual spring application of magnesium sulfate
may also reduce summer patch issues.
In addition, raising the mowing height during high stress
periods will reduce disease pressure. It is prevalent in compacted soils, so
improving internal drainage through core aeration, and deep-tine aeration will
help. If summer patch is an annual problem, consider overseeding resistant
varieties. If battling summer patch exclusively Barvette, Nuglade, Midnight,
Impact, and Sky are just a few of the Kentucky bluegrass varieties less
susceptible. Additional pictures from
Doug Watt at West Marshall High School can be found below.
Figure 4:
Summer Patch pictures courtesy of Doug Watt
