Bipolaris vs. Dollar spot symptoms; Pythium mycelium on bent
fwy (mouse over)
Weather review
The strong northwestern flow and eastern trough in the jet
stream kept northern IL in a cool and wet weather pattern
for the first half of August. The average daily temp for the
month remains about 2 degrees cooler than normal. Summer weather
is coming back into the region, however, and all of the moisture
on the ground and in the air will contribute to high relative
humidity over the next few days.
We have had a few queries about excessive moisture and high
relative humidity causing reduced roll speed on putting greens.
When RH is high, turf leaves do not translocate / transpire
water out of the plant as quickly and can remain fairly turgid
(as compared to a dry air environment). Also, moisture at
the soil surface and in the thatch layers can make the surface
softer and more resistant to ball roll. USGA Agronomist Keith
Happ has written a nice piece concerning the agronomic and
weather factors that affect green speed ("pace"
he calls it) in the July - August Green Section Record, which
can be read online (click
here) on the USGA website . This issue of the
GSR is also notable for containing an interesting and possibly
controversial article about moss control, and a great article
about suppression of Poa annua seeding by Kane and Miller
(shameless self promotion?!)…
Diseases
Dollar spot has finally "taken off" and become
the typical summer pest in northern IL. For some "beautiful"
pictures of recent dollar spot mycelial activity check out
the
latest OSU turfnote. We are also seeing a lot
of Bipolaris leaf spot and anthracnose on bentgrass (not just
Poa!) this year. This abnormal occurrence of these diseases
is probably due to the cooler and extremely wet weather that
have been the norm for the summer thus far. Vinclozolin (i.e.
Curalan/Touche) and iprodione (i.e. 26 GT) will not control
anthracnose, but will control leaf spot. DMI fungicides and
Heritage have worked well for anthracnose control. However,
keep in mind that turf severely affected with anthracnose
will take some time to re-heal. Bentgrass anthracnose usually
occurs on Penncross or Pennlinks, so if you are growing these
cultivars be especially on guard.
On August 6, we were surprised by 5 reports of Pythium activity
during weather that we thought was a little mild for it. Two
more reports came in today, 8/14, so the environment in some
microclimates must be conducive for disease development. Evidently,
in these microclimates the more than adequate moisture and
humidity made up for the less than adequate temperatures to
promote enough fungal biomass to incite disease. During this
period of Pythium activity, low temperatures have been in
the mid 60s and highs have only been in the lower 80s – perhaps
an indication of where we need to refine our Pythium model
(alert given when high temp > 86 and low temp > 68).
If Tom Skilling is correct, Thursday - Saturday, looks to
reach the adequate temperature range with highs approaching
90 during the day and lows in the high 60s to low 70s at night.
These temperatures could produce a Pythium EXPLOSION over
the weekend. Even for the most effective products, short spray
intervals (7-10 days) may be required under this expected
high disease pressure. Subdue and Aliette are best applied
preventatively 24-48 hours before disease pressure; Banol
and Koban have better short term curative activity. Phosphite
users: this may be your second big test of the season.
Insects
Japanese Beetle adult activity may be peaking right now in
northern IL, some supt's report a second application of insecticide
to protect desirable tree/shrub species. However, it does
appear that the JB populations have been much lighter this
year than in recent past. With the late emergence of the beetles
(both Japanese and masked chafers), annual white grubs should
also come on later this year in northern and central IL as
reported in
the recent issue of the Home Yard and Garden Pest Newsletter.
As reported, the later grub season should mean that imidacloprid
(Merit) and halofenozide (Mach 2) can still be used during
the first half of August. These insecticides take about 3
weeks to kill the grubs, but damage should not occur until
late August to early September. In southern Illinois, the
grubs should have hatched, with damage showing up by mid-August.
Treatment with trichlorfon (Dylox) is probably a better option
to get quicker control in southern Illinois.
Cutworms and sod webworms remain active and will continue
to be a problem (as are the feeding birds) on untreated areas.
Mound building ants are an ongoing problem as well, and we
still seem to be searching for an effective treatment - especially
on greens. Some of the newer bait products have a lot of potential
for control, but spreading bait on greens mowed daily at 1/8"
presents a problem….
Weeds
Based on our observations at the youth links at Golf House,
it looks like a great year for crabgrass, foxtails, and sedges!
With the heavy rains we have had in some parts of the region,
crabgrass could be a headache. Rain and high soil moisture
can wash or dilute out preventive applications, and some post-emerge
treatments may have been washed away as well. Moss and algae
reports continue to roll in. We have had some good moss control
results in small test areas with a "tank mix" of
4 oz / gal of Ultra Dawn and a tablespoon of baking soda (predissolved
in warm water before mixing). We are going to further adjust
rates of both the soap and soda in the mix to see if some
potential phytotoxicity can be avoided.
