Horticulture Hotline 11/23/25
By Bill Lamson-Scribner
The disease that attacks the turf while it is going into
dormancy (fall) or coming of dormancy (spring) has exploded on the Lowcountry’s
turf. While walking and driving around, it seems that large patch has invaded
the Lowcountry in a big way. As the cooler weather comes, the daylight hours
shorten, and the grass growth rate slows down, large patch fungus began to show
up in our lawns. Proving once again, the Lowcountry is the hardest place in the
world to grow grass and why it is so important to have a program for your lawn.
Do you see areas of your grass that are brown when other parts are green? Be
sure the areas that are brown are your turfgrass and not summer annual weeds (crabgrass...)
that have died (doubtfully if a reader of the Horticulture Hotline).
Large patch disease is always present in the soil; it just
manifests itself when the environmental conditions are right and your grass
cannot outgrow the damage. Without any sustained cold temperatures, this
disease is slowly spreading across lawns as the temperatures that favor its
growth keep coming into play. This prolonged fall is great for outdoor
activities like visiting local plantations, fishing, boating, golfing, shopping,
and working in the yard; however, the temperatures are also perfect for these
diseases to develop and spread. The grass is not fully actively growing (not
mowing as much) and it is not fully dormant (brown), so these are perfect
conditions for the disease to attack. Disease needs to be present (in the soil
always), susceptible host (your grass), and the right environmental conditions
(been nice weather for us – a slow transition is not good for the grass). These
three conditions make up the disease triangle.
Large patch fungus likes wet, heavy thatch, improper
nutrition, and/or compacted soils.
Culturally you need to manage your irrigation system, raise any low
areas, and correct drainage problems. Reducing
thatch (at Possum’s we have a great organic granular product for controlling
thatch), maintaining proper fertility levels, and aerating to alleviate
compaction, will also help control large patch. A healthy turf (following soil
test derived feeding schedule) with a soil with a lot of biodiversity (use of
cotton burr compost, SeaHume and other organics) has been shown to help manage
this disease.
As your grass is going into dormancy and the temperatures begin
to cool at night, large patch is ready to attack your grass. Large patch will
go inactive when the temperatures get very cold; however, it will become active
again when the temperatures favor the disease. If you have discolored areas in
your yard that appear to be a disease, check with someone that knows. Even if
it is during a cold phase and the disease does not appear to be active, you can
still put out a systemic fungicide for protection if you see that the weather
is warming. Our soils do not get so cold that the plant will not absorb the
fungicide with its roots. Remember treating a fungus with a systemic fungicide
is like getting a flu shot – you do it preventatively before you have the
disease. If it is too late to use it preventively, when you want the disease to
stop spreading, you can use the fungicide curatively. Treating preventatively
requires less product and less frequent applications of fungicides.
A good granular one-two punch control strategy is T-Methyl
and Strobe Pro G (both systemic fungicides that get into the plant). Reliant is
a good organic spray that is a good rotation partner. Use these products in
areas where you have had large patch previously at the preventive rates and
intervals recommended on the labels. Be sure to use T-Methyl with Strobe Pro G,
so you are switching chemistry classes and modes of action. Good control early
on can help avoid flare ups in the spring also. If you do not manage the
disease, the grass will thin, and weeds will take over. Two pictures show the
use of Strobe G preventatively and the other picture shows the large patch
fungus.
If you are growing ryegrass this fall, the conditions
have been perfect for Pythium as well. Pythium is a disease (not a fungus), and
it thrives in hot, humid, poorly drained, and overwatered areas. Warm humid
nights, grass blades that stay wet for long periods of time (have you ever seen
someone using a dew whip on a golf course green to knock the dew off so the
leaf blades dry quicker?), and wet warm weather will make this disease explode.
Warm nights and foggy mornings also make ryegrass susceptible to this disease.
Pythium travels super-fast through an area and can wipe out
large areas of turf overnight. Mowing, rolling, tarps on infields of baseball
fields, and surface water drainage will spread this disease rapidly. In 36
years of writing this column, I have never written about this disease; however,
the environmental conditions have been so perfect, I figured I better write
about it.
Sometimes in the morning, you will see something that looks
like cotton candy or cobwebs on the turf areas. The grass can also appear to be
greasy. Like any disease it is best to treat preventatively when you see
favorable environmental conditions in the forecast. Strobe, Reliant, and Subdue
(Mefenoxam) are good control products to rotate for control of this very fast-moving
disease.
What an awesome Lowcountry Fall! James Island County Park’s
Holiday Festival of Lights? Soil Test and Fertility Program from Possum’s?
Rats? Roaches? Fleas? Tree pruning and trimming? Transplant shrubs or trees?
Edge bed lines and sidewalks for the last time for a while? Rake or blow leaves?
Clean out beds that have an accumulation of mulch, leaves, or pine straw? Mulch
your beds after leaf drop? Moles?
Always read, understand, and follow product label. The
product label is a Federal Law.
Bill Lamson-Scribner
can be reached during the week at Possum’s Landscape and Pest Control Supply
(follow us on Facebook). Possum’s has three locations
