July we experienced timely rain on a weekly basis in most areas.
During the first two weeks of August, we experienced numerous heavy
rains (≥ 1.0”; some cells delivering > 4.0’ in some areas) and
extended overcast periods. These conditions are ideal for both
diseases and weeds. Heavy rain events cause havoc with mowing
operations and also stimulate incredible amounts of weed seed to
germinate. Crabgrass and goosegrass typically break-through in late
summer, since spring-applied preemergence herbicides have broken-down
and no longer provide protection. There are a multitude
of weed species that seem to “blow out of the ground” in late summer
following rain. Among the most difficult to control include sedges
(i.e., yellow nutsedge and Kyllinga), spurges and Dallisgrass. Given
warm and wet soils, weeds grow rapidly and become both obnoxious and
are perennial, turn brown in winter and do not become noticeable
again until early summer. Yellow nutsedge (YNS) plants sprout from
underground tubers and rhizomes or emerge from seed. Kyllinga
does not produce tubers, but its rhizomes are fleshy, wiry, more
numerous and longer, and spread rapidly. Seed dispersal is a
major mode of distribution of sedges. As sedge plants mature,
they develop shiny, yellow and three-ranked, triangular- shaped
leaves. YNS plants are easily hand-pulled. Conversely, mature mats of
Kyllinga require a shovel to remove. YNS seedheads do not develop in
routinely mowed turf, but Kyllinga seedheads are produced in mown
lawns, roughs and green surrounds. YNS can extend 2-3” high in lawns
and roughs in just a few days after mowing. Conversely, Kyllinga does
not grow as rapidly and blends in better. Indeed, many turf mangers
don’t recognize a Kyllinga problem until late August, when seedheads
become abundant. Kyllinga seedheads are yellow-green (eventually turn
brown) in which flowers develop in globe-like clusters.
Yellow nutsedge produces yellow,
that grow above turf canopies within a few days of mowing.
In late summer, dense Kyllinga patches become bright
Greenish-yellow globe-like seedheads of Kyllinga
are produced in abundance in late summer.
Kyllinga rhizomes are long, thick and wiry
making it very difficult to control.
there are no effective preemergence herbicides that target sedges.
Postemergence herbicides (e.g., Celero, Dismiss and
Prosedge/Sedgehammer) control YNS, but the problem is that they
emerge all summer and so multiple
applications become necessary. Kyllinga is especially
difficult to control given its extensive network of rhizomes and at
least two applications, and often more, are required. Professional’s
either swear by or swear at the aforementioned herbicides, but
Dismiss appears to be more effective on Kyllinga. Timing is
very important in control of Kyllinga. According to Steven McDonald’s
research (Turfgrass Disease Solutions), Kyllinga is best controlled
when the first application is made just after mats become apparent in
late May. A second application is needed 21-25 days later, but some
plants often survive via rhizomes. The bottom line is that Kyllinga
is an incredible foe and removing plants physically when first
observed is the best method of control.
and prostrate spurges are annual
broadleaf weeds, which are nearly identical in appearance. Spurge
seedlings emerge as soils warm in early summer and plants continue to
appear all summer. Young plants are inconspicuous until they begin to
grow above the turf canopy. Leaves initially are egg-shaped, but as
they mature they become elongated, and oblong to linear in
shape. Individual leaves may or may not have a reddish or
purple-colored spot near the center of leaves. Numerous stems radiate
from the base and grow prostrate. When stems become numerous they
form mats that can inundate turf. Plants produce a shallow taproot
and stems ooze a white, milky substance when cut. Inconspicuous
flowers aggregate in clusters in leaf axils and quickly produce seed.
Spurges are extremely difficult to control in summer. Products
containing clopyralid (e.g., Confront and Lontrel) work well, but
often two applications are needed once stems radiate. Clopyralid,
however, may not be used on lawns. For LCO’s, nothing seems to work
well, but antidotal observations suggest that Dismiss and Solitaire
(Dismiss + Drive) have good activity.
Spurges have oblong leaves that form on radiating
(sometimes with purplish spots) and are extremely difficut to
are three Paspalum
spp. (Dallisgrass, and bull and field/smooth paspalum) in our
regions, which are generically referred to as Dallisgrass. These
grasses are warm-season
perennials, and among the first to green-up in
spring. Leave die in winter and plants disappear, but stems and seed
survive. Dallisgrass has broad, coarse textured leaves and develops
in thick clumps. Leaves are flat, and may be sparsely to densely
hairy depending on species. A common biotype in our region produces
some purple-colored leaves in the center of clumps. Seedheads form in
late summer and seeds are born in rows on finger-like spikes and are
noticeably shiny, whitish, flat, and oval-shaped (similar to
goosegrass). Only MSMA is known to control Dallisgrass, but only is
labeled for use on golf courses and sod farms. Multiple
spot-applications of MSMA are required on 14-21 day intervals. This
herbicide will yellow turf and cause severe damage if not properly
applied. Pylex and Solitaire suppress Dallisgrass. For lawns, it is
extremely important to dig-out clumps as they appear and before
seedheads are produced.
Dallisgrass and related species produce broad-leaved
and some leaves may be purplish.
Field paspalum is related to Dallisgrass, has course
and produces flat, round seeds on finger-like spikes.