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ISSUE 5  JUNE 3, 1999

 

YELLOWING IN LAWNS AND MOSQUITO CONTROL IN RAIN BARRELS

    Several homeowners have reported that their lawns have yellow patches of turf about the
size of dinner plates, in spite of proper fertilization practices. With the samples that have been sent
in, and realizing the recent weather conditions, this unresponsive yellow coloration is likely the initial
stage of Necrotic Ring Spot, caused by the fungal pathogen Leptosphaeria korrae . This disease
happens to be the most commonly occurring patch disease on Kentucky bluegrass turfs. It is fortunately,
one of the few diseases that can be effectively controlled through an integrated management program
of biological, cultural, chemical, and genetic practices.

    This disease gets its start during the cool, moist conditions that often exist in the spring and fall, where
the patches that can be red in the fall or yellow in the spring, often go unnoticed until they merge together
into the larger dinner plate sizes that are now being noticed. In the summer, the infected plants that had
their root systems destroyed by the pathogen, begin to wilt even though the surrounding area has healthy
turf. The patches eventually turn straw colored, with a tuft of green grass in the center, giving a "frog
eye" appearance.

    For biological control, the turf should receive light, daily irrigations during periods of heat stress.
Having high moisture and thatch results in high populations of bacteria being maintained, some of which
help to produce antagonistic antifungal compounds that are inhibitory to the growth of the necrotic ring
spot fungus. Also, the use of organic fertilizer sources like Lawns Restore, Turf Restore, and Milorganite
have been shown to biologically manage this disease.

    Basic cultural practices like regular fertilization and frequent, as needed irrigation cycles during heat
stress periods will provide a measure of protection. Be sure the application matches the cultivar of
grass. Common grasses need only 1 to 2 pounds of N per 1000 square feet per year to produce
normal growth; elite grasses will require as high as 4 to 6 pounds of N per 1000 square feet. Over-
fertilization can cause excessive growth which renders the grass susceptible to this and many other
pathogenic organisms.

    Fungicides can be used as both curative and preventative. A good curative is benomyl that has
cytokinin-like properties which tend to stimulate growth. To be effective, this fungicide must be
drenched into the soil before they dry on the foliage, since they are translocated upward.

    Finally, the use of Kentucky bluegrass cultivars that appear to have resistance to this disease are
encouraged. Some that have proven effective in this are Midnight, Monopoly, Able I, and America.

    For those who collect rainwater in barrels for irrigation purposes can control mosquito larvae by
putting a couple of goldfish in each barrel. Another tactic is to spray some vegetable oil over the
surface of the water, and draw the water out from the bottom of the barrel. If you have any old
tires around, cut them in half! An old tire that holds water is a perfect breeding place for these pests!

Ron Smith
NDSU Extension Horticulturist and Turfgrass Specialist
Department of Plant Sciences
ronsmith@ndsuext.nodak.edu

 

SHELTERBELT INSECTS . . . WHAT TO WATCH FOR

    Throughout the growing season, a succession of insect pests feed on tree foliage in our shelterbelts
around the state. In most cases, these insects are present at low levels with little impact to the trees.
Outbreaks do occur, but are unpredictable. Impact on trees is determined by when they are
defoliated and how frequent. Defoliation of trees in the spring is more harmful than late summer.
Defoliation several seasons in a row depletes stored energy reserves leading to die back of
branches and roots.

    Some comments about the most frequent leaf feeding insects in shelterbelts are summarized
below.

    Spruce sawflies: There are five species which may attack spruce. The most common is the
Yellowheaded spruce sawfly. The caterpillar-like sawfly has a yellowish brown head and is shiny
olive green with paired grayish green lines running the length of the body. Larvae hatch from late
May to June. They feed on new foliage first, moving to older needles later. There is a tendency for
these sawflies to concentrate their attacks on trees previously defoliated.

    Forest Tent Caterpillar: They feed on a wide variety of deciduous trees. Outbreaks last for
4 to 5 years. Eggs are laid in the summer, but do not hatch until the next spring. The hairy larvae
have bluish bands with distinct white markings on the back. They can be found as soon as foliage
appears on trees. They feed for about 5 to 6 weeks. The caterpillars mass together when not feeding.
Two years or more of heavy defoliation leads to a decline in the health of trees.

    Cankerworms: These larvae hatch in spring. They are green to reddish brown to black with
pale stripes. Caterpillars crawl with a looping motion. Severe defoliation of deciduous trees in back
to back years leads to branch die back.

    Spiny Elm Caterpillar: The butterflies lay eggs in the spring. Larvae are black with numerous
white dots. There are red dots on the first seven abdominal segments. The body is covered with
numerous branched spines. The caterpillars mass together when feeding causing noticeable defoliation.
There is little permanent damage unless infestations persist for several years.

    Elm Sawfly: The adults emerge from late May to June; they are black, stout-bodied insects
with smoky wings. The adults look like large flies at first glance. The sawfly larvae hatch in mid June.
They are found primarily on elm and willow. The older larvae are yellowish green with a distinct blue
and black line down the middle of the back.

    Willow Sawfly: This sawfly may have two generations in some areas. Adults emerge in the spring.
The larvae are black with prominent yellow spots on the side of the body.

    Fall Webworm: Moths emerge in early summer to lay eggs. The caterpillars are covered with
long silky hairs. The bodies are white with a black stipe on the back. There are orange spots at the
base of the hairs on the side of the body. These caterpillars spin large silky webs around foliage.
The colony feeds within the web, expanding its size as more food is needed. The unsightly webs
provide protection to the caterpillars, making control difficult.

    Insecticides for use in shelterbelts to control these insect pests are limited to diazinon, carbaryl
(Sevin), and malathion. The caterpillars can also be treated with Bacillus thuringiensis (Bt)
products. The Bt’s will not control the sawfly pests. If treatments are limited to landscape plants,
there are other insecticide options available, such as chlorpyrifos (Dursban), cyfluthrin (Tempo),
and acephate (Orthene).

Phillip Glogoza
Extension Entomologist


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