Welcome to another issue of Pest Alert. Categories for topics are as follows, H - Herbaceous plants and flowers, W - Woody Plants, V - Vegetables, F - Fruit and L - Lawns.
DISEASES
W,F APPLE
SCAB activity is probably on the rise in many
areas of the state thanks to the recent rains.
Continue applications of fungicides for control of this fungal disease.
Fungicides such as Captan and Benlate should be effective
(read label for directions). Photo of
apple scab infection on apple leaves.
W BLACK
SPOT on
roses has been reported in many areas of the state.
Dark colored spots generally first
appear on lower leaves. The disease
can quickly spread to other parts of the plant during wet weather.
The first diseased leaves can be picked off to reduce the spread.
Mulching around the plant helps to reduce infection by covering up old
leaf debris, which acts as a source of the disease.
Protective sprays of Funginex are quite effective.
W Dutch
elm disease
is showing up across the eastern half of the state.
During the past several weeks elms throughout this area have exhibited
the typical symptoms of Dutch elm disease – wilting,
yellowing foliage, usually beginning on a branch or two then rapidly
spreading to the rest of the tree. The
symptomatic branches show the characteristic
brown streaking of the wood beneath the bark.
Some observers have remarked at the rapid progression of the disease this
year – surprised that a tree could become infected and die so quickly.
As we reported last year, these trees have probably been infected for at
least a year and perhaps much longer. With
the moisture we have experienced again this year across most of the state, the
large early-wood vessels rapidly carried the disease throughout the tree.
These infected trees should be removed as soon as possible as the disease
has most likely spread to the root system and has the potential to infect nearby
elms via root grafts. Several such
trees that were girdled near the base last week all showed brown streaking
indicating that the disease had spread from the canopy to the roots.
If healthy elms are nearby, within a distance less than their height from
the infected tree, the infected tree should be removed, the stump ground to
isolate the roots and a trench cut between the infected and health tree to
severe any root connection between the two trees.
V
EARLY BLIGHT
on tomato, potato and eggplant is off to a good start this year.
This disease causes small
spots that start out at about 3/8" in diameter on the leaves.
The spots are also characterized by a
target pattern of lines within the spots.
Many spots may merge together to cause larger areas of the leaves to die
but the spots will generally not cross a leaf vein.
Like Septoria leaf spot, this disease overwinters on diseased plant
debris from last year and is then spread to the lower leaves by splashing rain
or irrigation water. Control is
similar to that for Septoria leaf spot with Chlorothalonil (Daconil 2787)
treatments beginning at the first sign of the spotting for best control.
F
GRAY MOLD ON STRAWBERRIES
is a common problem. Clean
harvesting of all ripe fruit will greatly help to reduce problems with botrytis
gray mold. This very common fungal
disease grows rapidly on over-ripe or damaged fruit turning them
dark gray and causing them to become mushy.
Gray mold can quickly infest an entire fruit cluster under moist
conditions. Carefully harvest all
ripe fruit and remove infected fruit from the patch.
H
HOLLYHOCK RUST has been common again this year.
Symptoms are numerous,
small, raised, rust-colored spots on the leaves.
Thorough cleanup of old plant debris in the fall helps to reduce the
disease next season. Fungicide
treatment now would be of little value.
V
LATE BLIGHT, caused by Phytophthora infestans,
should be showing up on tomato and potato plants. This is a disease that can
kill entire potato and tomato plants in a few days under cool, wet weather. This
is the disease that was at the heart of the Irish potato famine, 150 years ago.
While late blight has occurred in the United States since 1992, the pathogen has
become more important in the past 5 years. About that time a new variant of the
fungus developed and spread across North America. This new form is more
aggressive and is resistant to the fungicide that had been used most commonly to
combat late blight.
Large
blotches of dead leaf tissue are characteristic of late blight. The dead
spots cross leaf veins, unlike any other disease of potatoes and tomatoes. Often
the dead areas will be bordered by a yellow halo. On the underside of the leaf,
a white, cobwebby growth may be present during wet weather. Dark,
streaky lesions may also be present on the stems of either tomato or potato.
The disease can be controlled in the home garden
by picking off diseased leaves and using fungicides such as chlorothalonil
or mancozeb that are approved for use on garden vegetables. Severely
infected plants should be removed from the garden. Many brands of fungicide with
these active ingredients are available from garden centers and discount stores.
Applications as often as every 7-10 days may be needed during periods of cool,
wet weather.
W MAPLE
ANTHRACNOSE may
begin showing up on trees in the state. Like
ash anthracnose, it causes fairly
large, irregularly shaped brownish spots, typically along the margin of the
leaf. However, these infected maple
trees will generally not drop as many leaves as ash trees do when they are
infected. Control strategies are
similar to that of ash so treatment now will not be very effective. Maple anthracnose is usually not as much of a problem so
preventative treatments are generally not needed. Young trees can be sprayed
with a protective fungicide like chlorothalonil in the spring when new
leaves are developing.
V SEPTORIA LEAF SPOT is already causing the characteristic spotting of lower tomato leaves. Typical symptoms include small dark colored spots on the leaves, followed by yellowing and leaf drop. The disease overwinters on diseased plant debris from last season and is spread to new plants by splashing rain. The first diseased leaves may be picked off to reduce spread but fungicide treatments are usually the best means of control. Chlorothalonil (Daconil 2787) treatments should begin with the first signs of the disease and continue throughout the rest of the production season.
INSECT CONTROL
W Ash
bark beetle damage
is causing some concern in the state. After the past several storms that have
crossed our state, homeowners picking up fallen branches have noticed
encircling rows of small holes in the broken ash branches.
A closer inspection of these branches will often reveal numerous
tunnels, similar in pattern to elm bark beetle tunnels or galleries, beneath
the bark. These tunnels are
constructed by the adults and larvae of the ash bark beetle. While extensive
tunneling can girdle a branch – resulting in its death – the injury
usually is limited to only heavily shaded, and declining, branches.
Thus there is generally little need for control, other than removing
the dying branches that the wind has not brought down.
Infested wood should be burned. Occasionally
highly stressed ash trees, those in flooded sites for instances, may have the
entire canopy and trunk successfully attacked killing the tree.
W
Asian
longhorn beetle, the exotic wood borer that has generated much
concern and tree loss in the Chicago area, has recently been found in New
Jersey trees. The larvae
burrow through hardwood trees, particularly maples and poplars, resulting
in tree decline and death. Current
control efforts are focused on elimination of pocket infestation by removing
and burning infested trees. The
insect is believed to enter the United States in pallet wood shipped from
China. The insect can survive in climates as cold as South Dakota so
it has the potential of showing up here as well.
Any pallet wood identified as coming from China should not be
stockpiled or stored but burned as soon as possible.
V CUCUMBER
BEETLES
are actively feeding on young cucumbers, pumpkin, squash and melon plants. These small
voracious eaters
can totally consume young seedlings or they may just feed enough to inoculate
the plants with bacterial wilt. In
either case you will want to be on the watch for these small black and yellow
striped beetles and use protective measures to reduce their damage.
Treatment with Carbaryl (Sevin), Esfenvalerate and rotenone
containing products should be effective.
V COLORADO
POTATO BEETLES
continue to plague home gardeners. Carbaryl
(Sevin), Esfenvalerate and rotenone can be effective but
there is a lot of potential resistance problems.
Bacillus thuringiensis var. tenebrionis (M_Trak)
is an option. There are no known resistance problems to it, but Bacillus is
only effective against very young larvae.
Keep potatoes well watered to decrease susceptibility to defoliation.
W HONEYLOCUST
POD MIDGE
injury should be showing up across the state soon.
The oblong,
pod-like galls form on the new leaflets of honeylocust.
Within each of these pods you can usually find several small, yellowish
larvae. The larvae pupate within
the pod after about 3 weeks and then emerge as small, mosquito-like flies.
There are several generations per year.
While the injury looks unsightly, it rarely results in any serious
decline for the tree. Sometimes a
few interior branches will decline and occasionally a young, stressed tree
will die. Recommended control is
Sevin
(carbaryl) when the new foliage begins to expand and
repeat every two weeks through June.
W,F
PEAR-
& ROSE-SLUGS have begun feeding on roses and on a wide
range of plants but seem to prefer cotoneaster. The slimy looking pests are actually the larvae of an insect
and not true slugs. They are
usually light green to dark green and often have a dark colored dab of fecal
material on their back. They feed
on the underside of the leaves and cause a skelotonization type damage.
They may defoliate plants in a few days when they are feeding in high
numbers. Sevin
(carbaryl), Malathion
and Orthene are quite effective in controlling these pests but best
results will be seen if the spray is directed on the undersides of the leaves.
F
PLUM CUCURLIOS
have been found feeding in apples and peaches and would likely be seen plums,
apricots and cherries too. These
adult is a snout-beetle that chews small holes into fruit and deposits its
eggs. The larvae, which is a
small grub, about ¼”
long tunnels around in the fruit. Peaches,
plums and apricot fruit will often exude
a sticky sap where the holes are in the fruit.
Once fruit is infected there is no treatment other than to pick off
fruit and get rid of it. Most
home orchard sprays will provide protection against cucurlios, but
Sevin (carbaryl), Malathion
and methoxychlor should also provide good protection.
V SQUASH
VINE BORERS are becoming active across the state.
These attractive bluish moths, which look like a
wasp, deposit eggs
near the base of squash, pumpkin, and occasionally melon vines.
Newly hatched larvae immediately burrow into the stem where they
continue to feed until they reach approximately one inch in
length.
This feeding eventually kills the vines, although it appears to happen
quickly because the vines suddenly wilt.
Vines must be protected from late June through mid August from egg
laying adults and newly hatched larvae with an insecticide application to the
base of plants. Dust formulations
are probably best for this insect, including Sevin (carbaryl), rotenone,
and methoxychlor, which is available
as Ortho Vegetable Garden Insect Dust
W
Spruce needleminer are flying throughout the eastern half of the state.
Previously infested trees can be identified by branches covered with
small clusters of discolored needles webbed tightly together.
A closer examination of these clusters will show that these needles are
hollowed out and there is a small exit hole near the base. The
adults, the life stage now present, are moths with dark brown wings with
grayish-white bands and have a total wing span of about ½ inch.
Trees that have been previously infested or are near infested trees,
can be treated with Sevin (carbaryl) at this time. Blue
spruce is the most common host, though Black Hills spruce is sometimes
infested as well.
W Zimmerman pine moth has been showing up in blue spruces from Spearfish to Watertown. Infested trees are generally 10 to 15 feet tall with the infested portion typically located in the upper 1/3 of the tree. Infested trees usually have scattered branches that are losing needles or are breaking. At the point near where these branches are attached to the trunk, there are numerous masses of reddish or gray pitch. A small white-bodied larva with a dark head is often found in association with these pitch masses. This insect is usually found in pines, Austrian or ponderosa, and rarely infests spruce. Treatments of spruces are only warranted if the tree is infested and only after the insect is positively identified. There is the possibility that the insect in question may not be a Dioryctria (the genus for the Zimmerman pine moth) and even if it is, there are at least two other possible species each with its own best treatment window.
WEEDS
L THE NEW WEED B GONEis a three-way combination of 2,4-D, MCPP and
dicamba. This improves the weed
spectrum controlled. The “old”
Weed B Gone is still available as a ready-to-use product
containing 2,4-D and MCPP. These products may be used in a small hand sprayer for spot
treating individual weeds like Canada Thistle in the lawn.
Remember to be extremely careful with broadcast treatments at this time
of year as so many vegetables, flowers and other ornamental plants are very
susceptible to damage from drift.
V TIME TO MULCH EARLY VEGETABLES. Remove existing weeds first.
Avoid using mulching materials that may contain weed or grass seed.
Do not use grass clippings for mulching if the lawn was recently treated
with pesticides that could damage or leave illegal residues on the garden crop.
Mow at least two times before using these clippings.
H,V,W RESIDUAL HERBICIDES. Avoid using residual herbicides for weeds in
gravel drives, cracks in sidewalks or in alleys. Ingredients such as prometon will move with rain and
the residual can be picked up by roots of non-target plants.
V ASPARAGUS
HARVEST
should be about complete for the season. It
is very important to allow these hardy vegetables to develop lots
of the ferny mature shoots for the rest of the season.
These shoots produce and store food reserves in the plant to get the
plant through the winter and provide energy for lots of nice big shoots next
spring.
V,H,L,W
WATER PROPERLY
when the plants need it. Generally
most lawns, gardens and flowers need about 1" of water per week.
If your area has not been receiving this amount, supplemental watering
may be needed. The important point
to remember is to water thoroughly when you do water. Try to saturate the root zone of what you are watering.
This means applying at least 1/2" at one time, preferably more like
1" should be applied at one watering.
Then allow the soil to dry before watering again.
You can tell when it is time to water by sticking your finger into the
soil to see if it feels moist in the top 2" of soil.
If it is dry, it is probably time to water.
Watering from below is generally better than overhead.
This can be done using soaker hoses or a drip system.
Overhead watering tends to waste water and can promote disease problems
if the foliage is allowed to go into the night wet.
Back to the Pest Alert page
Most recent revision Tuesday, June 27, 2000 by David F. Graper.
