Montgomery County
400 Bridge Street, Suite 2
Red Oak, IA 51566-1402
712-623-2592
FAX 712-623-2594
E-mail: drey@iastate.edu
HORTICULTURE
NEWSLETTER
DATE: August 2011
Bill Drey
Bill Drey
Montgomery County Extension Education Director
The fruit on my zucchini squash began to grow,
but quickly turned brown and rotted. Why?
The rotting of the small squash fruits could be due to poor pollination or blossom-end rot.
For squash fruit to develop fully, bees and other pollinators must transport pollen from the
male flowers to the female flowers. If the female flowers aren’t pollinated properly, the fruit will
begin to grow and then suddenly shrivel up and die. The rainy weather could be responsible for
poor pollination and rotting of the small fruits because bees and other pollinators are less active
in rainy weather. Drier weather conditions should increase pollinator activity.
Blossom-end rot is a physiological disorder that occurs on tomatoes, peppers, eggplant
and summer squash. On zucchini and other summer squash, the blossom end of the fruit begins
to rot and within a short time the entire fruit has rotted. Blossom-end rot is caused by a lack of
calcium in the developing fruit. In most cases, there is no need to apply calcium to the soil. Try to
maintain an even moisture supply by watering once a week during dry weather. Also, do not over
fertilize plants. Uneven moisture supplies and excessive nitrogen inhibit calcium uptake.
Plant and Insect Diagnostic Clinic Update - July 13,
2011
This article was published originally on 7/13/2011
The following are highlights and updates about samples and questions recently received in the
Plant & Insect Diagnostic Clinic:
Diseases
We are still getting quite a bit of samples and consults about conifers with needle browning
and needle drop (many of them due to environmental stress). We also had a spruce and white
pine injured by herbicide, most likely due to Imprelis (see this New York Times Article). On the
fruit and veggie side, we’ve received strawberry samples with leaf spot and leaf scorch and some
cherries with leaf spots and gummosis. We are also beginning to see Septoria leaf spot on
tomatoes and bacterial wilt on cukes and muskmelons.
It is the time of year when oak wilt symptoms would begin to show on oak leaves. Symptoms
are the browning of leaves on an entire branch. To test for oak wilt we need several branches
about 1/2 inch in diameter. Please see our pamphlet on Oak Wilt for more information.
Verticillium wilt is a very different wilt disease whose symptoms would also be appearing now.
Symptoms consist of wilting or browning leaves on a branch. Verticillium wilt affects many
species of trees and plants including maple, ash, lilac. For more information please see our
pamphlet Verticillium Wilt of Woody Plants.
Insects
Iowans have been out and about in the woods collecting ticks. In Iowa we have three
common tick species, the lone star tick, the American dog tick, and the Black-legged tick (aka the deer
tick). The black-legged tick is the only species known to carry Lyme disease in Iowa. Other
species rarely carry disease, but it is always important to let your doctor know if you become ill
and had a tick attacked for 24-36 hours. Ticks take a long time to become attached and feed. To
reduce the chances of any disease transmission it is important to check yourself for ticks after
returning from outside and to remove them promptly by pulling them out with a pair of tweezers.
Do not use alcohol or other substances on the tick. Agitating the tick could potentially lead to a
greater chance of disease transmission. For more information on ticks please see Ticks and
Tick-borne diseases in Iowa.
Bagworm activity has been reported in southern Iowa and in Clive (Polk County). Reporters
indicated the silken bags made from bits of plant debris as the caterpillar is feeding on the foliage
are already one-half to five-eights inch long. Now is the time to check and treat if bagworms are
found. See the April, 2010, Horticulture &Home Pest Newsletter for more information and control
options.
The annual cicadas are buzzing in the trees in late afternoon, and the cicada killer wasps are
right behind and right on schedule. See our website for more information on how to treat these
large, frightening, but non-aggressive digger wasps. Treat the ones you can't ignore!
Have you seen honey bee swarms? If so, you know it's quiet a spectacle, but the prudent
thing to do is watch from a safe distance and wait for them to move on, which usually takes only
a day or two. Kill the swarm with soapy water spray only if you must. A neighborhood beekeeper
may take the swarm, though not all beekeepers are interested in having and hiving wild bees, so
don't "bee" offended if your offer is turned down! More information on our website.
By Laura Jesse and Erika Saalau, Plant & Insect Diagnostic Clinic
Yard and Garden: Harvesting and Storing Potatoes
BY RICHARD JAURON
Iowa State University Extension specialists offer tips for harvesting and storing potatoes,
as well as dealing with spuds that are green or knobby. To have additional questions answered,
contact the experts at hortline@iastate.edu or call 515-294-3108.
When should I harvest my potatoes?
Potatoes can be harvested when the tubers are small and immature (“new” potatoes) or
when the crop is fully mature.
“New” potatoes are dug when the plants are still green and the tubers are greater than 1
inch in diameter. New potatoes should be used immediately, as they do not store well.
Potatoes grown for storage should be harvested after the vines have died and the crop is
mature. To check crop maturity, dig up one or two hills after the plants have died. If the skins on
the tubers are thin and rub off easily, the crop is not fully mature. Allow the crop to mature for
several more days before harvesting the potatoes. When harvesting potatoes, avoid bruising,
skinning or cutting the tubers. Damaged potatoes should be used as soon as possible.
Why are some of my potato tubers green?
Potato tubers actually are enlarged underground stems. When potato tubers are exposed
to light (either in the garden or storage), their skin turns green due to the formation of
chlorophyll. The chlorophyll itself is not a problem. However, higher levels of glycoalkaloids also
develop in the green tissue. Green tubers have a bitter taste and can cause nausea, headaches
and other health problems if eaten in large quantities.
Tubers with small green areas can be safely eaten if the green portions are cut off and
discarded. It would be best to discard potatoes that are largely green.
When growing potatoes in the garden, hill soil around the base of the potato plants to
prevent the tubers from being exposed to light. After harvesting, store potatoes in a dark
location.
How should I store my potatoes?
After harvesting the potatoes, cure the tubers at a temperature of 50 to 60 F and high
relative humidity (85 to 90 percent) for two weeks. The curing period allows minor cuts and
bruises to heal. Thickening of the skin also occurs during the curing process.
Once cured, store potatoes at a temperature of 40 F and relative humidity of 90 to 95
percent. Store the crop in a dark location, as potatoes turn green when exposed to light. If
storage temperatures are above 50 F, the tubers may begin to sprout in two or three months.
When stored below 40 F, potatoes develop a sugary, sweet taste. Sugary potatoes can be
restored to their natural flavor by placing them at room temperature for a few days prior to use.
Do not store potatoes with apples or other fruit. Ripening fruit give off ethylene gas, which
promotes sprouting of tubers.
Why are my potatoes knobby?
Fluctuations in soil moisture levels during tuber development may cause knobby potatoes.
Watering on a regular basis (about once a week) during dry periods will help prevent this
problem.
Yard and Garden: Lawn, Annual and Garden Care in
Hot Weather
| BY RICHARD JAURON
Iowa State University Extension specialists offer tips for taking care of your lawn, annuals
and garden in hot weather. To have additional questions answered, contact the experts at
hortline@iastate.edu or call 515-294-3108.
Is it necessary to water an established lawn during hot, dry weather?
Gardeners have two basic options when confronted with hot, dry weather. One option is to
do nothing and allow the grass to go dormant. The alternative is to water the turfgrass during dry
weather to maintain a green, actively growing lawn.
Cool-season grasses, such as Kentucky bluegrass, can survive long periods of dry
weather. In dry weather, the shoots of the turfgrass plants stop growing and the plants go
dormant. Dormancy is a natural survival mechanism for turfgrass. While the leaves have turned
brown and died, the turfgrass roots and crowns remain alive. Generally, Kentucky bluegrass can
remain dormant for four to six weeks without suffering significant damage.
Cool-season grasses are at risk of dying if dormant for more than six weeks. To ensure
survival of dormant grass, it’s best to water lawns that have been dormant for six weeks. Apply 1
to 1 ½ inches of water in a single application. Water again seven days later. The grass should
begin to green up after the second application.
When is the best time to water a lawn?
Early morning (5 to 9 a.m.) is the best time to water a lawn. A morning application allows
the water to soak deeply into the soil with little water lost to evaporation. When watering is
completed, the turfgrass foliage dries quickly. Watering at mid-day is less efficient because of
rapid evaporation; in addition, strong winds may cause uneven water distribution. Strong, midday winds also may carry water onto driveways, sidewalks or streets, wasting considerable
amounts of water. Watering lawns in late afternoon or evening may increase disease problems.
How frequently should I water my lawn? How much water should be applied per week?
Most cool-season lawns in Iowa require approximately 1 to 1 ½ inches of water per week.
When watering the lawn, apply this amount in a single application or possibly two applications
three or four days apart. Avoid frequent, light applications of water, which promote shallow
rooting and lush growth. Lush, shallow-rooted turfgrass is less drought tolerant. It also is more
susceptible to pest problems. To determine the amount of water applied by a sprinkler, place two
or three rain gauges within the spray pattern.
How frequently should I water annuals in containers?
The frequency of watering may vary considerably from container to container. Watering
frequency depends on the size and type of container, composition of the potting mix, plant
species and weather conditions. Some plants, such as impatiens, like an evenly moist soil.
Others, such as vinca, possess good drought tolerance.
Annuals growing in containers should be checked daily (especially in summer) to
determine whether they need to be watered. A few plants, such as New Guinea impatiens and
fuchsia, should be checked twice a day (morning and late afternoon or evening), as they dry out
quickly on hot, windy days.
When watering annuals in containers, continue to apply water until water begins to flow
out the drainage holes in the bottom of the container.
How often should I water my garden?
A deep watering once a week is usually adequate for fruit, vegetable and flower gardens.
When watering the garden, water slowly and deeply. Moisten the soil to a depth of 8 to 10 inches.
Most annuals, perennials, vegetables and small fruits perform best when they receive 1 to 1 ½
inches of water per week (either from rain or irrigation).
Yard and Garden: Tomato Disorders
| BY RICHARD JAURON
Tomatoes are the most popular vegetable crop in Iowa. Many diseases and disorders can affect
tomatoes during the growing season. Iowa State University Extension specialists describe the symptoms
and management of common problems. To have additional questions answered, contact the experts at
hortline@iastate.edu or call 515-294-3108.
Why are my tomatoes cracking?
Fruit cracking is a common problem on tomatoes. Cracks usually appear at the top or stem end of
the fruit. Cracks radiate out from the stem (radial cracks) or circle the fruit in concentric rings (concentric
cracks). Fruit cracking is associated with wide fluctuations in soil moisture levels. A heavy rain or deep
watering after a long, dry period results in rapid water uptake by the plant. The sudden uptake of water
results in cracking of ripening fruit. Generally, fruit cracking is most common on the large, beefsteak-type
tomatoes.
Fruit cracking can be prevented by supplying the tomato plants with a consistent supply of
moisture during the summer months. During dry periods, a thorough soaking once every seven days
should be adequate for most tomato plants. Conserve soil moisture by mulching the area around tomato
plants with dried grass clippings, straw, shredded leaves or other materials. Also, plant tomato varieties
that possess good crack resistance. Tomato varieties that possess good to excellent crack resistance
include Jetstar, Mountain Spring and Mountain Fresh.
Several of my tomatoes are misshapen. Why?
Misshapen (catfaced) fruit may be due to cool weather during fruit set. Exposure to 2,4-D or similar
broadleaf herbicides is another possibility. Catfacing is most common on large-fruited tomato varieties.
Affected fruit show leathery scars, bulges, or holes at the blossom end of the fruit. The incidence of
catfacing is typically highest on the early maturing fruit and declines during the remainder of the growing
season.
A blackish spot develops on the bottom of my tomato fruit. What is the problem and how can it be
prevented?
Blossom end rot is probably responsible for the blackish spots on the tomato fruit. Blossom end
rot is a common problem on tomatoes. It appears as a brownish black spot on the blossom end (bottom)
of the fruit. Secondary organisms invade the brownish black spot and cause the fruit to rot. Blossom end
rot is most common on the earliest maturing fruit that ripen in July and early August.
Blossom end rot is caused by a calcium deficiency in the developing fruit. Wide fluctuations in soil
moisture levels impair calcium uptake by the root system of the tomato plant. Excessive nitrogen
fertilization may also contribute to blossom end rot.
To reduce blossom end rot, water tomato plants on a weekly basis during dry weather to provide a
consistent supply of moisture to the plants (tomato plants require about 1 to 1½ inches of water per week
during the growing season). Mulch the area around the tomato plants to conserve soil moisture. Avoid
over-fertilization. There is no need to apply calcium to the soil as most Iowa soils contain more than
adequate levels of calcium.
Pick and discard fruit affected with blossom end rot. The removal of the affected fruit will allow the
tomato plant to channel all of its resources into the growth and development of the remaining fruit.
Blossom end rot can also occur on pepper, eggplant, summer squash and watermelon.
My tomatoes are developing white or yellow areas on the sides of the fruit exposed to the sun. Why?
The white or yellow areas on your tomatoes are due to sunscald. Sunscald occurs on fruit exposed
to the sun during periods of extreme heat. Initial symptoms of sunscald are the development of shiny
white or yellow areas on the fruit. Later, the affected tissue dries out and collapses, forming slightly
sunken, wrinkled areas. Secondary organisms invade the affected areas causing the fruit to rot.
Losses due to sunscald can be reduced by growing tomatoes in wire cages. Cage-grown tomato
plants provide good foliage protection for the fruit. Also, control Septoria leaf spot and other foliar
diseases which defoliate the plants and expose the fruit to direct sunlight.
Yard and Garden: Japanese Beetles
BY RICHARD JAURON
As Japanese beetles are spreading throughout Iowa and populations are increasing, more and
more gardeners are dealing with these very hungry garden pests. Japanese beetle adults feed on a wide
variety of plants. Iowa State University Extension specialists answer questions concerning these difficult
to control pests. To have additional questions answered, contact the experts at hortline@iastate.edu or
call 515-294-3108.
What are the Japanese beetle’s favorite food plants?
Adult Japanese beetles have been documented to feed on the foliage, flowers and fruits of more
than 300 different plants. Their top favorites are grape, cherry, apple, rose, raspberry and linden. A link to
a list of the Japanese beetle’s most- and least-favored woody plants can be found at the following
website: www.ipm.iastate.edu/ipm/hortnews/2010/7-14/japanesebeetle.html
Can Japanese beetles be effectively controlled by using traps?
In a word, no. Several kinds of traps are available that use a floral scent and/or sex attractant to lure
beetles into a net, jar or bag where the beetles can be contained till disposed of. In heavily-infested areas,
traps may catch hundreds or thousands of beetles in the course of the summer. Unfortunately, this is a
small percentage of the beetles in the area and makes no lasting impact on the beetle population or on the
plant damage experienced.
The use of traps is not recommended. Research conducted in Kentucky and elsewhere found the
traps do not control moderate to heavy infestations. The traps may attract more beetles than they catch
and actually add more beetles to the yard than would occur otherwise.
In isolated locations far away from other Japanese beetle infestations, and in very lightly-infested
areas, trapping may provide some benefit. Otherwise, traps will not make a difference.
Will treating my lawn for white grubs reduce the population of Japanese beetles on my plants next
summer?
It would be nice if life could be that simple, but the relatively small area you can treat (compared to
the grassy sites in the surrounding area) will not have any impact on the following year’s adult population.
Japanese beetle adults are very strong and capable fliers and may travel long distances from where they
developed as larvae in fence rows, roadside ditches and other grass sites, to where they are feeding. You
are likely to have beetles next summer whether you treat the grub stage in your lawn or not. Controlling
one life stage does not preclude potential problems with the other.
This does not mean you should not treat the turfgrass. If desired, high value turf can be protected
from the root-feeding larvae by treating the soil with a preventive insecticide in a timely fashion and
according to label directions. Most of the available insecticides must be applied before mid-August to be
effective as preventive treatments. Treating for grubs will protect the turfgrass. It will not prevent beetles
from feeding in your landscape the following year.
What is the life cycle of the Japanese beetle?
In Iowa, adult beetles emerge in mid-June through July. Japanese beetles are similar to other June
bugs in appearance and 3/8 inch long and 1/4 inch wide. The head and thorax are shiny metallic green and
the wing covers are coppery red. A distinguishing feature of the beetles is five tufts of white hairs on each
side of the abdomen.
Japanese beetle larvae are typical white grubs. The larvae are in the soil from August until June
where they feed on plant roots (especially turfgrass) and organic matter. The grubs are C-shaped and
approximately 1.25 inches long when full grown.
Japanese beetles are defoliating my linden tree. Will they kill it?
Japanese beetles feed on more than 300 different plants. However, lindens are one of their
favorites. Defoliation of well established, healthy lindens (and other trees) is usually not fatal. Defoliation
is most harmful to recently planted trees (those planted in the last two to three years) and trees in poor
health.
The foliage of recently planted and high-value trees can be protected with a soil-drench application
of a systemic insecticide, such as imidacloprid (Bayer Advanced Tree and Shrub Insect Control and other
products). To be effective, treatments must be made several weeks ahead of beetle emergence.
Sticky Situations on Cherry Trees
Have you noticed any gum oozing from cherry tree branches and trunks? It's called
gummosis, a sign that your cherry tree is under some sort of stress. That's right, trees can get
stressed! Gummosis is not a disease but can be associated with disease or insect damage to the
tree. Gummosis is most common on stone fruit trees such as plums, peaches, nectarines, and
cherries.
Gummosis is often associated with cankers, which are sunken lesions on trunks,
branches, or twigs. Cankers may be caused by mechanical injuries (such as lawnmowers or
pruning), insects, winter damage, sunscald, herbicide injury, and various fungal or bacterial
infections. In response to these stresses or injuries, a sticky amber ooze or gum is exuded from
these lesions (see pictures). With time, cankers may become more obvious, as branches swell or
form corky growths on the margins. Severe damage or infections may cause wilting of leaves and
eventual death of fruit-bearing wood.
Insects such as peach tree borers feed under the bark, creating wounds and tunnels on the
inner bark. As a result, branches exude gum through wounds. Fungal pathogens from the genus
Botryosphaeria may also infect cherry trees and cause cankers between the trunk and scaffold
limbs. These fungi are usually opportunistic and colonize plants when their defenses are low. On
the other hand, bacterial cankers caused by Pseudomonas syringae can sometimes become a
serious disease in commercial orchards. Bacteria colonize leaf surfaces and enter the tree via
wounds, creating oozing cankers and girdled limbs. Sometimes entire limbs may wilt and leaves
and fruit may show spots.
In summary, cherry gummosis is the plant's reaction to stress. Pathogens or insects may be
involved, but the best way to prevent gummosis is by taking an integrated management
approach. Avoid unnecessary mechanical injuries to your tree and prune under dry weather
conditions. Provide a good growing site (well-drained soils) for your tree and a balanced
fertilization program to promote vigorous growth. Also, practice good sanitation by pruning and
destroying cankered limbs.
Another 'New' Insect Pest in Iowa: European Elm Flea
Weevil
If your Siberian elm has leaves that look like they have been blasted with a shot gun then
it is probably being fed upon by a tiny, new insect called the European elm flea weevil, Orchestes
alni. USDA identifiers confirmed the first state record of the European elm flea weevil in Iowa on
July 13 based on samples submitted to the ISU Plant & Insect Diagnostic Clinic from Tama
County, Iowa, and forwarded to the USDA/APHIS/PPQ for confirmation. However it is probable
that European elm flea weevil has been in Iowa for a number of years.
This invasive insect causes primarily cosmetic damage to elms. We are not expecting this
insect to be harmful to tree health. The European elm flea weevil was reported in the northeastern
US in 1982 and has been in the upper Midwest since at least 2003.
European elm flea weevils are a small beetle about 2-3 mm long, and brown with darker
spots on its back. Although difficult to see with the naked eye it has a typical curved weevil
snout. It gets the name of flea weevil for its ability to hop and its hind legs are a bit enlarged, as if
it has been lifting weights.
The European elm flea weevils feed on American, Siberian, Chinese and hybrid elms, but
they prefer Siberian elms. The adults feed on leaves, and cause small holes all over the leaves.
The female weevil lays eggs along the leaf veins and the larvae feed within the leaves as
leafminers and leave blotchy dead areas on the elm leaf. The larvae pupate within the mine after
several weeks of feeding. They are reported to have a single generation each year. The adults
overwinter and in the spring lay eggs on the elm leaves. The larvae feed, pupate and the newly
emerged adults feed through the rest of the summer before overwintering.
So far in Iowa we have confirmed the European elm flea weevil from specimens in Tama
County and Dallas County and there is an additional photo report. We suspect once we start
checking we will find it through most of the state.
Links to more information and photos:
Morton Arboretum http://www.mortonarb.org/tree-plant-advice/article/757/european-elm-fleaweevil-orchestes-alni.html
Growing Garden Phlox
By Cindy Haynes, Department of Horticulture
There are many perennials that bloom reliably every summer. One that is particularly impressive in
my garden this summer is the garden phlox (Phlox paniculata). There are over 60 phlox species native to
North America. While many of these species are suitable for Midwestern gardens, garden phlox is
probably the most popular. Plants range in height from 1 ½ feet tall to over 5 feet tall. Blooms first appear
in mid-June in Iowa and may last for a month or more. Flower colors include lavender, white,
orange/peach, pink, red, and many with light or darker centers or "eyes". This prairie native prefers
sunny sites with moist, well-drained soils and good air circulation.
The "Achilles' heel" of many cultivars is susceptibility to powdery mildew. Powdery mildew is a
fungus that creates the appearance of a fine white dust or powder on the plant foliage. Powdery mildew
rarely kills affected plants but it can reduce vigor and be unsightly in the landscape. Twenty or thirty
years ago, most of the cultivars of garden phlox were susceptible to powdery mildew. The practical
management option was to pick the best color for your garden and hope that powdery mildew wouldn't
be horrible that year. If you were a perfectionist, you sprayed your plants every couple of weeks with a
fungicide to prevent powdery mildew. Today there are many newer introductions that are more resistant
to powdery mildew and therefore don't require fungicide treatment. Even the best of the best, however,
can occasionally get powdery mildew in hot, humid years. So, give them plenty of room and do not
overcrowd them in the garden. This will give plants plenty of air circulation. Frequent division may also be
necessary to further promote air circulation and keep plants vigorous.
The cultivar 'David' is the standard for powdery mildew resistant phlox and has been what the
newer cultivars are measured against. The Chicago Botanic Garden conducted a trial of phlox in an
attempt to determine which cultivars performed the best in the Midwest. Performance was based on
many factors including (but not limited to) flower production and incidence of powdery mildew. Below
are some of the top rated cultivars from the Chicago Botanic Garden trial of garden phlox. For more
information on the trial, see the Chicago Botanic Garden web site.
Cultivar
Bright Eyes
David
Eva Cullum
Franz Schubert
Katherine
Prime Minister
Robert Poore*
Flower Color
Pink with dark eye
White
Pink with dark eye
Lilac with dark eye
Lavender with white eye
White with red eye
Lavender
Height
2-3 feet
3-4 feet
2-3 ½ feet
2-3 feet
3-4 feet
2-3 feet
Comments
Fair resistance to powdery mildew
Fair resistance to powdery mildew
Fair resistance to powdery mildew
Fair resistance to powdery mildew
Good resistance to powdery mildew
Good resistance to powdery mildew
Newer cv.; considered good resistance
*not evaluated at Chicago Botanic Garden
This doesn't mean you shouldn't try other garden phlox – like the one pictured below ('Peppermint
Twist'). Some of the newest cultivars haven't been in production long enough for sufficient testing and
powdery mildew may arise (or maybe not!).
Upcoming Items and Events:
August 3
Archery—5:30 p.m.--Fairgrounds
August 5
Montgomery County Interagency Meeting—Extension Office—
8:30 a.m.
August 7
Muzzleloader—Phil Olson’s place—2:00 p.m.
August 8
Extension Council Meeting—5:30 p.m.—Extension Office
August 9
Static Exhibits to Iowa State Fair
August 23
Master Gardener Webinar—6:30 p.m. to 8:30 p.m.
August 28
22 rifle—David Olson’s place—2:00 p.m.
August 28
Shotgun—David Olson’s place—3:00 p.m.
August 31
Air Rifle—5:30 p.m.—Goldsmith Gallery
Montgomery County Extension Office
400 Bridge Street, Suite 2
Red Oak, IA 51566
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