August 19, 2005 Volume 4 Number 18
1. View from the Field
2. Dry Conditions - Pest Impacts?
3. Winter wheat, Aphids and Yellow Dwarf
4. White Mold in Soybeans
5. Soybean Rust Update
6. Soybean Aphid Management Decisions?
7. Growing Degree Days in NYS
8. Clipboard Checklist
9. Contact Information
View from the field
Reports are in from many areas of the Finger
Lakes and Western regions of NY that soybean aphid numbers are
dropping. Many factors are contributing: humid conditions encouraged
outbreaks of fungal pathogens, lady beetle populations have
continued to increase, or control with insecticides has been
successful. Now is the time to start watching fields for winged
aphids. As soybean pods fill and plants dry down, aphids with
wings will head for “greener pastures” - or in the case of soybean
aphids, buckthorn plants as an overwintering host. From the
TAg team fields in Orleans County, Nancy Glazier (NWNY Team)
observed that every field scouted has a lot of downy mildew.
As the pale spots of affected tissue darken and die, it can
look like other leaf spot diseases.
Corn rootworm adults are still abundant in fields where silking
was late in areas. Potato leafhopper adults and nymphs continue
to be sparse in most alfalfa fields.
Dry Conditions - Pest
Keith Waldron, NYS IPM
Wilting, curled and discolored leaves, stunted
plants, parched soil - all signs of drought stress. Dry conditions
are the norm in many areas of the state this week and rain dances
have had spotty success at best. Drought impacts harvest timing
decisions, yield and crop quality. What effects might these
dry conditions have on our common field crop pests?
crops with poor weed control, yield and quality impacts are
an issue. Potential for herbicide carryover may be another concern.
For fields where root or vascular injuries are (or have been)
present, dry conditions add to plant stress and make a bad situation
more obvious. As a general rule of thumb, sucking insects and
those that bore into plants, and diseases that damage roots
and vascular systems, have a greater impact during dry periods.
Corn rootworm, clover root curculio, and alfalfa snout beetle
larval damage, vascular diseases like Verticillium wilt, root
rots like Phytopthora (previously damaged plants) and crown
diseases like Fusarium crown rot are some problems that can
become more evident under dry conditions. Tunneling by stalk
boring insects like European corn borer (ECB) may show greater
impacts and worse if combined with a stalk rot like anthracnose.
On the flip side for ECB dry conditions cause high mortality
to ECB eggs and newly hatched larvae.
Dry conditions affect the balance of biocontrol provided
by beneficial fungal pathogens like Pandora and Entomophthora
spp, that help control common field crop arthropod pests. Reducing
efficacy of these biological control agents can increase risk
of some pests like spider mites, potato leafhopper, and aphids.
Dry conditions can interact with other stresses and pest
problems. High populations of potato leafhopper (PLH), a sucking
insect, for example, have been shown to interact with water
stress to produce even greater plant damage. Remember to
HALVE PLH thresholds for fields under drought stress…
Stalk rots of corn may be another issue for fields under
drought stress, particularly for those fields that had good
pollination. Gary Bergstrom described the situation as a “source
/ sink” issue. Plants are working hard to send photosynthates
to the developing kernels. Under dry conditions, that decrease
production of photosynthates, kernels win over stalks as the
place plants send their manufactured food to. As this happens
stalks lose out and become weakened and at risk for stalk rots
such as Diplodia, Anthracnose and Fusarium.
On the plus side, many field crop diseases can be less common
or severe during extended dry conditions. Diseases like anthracnose
leaf blight (corn), spring black stem (alfalfa), and Septoria
brown spot (soybean) are favored by overcast skies, frequent
showers, and moderate to high relative humidity. These types
of diseases require moisture and periods of wet leaves for fungal
spore germination and host infection. Rainy conditions can be
important for movement of disease inoculum. Locally, storms
can splash fungal spores and bacteria from one plant to another,
like eyespot of corn, and physically move disease organisms,
such as Phytopthora root rot, through the field. “Globally”
storm weather patterns are an important means of transporting
some diseases across great distances (rusts of corn, wheat,
soybean). Other good news? Lowered levels of infected crops
this season could translate to lowered overwintering inoculum
and potentially reduced risk to infect crops next season. Remember
the disease triangle? Presence of a susceptible host, virulent
pathogen, and favorable weather conditions. The actual incidence
and severity of foliar diseases next season will still depend
to a large extent on the weather patterns that develop.
Ken Wise, NYS IPM
Barley yellow dwarf virus, now
know as yellow dwarf virus (YDV) in wheat
is a serous disease across the country. This disease is transmitted
by several species of aphids that infest wheat. When infected
aphids feed on the plants they infect the wheat with the virus.
Winter wheat that is infected in the fall does not show symptoms.
Symptoms start to appear mid-spring as yellowing of leaves.
One management strategy is to plant wheat after the Hessian
fly free date in your region. This can limit the number of aphids
entering the fall seeded winter wheat fields. Another management
option is to plant a wheat variety that is resistant to YDV.
White Mold in Soybeans
Julie Stavisky, NYS IPM
2005 has been an unlikely season for severe
white mold outbreaks, but humid weather over the past several
weeks did provide the conditions for disease development in
some areas of New York State.
Highly productive, dense stands of soybeans favor white mold
development. The fungus survives from year to year in the soil
as hard black pellets called sclerotia. Sclerotia of white mold
must be present to cause the disease, though a small number
of sclerotia on the soil surface can lead to significant outbreaks
if wet, moist, cool conditions are present while plants are
flowering. Under these favorable conditions, sclerotia will
germinate and mushroom-like structures (apothecia) will form.
The apothecia produce ascospores which spread by wind and splashing
rain. Ascopsores require a nutrient source to grow, and soybean
flowers serve as ideal locations. The fungal mycelia colonize
dead flowers and the characteristic thick white moldy covering
on stems and pods develops. Interspersed with the white mold
on stems are the black sclerotia. Plants may wilt and die as
a result of infection. If white mold infection is late in the
season, yield loss will not be as severe. Temperatures over
90 degrees will stop disease development. During harvest, the
sclerotia on stems and pods may end up in the soil or residue,
or may stay with harvested seed.
The following photo shows the white mold infection on a plant
that is starting to wilt. (Thanks go to Mike Stanyard, NWNY
Team, for the photo)
A key to white mold management is to find strategies to prevent
the build-up of the pathogen in a field. Rotation to crops other
than soybean for at least 1 year (ideally 2 or more years) is
recommended. Additionally, weed management practices that reduce
weeds that serve as alternate host for white mold (for example
lambs quarters and pigweed) will help to decrease build-up of
the pathogen. It is also essential to avoid the planting of
contaminated or infected seed, and to avoid the movement of
infected soil with equipment. Varieties of soybeans that are
tolerant or moderately resistant to white mold should be selected.
Yield protection by spraying fungicides has not been documented
in New York.
Soybean Rust Update
New York State Soybean Rust Information Center
Asian Soybean Rust Status
Soybean rust was most recently confirmed in Hampton County,
South Carolina. This is the first report from South Carolina
in 2005. This is currently the most northern report of soybean
rust in the U.S. To date, Alabama has reported four counties
positive with soybean rust, Florida has reported eighteen counties,
Georgia has reported seven counties and Mississippi has reported
two counties. Scouting and spore trapping continues throughout
the soybean production areas of the U.S. Scouting of sentinel
plots in New York State continues this week and to date no soybean
rust has been found. The risk of soybean rust infection in New
York is currently considered to be low and no fungicide application
for soybean rust is advocated at this time. Growth stages in
New York State sentinel plots range from R5 to R6. (Last updated
Soybean aphid management decisions?
Keith Waldron, NYS IPM
Soybean aphids (SBA) are still here. Populations
are variable across the state but in some areas are still higher
than they have been in recent years. This is consistent with
other states reporting SBA issues across the country. NY soybeans
are typically at or above the R5 stage.
SBA thresholds for R5 and beyond have not been determined.
Michigan State University suggests average of 1000 SBA per
plant with increasing populations. If high SBA populations
are determined, check the field again over the next several
days. Static or decreasing SBA populations are what we’d hope
for. Increasing populations are not a good sign, but watch populations
of natural enemies. Some additional considerations in making
management decisions: Are soybean plants stressed? Are soybean
plants showing symptoms of aphid infestation (curled leaves,
sooty mold, honeydew, stunted plants)? If yes, these are not
good situations. Presence of winged aphids? Can be a sign the
population is getting ready to leave. Are natural enemies present?
If yes, they can do wonders at keeping SBA populations at bay.
Reality check Some recent questions from folks in
the field have added the caveat “tall” and “drilled” soybean
plants. Moving spray equipment into these fields is not easy.
Michigan IPM reports situations where this has led to poor insecticide
coverage and the need for additional sprays. Knocking out the
beneficial populations hurt these fields too and allowed a resurgence
of SBA numbers. Another reality is that pre-harvest interval
(PHI’s) for available insecticides is getting close. Ambush/Pounce/permethrin:
60; Warrior: 45; Lorsban and other chlorpyrifos products: 28;
Mustang Max and dimethoate: 21.
For more information see: Reproductive Soybean Development
Stages and Soybean
Days in NYS
March 1 - August 16, 2005
Base 50 F
Keith Waldron, NYS IPM
• Maintain crop production
activity records by field, including harvest date, pesticides
used, nutrient inputs including manure, etc.
• Check bunkers and silos. Prepare for corn silage.
• Check fall harvest equipment.
• Mow weeds around barn, grain storage bins, and farm buildings.
Alfalfa & Hay:
• Continue monitoring for potato leafhopper -harvest early
or spray on basis of need.
- HALVE PLH thresholds for fields under drought
• Monitor fields for weeds and diseases: record information
on type and location for future cropping decisions.
• Harvest third cutting of alfalfa about 40 days after second
• Record hay yields by field and quality by storage facility;
take samples for forage analysis
• Monitor corn rootworm adults at silking.
• Observe corn for weeds, stalk rots / lodging, and nutrient
and moisture deficiencies
• Monitor for soybean aphid, soybean rust, pod, stem and
• Continue manure management and release of biological control
agents (parasitic wasps) for house fly and stable fly control.
• Monitor young stock for cattle lice and mange mites
• Check condition of pastures and animals on pastures:
- supplement animals on pastures with hay as needed
- Evaluate need for face fly, horn fly, and stable fly control
Julie Stavisky: IPM Area Educator, Livestock
and Field Crops, Western NY
Phone: (315) 331-8415
Fax: (315) 331-8411
Keith Waldron: NYS Livestock and Field Crops IPM Coordinator
Phone: (315) 787 - 2432
Fax: (315) 787-2360
Ken Wise: Eastern NYS IPM Area Educator: Field Crops and Livestock
Phone: (518) 434-1690
Fax: (518) 426-3316