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This is a seasonal scouting report giving growers in the Eastern New
York area information on the presence of agricultural pests. The
report is written by
Ken Wise, IPM
Extension Area Educator for Livestock and Field Crops.
May 26, 2004
Alfalfa
Alfalfa Weevil
Tip Feeding is Increasing!
This week I have
seen an increase in the tip feeding by alfalfa weevil larvae. This
is a good time to check your fields for alfalfa weevil damage. Alfalfa
weevil larvae leave a small hole (aka SHOT HOLE) in the leaflets that
is called "tip feeding". The percent of stems showing feeding
damage is how we determine need for alfalfa weevil treatment.
Pick 50 alfalfa stems at random
throughout the field. Look for the small "shot holes"
in the leaves that indicate that larvae are feeding. Record the percentage of alfalfa
stems that show the "shot hole" feeding damage in the
top 3 inches of the canopy.
Before the first cutting, if 40% of
the stem tips show feeding damage, you are at the "action threshold".
The good thing is that alfalfa weevil can generally be controlled
by harvesting. If you reach an action threshold within a week of your
normal 1st cutting date, early harvesting will help avoid economic,
yield, and forage quality losses. Alfalfa weevils only have one generation
per year and are typically not a problem after first harvest. Occasionally,
weevil can damage alfalfa re-growth after harvest. This damage may
be more evident in the windrow areas, and can be more noticeable under
cool or droughty weather conditions. If you find that 50 percent of
the new growth is damaged, with many small larvae present, a chemical
control may be warranted. For more information check out our on-line
publication, IPM
for Alfalfa Weevil.
Are there good biological control agents for alfalfa weevil?
SEE NEXT WEEK'S REPORT FOR THE ANSWER!
Potato Leafhopper
We have seen potato
leafhopper in several areas of Eastern NYS in low numbers. As the
summer progresses and the weather starts to warm the populations of
potato leafhopper have the potential in increase rapidly.
For management information on potato leafhopper check our on-line
guide: Potato Leafhopper on Alfalfa Management
Guide,.
Field Corn
Checking Plant
Populations-Indication of Pest Issues
As corn starts to
emerge it is important to know your corn plant populations. Conducting
plant population checks is the first step to determining if there
are pest problems in the field. The pressing question is How
do I check my corn plant populations? It is suggested that you sample
in units that are one-thousandth of an acre. Please consider developing
the habit of sampling rows as they were laid down by the planter.
If the was planted to a six-row planter, then sample the six rows
that represent one pass of the planter. Watch tractor wheel tracks
and choose your next six-row sample that would correspond to with
the same six planter units. This way you would notice any variation
or patterns between the units of the planter. Make sure to sample
the appropriate length for your row width. Take at least 5 samples
as you cross the field.
Row Spacing (inches)
1/1000 of an acre
30
17 ft. 5 in.
32
16 ft. 4 in.
36
14 ft. 6 in.
38
13 ft. 9 in.
40
13 ft. 1 in.
After you are finished counting
plants in each sampling location take the average number of plants
and multiply it by 1000. This will give you the number of plants per
acre. For example if you had an average of 30 plants you multiply
it by 1000 and you would have 30,000 plants per acre. If your plant
population is more than10% lower than that expected it may indicate
a problem in the field. While many things could cause the population
reduction at least two pest related issues might be involved: early
season seed or seedling blights and/or seed corn maggot damage. For
more information on these pests view our on-line management guides
at: Field
Corn Diseases. or Early Season
Insect Pests in Field Corn
Soybeans
Soybean Aphids
Soybean aphids are
new pest to the northeast. We have only had it on our soybeans the
past 3 years. For the most part it has not caused damage to soybean
production with the exception of few fields in Central New York last
season. Soybean aphid has been a problem in other part of the
country. Soybean aphid is the only aphid that attacks soybeans in
the United States. This aphid is very small at a 1/16 of an inch long
when fully grown and may be yellow to yellow-green in color. Soybean
aphid has two black-tipped tailpipesor cornicles that can be seen
easily under a hand lens. They tend to colonize and are found on the
under side of the leaf. The threshold for soybean aphids is 250 or
more per plant through the V4 stage. You must take an average of 20-30
plants per field. This threshold allows for about 7 days for treatment
action. For more information on managing insect pest on soybean check
out our on-line publication: Soybean Insect
Pest Management Guide
Seed Corn Maggot a Problem in Soybeans
I have heard estimates
predicting record number of soybean acres will be planted in NY this
season. As we gear up for soybean production remember to consider
protecting stands from potential damage from seed corn maggot. Seed
corn maggot (SCM) is a problem on corn but will also feed on soybean
seeds. In the early spring, the female SCM fly searches fields with
high organic matter (decomposing plant material, fields with manure,
etc.) for soil cracks and germinating seeds in which to lay their
eggs. Maggots hatch from the eggs and feed by burrowing into germinating
seeds. These maggots are tapered, legless, appear to be headless,
pale yellowish-white, and reach a length of about a 1/4 inch long.
Symptoms in soybeans are that damaged seedlings may appear as "snake
heads" i.e. seedlings without cotyledons. Proper diagnosis requires
some digging in the gaps within a row to check for seeds and seed
health. Prevention of SCM in soybeans is the main method of management.
Use an insecticide seed treatment when you plant. For more information
on managing insect pest on soybean check out our on-line publication:
Soybean Insect
Pest Management Guide
Soybean Rust-Not Here but Keep Eyes Open
Some growers have
asked me if we have soybean rust in New York. Soybean rust is not
in New York or even in this hemisphere. While we do not have soybean
rust I think it is important to watch your beans for the disease.
Soybean rust is found in Asia, Australia, Africa and South America.
This fungal disease is easily and widely disseminated by wind-borne
spores. Soybean rust can be very destructive with yield losses from
10-80%, depending on how early in the season the plant is infected.
Soybean rust in the early stages is difficult to identify. It may
look like other foliar soybean diseases. An early symptom is a yellow
mosaic discoloration on the lower leaves of maturing plants at or
near flowering. As the rust advances it migrates to the center and
upper parts of the plant. This causes the leaves to turn yellow and
small brown pustules lesions appear. Tan or reddish brown surface
lesions, necrosis and eventual defoliation are symptoms of the advanced
stages of the disease. Pictures of the disease can be viewed on the
following website: Soybean
Rust Pest Alert. If you suspect you may have the disease
in your soybeans contact your local Cornell Cooperative Extension
Educator.
Small Grains
Cereal Leaf Beetle
While I have not
seen cereal leaf beetle this season they can be an occasional problem
in small grains. (My western NY colleagues began finding them two
weeks ago in Aurora and points west).
Some years they do reach action thresholds and need to be controlled.
Eggs can be found on the upper surface of the leaves near the midrib.
Eggs are elongate, yellow to brown about 1/16 inch long, and are laid
in chains of two or three. Small black slug-like larvae emerge from
the egg and reach about a 1/4 inch long. Larvae feed on the leaf surface,
leaving long narrow white strips between the veins. The adults are
3/16 inch long with metallic bluish-black head and wing covers. Cereal
leaf beetle is more of a problem in oats but can occasionally reach
threshold levels in wheat.
The threshold for cereal leaf beetle is three or more eggs and larvae
per stem before the boot stage of oats or one or more larvae per flag
leaf after the boot stage. Check 30 stems distributed throughout a
field to determine if the field are at an action threshold.
Thanks to: Kevin
Ganoe (Chenango, Otsego, Herkimer, Fulton & Montgomery Counties),
Jeff Miller (Oneida County) and Keith Waldron (NYS IPM) for contributing
to this week's report.
Cheers
Ken Wise
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