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Weekly Field Crops Pest Report 2007

July 19, 2007                Volume 6 Number 13

1. View from the Field

2. Know your corn rootworms

3. Do you know how to scout for Corn Rootworm?

4. An Army of Worms Invading: True or Fall?

5. Soybean aphids - Natural Enemies - Fungus Among Us

6. Soybean Aphid Update

7. Soybean Rust Update

8. Clipboard Checklist

9. Contact Information

View from the Field


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Western NY and Finger Lakes
Julie Dennis

Spider mites have been reported in soybeans in Cayuga, Seneca and Wayne counties.  The fields where these pests are being seen are in areas that seem to keep missing the spotty rain showers from the last several weeks.  Remember, hot, dry conditions tend to contribute to spider mite infestations. 

Soybean aphid numbers have taken off in areas of Ontario, Onondaga, and Cayuga counties in the past week.

Phytophthora root rot has been reported in soybeans.  Nancy Glazier, NWNY team, found a patch in Monroe County, and Sarah Woodard, Cayuga County CCE, found several affected plants.  Sarah also reports that downy mildew is around in soybeans. 

Corn rootworm beetles are beginning to emerge around the area.  Most reports are of low numbers of potato leafhoppers, except in new seedings.

Eastern NYS
Ken Wise

The soybean sentinel plot field in Columbia County I monitor was over threshold for soybean aphids last week (average of 600 aphids/plant).

The grower sprayed the field for soybean aphids on Saturday July 14.  What seems odd to me is that there is still a fair number aphids that seemed to have survived or re-infested the soybeans. These soybean aphids were mostly on the lower leaves. There were plants with as few as 10 aphids and some as high as 170 aphids/plant. The average of aphids/plant was far below threshold at 55 aphids/plant. Jeff Miller in Oneida County also reports that one of the fields they monitor for soybean aphids was over threshold.

Potato leafhoppers are alive and well making a nice yellow effect to alfalfa fields at the Cornell Research Farm at Valatie, NY. In one field after counting 3 samples (10 swings of the 15” sweep net = 1 sample) I counted 260 potato leafhoppers which is 3 times the threshold limit for 10 to 12 inch alfalfa.

Know your corn rootworms

Julie Dennis
NYS IPM

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Corn is starting to tassel, and I observed male corn rootworm adults for the first time in 2007 last week.  Corn rootworm beetles will be feeding on the pollen for the next few days, and then they are most likely to be observed in the silks of developing ears. Here’s a review of how to identify the adult rootworms:

Western corn rootworm (WCRW) adults are black and yellow beetles that are approximately 1/4 inch long. The female is yellowish with 3 black stripes on its back, while the male is solid black with a pale yellow area at the tip of its abdomen (see photo, and stay tuned for a picture of a male WCRW). Northern corn rootworm is slightly smaller than the western, and it is bright green in color (see photo).

The northern corn rootworm (NCRW) used to be the predominant species in New York State, but since the arrival of the western in the 1980’s, the western has become the dominant species. When scouting, 1 western corn rootworm equals 2 northern corn rootworm adults. During pollination, developing ears can tolerate many rootworms feeding on silks (10+ per ear) without suffering economic losses.

WCRW Female

NCRW

Do you know how to scout for Corn Rootworm?

Ken Wise
NYS IPM

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You will need to scout all corn fields that will be kept in corn next year from emergence of the tassel until pollination is complete. Pollination occurs for three weeks and monitoring takes about 20 minutes per field.  You will need to monitor each field once a week until you reach a threshold or until pollination is over. Look for gravid, (i.e. mature, egg laying) corn rootworm females beetles--the ones that, when you squeeze their bodies, release white eggs from their posteriors.

Here’s how you scout:

  • Are female beetles present? Mature and capable of egg laying? Conduct the squeeze test (see above) to determine if they are ready to lay eggs. 

  • Approach a corn plant carefully because the beetles will fly off if they disturbed too much.

    • Grasp the silk with one hand.

  • Count the beetles on the entire plant.

    • Start counting at the top working down.

    • Gently pull leaves away from the stalk so you count any beetles that may be hiding in the whorls.

  • For each corn plant monitored, record the total number of beetles observed. See the sequential sampling chart below.  Since western corn rootworms are potentially more damaging than their northern cousins, count each western (yellow striped) beetle observed as “one” and each northern (green type) as “1/2”.

  • Check several plants at random (not next to each other!) in several parts of the field.

  • Continue sampling at seven-day intervals until the ear silks are brown, approximately 3 weeks after tassels are first visible, pollination is complete or an above threshold number of beetles are found.

Using the Sequential Sampling Card for Corn Rootworm
  • Keep a running total (RT) of the number of corn rootworm beetles you have counted on each plant. Each northern corn rootworm has half the value of each western corn rootworm. The western corn rootworm does twice the damage to corn than does the northern. So if you count 3 westerns and 4 northern (2 western equivalent) on a plant you would have a total of 5 beetles.

  • If the number of corn rootworm beetles observed is smaller than the “N” (“Not at threshold”) number stop and scout 7 days later.

  • If the number of corn rootworm beetles observed is larger than the “T” (“At threshold” or “Treat”) number then you need to manage rootworms next year.

  • If the number of corn rootworm beetles observed fall between “N” and “T”, continue sampling additional plants until you finally go over or under.

  • In a very low or very high rootworm population a sampling decision can be made in sampling as few as 3 to 8 plants. For moderate populations more samples may be necessary to insure accuracy.

N= No Treatment

T = Treatment

RT = Running Total

 For more information on corn rootworm checkout our online publication: Corn Rootworm Management in Field Corn

An Army of Worms Invading: True or Fall?

Ken Wise
NYS IPM

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There has been recent discussion on armyworm in Eastern NYS and Vermont. There are two common types of armyworm that can feed on forage grasses, field corn and small grains. These are true and fall armyworms.

True armyworm (Pseudaletia unipuncta) larvae appear smooth , cylindrical, pale green to brownish when they are still small. Mature larvae are smooth, hairless, and brown with a narrow, mid-dorsal stripe and two orange stripes along each side.

True armyworm ranges in size from 1/8 inch to 1.5 inches long. These are normally a spring pest and the adult moth travels on storms from the south in May and lays eggs on grasses or small grains. They feed on grasses, small grains and field corn as they develop and are normally finished with their development by late June. There can be exceptions since I have seen true armyworm larvae into mid July feeding on field corn.

Fall Armyworm (Spodoptera frugiperda) larvae are green, brown, or black, and about 1/8 inch to 1.5 inches long. They have a dark head capsule usually marked with a pale, but distinct, inverted "Y." Along each side of its body is a longitudinal, black stripe, and along the middle of its back is a wider, yellowish-gray stripe with four black dots on each segment.

Signs of Armyworms! Because armyworms feed at night, look for chewed leaves, cut stems, lodged plants, pellet-like frass on the ground, and larvae hidden under plant canopy and surface residue. You will need to be aware that armyworms can move from field to field every quickly. If larvae are less than ˝ inch long when you monitor fields, and there are sufficient numbers and damage is present, an insecticide could be justified. Treat only the affected area and a 20 to 40-foot border around the infestation. Rarely does a whole field need to be treated for armyworm. Larger armyworm larvae, greater than 1/2 inch long, are much more difficult to control. These large larvae are more tolerant of insecticides, reducing the effectiveness and economic viability of this option.

Threshold Guidelines

Corn - More than 50% of plants show armyworm feeding, and live larvae less than 1 - 1/4 inches long are numerous in field

Grasses - no specific guidelines available, need for treatment based on the level of damage observed in relation to the expected value of grass harvest.

Soybean aphids - Natural Enemies - Fungus Among Us

Keith Waldron
NYS IPM

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Soybean field surveys conducted in 2002-2003 by Cornell Entomologists and the NYS IPM Program documented a rich diversity of natural enemies attacking soybean aphids (SBA). These biological control agents included various coccinellid species (lady bugs), lacewing and syrphid fly larvae, minute pirate bugs, spiders, 60 species of ground beetles and more. These surveys also found 2 parasitoids not previously described as attacking soybean aphids (see last weeks issue).

In addition to various arthropod species, Cornell Entomologist Ann Hajek and colleagues identified at least 7 species of entomopathogenic fungi attacking soybean aphids in central NY. These fungi include: Pandora neoaphidis, Neozygites fresenii, Lecanicillium lecanii, Conidiobolus thromboides, and Entomophthora chromaphidis, Zoophthora occidentalis and another undescribed species of Pandora. None of these pathogens had previously been reported from soybean aphids in the literature.

While many soybean fields have remained below threshold for SBA in NY this season, above threshold soybean aphid numbers have been reported in recent weeks. Relatively low populations of natural enemies have been observed in some of these fields and many are from areas that have experienced dry weather conditions. Recent rains are welcome and may create the conditions favorable to stimulate fungal diseases that help curb soybean aphid populations.

Fungal pathogens with the potential to cause substantial infection in soybean aphids are clearly present in New York State. Can insect diseases help moderate SBA populations? Given favorable weather conditions and sufficient inoculum, our experience while limited, has been favorable. For example, in 2003 SBA collections in heavily infested soybean fields yielded 3% to over 75% of the aphids infected with a fungal disease. One late planted field  tracked closely yielded an 84% infection by P. neoaphidis on August 8th. Although the plants were sensitive to damage (early pod fill stages), the grower decided not to spray with insecticide. Soon after, aphid populations were observed to decline precipitously on their own, as might have been predicted by the high rates of infection in samples collected.

Take home message?
Watch fields closely. Continue to monitor fields for presence of soybean aphids. Should monitoring detect a population at the 250 SBA's / plant threshold evaluate the crop for yellowing, stunting, leaf curling and other signs of stress and note the presence of natural enemies.  Resample the field within the week to determine if SBA populations have continued to increase.

Diseased aphids? What to look for...
Search for soybean aphids on the underside of leaves, stems and petioles. Healthy aphids have a greenish-yellow color. Diseased aphids appear "fuzzy" due to sporulation of the fungus and may be pinkish, white, tan, or brown in color. The photo shows a healthy soybean aphid compared to one infected with Pandora neoaphidis. Also in the photo is a smaller white cast aphid skin.

(Photo courtesy of James Liebheer, Cornell Entomology).

Soybean Aphid Update

Keith Waldron
NYS IPM

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Soybean aphid update - July 20, 2007.
Sentinel site soybean fields reporting this week range from the V2 - R2 growth stage, with most fields in the V5-R1 range. Soybeans generally 12-16 inches, a few R stage fields at 20-24 inches.
Frequent field monitoring provides useful information for making management decisions. Sentinel site reports this week from Monroe, Ontario, Oneida, Seneca, and Wyoming counties indicate soybean aphid populations all well below the 250 SBA / plant threshold. Onondaga county reports V7 soybeans at 250 - >500 SBA / plant.  Cayuga county reported data for six fields, all in R-stages. All fields are at or have gone over threshold. Four fields have been sprayed. Columbia and Cortland county sentinel fields were treated last week for above threshold SBA populations. The Wayne county sentinel site was treated for a spider mite infestation. Natural enemy populations vary across fields being monitored, numbers generally appear to be increasing since last week. It should be noted that field by field monitoring on individual farms has detected numerous situations where some fields have high SBA populations while others are much lower.

Recent rains are expected to provide welcome relief to areas facing dry conditions.  Aphid populations can also be disrupted by heavy rainfall events by washing them from leaves and exposing them to predators.  Rain may also help to create conditions more favorable to entomopathogenic disease epidemics with potential to moderate SBA populations.  Surveys in the next weeks will provide more insights. Growers are advised to continue monitoring fields for SBA's, crop condition and growth stage. If fields reach the 250 SBA / plant threshold, resample fields within a week to re-evaluate the population level before taking action. Watch for presence of winged (alate) aphid types on more heavily infested plants. An abundance of winged aphids often indicates the aphid population is preparing to emigrate. Notes could also be used to mention if any predators or parasitized aphids (mummies) are present or other general relevant observations.  It is recommended that notes of presence and/or infestation levels of other economically important pests of soybean such as foliar, stem and root rot diseases, white mold and Bean leaf beetle be noted.

For assistance on soybean growth stages and soybean aphid decisions see: "Reproductive Soybean Development Stages and Soybean Aphid Thresholds".

Thanks to: B. Aldrich, J. Lawrence, J. Degni, J. Dennis, M. Dennis, K. Ganoe, N. Glazier, J. Miller, M. Stanyard, B. Tillapaugh and K. Wise for sharing their Soybean aphid observations this week.

For more on the current national Soybean aphid perspective see: www.sbrusa.net.

Soybean Rust Update

Gary Bergstrom
Plant Pathology, Cornell University

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Soybean Rust

http://www.ppath.cornell.edu/soybeanrustny/

Weekly scouting is being done in twenty New York State sentinel plots located in the following counties: Cayuga, Chautauqua, Chemung, Chenango, Columbia, Cortland, Jefferson, Monroe, Oneida, Onondaga, Ontario, Oswego, Otsego, St. Lawrence, Seneca, Steuben, Suffolk, Wayne, and Wyoming. Plant stages in these plots reported to date range from V-2 to R-1. Low levels of septoria brown spot and downy mildew have been reported in some of these plots.

Soybean rust has been recently reported in the last week in several states in the Southeastern U.S. Mississippi reported their first find of soybean rust this year on kudzu in Wilkinson County. Texas reported soybean rust on soybean in a sentinel plot as well as a surrounding commercial field in Victoria County. Florida reported its first find on soybean this year in a sentinel plot in Marion County. To date in 2007, soybean rust has been detected in ten counties in Florida, five counties in Georgia and Alabama, five Parishes in Louisiana, four counties in Texas and one county in Mississippi. Weather in the Southeast remains favorable for rust development. (Updated July 16, 2007 )

Clipboard Checklist

Keith Waldron
NYS IPM

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General:
* Maintain crop production activity records by field, including harvest date, pesticides used, nutrient inputs including manure, etc.
* Enjoy your family. Take them swimming!

Established Alfalfa & Hay:
* Begin second harvest of alfalfa about 40 days after first cutting if weather conditions are favorable
* Record hay yields by field and quality by storage facility; take samples for forage analysis
* Top dress hay fields if necessary.    
* Monitoring alfalfa regrowth for potato leafhopper
* Monitor for diseases, particularly Verticillium wilt, record information on type and location for future cropping decisions.

Alfalfa Seedings:
* Continue monitoring for potato leafhopper, weeds and diseases.
* Monitor fields for weeds and diseases: record information on type and location for future cropping decisions.

Summer Forages: 
* Plant summer seedings. Plant birdsfoot trefoil by end of July.

Small Grains:   
* Watch wheat grain moisture. Be ready to combine at 18 percent.
* Adjust combine in preparation for winter grain harvest (late-July) or spring grain Harvest (early to mid-August). Contract custom-operation if necessary.
* Clean grain storage areas.

Corn:
* Monitor corn rootworm adults at silking.
* Observe corn for weeds and fertility
Soybeans:
* Monitor for soybean aphids, and other insects, including natural enemies such as lady bird beetles.
* Check droughty fields for presence of spider mites

Soybeans:
* Monitor for soybean aphids, and other insects, including natural enemies such as lady bird beetles.
* Check droughty fields for presence of spider mites
Livestock:      
* 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
- Evaluate need for face fly and stable fly control measures
* Check and clean pasture water supplies.

Equipment:
* Note any repairs to harvesting equipment as they are cleaned and lubricated.
- Repair forage harvest equipment as needed
* Ready combine for small grains or finalize arrangements for custom harvest

Contact Information


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Julie Dennis: IPM Area Educator, Livestock and Field Crops, Western NY
Phone: (315) 331-8415
Fax: (315) 331-8411
Email: js38@cornell.edu

Keith Waldron: NYS Livestock and Field Crops IPM Coordinator
Phone: (315) 787 - 2432
Fax: (315) 787-2360
Email: jkw5@cornell.edu

Ken Wise: Eastern NYS IPM Area Educator: Field Crops and Livestock
Phone: (518) 434-1690
Fax: (518) 426-3316
Email: klw24@cornell.edu