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Weekly Field Crops Pest Report 2007

August 29, 2007                Volume 6 Number 16

1. View from the Field

2. Stop! Check for Corn Ear Rot

3. Think Weeds in the Fall

4. How important is European corn borer in field corn?

5. Soybean Rust Update

6. Soybean Aphid Update

7. Clipboard Checklist

8. Contact Information

View from the Field

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Western NY and Finger Lakes Region
Julie Dennis

Soybean aphid numbers appear to be dropping or staying low in most fields I have observed this week.  Sarah Woodard, the scout with Cayuga County CCE reports that bean leaf beetles have been seen.  Here’s a photo showing the red phase of this pest.

In the Midwest, bean leaf beetles (BLB) often are a significant economic threat.  The first generation of BLBs appears in early July, and if the populations build sufficiently, the second generation of BLB, appearing in August, can cause substantial pod damage. Yields may be reduced 20-50%.

While BLB will feed on soybean leaves, the primary economic injury in the Midwest results from feeding on pods. Pods may be clipped from plants, or injured areas on pods may serve as entry points for fungal pathogens, thus causing reductions in seed quality.

Thresholds in the Midwest vary based on soybean price and insecticide costs, but they range from 3.5 to 12 beetles per foot of row.  Last year was the first year BLB was seen in NY, and only a few beetles were observed per field.  Minimal feeding injury occurred as a result of their presence.

We need to add this insect to our list of pests to watch for when we’re scouting the rest of this season and in 2008.

Eastern NYS
Ken Wise

This last week I saw several corn leaf diseases at the Cornell Research Farm in Valatie. One of theses diseases I rarely see appears to be gray leaf spot.

Gray Leaf Spot

Here is specific  information on gray leaf spot:

Pathogen: Fungus. Cercospora zeae-maydis

Description: Long (1/4 - 2 in.), narrow (1/8 to 1/2 in.) pale lesions with parallel sides. The lesions are gray to tan in color

Conditions Favoring: Warm, wet, humid weather. Dramatic crop loss can occur if blighting occurs within 3 weeks of silking. Gray leaf spot occurs in valley areas with persistent dew. It is most prevalent when corn follows corn and the residue remains on the surface (minimum and no-tillage).

Management Alternatives: Resistant hybrids. Clean plowdown and crop rotation.

Stop! Check for Corn Ear Rot

Ken Wise
NYS IPM

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Are you ready with the chopper or combine? STOP; check for corn ear rots first! Some kinds of fungi can create mycotoxins that are toxic to livestock. Taking a few minutes to check a field for certain ear rots can help you determine if you want to feed your field of corn to livestock. Pull back the husks on several plants and look for the presence mold growing on the ear of corn. The following are specific symptoms of certain ear rot diseases that can be found in NYS:

Fusarium Ear Rot appears as a white-to-pink or salmon-colored mold. This mold can begin with bird, deer or insect-damaged kernels. Fusarium ear rot may contain fumonisins which are mycotoxins that can be toxic to livestock.

Gibberella Ear Rot symptoms are pink to reddish colored mold. This disease starts near the tip of the ear and progresses down toward base of the ear. Gibberella can produce vomitoxin and zearalenone which is toxic to many kinds of livestock.

Diplodia Ear Rot symptoms appear as a thick white mold that usually starts near the base of the ear. This disease can also appear on the plant as raised black fruiting bodies on moldy husks or kernels. Diplodia does not produce any known toxins.

Cladosporium Ear and Kernel Rot symptoms appear as greenish black, blotched or streaked kernels scattered over the ear. This disease can also infect kernels that have been damaged by insects, birds, deer, hail, or frost. The disease can progress after the grain is harvested and stored.

Penicillium ear rot or blue eye symptoms range from a powder-like green or blue-green mold that is on and between the kernels and normally on the tip of the ear. If this disease progresses in storage it is referred to as blue eye because the germ is a bluish-green color. Penicillium ear rot can produce a mycotoxin called “ochratoxin”.

If you discover certain ear rot diseases make notes of the hybrid, tillage methods, rotation history, and planting date. By doing this you can avoid the disease occurrence in the future. The following is the effectiveness of specific management practices for corn ear rots:

Corn Disease
(Ear Rots)
Resistant Variety
Crop Rotation
Clean Plow
Down of Residue
Fungicides
Ear Rots
2
2
2
4
1= highly effective, 2= moderately effective, 3=slightly effective, 4= not effective, 5 = not usually economical,
Reference: Purdue University Field Crops Pest Management Manual

While there isn't any practical solution for coping with ear rots this late in the current season proper fertilization, timely weed control and reductions in insect pest pressure can help reduce risk of disease. For example: European corn borer (ECB) resistant Bt corn is at lower risk for injury by this insect. Lower risk means fewer ECB tunnels into stalks and less potential for fungi to infect through wounds and cause stalk rot. Also avoid continuous planting of corn under conservation tillage where stalk rot can be prevalent. If you are harvesting corn grain make sure you clean the grain bins. Keeping the proper temperature, moisture content and good aeration in the grain bin can reduce storage molds from developing. It is important to have regular inspections of the stored grain. This is essential to minimize risk of developing insect and mold associated storage problems. Harvest silage at recommended maturity and moisture level, and pack silage tightly and exclude air rapidly. Consider using organic acid preservatives if you can't exclude air or reduce moisture. If you had a lot of stalk rot and were growing for grain consider chopping earlier for silage to minimize lodging and combine losses. There are kits you can purchase to test your corn for different toxins on your own farm. The following are places where you can also test your corn:

Dairy One Forage Lab in Ithaca: For more information, call the lab at 1-800-496-3344 extension 172.

The Cornell College of Veterinary Medicine's Nutritional and Environmental Analytical Services Lab: More information is available on the web (www.vet.cornell.edu/public/neas/) or from lab manager Joe Hillebrandt at 607-257-2345

Think Weeds in the Fall

Ken Wise
NYS IPM

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In the fall, weeds are fully-grown and easily identified. Correctly identifying and recording significant weed infestations and their location is helpful for improving weed management decisions. Knowing the weed type and biology (broadleaf, grass, sedge, summer or winter annual, biennial, or perennial) is critical in selecting the right weed control measures. Remember, while herbicides are widely used for weed control other methods like crop rotation, cultivation, proper fertilization, planting dates, banding pre-emergence herbicides, crop spacing, plant populations, cover crops and combinations of these techniques should also be considered as part of an integrated weed control program. Conduct your fall weed surveys from late August through October. Sketch out a map of the field, walk each 1/4 of the field, and record the identity and relative infestation of the significant populations of weeds you observe. While no economic thresholds have been developed for weeds in New York, we recommend using a weed rating scale. The following scale can help you determine the severity of weed infestations in cornfields.

Evaluating Weed Presence- Weed Rating Scale:
Determine the intensity of each weed species as follows:

None: No weeds present

Few: Weeds present but very few plants within the field. Enough plants to produce seed but not enough to cause significant economic loss in the current year.

Common: Plants dispersed throughout the field, an average of no more than 1 plant per 3 feet (.91m)
of row, or scattered spots of moderate infestation.

Abundant: Fairly uniform concentrations across field. Average concentrations of no more than 1 plant per foot (.30m) of row or scattered spots of severe infestations.

Extreme: More than 1 plant per foot (.30m) of row for broadleaf weeds and 3 plants per foot of row for grasses, or large areas of severe infestations.

So take a few minutes and encourage growers to look at their fields---it will help save on weed control costs and increase crop production. Remember, if you don't look, you will never know. For more information on weeds in corn checkout our online publication: Weeds in Field Corn

How important is European corn borer in field corn?

Julie Dennis
NYS IPM

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The second generation of European corn borer (ECB) moths are still flying in search of a corn host on which to lay eggs.  As of the latest reports, ECB trap catches have declined at most western NY trap locations.  The trapping data is available from The Sweet Corn Pheromone Trap Network, coordinated by Abby Seaman with the NYS IPM Vegetable program.

While ECB causes much less worry in field corn than in sweet corn, concern about severe ECB infestations and the disease problems that may follow requires our attention.  The primary injury from the second generation of ECB is caused by the larvae tunneling into stalks and ear shanks (see photo), which can result in poor ear development, broken stalks (see photo), and dropped ears. The later in the kernel-filling period that an ECB infestation starts, the lower the yield impact will generally be.

To scout for ECB in August, look for egg masses on the undersides of leaves near ear level on the plant. Tunneling larvae can be found by looking for areas of frass (insect droppings) at the point of entry into the stalk. 

At times, a large infestation of ECB may cause a localized problem. Late harvesting and/or adverse weather conditions that cause plants to break at the points of injury may exacerbate those losses. Although the ECB damage can be conspicuous on an occasional plant, it does not generally cause significant yield losses in NY in corn harvested for grain or silage. Another reason to be concerned with an ECB infestation is that stalks or ears injured by ECB can be the entry point for disease-causing organisms. For more information, refer back to Check for Stalk Rots! in Weekly Pest Report 15.

Soybean Rust Update

Gary Bergstrom
Cornell Department of Plant Pathology

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New York State Soybean Rust Information Center

Weekly scouting is being conducted 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 reported this week range from R-3 to R-6. Low to moderate levels of Bacterial Pustule, Downy Mildew and Septoria Brown Spot have been detected this week in many of the NYS sentinel plots. Please view the 2007 NY State Soybean Rust Sentinel Plot Reports for specific county information.

New detections of soybean rust were recently made in soybean sentinel plots in single counties in Mississippi (Washington) and Oklahoma (Ottawa), two counties in Georgia (Decatur and Tift) and five counties in Alabama (Covington, Escambia, Marengo, Monroe, Washington). The confirmation in Ottawa County, Oklahoma is the northernmost detection of the disease in 2007. To date this year, rust has been reported in 25 counties in Texas (24 soybeans), ten counties in Alabama (six soybean), four counties in Arkansas (all soybean), 12 counties in Florida (four soybean), seven counties in Georgia (three soybean), 14 parishes in Louisiana (thirteen soybean), five counties in Mississippi (four soybean), and six counties in Oklahoma (all soybean). There also has been one account of soybean rust earlier this year in Mexico in the state of Veracruz on yam bean (Pachyrhizus erosus). (Updated August 27, 2007 )

Soybean Aphid Update

Keith Waldron
NYS IPM

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Soybean sentinel site - Soybean aphid update - August 24, 2007.

Sentinel site soybean fields reporting 8.20-24.07 have reached the reproductive growth R3-R6 stages.  Soybeans generally 30-36 inches or more.

Soybean aphid monitoring reports indicate soybean aphid population development is showing signs of slowing down. While some fields still remain at risk, many fields are at or approaching the R5-R6 growth stage, lessening risk of SBA impacts. Reports this week indicate many individual fields have low SBA populations (0-25 SBA / plant). Some observers report presence of winged aphids and white dwarf morphs.

Field observations from Cayuga, Columbia, Onondaga, Ontario, Wyoming counties report SBA populations below the 250 SBA / plant threshold. Fields continue to be at potential risk for aphid injury through the R4-R5 growth stages. Growers are advised to continue monitoring fields for SBA's, crop condition and growth stage and diseases. If fields reach the 250 SBA / plant threshold, resample fields within a week to re-evaluate the population level before taking action.

Thresholds are not currently available for SBA populations in R5 soybeans (beginning seed). Midwestern data however suggests actively increasing SBA populations exceeding 250 aphids/plant need monitoring and treatment at grower discretion. Midwestern research has not documented a yield protection benefit for spraying R6 growth stage soybeans for soybean aphids.
Thanks to: B. Alrich/S. Woodard, J. Dennis, B. Tillapaugh and K. Wise for sharing their soybean aphid observations this week.

Clipboard Checklist

Keith Waldron
NYS IPM

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General:
* Maintain crop records by field, including crop condition, inputs, observations, issues, concerns, etc.
* Prepare bunkers, silos for incoming silage.
* Mow around storage bins, barn and farm facilities
Alfalfa & Hay:
* Monitor fields for weeds and diseases record information on type and location, note stand condition for future cropping / rotation decisions.
Small Grains:
* Check grain storage bins for temp, moisture, air flow, drying conditions.
* Prepare for planting winter wheat after Hessian Fly-free date.
Field Corn:
* Harvest corn silage at 65 to 68% moisture and high moisture shelled at 25 to 30% grain, and high moisture ground-ear at 30 to 35% moisture.
* Record corn silage yields by field and quality by storage area, take samples for forage analysis
* Take Soil Samples for fertility analysis
* Take Fall Weed Survey following harvest. 
Soybeans:
* Monitor for crop condition and growth stage, white mold, soybean aphids, natural enemies, foliar diseases, sudden death syndrome (Fusarium solani f. sp. glyines), brown stem rot (Phialophora gregata f.sp. sojae), soybean rust
Livestock:
* Continue barn area sanitation to minimize house fly and stable fly populations in and around barns
* Monitor young stock for cattle lice and mange mites
* Check condition of pastures and animals on pastures
* Evaluate need for face fly, horn fly, and stable fly control for animals on pasture. Adjust paddock rotation as needed.
Equipment:
* Provide annual maintenance to manure, fertilizer, and pesticide application equipment
* Prepare combines for corn, soybeans
* Sharpen chopper knives. Check shear clearances, protective shields
* Note any repairs to harvesting equipment as they are cleaned and lubricated.

Contact Information

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Julie Dennis: IPM Area Educator, Livestock and Field Crops, Western NY
Phone/Fax: (315) 252-5440
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