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Weekly Field Crops Pest Report 2007

May 7, 2007                Volume 6 Number 4

1. View from the Field

2. Early Season Foliar Diseases of Alfalfa

3. Don't grub around with white grubs in field corn

4. Quantifying Row Crop Plant Populations

5. Black Cutworm in Field Corn

6. Blind Cultivation in Corn Part 2

7. Soybean Rust Status

8. Understanding Alfalfa Weevil Stage of Development and Growing Degree Days

9. Clipboard Checklist

10. Contact Information

View from the Field

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Eastern NYS
Ken Wise, NYS IPM

This week at the Cornell Research Farm at Valatie I spotted my first alfalfa weevil larvae. As the number of growing degree days increase you can expect to see more larvae in alfalfa fields that are in production for 2 years or older. See next week’s report on “How to Sample for Alfalfa Weevil."

Black cutworm moths have been monitored in abundance in Indiana by Christian Krupke, John Obermeyer, and Larry Bledsoe at Purdue University. Black cutworm moths ride storms from the south to the north. By knowing what is happening in other states we can start to watch for this potential pest early. Using traps and counting moths does not mean you will have a problem but it can be an indication of potential.  For more information on black cutworm please view the article below.

This was the first week I was able to get down to the Cornell Alfalfa Research plots at SUNY Cobleskill. The alfalfa looked very good. I could not find any signs of early season foliar diseases. I did find some adult Clover-root curculio weevils. Clover-root curculios can often be found cruising alfalfa this time of year. Unfortunately, there is not much we can currently do to manage this insect with the exception of rotating to a different crop. This pest builds in population in a field over time. These small weevils are 1/8 inch long and 1/16 inch wide with short, broad snouts. The adult weevil is brownish-black and covered with grayish hair and scales. Adult curculios chew the margins of leaves leaving C shaped notches. Clover-root curculio larvae feed below-ground on nodules, small rootlets, and chew out portions of the main root. As a result of larval feeding on roots, diseases such as fusarium crown and root rot can enter the plant. Clover-root curculio will feed on several types of clover and alfalfa.

Statewide and Finger Lakes NY
Keith Waldron, NYS IPM

Alfalfa weevil adults, eggs and 1st instar larvae were relatively easy to find in Geneva area alfalfa. Alfalfa weevil eggs were found inside tender stems of purple deadnettle and alfalfa. Look for small pin holes in stems about 2-4 inches above the soil surface. If you find a hole carefully slice through the stem to check for presence of eggs laid inside.

purple deadnettle

Picture of purple deadnettle
Picture of deadnettle with alfalfa weevil eggs inside at the site of the small holes.

Integrated Pest Management for Confined Dairy Animal Fly Pests an archive of the program originally broadcast May 3, 2007 as a web stream is now available for viewing on the NYS IPM Program website.

The two hour Dairy Fly Management Integrated Pest Management (IPM) program provides an overview on what one needs to know about managing house and stable fly populations in confined dairy facilities. The workshop presents IPM principles and practices to help producers avoid, minimize, or manage dairy house fly and stable fly populations. Topics include pest identification and biology, assessment techniques, management including discussions on cultural control, biological control using natural enemies, trapping, insecticides including insecticide resistance and suggestions for additional resources.

Early Season Foliar Diseases of Alfalfa

Ken Wise,

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Spring Black Stem: is favored by cool and moist weather in early spring. Symptoms appear as irregularly shaped brown to black spots that can merge to form a larger blotch. This disease can infect the petiole, form elongated blackened areas on the stems, and may be a contributor to a crown rot.

Spring Black Stem on alfalfa

Common Leaf Spot: proliferates when the weather is cool and wet. This disease first develops on the lower leaves near the soil surface and then progresses upward through the canopy. Common leaf spot appears as small, circular, dark brown to black spots, about 1/16 inch in diameter. When observed through a hand lens, tiny raised, light brown disk-shaped fungal fruiting bodies are visible in the center of mature lesions. See photo at: Common Leaf Spot

Leptosphaerulina Leaf Spot (aka “Lepto”): is also favored by cool and moist weather in early spring and late summer to early fall. The lesions usually start as small black spots and enlarge to oval or round “eyespots” 1/16 to 1/8 inch across. As lesions develop they become light brown or tan with dark brown borders; often surrounded by a chlorotic (yellow) area. This disease primarily attacks young leaflets but may also attack petioles and other plant parts. See photo at: Leptosphaerulina Leaf Spot

Downy Mildew: causes leaves to become blotched or chlorotic (light green or yellow). Many times young leaflets can become distorted. Often a dark purplish-gray fungal mat covers the underside of the leaves. This disease is common early in the spring. See photo: Downy Mildew

While alfalfa leaf spots may be easily found in most stands the real impacts for this harvest would be if 30% or more of the leaves on plants were shed as the result of infection.

For more information view our on-line management guide.

Don't grub around with white grubs in field corn

Julie Dennis,

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In your pre-season IPM check list for corn planting, is white grub a consideration? White grub injury might be a threat in fields that were previously in sod or planted to a cover crop last fall.

White grubs are the larval forms several scarab beetles, including Japanese beetles, May or June beetles, and European chafers.  White grubs spend their life in the soil, feeding on roots.  They are thick, white, soft-bodied insects from ¼ - 1 inch long.  They are typically observed in a C-shape when they are disturbed.

Sampling for grubs prior to corn planting involves digging up the soil in the suspected areas, and sifting through for grubs.  Several square-foot areas can be dug up, or better yet, a wider sampling of the field is possible using a golf cup cutter or similar sampling device.  One of the challenges of making a grub-management decision is that the various species present have different life cycles.  While Japanese beetle grubs live in the soil for a 1-year life cycle, May and June beetles may survive for several years in the soil.  Japanese beetle grubs are unlikely to feed after early June, but the others may continue their feeding throughout the season. For brave souls who love to identify insects, Ohio State University has an excellent guide to help with identification of grub species.

Management guidelines from Purdue entomologists suggest that if there are 2 or more live white grubs per cubic foot of soil, a soil applied insecticide labeled for white grub control may be warranted.  Check out the Cornell Guide for Integrated Field Crop Management for products labeled in NYS.

Quantifying Row Crop Plant Populations

Keith Waldron,

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Proper pH? – Check. N-P-K matched to soil test recommendation? – Check. Nice seedbed preparation? – Check. Timely planting? – Check. Plant Population? – Check?

How many corn seeds did you plant and what did you get?

It’s important to evaluate stands early to determine if the optimal plant population has been achieved. A good stand or a replant situation? One EZ method for determining plant populations is to count the number of plants per 1 / 1,000th of an acre. Determine the length of row you’ll need to count plants in by referring to the row width table below. Then determine the average of three sets of emerged plant counts found at several locations throughout the field to get the average number of plants per acre. Finally, determine the average number of plants found in the length of row sampled and multiply by 1,000 to get the average plant population.

Locate wheel tracks and make observations for each row planted. Check at least three areas within the field for consistency and to determine if all planter boxes were operating well.

Row Width (in) Length of Row per 1/1,000 of an acre






















A 10% reduction in number of plants observed vs number of seeds dropped is not uncommon. Large deviations from what was expected can signal a variety of potential problems. If your plant population counts are not up to snuff, sometimes waiting a few days and re-doing the estimate can make a difference if there is uneven germination from cool temps or variations in seeding depth. Other potential problems can be related to poor seed germination, planter calibration, performance and planting associated problems, poor soil conditions, seed rots or seedling diseases, seed corn maggot, wireworm, white grubs, birds, mice, and other factors.

Black Cutworm in Field Corn

Ken Wise,

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There have been signs of migrating cutworm moths to the south and southwest of NYS.  Since they ride storms that bring the adult moths from the south to the Northeast we should watch our corn for signs of feeding. Weedy grasses, winter annual broadleaves, and chickweed are favorite targets. If cutworm moths lay eggs in the field and the field is treated with an herbicide, hatching cutworm larvae bail off the dying weeds and look for greener food sources such as emerging corn seedlings. Cutworms can be an annual problem in some fields; particularly those with a history of poor weed control or have low wet areas in the field. Field margins, especially those next to ditch banks, grassy lanes, and hay fields are potential sites for infestation. Doing an early season plant population count is a good way to check corn fields for cutworm damage and other corn emergence problems.

Black Cutworm larvae vary in color from light gray to black with a pale brown to black head. Larvae have a greasy, shiny appearance with coarse granules present over their body. During the day larvae burrow into the soil next to the corn plant. These larvae curl into a C shape when disturbed. Symptoms of damage are leaf feeding, irregular holes in stems, notched and cut or missing plants. No-till fields and those with a lot of grass weeds are at particular risk to black cutworm. Monitor fields to find cutworm larvae when they are less than 1/2 inch long. If there are sufficient numbers and damage 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 cutworm. Larger cutworm larvae, greater than 1/2 inch long, are much more difficult to control. If the majority of cutworm larvae are 1/2 inch long or larger their damage is already done. These large larvae are also more tolerant of insecticides, reducing the effectiveness and economic viability of this option. Check out our on-line publication, Black Cutworm in Field Corn Management Guide.

Blind Cultivation in Corn Part 2

Ken Wise,

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Last week, I defined blind cultivation and talked about circumstances where it can be useful.  This week, I will discuss several tools or implements that are commonly used for blind cultivation.

The rotary hoe is a common mechanical weed control tool used in a blind cultivation system. This is a high speed tool to pluck tiny weeds from the soil. Spider wheels with curved teeth rotate around a strait staff. Alternate wheels are offset for maximum soil contact. A rotary hoe can be used for weed control pre-emergent or post-emergent. The fingers on the hoe are very aggressive and can damage the emerged corn if not preformed correctly. This weeder is very effective at up-rooting and killing weeds. The hoe can penetrate the soil 1 to 2 inches deep without damaging the crop. Increase your seeding rate by 2 percent/weeding pass to compensate for possible damage. In addition to its role in weed management, a rotary hoe is very effective at breaking up and aerating crusted soil conditions. If a rotary hoe is going to be used on post-emergent corn only cultivate up to about 6 to 7 inches tall. Do not expect to kill green weeds because their root systems have become too deep.  Soil with stones can damage and get stuck between the rotary hoe fingers.

A flex-tine weeder is becoming a common cultivator for early season broadcast weed control. This tool has multiple round or angle iron framing members that hold round or flat spring steel teeth that run about ½ inch deep into the soil, vibrating and moving around obstructions. This tool can be used pre-emergence or post-emergence when annual weeds are in the white root stage. Do not let weeds green-up because the root system will become too deep for the tines to up-root them. A flex-tine weeder can be used on corn up to 7 inches tall without much crop damage. While the rotary hoe is best for breaking up soil crusting the flex-tine weeder also does a good job at this if the tines are at a 45 to 80 degree angle. One advantage with using a flex-tine weeder is that a stony field does little or no damage to the tines. One disadvantage is the aggressive action can damage emerged corn if you are not careful. As you increase the angle of the flex-tines the more aggressive the soil disturbance and possible damage to the corn crop.

The spike-tooth harrow has been used for blind cultivation and can be effective. The harrow has horizontal bars that hold square metal rods about 8 inches long, turned at a 45 degree angle so that so that the corner runs forward. Make sure that the weeds are in the white root stage. While this works best as a pre-emergence control, it can be used post-emergence up to 7 inch corn.  Weeds are most effectively controlled when the weather is sunny and warm. Stones can be a problem for a spike-tooth harrow. Rocks can damage the teeth and/or get caught between teeth and can rip out rows of corn if not watched carefully.

By using blind cultivation a producer can reduce or eliminate the use of herbicides on the farm. If blind cultivation is combined with row cultivation later in the growing season the use of herbicides may not be needed. By using blind cultivation early in the season and just a post-application of herbicides later in the season a producer can reduce the use of herbicides on the farm.

Soybean Rust Status

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National Soybean Rust Commentary (updated: 05/02/07 )

Soybean rust was detected in a kudzu patch just north of Tampa in Pasco County , Florida . Fortunately, very dry conditions and a forecast of continued dry weather for Florida should limit development and spread of the disease. Soybean rust can no longer be found in many of the previously-infected kudzu patches in Florida , Georgia or Alabama . Scouting efforts have intensified in the south as soybean sentinel plots continue to be planted and monitored. Kudzu patches are also being scouted from Texas to South Carolina . Soybean rust has been detected on kudzu in 10 counties in Florida and in five counties in each of Georgia and Alabama . The disease was also detected on soybeans in one county in Texas , but that field has since been cultivated and planted with corn. (Source: USDA Public PIPE website.)

Understanding Alfalfa Weevil Stage of Development and Growing Degree Days

Ken Wise,

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I did find just a few 1st instar alfalfa weevil larvae this week.

You may wonder why you might see alfalfa weevil larvae now even if we have not reached the 280 growing degree days for eggs to hatch. The first thing is that each field has it own micro-climate. One field may be warmer than others. For example a south facing slope will accumulate growing degree days more quickly than other fields. The second thing is that the model below is based on when 50% of alfalfa weevil are in a specific stage of development.

Growing degree Days for peak (50%) Occurrence of Alfalfa Weevil growth stage:

Stage or Event

Accumulated growing degree days (48F base temperature)

Eggs hatch


Instar 1


Instar 2


Instar 3


Instar 4






Adult Emergence


CURRENT Accumulated Growing degree days (48F Base)
March 1 -May 7 , 2007


Base 48 F

Base 50 F







Clifton Park












*Missing Data

Clipboard Checklist

Keith Waldron,

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  • Emergency contact information (“911”, local hospital, Chem. Spill emergency contact, other?) posted in central posting area

  • Review EPA Worker Protection Standard training and posting compliance needs

  • Walk fields to check tile flow, check and clear drainage outlets.

  • Maintain crop records by field, including variety, planting date, pesticides used, nutrient inputs including manure, etc.

  • Watch for early season weeds


  • Finish corn planting by May 15, if soil conditions allow

  • Use corn insecticide seed treatment for seed corn maggot protection

  • Monitor for weeds, note presence of "who", "how many" and "where"

  • Adjust post emergence weed control actions

  • Determine corn plant populations, make notes on germination problems

Small Grains:

  • Monitor winter grains for crop stage, insect and disease problems

    assess crop for adequate stand and plant vigor

Alfalfa & Hay:

  • Monitor alfalfa seedings for weeds, insects & diseases.

  • Check established alfalfa stands for over wintering injury, frost heaving, alfalfa weevil, weed and disease problems.

  • Timothy stands: check fields for symptoms of cereal rust mite


  • Note any repairs needed for corn planter, seeding equipment, alfalfa harvesting equipment, and tillage implements as they are cleaned and lubricated.

  • Service corn planter as needed.

  • Calibrate manure spreaders - maintain records on amount spread per field

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

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