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Weekly Field Crops Pest Report 2007

July 12, 2007                Volume 6 Number 12

1. View from the Field

2. Aphid Mummies in Alfalfa

3. Why use Potato Leafhopper Resistant Alfalfa?

4. Dairy Barn Flies?

5. Soybean Defoliators: Do They Do Damage?

6. Corn Silks and Beetles

7. NYS Soybean Rust and Soybean Aphid Update

8. Clipboard Checklist

9. Contact Information

View from the Field

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Eastern NYS
Ken Wise

Aphids in the sentinel plot field in Columbia County have increased dramatically. Tuesday July 3 the average number of aphids was 260/plant and a week later on July 10 the average number of aphids/plant was 606. The aphids could be found anywhere on the plant with concentrations on new growth. There were a few 7-spotted lady beetles and some Asian multi-colored lady beetles. There were also some aphid mummies from parasitoid activity. It does not seem that predators are keeping up with aphid populations since the population is rising quickly. Many of the plants are starting to show yellowing of the leaflets.

I am starting to see a fair number of Japanese beetles feeding on leaflets of soybeans. The good thing is that soybeans can take A LOT of beetle damage before they cause yield loss.

Japanese Beetle on a Soybean Leaflet

For more information on Japanese beetles in soybeans read the article below.

Aphid Mummies in Alfalfa

Keith Waldron

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Walking fields is critical to early detection of crop problems. It's also a way to discover all sorts of interesting examples of ecology in action.  One such example, common in alfalfa this time of year, is the presence of what might appear to be bronzed colored aphids "resting" on alfalfa leaves.  "Resting aphids?" What are you really seeing? One type of biological control of pea aphids

Pea aphids [Acyrthosiphon pisum (Hemiptera: Aphididae)] tend to be found in low to modest numbers in NY alfalfa but are generally not an economic pest . These insects are a food source by many natural enemies such as lace wing and lady bird beetle larvae. The bronze colored "resting" aphids one may see on alfalfa leaves are aphid "mummies" the result of the aphid being parasitized by a type of tiny wasp. In NY, two types of wasps can be found: Praon pequodorum and Aphidius ervi both Hymenopterans in the family Braconidae.
Praon pequodorum is a native aphid parasitoid which includes the pea aphid in its host range. Aphidius ervi was introduced to the United States in the late 1950's and early 1960's for biological control of pea aphid. This species is now widely distributed in North American alfalfa, often achieving high levels of parasitism. A. ervi is the more common parasitoid we encounter attacking pea aphids in NY.

Who's who? Aphidius mummies are smooth. Praon mummies look like they have webbing around them, with the bronze colored aphid body sitting on top. See photo.

How did that happen?
When the female wasp finds a suitable host, she bends her abdomen under her legs and injects an egg in the aphid with her ovipositor. Aphids may continue feeding and reproducing for several days, until the egg hatches. When the egg hatches, the wasp larvae starts to eat the aphid from the inside and the larva completes its life cycle in the aphid body. Effective parasitization is obvious when the aphid swells and hardens into a leathery, brown colored "mummy". The parasite completes it's life cycle by emerging as an adult through a round hole at the rear of the mummy. Mummies can usually be seen 14 - 21 days after the first introduction is made. Development time is dependent upon the temperature and other environmental factors. One female wasp lays about 350 eggs in a lifetime. Most of these eggs are laid in the first five days after introduction.

The life cycle of Apidius ervi described above is excerpted from "Biological Control of Aphids with Aphidius ervi" by Cathy Thomas (PA Dept Ag IPM Program). The Vegetable and Small Fruit Gazette, April 2001, Volume 5, No. 4.

Note: Species of Aphidius and Praon have also been found to attack soybean aphids in NY - watch for mummies....

Why use Potato Leafhopper Resistant Alfalfa?

Ken Wise

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Have you had problems with potato leafhoppers (PLH) in your alfalfa? You know that large infestations of PLH in alfalfa can reduce the plant protein by 5% and yield by a half ton per acre per cutting. If you see V-shaped yellowing on the tips of the leaves you have a good chance potato leafhopper has been in your alfalfa. If V-shaped yellowing has appeared you have already lost protein and yield, plus the alfalfa will have slower re-growth after harvest and increased chance of winter kill. A good option for reducing losses to this insect pest is to plant PLH resistant alfalfa. Research has shown that potato leafhopper resistant alfalfa is consistently higher in quality than susceptible cultivars with or without potato leafhopper pressure. The benefits of PLH resistance are particularly obvious in years with high PLH infestations, a situation that can be expected at least once or more during the life of the typical alfalfa stand. Some of the most recent releases of PLH resistant alfalfa are as high as 85 percent resistant. (Note: a “ highly resistant” cultivar is 50% or more of the plants are resistant.) The newer potato leafhopper resistant varieties have comparable yields as susceptible alfalfa. You will still need to monitor this alfalfa because resistant does not mean that it is immune to the pest. In the first 3 to 4 weeks the young plants have not developed their resistance to PLH. The resistance is the granular hairs that grow in the surface of the leaflets. In the young plants these hairs do not become fully functional until about a month of growth. For management information check our on-line IPM guides: IPM for Potato Leafhopper in Alfalfa.

Dairy Barn Flies?

Keith Waldron

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Warmer temperatures and recent rains provide two ingredients that can lead to a rapid increase in house and stable fly populations - heat and moisture. Add undisturbed organic matter such as spilled feed / silage, straw or soiled bedding and conditions are quite favorable for a booming increase in house and stable fly populations.

Now would be a good time to walk barns with an eye for evaluating fly populations and the effectiveness of sanitation efforts.

Recall that each female house fly can lay between 100 and 150 eggs in each of the 4 - 6 batches of eggs produced over her 3+ week lifetime. At a constant temperature of 86 F, house fly eggs can hatch in 10 hours, go through their maggot stages in 5-6 days, pupate and emerge as adults in another 4-5 days. Total time egg to adult as few as 9 - 11 days.

Potential for population growth? One study showed that 25,000 to 40,000 stable and house flies could develop from bedding of a single calf hutch during the summer. Under favorable environmental conditions it is easy to see how fly populations can explode in a very short amount of time.

Shutting down fly production relies heavily on cultural practices that eliminate conditions favorable to fly breeding. Since house flies and stable flies both breed in moist undisturbed organic matter such as spilled feed, moist hay, wet grain, and manure-soiled bedding eliminating these conditions on a regular schedule reduces fly population growth by minimizing conditions favorable to successful fly breeding. Cornell's Veterinary Entomology program reminds us that sometimes innocuous routines such as dragging the hose between water buckets in a calf greenhouse can create great fly breeding spots.  Especially in the calf greenhouses and coveralls, try to keep the area in front of pens clean and dry.  Sweep up spilled grain regularly.

Likely Fly Breeding Locations are calf rearing areas, near water sources and feed troughs / bunks, adult animal resting areas, maternity and hospital pens, manure traps / conveyor systems. Outside areas adjacent to barns prone to fly breeding include the water and feed troughs in the animal loafing yard, base of stored big bales, and edges of bunk or standing silos. Hard to clean corners and other areas where organic matter can accumulate.

Evaluating Fly Populations: spot cards and direct observation. Spot cards provide an objective means to monitor relative fly activity over time. White index cards (3X5 inches) serve as a clean surface to collect fly "specks" left by resting flies. Cards can be mounted on posts, beams, walls, etc. Select areas 10 areas throughout the barn where flies are seen resting. Do not put cards in windy areas or within reach of curious "critters" and children. Draw a map to indicate card location and save as part of your fly management record.  Date and number the cards and change them weekly. After 1 week remove the cards and replace them with a fresh set. Count the number of spots found on each index card. One hundred (100) spots per card can be used as a guide to indicate a fly problem. Spot cards provide an objective means to monitor relative fly activity over time. Each farm can adjust this number to their individual tolerance threshold.

Check areas surrounding spot cards with high counts for fly breeding. Stable fly (the biting flies) monitoring involves direct observation to check the legs and bellies of 10 animals and count number of resting flies. Check calf legs for patches of thin hair which can indicate a reaction to stable fly feeding. Ten stable flies per animal are considered a high number. Keep records of spot card and stable fly counts for reference.

More information can be found in the Cornell IPM Factsheet: Integrated Management of Flies in and around Dairy and Livestock Barns at Veterinary Entomology Publications.

Soybean Defoliators: Do They Do Damage?

Ken Wise

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Japanese beetle and Mexican bean beetle are the main defoliators of soybeans in NYS. While they are minor pests, defoliation of soybeans sends up many red flags by growers. The question normally is how much leaf defoliation is too much in soybeans? The good thing is that soybeans can withstand much defoliation without losing yield. The soybean defoliation threshold is 35 percent of leaf area eaten or missing from V1 to just before bloom. During blooming through pod-filling stages, the threshold is 20 percent defoliation. The following pictures are a guide that depict 10, 20, 30 and 40 percent defoliation:

10 percent defoliation             20 percent defoliation

30 percent defoliation             40 percent defoliation

(Source: Purdue University Field Crops Pest Management Manual, 1/92)

Corn Silks and Beetles

Ken Wise

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Every year I see two kinds of beetles feeding on the silks of corn. These are corn rootworm beetles and Japanese beetles.  I have been asked many times “Does this feeding by beetles reduce pollination of corn?” Generally, these beetles do not affect pollination of corn. Corn rootworm beetles prefer to eat pollen. The corn plant can produce enough pollen to pollinate the ear of corn and still have plenty left over for the corn rootworm beetles. Sometimes when populations of corn rootworm beetles are high enough they will feed on silks. The good thing is that even a damaged silk can still receive pollen and will fertilize the ear. Reduced fertilization can only occur when the silk is clipped to less than a ˝ inch long before pollination. Japanese beetles also like to feed on the silks of corn. I have seen up to 8 or 9 on one ear of corn. The thing with Japanese beetles is that they prefer to feed on browning silks. When the silk has turned brown the ear of corn has already been pollinated. Japanese beetles also clump in certain areas of the field. Many times this is along edges and not the rest of the field.

Japanese Beetles on Feeding on Silks

NYS Soybean Rust and Soybean Aphid Update

Gary Bergstrom
Plant Pathology, Cornell University

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New York State Soybean Rust Information Center

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 V-5.

Soybean rust was confirmed on June 29th in a soybean sentinel plot in Assumption Parish, Louisiana. This makes six new positive rust finds in the month of June. Four of these are in Louisianna and two in Texas. With regular rainfall in Louisiana and surrounding states to the west and north, there is an increased chance of soybean rust being found north of Louisiana in the next few weeks. So far in 2007, soybean rust has been detected in 10 counties in Florida, five counties in each of Georgia and Alabama, five Parishes in Louisiana and three counties in Texas. (Updated July 9, 2007 )

Soybean aphid Update
Soybean aphid populations have been a mix this season. Indiana, Ohio, Illinois and South Dakota report low aphid populations. Michigan, Minnesota, Quebec and Ontario have reported fields above threshold and more widespread aphid infestations.
In NY, our SBR/SBA sentinel site network reports this week indicate soybean aphid populations are increasing. Soybean growth stages vary from V4-R1, across NY locations.

Soybean aphids this week in NY.
Central NY Cayuga/Seneca/Ontario counties have reported the highest SBA numbers so far this season, some cases well over 1,000 soybean aphids per plant for R1 stage plants. The sentinel site in eastern NY (Columbia county) has been over threshold each of last 2 weeks.

Western NY (Orleans County) - 1 field, V6 plants - < 25 SBA / plant
Central NY (Cayuga County) - 3 fields, R1 stage - 445 - 1000+ SBA / plant
North Central NY (Oneida County) - 8 fields, V6-R1 - 0 - 100 SBA / plant
Eastern NY (Columbia County) - V6 plants, 600 SBA / Plant
Soybean fields over threshold for SBA have typically had low populations of natural enemies. A number of over threshold fields have been at early bloom stage (R1). Unfortunately, some fields at V3-V6 have also gone over threshold. Growers are being advised to monitor fields closely and watch for increasing populations.

Recent rains will be helpful to mitigate the dry conditions found in central and western NY the past two weeks. Field corn showing drought stress symptoms in many areas. At least one location in western NY (Wyoming county) has reported spider mites in soybeans.

For more on the current national Soybean aphid perspective see:
More on soybean aphid biology and management.

Clipboard Checklist

Keith Waldron

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* Maintain crop records by field, including variety, planting date, pesticides used, nutrient inputs including manure, etc.
* Watch for weed escapes, any patches of herbicide resistant weeds?

* Check for armyworm, European corn borer, leaf blights, slugs, bird and deer damage
* Monitor tasselling fields for corn rootworm

Small Grains:
* Monitor winter grains for crop growth stage, insect and disease problems
         - evaluate crop for Fusarium head blight (Scab) and other grain head    diseases
* Check, clean, prepare storage bins to accept upcoming harvest?
* Mow around storage bins to remove rodent habitat, remove spilled grain
* Clean grain handling equipment (conveyors, wagons, trucks, combines, elevators, etc.) for signs of leftover grain - remove potential sources of stored grain insect infestations.

Alfalfa & Hay:
* Monitor alfalfa seedings for weeds, potato leafhopper and diseases.
* Check established alfalfa stands for potato leafhopper, weed and disease problems

* Monitor for soybean aphids, and other insects, including natural enemies such as lady bird beetles.
* Check droughty fields for presence of spider mites

Dairy Livestock Barn Fly Management:
* Check confined animals and barns for house and stable fly populations
* Sanitation, sanitation, sanitation - clean animal resting areas, feed troughs, minimize source of moist organic matter i.e. fly breeding areas in barn and in adjacent animal loafing yard
* Check waterers, drainage, roof gutters for leaks and potential overspill
* Begin fly monitoring: install "3X5" index card fly speck monitoring cards through out barn
* Order fly management materials: fly tapes, insecticide baits, natural enemies (parasitoids)

Dairy Livestock Pasture Fly Management:
 * Monitor animals for face, horn, and stable fly populations
* Check feed bunks and water sources for signs of stable fly breeding.
* Consider use of traps if horse and stable fly populations are a problem

* Note any repairs needed for recently used equipment: tractors, tillage implements, planters, etc. as they are cleaned and serviced.
* Service harvesting equipment, and tillage implements as needed.
* Calibrate manure spreaders - maintain records on amount spread per field
* Check, clean, adjust and service small grain harvesting equipment as needed.

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