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NY Weekly Field Crop Pest Report, 2005

July 22, 2005 Volume 4 Number 14

1. View from the Field

2. Know Your Corn Rootworms

3. Pea Aphids in Alfalfa

4. Common Smut on our Corn or Plate?

5. Pollen Islands Will Attract CRW

6. Corn Rootworm Scouting Tip: Are they Gravid?

7. Soybean Rust Update

8. Clipboard Checklist

9. Growing Degree Days in NYS

10. Contact Information

View From the Field

Western NYS
Julie Stavisky

Eastern NYS
Ken Wise

Keith Waldron
NYS IPM

Alfalfa: In a field in Wyoming County, I found zero potato leafhopper (PLH) but I observed many pea aphids. See Keith’s notes and an article below regarding aphids in alfalfa. From Seneca County, Mike Dennis reports that very low numbers of PLH nymphs are present in a 10-inch tall new seeding, and no PLH were found in an established alfalfa stand.

Corn: In Ontatio County, northern corn rootworms are emerging in droves from a field of continuous corn. Western corn rootworms were observed to be over threshold in a continuous corn field in Seneca County, though in other fields in Seneca County, numbers are low.

Soybeans: Aphids were seen in all fields I observed this week (Wayne County, Seneca County, Ontario County, and Cayuga County). About half of the fields I visited continue to have relatively low numbers (well below the threshold of 250 aphids per plant), while other fields have plants with over 1,000 aphids. In two heavily infested fields I scouted, plants are sticky and sooty mold is present, and some leaves are cupped. Given that lady beetle larvae and adults are abundant (and doing a great job of cleaning up aphids) and that the damage is already done, growers have made the decision to not use an insecticide. (For treatment with insecticide to be advisable, aphid numbers must be 250 per plant and increasing). Nancy Glazier (NWNY Team) reports that soybean aphid numbers continue to grow in the northern part of Orleans County, especially in areas where rainfall is lacking. Spider mites are a threat in soybean fields that have not had adequate rainfall (Orleans, Cayuga, and Ontario Counties).

This week at the SUNY Cobleskill Farm potato leafhoppers (PLH) on alfalfa were hard to find. There were many pea aphids which generally is not a problem on alfalfa in NYS. Alfalfa fields at the Cornell University Farm in Valatie were farm over threshold and showing PLH damaged leaves.

A few fields at the SUNY Cobleskill Farm were over threshold for corn rootworm. All of the beetles I observed were western corn rootworm. Generally, you see western corn rootworm before you see northern corn rootworm.

Japanese beetles were feeding on the silks of field corn at the Cornell University Farm in Valatie. There was silk clipping going on and as many as 5 to 6 beetles could be on a silk. Over all it appeared that about 1 in 10 ears of corn had Japanese beetles feeding on the silks. Here are a few photos of what I was seeing:

Japanese Beetles Clipping Silks

File written by Adobe Photoshop® 4.0

Soybean aphids still remain relatively low at the Cornell University Farm in Valatie. There was about an average of 50 aphids per plant. The soybeans were in the R-1 to R-2 stage of growth.

PLH resistant alfalfa comparison trial in Ithaca showing visible differences in color and plant height. Oneida VR planted as one of the PLH susceptible varieties ­ showing classic “V-pattern” leaf symptoms. Some pea aphid presence and many natural enemies abundant. Easily found adult and young growth stages of lady bird beetles (lady bugs), syrphid flies, lacewings, nabids, and spiders.

Pea aphid damage? Pea aphids are the common alfalfa aphid species found in NY. These aphids can be found in light green and rosy/peach color morphs. Aphids typically suck juices from the plants they feed on. Unlike some aphid species, pea aphids do not secrete toxins while feeding. Their primary damage is related to the amount of fluid removed from the plant. For this reason large numbers (several hundred per plant) are typically needed before plants are affected. In NY, pea aphid populations are largely controlled by natural enemies. Also given our usually adequate rainfall, pea aphids are typically not an economic problem for us. I.e. the plants are able to compensate for the moisture removed by the aphids. More pea aphid info and things to look for follow in an article by Julie Stavisky.

Know your corn rootworms

Julie Stavisky, NYS IPM

Rootworm adults are emerging in droves from corn fields. They are most often 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 º 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 photos). 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 without suffering economic losses.

WCRW Female WCRW Male

NCRW

Pea Aphids in Alfalfa

Julie Stavisky, NYS IPM

Is there any such thing as too many?

This week when I was sweeping alfalfa in Wyoming County to check for potato leafhopper, I should have had a measuring cup with me! Every time I took 10 sweeps, I estimate that the sweep net contained approximately a cup and a half of aphids. To continue my PLH searching, I resorted to taking a single sweep at a time. Can this many aphids be tolerated? Well, aphid numbers might not be our best indicator. Instead, answering several questions from observations that accompany a pea aphid infestation will be more useful. To have a significant economic impact, some of the following conditions would have to exist:

Are the plants drought stressed?

Are stunted plants observed?

Are heavy honeydew and/or sooty mold present?

Are leaves becoming curled, cupped or otherwise misshapen?

Are natural enemies absent?

If in doubt, cutting within the next week will help prevent a growing pea aphid outbreak from reaching economic proportions.

Here’s a photo of a plant showing a heavy (but non-economic) population of pea aphids:

Common smut on corn or on your plate?

Ken Wise

NYS IPM

I found a little bit of common smut on corn this week. Common smut forms white, soft galls that can be found on most any plant part on the corn plant above the ground. It is suggested that the galls form where hail or machinery have injured the plant. As the smut galls age they fill with dark brown to black spore masses. The good thing is that smut rarely kills the plant, and typically causes little if any yield loss. For pictures view this website: Common Smut

Corn smut is also edible at the right stage of growth. It is called the maize mushroom (Cuitlacoche) or the Mexican truffle. Many people in Mexico eat the immature smut galls as a delicacy known as Cuitlacoche. Some sweet corn growers produce smut galls as a high value crop and sell them to Mexican restaurants. If you like mushrooms you should like common smut. Check out this website if you think you would like to try maize mushrooms: Common Smut Recipes

Pollen Islands will Attract CRW

Keith Waldron,

NYS IPM

Remember those corn fields that had troubles with uneven emergence, ponding, compaction, fertilizer, herbicide, or other planting time issues? Drive by many of these fields this week and their up and down plant height patterns look more like a side view of a crazy roller coaster ride than the ideal production field… And now watch the pattern of tassel emergence. Whatever the reason for the uneven stand its effect on corn rootworm (CRW) populations can be very predictable. CRW beetles are pollen feeders and will zero in on plants producing pollen. So in fields with large differences in corn maturity expect that CRW beetles will “head to the islands” of pollinating corn. In fields of uniform crop growth stage, CRW egg laying is reasonably well distributed. (Recall that CRW females are capable of producing eggs about 3 weeks after they emerge…) In the case of the pollen island fields, CRW egg laying may be expected to be more concentrated in the areas where the pollen (food source) is. You can also expect that the highly mobile CRW beetles will follow the pollen sources from clump to pollinating clump…. Watch these areas closely for signs of potential silk clipping as hungry CRW populations build up in them ­ high numbers of CRW beetles could interfere with pollination and grain fill.

Since these areas can be at higher risk for egg laying ­ make a note of their location(s). Record any scouting information. Should egg laying be high enough in those “islands”, it is a good bet that they would be at higher risk for lodging from CRW larval feeding next year should corn be replanted into the same field. Better yet? If cropping schedules allow, this field may be a good candidate for rotation next year.

NOTE: The sequential sampling method for sampling CRW assumes the field is uniform in physiological development. This sampling procedure is dependent on an even distribution of corn rootworm beetles across the field. Fields with uneven development from uneven germination or water stress should not be sampled using this sequential sampling procedure since the beetles will be clumped on pollinating plants.

If sampling for CRW in fields with “uneven growth development” follow the method recommended in the Cornell Field Crops Guide. CRW counts are taken from 55 corn plants sampled at random. The threshold is 55 CRW beetles. When determining fields at risk recall that the Western corn rootworm beetles count as one and northern CRW beetles count as 0.5. For more information see: http://www.fieldcrops.org/ field corn insect (CRW) management (3.6.2.2).

Corn Rootworm Scouting Tip (Are They Gravid?)

Ken Wise, NYS IPM

Remember, when taking beetle counts you are monitoring to assess the potential that CRW's will lay enough eggs in the field to cause damage to next year's corn crop. Taking beetle counts is important but make sure you stop to check a portion of the female western CRW's for the actual presence of eggs. Squeeze the abdomens of the yellow and black striped CRWs and look for the small yellow - white eggs. It takes CRW about three weeks from the time the adult beetles emerge from the soil and mate until the time the females are gravid. In this time period you may find high CRW numbers in a field but since the females are not yet capable of laying eggs they are not causing an economic problem. This is the reasoning behind sampling the same field 2-3 times before making the management decision. Being pollen feeders and highly mobile, CRW's may relocate to another pollinating field during the 3 week period. Comparing the two types of fields, the second field is at greater risk from subsequent CRW damage since females (and their eggs) will have matured and are ready for deposit.

When is the best time to control corn rootworm if a field exceeds the action threshold?

  • The following year!

If there is a field over the action threshold what are the options for control next season?

  • The best option to control corn rootworm is crop rotation. Corn after corn is prime habitat for corn rootworm and will increase infestations from year to year.

  • Crop rotation is not always possible so ....... The second management option is the use of a soil-applied insecticide at planting. To select an insecticide registered for corn rootworm, please consult the Cornell Guide for Integrated Field Crop Management.

  • Additional CRW management technologies are now available. You can use insecticide treated seed to control moderate populations of corn rootworm infestations

  • You can also use Bt hybrids now for CRW.

How to Monitor for Corn Rootworm

Soybean Rust Update

Keith Waldron, NYS IPM

Septoria brown spot and bacterial blight have been observed in NY, but fortunately still no reports of SBR.

From the NYS soybean rust website: 2005 Soybean Rust Status

Soybean rust on soybeans has been reported in Florida , some adjacent counties in Alabama and Georgia as well as Mississippi. The most recent finds in Mississippi and Georgia were in sentinel plots. The most recent find in Alabama was the first detection in a commercial field. Scouting and spore trapping continues throughout the soybean production areas of the U.S. Scouting of sentinel plots in New York State continues this week and to date no soybean rust has been found. The risk of soybean rust infection in New York is currently considered to be low and no fungicide application for soybean rust is advocated at this time. Septoria brown spot is the most prevalent foliar disease in all 10 of the research protocol sentinel plots in New York State over the past two weeks. Bacterial blight has also been observed and soybean aphid populations are increasing. Growth stages in New York State sentinel plots range from V5 to R2 stages. Scientists are intensively monitoring soybeans in the path of recent tropical storms and are following the paths of Hurricanes Dennis and Emily for their potential to move soybean rust spores to wider areas of the U.S. (Last updated 7/19/05). For more see: http://www.ppath.cornell.edu/soybeanrustny/default.htm

Clipboard Checklist

Keith Waldron

General:

• Maintain crop production activity records by field, including harvest date, pesticides used, nutrient inputs including manure, etc.

Alfalfa & Hay:

• Continue monitoring for potato leafhopper- harvest early or spray on basis of need.

• Monitor for diseases record information on type and location for future cropping decisions.

Small Grains:

• Watch wheat grain moisture. Combining underway when moisture at 18 percent.

Corn:

• Monitor for foliar and stalk diseases, nitrogen and other nutrient deficiencies, European corn borer, weeds.

• Monitor corn rootworm adults at silking.

Soybeans:

• Monitor for soybean aphid, soybean rust, foliar diseases.

Livestock:

• Continue livestock facility sanitation management (manure, feed bunks and storage areas, waterers, etc.). Cleaner, less fly production

• Mow around facilities to minimize rodent habitat.

• 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.

Growing Degree Days in NYS

Keith Waldron,

NYS IPM

March 1 - July 20, 2005

Location

Base 50 F

Batavia

1321.4

Chazy

1106.05

Clifton Park

1571.2

Geneva

1335.355

Ithaca

1215.2

Prattsburg

1161.9

Source: http://newa.nysaes.cornell.edu/

Contact Information

Julie Stavisky: 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