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Eastern New York Field Crops Pest Report, 2004

This is a seasonal scouting report giving growers in the Eastern New York area information on the presence of agricultural pests. The report is written by Ken Wise, IPM Extension Area Educator for Livestock and Field Crops.

August 13, 2004

WHEAT

Winter Wheat, Aphids and Yellow Dwarf Virus

Barely yellow dwarf virus, now know as yellow dwarf virus (YDV) in wheat is a serous disease across the country. This disease is transmitted by several species of aphids that infest wheat. When aphids feed on the plants they infect the wheat with the virus. Winter wheat that is infected in the fall does not show symptoms. Symptoms start to appear mid-spring as yellowing of leaves. One management strategy is to plant wheat after the Hessian fly free date in your region. This can limit the number of aphids entering the fall seeded winter wheat fields. Another management option is to use wheat that is resistant to YDV.

SOYBEANS

Soybean Aphids are Dinner for Several Predators, Parasites and Fungi

Soybean aphids (SBA) have many predators. Of course we all know by now lady beetles enjoy having a feast on SBA. You might have not known that minute pirate bugs also like to have a main course of SBA. Green lacewing larvae are also effective predators of SBA (Pictures of Predators). The combination of the lady beetles, green lacewing larvae and minute pirate bugs have been reported to control up to 86 percent of SBA in a field (Reference). But of course there is more working against soybean aphids. There are also other insect predators that contribute to SBA reductions. Syrphid fly larvae are good predators of SBA as well as damsel bugs. There are also parasitoids that help control SBA. Parasitoids are little tiny wasps that lay their eggs inside the soybean aphids. Have you ever seen a parasitized aphid? They look like a tan colored mummy in the shape of the aphid (SBA Mummies). It does not stop with insects controlling SBA, there are also fungal pathogens. These fungal pathogens can be effective when populations SBA are high. The disease appears as a yellow to brown fuzzy looking aphid (Picture of Fungal Control of SBA). Under favorable conditions when the relative humidity is high the pathogen can move through a population killing SBAs very quickly.

Leaf Diseases as Compared to Soybean Rust

(Written By Julie Stavisky)

Soybean Rust is attacking soybean crops in the southern hemisphere. It has not yet been reported in the United States but experts warn that it may be only a matter of time. Your first line of defense should be the ability to identify this new pathogen from those that might be common to soybeans grown in New York State. The following are the differences in common foliar diseases of soybeans as compared to soybean rust:

Brown spot (Septoria leaf spot)

  • Symptoms appear first on lower leaves

  • Early signs are small irregular brown spots on upper and lower leaf surfaces

  • Later Symptoms are large brown-black necrotic blotches throughout the soybean canopy

Downy mildew

  • Early symptoms are yellowish spots on the upper surface of the youngest leaves

  • Spots turn to grayish brown with a yellow margin as infected leaves age

Powdery mildew

  • Powdery mildew has a distinctive powdery white appearance at all stages of infection, making it easy to distinguish from soybean rust

Soybean Rust

  • Early Symptoms: Small gray lesions on the underside of lower leaves; lesions increase in size and become tan or reddish brown.

  • Later Symptoms: Leaves of the whole plant turn yellow, and small brown or reddish raised pustules appear; the resulting necrosis causes leaves to drop.

If you think you might have soybean rust contract your County Extension Educator as soon as possible!

More information see: United Soybean Board, Soybean Rust Pest Alert, Soybean Diseases

FIELD CORN

Think Weeds in the Fall!
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

ALFALFA

Potato Leafhopper
I found only a few potato leafhoppers in alfalfa fields this last week at SUNY Cobleskill. For management information check our on-line IPM guides: IPM for Potato Leafhopper in Alfalfa

Thanks to: Keith Waldron and Julie Stavisky (NYS IPM) for contributing to this week's report.

Cheers
Ken Wise