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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.

June 11, 2004

Alfalfa
Double Trouble: Alfalfa Weevil & Potato Leafhopper!

I was monitored re-growth on a few alfalfa fields and found small 2nd and 3rd instar alfalfa weevil larvae. Tip feeding by alfalfa weevil larvae was 20 to 35 percent. Remember, that the action threshold for alfalfa weevil on 2nd cutting is 50 percent tip feeding with small larvae present. While the fields were not at threshold there were many small alfalfa weevil larvae. On top of that was an infestation of potato leafhopper that was not present the week before. While they were not at an action threshold, potato leafhopper can increase in numbers quickly with warm weather. Having two stresses on alfalfa re-growth could have the potential to cause yield and forage quality losses. In fields like these you should monitor them closely. For management information check our on-line IPM guides: IPM for Potato Leafhopper in Alfalfa and IPM for Alfalfa Weevil.

Field Corn
Western Corn Rootworm Imposter!

Every year a few good observant scouts ask me, “Why have western corn rootworm adults appeared in June.” Recently, I spotted a few of these western corn rootworm imposters in my garden. Do you know who these imposters are? “Striped Cucumber Beetle.” Striped Cucumber Beetle and Western Corn Rootworm look similar but are two different species of insects.

Striped Cucumber Beetle, Acalymma vittatum
The Striped Cucumber Beetle adult is about 1/4 inch long and the upper body surface is about equal black and yellow, the folded wing covers forming three longitudinal black stripes. The adult beetle starts appearing on several vegetable crops starting in mid-June.

Western Corn Rootworm, Diabrotica virgifera virgifera
The female Western Corn Rootworm is 5/16 inches long with three black strips alternating with yellow. Male Western Corn Rootworm is mostly black with a small area on the poster end that is yellow-green. The adult beetle begins to appear in field corn in mid-July.

Female Western Corn Rootworm

Striped Cucumber Beetle

Insect Markings

Stripes are less distinctive and do not extend to the tip of the abdomen

Both sexes have stripes, are clearly defined, and extend to the tip of the abdomen.

Insect size

5/16 inches long

1/4 inch long

Host range

Primarily Corn
Secondary Cucurbits

Primarily Cucurbits
Secondary beans, corn, potatoes and other crops

Emerge

July

June

Life cycle

1. Over-winter as eggs in the soil in the field
2. Eggs hatch and larvae feed on the corn roots starting in late May
3. Adults emerge at time of corn pollination. Males emerge first
4. Adults lay eggs in cornfields mid to late pollination
5. Adults die, eggs overwinter

1. Over-winter as adults in woodland litter or in the soil.
2. Lay eggs at the base of the plant in mid-June through mid-July
3. Larvae develop for 2 to 4 weeks on the roots, pupate in the soil.
4. Adults appear in early to mid-August
5. Adults produced this season overwinter

Learn more about the differences between Western Corn Rootworm and Striped Cucumber Beetle:
Cucumber Beetles, Corn Rootworms, and Bacterial Wilt in Cucurbits

Ground Beetles Look for Prey in Corn Fields

This week, I have seen several ground beetles in corn fields. Ground beetles are very good predators of several insect pests in corn and other crops. Generally, we think of them as those big black beetles we find in the garden or under rocks. There are more that 20,000 of species of ground beetles in the world ranging in size from very small to large. The adult beetles can appear in a fascinating array of colors, textures and spots. Many studies have shown that smaller fields with grassy margins can promote ground beetle predation. Both the soil-dwelling larvae and above-ground adults feed on several different kinds of insect pests. Currently, some entomologists in the country are researching on how much predation occurs on corn rootworm by ground beetle larvae. For a few good pictures and general information on ground beetles you can view this web-site: Ground Beetles

Yellow Nutsedge in Fields

There were large infestations of Yellow Nutsedge in several cornfields at the SUNY Cobleskill farm this week. So is yellow nutsedge a grass? No, it is a sedge!
Grasses have narrow leaves with parallel veins, one cotyledon, stem is round or flattened and hollow, while a sedge has narrow leaves with parallel veins, one cotyledon, stems triangular, and are solid inside. If you look at nutsedge roots you can generally find little tubers called nutlets. A good rule of thumb is: Sedges have edges, and yellow nutsedge has a three-sided stem. For management information check our on-line IPM guides Weeds in Corn

Soybeans
Seed Rots and Seedling Blight

Many different organisms cause seed rot and seedling blights. Most of these organisms are soil-borne and a few are seed-borne. Most seed rots and seedling blights proliferate in poorly drained, cold (less than 58 degrees) and wet soils.

Seed Rot: Many times the infected seed will not germinate. If the seed does germinated the radicle will become infected and rot. The rot can be tan, brown, gray or black and the seed or radicle will appear wet and mushy. Some of the organisms that infect seed are Pythium, Fusarium, and Rhizoctonia.

Seedling blight: It is difficult to determine which pathogen causes seedling blight in any one field. Many times it can be a complex of Pythium, Rhizoctonia and Phytophtora. Pythium can cause the seedlings to have a wet, rotted appearance, while Phytophtora generally appears as a dry, dark rot on the roots. Sunken, reddish-brown lesions on the hypocotyls is most likely a Rhizoctonia infection. The Rhizoctonia lesions are small when they first appear. As these lesions grow they can girdle the stem, causing the soybean plant to die. If the Rhizoctonia infected seedlings do not kick the bucket the infection will weaken the stem and may cause the plant to lodge after the pods form.

More on soybean diseases next week!

Small Grains

Cereal Leaf Beetle has Been Spotted in Eastern NYS!

Jeff Miller in Oneida County discovered cereal leaf beetle in wheat fields this week. Please check the last two issues of the pest report for identification, monitoring and thresholds for cereal leaf beetle.

Thanks to: Jeff Miller (Oneida County), Keith Waldron (NYS IPM) and Julie Stavisky (NYS IPM) for contributing to this week's report.
 
Cheers
Ken Wise