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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.
Alfalfa Weevil Larvae Found
I found 1st instar larvae at both SUNY Cobleskill (May 13) and at the Cornell Research Farm in Valatie (May 14). These larvae are a 1/16 of an inch long and appear in fields at the accumulation of 315 degree days (Base Temp. 48). You can find them hiding nestled in the tips of unfolded alfalfa leaf buds. Alfalfa weevil larvae leave a little SHOT HOLE in the leaflets that is called tip feeding. For pictures of alfalfa weevil larvae see: Alfalfa Weevil Larvae.
According to prediction models (May 17) alfalfa weevil development is quite different across Eastern NYS. In the northern portion of NYS it suggests that fields should be having 2nd instar larvae, while the lower Hudson Valley is experiencing 4th instar. Remember that the 4th instar larvae consume 80% of the total forage it will eat. That means that most damage to alfalfa occurs in the 4th and last instar before it pupates.
For more information check out our on-line publication, IPM for Alfalfa Weevil.
Important alfalfa diseases to know!
Anthracnose is a disease that occurs in warm and wet weather. Stems of infected plants wilt and stem tips bend over to form a Shepherds crook.Diamond-shaped lesions can appear on the lower parts of the stem about 1-3 inches above the soil line. Anthracnose may advance from infected stems into the crown tissue. The infected crowns appear bluish-black near the base of stems. Plants can appear straw colored and are scattered throughout the field. For pictures of anthracnose see: Anthracnose Picture
Verticillium wilt can be a serious disease limiting yield and stand life. An early symptom includes a characteristic V-shaped yellow foliar discoloration similar to potato leafhopper (PLH) injury. One way to tell the difference between PLH injury and verticillium wilt is by using a sweep-net. If you see the yellow V-shaped foliar discoloration and there are no PLHs in the net it is most likely verticillium wilt. As the disease progresses, leaflets wilt, turn yellow or pink, and often curl or twist. Stems of infected plants can remain green for long periods of time. Taproots appear healthy and sound, but in cross section appear to have a dark ring indicating damage to the water-conducting tissues, causing wilt symptoms. Verticillium wilt symptoms may be more obvious in the second cutting. For pictures of verticillium wilt see: Verticillium Wilt Picture
Sclerotinia crown and stem rot usually occurs during cool, moist weather in early spring and late summer. Infected stems become soft and water soaked, the infected plant appears yellow and weak. A characteristic white fluffy mass of mycelium (fungus body) grows over the plants or on the soil surface, infecting new plants as it grows. Seedlings are very vulnerable to this disease. As plants become weak and die, the fungus forms small (1/8 to a 1/4 inch), hard black sclerotia (pelletlike balls) on or in the stem or crown tissue. This disease is often associated with fall seedings, seedings into old pastures, or no-till seedings into previous legume sod. For pictures of sclerotinia crown and stem rot see: Sclerotinia on Alfalfa Picture
For more information on alfalfa wilts and crown rots see our online publication: Alfalfa Wilt and Rots Management Guide
Potato Leafhopper in Cherry Valley (Otsego County)
On May 19, during a field meeting in Cherry Valley we discovered potato leafhoppers in an alfalfa field. There was one potato leafhopper per 10 sweeps of the net. Do you know what potato leafhopper looks like? Remember adults are bright lime green, 1/8 inch long and can fly. Potato leafhopper nymphs are yellowish-green and look similar to the adult but do not have wings.
For management information on potato leafhopper check our on-line guide: Potato Leafhopper on Alfalfa Management Guide,
Early Season Corn Diseases!
Early season corn seed and seedling diseases can reduce plant populations, thus reducing yields. Some expected yield losses can range from about 5% to 10%. If your average silage harvest is 20 tons/acre, a 10% loss in yield would be 2 tons/acre. The following is how to identify early season seed and seedling diseases:
Seed decay is caused by a number of soil-inhabiting fungi such as Pythium, Fusarium, Diplodia, Rhizoctonia and Penicillium. The fungi can infect seed before it germinates causing mortality. Seeds infected with decay fungi are discolored and soft. Many times fungal material may grow on the seed. Often when the seed has rotted it may be completely decomposed and cannot be found.
Sometimes the seed may germinate and grow but will die as the plant emerges from the soil. Seeding blights are caused by many of the same fungi that cause seed decay. Seedling blight symptoms include discolored seedling coleoptiles and roots. Seedlings may have a wet, rotted appearance before they reach the soil surface. Above ground symptoms of blight may include seedlings that turn yellow, wilt and die.
For more information on early season disease management see: Field Corn Diseases.
Seed Corn Maggot
Remember to encourage field crop producers to use insecticide seed treatments for seed corn maggot. A little prevention will help ensure a good plant population. See the April 30th Pest Report for seed corn maggot biology or check out our on-line publication, Early Season Insect Pests in Field Corn