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Eastern New York Field Crops Pest Report, 2003

For 5/9/03:

Alfalfa at the SUNY Cobleskill farm was 8 to 12 inches tall (May 7).

Alfalfa Weevil Eggs Present!
Jeff Miller (Oneida County) and Kevin Ganoe (Chenango, Otsego, Herkimer, Fulton & Montgomery Counties) are finding many adult alfalfa weevils present in fields (May 7-8). I found tons of adult weevils and eggs laid in alfalfa stems at the SUNY Cobleskill farm (May 7).

The predominate question after eggs have been laid in stems is, „When will larvae hatch?‰ The 1st instar larvae hatch from eggs at 280 degree-days (base temp. 48F). This is just a few days at our typical spring temperatures. Newly hatched larvae are about 1/16 inches long and yellow to light green in color. As larvae feed, grow and molt they become green with white stripes down their back, have a dark brown head. Larvae ultimately grow to reach 3/8 inches long before pupation about early June in New York. Recall that these larger larvae have big appetites and are responsible for 80% of the alfalfa lost to weevil feeding.

Do you know the number of growing degree-days in your region today?
(Base Temp. 50F)

Alfalfa Weevil Eggs

Alfalfa Weevil Larvae

Check out our on-line publication, IPM for Alfalfa Weevil. 1.2 Mb pdf file

Clover-root curculio, What is that?
While scouting a 2nd year alfalfa field I encountered droves of adult clover-root curculio. Some of you might ask, "What are clover-root curculio weevils?" Well, I am glad you asked; adult clover-root curculio weevils are 1/8 inch long and 1/16 inch wide with short, broad snouts. The adult weevil is brownish-black and covered with grayish hair and scales. Adult curculios chew the margins of leaves leaving C shaped notches. Clover-root curculio larvae feed on nodules, small rootlets, and chew out portions of the main root. As a result of larval feeding on roots alfalfa diseases can enter the plant.

Picture of an adult Clover-root curculio

Picture of the larvae of the Clover-root curculio

Ischnopterapion virens: I discovered many tiny blue weevils called Ischnopterapion virens in a clover field at SUNY Cobleskill (May 7). This weevil is native to Europe and is relatively new to the United States. Adults are metallic blue, about 3/16 inches long, with a distinctive snout and straight antennae. Adults make small circular holes in leaves of white clover. Larvae tunnel in the runners of clover and stems of red clover. The economic damage status of this weevil is not known.

Field Corn

Corn fields at the SUNY Cobleskill farm are in the process of being prepared for planting (May 7).

True Armyworm
Lisa Fields (Schoharie County) reports finding only one armyworm moth in two traps (May 7). At the SUNY Cobleskill farm no moths were captured in the pheromone traps (May 7).

Black Cutworm
Are grass weeds a problem in your corn? Could be just what a mother black cutworm moth is looking for. Grasses, winter annual broadleaves, and chickweed are favorite targets. If cutworm moths lay eggs in the field and the field is treated with an herbicide, hatching cutworm larvae bail off the dying weeds and look for greener food sources such as emerging corn seedlings. Cutworms can be an annual problem in some fields; particularly those with histories of poor weed control or have low wet areas in the field. Field margins, especially those next to ditch banks, grassy lanes, and hay fields are potential sites for infestation. Doing an early season plant population count is a good way to check corn fields for cutworm damage and other corn emergence problems.

Black Cutworm larvae vary in color from light gray to black with a pale brown to black head. Larvae have a greasy, shiny appearance with coarse granules present over their body. During the day larvae burrow into the soil next to the corn plant. These larvae curl into a „C‰ shape when disturbed. Symptoms of damage are leaf feeding, irregular holes in stem, notched and cut or missing plants. No-till fields and those with a lot of grass weeds are at particular risk to black cutworm. Monitor fields to find cutworm larvae when they are less than 1/2 inch long. If there are sufficient numbers and damage present, an insecticide could be justified. Treat only the affected area and a 20 to 40-foot border around the infestation. Rarely does a whole field need to be treated for cutworm. Larger cutworm larvae, greater than 1/2 inch long, are much more difficult to control. If the majority of cutworm larvae are 1/2 inch long or larger their damage is already done. These large larvae are also more tolerant of insecticides, reducing the effectiveness and economic viability of this option.

Check out our on-line publication, Black Cutworm in Field Corn Management Guide 912K pdf file

Have a good week!
Ken Wise