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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.

May 26, 2004

Alfalfa Weevil Tip Feeding is Increasing!

This week I have seen an increase in the tip feeding by alfalfa weevil larvae. This is a good time to check your fields for alfalfa weevil damage. Alfalfa weevil larvae leave a small hole (aka SHOT HOLE) in the leaflets that is called "tip feeding". The percent of stems showing feeding damage is how we determine need for alfalfa weevil treatment.

  • Pick 50 alfalfa stems at random throughout the field.

  • Look for the small "shot holes" in the leaves that indicate that larvae are feeding.

  • Record the percentage of alfalfa stems that show the "shot hole" feeding damage in the top 3 inches of the canopy.

Before the first cutting, if 40% of the stem tips show feeding damage, you are at the "action threshold". The good thing is that alfalfa weevil can generally be controlled by harvesting. If you reach an action threshold within a week of your normal 1st cutting date, early harvesting will help avoid economic, yield, and forage quality losses. Alfalfa weevils only have one generation per year and are typically not a problem after first harvest. Occasionally, weevil can damage alfalfa re-growth after harvest. This damage may be more evident in the windrow areas, and can be more noticeable under cool or droughty weather conditions. If you find that 50 percent of the new growth is damaged, with many small larvae present, a chemical control may be warranted. For more information check out our on-line publication, IPM for Alfalfa Weevil.

Are there good biological control agents for alfalfa weevil? SEE NEXT WEEK'S REPORT FOR THE ANSWER!

Potato Leafhopper
We have seen potato leafhopper in several areas of Eastern NYS in low numbers. As the summer progresses and the weather starts to warm the populations of potato leafhopper have the potential in increase rapidly.
For management information on potato leafhopper check our on-line guide: Potato Leafhopper on Alfalfa Management Guide,.

Field Corn

Checking Plant Populations-Indication of Pest Issues

As corn starts to emerge it is important to know your corn plant populations. Conducting plant population checks is the first step to determining if there are pest problems in the field.  The pressing question is How do I check my corn plant populations? It is suggested that you sample in units that are one-thousandth of an acre. Please consider developing the habit of sampling rows as they were laid down by the planter. If the was planted to a six-row planter, then sample the six rows that represent one pass of the planter. Watch tractor wheel tracks and choose your next six-row sample that would correspond to with the same six planter units. This way you would notice any variation or patterns between the units of the planter. Make sure to sample the appropriate length for your row width. Take at least 5 samples as you cross the field.

Row Spacing   (inches)           1/1000 of an acre

30                                            17 ft. 5 in.

32                                            16 ft. 4 in.

36                                            14 ft. 6 in.

38                                            13 ft. 9 in.

40                                            13 ft. 1 in.

After you are finished counting plants in each sampling location take the average number of plants and multiply it by 1000. This will give you the number of plants per acre. For example if you had an average of 30 plants you multiply it by 1000 and you would have 30,000 plants per acre. If your plant population is more than10% lower than that expected it may indicate a problem in the field. While many things could cause the population reduction at least two pest related issues might be involved: early season seed or seedling blights and/or seed corn maggot damage. For more information on these pests view our on-line management guides at: Field Corn Diseases. or Early Season Insect Pests in Field Corn


Soybean Aphids

Soybean aphids are new pest to the northeast. We have only had it on our soybeans the past 3 years. For the most part it has not caused damage to soybean production with the exception of few fields in Central New York last season.  Soybean aphid has been a problem in other part of the country. Soybean aphid is the only aphid that attacks soybeans in the United States. This aphid is very small at a 1/16 of an inch long when fully grown and may be yellow to yellow-green in color. Soybean aphid has two black-tipped tailpipesor cornicles that can be seen easily under a hand lens. They tend to colonize and are found on the under side of the leaf. The threshold for soybean aphids is 250 or more per plant through the V4 stage. You must take an average of 20-30 plants per field. This threshold allows for about 7 days for treatment action. For more information on managing insect pest on soybean check out our on-line publication: Soybean Insect Pest Management Guide

Seed Corn Maggot a Problem in Soybeans

I have heard estimates predicting record number of soybean acres will be planted in NY this season. As we gear up for soybean production remember to consider protecting stands from potential damage from seed corn maggot. Seed corn maggot (SCM) is a problem on corn but will also feed on soybean seeds. In the early spring, the female SCM fly searches fields with high organic matter (decomposing plant material, fields with manure, etc.) for soil cracks and germinating seeds in which to lay their eggs. Maggots hatch from the eggs and feed by burrowing into germinating seeds. These maggots are tapered, legless, appear to be headless, pale yellowish-white, and reach a length of about a 1/4 inch long. Symptoms in soybeans are that damaged seedlings may appear as "snake heads" i.e. seedlings without cotyledons. Proper diagnosis requires some digging in the gaps within a row to check for seeds and seed health. Prevention of SCM in soybeans is the main method of management. Use an insecticide seed treatment when you plant. For more information on managing insect pest on soybean check out our on-line publication: Soybean Insect Pest Management Guide

Soybean Rust-Not Here but Keep Eyes Open

Some growers have asked me if we have soybean rust in New York. Soybean rust is not in New York or even in this hemisphere. While we do not have soybean rust I think it is important to watch your beans for the disease. Soybean rust is found in Asia, Australia, Africa and South America. This fungal disease is easily and widely disseminated by wind-borne spores. Soybean rust can be very destructive with yield losses from 10-80%, depending on how early in the season the plant is infected. Soybean rust in the early stages is difficult to identify. It may look like other foliar soybean diseases. An early symptom is a yellow mosaic discoloration on the lower leaves of maturing plants at or near flowering. As the rust advances it migrates to the center and upper parts of the plant. This causes the leaves to turn yellow and small brown pustules lesions appear. Tan or reddish brown surface lesions, necrosis and eventual defoliation are symptoms of the advanced stages of the disease. Pictures of the disease can be viewed on the following website:  Soybean Rust Pest Alert.  If you suspect you may have the disease in your soybeans contact your local Cornell Cooperative Extension Educator.

Small Grains
Cereal Leaf Beetle
While I have not seen cereal leaf beetle this season they can be an occasional problem in small grains. (My western NY colleagues began finding them two weeks ago in Aurora and points west). Some years they do reach action thresholds and need to be controlled. Eggs can be found on the upper surface of the leaves near the midrib. Eggs are elongate, yellow to brown about 1/16 inch long, and are laid in chains of two or three. Small black slug-like larvae emerge from the egg and reach about a 1/4 inch long. Larvae feed on the leaf surface, leaving long narrow white strips between the veins. The adults are 3/16 inch long with metallic bluish-black head and wing covers. Cereal leaf beetle is more of a problem in oats but can occasionally reach threshold levels in wheat.

The threshold for cereal leaf beetle is three or more eggs and larvae per stem before the boot stage of oats or one or more larvae per flag leaf after the boot stage. Check 30 stems distributed throughout a field to determine if the field are at an action threshold.

Thanks to: Kevin Ganoe (Chenango, Otsego, Herkimer, Fulton & Montgomery Counties), Jeff Miller (Oneida County) and Keith Waldron (NYS IPM) for contributing to this week's report.

Ken Wise