Weekly Field Crops Pest Report 2007
View from the Field
Western NY and Finger Lakes Region
Janice Degni (CCE South Central NY Dairy & Field Crops Program) and I were checking deer-grazed soybeans at a field edge when we discovered soybean aphids present on plants. Numbers were very low, between 1 and 4 aphids per plant. Buckthorn, the overwintering host of soybean aphids, was abundant in the adjacent hedgerow. While it is important to begin scouting soybeans early, our experiences in NY and in the Midwest over the past several years demonstrate that this early infestation is unlikely to become a serious threat to soybeans. Natural enemies, including ladybugs, will help keep aphids in check.
How significant was the deer grazing we saw? This photo shows:
Fortunately the areas affected were small.
In several no-till soybean fields in Cayuga County, I observed thin plant stands. Digging in the rows revealed beans just barely covered with debris, drying out. Some injured or destroyed seeds were present, too, as shown in the following photo:
With a little more digging, we found millipedes:
Millipedes are common in the soil. Usually, they play a beneficial role by feeding on decaying plant material. Occasionally, these arthropods (not insects) will damage seeds and emerging plants. The distinguishing characteristic of millipedes is their number of legs: they have four legs per body segment.
Potato leafhoppers are found in most alfalfa fields that I scouted in Eastern NYS. I did not find any fields over threshold this week as did last week. As the summer goes on potato leafhopper populations will rise as the heat increases. Potato leafhopper has the potential to increase in infestation levels very quickly as the temperature increases.
I am still finding 1st and 2nd instar larvae in alfalfa in upper Hudson Valley and Cobleskill regions. Alfalfa weevil can be a problem on alfalfa regrowth if the larvae are still small. The action threshold for alfalfa 2nd cutting is 50% tip feeding.
I observed slug damage on several corn plants this week. Slugs can be a minor problem when conditions are wet. Slugs do windowing type damage (leaf tissue eaten with one clear layer of cells left, that looks like a window), and leave a slime trail (a shiny trail near its feeding damage). Here is a picture of SLUG damage on corn.
Russ’s Weed Alert: LAMBSQUARTERS CONTROL ISSUES WITH GLYPHOSATE
Russell R. Hahn
As you may recall from comments made at winter meetings, there were several reports of less than desirable common lambsquarters control with glyphosate in Roundup Ready (RR) soybeans around NY State in 2006. In each case, the grower and/or crop advisor wondered whether these survivors were glyphosate-resistant.
We are most familiar with the initial report, which was from Cayuga County. Although this cash cropper grows both corn and soybeans, he has never grown RR corn and the main field in question only had RR soybeans twice during the past 10 years. In addition to the two in-season glyphosate applications when the fields were in RR soybeans, this field received two late-season glyphosate applications, once following wheat and once for quackgrass control later in the fall, during that 10-year period. Clearly, this lambsquarters population had not been subjected to excessive selection pressure from repeated glyphosate applications. Yet, there were lambsquarters plants, perhaps 12 inches tall at the time of spraying, that survived an application of 44 fl oz/A (2X) of glyphosate (5.5 lb ai/gallon). Seed was collected from these survivors for follow-up in the greenhouse. Through the course of three separate plantings, we tried to determine if this is a glypohsate-resistant biotype or if there is some other reason for the lack of control with glyphosate. In addition, we evaluated the effect of added surfactant and two tank-mix partners that might improve the lambsquarters control.
Plants from the first planting were sprayed with 44 or 88 fl oz/A (2X or 4X the normal rate) of fully loaded glyphosate (5.5 lb ai/gallon) when the plants averaged 3 or 5 inches tall. When lambsquarters averaged 3 inches tall, all of the plants died at these rates. When plants averaged 5 inches tall, most of the lambsquarters plants survived both the 44 and 88 fl oz/A applications, however, 88 fl oz/A did cause greater injury than 44 fl oz/A. Additional plants from this first planting were sprayed with 88, 176, or 352 fl oz/A (4X, 8X, or 16X the normal rate) when they averaged 12 inches tall and were flowering. At this advanced stage of development some of the plants survived at rates up to 176 fl oz/A (8X) but all were controlled at 352 fl oz/A (16X). A second planting was made to refine the relationship between lambsquaters’ size and control with glyphosate by more carefully selecting plants of the correct size for each application than with the first treatments. When sprayed with 88 fl oz/A of glyphosate, 3-inch lambsquarters was once again controlled, 5-inch lambsquarters was not consistently controlled, and 7-inch lambsquarters was injured but not controlled. These initial results suggest that these lambsquarters are not glyphosate resistant since small (3 inches) plants were controlled with 44 fl oz/A (2X) of glyphosate and even maturing plants were controlled at an extremely high rate (16X). The results do suggest that the size of the lambsquarters at the time of application is perhaps of greater importance than with some other annual broadleaf weeds when applying glyphosate alone in RR crops. Although problems with lambsquarters control have been reported in other states as well, no one has reported (on an international web site) that they have confirmed glyphosate-resistant lambsquarters as of June 6, 2007.
A third planting was used to see if additional surfactant would have an effect with a “normal” application rate of 22 fl oz/A. Although we spray in 20 gallons/A (higher than many commercial applications) and this volume may reduce the concentration of surfactant from the fully loaded glyphosate below optimum, the addition of extra non-ionic surfactant (1 qt/100 gallons of spray or 0.25% by volume) did not improve performance of the 22 fl oz/A glyphosate application on 7-inch lambsquarters. In addition, some of these 7-inch plants were used to determine whether tank-mixing FirstRate or Harmony GT XP with glyphosate would improve lambsquarters control. The tank-mix of 22 fl oz/A of glyphosate with 0.3 oz/A of FirstRate did not consistently control the 7-inch lambsquarters. On the other hand, the tank-mix of 22 fl oz/A of glyphosate with 1/12 oz/A of Harmony GT XP did control the 7-inch lambsquarters. Although we added 0.25% by volume of non-ionic surfactant to these treatments, it is not clear that this would be necessary with fully loaded glyphosate formulations being sprayed in 5-20 gallons/A of spray solution. The additional cost for this Harmony GT XP would be about $1.20/A but would clearly be a good investment if you’ve experienced difficulty controlling lambsquarters with glyphosate alone or if you have lambsquarters taller that about 3 inches at the time of glyphosate application.
Seed Corn Maggot in Soybeans
Seed corn maggots occasionally attack soybean seeds and seedlings before plants emerge from the soil. Generally, stand reduction does not impact soybean yield potential as directly as corn yield potential is impacted because of the ability of the remaining soybean plants to compensate and fill in gaps. Rarely is damage severe enough to warrant re-planting.
Sources of fresh organic matter draw in the adult female seed corn maggot flies. The adults look like a small, slender version of a house fly (they’re about half the size of the house fly). They lay eggs in fresh organic matter, including weeds on the soil surface (or recently incorporated into the soil), recently applied manure, or debris left on the soil surface in a no-till situation.
The seed corn maggot is a small, yellowish-white, headless, legless larva. The body is tapered in the front with two small black mouth hooks. The maggots seek out seed, then feed directly on the seed before it germinates, and may additionally attack stems on seedlings before they push through the soil. These seedlings seldom survive. Delays in germination resulting from cool weather give seed corn maggot more time to find a seed and do damage before the plant is vigorously growing.
What is our job now? It’s time to scout newly planted fields as seedlings emerge. Look first for gaps in the stand. Then, focus on plants at several locations in a field, and assess the color and growth stage of the plants. Plants that have a yellowish coloration or appear stunted or wilted may be injured. If cotyledon-stage plants show signs of damage, dig up the soil around the plants to detect the presence of the maggots.
Potato leafhopper identification and what can it do to alfalfa?
Potato leafhopper is a lime-green insect about 1/8 inch long and rides the storms that come from the south, looking for alfalfa and other host plants. The adult females are strong flyers and move from plant to plant laying 2-3 eggs per day. Bright yellow-green nymphs (looking much like adults, but smaller and wingless) hatch from the eggs to feed on plant juices. Nymphs and adults alike use their needle-like mouthparts to suck juices, replacing them with toxic saliva. Once you see V-shaped yellowing on the tips of the leaves it's too late. Potato leafhopper has likely reduced plant protein by 5% and yield by about .10 - .25 ton per acre pre cutting. New seedings are at higher risk to potato leafhopper damage. Crop stress from this insect can impact production this season as well as affect production potential for subsequent years. The key is to scout fields before the damage has already occurred. For more information on potato leafhopper checkout our online Potato Leafhopper Management Guide
Soybean Rust Update, NYS
USDA Public Soybean Rust Web Site (Pest Information Platform for Extension and Education - PIPE)
United States Soybean Rust Commentary (updated: 06/06/07)
Growing Degree Days in NYS
Growing degree Days for peak (50%) Occurrence of Alfalfa Weevil growth stage:
(Note: for alfalfa weevil predictions use Base Temp of 48F)
CURRENT Accumulated Growing degree days (48F Base)
* Initial stand assessment: plant populations, seedling diseases and insects
SEED GROWERS FIELD DAY
NYSIP Foundation Seed Barn
WEED SCIENCE FIELD DAYS
Valatie Research Farm – July 6
Robert B. Musgrave Research Farm- July 11
H.C. Thompson Research Farm- July 12
AURORA FIELD DAY
ROBERT MUSGRAVE RESEARCH FARM
Julie Dennis: IPM Area Educator, Livestock and Field Crops, Western NY
Keith Waldron: NYS Livestock and Field Crops IPM Coordinator
Ken Wise: Eastern NYS IPM Area Educator: Field Crops and Livestock