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5/30/2011 - 6/5/2011

Stalk Borer Scouting Dates for 2011

Erin Hodgson, Department of Entomology and Adam Sisson, Corn and Soybean Initiative

The stalk borer, Papaipema nebris, is a native insect to North America and has a wide host range (more than 175 plant species). Female moths prefer to lay eggs in narrow-leaved perennial grasses like tall fescue, giant foxtail and quackgrass. When eggs hatch, the larvae burrow into the grass and kill the top of the plant, which is sometimes referred to as leaving a “dead head” plant. Eventually the larvae get too big for the grass and migrate to larger plants like corn, sunflower and sometimes soybean.


Description

Stalk borer larvae have three pairs of true legs and four pairs of fleshy prolegs. The body is creamy white and dark purple with brown stripes. Often there is a creamy white stripe running down the back. A distinctive feature is an orange head with two dark lateral stripes (Figure 1). The adults are dark grey and brown colored moths, with jagged white lines and two to three clusters of white spots.
 

Figure 1. Stalk borer larva.
Photo credit Marlin E. Rice.


Scouting

Begin scouting when 1,300-1,400 growing degree days (base 41 F) have accumulated. About 10 percent of stalk borer larvae movement has occurred when 1,400 degree days accrue. The map below (Figure 2) shows the estimated dates to begin scouting for stalk borer. The earliest scouting date, June 11, occurs in southeast Iowa. The date to begin scouting in south central and southwest Iowa are June 14 and June 12, respectively. Scouting should begin in east central Iowa June 17, central Iowa on June 20 and west central Iowa on June 18. The northwestern and north central climate divisions should begin scouting June 23 and finally, June 24 for the northeastern division.
 

Figure 2.  Estimated date to begin scouting for stalk borer in Iowa climate divisions.
Estimates are based on accumulated growing degree days (base 41°F). Begin scouting around 1,300-1,400 degree days.


Look for larvae inside the whorls to determine the number of plants infested. The larvae are not highly mobile and typically only move into the first four to six rows of corn. Look for new leaves with irregular feeding holes or for small larvae resting inside the corn whorls. Larvae will excrete a considerable amount of frass pellets in the whorl or at the entry hole in the stalk. Young corn is particularly vulnerable to severe damage, but plants are unlikely to be killed once reaching V7 (seven true leaves).


Damage

Corn is infested when stalk borer larvae move to find bigger host plants, typically adjacent to grassy edges of emerging corn. The most susceptible stages of infestation are at V1-V5, or about 2-24 inches in plant height. Larvae can damage corn by defoliating leaves and burrowing into stalks. Stalk borers do not typically cause economic damage when feeding on the leaves, but can clip newly emerging plants and cause death. More often, larvae kill corn plants by entering the stalk and destroying the growing point (i.e., flagging or dead heart). A dead heart plant will have outer leaves that appear healthy, but the newest whorl leaves die and can cause a barren plant.


Management

Stalk borer infestations are more likely in corn surrounded by giant ragweed. Although minimizing weeds in and around corn will discourage egg-laying females, using herbicides to kill weeds can force stalk borer larvae to find new host plants. Long term management requires controlling grass edges so that mated females will not lay eggs in that area during the fall. Mowing grassy areas adjacent to corn fields the second week of August will make borders unattractive to adults.

Fields with persistent stalk borer infestations should be monitored every year. Applying insecticides to infested corn is not effective because the larvae are protected once tunneled into the stalk. Instead, target foliar applications to larvae as they migrate from grasses to corn.

To prevent stand loss, scout and determine the percent of infested plants. The use of an economic threshold (Table 1), first developed by ISU entomologist Larry Pedigo, will help determine justifiable insecticide treatments based on market value and plant stage. Young plants have a lower threshold because they are more easily killed by stalk borer larvae.


Table 1. Economic thresholds (percent infested plants) for stalk borer in corn, based on plant stage, expected yield and market value.


If an insecticide is warranted, some products can be tank-mixed with a fast burndown herbicide, or applied seven days after a slow burndown herbicide. Border treatment should be considered if infestations are localized. Insecticides must be well-timed so that products are reaching exposed larvae before they burrow into the stalk. Make sure to read the label and follow directions, especially if tank-mixing with a herbicide, for optimal stalk borer control.

For more information on stalk borer biology and management, read a recent Journal of Integrated Pest Management article by Rice and Davis (2010), “Stalk borer ecology and IPM in corn.”

 

 

Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847. Adam Sisson is a program assistant with responsibilities with the Corn and Soybean Initiative. Sisson can be contacted by email at ajsisson@iastate.edu or by calling 515-294-5899.

Iowa State Research Farm Field Days to Begin June 15

Mark Honeyman, Research and Demonstration Farms

The latest in field-based research of crop production and management will be on display beginning June 15 at Iowa State University Research and Demonstration Farm field days across Iowa.

Field days consist of tours of research and demonstration plots at the farms. Topics vary for each farm depending on local interest and conditions.

The public is welcome to attend the field days, which take place rain or shine. They are free unless noted.

The latest schedule and information are available on the research and demonstration farms web site at: http://www.ag.iastate.edu/farms/fielddays.php

Visitors are asked to follow these guidelines when attending a field day at a farm with livestock, marked with an asterisk.
• There is a five-day waiting period prior to visiting Iowa State livestock farms if you have recently returned from travel outside the United States.
• If you have visited another livestock farm, you are asked to change clothing and footwear.
• Visitors are not allowed to bring food to the research farms.
• If you have any questions, call the Research and Demonstration Farms office at (515) 294-5045.

 

2011 field day schedule 

Southeast Research and Demonstration Farm
June 15, 1 p.m., Crawfordsville
Topics: Corn fungicides, cover crops, nematodes and grain marketing
From Crawfordsville, the farm is located one and three-quarter miles south, two miles east on G62 and three-quarters of a mile north on the Washington/Louisa county-line road.

Northern Research and Demonstration Farm
June 28, 9:30 a.m., Kanawha
Topics: Pre-emergence weed control, foliar fertilizer on soybeans, land rolling of soybeans and current crop topics
The farm is located just south of Kanawha on county road R35.

Northwest Research and Demonstration Farm
June 29, 9 a.m., Sutherland
Topics: Weed management, trees as a biomass source, surface water runoff, crop management and grain handling
The farm is located 11 miles north of Cherokee on U.S. Highway 59 and a quarter mile east on county road B62.

Northeast Research and Demonstration Farm
June 29, 1 p.m., Nashua
Topics: Farm and weather review, weather and crop forecast, field drainage issues, corn soybean disease management and nematodes
The farm is located one mile west of the Highway 218 and B60 intersection in Nashua, one mile south and a quarter mile east.

Horticulture Research Station
July 19, 8 a.m., Ames, $25 registration fee includes lunch (pre-registration form: http://www.hort.iastate.edu/news/)
The station is three miles north of Ames on Highway 69, turn east on 170th Street and the station is about one and a half miles on the north side.

Armstrong Research and Demonstration Farm*
Aug. 9, 9:30 a.m., Lewis
Topics: Corn fungicides, corn nematodes and soybean management
The farm is 11 miles southwest of Atlantic on Highway 6, one-half mile south on M53 and three-quarters of a mile east.

Agricultural Engineering and Agronomy Research Farms
Aug. 25, 9 a.m., Boone
Topics: Corn management research, corn fungicides and diseases, precision ag tools and strip tillage
The farms are west of Ames on Highway 30 at 1308 U Ave.

Northwest Research and Demonstration Farm (On-farm trials)
Aug. 31, 6:30 p.m., Dordt College northern farm
The farm is located 2 miles north of Sioux Center on Highway 75.

Southeast Research and Demonstration Farm
Sept. 8, 1 p.m., Crawfordsville
From Crawfordsville, the farm is located one and three-quarter miles south, two miles east on G62 and three-quarters of a mile north on the Washington/Louisa county-line road.

 

Demonstration Garden Field Days

Many of the farms plant and maintain vegetable and flower gardens with help from the Iowa State horticulture department to give the public gardening ideas and display new varieties available in Iowa. This year’s Home Demonstration Garden Field Days are devoted to children and cats.

One feature is the numerous flowers and vegetables named after storybook characters. Another section of the garden showcases summer squash with feline-friendly names like cougar, jaguar and leopard.

The gardens also feature a variety of “bumpy” pumpkins, sunflowers and many new flowers and vegetables.

FARM--DATE--TIME
Northwest, Rock Rapids (Lyon County Fairgrounds)--July 26--6 p.m.
Armstrong* --July 28--6:30 p.m.
Northeast--July 30--4 p.m.
Muscatine Island--Aug. 2--6:30 p.m.
McNay*--Aug. 3--6:30 p.m.
Northern--Aug. 4--6:30 p.m.
Southwestern Community College (Creston)--Aug. 5--6:30 p.m.
Horticulture Station--Aug. 11--6:30 p.m.

Special tree care and management field day:
Northwest, Sutherland--Aug. 10--6:30 p.m.


 

Mark Honeyman is coordinator for the Iowa State University Research and Demonstration Farms. He can be contacted at 515-294-4621 or at honeyman@iastate.edu

Start Scouting Beans for Damping Off

Alison Robertson, Department of Plant Pathology; and Erin Hodgson, Department of Entomology
 

Damping off severely impacts stand

This past Friday, we drove to western Iowa to collect damped-off soybean seedlings for a research project (see ‘Fields with damped off seedlings required for research project’). The field we visited was a farmer’s nightmare and, dare I say, a pathologist’s ‘happy place’. Stand was severely affected (Figure 1). Both pre-emergence and post-emergence damping off (Figure 2) was prevalent. Seed, barely emerged seedlings and seedlings at growth stages VC and V1 were rotted or yellowed and wilted. A soft, watery-brown rot was common on the hypocotyl and roots of affected seedlings (Figure 3).

It is difficult to tell from the symptoms exactly what pathogen is the cause of this damping off, however, since this field was planted in early May and the soil has very high clay content and is prone to flooding, we suspect Pythium species. Isolations will be made in the lab to identify the causal organism.

The grower who owns this field chose not to use a seed treatment fungicide. Based on the cropping history, soil type and disease history, this was probably a good candidate field for a seed treatment.


Figure 1. Soybean stand severely impacted by damping off
 


Figure 2. Damped off soybean seedlings



Figure 3. Soft brown watery rot of hypocotyl of a damped off soybean seedlings

 

Seed treatment fungicides and insecticide significantly improve emergence in early planted soybean demo

In July, we will be doing a workshop session on soybean seed treatments at the Crop Management Clinic at the ISU Field Extension Education Laboratory near Boone. In preparation for the clinic we planted microplot demonstrations. We inoculated half the microplots with Pythium species, and half with Fusarium virguliforme, the causal organism of SDS. Four commercial seed treatments, one seed treatment in development and an untreated check are show-cased. The plots were planted April 15, just as the cold, raining period set in. 

Emergence occurred approximately 24 days after planting (dap). We took seedling counts at 28 dap. In the Pythium-inoculated plots, 42 percent of the untreated seed emerged (Figure 4) compared to 72 percent to 89 percent (Figure 5) for the treated seeds. In the F. virguliforme-inoculated plots, emergence was 28 percent for untreated seed and 8 percent to 89 percent for treated seed. You don’t need much more evidence that seed treatments pay for early planted beans particularly when it is cold and wet.



Figure 4. Untreated soybean seedlings planted into a microplot inoculated with Pythium spp
.
 


Figure 5. Treated soybean seedlings planted into a microplot inoculated with Pythium spp.


Still looking for fields with damping off

I am still looking for soybean fields with damping off problems. I need to collect 50 symptomatic seedlings from the field. Please contact me by email alisonr@iastate.edu or call 515-294-6708 if you know of a field.

 


Alison Robertson is an assistant professor in the Department of Plant Pathology with extension and research responsibilities; contact at
alisonr@iastate.edu or phone 515-294-6708.  Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847.



This article was published originally on 6/6/2011 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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