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Early Season Scouting for Soybean Aphids

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Armyworm Flight - Crookston, July 05, 2005.

The light trap in Crookston maintained by Mike Hanson, a member of the NWROC Entomology staff, caught over 300 moths in a 3 night period last week (June 23 – 27 moths, June 24 – 81 moths, June 25 – 208 moths). Catches this size have been linked to armyworm outbreaks but it is not a given that this will occur. This flight indicates scouting is recommended but does not infer application is necessary!! It is important to consider all of the information…..

Armyworm Biology - Armyworms do not overwinter in the Red River Valley; populations can only be re-established by immigrants, arriving on southerly winds in the spring or early summer. These wind events are often linked with changing weather fronts. Adult armyworms live for approximately 2-3 weeks, with the females able to lay eggs for about 7-10 days of that time (see Table 1 below). Eggs hatch in 7-10 days and the first instar larvae feeds very little. It takes 3-5 days to complete the earlier larval instars (stages) and food consumption essentially triples at each stage. Still, the heavy feeding which causes the greatest yield damage doesn’t occur until the caterpillar is in it’s 5^th instar – about 2 weeks post hatching (or 3 weeks after the peak flight). The 5^th and 6^th instars can cause considerable damage to small grains, consuming the flag and lateral leaves and then possibly clipping the tillers themselves.

This graphic kindly supplied by P. Glogoza and C. Holen, June 28 issue of Cropping Issues in NW Minnesota

Treatment Decisions - Armyworm populations can be impacted by a number of factors. Low temperatures may prevent adult moths from flying and mating or may slow egg development, rain can wash younger caterpillars off of leaves to the ground where they are subject to increased predation, parasitic wasps often infect armyworm caterpillars (the eggs of these beneficial insects appear as white or brown capsules along the backs of the caterpillars), and fungal diseases can infect caterpillars and significantly decrease populations. If any or all of these factors occur, any outbreak stands a good chance of fizzling out. Consequently, treatment decisions shouldn’t be made simply on the basis of trap catch data, especially the decision to add an insecticide to a fungicide application in the next week. Although it is tempting to add an insecticide to fungicide applications applied this week, be aware, it may not address the problem entirely. None of the insecticides registered against armyworms in small grains are very effective against the eggs (the stage most likely to be present in the field at this time). Because the adult moths will be laying eggs until late this week (remember, the females lay eggs for 7-10 days, and once laid the eggs take another 7-10 days to hatch) an insecticide application at this time may not be effective. And given the recent weather, residual activity of the registered products may not be long enough to deliver sufficient mortality of caterpillars hatching over the next 1-2 weeks. In addition, armyworms populations are often not evenly spread throughout a region; anyone who can remember the past few outbreaks knows it isn’t unusual for neighboring fields to have very different infestation levels. Economically, it may be a better decision to scout over the next 1-3 weeks for armyworms and make treatment decisions on a field by field basis. In this way, armyworms can be detected while still small, prior to significant yield loss.

Scouting, Thresholds & Treatment – Scout for armyworms at grassy margins of the fields, low, weedy areas in fields or in lodged grain; populations are more likely to develop in these areas first. Armyworms prefer the edges of leaves first and are messy, wasteful eaters. Because they generally retreat during the day under soil and plant residue on the ground and feed more often beginning at dusk (see image above), it’s easier to scout for armyworm damage than the armyworms themselves. Look for leaves that have been notched, cut and partially eaten leaf material on the ground, and small round pellets (armyworm frass = bug poop) near the base of the plants.

Consider applying insecticide if: there are 4-5 armyworm larvae per sq. ft., caterpillars are ¾ - 1 ¼ in. long, leaf feeding or head clipping is found, and parasites are not evident. By the time armyworms are more than 1 ½ in long, they have stopped feeding and are getting ready to pupate. At this point the damage has already been done and control applications will probably not provide an economic return.

A number of insecticides are registered against armyworms in small grains (see Table 2 below). Because we are already into July, pay particular attention to the PreHarvest Interval (PHI) when selecting an insecticide.

ALWAYS check the label.

This graphic kindly supplied by P. Glogoza and C. Holen, June 28 issue of Cropping Issues in NW Minnesota

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Soybean Aphids - They’re Baaaack (maybe…) – June 6, 2005

Soybean aphids showed up on soybean in SE MN last week and WC MN this week. Very low numbers of aphids have been found on very early plants (V0 / V1) in a number of locations from the SE corner of the state up to the Rosemont research & Outreach Center, just south of the Cities. Aphids were reported from just south of Underwood (outside Fergus Falls) by Doug Holen. The plants are in V1 and this is very early for us to have aphids in the region!! . Aphids have also been reported from soybeans in Iowa, Illinois, Michigan, and Indiana. This is the earliest soybean aphids have been found in soybeans in the north central states. This doesn’t necessarily mean that we’re in for a big aphid year. Lots of things could still happen; the weather might not favor aphid reproduction, we may not get a lot of immigrants contributing to our populations up here, predator populations may increase and hit the aphids hard, or fungal diseases might just kick in and keep aphid numbers low as well. It does mean we should keep our eyes open and scout soybeans for aphids a bit earlier than we usually do.

In the west central and northwest MN and eastern ND, yield loss from soybean aphid tends to come from a decrease in seed size caused by populations that develop later in the season (R1-R4). However, earlier developing populations of the aphid will cause stunting of the young soybean plants, resulting in fewer nodes and fewer pods. This early season yield loss is often much more severe than the late season loss we generally experience. Even more reason to ‘Scout Early – Scout Often!”

Some information on early season scouting for soybean aphids is available on the Red River IPM website at:

http://www.nwes.umn.edu/ent/redent.html

Remember to look for other signs of aphid presence, such as cast skins, ants, or lady beetles.

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Cutworms in Sugarbeet – May 23, 2005.

There have been multiple reports of cutworms in sugarbeet in the last week and even with the unseasonably cold temperatures earlier in the month, they’re appearing pretty much on schedule. Both Red-Backed and Dark-Sided cutworms occur in the Red River Valley and both have similar life cycles. They both over-winter as eggs laid by the moths in cultivated fields at the end of summer. The following late May/early June, the eggs hatch and the caterpillars move onto seedling crops.

Scouting - Cutworms feed mostly in the evening and at night and so are difficult to locate in the daytime. Their feeding causes wilting, death and occasionally they’ll cut the entire seedling off near ground level. Scouting for these worrisome worms is best done by looking for wilting or dying plants and then looking in the top 1”-2” of soil at the base of these plants.

Thresholds & Treatment – An economic return on treatment can be expected when 4% - 5% of beets seedlings are cut in a field. Pesticides are best applied in the evening resulting in high levels of insecticide present during the cutworms’ period of greatest activity. In addition, in the evening the canopy will tend to have higher humidity and perhaps some dew to carry the insecticide over the plant surfaces in greatest danger of feeding damage. For the same reason, liquid formulations tend to be more effective against cutworms. To assist in delivering the insecticide to the caterpillars, break up severe soil crusting prior to, or during application. Some insecticides registered for use against cutworms in sugarbeet appear below (remember to always check the label for registration details).

INSECTICIDE	DOSAGE IN LB AI/ACRE	PRODUCT PER ACRE	RESTRICTIONS ON USE
Asana XL RUP	0.03 - 0.05	5.8 - 9.6 fl oz	Use as a seedling spray treatment. Do not exceed 0.15 lb ai/acre per season. Apply with a minimum of 2 gal per acre. Do not apply within 21 days of harvest.
carbaryl (Sevin)	1.5	variable	This treatment is most effective against cutworms feeding on upper portions of plants. Repeat application as necessary up to 2 times but not more often than every 14 days. Do not apply within 28 days of harvest. Do not apply more than 3 pounds of active ingredient per acre per crop.
Chlorpyrifos    Lorsban 4E RUP ___________         Nufos 4E RUP	1.0 ________ 1.0	2 pt ________ 2 pt	Do not apply within 30 days of harvest. Do not allow livestock to graze in treated areas and do not harvest treated beet tops as feed for meat or dairy animals within 30 days of last treatment. Do not apply more than 8 pt/acre (broadcast basis) or make more than 4 applications per season.
Lorsban 15G	1.5 - 2.0	10.0 - 13.4 lb (6.6 - 9 oz/1,000 row ft)	Granules must be applied behind furrow openers and ahead of press wheels as a 4- to 5-inch band at planting. Do not apply in-furrow or modified in-furrow. Lightly incorporate with chains or tines behind press wheels for best results. Do not apply granules in direct contact with the seed. Do not make more than one application per year.
Lannate LV RUP	0.45	1.5 pt	Apply for variegated cutworm control. Do not apply within 7 days of harvest. Do not feed tops to livestock within 30 days of last application. Field re-entry interval is 48 hours. Do not apply more than 4.5 pounds active ingredient per acre per crop. Do not make more than 10 applications per crop.
Lannate SP RUP	0.45	0.5 lb	Apply for variegated cutworm control. Do not apply within 7 days of harvest. Do not feed tops to livestock within 30 days of last application. Field re-entry interval is 48 hours. Do not apply more than 4.5 pounds active ingredient per acre per crop. Do not make more than 10 applications per crop.
Methyl parathion 4EC RUP	0.25 - 0.38	0.5 - 0.75 pt	Do not apply within 20 days of harvest; or 60 days of feeding tops to animals. Do not enter fields for 48 hours after application.
Mustang 1.5 EW RUP	0.028 - 0.05	2.4 - 4.3 fl oz	Apply to foliage using a minimum of 2 gallons of water per acre by air or 10 gallons per acre by ground. Do not apply within 50 days of harvesting tops or roots. Do not apply more than 0.15 pound active ingredient per acre per season.
Mustang Max RUP	0.014 - 0.025	2.24 - 4 oz	Apply in-furrow or in a 3-4 inch T-band (band over the open furrow) at planting in a minimum of 3-5 gallons of finished spray per acre. Do not apply more than 0.075 pound active ingredient per acre per season. Registered for 24 (c) special local need sale and use in sugarbeet in ND (SLN no. ND-030003), MN (SLN no. MN-030001), MT (SLN no. MT-030001), WY (SLN no. WY-030003), and other western states. SLN registration expires before 2008 growing season.

RUP - Restricted use pesticide

ALWAYS check the label.

Table from:

2005 Field Crop Insect Management Recommendations
compiled by Phillip Glogoza, Extension Entomologist,
in cooperation Janet Knodel, Mark Boetel, Denise Olson, and Gary Brewer
Department of Entomology
North Dakota State University

North Dakota State University
NDSU Extension Service
E-1143, January 2005
For use in 2005 only

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Selected Past IPM Updates

June 06, 2005 – Soybean Aphids – they’re back

May 23, 2005 – Cutworms in Sugarbeets

June 20, 1999 - Potato Leafhopper, Grasshoppers, Cereal Insects
Sept 12, 1999 - Impact of Aster Yellows on Canola May be Greater Than You Think
Aug 31, 1998 - Lygus in Sugarbeets
July/Aug, 2000 - Armyworm Outbreak in RRV
Fall, 2000 - Soybean Aphid, A New Insect Pest in Minnesota Soybeans
Fall, 2001 - Soybean Aphid in NW Minnesota
August, 2001 - Lygus in Sugarbeets
May 2002 - Cutworms in Sugarbeets
July 2002 - Armyworms in Small Grains
July 2002 - Grasshoppers in The Red River Valley
July 2003 - Leafminer in Sugarbeets

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Publications Available for Download

Insects

Grasshoppers -
Minnesota Grasshopper Management - 2002 with color graphics
Minnesota Grasshopper Management Brochure with scouting and control information (available as a PDF file designed to be a tri-fold brochure).

Scouting -
Scouting for Insects in Wheat, Alfalfa, and Soybeans - a manual prepared for the University of Minnesota Extension Service Field School, held at the Northwest Experiment Station, Crookston, MN, July 7-8, 1998.
Early Season Scouting for Soybean Aphids - A guide to scouting early season soybeans for soybean aphid.

Questions? Comments? E-mail us at:

imacrae@tc.umn.edu