Get the Jump on Armyworms in Alfalfa, Wheat

Get the Jump on Armyworms in Alfalfa, Wheat

March 28, 2014

Winter conditions in western Nebraska this year have been conducive to the overwintering of some insects. Of particular concern to crop producers is the cutworm.

Army cutworms at various larval stages

Figure 1. The army cutworm overwinters in various larval stages. (Photos by Jeff Bradshaw)

 

Army cutworms on soil

Figure 2. Even large army cutworm larvae can blend in well with their surroundings.

Damaging populations of army cutworms have already been reported in alfalfa and wheat in northwest Kansas. As conditions gradually warm up, insect activity will increase and growers should be scouting for insects, particularly cutworms, in wheat and alfalfa.

In western Nebraska, the most damaging cutworm is the army cutworm (Figure 1). Economic damage from other cutworms, such as the pale western cutworm, dark-sided cutworm, and variegated cutworm, is rare. The army cutworm damages alfalfa, wheat, and sugarbeet as well as various rangeland grasses.

Army Cutworms

In late September and October, army cutworms lay 1,000 to 3,000 eggs directly on bare soil, such as in newly planted winter wheat or heavily grazed patches of range.  After rainfall, eggs will hatch over an extended period, leading to a variety of caterpillar sizes feeding and developing as long as temperatures are adequate. When the weather turns colder, the caterpillars burrow down into the soil to spend the winter. Come April, large larvae can sometimes be abundant in winter wheat fields.

In 2011, moderate populations of the adult army cutworm moth (or "miller moth") could be found in sheltered areas during the day (see http://panhandlepests.blogspot.com/2011/06/miller-moths-continued.html). These moths contributed to a large population of larvae in 2012 and high populations in turn contributed to large populations in spring 2013. As we move into April and wheat breaks dormancy, this would be a good time to scout for cutworm activity.

Scouting and Treatment Recommendations

To scout for army cutworms use a treatment threshold of four or more cutworm larvae per square foot of winter wheat or alfalfa. However, for stressed, thin stands of wheat or for newly established alfalfa stands, use a threshold of two or more larvae per square foot. New or stressed stands of alfalfa require a lower threshold because they are more prone to damage from cutworms. Army cutworms only feed at night and seek out dark sheltered areas during the day, so turn over clots of loose soil and residue for accurate cutworm counts (Figure 2).

If army cutworm counts are above the threshold, consider an insecticide application. See Table 1 for a selection of chemical control products. Always read pesticide instructions carefully before use.

Jeff Bradshaw, Extension Specialist, Panhandle REC
Julie Peterson, Extension Specialist, West Central REC

Table 1. Insecticides labeled for cutworm control in alfalfa and winter wheat.
Mode of ActionProduct NameCommon NameRateRestrictions/Comments
Alfalfa
3 R Baythroid XL beta-cyfluthrin 0.8-1.6 oz/A Do not apply within 7 days of harvest or grazing. REI 12 hours
1B R Lorsban 4E,
Nufos 4E
chlorpyrifos

1-2 pt/A

Do not harvest or graze within 7 days after application of 1/2 pint, within 14 days after application of 1 pint, or within 21 days after > 1 pint per acre. REI 24 hours.
3 R Mustang Max zeta-cypermethrin 2.24-4 oz/A Do not apply within 3 days of harvest or grazing. REI 12 hours.
3 R Proaxis gamma-cyhalothrin 1.92-3.2 oz/A Do not apply within 1 day of harvest for forage or within 7 days of harvest for hay. REI 24 hours.
3 R Warrior II with Zeon, and generics lambda-cyhalothrin 0.96-1.6 oz/A Do not apply within 1 day of harvest for forage or within 7 days of harvest for hay. REI 24 hours.
Wheat
3 R Baythroid XL beta-cyfluthrin 1-1.8 oz/A Do not apply within 30 days of harvest or 3 days of grazing. REI 12 hours.
1B R Methyl 4EC* methyl parathion 0.75-1 pt/A For climbing cutworms (e.g., army cutworms). Do not apply within 15 days of harvest. REI 4 days
1B R Lorsban 4E
Nufos 4E
chlorpyrifos 1 pt/A Do not apply within 28 days of harvest. REI 24 hours.
3 R Mustang Max zeta-cypermethrin 1.28-4 oz/A Do not apply within 14 days of harvest. REI 12 hours.
3 R Proaxis gamma-cyhalothrin 1.92-3.2 oz/A Do not apply within 30 days of harvest. REI 24 hours.
3 R Warrior II with Zeon,
and generics
lambda-cyhalothrin 0.64-1.6 oz/A Do not apply within 30 days of harvest. REI 24 hours.
* Product not suitable for chemigation
R = Restricted Use Pesticide
REI = Re-Entry Interval
IRAC Mode of Action Classification
Group 1 = Acetylcholine esterase inhibitors; 1A = Carbamates; 1B = Organophosphates
Group 3 = Sodium channel modulators