Kohlrabi-Cutworm

Includes

Black cutworm (Agotis ipsilon)
Variegated cutworm (Peridroma saucia)

Pest description, crop damage and life history

See:

Biology and life history During mild winters, the black cutworm overwinters in field debris and brush as a pupa. Otherwise, it flies in from warmer climates in late spring.

The variegated cutworm overwinters in the soil or under trash as a partially mature larvae. The larvae begin feeding in early spring and may do damage to seedlings. Larvae mature in late April and May and pupate in earthen cells in the soil. Adults emerge in late May and June.

Eggs hatch in 4 to 7 days, and larvae begin to feed on plant foliage. Larvae feed for 4 to 6 weeks, then pupate in the soil. Adults emerge in late August and lay eggs which hatch into larvae. These form the overwintering stage for the variegated cutworm. There are two generations each year.

Pest monitoring Pheromone traps can be used to monitor for cutworms in conjunction with field scouting. Moth counts in excess of two black cutworm moths per trap per day indicate significant egg laying pressure. When moth counts exceed this level, intensify field scouting at crop emergence and during stand establishment.

If the cutworm population is reducing the plant stand, treat during the seedling stage. Frequently, the damage is most serious at the edges of a field, but stand loss can occur in a spotty pattern throughout the field.

Usually, it is necessary to dig in the soil to find black cutworm larvae and to determine the extent of the infestation and the size of the cutworms involved. Larvae normally hide under debris on the soil surface during the day, but are active, voracious feeders at night.

Since extensive damage may occur in a short period of time, inspect plant beds and newly set plants frequently. In North Carolina, an economic threshold of 5% injured plants has been established for cutworms infesting newly set or young plants (within 3 weeks after transplanting). In Ontario, Canada, the guideline for black cutworm on many seedling vegetables is also 5% plants infested.

Management-biological control

Cutworms are attacked by a number of predators, parasites, and diseases. Many of these natural control agents are not effective on pale western and black cutworms because of their subterranean nature. It is not known if any of these natural enemies can control cutworm populations, but their presence should be noted.

Management-cultural control

Cutworms are most injurious in fields with high plant residue. Historically, cutworms are a problem in early, spring-seeded seedling fields. Tillage prior to seeding is an effective means of reducing cutworm damage. A thorough harrowing between rows may reduce the number of cutworms feeding actively in established fields.

Management-cultural control

Weed control is important. Lambsquarters and wild mustard attract egg-laying females and provide a source of food for larvae. Fall tillage can help destroy overwintering pupae.

Home gardeners: Control weeds, grasses, and debris in the vegetable garden that provide cover; hand-pick cutworm larvae, using a flashlight to find them, if practical. Scratch the soil at the base of plants to find larvae in the daytime.

Management-chemical control: HOME USE

Apply any one of these materials to the soil surface at first sign of cutworm activity. Consult label. Minimum preharvest interval (PHI) varies with crop. Difficult to control. Where cutworms are on the soil surface, a carbaryl drench, when bees are not present, may help.

  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • Bacillus thuringiensis var. kurstaki (Btk)-Some formulations are OMRI-listed for organic use.
  • bifenthrin
  • carbaryl
  • cyfluthrin
  • cyhalothrin
  • gamma-cyhalothrin
  • kaolin-Applied as a spray to foliage and stems it acts as a repellent to some insect pests. Some formulations are OMRI-listed for organic use.
  • lambda-cyhalothrin
  • permethrin
  • plant-derived essential oils (such as rosemary)-Some formulations are OMRI-listed for organic use.
  • pyrethrins-Some formulations are OMRI-listed for organic use.
  • spinosad-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin

Management-chemical control: COMMERCIAL USE

  • alpha-cypermethrin (Fastac EC) at 0.014 to 0.025 lb ai/a. PHI 1 day. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.075 lb ai/a per season.
  • azadirachtin (Neemix) at up to 0.04 lb ai/a. PHI 0 days. REI 4 hr. Neemix is OMRI-listed for organic use.
  • Bacillus thuringiensis (Javelin) at 0.12 to 1.5 lb/a. PHI 0 days. REI 4 hr. Acts slowly; may need multiple applications. Add an appropriate spreader-sticker to enhance control. Most effective on small larvae. Some formulations are OMRI-listed for organic use.
  • beta-cyfluthrin (Baythroid XL) at 0.007 to 0.013 lb ai/a. PHI 0 days. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.1 lb ai/a.
  • beta-cyfluthrin/imidacloprid (Leverage 360) at 0.07 lb ai/a. PHI 7 days. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.1 lb ai/a beta-cyfluthrin or 0.2 lb ai/a imidacloprid per season.
  • bifenthrin (Brigade WSB) at 0.033 to 0.1 lb ai/a. PHI 7 days. REI 12 hr. Retreatment interval 7 days. Limit 5 treatments. Do not exceed 0.5 lb ai/a per season.
  • bifenthrin (Capture LFR) at 0.04 to 0.08 lb ai/a soil applied in furrow with seed or transplant. REI 12 hr. Some formulations are
  • bifenthrin/IBA (Empower 2) at 0.04 to 0.1 lb ai/a. PHI 7 days. REI 5 days. Do not exceed 0.5 lb ai/a per season. Retreatment interval 7 days. Limit 5 treatments.
  • bifenthrin/imidacloprid (Brigadier) at 0.06 to 0.095 lb ai/a. PHI 7 days. REI 12 hr. Do not exceed 0.24 lb ai/a imidacloprid and 0.24 lb ai/a bifenthrin. Retreatment interval 7 days. Maximum 5 applications.
  • bifenthrin/zeta-cypermethrin (Hero) at 0.04 to 0.1 lb ai/a. PHI 7 days. REI 12 hr. Retreatment interval 7 days. Limit 5 applications. Do not exceed 0.45 lb ai/a per season.
  • carbaryl (Sevin 5 Bait) at 2 lb ai/a as granule. PHI 3 days. REI 12 hr. Retreatment interval 7 days. Limit 3 treatments per year.
  • chlorantraniliprole/lambda-cyhalothrin (Voliam Xpress) at 0.049 to 0.078 lb ai/a. PHI 3 days. REI 24 hr. Retreatment interval 5 days. Do not exceed 0.24 lb ai of lambda-cyhalothrin or 0.2 lb ai of chlorantraniliprole per acre per growing season.
  • chlorpyrifos (Lorsban 75WG) at 0.5 to 1 lb ai/a foliar; 2.25 lb ai/a soil. PHI 21 days foliar; 30 days soil. REI 24 hr. Do not exceed 3 applications per season.
  • Chromobacterium subtsugae (Grandevo) at 0.3 to 0.9 lb ai/a per 100 gal. PHI 0 days. REI 4 hr. OMRI-listed for organic use.
  • cryolite (Kryocide) at 7.7 to 15.4 lb ai/a. PHI 7 days REI 12 hr. Do not exceed 94 lb ai/a per season. Some formulations are OMRI-listed for organic use.
  • cyfluthrin (Tombstone) at 0.013 to 0.025 lb ai/a. PHI 0 days. REI 12 hr. Do not exceed 0.2 lb ai/a per season.
  • cyfluthrin/imidacloprid (Leverage 2.7) at 0.08 lb ai/a. PHI 7 days. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.17 lb ai/a cyfluthrin or 0.24 lb ai/a imidacloprid per year.
  • cypermethrin (Holster) at 0.05 to 0.1 lb ai/a. PHI 1 day. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.6 lb ai/a per season.
  • (Belt SC) at 0.063 to 0.075 lb ai/a. PHI 8 day. REI 12 hr. Do not exceed 0.225 lb ai/a per season. Retreatment interval 5 days.
  • gamma-cyhalothrin (Declare) at 0.0075 to 0.0125 lb ai/a. PHI 1 day. REI 24 hr. Do not exceed 0.12 lb ai/a per season. An oil or nonionic surfactant improves performance.
  • lambda-cyhalothrin (Warrior II) at 0.015 to 0.025 lb ai/a. PHI 1 day. REI 24 hr. Retreatment interval 5 days. Do not exceed 0.24 lb ai/a per season.
  • lambda-cyhalothrin/thiamethoxam (Endigo ZC) at 0.064 lb ai/a. PHI 1 day. REI 24 hr. Retreatment interval 7 days. Do not exceed 0.24 lb ai/a of lambda-cyhalothrin or 0.172 lb ai/a of thiamethoxam per season.
  • zeta-cypermethrin (Mustang) at 0.028 to 0.05 lb ai/a. PHI 1 day. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.3 lb ai/a per season.

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