IPM Threshold Guide for Vegetable Crops

Plant Emergence (or Transplanting) to Beginning of Heading or Reproductive Development

CABBAGE ROOT MAGGOT

• Control when planting

FLEA BEETLES:

• > 50%of newly emerged plants infested and "shothole injury" is present.
• Treatment thresholds for leafy cultivars not available

CABBAGE APHIDS AND OTHER APHID SPECIES

• Broccoli and Cauliflower:  infestations of all species combined reach nearly 100%
• Brussel Sprouts:  > 15% of plants are aphid infested from transplanting till 3 weeks before harvest
• Cabbage:  2% of plants are infested with 5 or more aphids on leaves

THRIPS

• Fresh market cabbage:  > 20%of plants infested

IMPORTED CABBAGEWORM, CABBAGE LOOPERS & DIAMONDBACK MOTH CATERPILLARS

• Sample 50 plants - treat when count is > 0.5 larval units per plant
• Weighting factor for larval unit determination:
  • Cabbage Looper: large=1.0 small=0.7
  • Imported Cabbageworm: large=0.07 small=0.1
  • Diamondback Caterpillar: any size=0.1

Heading or Sprout Development

CABBAGE APHIDS AND OTHER APHIDS

• Treat when 2% of plants are infested with > 5 aphids

IMPORTED CABBAGEWRM, CABBAGE LOOPERS & DIAMONDBACK MOTH CATERPILLARS

• Cabbage – treat when count is > 0.5 larval units per plant
• Broccoli, Cauliflower and Brussel Sprouts – treat when > 1 caterpillar per 25 plants

Plant Emergence to Three Leaf Stage

SPOTTED AND STRIPED CUCUMBER BEETLES 

• For wilt susceptible cucumbers and muskmelons – use systemic insecticide treatment at planting time Provisional threshold for pickling cucumbers – foliar insecticide when 20% of plants are infested with cucumber beetles

Three Leaf Stage to Harvest Maturity

MELON APHID

• Provisional threshold > 20% of runners have > 5
  aphids on leaves

THRIPS

• Heavy infestation, leaf injury, plants not actively
  growing

SPIDER MITES

• > 50% of runners show early leaf injury on crown
  leaves and live mites present

SPOTTED AND STRIPED CUCUMBER BEETLES

• Thresholds not available
• Treat moderate to high CB infestations levels on wilt susceptible varieties
• Treat all cucurbits when high CB infestations cause excessive fruit damage

LEAFHOPPERS

• Severe leaf injury expected to retard fruit maturity and affect yield

SQUASH VINE BORER

• As soon as moths are trapped

Bloom to Harvest

PLANT BUGS (LYGUS)

• Early bloom to harvest >6-10 adult/nymphs per 20
  sweeps
• After mature bud set >20-40 adults/nymphs per 20
  sweeps

CORN EARWORM

• > 50% of larvae are > 1/2"

Fordhook Lima Beans:

• Up to 4 weeks from harvest > 1 larvae per 6' of row
• Less than 4 weeks from harvest 3 larvae per 6' of
  row

Baby Lima Beans:

• > 1 larvae per 6' of row, from late flat pod stage to
  harvest

PEA APHID 

• 50 aphids per sweep or 5-10 per Plant

Early Fruit Set to Harvest 

GREEN PEACH APHID 

• Before fruit formation > 2 aphids per leaf
• Once fruit is present 4 aphids per leaf 

PEPPER MAGGOT 

• As soon as flies are caught on sticky traps 

EUROPEAN CORN BORER 

• When fruits are forming on plants > 25 moths
• black light trapped per 5 days
• Shorten treatment schedules if > 100 moths black light trapped per 5 days, or apply sprays according to specific pheromone trap catch instructions 

CORN EARWORM 

• When fruits are forming on plants, >100 moths black light trapped per 5 days, or apply sprays according to specific pheromone trap catch instructions

Early Fruit Set to Harvest 

POTATO FLEA BEETLE

•  >20% leaf loss 

COLORADO POTATO BEETLE 

• Overwintered >5 adults per 10 plant clusters and
• > 10% of shoots chewed off at ground level 

ALL STAGES

Chemical treatments: 

• Defoliation 20% and density per 10 plant clusters
• > 5 adults or > 40 small larvae or 15 large larvae or combination of any 2 stages, at 1/2 above levels 

Bt treatment: 

• 10% plant infestation,
• > 30% eggs hatched (trigger date)

Greater Than 12" Shoots to Bloom

GREEN PEACH APHID, POTATO APHID

• Prior to bloom - 2 per leaf
• During bloom - 4 per leaf
• Within 2 weeks of vine kill - 10 per leaf

MELON APHID

• Prior to bloom >1 per leaf
• During bloom > 2 per leaf
• Within 2 weeks of vine kill > 5 per leaf

POTATO LEAFHOPPER

• > 3 adults per sweep or > 1 nymph per 10 leaves

EUROPEAN CORN BORER

• 100 moths black light trapped per 5 days, or apply
  sprays according to specific pheromone trap catch
  instructions, or 5% of leaves are infested with egg
  masses.

Bloom to 50% Leaf Yellowing or Vine Kill

COLORADO POTATO BEETLE

• Defoliation > 30% and potential for further damage

SNAP BEAN INSECTS 

• Plant Emergence to 3rd Trifoliate Stage 

SEEDCORN MAGGOT 

• 5 to 10 maggots per seed 

THRIPS 

• > 6 per leaflet with leaf injury 

SPIDER MITES 

• > 20 live mites per leaflet 

BEAN LEAF BEETLE AND MEXICAN BEAN BEETLE 

• Pre trifoliate stage 6 or more per row foot
• Post-trifoliate stage 20% leaf loss, > 2 per plant 

Prebloom Stage (3rd Trifoliate to Bud) 

POTATO LEAF HOPPER 

• > 5 adults+nymphs per sweep 

MEXICAN BEAN BEETLE 

• > 20% defoliation 

BEAN APHID 

• 50% or more have 5 or more aphids per terminal, distributed throughout 

GREEN CLOVERWORM 

• >20% defoliation and >15 larvae < 1"per sweep 

Bloom to Harvest 

LEAFHOPPERS 

• During podset >25 per adults/nymphs per sweep
• During bloom >12 adults/nymphs per sweep 

MEXICAN BEAN BEETLE 

• Defoliation > 10% during podding and population present 

EUROPEAN CORN BORER

•  >25 moths black light trapped per 5 days, or apply sprays according to specific pheromone trap catch instructions 

CORN EARWORM 

• > 100 moths black light trapped per 5 days, or apply sprays according to specific pheromone trap catch instructions

CUTWORM 

• 1-2 leaf - 10% damaged plants
• 3-4 leaf - 5% damaged & 4 larvae per 100 plants 

WHITE GRUB 

• Heavy soils - 2 per sq. ft.
• Sandy soils - 1 per sq. ft. 

WIREWORM 

• 1 per bait station 

SLUG 

• Spike to 3 leaf - 5 per plant 

STALKBORER

• 4%, 6% or 10% damaged at the 2, 3 or 4 leaf stage 

ARMYWORM 

• 35% of plants > 50% defoliated & larvae < 3/4” 

EUROPEAN CORN BORER 

• Not irrigated - 80% infested with live larvae
• Irrigated - 50% infested with live larvae 

CORN ROOTWORM

• 1 Western or 2 Northern per plant 

FLEA BEETLE 

• For Stewart’s wilt susceptible varieties from spike stage to silking >5% of plants infested 

CORN EARWORM 

• At tassel emergence >15% tassel infestation From tasseling to harvest -1st spray at 30% silk and apply subsequent sprays according to 5-day black light trap catch, or apply sprays according to specific pheromone trap catch instructions

Plant Emergence or Transplant to 10" Plants 

COLORADO POTATO BEETLE 

Overwintered CPB: 

• At plant emergence - adults reducing plant densities below recommended levels for maximum yield
• Actively growing > 15 adults per 10 plants 

10" Plants to Early Fruit Set 

COLORADO POTATO BEETLE 

All stages 

• Chemical Treatments: Defoliation 20% throughout and > 20 adults and/or larvae per 10 plants
• Bt Treatment: 10% plant infestation with egg masses and > 30% eggs hatched (trigger date) 

10" Plants to Early Fruit Set 

POTATO APHID, GREEN PEACH APHID 

• Natural controls not present and > 20% of terminals are infested 

SPIDER MITES 

No specific threshold - treat during hot dry weather when damage is noticed due to heavy infestations 

HORNWORMS 

20 % defoliation and further damage potential 

Early Fruit Set to Fruit Maturity or Vine Kill 

COLORADO POTATO BEETLE 

• Defoliation potential > 10% or > 2% of plants have at least 1 freshly-injured fruit 

TOMATO PINWORM 

• Active leaf mines > 0.7 per trifoliate leaf 

TOMATO FRUITWORM

•  > 5 damaged fruit in sample of 200 (2.5% damage)

ANNUAL WEEDS 

# per 25 sq. ft. to cause 10% loss: 

• Cocklebur - 3
• Jimsonweed or Velvetleaf- 3
• Pigweed, Lambsquarters or Morningglory - 5
• Annual grasses - 20 

PERENNIAL WEEDS 

% of field infested: 

• Light <5%
• Moderate <10%
• Heavy <30%
• Severe >30% 

NOXIOUS WEEDS 

no threshold, eliminate all