Updated: July 26, 2021
This reference was adapted from the University of Maryland and Delaware Cooperative Extension Filed Crop and Vegetable IPM Pest Management Manuals.
Compiled R. D. Myers 2000; Updated 2018
Compilation and layout assistance by Carol Jelich, Master Gardener, Anne Arundel County
Reviewed by Galen Dively, Terrance Patton, and Sandra Sardenelli, University of Maryland, College Park
ECONOMIC THRESHOLD
Level of pest activity when control action is suggested to prevent economic injury
COLE CROP INSECTS
| 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: Heading or Sprout Development |
| CABBAGE APHIDS AND OTHER APHIDS | Treat when 2% of plants are infested with > 5 aphids |
| IMPORTED CABBAGEWORM, 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 |
CUCURBIT INSECTS
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 |
Three Leaf Stage to Harvest Maturity | |
| 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 |
LIMA BEAN INSECTS
| 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 Baby Lima Beans:> 1 larvae per 6' of row, from late flat pod stage to harvest |
PEA INSECTS
| PEA APHID | 50 aphids per sweep or 5-10 per plant |
PEPPER INSECTS
| 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 mothstrapped per 5 days, average Shorten treatment schedules if > 100 moths trappedper 5 days |
| CORN EARWORM | When fruits are forming on plants, >100 moths trapped per 5 days (see sweet corn section for MDA Pest Survey website link) |
POTATO INSECTS
| Plant Emergence to 12" Shoots | |
| POTATO FLEA BEETLE | >20%leaf loss |
| COLORADO POTATO BEETLE | Overwintered >5 adults per 10 plant clusters and > 10%shoots chewed off at ground levelAll 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 |
| Greater Than 12" Shoots to Bloom | |
| 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 trapped per 5 days (reduce if host plants unavailable) 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 trapped per 5 days |
| CORN EARWORM | > 100 moths per 5 days |
SWEET CORN INSECTS
| 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 trap catch |
TOMATO INSECTS
| 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 |
| 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) |
WEEDS OF FIELD CROPS
| ANNUAL WEEDS | # per 25 sq. ft. to cause 10% loss: co*cklebur ------------------------------------------------ 3 |
| PERENNIAL WEEDS | % of field infested: Light <5% Heavy <30% Moderate <10% Severe >30% |
| NOXIOUS WEEDS | no threshold, eliminate all |
IPM DEFINITIONS
Economic Injury Level - EIL
“The lowest pest population density that will cause economic damage. At the EIL the Cost of Control equals the Benefit of Control.”
Economic Threshold (Action or Treatment Threshold) - ET
“The density of a pest at which control measures should be implemented to prevent an increasing pest population from reaching the EIL - ET is generally 80% of the EIL.”
