Fruit & Vegetable Crop Pest Management

Fruit & Vegetable Crop Pests

Guidelines and Recommendations

General

1. General Scouting Pattern: 5 consecutive plants in 10 locations for up to 50 acres; add one additional sampling location for every 10 acres of land; V- shape should be used to cover entire field

2. Before Heading: Be sure to check for insects feeding deep in the whorl

Pest

When to Sample

Action Threshold

Thrips Spring Planted; From transplanting/plant emergence to harvest 20 % plants infested – treat before thrips move deep into wrapper leaves
Aphids Generally Spring Planted; Seedling Stage Plants Rarely a problem in our area; 10 % of the plants with one or more colonies per plant
Imported Cabbageworm Spring Planted Cabbage; Seedling Stage to Harvest; overwinters in the Mid-Atlantic Pre-Heading: 20% plants infested
Heading to Harvest: 5% plants infested
Cabbage looper Generally a pest of fall planted cabbage; migratory pest; Can attack spring planted fields in June if migrates early to our area Pre-Heading: 20% plants infested
Heading to Harvest: 5% plants infested
Diamondback moth larva Spring and Fall Planted Fields; Significant problem with fall plantings; overwinters in the Mid-Atlantic Feeding in the heart preheading: 5 % infested
Feeding on wrapper leaves preheading: 20% infested plants
Heading to Harvest: 5 % infested plants

University of Delaware IPM Program
Joanne Whalen – Extension IPM Specialist

Bill Cissel – Extension IPM Agent

I. General Insect Scouting Guidelines

Begin scouting fields as soon as plants are transplanted or emerge from the ground. Certain insects can colonize a field very quickly and cause direct damage to emerging or newly transplanted plants. Others can transmit diseases. Twice weekly scouting may be necessary when population pressure is high and insects are developing quickly. Pay particular attention to the edges of fields, where localized “hot spots” of insect activity may be found. Before plants begin to vine, inspect each of 5 plants for general appearance and insect occurrence. After plants vine and individual plants are indistinguishable, inspect 10 leaves and 5 fruit at each of five plant areas in the field, recording insect presence and damage.

The following are the key insect/mites pests of cucurbits

SEED CORN MAGGOT

This insect is primarily a problem in early-planted fields, especially during cool, wet growing seasons. Only a few maggots per seed or plant can significantly reduce stands. Maggots overwinter as puparium in the soil with flies emerging as early as late February. Eggs are laid in freshly plowed fields as well as in greenhouse flats before transplanting into the field. Outbreaks are favored by planting into freshly plowed ground that is high in organic matter; freshly manured fields; and/or heavy crop residues (e.g. small grain covers) where spring tillage is delayed and/or surface residue is visible after spring tillage operations.

Monitoring and Decision-Making: Scouting and applying rescue treatments after the damage is observed are ineffective. Management options must be applied to high-risk fields prior to planting for direct-seeded fields or prior to laying the plastic strip for transplanting.

STRIPED AND SPOTTED CUCUMBER BEETLES

Both species of cucumber beetles are known to infest cucurbit fields. The striped cucumber beetle has a black head, yellow thorax and three black stripes along the length of its body. The spotted cucumber beetle is similar in size but has a yellowish-green body and 12 black spots on its back. Beetles overwinter in nearby hedgerows and woodlands feeding on alternate weed hosts in the early spring. As soon as melons are planted in May, beetles migrate to the field and begin feeding on young seedlings. Although most watermelon cultivars have good bacterial wilt resistance, heavy beetle populations (greater than 5 per plant) can severely affect stand establishment during the cotyledon stage. Once the first three leaves are established, plants generally compensate for damage and growth delays before harvest. In comparison, cucumbers and muskmelons are extremely susceptible to damage. Early detection and control is critical in these crops.

Monitoring and Decision-Making: Sampling should begin as soon as transplants are set in the field or at plant emergence. Sample fields twice a week, especially along field margins next to overwintering areas. During hot, windy days, look for beetles hiding in cracks in the soil surface and under the plastic mulch. Examine 5 plants in 5-10 locations throughout a field and count the number of beetles per plant. Foliar treatment will be needed if you find 2 beetles per plant and beetles are affecting stand establishment during the cotyledon stage for watermelons. Treatments may be needed sooner on fresh market cucumbers and muskmelons. Pickling cucumbers can compensate for at least a 10 percent stand loss. Beetles should be controlled before they feed extensively on cotyledons and first true leaves. Multiple applications are needed if beetles continue to re-invade fields.

MELON APHID

Melon aphids are the predominant species attacking cucurbits grown in the Mid-Atlantic region. They vary in size and color from light yellow, green to black. Infestations begin when winged forms fly to the fields in late May. In-season, only colonies of wingless forms are generally found on plants. They can be identified from other aphids by the black cornicles or “tailpipes” found on the abdomen. The cornicles are entirely black from the tip to where they attach to the abdomen. They feed mainly on the undersides of the leaves resulting in cupping of leaves, leaf distortion, plant stunting, and a reduction in the quality and quantity of fruit. In addition to feeding damage, the melon aphid is one of the chief vectors of cucumber mosaic virus. Infestations are usually higher in hot, dry summers following cool springs that reduced the efficiency of natural enemies. In addition, over fertilization with nitrogen can increase aphid populations.

Monitoring and Decision-Making: Scouting should begin as soon as plants form runners. Look for wilting and curled leaves that will be found in small-scattered spots throughout the field. Examine 5 runners in 5-10 locations throughout a field and record the percentage of runners with 5 or more aphids per leaf. The level of natural controls (e.g. lady beetles, lacewings, and parasitized aphids) should also be considered when making a treatment decision. A foliar treatment should be applied if beneficial insect populations are low and you find 20% or more of the runners infested with 5 or more aphids per leaf.

SPIDER MITES

Although spider mites can attack all cucurbits, they are a serious pest of watermelons, especially during hot, dry weather. Infested plants appear yellow and become visible from a distance. They are primarily found on the undersides of leaves making the leaves appear tan or yellow and have a “crusty appearance”. Mites feed on the plant sap and can defoliate vines in a few weeks in hot, dry weather. Defoliated plants tend to yield small, poor quality fruit.

Monitoring and Decision Making: Since mite infestations generally begin along field margins next to grassy areas, near rye windbreaks, and in the sandiest areas of fields, be sure to carefully sample these areas early in the season. Since we are limited in our insecticide control options, early detection is critical. Once populations explode in hot, dry weather, control is extremely difficult. Look for the early signs of white stippling on the crown leaves. Mites can be identified by shaking leaves onto a sheet of white paper and watching for moving specks or by using a hand lens to count the number of mites per leaf. Examine 5 crown leaves in 5-10 locations throughout a field for the presence of mites and feeding damage. A treatment should be applied when 20-30% of the crown leaves are infested with 1-2 mites per leaf. In addition, do not mow adjacent grassy areas or windbreaks that harbor mites and force mites to disperse into the field.

THRIPS AND LEAFHOPPERS

Thrips are generally a problem early in the season when plants are drought stressed. They are generally found on the undersides of leaves producing silver flecking near the large leaf veins. Examine 5 crown leaves in 5-10 locations for the presence of thrips and rate the feeding injury as light, moderate or heavy. . Although no thresholds are available, controls may be needed if the thrips population is heavy, leaf feeding is present and plants are not actively growing.

The potato leafhopper is the predominant species causing damage to cucurbits in this region. It is a migratory pest appearing in the Delmarva region in early May. Although generally a problem after bloom in cantaloupes and pumpkins, leafhoppers can damage watermelon during hot, dry weather. In combination with spider mites and thrips, economic losses can occur. Examine runners in 5-10 locations for the presence of leafhopper nymphs. A sweep net can also be used to sample for adults. Controls will be needed if “hopper burn” is detected on leaf edges and injury is expected to retard fruit maturity and yield.

 

II. General Disease Scouting Procedures

 

(a) Early Season: When plants begin to run (vine) or as bush types flower, select 5 representative sites from which to make counts. At each site inspect 2 older leaves on each of 5 plants for presence of each disease. During a wet spring particularly note presence of Septoria, scab, and angular and bacterial leaf spot, as subsequent fruit infection can occur. Record how many plants are infected. A total of 50 leaves should be inspected for the field.

(b) Later Season: After the rows close for the vining types or for bush types when plants have fruit set and fruit is enlarging, it is better to examine 10 leaves/area and 5 fruit at each location. Initial occurrence of powdery mildew will be found on summer squash so check these plantings first for the presence of mildew. Calculate and record the percent plants infected. In addition, give each field an overall disease severity rating for each disease present according to the following scheme:

 

1 = first occurrence of the season on leaves
2 = few leaves (1-3) of each plant infected
3 = moderate number of leaves (3-8) infected on each plant, first occurrence on stems and fruit
4 = each plant severely infected (9-all leaves), infected stems and fruit now common
5 = total vine destruction with heavy fruit infection

 

The presence of all diseases except Phytophthora blight, Fusarium crown and foot rot, Fusarium wilt, and Sudden wilt will be evaluated on a percent plants infected basis. Phytophthora and Fusarium crown rot and the wilt diseases will be noted when present since they can be somewhat sporadic in their occurrence on a given farm. It is also important that the different crops be scouted separately for purposes of disease evaluation; however, cross-infection is common, especially if the different cucurbits are grown in close proximity to one another.

(c) Generalized Disease Occurrence

 

The presence of all diseases except Phytophthora blight, Fusarium crown and foot rot, Fusarium wilt, and Sudden wilt will be evaluated on a percent plants infected basis. Phytophthora and Fusarium crown rot and the wilt diseases will be noted when present since they can be somewhat sporadic in their occurrence on a given farm. It is also important that the different crops be scouted separately for purposes of disease evaluation; however, cross-infection is common, especially if the different cucurbits are grown in close proximity to one another.

(c) Generalized Disease Occurrence

 

Initially at Border Rows Localized Systematic Sampling & Action Thresholds
Viruses, especially CMV introduced by aphids (other viruses may be more randomly distributed) Fusarium Crown and foot rot; Phytophthora Blight; poorly drained areas of field Angular leaf spot (a), Bacterial leaf spot (a) & Bacterial wilt (b), Scab (a, c) & Septoria leaf spot (a, c) Powdery (a) & Downy mildew (a) Alternaria leaf blight (a), Gummy stem blight (b) & Anthracnose (b),Plectosporium blight (formerly Microdochium blight) (b) & Ulocladium leaf spot (a) (Fusarium crown and foot rot, Fusarium wilt & Sudden wilt can be scouted for, but no controls are available).

 

Action thresholds

 

a = symptoms on one leaf of 25-50 examined
b = preventative when fruit begin to develop (GSB ) or if symptoms are present.
c = mean temperatures (58-64F for Septoria) (63-70F for Scab) with wet weather for spore dispersal and infection.
d = monitor insect vectors to initiate treatment.

 

(d) Disease Occurrence on Specific Cucurbits

 

The importance of each disease for a particular cucurbit crop is given, where NA = not applicable (resistant varieties exist, as noted, or plants are not susceptible); X = occurs, but not damaging levels; XX = moderate susceptibility; XXX = severe.

(1) Cucumbers

 

(a) Bacterial

 

NA, Res. Angular leaf spot – Most cucumber varieties are resistant, so if leaf spots occur on cucumber, the disease could be Ulocladium leaf spot (see below); ALS is most common still on Watermelons.

XXX Bacterial wilt — Can infect all cucurbits except watermelon and gourds – Control is based upon control of the cucumber beetle vector.

(b) Fungal

 

X Downy mildew – Infects all cucurbits, but pathotypes vary – Inoculum introduced into the area; requires warm and moist conditions for infection and subsequent spread

XXX Fruit Rots – most important on for pickling cucumbers

 

(2) Melons

 

(a) Bacterial

 

XX Bacterial wilt — Can infect all cucurbits except watermelon and gourds – Control is based upon control of the cucumber beetle vector.

 

(b) Fungal

 

XX Alternaria leaf blight – Can be a problem if short rotations are used (less than 2 years). Fungus is seedborne, so could occur any season.

XX Anthracnose — Can infect all cucurbits, but pathotypes vary – A problem during warm (hot) seasons with adequate rainfall and high relative humidity.

X Fusarium crown and fruit rot – A soilborne pathogen, it can cause a crown or foot rot of many cucurbit seedlings, or a fruit rot of pumpkin and winter squash; control based on 3 year rotation.

XXX Fusarium wilt – This soilborne pathogen is specific to melon; Previous history of farm reporting loses is important; 5-7 year rotation.

XX Downy mildew – Infects all cucurbits, but pathotypes vary – Inoculum introduced into the area; requires warm and moist conditions for infection and subsequent spread

XX Gummy stem blight (black rot on fruit) — All cucurbits – Symptoms can be variable on leaves, often without characteristic fruiting bodies which appear as black dots (pycnidia or perithecia of fungus).

X Phytophthora blight — All cucurbits – Soilborne disease dependent on excess moisture (rainfall or irrigation) to spread inoculum in poorly drained areas of the field.

 

X Powdery mildew — All cucurbits – Occurs every season, beginning first on older leaves in crown of plant. Some melon varieties have resistance to certain races of PM.

 

X Scab — Most cucurbits – Important at beginning and during a cool and wet season.

 

X Septoria leaf spot — Important at beginning and during a cool and wet season; scout for 1-2 mm whitish spots with black pycnidia (or water-soaked spots if frequent rains have occurred). Rarely a serious problem on foliage, and no fruit infection has been noted in melons.

 

(c)Viral

XXX Cucumber mosaic — All cucurbits— Usually the first virus infecting melons; wide host range including lettuce, pepper, and tomato. Use of early season row covers may exclude aphids transmitting virus.

XXX Watermelon mosaic — All cucurbits— Usually the second most important virus infecting melon.

XX Papaya ringspot-type W — All cucurbits

XX Zucchini yellow mosaic – All cucurbits.

 

III. General Weed Scouting

 

Making a Weed Map: Weeds or weed species may not be evenly distributed over a field. Where localized areas of severe infestations are found or atypical conditions exist (poorly drained area, high spots, field edges), weed infestations may be recorded on a weed map. A weed map illustrates problem areas and provides information for future control decisions. When weed maps are kept over a period of years for a given field, changes in location and population can be noted and control decisions adjusted accordingly. Areas of severe infestations can be targeted for specific control practices, rather than treating a larger area needlessly or failing to control problems at all.

First, make a rough sketch of the field, including landmarks, boundaries, crop row direction, compass directions, roads, planting date, date of map preparation, and any other important details. Then the following information should be indicated on the map:

Weed species, or if this is unknown, some effort should be made to distinguish annuals from perennials, and broadleaf species from grasses and from yellow nutsedge.

Abundance of each species estimated according to the following system: 0 = None; 1 = Scattered, few weeds; 2 = Slight, 1 weed /6 row feet; 3 = Moderate, 1 weed/3 row feet; 4 = Severe, > 1 weed/3 row feet

Distribution of weeds in the field is important and can be rated as follows: SPOTTY – found in a few places around the field; LOCAL – found in a small portion of the field; GENERAL – found throughout the field

Weed size – The following size ratings can be used: WHITE SPROUTS – seeds are just germinating or emerging; TINY – weeds show only cotyledons or first true leaf; SMALL – weeds less than 1″ tall or less than the diameter of a quarter; LARGE – weeds more than 1″ tall or more than the diameter of a quarter.

Throughout the season, at least two weed maps should be prepared. Timing should be as follows:

 

1. Early – soon after planting: Purpose: to evaluate the success of the current season program.

2. After Harvest. Purpose: to evaluate next season’s weed control needs.

 


 

University of Delaware IPM Program

 


Joanne Whalen – Extension IPM Specialist

 

Bill Cissel – Extension IPM Agent

I. Pre-planting Decisions

  • Select varieties with disease resistance for downy mildew.
  • Rotate fields with non-legume crops and plow under crop residue to avoid root rot.

II. Emergence to Third Trifoliate

A. Spider Mites:

  • Sampling: Field should be scouted on a weekly basis from early July through early August, especially during hot, dry seasons. Begin sampling along field borders and look for signs of white stippling near the base of leaves. Examine 10 leaves in 5 to 10 locations throughout a field and count the number of mites per leaf.

  • Thresholds: Treatment is recommended when white stippling is first noticed and you find 20 mites per leaflet. Rainfall and high humidity can help to reduce mite development and survival. However, rain will not provide enough suppression when heavy populations are developing under high temperatures.

B. Mexican Bean Beetle and Bean Leaf Beetle

  • Sampling: Begin sampling fields at plant emergence especially along field margins next to overwintering sites. Record the percent of stand reduction, estimate the percent defoliation and count the number of beetles per plant.

  • Thresholds: (a) Before the First Trifoliate: 6 or more beetle per row foot and 75% stand reduction (b) First to Third Trifoliate: 2 or more beetles per plant and 20% defoliation

III. Prebloom Stage: Third Trifoliate to Pre-Bud

A. Potato Leafhopper

  • Sampling: Using a standard 15-inch diameter sweep net, take 10 sweeps in 10 locations throughout a field. Count the number of leafhopper adults and nymphs and calculate the number of leafhoppers per sweep.
  • Thresholds: Treatment should be applied if populations exceed 5 or more per sweep.

B. Mexican Bean Beetle

  • Sampling: At this stage, counting the number of beetles per plant is too time consuming. Instead, estimate the percent defoliation to the nearest10% on 5 plants in 5 to 10 locations throughout a field. It is also important to determine the predominant life stage present (eggs, adults, larvae or pupae).
  • Thresholds: A treatment should be applied if defoliation exceeds 20%. Controls should be delayed if the predominant life stages are eggs and/or pupae.

C. Bean Aphid

  • Sampling: Aphids are generally found on the lower leaf surfaces and terminal buds. Sample 5 terminals in 5-10 locations throughout a field and count the number of terminals infested with 5 or more aphids.
  • Thresholds: Treatment is recommended when populations are found throughout a field and 50% or more of the terminals have 5 or more aphids per terminal.

D. Green Cloverworm

  • Sampling: Using a standard 15-inch sweep net, take 10 sweeps in 10 locations throughout a field and count the number of larvae per sweep.
  • Thresholds: Apply an insecticide treatment if defoliation exceeds 20% and the cloverworm numbers exceed 15 larvae per sweep.

IV. Bud Stage through Harvest

A. Stinkbugs and Lygus Bug

  • Sampling: Sampling should begin at the bud stage and continue on a weekly basis until 5 days from harvest. Using a standard 15-inch sweep net , take 10 sweeps in 10 locations throughout a field. Sampling should be done early in the morning or late afternoon when insects are most active.

  • Thresholds: Treatment should be applied if the adult and/or nymphal count exceeds 15 per 50 sweeps.

B. Corn Earworm

  • Sampling: Monitoring should begin at full bloom and continue on a twice a week basis until harvest. Using a 3 foot drop cloth placed between two rows and shaking the plants over the cloth, sample a minimum of 10 locations throughout a field. Each shake sample covers 6 foot of row. Count the number of larvae and estimate the average larval size.

  • Thresholds: When possible, treatment should be delayed until at least 1/3 of the larval population has reached ½-inch in size. Treatment should be applied when you find one or more larvae per 6 foot of row.


 

University of Delaware IPM Program
Joanne Whalen – Extension IPM Specialist

Lima Bean Breeding Overview

I. Pre-planting Decisions

  • Use a combination of cultural practices to reduce problems from seed corn maggot: plow down cover crops 3-4 weeks before planting; completely bury cover crops or previous crop residues to reduce adult fly attraction to rotting organic matter; avoid use of heavy manure applications close to planting and allow manure to age before incorporating; and in direct seeded field attach a set of drag chains behind the planter to reduce the moisture gradient.

II. Plant Emergence to Three Leaf Stage
A. Striped and Spotted Cucumber Beetles

  • Sampling: The greatest amount of feeding injury and disease transmission occurs from planting until runner formation Sampling should begin as soon as transplants are set in the field or at plant emergence. Sample fields twice a week, especially along field margins next to overwintering areas. During hot, windy days, look for beetles hiding in cracks in the soil surface and under the plastic mulch. Examine 5 plants in 5-10 locations throughout a field and count the number of beetles per plant.

  • Thresholds: Even if soil insecticides are used, fields should be checked to be sure that control is adequate, especially during cool, wet conditions. Treatments should be applied before adult beetles feed extensively on cotyledons and first true leaves. Sprays should be applied at plant emergence and repeated weekly if beetles continue to invade fields.

III. Three Leaf Stage to Harvest Maturity

A. Melon Aphid

  • Sampling: Scouting should begin within a week of planting. Once runner form, look for wilting and curled leaves that will be found in small-scattered spots throughout the field. Examine 5 plants in 5-10 locations throughout a field and record the percentage of plants with 5 or more aphids per leaf. The level of natural controls (e.g. lady beetles, lacewings, and parasitized aphids) should also be considered when making a treatment decision.

  • Threshold: A foliar treatment should be applied if beneficial insect populations are low and you find 20% or more of the plants infested with 5 or more aphids per leaf.

B. Spider Mites

  • Sampling: Since infestations generally begin along field margins next to grassy areas, near rye windbreaks, and in the sandiest areas of fields, be sure to carefully sample these areas early in the season. Look for the early signs of white stippling on the crown leaves. Mites can be identified by shaking leaves onto a sheet of white paper and watching for moving specks or by using a hand lens to count the number of mites per leaf. Examine 5 crown leaves in 5-10 locations throughout a field for the presence of mites and feeding damage.

  • Thresholds: A treatment should be applied when you find  20-30% infested crown leaves with 1-2 mites per leaf.  In addition, do not mow adjacent grassy areas or windbreaks that harbor mites and force mites to disperse into the field.

C. Thrips

  • Sampling and Decision-Making: Thrips are generally found on the undersides of leaves producing silver flecking near the large leaf veins. Examine 5 crown leaves in 5-10 locations for the presence of thorps and rate the feeding injury as light, moderate or heavy. Although no thresholds are available, controls may be needed if the thrips population is heavy, leaf feeding is present and plants are not actively growing.

D. Potato Leafhopper

  • Sampling and Decision-Making: Examine runners in 5-10 locations for the presence of leafhopper nymphs. A sweep net can also be used to sample for adults. Controls will be needed if hopper burn is detected on leaf edges and injury is expected to retard fruit maturity and yield.

E. Striped and Spotted Cucumber Beetles

  • Sampling: After runners form, transmission of disease is less likely and stem damage is rarely economic. However, if beetle populations are high infestation levels should be rated as light, moderate, or heavy.

  • Thresholds: Treatment should be applied if adults are feeding on small fruit resulting in reduced quality. In cantaloupes, high beetle populations before and after bloom should be controlled to avoid larval damage to the surface of the rind where the fruit meets the soil surface.

I. Pre-planting Decisions

  • Rotate field away from previous years solanaceous crop.
  • Dispose of cull piles
  • Use certified seed potatoes
  • Eliminate volunteers
  • Obtain access to weather-station information for late blight forecasts

II. Plant Emergence to 12 Shoots (scout twice weekly)

A. Flea Beetle: Damage will appear as small round holes in the leaves.

  • Sampling: if small round holes are present in the leaves, take 10 sweeps in 10 locations. Also, rate the infestation level as absent, light, medium or heavy.
  • Threshold: Although generally not a problem when soil systemic insecticides are used, the feeding injury should not exceed 20% leaf loss. A treatment should be considered if you find 2 or more beetles per sweep and defoliation is greater than 20%.

B. Overwintered Colorado Potato Beetle (CPB) Adults

  • Sampling: Begin scouting at plant emergence for adults. Fields should be sampled twice a week. Be sure to watch for movement of adults from adjacent fields that were planted in a host crop the previous season. Check for adult beetle on 5 consecutive in 10 locations. Record the number of beetles and the percent defoliation.
  • Threshold: 5 adult beetles per 10 plants and greater than 10% defoliation.

C. Colorado Potato Beetle (CPB) – All Life Stages

  • Sampling: Begin scouting fields at plant emergence for eggs, small larvae (first and second instars), large larvae (third and fourth instars), and adults. Check 5 consecutive plants in 10 locations for fields up to 40-50 acres in size.
  • Thresholds: 
 

Number of CPB per 50 Plant /Stem Sample

  Adults Small Larvae Large Larvae
Low 0-15 0-75 0-30
Medium 16-24 76-199 31-74
High 25 or > 200 or > 75 or >

 

  • Treat when you find the high level of any one stage present or
  • Treat when you find any two life stages at the medium level
  • A defoliation threshold of 20% should also be considered for Superior potatoes. This will vary with the variety and the producer.

D. Aphids

  • Sampling: Sample for aphids at the same ten sites sampled for CPB
    Collect 5 leaves at each of the 10 sites site but not from consecutive plants
    Early Season: collect leaves from the entire plant
    Mid-Season: concentrate on sampling from mid-lower sections of the plant

  • Thresholds
    Green Peach Aphid and Potato Aphid

Prebloom:

Prebloom: 2 per leaf (100/50 leaves)
Bloom: 4 per leaf (200/50 leaves)
2 weeks from vine death: 10 per leaf (500 per 50 leaves)

Melon Aphid:
At all stages, reduce the threshold per leaf by one half.

E. Late Blight

  • Sampling: Look for large, black or purplish lesions on stems or leaves and the telltale white mold growth usually on the undersides of the foliage. Be sure to check the leaves and stems under the crop canopy where the disease is most likely to get established first. Scouting should be concentrated in low-lying areas, field edges along creeks and ponds, near center pivot irrigation rigs, and in areas near woodlots or any area where leaves remain wet for long periods of time.

  • Threshold: Although no threshold is available, the use of prediction systems can be used to time fungicide applications. The first fungicide should be applied when 18 severity values are accumulated.

III. Greater than 12 shoots (> 12 inches) to Harvest

A. Colorado Potato Beetle – sample as above growth stages

B. Aphids – same as above growth stages

C. Potato Leafhopper

  • Sampling: Begin sampling as soon as leafhopper adults are first active in alfalfa in the area or when adults are first noticed jumping from the foliage as you sample for other insect pests. Take 10 sweeps in 10 locations for adults as you are sampling for other pests. As you sample for aphids on the leaves, be sure to count the number of nymphs per leaf as well.

  • Thresholds:
    • Treat if you find 0.5 adults per sweep and 0.1 nymphs per leaf or
    • Treat if you find 0.5 – 1 adult per sweep and nymphs and/or adults have been present for > 2 weeks or
    • Treat immediately if you find 1 – 1.5 adults per sweep and nymphs are
      present or within one week if no nymphs are detected
    • Treat immediately if you find > 1.5 adults per sweep

D. European Corn Borer (ECB)

  • Sampling: Be sure to watch local blacklight trap catches and take note of ECB moths flushed out of the plant canopy as you sample for other pests. One moth catches in the BLT reach 10 per night, begin looking for small entrance holes of small larvae entering the leaf petioles, leaf mid-ribs, and upper nodes on 5 main shoots in each of 10 locations to determine the percent infested shoots

  • Threshold:
    • The first treatment should be applied when 10 % (fresh market) or 25% (processing) of the shoots show at least one entrance hole caused by small larvae.
    • Fields should be re-sampled within 5 days of a treatment to determine if additional egg hatch and terminal damage has occurred .
    • A second treatment should be applied 7-10 days after the first treatment if moth catches are above 10 per night and terminal injury has increased.

E. Late Blight – Sample same as above. The use of prediction systems can now be used to determine spray intervals for late blight.


 

University of Delaware IPM Program

Joanne Whalen, Extension IPM Specialist

I. Pre-planting Decisions

Use a combination of cultural practices to reduce problems from seed corn maggot: plow down cover crops 3-4 weeks before planting; completely bury cover crops or previous crop residues to reduce adult fly attraction to rotting organic matter; reduce use of heavy manure applications and let manure age before incorporating; and use a set of drag chains behind the planter during seeding to reduce the moisture gradient.

  • Use a seed treatment containing chlorpyrifos or thiamethoxam if a combination of factors favoring seed corn maggot exist.
  • Obtain access to weather-station information for white mold forecasts
  • Rotate fields with non-legume crops and plow under crop residue to avoid root rot
  • Select varieties with rust resistance

II. Emergence to Third Trifoliate

A. Thrips:

  • Sampling: Sample for thrips from plant emergence through bloom. Collect 5 leaves in each of 10 locations throughout the field and count the number per leaflet. Leaflets should be selected from the middle and top half of non-consecutive plants.
  • Thresholds: An insecticide treatment may be needed if thrips populations exceed 6 per leaflet. If plants are drought stressed and other insects are present, the threshold may need to be reduced by one third to one half.

B. Spider Mites:

  • Sampling: Field should be scouted on a weekly basis from early July through early August, especially during hot, dry seasons. Begin sampling along field borders and look for signs of white stippling near the base of leaves. Examine 10 leaves in 5 to 10 locations throughout a field and count the number of mites per leaf.
  • Thresholds: Treatment is recommended when white stippling is first noticed and you find 20 mites per leaflet. Rainfall and high humidity can help to reduce mite development and survival. However, rain will not provide enough suppression when heavy populations are developing under high temperatures.

C. Mexican Bean Beetle and Bean Leaf Beetle

  • Sampling: Begin sampling fields at plant emergence especially along field margins next to overwintering sites. Record the percent of stand reduction, estimate the percent defoliation and count the number of beetles per plant.

  • Thresholds: (a) Before the First Trifoliate: 6 or more beetle per row foot and 75% stand reduction (b) First to Third Trifoliate: 2 or more beetles per plant and 20% defoliation

III. Prebloom Stage: Third Trifoliate to Pre-Bud

A. Potato Leafhopper

  • Sampling: Using a standard 15-inch diameter sweep net, take 10 sweeps in 10 locations throughout a field. Count the number of leafhopper adults and nymphs and calculate the number of leafhoppers per sweep.
  • Thresholds: Treatment should be applied if populations exceed 5 or more per sweep.

 

B. Mexican Bean Beetle

  • Sampling: At this stage, counting the number of beetles per plant is too time consuming. Instead, estimate the percent defoliation to the nearest10% on 5 plants in 5 to 10 locations throughout a field. It is also important to determine the predominant life stage present (eggs, adults, larave or pupae).
  • Thresholds: A treatment should be applied if defoliation exceeds 20%. Controls should be delayed if the predominant life stages are eggs and/or pupae.

C. Bean Aphid

  • Sampling: Aphids are generally found on the lower leaf surfaces and terminal buds. Sample 5 terminals in 5-10 locations throughout a field and count the number of terminals infested with 5 or more aphids.
  • Thresholds: Treatment is recommended when populations are found throughout a field and 50% or more of the terminals have 5 or more aphids per terminal.

D. Green Cloverworm

  • Sampling: Using a standard 15-inch sweep net, take 10 sweeps in 10 locations throughout a field and count the number of larvae per sweep.
  • Thresholds: Apply an insecticide treatment if defoliation exceeds 20% and the cloverworm numbers exceed 15 larvae per sweep.

E. European Corn Borer

  • Sampling: If egg hatch occurs before bloom, young larvae feed on the leaves for a
    7-10 days before boring into the stems. Sample 5 plants in 5-10 locations for the presence of small larvae beginning to bore into stems. Blacklight trap counts over 20 moths per night also indicate the potential for stem feeding.
  • Thresholds: Treatment should be applied at the pre-bud stage when ECB moth catches exceed 20 per night in local blacklight traps and/or when first small larvae can be found boring into stems.

IV. Bud Stage to Harvest

A. European Corn Borer (ECB):

  • Sampling: Sampling is based on monitoring moth catches in local blacklight traps. For the most precise decisions, traps should be placed within one mile of each field. Traps should be serviced 3 times per week, preferably daily when moth activity increases.

  • Thresholds: The most critical time for corn borer treatment occurs at the bud-early bloom and pin stages. As a general guideline, treatment should begin when trap catches average 5 ECB moths per night. However, if moths can be observed readily in a field and trap catches have not reached 5 per night, sprays should still be applied at the bud-early bloom and pin stages. After the pin spray, the following thresholds and spray intervals should be used:

Number ECB Moths/ 5 Days Spray Interval
less than 10 no spray
11 – 25 7 Day
26 – 50 6 Day
51 – 75 5 Day
76 – 250 4 Day
250 + 3 Day

 

B. Corn earworm (CEW)

  • Sampling: Blacklight traps, pheromone traps, and direct observation of moths in fields should be used to monitor moth activity. A standard drop cloth can be used to detect small larvae.
  • Thresholds: As a general guideline, sprays should be applied on a 3-7 day schedule when blacklight trap catches exceed 20 per night. The spray interval will vary depending on corn borer moth activity and temperature.

C. White Mold

  • Sampling: Watch for the development of white mold, especially in narrow row plantings
  • Thresholds: Treatments will be needed when the soil is moist for 6-10 days before bloom. Treatments should be applied when 70 to 80 percent of the plants have one or more blossoms open. A second treatment is needed in 5 to 6 day if the soil remains wet and blossoms are still present.

 

University of Delaware IPM Program
Joanne Whalen – Extension IPM Specialist
 Bill Cissel – Extension IPM Agent

I. Pre-planting Decisions

  • Site selection and crop rotation for disease management
  • Use a combination of cultural practices to reduce problems from seed corn maggot: plow down cover crops 3-4 weeks before planting; completely bury cover crops or previous crop residues to reduce adult fly attraction to rotting organic matter; reduce use of heavy manure applications and let it age before incorporating; and attach a set of drag chains behind the planter during seeding to reduce the moisture gradient.

II. Spring Planted Spinach

A. Seed Corn Maggot

  • Sampling and Decision Making: No sampling methods are available for seed corn maggot before planting. During cool, wet conditions, a combination of the above cultural practices and a broadcast application of an insecticide will be needed to achieve effective control.

B. Aphids

  • Sampling: Check 10 plants in 10 locations for the presence of aphids. Be sure to sample the undersurface of leaves.
  • Thresholds: On seedling stage spinach, controls should be applied if you find one aphid per plant. In established fields, apply treatments if you find 4-10 aphids per plant.

C. Flea Beetles

  • Sampling: Monitor newly emerged seedlings for damage which appears as small pits or irregularly shaped holes.
  • Thresholds: A treatment should be considered if you find several damaged rows. Spot treatment of outside rows can be effective.

III. Fall Planted and Overwintered Spinach

A. Garden Webworm and Beet Webworm

  • Sampling: Check for small larvae feeding in the leaves and buds of small plants. Examine 10 plants in 10 locations throughout a field.
  • Thresholds: Treatments should be applied when 5% of the plants are infested with small larvae and before significant webbing has occurred.

B. Beet Armyworm

  • Sampling: Once seedlings emerge, check fields twice a week for small larvae. Check 10 plants in10 locations count the number of larvae per plant.
  • Thresholds: On seedling plants, treatment should be applied if you find one larva for every 10 plants. On established plants, treatment should be applied if you find one larva for every 2 plants.

C. Aphids

  • Sampling: Check 10 plants in 10 locations for the presence of aphids. Be sure to sample the undersurface of leaves.
  • Thresholds: On seedling stage spinach, controls should be applied if you find one aphid per plant. In established fields, apply treatments if you find 4-10 aphids per plant.

D. Leafminers

  • Sampling: Check young seedlings on a weekly basis for mining on the cotyledons and first true leaves. Examine 10 plants in 10 locations. Be sure to examine the undersurface of the leaves where the mines are most obvious.

  • Thresholds: Treatment should be applied when you find eggs or mines on 50% of the plants or if you find an average of one or more mines per leaf. As a field approaches harvest, treatments should be applied so that no more than 5% of the leaves have mines.

 

 

University of Delaware IPM Program
Joanne Whalen – Extension IPM Specialist

I. Plant Emergence Until Tassles Visible:

Examine 10 consecutive plants in 10 locations for the presence of insect feeding damage for a field up to 50 acres in size; Add one additional sampling site for each additional 10 acres

Pest Species

When to Sample

Action Threshold

Flea Beetle Emergence to 6-Leaf Stage 5 % of the plants infested
Cutworms Emergence to 6-Leaf Stage 1-2 leaf stage: 10% of plants with feeding or 3 % cut plants and larvae present3-4 leaf stage: 5% plants cut and larvae present
European Corn Borer Early Whorl to Tassel Emergence-mainly a problem in early planted corn Early Season Varieties/Super Sweets/Sugar Enhanced: 15% plants infested’Silver Queen Type’: 30% plants infested
Fall Armyworm Emergence to Pretassel – early detection critical when worms are small; mainly a problem in late planted corn 12 – 15 % plants infested and worms less than one inch long – multiple applications may be needed
Sap Beetle Tasseling to Harvest 5% plants infested
Corn Leaf Rust Late June – Early July – emergence to late whorl note presence and absence esp on susceptible varieties

II. First Ear Shanks Visible Until Harvest:

  • The decision to treat is based on blacklight and pheromone trap catches.
    The first sprays should be applied when ear shanks are visible — once silk is present worms may already be in the ears.

Action Thresholds for Silk Stage Sweet Corn:

 

A. Based on Corn Earworm Blacklight Trap Catches (conservative system)

Number of Moths Caught per Seven Days Silk Spray Schedule
<1 No Spray
1 6 day
2 5 day
3 4 day
4-30 3 day
>30 2 day

B. Based on Corn Earworm Pheromone Trap Catches

Generally used as a guideline in combination with light trap information. Requires use of a wire mesh trap and Hercon CEW pheromone lure placed with the base of the trap at silk height in fresh silking corn. Check traps 3 times per week throughout the growing season.

Number of Corn Earworm Moths Caught
Per day Per 5 days Per week Spray Interval
<0.2 <1 <1.4 No Spray
0.2-0.5 1.0-2.5 1.4-3.5 6 day
0.5-1.0 2.5-5.0 3.5-7.0 5 day
1.0-13.0 5.0-65.0 7.0-91.0 4 day
>13.0 >65.0 >91.0 3 day

In some cases corn earworm catches are very low; however, corn borer and fall armyworm pressure is high. If no sprays are called for CEW, the following spray schedule should be used:

Corn Borer/Fall Armyworm/Sap Beetle Spray Schedule
ECB light trap catch is >100 per 5 days 4 day
ECB light trap catch is 51-100 per 5 days OR FAW infestations in whorl stage is >30% OR sap beetle infestation is > 10% 5 day
ECB light trap catch is 25-50 per 5 days & FAW infestations in whorl stage is <30% & sap beetle infestation is < 10% 6 day
ECB light trap catch is <25 per 5 days & FAW infestations in whorl stage is <30% & sap beetle infestation is < 10% No Spray

 

Pest Scouting Guidelines Treatment Thresholds General Comments
Cucumber Beetles Examine 5 plants in 5-10 locations for the number of beetles per plant and % plants showing injury (light, moderate, heavy) 2 per plant – Most important on young seedlings-Carefully check field margins, under plastic, cracks in ground around base of plants
Thrips Examine 5 crown leaves in 5-10 locations for the presence of thrips and feeding injury(silver flecks esp near large leaf veins) Leaf injury is heavy and plants are not actively growing Generally a problem early, when plants are drought stressed
Melon Aphid Examine 5 runners in 5-10 locations and record the % of the runners infested with 5 or more aphids per leaf 20% or more of the runners infested with 5 or more aphids per leaf – Generally occurs in spots- Be sure to note presence of beneficials
Spider Mites Examine 5 crown leaves in 5-10 locations for the presence of mites and mite injury 20-30% of the crowns infested with 1-2 mites per leaf – Be sure to sample carefully near rye strips and in the sandiest areas of the field
Leafhoppers

Examine 5 runners in 5-10 locations for the presence of leafhopper nymphs. A sweep net can also be used to check for adults.

Detection of “hopper burn” on leaf edges – Begin to watch for migrant adults after bloom 

Additional guidelines and recommendations for field crops.


 

Field Crop Pest Management >