Field Scouting and Economic Thresholds

Quick Links

• Alfalfa
• Canaryseed
• Canola
• Clovers
• Dry Beans
• Field Corn
• Flax
• Lentils
• Peas
• Potatoes
• Rye
• Small Grain Cereals (wheat, barley, oats)
• Soybeans
• Sunflowers

Alfalfa

Sap Or Fluid Feeders

• Lygus bugs/Alfalfa plant bug
  • Typical Damage: Field blooms poorly or not at all. Flower buds blasted, whitish, and dry; flowers dropping off before fully open. Collapsed seed.
  • When and How to Monitor: Look for plant bugs when monitoring alfalfa in June through mid-August. Make five 180º sweeps with a 15-inch (40 cm) insect net through alfalfa canopy at each sampling site. Record total number of plant and lygus bugs (both nymphs and adults) captured. Calculate average number per sweep.
  • Economic Threshold: Hay: Control not recommended. Seed alfalfa at bud and early bloom: 8 lygus bugs/sweep (40 in 5 sweeps); 4 alfalfa plant bugs/sweep; or 5 bugs if the plant bug population is a combination of lygus bugs and alfalfa plant bug. If insecticides are used, attempt to spray before the onset of bloom. Protecting insect pollinators in seed production fields is very important.
• Potato Leafhopper
  • Leafhoppers are most severe in new seedings and in regrowth under hot dry weather.
  • When and How to Monitor: Take 20 180º sweeps from 5 areas of the field. Avoid field edges. Determine the average number of potato leafhoppers per sweep.
  • Economic Threshold: For 9 cm stem height = 0.2 adult leafhoppers per sweep; 15 cm stem height = 0.5 adults per sweep; 25 cm stem height = 1 adult or nymph per sweep; 36 cm stem height = 2 adults or nymphs per sweep.
• Pea Aphid
  • Typical Damage: Suck juices from plants; stunt growth; cause premature drying.
  • When and How to Monitor: Look for when monitoring in July through August. Take 5 sweeps at each location. Monitor fields closely during periods of slow plant growth.
  • Economic Threshold: 100-200 aphids/180° sweep when crop is moisture stressed, or until mid-August.

Defoliators

• Alfalfa Weevil
  • Typical Damage: Feed on developing buds and leaves. Stunt growth.
  • When and How to Monitor: Start scouting fields in mid- May. Look for shot holes initially, then clipping along the edges of leaves and pinhole damage. For determining if levels are at threshold in hay crops, collect 30 stems in an M-shaped pattern, place them inside a white pail and beat them against the side to knock off larvae. Do not include younger first and second instar larvae (3 mm or less) in the counts. Determine the average height of the crop as well.
  • Economic Threshold:
    • Alfalfa Hay: One of the best control strategies is to cut fields for hay early. If early cutting of the hay crop is not possible, treatment thresholds are based on the following measurements of plant height and levels of larvae: <30 cm – 1 larva/stem; <40 cm – 2 larvae/stem; 3 larvae per stem is generally economical to control regardless of height of crop. On regrowth for second crop, 2 or more active larvae per crown (4 to 8 larvae/ft2) will require insecticide application.
    • Alfalfa Seed: 20 to 30 3rd or 4th instar larvae/sweep (90º = straight sweep) or 35 to 50% of foliage tips showing damage. In some instances it may be practical to just treat hotspots and not entire fields.

Canaryseed

Sap Feeders

• Aphids
  • When and How to Monitor: Start checking for aphids when monitoring during the early heading stage of canaryseed. The head should be bent and closely inspected for aphids hiding along the small stem inside the canaryseed head. Also check the stems, underside of leaves, and in the canaryseed boot.
  • Nominal Threshold: 10 to 20 aphids on 50% of the stems prior to the soft dough stage.

Canola

Scouting Calendar

Early-season: Flea beetles, cutworms, red turnip beetle, diamondback moth

Mid-season: Diamondback moth, cabbage seedpod weevil, grasshoppers

Late season: Bertha armyworm, diamondback moth, Lygus bugs, grasshoppers, alfalfa looper

• Cutworms
  • Typical Damage: Notched, wilted, dead, or cut-off plants (weed or crop seedlings). Plants missing from rows, bare patches appearing in field.
  • When and How to Monitor: Look for cutworms, and evidence of cutworm feeding, when monitoring canola in late May to mid-July. Often cutworms will be close to the cut or shriveled plants that they have just damaged. Cutworms will sometimes be most abundant in patches or a specific area of a field.
  • Nominal Threshold: 25-30% stand reduction. Sometimes it is most economical to just treat infested patches, and not whole fields.

Sap Or Fluid Feeders

• Lygus bugs
  • Typical Damage: Attacked buds appear shrunken and bleached white. Damaged seeds appear dark brown and shriveled.
  • When and How to Monitor: Monitor from when flowering is complete until seeds within the pod have become firm. Make 10 sweeps with a 38 cm diameter insect net at each of at least 5 sampling site. If while doing these samples populations appear to be of concern, take additional samples; a minimum of 15 samples is needed to accurately determine whether controls are economical. Sample canola for lygus bugs on a sunny day when the temperature is above 20°C and the crop canopy is dry.
  • Economic Threshold: 10-18 lygus bugs/10 sweeps from when flowering is complete and seeds are enlarging in the lower pods to when seeds in the lower pods are full size and translucent; and 15-25 lygus bugs/10 sweeps when seeds in the lower pods are green. Controls are not recommended when seeds are ripening (yellow or brown). When precipitation is greater than 100 mm from the onset of bud formation to the end of flowering, the crop may partially compensate for plant bug damage.
    • A table of specific economic thresholds for various expected values of canola seed and costs of control for lygus bugs in canola can be found at: http://www.gov. mb.ca/agriculture/crops/insects/fad12s00.html.
• Aphids
  • Economic Threshold: Control aphids in canola if densities exceed 25 aphids/10 cm shoot tip after flowering.

Defoliators

• Flea beetles
  • Typical Damage: Shot-holes in leaves to complete destruction of seedling plants in late May through June. Holes chewed in pods in August (occasional).
  • When and How to Monitor: Look for when monitoring in May through June when crop is in seedling stage. Examine 10 plants at random at each stop. Estimate overall percentage leaf loss.
  • Economic Threshold: When 25 percent of leaf surface is destroyed and flea beetles are present. If damage is only along the field margins and beetles are still congregated there, then control measures should be applied to the damaged areas only.
• Cabbage Seedpod Weevil
  • When and How to Monitor: Sample at 10 to 20 percent flower. Do 10 sweeps (180 degrees) at a minimum of 4 locations; field edge, 50 metres into the field, and repeat the 2 sets at the opposite end of the field. If weevil numbers are close to the threshold the estimate may be improved by taking additional samples.
  • Economic Threshold: 25 to 40 weevils per 10 sweeps.
• Diamondback moth
  • Typical Damage: Flowers clipped or chewed, outer layers of stem and pods chewed, holes chewed in pods.
  • When and How to Monitor: Look for when monitoring in late – May through early September. Observing for adults and larvae while taking sweep net samples can determine the presence and relative abundance of diamondback moth in the field. If levels appear to be of concern, shake plants within a 50 cm x 50 cm area and count larvae on the ground or surface (such as a sweep net) that plants were shaken over. Another alternative is to clip or pull the plants and knock over a light colored surface (such as a sweep net, jacket, hood of a car, etc.). Multiply by 4 to get the number of larvae per square metre. Do this in at least 5 areas of the field.
  • Nominal Threshold: 100 to 150 larvae/m2 in immature to flowering plants. 200 to 300 larvae/m2 in plants with flowers and pods.
    • Note that these threshold numbers are based on stands averaging 150-200 plants/m2. In areas where stands are thinner, the economic threshold should be lowered accordingly. A nominal threshold of 25-33% defoliation with larvae still present can be applied for canola at seedling stage.
• Bertha Armyworm
  • Typical Damage: Outer layers of stems and pods chewed resulting in whitish appearance, holes chewed in pods.
  • When and How to Monitor: Look for larvae when monitoring fields in late July through early August. At each stop, shake plants in a 1/4 m2 (50 cm x 50 cm) area and carefully check soil surface for dislodged larvae. During heat of the day, larvae will often be found under leaves on soil surface.
  • Economic Threshold: A loss of 0.058 bushels/acre for each larva/m2 can be expected. Multiplying 0.058 X average number of larvae per m2 X expected seed value (dollars/bushel) will determine the economic loss (in dollars/acre) due to the larvae. Only if control costs (insecticide plus application costs) can be applied for less than this economic loss will insecticide applications be economical. Yield loss may be greater for canola under moisture stress.
  • At an expected seed value of $6.00/bushel, the economic threshold will be between about 20 and 34 larvae/m2, depending on control costs. At an expected seed value of $8/bushel, the economic threshold will be between about 15 and 26 larvae/m2, depending on control costs. Tables showing specific economic thresholds at various expected seed values and control costs can be found at: http://www.gov. mb.ca/agriculture/crops/insects/fad03s01.html.

Clovers

Defoliators

• Sweetclover Weevil
  • Typical Damage: Adults chew crescent-shaped and jagged notches in leaves and can completely defoliate plants.
  • When and How to Monitor: Inspect clover seedlings for weevil damage in spring as the seedlings emerge. In midsummer and throughout August, inspect first-year clover stands for damage along crop margins. Invading weevils move into these stands only as far as necessary to satisfy their food requirements, so an insecticide application to affected field margins is usually all that is required. Visually estimating the number of weevils per plant must be done carefully because weevils fall from plants easily and are difficult to see on the ground.
  • Economic Threshold: 1st year stands: 1 weevil adult/ 3 seedlings (1/5 seedlings under dry conditions). 2nd year stands: 9-12 weevil adults/plant.

Dry Beans

Belowground Feeders and Cutworms

• Seedcorn Maggot
  • Typical Damage: Seedcorn maggot attacks bean seed, preventing sprouting or weakening seedlings. The yellowish white maggot is found burrowing in the seeds or emerging stem. Seedcorn maggots are usually most severe in wet, cold seasons and on high organic matter soils.
• Cutworms
  • When and How to Monitor: To find cutworms, dig in the soil to a depth of 2.5 to 5 cm at the base of recently damaged plants.
  • Nominal Threshold: Treatment is warranted when one cutworm or more is found per metre of row and the larvae are still small (less than 2 cm long).

Sap Feeders

• Leafhoppers
  • Typical Damage: Foliage becomes dwarfed, crinkled, and curled. Small triangular brown areas appear at the tips of leaves, gradually spreading around the entire leaf margin.
  • When and How to Monitor: Leafhopper adults are quick and can be observed by running your hand over the top of the plants as you approach them and observing adults that fly off the plants. On the same plants, turn over each leaf to determine the number of nymphs per trifoliate.
  • Economic Threshold: Unifoliate stage – 0.25 leafhoppers per trifoliate; second trifoliate stage – 0.5 leafhoppers per trifoliate; fourth trifoliate stage – 1.0 leafhopper per trifoliate; first bloom – 2.0 leafhoppers per trifoliate.

Defoliators

• Grasshoppers
  • Economic Threshold: Substantial yield loss does not occur until up to 35% defoliation occurs before bloom and 15% after bloom.

Field Corn

• Cutworms
  • Typical Damage: Notched, wilted, dead, or cut-off plants (weed or crop seedlings). Plants missing from rows, bare patches appearing in field.
  • When and How to Monitor: Look for cutworms, and evidence of cutworm feeding, when monitoring corn in late – May to mid-July. Often cutworms will be close to the cut or shriveled plants that they have just damaged. Cutworms will sometimes be most abundant in patches or a specific area of a field. At each stop, examine 100 plants in a row. Calculate percentage of plants cut off or showing leaf feeding.
  • Economic Threshold: When 2-4% of plants are cut below the ground or when 6-8% of plants are cut above the soil surface, and cutworms less than 1 inch long are present. Sometimes it is most economical to just treat infested patches, and not whole fields.
• European corn borer
  • Typical Damage: Shot-holes in leaves. Holes in stalk, tassels and ears. Damage may cause stalk breakage prior to harvest or cobs to fall to the ground. Nutrient flow in the plant may be restricted, resulting in smaller cobs. When and How to Monitor: Begin looking for European corn borer when field scouting in early July. At 5 locations, examine 10 plants for young larvae and egg masses. Calculate percentage of plants infested. Scout every 5 to 7 days until the end of July or larvae start to tunnel into the stalks.
  • Economic Threshold: The level of European corn borer where control becomes economical depends on the value of the crop, and cost of control. Information on determining specific economic thresholds for European corn borer in corn can be found at http://www.gov. mb.ca/agriculture/crops/insects/european-corn- borer.html, or from your local agriculture office. These thresholds are based on a 5% yield loss per corn borer per plant on average. If the majority of larvae have  bored into the stalk, do not apply insecticide, as they are ineffective once the larvae have entered the stalk.
• Armyworms
  • Economic Threshold: For corn past the 6-leaf stage, if 50% of the plants are showing damage and have larvae smaller than 2.5 cm (1 in.), insecticide treatment may be warranted. As long as the growing point of the plant is not damaged, the corn plant is usually able to recover from moderate feeding.

Flax

• Cutworms
  • Typical Damage: Notched, wilted, dead, or cut-off plants (weed or crop seedlings). Plants missing from rows, bare patches appearing in field.
  • When and How to Monitor: Look for cutworms, and evidence of cutworm feeding, when monitoring in late May to mid-July. Often cutworms will be close to the cut or shriveled plants that they have just damaged. Cutworms will sometimes be most abundant in patches  or a specific area of a field. In areas of the field where cutworm damage is noticeable, check around damaged plants in a 0.25 m2 (50cm x 50cm) area. Use trowel or shovel to carefully search through top 5 cm of soil for cutworm larvae. Multiply the number of cutworms found by 4 to get the number per m2. Repeat in several locations to get an accurate assessment of what cutworm levels are.
  • Economic Threshold: 4-5 larvae/m2. Sometimes it is most economical to just treat infested patches, and not whole fields.
• Aphids
  • Typical Damage: Extract plant fluids from the stems, leaves and developing bolls. Can cause fewer seeds to be produced.
  • When and How to Monitor: The easiest way to detect aphids in flax is to sample the upper portions of the plant with an insect sweep net when the crop is in full bloom, or tap plants over a white tray or bucket. If aphids are found, fields need to be more closely inspected by randomly sampling plants. To inspect plants, lightly tap the plants on a white surface, such as a tray or the canvas of a sweep net, to dislodge the insects. Plants can be severed at the base prior to tapping if desired. Inspect a minimum of 25 plants at full bloom and 20 plants at early green boll randomly in the field to provide an accurate estimate of aphid density. Record total number of aphids and calculate average per plant.
    • If control is not warranted at full bloom, aphid densities should be assessed again at the green boll stage.
  • Economic Threshold: Varies with crop value and control costs, but generally about 3 aphids per main stem at full bloom or 8 aphids per main stem at the green boll stage.
    • The yield loss of flax is 0.3346 bushels/acre per aphid per plant for crops sampled at full bloom and 0.1275 bushels/acre per aphid per plant for crops sampled at the green boll stage.
    • The potato aphid is highly susceptible to attack by fungi (especially in years of high rainfall and humidity in late June and July). Aphid populations sampled at full bloom that have many diseased insects should be sampled again at the early green boll stage to determine the effect of the disease on aphid densities.
• Beet webworm
  • Nominal Threshold: >10 larvae/m2

Lentils

• Grasshoppers
  • When and How to Monitor: Look for when monitoring fields from the early bud stage through pod development.
  • Economic Threshold: 2 grasshoppers/m2 during the flowering and podding stages, especially if two-striped grasshopper is the dominant species.
• Lygus Bugs
  • When and How to Monitor: Look for lygus bugs when monitoring lentils during blooming and podding by using a sweep net, making 25 180° sweeps in at least 5 randomly selected places in a field. Afternoon sampling provides more accurate estimates than morning sampling.
  • Threshold: As a nominal threshold, insecticide treatment is recommended when 7 to 10 Lygus bugs are collected per 25 sweeps.
• Pea aphid
  • Economic Threshold: 30-40 aphids per 180° sweep of a 38 cm (15 inch) diameter insect net, and few natural enemies are present, and when aphid numbers do not decline over a 2-day period.

Field Peas

• Cutworms
  • Nominal Threshold: 2 to 3 cutworms per square metre.

Sap Feeders

• Aphids
  • When and How to Monitor: Look for when monitoring field peas at the beginning of flowering. Take 180° sweeps or check 10 8-inch (20 cm) plant tips at each stop. Record total number of aphids and calculate average per sweep or plant tip.
  • Economic Threshold: If, at the beginning of flowering, there are 9 to 12 aphids per sweep or 2-3 aphids per 8-inch (20 cm) plant tip, an insecticide application when 50 percent of plants have produced some young pods will be cost-effective.

Potatoes

• Aphids
  • Typical damage: Several species of aphids are sap feeders on potato leaves. At very high numbers this sap feeding may cause plants to wilt in small localized areas of the field as “aphid holes”. The greatest injury is due to transmission of viruses. Identification and control of aphids is critical in potato seed production to prevent virus spread. In commercial production tuber quality may be reduced by net necrosis of tubers.
  • When and How to Monitor: Aphid identification and scouting should start in early July when aphids begin to be observed in fields. Sample 25 lower canopy leaves from each of 4 areas in the field (100 leaves in total). Count potato aphids and green peach aphids on each compound leaf, using a magnifying device to identify the species.
  • Economic threshold: For seed potatoes = 3-10 green peach aphids/100 leaves. For processing potatoes = 30-100 green peach aphids/100 leaves. There are no economic thresholds for buckthorn and potato aphids. These thresholds relate to transmission of potato leafroll virus and are not useful in determining infectivity  relative to potato virus Y. No economic thresholds have been established for aphids that relate to potato virus Y transmission.
• Leafhoppers
  • Typical damage: the potato leafhopper injects a toxin into the plant which results in hopper burn, a yellowing and curling of the tips and margins of the leaflets, which ultimately turn brown and brittle. Damaged plants die prematurely and yield may be reduced.
  • When and How to Monitor: Nymphs are scouted by visual inspection; sample 100 plants from 3-5 areas of the field. Count the wingless nymphs on compound leaves taken from mid canopy. Adults are sampled with a sweep net (20 sweeps per location at 5 locations for a total of 100 sweeps).
  • Economic threshold: Nymphs-1 nymph per 10 leaves. Adults-1 leafhopper per sweep.
• Colorado potato beetle
  • Typical damage: Larvae feeding may cause extensive defoliation of leaves and is capable of transmitting spindle tuber virus and bacterial ring rot.
  • When and How to Monitor: Start scouting for larvae 2 weeks after crop emergence. On field edges, count number of beetles on 20 separate plants. Record % defoliation of leaves. Repeated scouting is required since beetles have developed resistance to many insecticides and 2 generations may occur during the year.
  • Economic threshold: Economic threshold based on beetle numbers may vary by cost of treatment, expected returns and variety. Typical thresholds are 18 larvae/ 20 plants for Russet Burbank vs 6 larvae/20 plants for Norland. Treat when defoliation exceeds 10%.
• Potato flea beetle
  • Typical damage: Beetle feeding causes “shot holes” in the leaves. Two generations may attack the foliage.
  • When and How to Monitor: Estimate feeding damage on the leaf or numbers of beetles on plants.
  • Economic threshold: Early in the season treat if greater than 10% defoliation. Later in the season (August) treat if greater than 25% defoliation or with greater than 65 beetles per plant for Norland or 300 beetles per plant for Russet Burbank.

Rye

Information on typical damage, when and how to monitor, and economic thresholds for cutworms, aphids and armyworms in rye can be found in the section on field scouting in small grain cereals (wheat, barley, oats).

Small Grain Cereals (wheat, barley,  oats)

Belowground and Surface Feeders

• Cutworms
  • Typical Damage: Notched, wilted, dead, or cut-off plants. Plants missing from rows, bare patches appearing in field.
  • When and How to Monitor: Look for cutworms, and evidence of cutworm feeding, when monitoring in late May to mid-July. Often cutworms will be close to the cut or shriveled plants they have just damaged. Cutworms  will sometimes be most abundant in patches or a specific area of a field. In areas of the field where cutworm damage is noticeable, check around damaged plants in a 0.25 m2  (50cm x 50cm) area. Use trowel or shovel to carefully search through top half to 1 inch of soil  for cutworm larvae. Multiply the number of cutworms found by 4 to get the number per m2. Repeat in several locations to get an accurate assessment of what the cutworm levels are.
  • Economic Threshold: Pale western cutworm – 3-4/m2; Redbacked and army cutworm – 5-6/m2. Well established fall-seeded crops or spring seeded crops with good moisture conditions can tolerate higher numbers. Sometimes it is most economical to just treat infested patches, and not whole fields.

Sap Feeders

• Aphids
  • Typical Damage: Visible wilting of plants, yellow patches in fields, plants are sticky.
  • When and How to Monitor: Look for aphids when monitoring prior to the soft dough stage. While monitoring the field, using a sweep net or tapping plants over a white tray or bucket can alert you to the presence and relative abundance of aphids. If aphid levels appear concerning, a more thorough examination is needed. Count aphids on 20 randomly selected stems in each of 5 areas. Counts should be at least 50 paces apart, and observations should be made well into the center of  the field. Too frequently farmers become alarmed after checking a few plants along the margins, especially near shelterbelts, where populations are high. Record the total number of aphids and calculate the average per plant.
  • Economic Threshold: 12-15 aphids/stem prior to the soft dough stage.
    • Cereal Aphid Manager is a mobile app that helps growers determine aphid populations by predicting what the aphid population will be in seven days along with beneficial insect pressure on the population and suggests if insecticide application is necessary. https://open.canada.ca/en/app/cereal-aphid- manager-mobile-app
• Barley Thrips
  • When and How to Monitor: Sampling should begin when the flag leaf is first visible and continue until the head is completely emerged from the boot. Barley thrips exhibit an edge effect; there are usually more thrips near protected field margins than other areas of the field. Most thrips can be found under the top 2 leaf sheaths. Unroll the leaf sheaths away from the stem to find the thrips.
  • Economic Threshold: Insecticide treatments are only effective when applied before heading is complete. Treat when thrips are equal to or greater than the number calculated by: Threshold (Thrips/stem) = (Cost of Control ÷ expected $ value per bushel)/0.4

Defoliators

• Grasshoppers
  • Typical Damage: Black strips along margins of newly emerging crops, head clipping later in season.
  • When and How to Monitor: Look for grasshoppers when monitoring fields from late – May through to harvest. Check along edges of crop, particularly areas adjacent  to hayland, pastures and roadsides. Estimate number of hoppers/yard2 (m2).
  • Economic Threshold: 8-13 grasshoppers/m2. Early in the season, when grasshoppers are small, 18 grasshoppers/ m2 and visible crop damage may be a more appropriate threshold.
    • A rough estimate for an economic threshold for grasshoppers in crops to be used as greenfeed has been suggested at 20 grasshoppers/m2 or higher.
• Armyworms
  • Typical Damage: Leaves stripped from plants, awns chewed from heads, heads clipped.
  • When and How to Monitor: Check the soil surface for armyworms, and the plants for feeding, when monitoring in mid- June through early-August. At each stop shake plants and carefully check soil surface for dislodged larvae. During the day larvae may be under plant trash, soil clods or in soil cracks. Check the backs of armyworms for parasite eggs.
  • Economic Threshold: Four unparasitized larvae, smaller than 2.5 cm (1 inch) per square foot. If heads are being clipped, treat when two or more armyworms per square foot are present. For migrating Armyworms: Treat a couple of swaths ahead of the infestation in the direction of movement to form a barrier strip.

Seed Feeders Only

• Wheat Midge (wheat only)
  • When and How to Monitor: Monitor wheat in July when crop emerges from boot stage until flowering. Check crop canopy at dusk for signs of wheat midge adult activity. At each stop, examine 10 heads. Record the number of midge adults observed on or near heads. Calculate average number of midge per head.
    • Sticky traps may be used to capture adult midge activity in wheat fields.
  • Economic Threshold: For yield only: 1 adult midge per 4 to 5 heads. At this level of infestation, wheat yields will be reduced by approximately 15% if the midge is not controlled. To maintain optimum grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage.

Soybeans

• Cutworms
  • A nominal threshold that may be used for cutworms in soybeans is 1 or more larvae per three feet of row and larvae are small (less than 2 cm), or 20% of plants cut.
• Soybean Aphid
  • Typical Damage: Soybean aphids suck sap from soybean plants. Infested leaves may wilt or curl when infestations are large. Other symptoms may include plant stunting, reduced pod and seed count, and yellowing of leaves.
  • When and How to Monitor: Check 30 plants (6 plants in 5 areas) per field. Examine the entire plant and estimate populations of soybean aphids (counting exact numbers will not be possible or practical with higher populations). Once soybean aphid numbers reach 250 aphids per plant, scout the field frequently to determine if soybean aphid numbers are increasing. A population can stay at 250-300 aphids per plant and not cause economical yield loss. If the aphid levels are not rising above 250-300 per plant, there is a good indication that field conditions are favouring natural enemies (such as beneficial insects and fungi) that are helping control the aphids. An app called Aphid Advisor can be used to integrate common natural enemies of soybean aphids into the management decision (http://www.aphidapp.com/).
  • Economic Threshold: When there are on average at least 250 aphids per plant and the population is increasing, and the plants are in the R1 (beginning bloom) to R5 (beginning seed) growth stages, treatment would be economical. This threshold gives an approximate 7-day lead time before aphid populations are expected to exceed the economic injury level (670 aphids per plant), where cost of control is equal to yield loss. When soybean aphid populations are not actively increasing above 250 aphids per plant, natural enemies are keeping up with the aphid population. Do not use an insecticide in this case, as it will kill the natural enemies which may enable the aphid population to increase above the economic injury level.

Sunflowers

Belowground and Surface Feeders

• Cutworms
  • Typical Damage: Notched, wilted, dead, and cut-off plants (weed or crop seedlings). Plants missing from rows, bare patches appearing in field.
  • When and How to Monitor: Look for cutworms, and evidence of cutworm feeding, when monitoring sunflowers in late May to mid-July. Often cutworms will be close to the cut or shriveled plants that they have just damaged. Cutworms will sometimes be most abundant  in patches or a specific area of a field. In areas of a field where cutworm damage is noticeable, check around damaged plants in a 0.25 m2 (50 cm x 50 cm) area. Use trowel or shovel to carefully search through top half to 1 inch of soil for cutworm larvae. Multiply the number of cutworms found by 4 to get the number per m2. Repeat in several locations to get an accurate assessment of what the cutworm levels are.
  • Nominal Threshold: 1 cutworm or more per square foot (30 by 30 cm) or if there is a 25 to 30% stand reduction. Sometimes it is most economical to just treat infested patches, and not whole fields.

Defoliators

• Sunflower Beetle
  • Typical Damage: Adults: Leaves of seedling plants chewed or completely destroyed late May through June, shot-holes or large areas of leaves chewed July through August. Larvae: Leaves of plants chewed or completely destroyed.
  • When and How to Monitor: Adults: Look for when monitoring sunflower seedlings in May through June. Examine 10 plants at random at each stop. Larvae: Look for when monitoring sunflowers in July through mid- August. Examine 10 plants at random at each sampling site. Peel back leaves around growing tip and record total number of larvae found. Calculate average number per plant.
  • Economic Threshold: Adults: 1-2/seedling; Larvae: 10 to 15/plant or 25-30% defoliation.

Insects affecting the seeds

Pests of Seed Only

• Red Sunflower Seed Weevil
  • Typical Damage: Seeds partly or completely destroyed, exit hole in hull. Shriveled kernels, kernels completely destroyed.
  • When and How to Monitor: Monitor fields when ray petals being to form and continue every 2 to 3 days until pollination is complete. When scouting, use the X pattern and begin counts at least 70 to 100 feet into the field to avoid margin effects. Examine 5 plants at each site for a total of 25 plants. For checking individual sunflower heads, brush the face of the head vigorously to bring the weevils to the surface, or use a commercial preparation of mosquito repellent containing diethyl  toluamide (DEET) to spray the heads. This will cause the weevils to move out of hiding spots. Record total number of weevils and calculate average per head.
  • Economic Threshold:
    • Confection Sunflowers: 1-2 weevils/plant. Control is based on a need to keep seed damage below 3 or 4% because of industry standards.
    • Oilseed sunflowers: 12-14 weevils/head.
    • The ideal plant stage to treat is when most plants in the field are at 40% pollen shed (R5.4).
• Banded Sunflower Moth
  • When and How to Monitor: Look for banded sunflower moth adults when monitoring fields in the late bud (R-4) to early bloom (R5.1) plant growth stage. Count moths on 20 plants from 5 different sites for a total of 100 plants. Sampling in early evening or early morning when the moths are most active gives the most accurate counts.
    • Sampling strategies based on scouting for adult moths during daylight hours, and counting eggs, have also been developed.
  • Economic Threshold: 1 moth per 2 plants when monitoring in the early evening or early morning.
    • If monitoring for eggs or adult moths during daylight hours, tables for determining economic thresholds can be found at: http://www.ag.ndsu. edu/extensionentomology/field-crops-insect-pests/ Documents/sunflower/e-823-banded- sunflower- moth. If treatment is warranted, it should be applied at the R5.1 sunflower plant growth stage.
• Lygus bugs
  • Economic Threshold: Confection – One adult lygus bug per 9 heads can result in economic losses through the reduction in seed quality. Lygus bug management  should be initiated between when the inflorescence begins to open (R4) to early bloom (R5.1) stages if adult densities reach economic levels. No control is needed in oilseed sunflowers not used for human consumption.