ISSUE 10 July 16, 2009
SCOUT FOR SOYBEAN APHIDS
This past week >50 fields were scouted for soybean aphid across North Dakota. Soybean aphids were found in southeastern North Dakota in Barnes, Cass, Richland, Sargent and LaMoure Counties, central North Dakota in Stutsman County and northeastern North Dakota in Grand Forks County. The number of soybean aphids per plant is low (<25 aphids per plant) and 10% of the plants have aphids. Minnesota also reported low levels of soybean aphid with 100-400 aphids per plant on 20-30% of the plants near Lamberton and Morris (Source: B. Potter, UMN). With moderate temperatures between 75 and 86 F for our daily highs, reproduction is optimal for soybean aphid development. The pre-reproduction period takes about 5 to 7 days before aphids begin giving birth to nymphs. Scouting soybean fields is a must during the next few weeks.
When scouting a soybean field, remember that many different insects inhabit soybean fields throughout the season. It’s important to be aware of aphid predators, because they play a major role in reducing early populations of soybean aphids. A new resource on biological control of soybean aphids in the North Central States can be found at:
Research results have indicated that early-season applications of insecticides for control of sub-economic populations of soybean aphids have caused more harm than good. So, ‘SAY NO’ to early-season insecticide applications for management of soybean aphids. In fact, early-season insecticides can aggravate other secondary insect pests like spider mites. Wait to treat until 250 aphids per plant are present on 80% of the plants in field. Remember, there is NO yield loss at the 250 aphids per plant level (economic threshold) and it also provides a 7-day window to apply any necessary insecticides without yield loss.
COLORADO POTATO BEETLE ACTIVITY ON POTATO
Adult Colorado potato beetles are laying eggs and eggs are hatching into small larvae in our insecticide plots in Glyndon, Minnesota. Adult beetles are 3/8 inch long, with oval body and a yellow-brown color with 5 black stripes on each wing cover (Fig. 1). Eggs are laid on the underside of leaves in clusters of 10 to 30 and are orange-colored when ready to hatch (Fig. 2). The larvae are 1/8 to 3/8 inch long, brick red to light orange in color (Fig. 2). Adults and small larvae have been observed feeding on potato foliage causing <5% defoliation. No large larvae observed yet. When populations are high, insecticide spraying should be timed for 15 to 30% egg hatch.
Figure 1. Colorado potato beetle adult (J. Knodel)
Figure 2. Young larvae and eggs of
Colorado potato beetle (G. Fauske)
BEAN LEAF BEETLES IN SOYBEANS
Bean leaf beetles have been reported in soybeans in LaMoure County near Kulm and in Dickey County near Oakes. The Kulm field had high levels of adults and defoliation, and a foliar insecticide spray was needed for control. Adult bean leaf beetles emerge from overwintering sites and move into soybean or dry bean fields. Adults are yellow to reddish-brown and have three to four black spots with a black border on the wing covers (Fig. 3). Early feeding injury to leaves appears as small round holes between the leaf veins (Fig. 4). Treatment thresholds from other regions are 3 to 7 beetles per sweep. Treatment thresholds based on defoliation are 50% defoliation during early vegetative, 40% defoliation during pre-bloom, 35% defoliation during bloom and 20-25% defoliation during pod set to fill. Late season feeding on the foliage and pods by the new adults that emerge in August can be more important than early season feeding, if viruses are present. This may increase the risk of virus transmission and cause secondary infections (rotting and discoloration) from fungi and bacteria. Bean leaf beetles are the vector of Bean Pod Mottle Virus (BPMV). In 2007, BPMV was detected in 6% of soybean fields sampled in the southeastern part of ND (Source: Dr. B. Nelson, Dept. of Plant Pathology, NDSU).
Figure 3. Bean leaf beetle adult (N. Wright,
Florida Dept. of Ag. And Consumer Services,
Figure 4. Feeding injury of bean leaf
beetle on dry beans (J. Knodel)
HESSIAN FLY INFESTATION IN NORTHEASTERN NORTH DAKOTA
A severe infestation of Hessian fly was observed in Pembina County near Crystal. The 2-4 leaf wheat was killed in localized spots causing a thin stand. Close examination of the affected wheat plants revealed several larvae per plant with some in the ‘flaxseed’ prepupal stage. The adult Hessian fly is a small (1/8 inch long), sooty-black, fragile two winged insect and resembles a mosquito (Fig. 5).
Figure 5. Hessian fly adult (S. Bauer,
Larvae are maggot-like (headless and legless), about 1/6 inch long and white in color when mature (Fig. 6). When the larva becomes full grown, its skin become hardens and turns brown to form a puparium or "flaxseed" (prepupal stage) (Fig. 7).
Figure 6. Hessian fly larva
Figure 7. Hessian fly "flaxseed" stage (J. Knodel)
There are two or more generations per year in North Dakota. The first generation infests seedling wheat causing dead plants and thin stands when infestations are heavy (Fig. 8). The second generation infests the jointing stage just above the node between the leaf sheath and stem causing stem lodging and reduction in the quantity and quality of the grain. Use of resistant varieties and cultural control (crop rotation, delayed fall planting of winter wheat) are the primary pest management strategies used in North Dakota. Insecticides are seldom needed in North Dakota. However, systemic seed treatments or at-plant insecticide treatments can provide some control, when it is known that Hessian fly populations are high. Timing of foliar insecticide sprays are difficult due to problems in predicting fly emergence and because of their wide emergence period. Insecticides may not provide a long enough residual to control flies that move into the infested field from adjacent areas.
Figure 8. Hessian fly injury to wheat (J. Knodel)
SUNFLOWER INSECT TRAP NETWORK FOR BANDED SUNFLOWER MOTH AND SUNFLOWER MOTH
The National Sunflower Association is again coordinating a multi-state trapping network for banded sunflower moth and sunflower moth in cooperation with NDSU Extension Entomology and USDA ARS. Adult banded sunflower moth are emerging and present at low densities based on pheromone trap reports. Sunflower moth which migrates into North Dakota from the southern U.S. is also low. Dr. Larry Charlet, Sunflower Research Entomologist UDSA ARS, and Dr. Anitha Chirumamilla, NDSU Entomology post-doctoral scientist, recently traveled down to Kansas and reported low densities of adult sunflower moths in Kansas. This is good news for North Dakota, because the number of sunflower moths that arrive in North Dakota depends on the population levels in the southern states (reservoir of moths) and favorable southerly wind flows into North Dakota. Moth maps from the sunflower insect trap network are posted weekly on the National Sunflower Association website (click on "Moth Maps.")
APHIDS ON FIELD PEAS
(Source: J. Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives)
Some economic levels of aphids (Fig. 9) in peas and control have been reported from the north central and central regions of North Dakota. One of the big questions this week is how and at what stages aphids injure peas? Aphid feeding on peas in the flowering and early pod stage can result in lower yields due to less seed formation and smaller seed size. Protein content and other quality issues do not appear to be affected.
Figure 9. Pea aphids (W. Cranshaw, Colo. State Univ.)
The following table relates the yield loss in peas for average aphid counts from 1 to 8 per 20-cm tip of a field pea stem when about 25 % of the crop has begun to flower.
Aphids per tip
% yield loss
Most of the damage that aphids do to peas is to the pods before they start to fill. If you think that most of the pods have already started to fill, spraying would be too late and would not be economical.
Economic Threshold: At the beginning of flowering, an insecticide application would be economical when 9 to 12 aphids per sweep (or 90 to 120 aphids per 10 sweeps) are present. When 50% of the plants have young pods, an insecticide application would be economical when an average of 2 to 3 aphids per plant tip (upper 6 inches of shoot) are present. There are several plant tips per plant, so take an average from several tips per plant. Population estimates should be calculated by averaging counts taken from at least five separate areas of the field. One application per season should give satisfactory control of pea aphids. Insecticides registered are listed in the "2009 North Dakota Field Crop Insect Management Guide."
BEE ALERT! PROTECT OUR HONEY BEES WHEN SPRAYING INSECTICIDES IN FLOWERING CROPS
Honey bees and native pollinators (Fig. 10) are a vital part of our agricultural food production. The value of bee pollination is estimated at 14.6 billion dollars in the U.S.! With the reduction in number of both domestic and wild bee colonies due to Colony Collapse Disorder and other diseases, the value of honey bees, native bees and pollination has increased. This increases the importance of protecting bees from pesticide poisoning.
Figure 10. Bee on flower (J. Knodel)
Bees are attracted to blooming field crops (canola or sunflower) and even weeds (dandelion, wild mustard, white clover, goldenrod, etc.) in the field for nectar and/or pollen. Bees are attracted to plants that produce sweet exudates from extrafloral nectaries or from aphids feeding on plants. Pools of water in fields may also draw bees into fields, especially during dry periods.
Because bees forage up to 3 miles or more from their hive, all beekeepers within 2 to 3 miles of the area to be treated should be notified at least the evening before the insecticide is to be applied. The names of beekeepers in your area can be obtained by going to the North Dakota Department of Agriculture website.
Producers / Agronomists can reduce pesticide hazards to bees by following these general guidelines:
Insecticide toxicity is generally measured using LD50 or the exposure level that causes 50% of the population exposed to die. Bee toxicity thresholds are set at:
It is not possible to list all the insecticides registered in North Dakota and their toxicity to bees in this short article. However, some of the common insecticides used in field crops are all highly toxic to bees: acephate (orthene), carbaryl (sevin), chlorpyrifos (Lorsban4E), cyfluthrin (Baythroid), dimethoate (dimate), esfenvalerate (Asana), carbofuran (Furadan), indoxacarb (Steward 1.25EC), lambda-cyhalothrin (Warrior), methomyl (Lannate), and zeta-cypermethrin (Mustang Max). Since many of the commonly used insecticides are highly toxic to bees, it is very important to protect bees from pesticides poisoning. For more information, see "How to Reduce Bee Poisoning from Pesticides" from a Pacific Northwest Extension publication:
Note: Mention of a product is not intended to be an endorsement to the exclusion of others, which may be similar.
SUNFLOWER MAGGOTS IN SUNFLOWERS
Adult sunflower seed maggot and other sunflower maggots have been observed in sunflower fields this past week. There also have been some inquiries on the presence of sunflower maggots in sunflower and whether producers should be concerned with their presence. First, let’s identify the three different species of sunflower maggots and review their biology and damage:
Sunflower receptacle maggot, Gymnocarena diffusa - This species is the largest of the three with a body length of 0.4 inch and a wing span of approximately 0.75 inch (Fig. 11). The eyes of this species are bright green and the wings have a yellowish-brown and somewhat mottled appearance. G. diffusa larvae attain a length of nearly 0.3 inch at maturity. The larvae taper from the front to rear and are yellowish-white in color (Fig. 12).
Figure 11. Gymnocarena diffusa adult
Figure 12. Gymnocarena diffusa larvae
Life Cycle: Adults of G. diffusa emerge from late June through early July after sunflower buds reach 2 to 4 inches in diameter. Eggs are laid on the bracts of the developing sunflower heads. Egg laying occurs from mid-July through August. Newly emerged larvae tunnel into the spongy tissue of the receptacle. Damage to the head is negligible. After 30 days, mature larvae cut small emergence holes on the underside of the receptacle and drop into the soil to pupate. Overwintering pupae are found about 7.5 inches deep in the soil by August or early September. Some larvae will pupate in the sunflower head. There is only one generation per year in North Dakota.
Damage: The maggots of G. diffusa feed on the spongy receptacle tissue of the sunflower head and feeding may cause partially deformed heads. Larvae do not feed on developing seeds. Damage by sunflower receptacle maggots has been negligible and no insecticide treatment is recommended.
Sunflower maggot, Strauzia longipennis - Adults of this species have a wing spread of about 0.5 inch and a body length of 0.25 inch (Fig. 13). The wings bear broad, dark bands that form a fairly distinct F-shaped mark near the tips. The larvae of S. longipennis are creamy white, headless and legless, as are the other two species (Fig. 14). They taper slightly at both ends and attain a length of about 0.28 inch at maturity.
Figure 13. Strauzia longipennis adult
Figure 14. Strauzia longipennis larvae
Life Cycle: S. longipennis has one generation per year. This insect overwinters as larvae in plant debris in the soil. Pupation and adult emergence are completed in early June. Females lay eggs in the stem tissue of young sunflower, and larvae feed in the pith tissue for much of the growing season.
Damage: While infestation levels of S. longipennis have occasionally reached nearly 100 percent tunneling in stalks, damage (stalk breakage) from larval feeding is usually light. Damage by S. longipennis is mainly in the stalks and no insecticide treatment is recommended.
Sunflower seed maggot, Neotephritis finalis -This sunflower maggot is the smallest of the three species with the adult having a body length of about 0.25 inch and a wing span of approximately 0.28 inch (Fig. 15). The wings have a brown lace-like appearance. N. finalis larvae attain a length of 0.19 inch at maturity (Fig. 16). The small, brown pupa of N. finalis is found in the face of the sunflower bud, usually surrounded by a small number of damaged florets (Fig. 17).
Figure 15. Neotephritis finalis adult (J. Knodel)
Figure 16. Neotephritis finalis larvae (J. Knodel)
Figure 17. Neotephritis finalis pupa (J. Knodel)
Life Cycle: Unlike the other two species of sunflower maggots, two complete generations per year of N. finalis occur in North Dakota. Adults of N. finalis emerge during the first week of July. Egg deposition occurs on the corolla of incompletely opened sunflower inflorescences. The total larval period is 14 days. The first generation of N. finalis pupates in the head and the second generation overwinters in the soil as pupae.
Damage: The magnitude of damage to sunflower seeds by N. finalis larvae depends largely on the stage of larval and seed development. Seed sterility occurs when newly emerged larvae tunnel into the corolla of young blooms. Observations indicate that a single larva feeding on young flowers will tunnel through 12 ovaries. Mature larvae feeding on older sunflower heads will destroy only one to three seeds. Research funded by the National Sunflower Association is being conducted by NDSU Entomology to determine field monitoring techniques, the impact of sunflower seed maggot on sunflower yield loss, and what the ‘best’ pest management strategies are for control of sunflower seed maggot. Dr. Saddha Ganehiarachchi is the post-doctoral scientist working on the project with Drs. Knodel and Charlet.
Janet J. Knodel