ISSUE 8 June 23, 2005
COTTONY ASH PSYLLID IN NORTH DAKOTA
The Cottony Ash Psyllid, Psyllopsis discrepans (Flor), is a European insect recently detected in Bismarck by Assistant City Forester Jeff Heintz, and subsequently found in Fargo by Plant Protection Specialist Justin Knott. This aphid-like insect damages varieties of Black and Manchurian Ash. Damage appears as leaflet curling from the edges and tips, or a more general leaflet and leaf crumpling and deformation known as ‘cauliflowering.’ Some trees in Bismarck show severe damage. The damage appears similar to that of certain herbicides.
Adults are small, 3 mm in length. Coloration is yellow with black markings; the wings are clear, shading to smoky_brown towards the apices. Nymphs extrude a filamentous whitish wax, hence the common name of the insect. Because there are many native species of psyllids (also known as jumping plantlice), specimens should be submitted to professional entomologists for final determination.
This insect, which usually can be found on the undersurfaces of leaflets, imbibes phloem with its piercing-sucking mouthparts. It inserts feeding stylets into the leaf mid-rib or veins. The feeding injury and liquid removal causes leaflet curling, the more general deformation may be due to high psyllid numbers, or, based on evidence from other psyllid species, due to salivary secretions. This species overwinters as eggs, in our area may have as many as three generations annually.
Cottony ash psyllids are native to Central Europe and Scandinavia and were first reported in North America from a single male specimen found in Nova Scotia in 1921. Recent reports from the year 2000 and continuing, are from Edmonton and Calgary, Alberta. Populations in North Dakota may be the result of natural wind dispersal or an inadvertent introduction on plant materials.
Cottony ash psyllids have been found on the variety of Black ash known as ‘fall gold’ and the Manchurian ash variety ‘Mancana.’ This insect has also been found on hybrids of Black and Manchurian ash such as ‘Northern Treasure’ and ‘Northern Gem.’ As yet, White ash, a rare ornamental in ND, has not been examined and Green ash, one of our mainstay shade trees, appears to be unaffected. Currently, the winged adult stage is present and foliar damage is from insects of the first generation. This psyllid can cause severe leaf deformation although with the exception of some trees in south Bismarck, much of the damage observed thus far has not been severe. It is unclear what damage the second generation may cause now that the leaves are fully expanded. There is evidence that well watered trees are less susceptible to damage. We are collaborating with Canadian entomologists to determine management protocols for this insect.
Dr. Gerald Fauske, Research Collection Manager, NDSU
Justin Knott, Plant Protection Specialist, ND Dept. of Agriculture
David Nelson, State Entomologist, ND Dept. of Agriculture
Michael Kangas, Forest Health Specialist, ND Forest Service
SUGARBEET ROOT MAGGOT UPDATE
Sugarbeet root maggot fly counts at many monitoring sites, including Pembina, north central Walsh and central Cass counties, have been higher this year than the past several years, suggesting that populations are on the rise. Effective insecticide applications in highly infested areas may not only be important for protecting this year’s crop, but could also reduce the intensity of infestations in the 2006 production season.
Fly activity remains at fairly high levels, with the most severe infestations occurring between the cities of St. Thomas and Grafton, ND (especially in the townships of St. Thomas, Elora, Glenwood, and Martin). Activity is expected to drop considerably by early next week. Therefore, growers planning to make a second liquid insecticide in a split-treatment program (or those that observe an unexpected flare-up of activity) should apply the material as soon as possible.
APHIDS INFESTING AREA SMALL GRAIN CROPS
Cereal aphids are beginning to show up in ND small grain fields. Most reports are coming in from the southwest part of the state. Activity is also surfacing across the much of the southern tier of ND counties, as well as in southern and western MN. Aphids can usually be found in area field crops each growing season, but do not always reach economically damaging levels.
Description. Aphids are tiny, soft-bodied, pear-shaped insects with tapered, thread-like antennae. Most have two tailpipe-like structures called "cornicles" that protrude from the posterior end of their abdomen. Most aphids of concern are lime or yellowish-green to blue-green in color, and are about 1/3 to 3/16-inch long. The most common aphid pests of small grain crops in North Dakota are the greenbug, English grain aphid, and bird cherry oat aphid (Fig. 1). None of these species are known to overwinter in the state. They migrate into the region from southern areas in late spring.
Fig. 1. Economically important aphids
of ND small grain crops
Damage. Aphids injure small grain by using piercing/sucking mouthparts to feed on plant sap. They reproduce quickly under favorable conditions for development, and the resulting infestations are capable of causing major yield reductions. An added concern is the potential of aphids to transmit barley yellow dwarf virus. High aphid populations are capable of quickly spreading this disease throughout entire fields. Small grain fields are quite variable in growth stage this year because some were planted very early while others were planted late due to excess soil moisture. Impacts of aphid infestations are most severe in late-seeded grain fields because young plants are less capable of withstanding feeding injury. Such fields should be monitored closely. Aphids are also more problematic when cool and wet periods occur during spring and early summer, which further justifies careful monitoring of grain fields this year.
Treatment threshold. North Dakota producers and crop scouts should be vigilant about monitoring grain fields during the next few weeks. Economic yield loss is most likely when significant aphid damage occurs during vegetative to boot stages. Field monitoring should begin at stem elongation and continue until the heading stage of wheat. Treatment with an insecticide is probably justified if at least 85% of stems have at least one aphid present before heading. Economic return from an insecticide application will be reduced if it is made after flag stage.
Pockets of armyworm activity have been observed in small grain fields in southwestern North Dakota during the past ten days, although insecticide applications have not been reported. Armyworm infestations occasionally develop in our area following migrations of moths from southern states in late spring and early summer.
Moths typically lay their tiny white eggs at the bases of plants in moist, shady areas, and prefer sites with lodged and/or hail-damaged grassy weed or crop plants. Eggs hatch and larvae (Fig. 2) quickly begin feeding on nearby plants. Moth flights can occur over a few weeks time, so it is not unusual to find a wide size range of larvae present. Early detection of armyworm infestations is difficult because they feed at night and hide under vegetation or in loose soil during the day. Damage is sometimes obscured by wind injury or the dense small grain plant canopy itself. Armyworms are a favorite food of birds, so significant bird activity in a grain field can be an indicator of an armyworm infestation.
Fig. 2. Late-instar armyworm larva.
Scouting for armyworms in small grain fields involves parting the plant canopy back and searching for feeding injury or fecal pellets. If either is evident, look for larvae under plant trash, soil clods or in soil cracks. Field can also be checked during evening hours (when larvae are most active) by shaking plants and using a flashlight to count dislodged larvae on the ground. Whether sampling during the day or in the evening, it is important to sample as many locations in a field as practical (at least 5 sites per field). To avoid economic loss from armyworms, treat with a registered foliar insecticide when an infestation reaches 4 to 5 larvae per square foot. As the name implies, armyworms will assume the "army" habit and move in large numbers to neighboring fields when the food supply becomes depleted in the original feeding site. Applying a foliar insecticide as a barrier treatment to a strip of plant material ahead of the infestation in the direction of movement can provide good protection of neighboring fields if timed correctly.
Options for aphid and armyworm control in small grains can be found in the 2005 Field Crop Insect Management Recommendations guide. It is online at:
Always read, understand, and follow all pesticide labeling instructions and precautions - it’s the law.
Research & Extension Entomologist
BARLEY THRIPS POPULATIONS INCREASING IN BARLEY
It is somewhat surprising to see high populations of barley thrips with the cool, wet spring weather and vigorously growing crop conditions. Typically, hot dry weather conditions increase populations of barley thrips to levels that may result in crop losses.
Barley thrips are small dark brown to black insects about 1.1 to 1.8 mm long. Females have feathery wings while males are wingless. Immatures (larvae) are wingless pale yellow, white or green with red eyespots. Larvae are difficult to see due to their light, almost transparent color and extremely small size. Adult and immature thrips have a long, narrow body shapes.
Female thrips overwinter as adults in debris in fields and shelterbelts. Thrips emerge in late May and early June and move into winter wheat/rye and eventually into early seeded barley (preferred host). Occasionally, barley thrips will feed on hard red spring wheat and durum as well.
Adult and immature thrips cause damage by feeding on succulent plant tissues (puncturing plant cells and sucking out the contents). Feeding injury symptoms are a whitened or bleached appearance in plants and this often results in gooseneck-shaped stems and heads under severe pressure. Pollen feeding by barley thrips may result in poor head filling and reduced seed germination. Intensive feeding at the beginning of head formation produces small, shriveled grains. Often there is no seed development at the top and bottom of head and intermediate grains are shriveled.
Scout for barley thrips from flag leaf to heading. Barley thrips can be found by unrolling the flag leaf away from the stem. Remember, populations will probably be higher at the field edges. The economic threshold is 7-8 barley thrips per plant before the crops is fully headed. One thrips per stem results in a 1.25 bushel per acre loss! Once the barley crop heads the insect damage is done and no insecticide treatment is advised. The only registered insecticide for barley thrips control in North Dakota is methyl parathion 4 EC at 4-6 fl oz. per acre (do not enter treated fields within 48 hours after application).
SECTION 18 EXEMPTION APPROVED - MUSTANG MAX FOR GRASSHOPPER CONTROL IN FLAX IN ND
This exemption allows ground or aerial application of Mustang Max (FMC) at a rate of 2.8 to 4 fluid ounces of product per acre from June 10 to September 20, 2005. A maximum of 8 fluid ounces per acre may be applied per season. Although early grasshopper levels have been low with the cool, wet spring, we will need to continue to watch the later adult populations. Adult grasshoppers migrate from maturing small grain fields, drying grasses, canola and other crops to flax fields in late summer into fall. Flax is a preferred host crop later in the season, since plants will be green and attractive to grasshoppers as adults. Large groups of adult grasshoppers can migrate and move long distances, 30 miles or more, to find flax fields, and cause crop losses quickly.
The exemption use directions have been posted on the North Dakota Department of Agriculture Section - 18 page
and the NDSU Pesticide Program page
ADULT SUNFLOWER BEETLE EMERGENCE UNDERWAY!
Adults sunflower beetles can be found in sunflower fields now. The head of the adult is reddish-brown and the thorax (area between head and abdomen) is pale cream-colored with a reddish-brown patch at the base. Each wing cover is cream-colored and has three dark stripes that extend its length. A shorter lateral stripe ends at the middle of the wing in a small dot that resembles an exclamation point. The beetle is about ½ inch long when mature.
Adult Sunflower Beetle
Damage due to adult feeding begins soon after beetles emerge from hibernation. They seldom feed on the cotyledons, but the first true leaves may be severely damaged or completely consumed. If beetles are abundant, fields may be severely defoliated. Adults feed predominately on leaf margins during the day. Damage may be most noticeable in field margins. In the seedling stage, one-two adults per seedling plant is the recommended economic threshold.
Eggs will hatch into larvae in about a week. Sunflower beetle larvae are yellowish-green with a brown head capsule and humpbacked in appearance. Newly hatched larvae are about 1/16 inch, and will reach a length of about 3/8 inch when fully developed. Larvae feed over the entire leaf surface for about six weeks during the night. When larvae are numerous, damaged leaves take on a lacy appearance. During the daytime, larvae typically rest in the terminal growth area where they are easily found in leaf axils and flower buds. If larval feeding is severe, defoliation can reduce yield by poor seed set or fill. When foliar defoliation reaches 25-30% in late vegetative stages of sunflower and larvae are less than ¼ inch, a treatment may be warranted.
Sunflower Beetle Larvae
Area Extension Specialist
North Central Research Extension Center