ISSUE 15 September 13, 2007
2007 IPM SURVEY REPORT ON INSECT PESTS IN NORTH DAKOTA
The 2007 IPM Survey is summarized below for the major insect pests of agricultural crops surveyed in ND: wheat, barley, canola, soybean, and sunflower. Survey scouts operated out of the Dickinson Research Extension Center, the North Central Research Extension Center (Minot), the Carrington Research Extension Center, the Devils Lake Area Extension Office, and the Fargo Experiment Station.
Scouts swept for grasshoppers using a 15-inch sweep net in field edges. Populations of nymphs and adults were generally below treatment levels throughout ND (Fig. 1 & 2). Summer weather conditions were not as favorable "hot and dry" for grasshopper outbreaks in 2007 as in 2006. There were sporadic reports of higher grasshopper populations, primarily in the north central region.
More than 1100 wheat fields were surveyed in all 53 counties of ND during 2007. This number represents approximately one field surveyed per 6,700 acres of wheat. The survey was initiated on May 29 and continued through August 9, 2007. Crops were surveyed from the 1-leaf stage through hard kernel (ripening) stage. Field scouts surveyed for insect pests on winter wheat, hard red spring wheat, and durum wheat.
Small Grain Aphids: Aphids were counted on 100 stems (20 stems at 5 locations) and recorded as the percent of infested stems. Aphids were found in 19% of all fields surveyed and observed from mid-June to late July (Fig. 3). The average percent of infested stem was 2.4%, with ranges from 0 to 82%. Peak population densities occurred during late June to early July. The treatment threshold is when 85% stems have one or more aphids present, prior to completion of heading. There was sporadic spraying for wheat aphids.
Wheat stem maggot: Maggots were counted on 100 plants (20 tillers at 5 locations) and recorded as the percent of plants infested with white heads. Maggots were found in 46% of all fields surveyed from heading to maturity. White heads were observed from late June to end of July (Fig. 4). The average percent of infested plants with white heads was 17% among the positives, with ranges from 1 to 54%.
A total of 318 barley fields were surveyed in 33 counties in ND during 2007. This number represents approximately one field surveyed per 3,500 acres of barley. The survey was initiated on May 29 and continued through August 3, 2007. Crops were surveyed from the 1-leaf stage through hard kernel (ripening) stage.
Small Grain Aphids: Aphids were counted on 100 stems (20 stems at 5 locations) and recorded as the percent of infested stems. Aphids were found in 23% of all fields surveyed and observed from mid-June to late July (Fig. 5). Peak population densities occurred during late June to early July. The average percent of infested stem was 3.5%, with ranges between 0 and 100%. There was sporadic spraying for aphids on barley.
Barley thrips: The number of barley thrips inside of the leaf sheath was counted from ten plants at 4 locations (total of 40 plants per field) and the average number of thrips per stem was recorded. Barley thrips were low and observed during June. The average number of thrips per stem was only 2.4, with ranges between 1 and 15 among the positives (Fig. 6). Population densities were the highest in the central and south central regions of the state where it was dryer in the early summer.
CANOLA TRAP NETWORK
A total of 18 pheromone traps in 14 counties were monitored for two Lepidopteran insect pests of canola in the major canola growing areas of ND: Bertha armyworm, and Diamondback moth. Pheromone traps were monitored from mid-June to late July. The green bucket unitrap and the winged sticky trap were used for Bertha armyworm and Diamondback moth, respectively. Trap data provides growers, Ag consultants, Ag field researchers, and county extension agents/specialists with an "early" risk warning system of when these insect pests are active and their population levels.
Bertha Armyworm: Bertha armyworm populations were low and the peak flight occurred during early to mid-July. The highest trap catches were located at trap sites in the north tier of ND – Cavalier and Ramsey counties (Fig. 7). The majority of the trap sites, about 94%, had cumulative trap catches below 300 and was at "low" risk of larval infestation. Overall, the 2007 trapping season showed a slight increase in cumulative trap catches from previous years. However, cumulative trap catches in 2007 marks the forth year in a row with low risk for bertha armyworm infestations. Canola fields did not require any insecticide treatments for control of the bertha armyworm in 2007.
Diamondback Moths: Diamondback moth populations increased during late June to early July, probably representing the second generation. Field scouting is recommended when more than 100 diamondback moths are captured per trap week for several weeks prior to the susceptible crop stage, bloom to early bud development. Sites with the highest trap counts per trap season included the north central and eastern regions of ND (Fig. 8). Some canola fields required an insecticide spray for control of diamondback moth in 2007.
A total of 303 soybean fields were surveyed in 31 counties in ND during 2007. This number represents approximately one field surveyed per 12,871 acres of soybeans. The survey was initiated on June 1 and continued through August 9, 2007. Crops were surveyed from the V1 through R5 crop stages.
Soybean aphid: Aphids were counted on 4 plants from five locations for a total of 20 plants. If aphid population density exceeded 250 aphids per plant (economic threshold), aphid density was estimated. Aphids were found in 23% of all fields surveyed and observed from late June to end of survey (early August). Peak population densities occurred from late July to end of survey. The average percent of infested stem was 4%, with ranges between 0 and 90% (Fig. 9).
The average number of soybean aphid per plant was only two, with ranges between 1 and 13 among the positives (Fig. 10). In contrast to 2006, soybean aphid was not major insect pest problem in 2007. An estimated 10% of the soybean fields were treated in the Red River Valley and the southeast region of ND. Treated fields were often infested with other pests, such as green cloverworm and bean leaf beetle as well as soybean aphid.
A total of 137 sunflower fields were surveyed in 38 counties in ND during 2007. This number represents approximately one field surveyed per 1,000 acres of sunflowers. The survey was initiated on June 18 and continued through August 14, 2007. Crops were surveyed from the V4 through R5 (flowering) crop stages.
Sunflower Beetle: The number of adult and larvae sunflower beetles were counted on 10 plants from five locations for a total of 50 plants per field. Populations of sunflower beetles were very low. Adults were found in 4% of the sunflower fields surveyed and the average number of adults per plant was one (Fig. 11).
Most of the sunflower beetles were observed in the northeastern region of ND. No larvae were observed. These numbers are well below the economic threshold levels, 1 to 2 adults or 10-15 larvae per plant, for sunflower beetle. Overall populations of sunflower beetles continued to be very low in 2007, as in 2006. One of the possible reasons for the decline of sunflower beetles has been the recent use of insecticide seed treatments in sunflowers, which control sunflower beetles and other insect pests.
Banded Sunflower Moth: A total of 22 pheromone traps in 15 counties were monitored for banded sunflower moth using the wing styled trap design. Trap catches were high in most major sunflower growing regions, especially in the north central, southwest, and central regions of ND (Fig. 12). Many sunflower fields were treated for banded sunflower moth in 2007.