ISSUE 4 May 23, 2002
COLD WEATHER KEEPS INSECTS QUIET
The cold weather had kept insect activity to a minimum. The soil insect threat, such as wireworm or seed corn maggot, has been difficult to assess with slow emergence of crops. With the warming conditions, check stands early to determine if these insect pests have created any problems. In trees, leaves are developing rapidly and the Forest Tent Caterpillar should be feeding soon in eastern ND.
WHEAT MIDGE RISK WINDOW HERE
Degree days have been slow to accumulate. As mentioned last week, the northen half of the state had not reached the 200 DD mark. The northern most ND counties were just reaching that level at the time this report was written. By the end of the week, all counties should be in the planting risk window.
MOTH FLIGHTS AROUND REGION
There have been several inquiries about moths showing up around homes and workshops. The moths have been found in the morning, hiding under rags, seed bags, coveralls, etc.
The moths have been identified as Army cutworms. Remember in issue 2, reference was made to a south Dakota infestation and risk in southwest ND. Well, the larvae to the south of ND have completed their development, are emerging as moths, and are now migrating. Eventually, they should make their way westward, but some have been blown into the region.
These army cutworm moths pose no threat. They have only one generation per year and wonít lay eggs until late summer. However, if they have flown into the area, there are other moths that may be moving as well.
Color variations of Army cutworm moths (photos by Dr. Gerald Fauske, NDSU Dept. of Entomology)
Wing appearance of the True armyworm (note the white spot on the forewing)
If you want more information on moths in North Dakota, an online identification guide has been compiled by Dr. Gerald Fauske, NDSU Entomology Research Specialist. The site provides pictures and keys to aid in identification of moths collected in our state. It can be found at:
SUGARBEET ROOT MAGGOT: DEVELOPMENT SLOW, DELAYED EMERGENCE LIKELY
As one would expect, the cool temperatures that predominated throughout the Red River Valley (RRV) this spring have likely slowed development of the overwintered sugarbeet root maggot populations. For several years, NDSU has been collecting root maggot emergence and adult fly activity data and correlating it back to soil and air temperature accumulation to develop a predictive model. Typically, peak fly activity occurs in current-year sugarbeet fields on the first warm (80 degrees Fahrenheit or above) day following the accumulation of 600 degree-day units (DD). As of May 15, 2002, DD accumulations in the Red River Valley ranged from 93.3 DD at Baker, MN to 102.1 and 140.7 at St. Thomas and Wahpeton, ND, respectively. In more "normal" springs over the course of the past several years, these sites have exceeded 200 DD and have approached 300 units by this time. Thus, we expect that peak emergence from previous-year fields and subsequent peak activity in current-year beets to be delayed. How much? Unfortunately, that is the $64,000 question, and the answer will come as the weather runs its course over the next few weeks. Given the current DD levels and anticipated daily accumulation rates, peak activity is not likely to occur before mid-June, irrespective of location within the Valley. However, one should remember that RRV soils can warm up quickly and, therefore, maggot development could be accelerated if a warm trend were to occur within the coming weeks.
ROOT MAGGOT CONTROL FOR REPLANTING SUGARBEET FIELDS
A few small pockets of early-planted Red River Valley sugarbeets have needed to be planted due to losses from frost damage, wind-blown soil, or rotting seed in cold, moist soils. Growers are advised that replanted beets will be smaller and more vulnerable to attack during the root maggot larval feeding period than older, more established plants. Therefore, growers in areas where high maggot populations are anticipated are advised to consider two management options: 1) apply another granular material at replanting of the crop; or 2) apply a postemergence treatment of either a liquid or granular insecticide. It is critical to note that use of Counter 15G, Counter CR, and Lorsban 15G is limited to one application per year. Therefore, if one of these products was applied on a particular field at initial planting, another material must be used for the succeeding application.
Research & Extension Entomologist
FLEA BEETLE ACTIVITY IN CANOLA LOW SO FAR
There has been little feeding activity from flea beetles on canola in the north central and northwest regions so far. Most of the canola is planted. Some of the earlier planted canola is just starting to emerge. The weather conditions have not been favorable for flea beetle movements from their overwintering site to new fields. Itís been too windy and cool. There was one report from the southwest region near Mott where flea beetles were feeding and causing significant damage to mustard. Flea beetles will feed on mustard when canola isnít around. However, canola is the preferred host of flea beetles.
Field monitoring for flea beetle activity should begin in newly emerged canola fields. Assess the canola field for presence of flea beetles and their feeding damage or pitting for the first 14 days after crop emergence, or until plants have reached the 4-leaf stage. Fields should be checked daily to identify damage as it develops and to make timely management decision.
The amount of defoliation should be used as a guide to determine the need for management action. Injury often occurs first at the field edges, particularly where a shelterbelt/grassy area borders a field. To determine the extent and distribution of damage, start at the field margins and walk into the field, selecting plants at various random intervals. Estimate percent defoliation for each plant selected. The economic threshold for a foliar application is when an average of 25% of the surface area of cotyledons and first true leaves has been injured and beetles are present. If leaf damage is less than 25% and the crop is actively growing, the crop can usually recover. Watch fields closely in hot, dry weather, when flea populations can rapidly increase.
Fields that have been planted with a seed treatment should still be scouted during the first two weeks after canola emergence. If the seed was in the ground for a long time prior to emerging, protection from the insecticide seed treatments could be reduced. Fields that are planted to seed treatments only on field edges should be scouted as well. The beetles readily fly when temperatures exceed 64oF and will move quickly into the fieldís interior. Beetles are most active during sunny, warm, calm and dry weather conditions. Feeding activity is expected to increase next week when temperatures warm up to 70NF.
Area Extension Specialist