Sticky-stake counts conducted on Friday, May 18 and Monday, May 21 indicated that the following areas appear to be likely hotspots for fly activity this year:  Auburn, Forest River, and St. Thomas, ND.  It should be noted though, that although several other areas have the potential for producing relatively high infestations.  Daily and cumulative counts for all monitoring sites can be viewed at: http://www.ndsu.edu/entomology/.  Just click on the “INSECT RESOURCES” link on the main page, and download the dated Adobe Acrobat (pdf) file.

SBRM fly activity is significantly impacted by weather. This has allowed us to develop a degree-day (DD) based model to predict the timing of peak activity of SBRM flies in current-year beet fields. Peak fly activity can occur at any time after the accumulation of 600 DD; however, NDSU research indicates that peak takes place, on average, at about 650 DD. It is important to note that warm weather (around 80°F), and calm to low-wind conditions are most conducive to fly activity. Flies will remain relatively inactive in cool, rainy, or windy conditions.  To determine degree-day totals for fields in your area, consult the Root Maggot application on NDAWN at: http://ndawn.ndsu.nodak.edu/sugarbeet-root-maggot.html.  The site also includes a “help sheet” with information on how to use the model, recommendations for whether insecticide applications are needed, and pointers on when to apply them.  A preliminary, extended forecast for anticipated DD accumulations and associated peak fly activity dates in the southern, central, and northern RRV is presented in Table 1.

Growers in hotspots or high-risk areas for SBRM infestation should consider applying a postemergence insecticide, especially if an insecticidal seed treatment or a low to moderate rate of an at-plant soil insecticide was applied. Postemergence granules are usually effective if applied between 2 weeks and 5 days before peak fly, but will also likely be beneficial if applied within a 1-2 days (before or after) peak.  Light to moderate rainfall after granular applications typically improves performance.  Postemergence liquid insecticide applications should be targeted for peak fly, but will provide good results if applied within 2-3 days before or after peak.  As Table 2 indicates, there is still plenty of time to apply either a granular or liquid material for SBRM control this season.

For more guidance on postemergence control strategies, consult the “Insect Control” section of the 2012 Sugarbeet Production Guide or the “Sugarbeet Insects” section of 2012 Field Crop Insect Management Recommendations.  Online versions of these publications are located at:

http://www.sbreb.org/Production/production.htm

and

http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm

Mark Boetel

Research & Extension Entomologist

mark.boetel@ndsu.edu

At 300 DD, field scouting is initiated for alfalfa weevil adult. The 300 DD base has expanded to the southern half of North Dakota and up into Grand Forks area from last week. See last issue 4 of Crop & Pest Report for more information.

Janet J. Knodel

Extension Entomologist

janet.knodel@ndsu.edu

http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/ICG_12/e1143_all.pdf#page=23

Janet J. Knodel

Extension Entomologist

janet.knodel@ndsu.edu

The alfalfa weevil DD accumulation is displayed in the map of North Dakota for May 14, 2012 (source:  NDSU NDAWN – Applications – Insect Degree Days).

At 300 DD, field scouting is initiated for alfalfa weevil adults. As you can see from the DD map, only the southeastern corner of North Dakota including Cass, Ransom, Sargent, Dickey and Richland has reached 300 DD. Alfalfa weevil adults are identified by dark brown band down the back of small (¼ inch) brown snout beetle. Two other weevils that can be confused with the alfalfa weevil are the clover root curculio and Sitona weevil, but neither have the dark brown band down the back. Adults chew holes in leaves. After several weeks, females lay up to 40 eggs in stems. Major leaf feeding is caused by the larvae at 504-595 DD. When leaf feeding is observed, cutting the fields early is one of the best strategies for control.  After cutting, monitor carefully for signs of damage or delayed regrowth, particularly in the swath area where larvae may be concentrated. When early cutting of the crop is not possible, treatment should be considered when 30% of the plants show feeding damage and larvae are still present.

Janet J. Knodel

Extension Entomologist

janet.knodel@ndsu.edu

Continue to scout all cereal grains (winter wheat, spring wheat, barley, oat) from the vegetative to boot stages for cereal aphids. Strong southerly winds will continue to blow aphids into North Dakota, so population levels need to be monitored closely. The action thresholds is 85% stems with more than one aphid present or 12-15 aphids per stem, prior to complete heading.

Janet J. Knodel

Extension Entomologist

janet.knodel@ndsu.edu

These names are: Macrosteles quadrilineatus, M. fascifrons, and M. divisus. The first two were ultimately separated by hosts - M. fascifrons is a darker marked species feeding on rushes. That leaves the confusion between M. quadrilineatus and M. divisus. The older literature confused these two species and both species were claimed as vectors of aster yellows. More recent literature indicates that primarily M. quadrilineatus is a good vector of aster yellows. Since Macrosteles species are sap feeders, extension entomologists believe that M. divisus would be capable of transmitting plant diseases as well. Macrosteles divisus is the species being observed in wheat in South Dakota and Nebraska (Source: A. Szczepaniec, SDSU & R. Wright, UNE). Populations of M. divisus in South Dakota wheat fields have declined recently due to severe thunderstorms. This may be good news for North Dakota, since most of our leafhopper problem species are immigrants this time of year.

In order to settle the taxonomic and disease vectoring questions for our area, specimens of Macrosteles from crop fields are being mailed to Ottawa for re-confirmation of the identification since leafhopper taxonomy is very complex. We also are sending leafhoppers to Dr. Olivier of Agriculture and Agri-Food Canada in SK to be bioassay for the presence of aster yellows using PCR.

There are lots of questions about spraying for leafhoppers with the herbicide application in wheat or barley; however, there is no research data to support whether it would be economical to spray for high populations of leafhoppers in wheat or barley. So, our message is still the same and each field should be handled based on the producer’s decision and risk level.  See article below entitled ‘Not all Yellows are Created Equal’ for more information.

 Janet J. Knodel

Extension Entomologist

janet.knodel@ndsu.edu

These are all winged adults and so are likely the populations from the southern part of the state that are migrating north. We don’t have any data on what impact on yield these higher populations of leafhoppers may have on small grains but sap-feeding leafhoppers generally don’t impact yield. Having said that, leafhopper populations in typical years are much lower; in dry conditions, sap feeders have been known to exacerbate drought stress. Generally, leafhoppers are more important as vectors of the disease, Aster Yellows (AY). Caused by a phytoplasm, AY can infect wheat, and under the right conditions cause yield loss. Symptoms show up a couple of weeks after infection by the leafhopper and include yellowing of leaves, often accompanied with reddish or purple coloration (similar to BYDV). 

There have been several reports from the northern RRV of yellowing in small grains fields (see figure on right). While the primary symptom of Aster Yellows is yellowing leaves, it’s felt that leafhopper populations have not been established in the northern part of the valley long enough for AY to be the cause of this discoloration. On the other hand, there’s some indication that yellowing now being seen in the northern RRV is likely related to nitrogen and potassium deficiencies. Even in fields which typically have high potassium or good nitrogen levels, the dry soil conditions may be making these nutrients unavailable to the plants. So, yellowing may not necessarily be AY, but something else.

There have been a lot of questions about adding insecticide along with the next herbicide application in efforts to kill off leafhopper populations. Technically, not a difficult practice; almost any insecticide labeled in small grains will kill leafhoppers, and the small, thin crop canopy means there will be less of a deleterious effect of applying insecticides with the lower pressure and larger drop size you get from herbicide nozzles. But, as we currently have no data on the effect on grain yields of these high leafhopper populations, nor on how much AY is being transmitted in the field, we cannot provide a recommendation for or against this practice.

If you considering treating fields, there are a few points to keep in mind about your expected outcomes (you may need to modify your expectations):

1. AY phytoplasm is transmitted very quickly by the leafhoppers (just like non-persistent virus by aphids). If you have heavy populations of leafhoppers in your fields, plants may already be infected with AY. We know from experience that insecticides, both foliar and seed treatments, are not effective in managing quickly transmitted plant diseases (e.g. PVY in potatoes). In the time the insecticide takes to do its job, the disease can be transmitted. Consequently, don’t be too surprised if there are AY infected plants in fields later this season after you had successful leafhopper control. 
2. AY symptoms can be similar to those caused by a number of nutrient and other disease factors, including early-season tan spot, BYDV, nitrogen or potassium deficiencies. Removing the leafhoppers will not be effective in solving the underlying cause of yellowing.
3. The thin crop canopies make for a reduced expectation of insecticide residual.  They allow UV light, wind, and any moisture available onto all the leaves. These are the environmental factors that break down the active ingredients in insecticides. The plants are also still relatively small, meaning more vegetative material is going to develop, none of which will be protected by insecticide.
4. Shorter residual means potential re-infestation by immigrating populations of leafhoppers. Keep scouting fields.
5. Early spraying may remove predator insects that can limit later populations of aphids.  If we get aphids later in the season, sprayed fields may require re-treatment.  If aphids infest local grain fields, keep a close eye on their numbers (See ‘Continue to Scout for Cereal Aphids’ article).
6. Leafhopper populations in the south are decreasing so we may well see similar dynamics here in the next week or two.

Bottom line – we can’t recommend spraying, we can’t recommend not spraying – we just have no data.  But even if a field is treated, you may have to modify your expectations.

 Ian MacRae (UMN)

Jochum Wiersma (UMN)

Janet Knodel (NDSU)

Bruce Potter (UMN)

The third type of cutworm migrates up from southern states on favorable winds. Examples are the variegated cutworm, black cutworm and western bean cutworm. They do not overwinter in North Dakota. Variegated cutworms will lay eggs into the emerging field crops, but prefer pastures, and grassy weeds in fields that have not been tilled. These cutworms could become a pest problem in spring-planted field crops. Western bean cutworm is a new cutworm to North Dakota and is a major insect pest of corn and dry beans in other states.

The latter two types of cutworms illustrate the importance of field scouting for larvae to determine if your field is at action threshold. The key to controlling cutworms is frequent and regularly scouting, and proper timing of insecticide applications at action thresholds, preferably at night, when the crop is emerging. Action thresholds and insecticides labeled for cutworms in field crops are listed in the 2012 Field Crop Insect Management Guide at: 

http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm

Another good website to help you identify cutworms is “Moths of North Dakota.” Click on the “Photo gallery” and then “Pest Species & Common Moths.” 

https://www.ndsu.edu/pubweb/~gefauske/ndmoths/home.htm

Janet J. Knodel

Extension Entomologist

Start scouting all cereal grains (winter wheat, spring wheat, barley, oat) for cereal aphids, because the greatest risk of yield loss from aphids feeding on grains is in the vegetative to boot stages. Look on the underside of leaves and near the base of the plant for small, green, and pear-shaped aphids. The most common aphids on cereal grains in North Dakota are greenbugs, English grain aphids and bird cherry oat aphids. These aphids do not overwinter in North Dakota, and migrate into the region from the south in late spring. Greenbug is pale green with darker stripe down back. Bird Cherry Oat Aphid is olive green, brownish patch at the base of cornicles. English Grain Aphid is bright green with long black cornicles. The greenbug is the most injurious because it injects a toxin with its saliva during feeding. The English grain aphid is the most common aphid seen in small grains. Its population grows rapidly when feeding on wheat heads. The bird cherry oat aphid feeds primarily on leaves in the lower part of the small grain plant. These aphids transmit barley yellow dwarf virus. When aphid populations are high, the disease can spread through small grain fields. At greatest risk are later-planted fields which attract migrating aphids that are moving from more mature fields.

Cereal Aphid Thresholds:  To protect small grains from yield loss due to aphid feeding, the treatment threshold is 85% stems with more than one aphid present or 12-15 aphids per stem, prior to complete heading. Aphid populations at or above the thresholds will result in economic injury to plants.

Janet J. Knodel

Extension Entomologist