Variegated Cutworm in
Sugarbeet – July 14, 2007
There have been reports of
variegated cutworm in sugarbeet. We
have had this problem before, back in August 2001, both variegated and black 
cutworm were a problem
in beets. Cutworms are climbing
feeders and it is not uncommon to see them feeding in the daytime, unlike many
other species. At this stage damage
is generally minor but with large populations, feeding damage can occur to the
younger growth in the crown.
They are relatively easy to scout - individual caterpillars can be easily seen, defoliation will be visible and there will be considerable frass present. The caterpillars are medium to dark grey with a light stripe on the side and small, somewhat diamond shaped yellow or orange spots on the top near the head. Younger larvae are ~.25” long while the mature, ready to pupate worms can be 1.5” – 2” long. When scouting, pay close attention to land adjacent to grassy borders and to weedy patches neighboring or in the field.
Because it feeds in the canopy, it is susceptible to foliar applications of insecticides. Some research indicates pyrethroid insecticides may be more effective but remember possible efficacy issues with these chemistries if applying at high temperatures (in the 90’sF). Control is recommended when populations reach 3-5 larvae/sq.ft. in late season beets, post canopy closure.
Grasshoppers Starting to Hatch – June
27, 2007
There have been numerous reports of grasshoppers beginning to hatch in the egg production areas (CRP and other non-tilled areas like roadsides, ditches, etc). There is a new version of Minnesota Grasshopper Management with updated insecticide recommendations available at:
Minnesota Grasshopper
Management – 2007
Small
Grain Insect Update – June 19, 2007
Aphids - Surveys indicate that although cereal aphid numbers are increasing, they’re not increasing as quickly as they did last year. Much of our grain in the northern RRV is flowering and fields are reporting anywhere from 30% through to 90% of stems with aphids (remember the threshold is 80% - 85% of stems with aphids, when populations are that heavy, then the probabilities say there’s likely to be >12 aphids/stem across the field). Slow growth may mean that fields with low numbers now will remain below threshold at/after heading. Research shows that the amount of aphid damage necessary to cause economic loss increases as the plant matures. This is partly because there are decreasing opportunities to lose yield; early in the crops life, aphid feeding may stunt the plant and/or decrease the number, size and weight of kernels. As the plant grows, stunting is no longer an issue; around flag, aphid feeding may decrease kernel numbers, size & weight, by late boot it can affect only kernel size and weight, by heading it can affect only weight, and so on. This is why it is unlikely to get an economic return from aphid treatments at/after heading. If a field is already at threshold but will be treated for fungicide in the future, make an economic decision regarding your insecticide application; you may lose yield by delaying aphid treatments depending on how long you plan to delay application (check out the discussion about aphid days and loss below).
Armyworms – Very high light
trap captures have occurred over the past week at Lamberton and in 
the flights so begin scouting for these
insects next week.
Some Information - Armyworms do not overwinter in northern MN. Populations are re-established annually by immigrants, arriving on southerly winds in the spring or early summer. These wind events are often linked with changing weather fronts. Adult armyworms live for approximately 2-3 weeks, with the females able to lay eggs for about 7-10 days of that time. Eggs hatch in 7-10 days and the larvae go through 6 stages (instars). It takes 3-5 days to complete the earlier larval instars and food consumption essentially triples at each instar. Still, the heavy feeding which causes the greatest yield damage doesn’t occur until the caterpillar is in the 5th instar – about 2 weeks post hatching (or 3-4 weeks after the peak flight). The 5th and 6th instars can cause considerable damage to small grains, consuming the flag and lateral leaves and then possibly clipping the tillers themselves.
Armyworm populations can be impacted by a number of factors. Low temperatures may prevent adult moths from flying and mating or may slow egg development, rain can wash younger caterpillars off of leaves to the ground where they are subject to increased predation, parasitic wasps often infect armyworm caterpillars (the eggs of these beneficial insects appear as white or brown capsules along the backs of the caterpillars), and fungal diseases can infect caterpillars and significantly decrease populations. If any or all of these factors occur, outbreaks stand a good chance of fizzling out. Consequently, treatment decisions shouldn’t be made simply on the basis of trap catch data, especially the decision to add an insecticide to fungicide being applied within a week of a high trap catch. Although its tempting to save application costs, it may not address the problem entirely. None of the insecticides registered against armyworms in small grains are very effective against the eggs, the stage most likely to be present in the field for the first 7-14 days after a high trap catch (females will be laying eggs for 7-10 days, and once laid the eggs take another 7-10 days to hatch). In addition, the residual activity of the registered products may not be long enough to deliver sufficient mortality of caterpillars hatching over the next 1-2 weeks. Add to that the fact that armyworm populations are often not evenly spread throughout a region and neighboring fields frequently have different infestation levels. Economically, it’s a better decision to scout over 1-3 weeks after a flight and make treatment decisions on a field by field basis. In this way, armyworms can be detected while still small, prior to significant yield loss.
Scouting, Thresholds & Treatment – Scout for armyworms at grassy margins of the fields, low, weedy areas in fields or in lodged grain; populations are more likely to develop in these areas first. Armyworms prefer the edges of leaves first and are messy, wasteful eaters. Because they generally retreat during the day under soil and plant residue on the ground and feed more often beginning at dusk, it’s easier to scout for armyworm damage than the armyworms themselves. Look for leaves that have been notched, cut and partially eaten leaf material on the ground, and small round pellets (armyworm frass, i.e. bug poop) near the base of the plants. Consider applying insecticide if: there are 4-5 armyworm larvae per sq. ft., caterpillars are ¾ - 1 ¼ in. long, leaf feeding or head clipping is found, and parasites are not evident. By the time armyworms are more than 1 ½ in long, they have stopped feeding and are getting ready to pupate. At this point the damage has already been done and control applications will probably not provide an economic return.
Small Grain Aphids Update – June 11, 2007
Quick
surveys of several small grain fields around Crookston this morning (June 11) showed
very low but relatively wide spread populations of cereal aphids (mostly Bird
Cherry Oat aphid). About 50%
of plants sampled had aphids but the numbers are low (~2-5/plant). But
because the proportion of plants with aphids is rising and the numbers down in
the SW part of the state are high and we’re still getting southerly
winds. Added into that,
they’re seeing lots of Barley Yellow Dwarf in
Total CAD isn’t the whole story, however. The rate of yield loss decreases as the plant matures. There are a number of reasons: physiological changes in the plant and maturation of the grain make it less susceptible to aphid damage, after heading the plant starts to become less suitable as a host, aphid populations start to decline, and natural mortality factors, such as predators, start to impact the population so that aphid populations generally start to decline within 2 weeks after heading. From heading on, there usually isn’t enough time to accumulate sufficient aphid days to cause the amount of yield loss that would economically justify an insecticide application.
Data suggests that the way CAD accumulate also influences the amount of resulting yield loss. Lower populations of bird-cherry oat aphids that fed over a longer period caused greater yield loss than did higher populations feeding for a short period even though the CAD were about the same. So, generally speaking: the longer they feed, the more damage they do…
The Bottom Line – Keep an eye on the populations for now and see what happens, don’t treat before threshold, and don’t wait for fungicide application at heading if you’re at threshold now.
Moths in Small Grains – June 01, 2007
There have been numerous reports
of moths in small grains throughout the RRV. We have had wind events that are of the
type that bring us insects from the south (see below) – but in this case
it’s not likely a problem. By
far the most common moth in grain fields this week was the Forage Looper, Caenurgina erechtea (in case you want to look it up what little literature there is on this
critter). They are common
throughout most of
They have a light brown forewing, the females have two contrasting darker bars on the forewing while the males (not as fashion conscious!) have bars that are not contrasting in color but are outlined in a darker color. The larvae are foliar feeders on clover, alfalfa, grasses, and ragweed and may feed at night while hiding in the day. I have not been able to find any reference to them feeding on small grains but they have been reported as occasional pests on alfalfa and sometimes clover so forage producers might want to keep an eye on them.
These moths will flush up ahead of you as you walk through the field and make quick, fluttering type flights before diving back down to the plants again. It belongs to the family Noctuidae, sometimes called the Owlet or Miller moths. Moths in this family typically are night fliers but adult Forage Loopers are active both in the day and night. Because the Miller (Owlet) moths are attracted to lights, they’re often the ones found around your outdoor lights at night. Adult Miller moths feed mostly on nectar or other sweet fluids.
Click on images for larger versions
Aphids in Small Grains – May 30, 2007
There have been some limited reports of winged aphids in small grains in the region. It’s possible that we’re getting our aphids a bit early this year. The aphids we get in small grains cannot overwinter in the region, rather populations need to be re-established annually from locations to the south. And there appear to be significant source populations in those state this season; in Nebraska, Barley Yellow Dwarf is reported as being wide spread throughout the south-central and southeastern parts of the state and in Kansas Bird Cherry-Oat aphids were prevalent throughout the eastern 2/3 of the state but seem to be decreasing now. We have also had at least two wind events that could have moved cereal aphids into the region (one of which is shown in the figure below). It’s important to note this doesn’t mean we have aphids, just that scouting is recommended. Appropriate treatment timing for aphids is around flag leaf, earlier than that and there is still a good potential for re-infestation, later than that and there is a decreasing chance for economic return. Thresholds for aphids in the northern great plains are when approximately 80% of stems have aphids present. This threshold is designed to prevent yield loss from aphid feeding, it does not incorporate losses from BYDV.
The map below shows a wind event
that crossed both
Selected Past IPM Updates
August 3, 2006 - Tank
Mixing Insecticides & Fungicides in Sugarbeet
July 25, 2006 -
Two-Spotted Spider Mite Feeding Damage
July 19, 2006 -
Soybean Aphid regional Update
June 16, 2006 - Orange Wheat Blossom Midge in Southern
MN? Let’s Find Out!
May 30, 2006 -
Soybean Aphid Makes A VERY Early Arrival
May 19, 2006 -
Cutworms in Sugarbeet
June 16, 2006 - Orange Wheat Blossom Midge in Southern
MN? Let’s Find Out!
May 30, 2006 -
Soybean Aphid Makes A VERY Early Arrival
May 19, 2006 -
Cutworms in Sugarbeet
July 05, 2005 –
Armyworm Flight, Crookston
June 06, 2005 –
Soybean Aphids – they’re back
May 23, 2005 –
Cutworms in Sugarbeets
July 2003 - Leafminer in
Sugarbeets
July 2002 -
Armyworms in Small Grains
July 2002 -
Grasshoppers in The Red River Valley
May 2002 - Cutworms
in Sugarbeets
Fall, 2001 - Soybean
Aphid in NW Minnesota
August, 2001 -
Lygus in Sugarbeets
July/Aug, 2000 -
Armyworm Outbreak in RRV
Fall, 2000 - Soybean
Aphid, A New Insect Pest in Minnesota Soybeans
June 20, 1999 - Potato
Leafhopper, Grasshoppers, Cereal Insects
Sept 12, 1999 -
Impact of Aster Yellows on Canola May be Greater Than You Think
Aug 31, 1998 -
Lygus in Sugarbeets
Publications Available for Download
Insects
Grasshoppers -
Minnesota Grasshopper
Management - 2002 with color graphics
Minnesota Grasshopper
Management Brochure with scouting and control information (available as a
PDF file designed to be a tri-fold brochure).
Scouting -
Scouting for Insects
in Wheat, Alfalfa, and Soybeans - a manual prepared for the
Early Season
Scouting for Soybean Aphids - A guide to scouting early season soybeans for
soybean aphid.