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IPM Stuff Newsletters: Issue
1 - February 18, 2009 IPM Stuff Classics Corn
Planting Depth - 3/5/99 SWROC Pages: Home Page Other Cropping Newsletters: Minnesota Crop eNews - Regional Newsletters Minnesota Fruit and Vegetable IPM News The Bulletin - Other States IPM Newsletters
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Integrated Pest Management Newsletters and Information IPM Stuff Print this newsletter using Acrobat Reader Table of Contents:
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Crop WeatherKeep up to date on all the crop weather details during the growing season at the SWROC's weather page.
Moisture stress was visible in many fields late last week and early this week. The Morris area is particularly dry. Many areas, including Lamberton, received a welcome shot of moisture and are looking quite perky again. Other parts of SW MN are on the wetter side or have missed significant rain and need some soon. It's a typical SW Minnesota summer growing season-variable and flirting with drought.
WheatThere is nothing more that you can do with the 2009 Southern Minnesota spring and winter wheat crop, other than waiting to combine in a few weeks. Fields that had significant rainfall the past couple days should fill well. The cooler temperatures occurring recently and those that are forecast should be perfect. Recent rainfall might favor leaf disease but yield impacts on dough stage wheat should be slight. Other than severely dry areas, most of the wheat looks good.
AlfalfaPotato Leafhopper populations have increased. Pay attention to third cutting and new seedings. Jim Nesseth reported hopperburn on re-growth in Jackson County. I would expect leafhoppers to be more numerous in areas with more frequent rainfall as weather systems bring in adult leafhoppers from the south.
Treatment thresholds (leafhoppers/pendulum sweep) are:
CornCorn is V11 and up in most fields. We could start seeing some tassels in early planted fields next week. From this point forward moisture stress will have an increasing impact on yield. After tassel emergence, root development, for the most part, and leaf development is over. Corn is the most vulnerable to root lodging just before tassel as brace root development has not been completed. In fact, I observed scattered root lodging from Milroy to Morris today. What I observed was minor.
Eyespot is present at low levels in a few fields. Eagle-eyed consultant Mark Bernard spotted symptoms of this leaf-spotting fungus in some corn on corn situations. Otherwise, corn that I have looked at is clear of foliar disease.
Corn rootworm Pupation is occurring. I would expect the first adults late next week with emergence stretching into September.
Just when you think you've seen everything. Things were a bit boring as far as insect problems this spring. Then, Marty Lovrien called last Wednesday. He asked if I wanted to see something odd in a irrigated Sherburne county corn field. It would add to a long day of driving but curiosity got the better of me. When I arrived at the location, I met the producer, his son and a collection of agronomic gray beards. After a brief period of visiting with a few folks I hadn't seen for quite a few years, we headed to the field to see an insect infestation that none of us were familiar with. Through dexterous use of the diagnostic handbooks and the internet, the first responders to the scene had the problem correctly identified as corn blotch leafminer. In the past, I have observed the occasional corn plant with leafminer symptoms but nothing like the injury witnessed here. The damage was impressive and flies, larvae and pupae were present. Some upper leaves of 10-leaf corn were injured with damage increasing in lower leaves. Today, I observed adults and larval damage at very low levels and more typical levels at the West Central Research and Outreach Center, Morris, MN.
Why was this particular field (fields) so severely infested? Presumably a unique set of environmental circumstances favored this insect. Another possibility might be a dramatic reduction in biological control organisms from any one of a number of possible causes. If you know of heavy infestations of this insect I'd appreciate hearing from you. It would be interesting to see how widespread the problem is and if there is any common environmental denominator. What follows is an overview of what we know about this insect and is, for the most part, paraphrased from the references listed:
The corn blotch leaf miner, Agromyza parvicornis Loew, is an uncommon and infrequent pest of corn. This fly is in the family Agromyzidae and related to the alfalfa blotch leafminer. Damage is caused by larvae tunneling (mining) in the leaf resulting in a loss of photosynthetic area. It is widely distributed in the U.S. and southern Canada. The early work on biology of this insect was published by W.J. Phillips in 1914 (I have not gotten my mitts on this primary reference yet but will soon). The insect rarely causes economic damage and is usually controlled by a large number of natural enemies. In recent years, unusually high populations of the insects occurred in Nebraska (1995). Other states including Wisconsin, Indiana, Illinois, Florida, and Idaho have had localized outbreaks since.
Corn blotch leafminer adults are gray, about ¼ inch long and resemble small houseflies. The female pushes back leaf epidermis and lays its eggs inside corn leaves. The host range may include several other grass species (barnyard grass and crabgrass) in addition to corn.
The egg laying produces causes small but obvious scars. Females can lay 100 or more eggs during its lifetime. The eggs hatch in 3-5 days and larvae begin feeding inside corn leaves leaving visible tunnels under the epidermis. The larvae have mouth hooks that scrape away green leaf tissue between the surfaces of the leaf. Larvae feed for approximately one week with the tunnel widening near the end as the larva grows. Larvae and frass can be seen in larger, more transparent, mines on leaves. An individual leaf can be infested by many larvae. Heavy mining can kill parts of the leaf and the removal of green tissue prevents photosynthesis in the affected parts of the leaf. On larger, upper leaves, only one side of the leaf might be mined, damage less visible and yield impacts decreased.
Larvae leave the plant to pupate in the soil. Adults emerge in two to three weeks, the entire life cycle being completed in 4-6 weeks, depending on temperature. The insect has 3-5 overlapping generations, and is presumed to complete fewer generations in northern areas. The insect probably winters as a larva in warmer areas or a pupa, the latter most likely in Minnesota.
Yield loss, if it occurs is likely through loss of photosynthetic area. Nebraska information indicates that yield loss can be estimated using hail adjusting charts.
Because of infrequent occurrence of economic injury, there are no scouting methods or economic thresholds developed for corn blotch leafminer. Treatment is generally not recommended. Larvae are protected from insecticide within the leaf. Control would have to be directed against the adults and timing is difficult with multiple overlapping generations. Insecticide applications have a downside risk in potentially further reducing parasite populations.
Corn blotch leafminer adults and mines in corn leaf
Corn blotch leafminer pupa
Corn blotch leafminer damage. Larvae are visible in tunnels near center of photo.
Corn blotch leafminer injury. Mines and oviposition scars.
Selected References: Alvarez, J.M, G. Harding and R. Findlay 2002. Identifying the Corn Blotch Leafminer. CIS 1078.
Goyal, G and G.G. Nuessly. 2008. Featured Creatures: corn blotch leafminer. Agromyza parvicornis Loew (Insecta: Diptera: Agromyzidae).
Steffey, K.L, M.E. Rice, J.
All, D.A. Andow, M. E. Gray, J.W. Van Duyn (eds.). Handbook of corn
insects. 1999. The Entomological Society of America
Wright R.J. 2006. Corn blotch leafminer. NebGuide.
Wright R.J. July 2, 2009. Pers. Comm.
SoybeansSoybean aphids are present at very low levels. Populations in research plots at Lamberton and Morris are increasing but not unusually quickly. More heavily infested areas are now at 20-30% of the plants with aphids. Numbers/plant are remaining fairly low but individual plants with 100-400 aphids/plant were observed at both locations. Each field is unique and some large geographic areas have few aphids at this time. I'd say that most fields are still at yellow alert with a few at orange alert. This could change fairly quickly. I would recommend spending some time late this week and early next week getting a feel for aphid populations in your area. The economic or treatment threshold through the R5 stage is: 80% or more with aphids and an average of 250 soybean aphids/plant. If your aphid populations seem unusually pessimistic this year, they may have come from Lamberton. Any aphids observed complaining how bad the crop is might have been in contact with George Nelson at Morris.
Spider mites Al Van Grow reported two-spotted spider mites in southern Brown County, Ken Ostlie has observed spider mites in Dakota County and Paul Gronenberg has seen some spider mite activity in West Central MN, all droughty areas. Populations were not at economic damaging levels, yet. Spider mite populations are favored by hot, dry weather and can damage a wide range of crops. Spider mite populations are poorly controlled and can be flared by insecticide applications - a reason to avoid insecticide applications for imaginary soybean aphids.
Department of Entomology |
False
Japanese beetles were observed in near St. James last week. Emerging
adults were numerous in an area with sandy soil. The brown beetles have
a dull metallic green iridescence (which does not show well in the photo)
on head and thorax. They are similar in overall appearance to a small
(less than ½ inch) June beetle and in fact are a member of the same
family (Scarabidae). The native false Japanese beetle is similar in
appearance to the more destructive and introduced Japanese beetle. The
latter is not yet a problem in SW Minnesota. False Japanese adults lack
the bright green metallic iridescence on the head and thorax, coppery
iridescence on the elytra (hardened front wings) and five white tufts
of white hairs along the side of the upper abdomen of the Japanese beetle.
False Japanese beetles are not shy and from a perusal of fact sheets
are often mentioned to be attracted to white including flowers, and
clothing. False Japanese beetles are more common in sandy soils and
another common name is the Sandhill chafer. Larvae feed on roots and
adults feed on foliage. Neither stage is generally considered a pest.
Harvestland agronomists observed non-economic soybean leaf feeding by
adults and provided the specimens. Soybeans in the R1/early R2 stage
can tolerate 35% defoliation without yield loss.