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IPM Stuff Newsletters: Issue
9 - August 22, 2008 Sign up for the SWROC Crop Production list serve by e-mailing Molly Werner 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: If you receive these newsletters as forwards and would like to be on the mailing list subscribe send a request to Molly Werner. You get what you pay for. This is a free newsletter.
This has been a tough spring in Southwest MN as it has been in much of the Corn Belt. If your own difficulties in getting fields planted aren't enough to convince you, the soil moisture at the U of M Southwest Research and Outreach Center; Lamberton, MN (SWROC) is considerably above average. Temperature observations, rainfall and other weather trivia are updated daily and summarized weekly on the SWROC website.Yup, we're colder and wetter than average but weather likes to change. As always, the biggest driver for crop yields will be the weather during the growing season. A Sunday trip into eastern South Dakota showed intense field activity. Both corn and beans were being planted at a high rate of speed along MN 68 from New Ulm past Yellow Medicine County. Some early planted corn is now up and can be rowed. Some low spots look tough but from the road, but things look good in my windshield survey. Some areas are close to done with planting; some are just getting a good start. The cold, mostly open, winter and cold spring may lead
to relatively low levels of some of the insects that overwinter here.
Less insect activity than usual seems apparent when walking around outside.
The increased use of corn rootworm insecticides and seed applied insecticides
included with Bt hybrids should minimize several early season corn insects-
if there were any there to need minimizing. At this point, 2008 is shaping
up as a low insect year but the situation could change quickly. That's
probably OK because most have had enough stress just getting the crop
in the ground. Early Season Corn Stand Evaluations Corn scouting should begin in earnest as soon as fields can be rowed. I am guessing that most of you have already looked at some early planted corn before emergence to determine the need for a rotary hoe. Initial scouting efforts should focus on evaluating stand.
Determining the cause in areas with poor emergence might require some detective work because there are many potential causes of poor stand.
Was seed planted? My suggestion is to start with the obvious. Most of us can make a mistake once in a while and any mechanical device is predestined for failure.
How about planting depth? Shallow planted corn might emerge more quickly but may emerge less evenly than corn planted a bit deeper. Shallow planted corn (< 1 ½ inches) is exposed to greater temperature fluctuations and less consistent moisture. Shallow seeded corn is also at risk for poor root development and root feeding insect damage when it does emerge.
What is the seedbed condition? Poor seedbed preparation aggravates seed placement and emergence issues. Sidewall compaction and opening seed furrows leading to seed/seedling desiccation are common when fine textured soils are worked wet. Heavy rains and standing water can lead to crusting and emergence issues.
Did the seed germinate? Lack of moisture or cold conditions are the primary cause of poor germination; both conditions are more likely to occur with shallow planting. Once in a great while, poor vigor seed has a hard time with stressful conditions.
Has the seed rotted? While fungicide seed treatments do an adequate job of protecting corn seed and emerging seedlings from fungal pathogens (usually Pythium and Fusarium) but can occasionally be overwhelmed under prolonged very wet, cold conditions. Some early planted corn was under water for a considerable amount of time. Drowning, or lack of oxygen, can sometimes be a reasonable explanation for death and subsequent decay of corn seed and seedlings.
Is there evidence of insect feeding? Seedcorn maggot and wireworms are the two insects most often associated with corn emergence failures in SW Minnesota. Seedcorn beetles can also occasionally reduce stand. Slow emerging corn is at greater risk from these below ground pests. White grub damage usually shows up later. There is no effective rescue treatment, for these insects after corn is planted. Cruiser® and Poncho® neonicotinoid insecticide treated seed and labeled corn rootworm insecticides should provide some protection for these insects.
Several species can have multi-year life cycles depending on food supply and climate. The germ of the seed and the mesocotyl or growing point of larger corn may be attacked. Above ground symptoms are wilted plants or stunting. Stunted plants are often purple as with phosphorus deficiency or dark blue green in color. Wireworms and their feeding injury occur below ground. Damage is often worse in cooler springs for two reasons. Corn development is slowed and corn plants are more vulnerable when small. Wireworms prefer cooler temperatures and will move down in the soil profile as surface temperatures warm. Larger wireworms may hang out for a last "bite" even in warm soils.
A labeled corn rootworm soil
insecticide or neonicotinoid insecticide treated corn seed are recommended
in replant situations. Wireworm larvae are attracted to geminating seed.
It is not unusual to find wireworm larvae near corn seeds killed by other
factors.
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The
Seed corn maggot is the larva of a fly. The adult resembles a small
housefly. Damage from this insect is worse when corn emergence is delayed.
Egg- laying adults are attracted to decaying organic matter. Fields at
highest risk are those with heavy applications of solid manure and where
a green manure (including heavy weed infestations) has been worked in.
Seedcorn maggot larvae are small white maggots and have weak mouthparts
able to attack corn seed after softened by water uptake. Some tunneling
in below ground tissues may occur. The larvae attack the seed of both
corn and soybeans. Seedcorn maggots have very quick life cycles. Often
only the dark oval pupae, empty pupal cases or feeding damage are found
by the time stand loss is detected. Labeled planter box treatments, neo-nicotinoid
insecticide seed treatments and corn rootworm insecticides provide control. 
Several
species of wireworm occur in Minnesota. The predominate species observed
in 2001 SW MN corn was the corn wireworm, Melanotus similis. Wireworms
are the larval stage of click beetles. They are "wormlike" with an elongate
body, distinct heads, small but visible legs and a hard textured body.
Most species are dark orange, although a cream colored species also causes
problems in SW MN. Unless you've score a direct hit with the trowel, they
are very active when disturbed. Wireworm can often be observed when digging
in fields in early spring. Finding them does not mean stand loss is inevitable.
Historically, wireworm problems have been associated with fields planted
after sod but can injure fields in a corn-soybean rotation. Wireworm problems
are most frequently encountered in high organic matter, low-lying areas
and especially on alkali rims in this part of the world. 