Volume 2, Issue 8
August 2, 2019
This newsletter is an update on current topics and events in agriculture in Boone, Dallas, Jasper, Madison, Marshall, Polk, Story, Tama, and Warren counties.

Meaghan Anderson
Extension Field Agronomist

ISU Extension & Outreach
220 H Avenue
Nevada, Iowa 50201
Office:  515.382.6551
Cell:     319.331.0058

Upcoming Events

IDALS Apr 19 - Dec 19 Pesticide Testing Schedule

July-Aug - Farmland Leasing meetings, various locations

Aug 6-8 - Beef Feedlot Short Course, Ames

Aug 8 -
Conservation Practice Showcase Field Day, Madrid

Aug 9 -
Iowa State Fair Weed ID Contest, Des Moines

Late August -
Regional Soil Fertility Workshops, various locations

Aug 13 -
K-State UAV Roadshow (Free field day), Boone

Aug 15 -
Crop Disease Clinic, Boone

Aug 20-22 -
Iowa Drainage School, Nashua

August 28 - Ag Engineering and Agronomy Farm Field Day, Boone

Sept 9 - Ag Coffee - prep for fall harvest, Toledo

Handy Links

Central Iowa Crop Update
Updates from an agronomist and weed nerd in central Iowa.

In this issue:

  • Weather conditions
  • Thistle caterpillars - will they be back?
  • Scout for soybean gall midge
  • Scout for Palmer amaranth

Weather conditions

The Drought Monitor releases a new map every Thursday, and the data is valid as of the Tuesday AM before the map is released. Several central Iowa counties have shown up on the map due to low rainfall and the reduced root growth this growing season adding to the stress. Luckily, several of these counties received some welcome rain this week. We need continued rains to support these crops, especially with many of them having shallow or restricted root growth; the forecast seems pretty clear so we will wait and see. You can read up on some data from ISU about corn water use here.

The short term forecast for early August is still for above average likelihood of cooler and wetter conditions. Read more about the forecast from the National Weather Service Climate Prediction Center. 


Thistle caterpillars - will they be back?

The second generation of thistle caterpillars should be pupating or coming out as butterflies now. By Monday (July 29), I started noticing large numbers of butterflies out again on our rural roads. Expect to see more in the coming days. While this species is known to have two generations in Iowa in the summer, we are waiting to see if there will be a third generation of caterpillars in our soybean fields.

I will not be totally surprised if we see more caterpillars in soybeans. Scout soybeans closely over the next several weeks, especially those soybeans that are later planted or had large populations earlier in the season. I expect the third generation will be less damaging than the last one, but we will know more in the next couple weeks.

Photos of thistle caterpillars and the adult, a Painted Lady Butterfly.


Scout for soybean gall midge

We recently learned that soybean gall midge is creeping closer to central Iowa and has been identified by an agronomist in Adair and Guthrie counties. Please scout the edges of soybean fields for dying plants or those with galls, scarring, or browning at the base of the stem. Inside the stem, tissue will be brown and we can often find the larvae present inside the stem. Larvae are easy to spot as the 3rd instar is bright orange. 

Soybean stems with scarred, brown tissue and galls forming on some stems. These stems will be brittle and plants can fall over while still appearing healthy from above or can wilt and appear to be diseased.

Soybean gall midge larvae have three instars. The 3rd instar is bright orange.

These resources will help with scouting and identification of soybean gall midge in soybean fields. Please reach out if you think you've found them.

Scout for Palmer amaranth

This is the time of year where Palmer amaranth becomes easy to distinguish from waterhemp in crop fields and other areas. Now is a great time to take a closer look at that waterhemp and make sure it is what you think it is.

Palmer amaranth is relatively new to Iowa and still fairly unusual to find, but it is an aggressive relative of waterhemp, our worst weed in most crop fields. If we identify this plant when infestations are new, eradication is feasible. Persistent scouting of at-risk areas is imperative to keep Palmer amaranth from making permanent infestations in crop fields. It's important to be checking any farm field that:
  • had Palmer amaranth identified previously;
  • is a part of a farm utilizing out-of-state feed or bedding;
  • receives manure from a farm that uses out-of-state feed or bedding;
  • utilizes out-of-state equipment, either by purchase, rental, or custom work; or,
  • fields near areas of high grain traffic.
Palmer amaranth will have:
  • smooth stems that lack hair
  • separate male and female plants
    • males produce pollen and will not release small, black seed if you rub the seedhead
    • females are key to making an identification, as they will have long terminal inflorescences (flower stalks) and bracts surrounding flowers that will be sharp to touch

Here's a photo comparing the flowers up close on a female waterhemp and female Palmer amaranth.

A female Palmer amaranth plant has long terminal inflorescences with sharp bracts surrounding flowers.

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