Blog

By: Daren Mueller and graduate students, Xavier Phillips and Chelsea Harbach

Some are noticing plants with green, yellow or purple stems. A few years ago we wrote a longer article on green stem, but since then we have been trying to sort through the root causes of green stem disorder. Here is what we now know:

As harvest begins and other plants in the landscape senesce, many insects and arthropods move to find overwintering habitat. Sometimes these animals seek out shelter in cracks and crevices of human structures such as houses and storage buildings. Common invaders include boxelder bug, lady beetles, millipedes, crickets, clover mite, pine seed bug and spiders. Pests enter structures accidentally and are generally harmless to people and property.

All across Iowa, the edges of woods are lined with plants bearing clusters of white flowers.  There's a good likelihood those plants are white snakeroot, a native perennial in the Asteraceae family.   The plant is best known for its role in milk sickness, an ailment responsible for the death of large numbers of settlers moving into the midwest in the 1800's.  Milk sickness was caused by cows grazing on white snakeroot.

Short Version:  493 miles in 12 hours; 2 out of 3 known Palmer amaranth sites well managed; no new infestations found.

Long Version:  I went to the three Palmer amaranth infestations in western Iowa that I am aware of.  This is the third year I’ve visited the Harrison county site, and the second for the others.

The last few weeks have been full of soybean aphid discussions. Populations have been going up, down and otherwise looked sort of bumpy this summer. Many fields exceeded the economic threshold of 250 per plant and were treated with foliar insecticides in August, particularly in northern Iowa. My lab had our big spray day last week, as aphid numbers approached the threshold. Of all the products we are using, we are seeing good efficacy, or knockdown, for soybean aphid.

Corn rootworm adult emergence is underway in Iowa. The three species of rootworm found in Iowa include the northern corn rootworm (NCR), southern corn rootworm (SCR), and western corn rootworm (WCR). Adults of all three species can be found until the first frost. Knowing how to distinguish the three species is important for making management decisions for future growing seasons.

Wild parsnip is an invasive plant commonly found in roadsides, pastures, restored prairies and other areas with full sun and minimal disturbance.  It is a biennial that forms a rosette with 'celery-like leaves' (Fig. 1.) and an umbel with yellow flowers (Fig. 2).

Are you seeing yellow-ish spots showing up in your soybean fields, especially in compacted parts of the field? This could be the start of Sudden Death Syndrome (SDS). With how wet its been there year, we've had the ideal conditions for disease development. 

Foliar symptoms of SDS, which look similar to foliar symptoms of BSR.

Waterhemp continues to be a problem in parts of northwest Iowa.  There is a fair amount of waterhemp that survived the glyphosate and/or Flexstar applications in late June. 

There is also a new crop of waterhemp that has germinated recently.   That fact is surprising since it has been fairly dry in July for a lot of northwest Iowa.

Proper selection of adjuvants is essential for effective weed control with herbicides.  Unlike herbicides, adjuvants are not regulated - thus anything can be marketed for this purpose and manufacturers are not required to describe the active ingredients.  This leads to the introduction of questionable products making unrealistic claims.  The newest ruse is the promotion of products with the supposed ability to overcome glyphosate resistance.

Most agronomists are aware of the movement of Palmer amaranth into Iowa.  Although known Iowa infestations are limited to five counties (Harrison, Fremont, Page, Lee and Muscatine) we are confident that it is present in many more counties.  We are pleased by the number of people who have notified us upon encountering suspect Palmer amaranths.

Yesterday during my class at FEEL, I asked participants to go out in the corn and soybean plots and find pests. It didn’t take too long to find a few plants loaded with soybean aphid. It was the largest natural colonies I have seen this summer (potentially exciting for my research but not great for farmers). They also found potato leafhopper, green cloverworm, Japanese beetle and corn rootworm. Not too surprising given its mid-July, and soybeans are blooming and corn is silking.

In case you want to try something a little different, you may be interested in listening to a podcast about field crop pest management. If you are new to podcasting, it is basically an audio file. Some people listen to podcasts on their computer/smart device, in their vehicles while traveling, or on a mp3 player (e.g., i-pod).