Integrated Crop Management News

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Can Weed Seed Production be Reduced with Late-season Herbicide Applications?

August 30, 2019

Problems caused by unfavorable conditions this season have resulted in greater than normal weed escapes. These weeds may reduce crop yields and definitely will contribute to future weed problems via new seed. While it is too late to protect crop yields, a common question is whether herbicides can be used to reduce the quantity of viable weed seed produced by weeds. While there is no simple answer due to the many different scenarios across the state, in most situations late-season applications are not warranted.  

Upper Soybean Leaves Began Showing Potassium Deficiency Symptoms Since Early August in Some Iowa Fields

August 23, 2019
Soybean potassium deficiency symptoms at early vegetative growth stages.

Since early August, soybean in several fields began showing typical potassium (K) deficiency symptoms on leaves located in the middle to upper canopy. This is not surprising in fields or portions of fields with soil-test values in the very low or low K soil-test interpretation categories that did not receive adequate preplant K fertilization. Potassium deficiency symptoms are well-known and very common in older leaves during early growth stages.

Scout Now for Palmer Amaranth

August 1, 2019
Palmer amaranth leaf with petiole longer than leaf blade

Now is a great time to scout for Palmer amaranth (Amaranthus palmeri) in Iowa crop fields. As of late 2018, this species had been identified in over half of Iowa’s 99 counties. While new identifications have waned since the widespread introductions in 2016, Palmer amaranth is a species to watch out for in virtually any Iowa crop field.

Assessing Corn Rootworm Activity Using Sticky Traps

July 23, 2019
Western corn rootworm.

Western and northern corn rootworm are major corn pests in Iowa and surrounding states (Photos 1 and 2). Farmers have seen several management changes, including the release of four Bt-rootworm traits to suppress corn rootworm larvae since 2003. Although both species are persistent pests, western corn rootworm is particularly adaptable. The Gassmann Lab at Iowa State University (ISU) has confirmed western corn rootworm resistance to all Bt rootworm traits in Iowa.

Potato Leafhopper Management in Alfalfa

July 23, 2019
Hopperburn.

There have been some reports of potato leafhopper activity and plant injury in Iowa alfalfa this season. Some fields experienced winter injury and the cooler spring provided a slow start to plant growth in 2019. It is time to think about assessing alfalfa stands. Potato leafhoppers (Photo 1) do not overwinter in Iowa, but they are persistent alfalfa pests every growing season. Storms along the Gulf of Mexico bring adult potato leafhoppers north and drop them into fields every spring.

Have Our SCN Sorrows Been Drowned?

June 23, 2019

Those looking for any piece of good news in all of the rain-soaked suffering that has occurred in 2019 have asked “Will all this rain and flooding drown SCN”?  Unfortunately, the answer is “no.” The reasons why are explained. And a small bit of good news about the wet growing season and SCN is offered up in this article as well.

Corn Rootworm Egg Hatch Peaking in Southern Iowa

June 18, 2019
Corn rootworm injury.

Corn rootworm egg hatch in Iowa typically occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. In 2019, the average hatching date will be behind the average, due to cool spring temperatures. Development is driven by soil temperature and measured by growing degree days. Research suggests about 50% of egg hatch occurs between 684-767 accumulated degree days (base 52°F, soil). Most areas in Iowa have reached peak corn rootworm egg hatch (Fig. 1).

Stalk Borers Worth Scouting in Iowa This Summer

June 18, 2019
2019 degree day map for stalk borer.

Within the last week, I have heard about higher-than-normal stalk borer infestations along field margins compared to previous years. According to degree-day tracking of 2019, the caterpillars should be moving from overwintering hosts to corn throughout Iowa this week.

Japanese Beetles Get a Slow Start to 2019

June 17, 2019
2019 degree day map for Japanese beetle.

Several reports from ISU Field Agronomists have indicated Japanese beetles are emerging in southern Iowa. The emergence is about 7-10 days behind the last few years, due to slowly accumulating degree days in 2019. Literature shows Japanese beetle adults need about 1,030 growing degree days (base 50°F) to complete development and will continue emergence until around 2,150 degree days. Based on accumulating degree-day temperatures in 2019, Japanese beetle adults should be active in some areas of southern Iowa this week (Figure 1).

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