Iowa Field Reports: Corn Rootworms, Spider Mites, and Soybean Gall Midge

    Corn earworm feeding injury. Photo: Mississippi State Universtiy

    Corn rootworms, spider mites, soybean gall midge, and the hot and dry conditions were common questions or issues received or observed by ISU Extension and Outreach field agronomists this past week. Read on for more specifics about what’s happening around the state.

    Northwest Iowa

    Joel DeJong (Region 1): “About half of the area has received good rainfall in July, while the other half has missed out. Some cornfields look great and with recent rain, have great potential yet this year. Cornfields that continually miss rainfall are starting to fire. Some discussion about an early silage harvest in about 10 days or so has begun in those drier areas. The 90-day rainfall percent of normal map delineates these areas quite well.

    “I would note, the total inches of precipitation for “normal” is the lowest in the NW corner of the state. Spider mites in soybean and corn have been a topic of contacts this past week, with a few reports of low levels of soybean aphids, continued discovery of gall midge, and corn rootworms. This would be a good week to start taking a good look at fields for soybean aphids, since some reports from Minnesota seem to be showing an increase in numbers.

    “Watch for spider mite injury while out there, too. Oat yield reports ranged from over 100 bu/acre in the area that has had rainfall, down to in the 30’s for the dry areas – a good indicator of the variation. Finally, every day has been hazy due to smoke. As we fill kernels, I do wonder how much of an effect this will have on final yield.”

    Gentry Sorenson (Region 2): “Rainfall with varying amounts were reported across the area last week, with all of it being welcomed.  Rainfall totals per the Iowa Mesonet ranged from .25 inches in Estherville to .96 inches in Pocahontas.  The cooler weather this week is welcomed after the warm weather we received last week. I have observed little to no disease in corn fields that I have walked.

    “Fungicide applications were made in soybeans last week and corn fungicide application should be close to being wrapped up.  Stress from the heat and lack of rainfall was observed last week as corn plants were rolling leaves during the warmer days and some cornfields also have started to fire on the bottom leaves. Stressed soybeans leaves in dry areas in fields have displayed a lighter silver green color as the leaves have flipped over.

    “Soybeans are at R3 to R4 and corn is at the R3 growth stage.  Incoming questions were about corn rootworm beetle control and off target injury to soybean.”

    North Central Iowa

    Angie Rieck-Hinz (Region 3): “Corn is R2 to R3 with most corn at R3.  In the dry areas lower leaves are firing.  Disease pressure continues to be low to mostly non-existent.  I am still getting communications about rootworm pressure (western corn rootworm). Soybeans are R4 to R5. The condition of soybeans, primarily south of Highway 20, shows noticeable deterioration from the lack of moisture and the heat of last week.

    “I am still getting calls about spider mites and I anticipate those concerns will continue as temperatures climb later this week and rainfall continues to be spotty.  I have noticed some Frogeye leaf spot in soybeans this past week, but very, very low pressure.  Dry pasture conditions have some folks feeding hay already. Most of the oats are harvested.”

    Northeast Iowa

    Terry Basol (Region 4): “Corn ranges from blister (R2) to milk (R3) and the soybeans range from beginning pod (R3) to full pod (R4). The dry conditions in NE Iowa are a concern as some cornfields are starting to fire in the lower canopy. Also with corn being at the R2 to R3 stage, it is most susceptible to kernel abortion, resulting in tip-back, as the last kernels fertilized are the first to be aborted by the corn plant.

    AgFax Weed Solutions


    “On the corn side, corn rootworms have been a big concern in both continuous corn fields and corn fields that were soybeans last year. Problem fields have been identified due to corn lodging or have goosenecking. Upon further investigation in those fields and digging roots, you can see a lot of larval feeding. Applications to control adult corn rootworms have been initiated in severe fields across the territory to help eliminate silk feeding and protect the crop as well as decrease the future populations.

    “Shifting to soybeans, growth regulator drift calls on soybeans have decreased over the last week while fungicide applications have been in full swing. Continue to scout for soybean defoliator insects like grasshoppers and Japanese beetles, as they can still impact the potential yield for the growing season and continue to be present in soybean fields. For more information on defoliators, check out this article here

    “Small grains, have for the most part, been harvested in the area. The third cutting of hay is well underway, and most of it should be harvested by the end of the week. Rainfall totals this past week ranged from about 0.10 up to 3 inches in isolated areas with the Northeast Research and Demonstration Farm near Nashua receiving 0.34 inches. The northern part of the territory looks pretty good, as it’s received a couple of rain events that the southern two-thirds of the territory hasn’t.”

    Josh Michel (Region 5): ““Most of Northeast Iowa received some timely rainfall over the week and weekend. Areas from Waukon down to Dubuque received up to 2 inches of precipitation, while the area along Highway 20 from Manchester to Independence received only around 0.20 inches. The rainfall, along with some cooler night temperatures will help provide some relief to any drought stressed crops. Corn is generally around R2, and soybeans are generally around R3 to R4.

    “Alfalfa and pasture growth continues to be slow, but recent rains will help. Oat harvest continues, with reports still coming in of average to slightly above average yields and test weights. Insect related field calls have centered around corn rootworm management, Japanese beetles, spider mites, and potato leafhoppers. Other field calls have included questions pertaining to forage seedings, small grains management, disease pressure and fungicide applications.”

    Southwest Iowa

    Aaron Saeugling (Region 10): “Southwest Iowa received a nice rainfall last Friday and Saturday.  Most locations received from 1 to 4 inches of rainfall.  Corn and soybeans look amazing while considering the lack of rainfall all season in Pottawattamie, Cass, and Adair counties.  Most fungicide applications have been applied to corn and soybeans with some insecticide added for control of Japanese beetles and corn rootworm beetles.

    “Corn rootworm pressure has been heavy this season compared to years past, and consequently some fields will be challenging to harvest.  Corn is in the R2 to R3 stage and most soybeans are in the R3 to R4 growth stage.”

    Central Iowa

    Meaghan Anderson (Region7): “The rainfall over the weekend for most of my counties brought a much-needed 0.75 to several inches to most of central Iowa. Northeast Story, Marshall, and Tama counties missed out on the majority of it, though. Crops are holding on well, but soybeans and corn on lighter soils or compacted areas have been showing significant stress. Corn is in the blister (R2) to milk (R3) growth stage and corn rootworms have been the hot topic lately.

    “Soybeans are in the beginning pod (R3) to full pod (R4) stage and aside from dicamba, insects have been a popular topic as well. Soybean gall midge was recently discovered in Polk County, and has been known to be present in Madison, Dallas, and Boone counties. Farmers in these counties should be scouting their soybean fields for this new pest. Disease pressure continues to be very low in both crops, but I’ve observed low levels of Physoderma brown spot on corn and sudden death syndrome (SDS) in soybean.”

    East Central, Southeast, and South Central Iowa  

    Rebecca Vittetoe (Region 8): “After the heat during the week, some cooler temperatures and nice rain come towards the end of last week. Rainfall totals ranged from trace amounts in parts of Benton, Linn, and Jones counties to closer to 2 or more inches in parts of Marion and Mahaska counties. Corn is mostly R2 to R3 and soybeans are mainly R3 to R4. Some cornfields have started to fire in the lower canopy and thinner hillsides in soybeans have started to look more yellow.

    “Disease pressure remains low in both crops. I did get my first report of some southern rust found in Johnson County and also started observing early foliar symptoms of sudden death syndrome (SDS) in some soybean fields. Corn rootworms continued to be a hot topic of discussion last week along with concerns about spider mites. The other more frequently asked question this last week was on late summer seeding of forages.”

    Virgil Schmitt (Region 9): “ Rainfall during the last week in the counties I cover was generally ranged from a few tenths along I-80 to an inch near the Missouri border and to over two inches along and north of Highway 30. In general, temperatures during the last week in the counties I cover were 1-2 degrees above normal. Corn is generally R2 and soybeans are generally R4. There are few insect or disease problems at this time.

    “Fungicides are being applied in some fields even though there is little evidence of disease pressure. Calls and farm visits last week mostly involved corn rootworms, pesticide drift, cover crops, and late-summer forage seedings.

    Clarabell Knapp (Region 11): “Most of the are received rainfall on Friday and Saturday, totals ranged from 1 to 3 inches. This brought some needed relief from the hot and dry weather for corn, soybeans, and hay crops. Fungicide applications are slowing down as most of the corn is staging at R3 and soybeans at R4. Areas that experienced large amounts of rain and fields with low spots are starting to show symptoms of nitrogen firing on the bottom leaves.

    “Hay and alfalfa fields are continuing to be harvested for second cutting. There has been a lot of potato leafhopper pressure in the alfalfa fields (see picture below) which is to be expected from the recent weather. I have not seen a lot of disease pressure in corn or soybean fields but have found a few leaves with gray leaf spot.




    The Latest


    Send press releases to Ernst@Agfax.com.

    View All Events


    Send press releases to Ernst@Agfax.com.

    View All Events