Iowa Field Reports: Spider Mites, Corn Rootworms, and Drought Concerns

    Is this field yellowing from spider mite feeding, only one way to find out! Photo: Purdue University

    With parts of northern Iowa now being in a D3 or extreme drought and other areas on the drought monitor expanding, the drier conditions are a concern with what impact they are having on the crops as well as forage availability. Other concerns coming from the field this past week included spider mites as well as corn rootworms. Read on for more specifics about what’s happening in fields across the state.

    Northwest Iowa

    Gentry Sorenson (Region 2): “Rainfall last week ranged from 0.2 inch in western Emmet County to over an inch per the Iowa Mesonet in the area.  Emmet, northern Clay, the eastern edge of Dickinson and the northwestern part of Kossuth counties have been moved from the severe drought to the extreme drought intensity.

    “In those areas I have seen tip back on corn ears in many cornfields with aborted kernels on the tips.  In soybeans, we have seen stress observed with visual signs of flipped leaves giving the field a silver green colored appearance along with reduced vegetative growth.  Soybean growth stage is at R4 with some soybeans more advanced.

    “Spider mites have been observed in some growers’ fields, so continue to scout your fields for spider mites along with other pests.  Incoming questions were concerning lack of rainfall, spider mites, and off-target herbicide injury to soybeans.”

    North Central Iowa

    Angie Rieck-Hinz (Region 3): “Corn is R3 to R4. Soybeans are R5.  With the introduction of a D3 (Extreme) Drought in all of Franklin County, and parts of Cerro Gordo, Wright and Hardin counties, concerns are deepening about forage and pasture supplies, corn nitrate issues with silage, and continued crop stress in corn and soybeans.

    “Rainfall received over the weekend of August 7 and August 8 was highly variable, but Hampton received 2.1 inches of much needed rain. This will likely not impact drought conditions very much as we face a very hot and humid second week of August. There is a lot of mowing and baling of road ditches, grass waterways and CRP.

    “Notable phone calls and conversations this past week included many discussions about “edge effect” and the continued presence of high numbers of corn rootworm beetles.”

    Northeast Iowa

    Terry Basol (Region 4): “ Corn ranges from milk (R3) to beginning dough (R4) and the soybeans range from full pod (R4) to beginning seed (R5). The Northern counties of the territory are looking really good, as they have been able to catch some extra rain events, but as you move south in the territory, soil moisture conditions are a lot drier.

    AgFax Weed Solutions


    “For the southern half of the territory, crops are showing moisture stress, particularly in the lighter soil textures of the field. Corn is starting to fire on the bottom canopy with leaf rolling in the hot temperatures. Soybeans are turning their leaves so that the bottom of the leaf is turned upwards to help reduce water loss in the plant.

    “As far as pest activity, continue to scout drought affected soybean fields for two-spotted spider mites as well as defoliators such as Japanese beetle, grasshoppers, and bean leaf beetles. Disease presence in corn and soybean fields have been very low due to the warm dry weather conditions. We were blessed with some precipitation this past week that helped the whole territory.

    “For the NE Iowa Research and Demonstration Farm, the Iowa Mesonet reports 5.94 inches this past week, in which 5.85 inches resulted from Sunday, August 8. Within the territory, accumulations ranged from 0.5 up to 8 inches in isolated areas of Floyd and Chickasaw counties.”

    Josh Michel (Region 5): “Most of NE Iowa was fortunate to receive some timely rainfall as area crops are quickly maturing. Areas in the northern part of the region and along the Mississippi River received heavier amounts of up to 1.5 inches, while areas along and south of Highway 20 from Manchester to Independence received around 0.25 to 0.50 inch of precipitation.

    “Corn is generally around R3 to R4, while soybeans are generally around R4 to R5. Alfalfa and pasture growth has benefited from the recent rains, and the third cutting harvest of alfalfa is well under way in most areas. Oat harvest is pretty well finished up, with many reports of average to slightly above average yields and test weights.

    “Recent field calls have centered around corn rootworm management, alfalfa and new forage seedings management, disease pressure and fungicide applications.”

    Central Iowa  

    Meaghan Anderson (Region7): “Much of central Iowa received more than 0.5” of rainfall in the last week, another welcome drink the crop needed very much. Corn is in the blister to dough (R3 to R4) stage and some earlier maturing varieties are at ¼ milk line. Corn in the northern part of my area has been showing some significant stress from the drought, but most fields are holding on well.

    “Soybeans are mostly in the R4 to R5 (beginning pod) stage and some areas seem to be yellowing already. Volunteer corn plants in soybean continue to be very attractive to corn rootworm beetles and will be a likely location for egg-laying yet this year.

    “Calls continue to trickle in about two-spotted spider mites and corn rootworm. More phone calls have come in recently about seeding pastures and cover crops as we look toward fall, crop harvest, and cooler weather.”

    East Central, Southeast, and South Central Iowa  

    Rebecca Vittetoe (Region 8): “Last week was a fairly dry week across EC Iowa, but some areas did receive some much-needed rain over the weekend. Rainfall totals ranged from 0.1 to 1 or more inches. The heavier rainfall totals were more from parts of Benton, Linn, and Jones counties.

    “The drier conditions are becoming more apparent in parts of EC Iowa, especially parts of Benton, Linn, and Jones, and Poweshiek counties. Some cornfields have started to fire, and you can see the stress in soybean fields with the plants flipping their leaves over and giving the fields that silverish appearance.

    “I have received a few questions about yellowing in soybeans mainly on thinner soils that is not due to SDS, SCN, spider mites, or early senesce. The fields I’ve looked at, it looks more like a nitrogen deficiency to me. I have also received a few more reports on southern rust and tar spot in corn and seeing a little SDS in some soybean fields.

    “Corn rootworms continue to be generating a lot of questions and discussion as well. Corn is mainly in the R3 (milk) to  R4 (dough) stage, and soybeans are mainly R4 (full pod) to R5 (beginning seed). Other calls or questions focused on late-summer forage seedings, cover crops, and pesticide drift from aerial applications.”

    Virgil Schmitt (Region 9): “Rainfall during the last week in the counties I cover was generally less than 0.5 inch. In general, temperatures during the last week in the counties I cover were normal to 2 degrees below normal. Corn is generally R3, and soybeans are generally R5.

    “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. Two public areas, one in central Clinton County and one in northern Henry County, received significant drift from aerial fungicide applications.

    “Calls and farm visits last week mostly involved corn rootworms, pesticide drift, weed management, insect management, cover crops, and late-summer forage seedings.”

    Clarabell Knapp (Region 11): “The past week has been more of a quiet one as field applications wind down along with second cutting of hay beginning to wrap-up. On Thursday, much of the area received a few tenths of rain. Cornfields are typically around the R4 stage while soybeans are in the R4 to R5 growth stage. There has been little insect and disease pressure, but I have seen some gray leaf spot and southern rust in corn.”




    The Latest


    Send press releases to Ernst@Agfax.com.

    View All Events


    Send press releases to Ernst@Agfax.com.

    View All Events