Variable rainfall, low foliar disease pressure in corn (common rust, southern rust, gray leaf spot, bacterial leaf streak, tar spot), SDS in soybeans, yellow soybeans, soybean aphids, corn rootworm pressure, and weed escapes were some of the more common observations or question topics received by Iowa State University Extension and Outreach Field Agronomists over the last week. Read on for more specifics about what’s happening around the state.
North Central Iowa
Angie Rieck-Hinz (Region 3): “Rainfall for the week of July 15 through 22 was highly variable across the area, from 0.3 inch at Webster City to nearly 3 inches near Iowa Falls. Corn is VT to R2, but within field variability is very common this year. I have seen a little gray leaf spot and a little bacterial leaf streak, some physoderma, but by far the most common disease I am seeing is common rust. I have also found assorted species of aphids in corn and the rootworm beetles are becoming more common. Soybeans are R2 to R3. I have had two reports of soybean aphids, but at very low levels, so this is the time to scout for soybean aphids. The usual diseases are found in soybeans, frogeye leaf spot and bacterial blight, and while I have not found white mold, I highly anticipate it is present in some fields. Oats, winter wheat and alfalfa are all being harvested. Asian copperleaf was confirmed in Hardin County thanks to the astute observation of a local farmer/dealer and a second field was confirmed in Wright County by a retailer."
Northeast Iowa
Terry Basol (Region 4): “The last couple of weeks have been favorable for completing field operations and finishing herbicide applications. Corn ranges from VT to R2 (blister) depending on planting date. Continue to scout corn for foliar diseases. To help with fungicide decision making there is a new tool available at the Crop Protection Network (called the Corn Fungicide ROI Calculator) that utilizes land grant university research data from across the United States and Canada for the potential return on investment for a corn fungicide application across a variety of user-defined factors. Soybeans range anywhere from R1 to R3 (where a pod is 3/16 inches long at one of the four uppermost nodes on the main stem with a fully developed trifoliolate leaf node), with the early planted fields entering the R4 growth stage (whereas there’s a pod that is now ¾ inches long at one of the four uppermost nodes). Second pass herbicide applications have finished up, and the drier weather in the past couple of weeks have really helped the soybeans. Continue to scout soybeans for diseases, particularly phytophthora root rot due to excessive moisture this growing season. For more information, Also, scout for insect activity and those that cause defoliation injury to soybeans. Small grain harvest has begun in the area, with most of the rye already completed and a really good start on the oats. According to the National Agricultural Statistics Service (NASS) as of July 21st, 44 and 27 % of the oat crop has been harvested in NC and NE Iowa, respectively. Second cutting hay has pretty much been completed in the area. Precipitation has varied across the area, where my southern counties (Grundy and Black Hawk) have received more rain than the northern two-thirds of the territory. Rainfall for the territory ranges from less than a half an inch to over 3 inches in the last couple of weeks. According to the Iowa Mesonet, the NE Iowa Research and Demonstration Farm near Nashua received 0.17 inch of rain the week of July 8, and 0.01 inch for the week of July 15.”
Josh Michel (Region 5): “Last Monday evening, a derecho swept through NE Iowa. Fortunately, crop damage was minimal with the worst damage occurring in parts of northern Dubuque County. Along with high winds, the storm was accompanied by heavy rainfall. Up to 1.5 inches fell in parts of Delaware and Dubuque counties, while counties further north only received 0.10 to .25 inch. Aside from the derecho, farmers were able to take advantage of several days of dry weather to finish up the current crop of alfalfa and begin harvesting oats. Earlier-planted corn is being to reach brown silk, while the rest of the corn fields are beginning to tassel. Disease pressure remains low, as fungicide applications have started occurring across most of the area. Japanese beetles and CRW adults have been found feeding on silks. Soybeans are generally around R2 to R3. Japanese beetles continue to be found but have been below threshold limits. Most of the field calls last week centered around wind damage assessments, forage management, disease management, insect ID and control and possible nutrient deficiencies.”
Central Iowa
Meaghan Anderson (Region 7): “Most of central Iowa received a small amount (less than 1 inch) of rain overall in the last week, but the eastern part of my territory did receive more with the derecho that came through early last week. Corn and soybean are marching right through their reproductive stages, with corn mostly R1 (silk) to R2 (blister) and soybeans mostly in the R2 (full bloom) to R3 (early pod) stage. Corn remains variable, with much of the crop looking very nice considering its rough start. While walking fields, I can find very low levels of disease pressure (common rust, southern rust, gray leaf spot, tar spot, bacterial leaf streak), nitrogen deficiency, sulfur deficiency, and an abundance of corn rootworm pressure (depending on the field). Some soybean fields have persistent yellow patches, the cause of which varies from field-to-field; some are still waterlogged, some are nitrogen deficient from early water and poor growth, and some have soybean cyst nematode as well. Weed pressure will soon be breaking through the canopy in many soybean fields. Asian copperleaf continues to emerge under the canopy in the Boone County field I’ve been monitoring. Most phone calls have been about last opportunities to kill weeds, corn rootworm pressure and management, and fungicide decisions.”
East Central, Southeast, and South-Central Iowa
Rebecca Vittetoe (Region 8): “The last week has brought some more mild temperatures for July, and rainfall totals over the last week ranged from 0.4 to 4 + inches of rain. Most of that rain came last Monday, July 15. With that rain came some stronger winds which did cause some of the later planted corn fields to have some leaning and/or brittlesnap. Overall, though, pretty minor. Corn is mostly R1 to R3, and soybeans are R2 to R3. Disease pressure continues to remain low in fields, but I can find a mixed bag of diseases in corn including tar spot, gray leaf spot, common rust, and bacterial leaf streak. I’ve also heard some reports of southern rust as well. In soybean fields I can find bacterial diseases but have also found some sudden death syndrome and phytophthora. On the insect side, I’ve been seeing and hearing reports of corn fields with high corn rootworm pressure as well as Japanese beetles in both soybean and corn fields. Continue to monitor alfalfa fields for potato leaf hoppers. Other issues observed in fields this last week included nutrient deficiencies, yellow soybeans, herbicide injury, and weed escapes.”
Virgil Schmitt (Region 9): “Rainfall during the last week in the counties I cover was from less than 0.1 to over 2 inches, with the smallest amounts in southern Lee County and the largest amounts in Scott and Clinton counties. Most corn is R1 to R2 and looks good. Most soybeans are at R3 to R4 and look good. Oats continue to mature look good. Hay making continues to a challenge with the frequency of rainfall. A great deal of rained-on hay is being baled, with associated lack of quality. All crops continue to have few disease or insect issues except potato leafhoppers continue to be above threshold in many alfalfa fields. Contacts last week mostly involved fungicides for both corn and soybean and herbicide injury to soybeans.”
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