Crop Update August 2 - August 9

The dry and droughty conditions, spider mites, soybean aphids, and dicamba drift are common issues ISU Extension field agronomists are seeing across the state. Read on for more information about your region's crop progress and field conditions.

Northwest Iowa

Paul Kassel (Region 2): “Corn is most of my area is the milk to dough stage. There is some concern that the pace of the crop maturity has increased and may cause a loss of yield potential. Corn that pollinated on July 20 has reached dough stage by August 6. Typically this developmental process takes three weeks. Rainfall deficits continue to cause concern. Parts of Clay, Palo Alto, Kossuth, Buena Vista, Pocahontas and Sac have been particularly dry – with many locations in these counties receiving 4-7 inches of rain since May 20.  The rainfall deficits for those same areas are about 3-6 inches below normal. Dicamba injury to non-RR Xtend soybean varieties continues to be an issue. Many of these dicamba injured soybean fields have been really slow to recover. Soybean aphids currently appear to be at a low level; however, farmers are encouraged to check fields for at least another two weeks. Soybean aphids that exceed the 250 aphids per plant threshold can cause yield loss in a soybean crop through the R5.5 or early pod stage.”

Corn in Clay county stressed by dry weather Photo by Paul Kassel. 

North Central Iowa

Angie Rieck-Hinz (Region 3): “Of the 9 counties I cover, only two, Worth and Cerro Gordo, do not show up on the US Drought Monitor (as of August 1). Two counties, Calhoun and Webster are shown in the moderate drought area, and the remaining 5, Humboldt, Wright, Hamilton, Hardin, and Franklin show up as abnormally dry or as experiencing moderate drought, with condition becoming drier the further west you go. Corn is R2 to R3, the western part of my area is experiencing firing of lower leaves due to the dry conditions. Soybeans are R3 to R4. I continue to see planes applying fungicide, despite low level of disease incidence. I have seen some common rust and grey leaf spot in corn, but neither are significant or widespread. Soybean aphids are present, but so far I have seen low numbers and folks should continue to scout for spider mites. While phone calls regarding off-target movement of dicamba have slowed down, I am still receiving calls each week.”

Central:

Mark Johnson (Region 7): “The nine counties I serve continue to miss rains and continue to be dry.  All nine are in either the abnormally dry or the moderate drought categories. Many spots where the ground was worked too wet or the planting was done with the soil too wet are showing  drought symptoms.  Soil compaction is also showing, as is side hill seep areas.  There will be wild swings in yield monitor displays across fields and even within passes this year in our area. A good soaking rain would be a big help in many areas. We are seeing tip back on ears, and if we don’t get a good rain soon, we will see many ears with small kernels and less bushels/acres than hoped for.  Hopefully rains will come in time to help soybean yields.”

Southwest and West Central:

Aaron Saeugling (Region 6): “Corn is in the R3 to R4 stage. Isolate areas of field showing moisture stress last week and firing on the lower leaves have begun.  Initial ear samples appear disappointing to most farmers.  Corn on corn fields are taking a hit this season. There is still some fungicide being applied to corn. Soybeans are the focus of most aerial applications now with insecticides and fungicides being applied. Soybeans are in the R3 to R5 stage. Waterhemp is commonly being seen in fields.  Japanese beetles and also bean leaf beetle feeding is present.  Minor soybean disease pressure is present is most fields.  Poor soils are really showing stress and early maturity soybeans are changing. Pasture and hay conditions continue to deteriorate.  Most pastures are brown with little regrowth.  Rain is needed soon for good fall grazing to resume. Creep feeding has begun and also supplementing cows in isolated areas.”

Mike Witt (Region 11): “Isolated areas of very bad crops are present in the west central region of Iowa. Rain is hit and miss and as a result, firing is starting to occur on the bottom leaves in corn fields. There are significant differences in corn hybrids that are surviving the water stress this season. Bean leaf beetles and Japanese beetles are the main insects of concern; however, very few crop fields have reached a threshold for damage. The main disease that have been found in corn would be common rust and Seoptoria brown spot in soybeans. Remember that scouting should be done prior to using insecticides or fungicides applications. Dicamba damage in soybeans continues to be a problem across the region. Please report the issues to either your ISU agronomist, IDALS, local agronomists or others in the area. The more people that acknowledge the damage in a constructive, problem solving approach, the more it can be solved without the need to individual blame. Mistakes always happen, but dealing with these mistakes is what solves the problems for next season and beyond. There is still potential for good crop yields across west central Iowa but they will not be consistent within or across acres with some reductions occurring.”  

Southeast and South Central: 

Rebecca Vittetoe (Region 8): “The corn, soybeans, pastures, and alfalfa are really showing the effects of the drought. The drought monitor as of August 1 shows my counties either being in a severe drought or a moderate drought. Most corn is in the R3 to R4 stage, but I’ve seen some corn that is already at R5, or dent. We are seeing quite a bit of tipping back on ears and also zippering of ears. Some farmers are green chopping and others are going to be starting silage soon. Keep an eye on nitrate levels as they can be high in drought stressed corn that is stunted or not growing normally. Also keep your eyes out for Aspergillus as we’ve had the right conditions to see this ear mold show up. Soybeans are mostly in the R2 to R4 growth stage. I’ve seen a few fields that are starting to change already. Pastures and hay fields could really benefit from some rain. A lot of the alfalfa is only 6 to 8 inches tall and flowering. Do you cut or not cut the alfalfa? This has been a common question this past week. Dr. Dan Undersander from the University of Wisconsin has a good article on managing alfalfa in a drought. In the article, he recommends not to cut alfalfa if it is less than 10 inches. Other common calls last week include spider mites, Group 4 herbicide drift in soybeans, and nitrate testing in corn for silage."

Zippering is becoming a another common pattern of poor kernel set observed in corn fields this year. Zippering is the result of an ear missing one or more entire rows of kernels along one side of the cob due to some combination of pollination failure or kernel abortion. Photo by Rebecca Vittetoe. 

Virgil Schmitt (Region 10): “Most of my area received less than 0.5 inch of rain last week, with the areas needing it the most receiving the least. Drought continues to be an issue in my area along and south of Highway 92. Rust is showing up on some of the forage greases. Corn is mostly R3 to R4 and generally looks good except for areas with moisture stress. Common rust is the only disease that is common. Soybeans are mostly R4 to R5 and generally are healthy. Calls last week focused on Japanese beetles, bean leaf beetles, Palmer amaranth, and dicamba drift.”

Map showing percent of normal rainfall for Iowa for the last 30 days. Source: http://www.weather.gov.

Find your local ISU Extension and Outreach field agronomist here!