Soybean aphids, two-spotted spider mites, fungicide decisions despite little disease pressure, and the hot and dry conditions were some of the more common issues or questions Iowa State University Extension and Outreach Field Agronomists have seen or heard about in fields across the state over the last week. Read on for more specifics about what’s happening around the state.
Gentry Sorenson (Region 2) “The region did not receive any measurable rainfall last week. Corn is around the R3 growth stage. Corn disease pressure remains low in the fields that I have scouted. Rootworm beetles are present in corn fields, and evaluation of corn rootworm feeding now will help with management decisions for next year. The soybean growth stage ranges from R3 to R4. I have heard scattered reports of soybeans aphids present and of a few fields that have been treated. Oat harvest was on going last week with many fields harvested and completed. Field calls or phone questions have been about herbicide carryover in soybeans.”
Josh Michel (Region 5): “Scattered severe storms delivered anywhere from 0.25 inch, up to 1.5 inches of rain throughout NE Iowa last week and over the weekend. These timely rains were well received after many crops experienced prolonged heat stress from very warm temperatures. Despite very low disease pressure, fungicide applications continue as most corn fields are R1 to R3. Corn rootworms and Japanese beetles can still be found along most field edges. Soybeans are generally around R2 to R4. Japanese beetles and grasshoppers continue to be the main leaf defoliators at this time. Oats continue to be harvested for grain and the third crop of alfalfa has started in some areas. Potato leafhoppers can be found in most alfalfa fields and scouting should continue till a cutting occurs. Field calls last week centered around fungicide applications and timing, crop damage assessments, insect identification and forage management."
Meaghan Anderson (Region 7): “Some central Iowa farmers received a small but very welcome rainfall last week. Overall, crops are holding on well despite the dry conditions but some areas in fields are beginning to show stress. I’ll be doing my rain dance in hopes that we get some more soon for the corn, soybeans, pastures, and any new seedings that people may want to do in August. Corn is mostly R2 to R3 and still has very little disease pressure in the canopy. The tar spot in Boone County that I’ve been watching for weeks has now reached the ear leaf on numerous plants but still only about 1 spot per leaf. Rootworm beetles and Japanese beetles are apparent on ears in some fields. Soybeans are mainly in R4 (full pod) growth stage with some fields on either side of that stage. Disease pressure is fairly low in fields, but I have noticed what looks like the start of SDS in the canopy, as well as some downy mildew. Continue to scout fields for late-season issues like two-spotted spider mites, especially if we continue to miss rains. Phone calls in the last week have been about fungicide applications, staging crops, tar spot, and weed control.”
Aaron Saeugling (Region 10): “Well, one consistent thing about 2023 is living on the edge concerning moisture conditions and crop development. Very inconsistent rainfall and hot temperatures late last week is accelerating crop development in SW Iowa at a rapid pace. Typically, this is not positive for final yield for both corn and soybean. Corn is in the R2 to R3 stage and soybeans are in the R2 to R4 stage. Disease can be found in fields but at extremely low severity. There has been some reported insect pressure in alfalfa and soybeans. On Friday, July 28 the extremely hot temperatures were detrimental to yield on moisture stressed areas. Keep in mind we are now in the most critical phase for moisture stress in both corn and soybeans. Three key factors make up soybean grain yield. Total number of pods per plant, number of seeds per pod, and weight per seed. In early planted soybeans, the number of pods most likely is determined now so we will need significant rainfall to maximize the seeds per pods, and seed weight. Corn is very similar in determining final yield with rows around per ear, kernels per row and ears per acre. The number of kernels around was decided back around V6, so now we need to maximize kernel weight per ear. We are rapidly entering the 4th quarter of football game!”
East Central, Southeast, and South-Central Iowa
Rebecca Vittetoe (Region 8): “The last week brought hot temperatures and another week of spotty rainfall across EC Iowa. While most areas received minimal rainfall, higher rainfall totals for the week were in Johnson, Iowa, Poweshiek, Benton, and Linn counties. Corn is mainly in the R2 to R3 stages, and soybeans are in the R3 to R4 stages. Disease pressure remains low in both corn and soybeans, but I have noticed a little more gray leaf spot showing up in corn fields that I’ve been in. I’ve also noticed some downy mildew in soybeans. Besides the questions coming in on fungicide application decisions last week, the other big question of the week was on two-spotted spider mites showing up in some soybean fields.”
Virgil Schmitt (Region 9): “Rainfall in the last week in the counties I cover ranged from 0.05 inch in southern Lee County to over 2.5 inches in Jackson and northeast Clinton counties. Rainfall continues to be very hit-and-miss. Most corn is R2 to R3 and generally looks good to excellent except in areas of coarse soils, clay soils, and compacted areas. Most soybeans are R3 and generally look good to excellent. A few fields have spotty phytophthora root rot. Two-spotted spider mites are present in spots near the edges of some fields. Phone calls, emails, and field visits last week mostly involved the need, or lack thereof, for fungicide applications.”
Clarabell Probasco (Region 11): “South central Iowa experienced another week of minimal to no moisture and some very high temperatures. Crops began showing signs of the drought and heat stress very early on in the week. Spotty showers provided some minimal relief in areas, but there is still a great need for adequate rainfall in the coming weeks. Many corn fields are in the R3 stage with soybean fields in the R4 growth stage. Pasture and hay fields continue to struggle with regrowth. Alfalfa and hay cuttings continue to be lower than average tonnage harvested. Insect and disease pressure remains low across the region.”
Check out the map below to find your local ISU Extension field agronomist and find their contact information here