By Rebecca Vittetoe
Corn fields around the state, if not tasseling currently, will be soon. Soybeans are mostly in the R2 to R3 stages. Overall, disease pressure remains low with reports of gray leaf spot and bacterial leaf streak being found in corn and bacterial blight, septoria brown spot and phytophthora being found in soybeans. Insects reported include Japanese beetles, grasshoppers, and corn rootworm beetles. Read on for more specific on what ISU Extension field agronomists are hearing and seeing in fields around the state.
Cherokee, Ida, Lyon, Monona, O'Brien, Osceola, Plymouth, Sioux, Woodbury counties
“Many corn fields across the region are R1. Fields are tasseling relatively evenly, but there are some exceptions to that. Bean fields are R2 to R3 and are looking healthy and relatively weed free. Calls this week have been on herbicide damage and fungicide decisions. Disease and insect pressure have been relatively low, but scouting each fields at this time is key. Some hybrids could me more or less susceptible to disease, and some fields will have different conditions and histories. Make fungicide and insecticide decisions based on your field conditions for the benefit of your cost of production and the longevity of the products. Crops seem to be handling high temperatures well at this time, but some additional precipitation in this corner of the state would be beneficial.”
Cerro Gordo, Franklin, Hamilton, Hardin, Humboldt, Webster, Worth, Wright counties
“Corn is very late vegetative stages to R1. Disease pressure remains at low severity and low incidence. My college Gentry Sorenson and I took a tour of Alison Robertson’s Cardinal Fungicide Trial at the Northern Research Farm on July 13, (no treatments applied), and we found one tiny gray leaf spot lesion, two northern corn leaf blight lesions, and some common rust, none of which would warrant concern. Subsequently, I looked at two cornfields later that afternoon and found no disease. I have also been seeing both northern and western corn rootworm beetles. In fields north of Hwy 3, you will find potassium deficiency on lower corn leaves due to dry soils. In most cases, this is due to lack of soil moisture to move K into the plant, not due to low soil tests. Recent rains should help alleviate this problem. Soybeans are R2 to R3. Last week I was seeing a very slight increase in numbers of thistle caterpillars, and the Japanese beetle feeding along field edges has increased. Remember, in R stage soybeans you need 20% defoliation to consider a treatment (this is slightly different than what the Crop Protection Network states). You can use this tool, developed by Crop Protection Network to help calibrate your sight for defoliation: Soybean Insect Defoliation Training. Remember 20% defoliation is across the entire plant. Patches of Phytophthora are showing up in soybean fields in low, or wet spots.”
Source : iastate.edu