Regional Crop Update: July 6 - July 14, 2026

Jul 16, 2026

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.

Leah Ten Napel (Region 1)

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.”

Angie Rieck-Hinz (Region 3)

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

Video: Turning Plant Defense Into a Management Strategy

Turning Plant Defense Into a Management Strategy

Understanding how a plant responds to stress is one thing.

Using that knowledge to make better management decisions is another.

Systemic acquired resistance, or SAR, is the plant's more direct defense response. When stress or infection occurs, the plant begins signaling throughout its system and preparing defensive compounds.

But if we know that response exists, can we help prepare the plant before the stress arrives?

The answer starts with understanding what triggers the response and what the plant needs to carry it out.

The Trigger and the Fuel

Salicylic acid plays an important role in triggering the SAR pathway.

Think of it as turning the truck on.

The engine may be running, but it still needs fuel to do the work.

In this case, manganese plays an important role in supporting the enzyme systems involved in the plant's defensive response.

This makes manganese status an important part of the conversation. Whether a producer is using tissue testing, sap analysis, or simply scouting for visible deficiency symptoms, the goal is to make sure the plant has adequate manganese available.

Manganese is required in relatively small amounts, but that does not make its role small.

If the plant receives a signal to defend itself but lacks the nutrition needed to support that response, it may struggle to carry out the process efficiently.

The trigger matters.

The fuel matters too.

Prepare Before the Stress Arrives

The best time to think about stress management is before the plant is overwhelmed.

Once a crop is already struggling, management can quickly turn into a game of catch-up.

This is similar to nitrogen management. Once a plant becomes severely deficient, correcting the problem does not necessarily erase the time and yield potential already lost.

Plant defense can work the same way.

Low-rate, targeted approaches designed to support the SAR pathway may fit best ahead of an expected stress event rather than after significant damage has already occurred.

That requires producers to think about predictable stress.

We may not know exactly what the weather will do tomorrow, but we generally know summer heat is coming. We know certain field conditions increase disease pressure. We know a herbicide application can temporarily stress a crop as the plant processes the chemistry.

Even a properly timed and labeled herbicide application can create a temporary response in the plant.

That does not mean the herbicide is bad.

Weeds can create significantly more yield loss than the temporary stress caused by controlling them.

The question is not whether we should eliminate every stressor.

The question is whether we can better prepare the plant to manage necessary and predictable stress.

Not All Stress Is Bad

Stress is a normal part of plant growth.

A perfectly stress-free environment does not exist in the field.

In fact, some stress is necessary for normal plant development. A plant responds to wind, temperature, moisture, sunlight, and countless other environmental signals throughout the season.

The environment is stress.

The plant's job is to manage it.

Problems begin when the stress load becomes greater than the plant's ability to respond.

Extreme heat, drought, high salt concentrations, disease pressure, and even certain management practices can add to that load.

This is where understanding SAR becomes useful.

Instead of waiting until the plant is visibly struggling, producers can begin identifying periods when stress is likely and make management decisions around those windows.

ISR Starts With the Soil

While SAR is a more direct defense response, induced systemic resistance, or ISR, brings the conversation back to soil health.

The longevity of a farm is closely connected to the health of its soil.

Carbon plays a major role because it supports biological life within the soil. Bacteria, fungi, and other organisms interact with plant roots and influence how the plant grows, accesses nutrients, and prepares for stress.

This is why soil health cannot be reduced to one product or one application.

It is a system.

Keeping living plants in the field longer can support biological activity. Cover crops may fit some operations. Better water management can improve soil conditions.