Early Season Crop Scouting

As crops emerge, early-season scouting provides an opportunity to evaluate planting success and identify emerging disease or insect issues. Knowing how things are looking can help you make more informed management decisions. The following sections outline key considerations and tips for effective early-season scouting.  

Tools

Before you head out to the field, there are several tools that are a must-have for early-season crop scouting.  

• A tape measure to take stand counts. As the saying goes, “If you don’t measure it, you can’t improve it.”
• A seed digger, trowel, or spade to dig up seeds or plants to evaluate planting depth, seedling diseases and below-ground feeding insects, like seed corn maggots. A square-bottom spade is particularly effective. You can easily push it into the ground a few inches from the furrow, pop open the furrow, and expose the furrow wall and evaluate planting depth, seed placement, sidewall compaction, and early rooting issues.

For a more thorough list of tools and resources for crop scouting, see the encyclopedia article “Crop Scouting Basics”.

Crop Growth Stage 

Any time we are out scouting in a field, take time to note what growth stage the crop is at. Besides understanding what is happening to the crop at that growth stage, knowing the stage can also be critical for things like pesticide applications. For example, some herbicide labels restrict applications based on crop stage. Additionally, decisions of side-dressing fertilizers may also be impacted by the growth stage of the crop. 

The Corn Growth Stages and Soybean Growth Stages articles are great refreshers on what to look for when identifying those stages.

Early Season Crop Diseases

The first principle of crop scouting is to determine what is normal and what is not normal. Knowing what a healthy plant looks like is key to identifying seedling diseases. Plants communicate in color and growth. 

When scouting for seedling diseases look for yellowing, wilted, stunted, dead or missing plants. In corn, look for discolored or rotten mesocotyls, seminal roots and nodal roots. In soybeans, look for seedlings that pull easily from the soil, discolored or rotting root tissue, and lesions that form on the taproot or hypocotyl.  

While there may be nothing you can do to fix the problem this year besides replanting if necessary, scouting for seedling diseases can help you make management decisions for future years.  

Favorable Conditions for Seedling Diseases

Certain weather and soil conditions favor specific seedling disease pathogens. Cool, wet soils favor Fusarium and Pythium species; warm, wet soils favor Phytophthora; and warm, moist soils favor Rhizoctonia.

Laboratory diagnosis is required identify the pathogen causing the symptoms. Plant samples can be sent to the ISU Extension and Outreach Plant and Insect Diagnostic Clinic for confirmation. 

Knowing what disease(s) is present can help you choose hybrids and varieties that have good disease scores in the future and can guide decisions on the use of fungicide treated seed.  

Early Season Insects

Many insects can pose a potential threat to seedlings and small crops during the early growing season. In this article, early growing season is assumed to be from planting through the first week in June; however, risk is more closely related to crop growth stage and accumulated growing degree days than to calendar date. Insect injury can cause stand loss and loss of leaf tissue (photosynthetic capacity); both of which can contribute to yield loss.  

Because insects are small, mobile, and sometimes nocturnal feeders, it may be difficult to find the culprit, so scouting for signs of plant damage such as leaf-feeding, plant-cutting, or missing plants is important. Insects feeding belowground can cause thin or irregular stands and poor germination. It is important to dig up seeds or seedlings to determine if an insect pest is present. 

Some insects, such as cutworms, can clip plants at the soil surface; some insects may be nocturnal and burrow into the soil during the day, making it difficult to identify the culprit. Leaf-feeding is more obvious, and sometimes the insect may be present. In cases of shot-hole feeding, splitting the plant may be necessary to identify what insects are feeding in the whorl.  

Common early-season corn and soybean insect pests include: 

• Black cutworm
• Bean leaf beetle
• Seedcorn maggot
• Stalk borer 
• True armyworm
• White grubs 
• Wireworms  

The insect pest forecasting page on the ISU Mesonet provides updated growing degree day information and also includes guidelines for when to scout for some of these insect pests based on growing degree days. Additionally, This Crop Scout Insect Pest Calendar provides a handy reference as to when to scout and pest control windows. This resource was developed by Brian Lang, retired extension field agronomist. If you are located in southern Iowa, you may anticipate earlier insect pest activity based on warmer temperatures.  

Consult the ISU publication, CSI 14, Field Crop Insects for additional information on insect identification, scouting and management tips.  

Summary

In summary, early season crop scouting can help you make management decisions for possible replant situations, treatment that may include a whole field or only border rows, and future seed and seed treatment decisions. 

Don’t forget to use all resources available to you such as reference materials, your Extension field agronomist, crop consultant or retail agronomist.