"I enhanced the soil in spring with compost and rotted manure"

Ok but what have you fed them? What nutrient supplements have you provided?

Both of those are soil amendments, not fertilizers and what low levels of nutrients they might provide IF you have an active soil food web are quickly used up early in the season. Corn especially is a big nitrogen hog and requires supplemental feedings at various stages of growth.

Dave

My first thought is also fertilizer. I realize that you may have grown successfully in this soil in previous years, but by doing so you will have reduced the fertility of the soil.

It's also possible that the weird year stressed the plants in terms of heat/cold/water and made them more vulnerable to pests and diseases. But I'm voting for insufficient fertility.

Thanks for the feedback. I did fertilize with an organic general dry fert in spring, but nothing since. I am going to say you are all probably right, low fertility sounds right. What does everyone else use as standard fertilizer and what are your application times ?

You have to understand that dry organic fertilizers only work, are only usable by the plants, if you have a well developed soil food web, a high level of soil bacteria and residents to pre-digest them. Basic physics of organic gardening. Their application rate all depends on how well developed that micro-herd is.

Dry granular synthetics require only water to dissolve them so the plants can use them.

Liquid organics are already predigested and available to the plants. Same with synthetic liquids. Application rates and frequency are normally listed on the labels for a garden as a whole. But it is the individual plants that will tell you when they need to fed because those needs vary from crop to crop. For example, corn needs much more nitrogen than most any other crop, leafy greens need much more than root crops, etc. And the timing of applications varies from crop to crop too. So you have to learn about the needs of each crop you grow in the garden.

There is no such thing as a standard fertilizer. There are hundreds to choose from - both organics and synthetics and dry or liquids. All gardeners have their preferences. But it is pretty safe to say that all crops, all gardens, need regular feedings of some kind throughout the growing season rather than just once at the beginning regardless of what you choose to use.

Dave

And the amount to use is stated on the label.