Ag 101 Week 21

What’s Your Threshold?

This spring has been extremely challenging for growers in the northeast and other parts of the country.

I find myself saying the same thing throughout the spring season, “The weather has not been on our side.” Growers are facing extreme weather events that are leading to increased crop damage, insect, and disease pressure resulting in decreased yields or total crop loss.

I also hear myself saying,

“Summer doesn’t matter if you don’t have a good spring.”

I realize that statement is dependent on the crop your growing and how you manage your farm. I’m usually referring to management decisions made before their growing season gets started, then during the summer months they have to live with them. But lately, spring weather conditions have lead to more challenges effecting the rest of the growing season.

This year I have growers that will no longer be growing crops like strawberries due to weather conditions being so unfavorable they can’t afford the risk. For economic reasons they need to focus on crops they can manage in the weather conditions we are now experiencing. Management has now taken on a whole new level of importance.

At the opening day for a local market this week, vendor numbers where low due to spring weather impeding their ability to bring sellable products. One farmer and I were discussing the amount of hail damage on his lettuce and if he could even sell it for an amount that would at least cover his travel expenses for that day.

As I’m writing, it’s raining for the 6th day this week, I know the sun will eventually come out, and things will start to perk up and grow again. Before we know it, we will be in the dog days of summer, and everyone will be hoping for some rain, so they don’t have to run their irrigation. It is a never-ending cycle.

All of this and experiencing my own crop loss this week due to a hungry family of bunnies has me thinking about what threshold a grower can tolerate before they have to make management decisions about harvesting, spraying, or even writing a crop off as a total loss. Do most farmers even know what factors to consider or how to establish a value? And, do they have a plan in place if that threshold is reached.

The dictionary definition of threshold is

ˈTHreSHˌ(h)ōld/ noun

noun: threshold; plural noun: thresholds

2.     the magnitude or intensity that must be exceeded for a certain reaction, phenomenon, result, or condition to occur or be manifested.

"nothing happens until the signal passes the threshold"

synonyms: lower limit, minimum "the human threshold of pain" a limit below which a stimulus causes no reaction.

"everyone has a different pain threshold"

But what does threshold mean in agronomic terms?

Every farmer needs to establish their “pain” or economic threshold they can withstand to keep themselves profitable and in business for years to come.

First, let’s look at specific thresholds-

Economic injury level(EIL) - The smallest number of insects (amount of injury) that will cause yield losses equal to the insect management costs. EIL is also referred to as the break even point.

When pest density is above the EIL - damage exceeds the cost to control

When pest density is below the EIL - damage is lower than the cost to control

Economic threshold - The pest density at which management action should be taken to prevent an increasing pest population from reaching the economic injury level.

The economic threshold is also referred to as the action threshold. That is the point at which insect numbers (population) have gotten to the point you need to mitigate them through cultural practices or inputs such as spraying in order not to reach the economic injury level.

You as a grower have to determine what is the pest density that will justify the cost of applying control measures.

Deciding levels and thresholds at which you have to reach before action is taken can include using formulas and having an understanding of the pest and crop it is affecting.

I work with a specialty grower that produces a niche crop. He sells to high-end wholesale buyers only. He knows the value of his crop and grows a certain number of plants to accommodate a 25% loss. All his management decisions are based on that, and it works for him.

I grow in my backyard. I grow whatever I feel like that year. I give most of it away and eat what is leftover. I know the value and can assume a 100% loss. It works for me.

It’s a good thing it's easy for me to write my season off as a complete wash. The rabbits have decimated everything I planted, and they keep coming back night after night to clean up what they left behind. I realize I’m not growing for profit this year so let them eat, and I’ll figure something else out when I have more time. 

Both of us have established the level of pain or our threshold we can tolerate and how to plan for it. He grows more plants to accommodate; I live with it.

But what if you are growing for market and need to establish that number.

Here are several factors to take into consideration-

1. How much aesthetic or economic damage can be tolerated?

2. What is the value and production costs of the crop at various levels of damage?

3. What is the history of the field?

4. Do you understand the difference between injury and damage and what level is tolerable?

Injury - the effect of pest activities

Damage – monetary value lost due to the pest activities causing injury

5. How much do the control measures cost?

6. Is the insect or disease distributed in the field so effective control can be reached without further crop disturbance?

7. Do you have the ability to control the pest quickly and effectively?

8. Do you have a market or use for a less than perfect product?

9. Do you have the ability grow enough to make up for a certain percentage of loss?

Lastly, here is a simple equation that can be used in conjunction with the factors above to help establish a comfortable threshold for your farming situation

EIL (Economic Injury level) = C*N / V*I

C = cost of controlling the pest per acre

N = number of pests injuring the commodity per acre

V = value of the commodity per acre

I = percentage of commodity injured (% loss expressed as a decimal)

EIL is expressed as the number of pests per acre or pest density that justifies the cost of applying control methods i.e. spraying

Why is all of this important?

Bottom line you need to stay profitable to stay in business. Having established thresholds will help make management decisions to do so, even if it is as simple as growing more to accommodate a percentage of loss or knowing at what pest density you can justify the cost of applying control measures.

Extremely unprofitable broccoli, thanks to the family of rabbits living in our hedge

Extremely unprofitable broccoli, thanks to the family of rabbits living in our hedge