Weather

May 7, 2021

There is nothing that gets talked about in agriculture more than the weather. For one, it is a way to get personal without being intrusive. It is personal because what happens at my place will not be the same as what happens down the road or across the county. Every place is unique.

Rainfall amounts vary from farm to farm and even sometimes on a farm. The TV or radio weather person is always the brunt of jokes. They can predict the weather but they can never really get it completely accurate due to natural changes. The invention of radar has made the job a lot easier and at the same time complicated. I have gained an appreciation for their job. Many a summer day, hoping for rain, I watch the radar and see the rain coming, only to see it dissipate just before getting to my place. It is frustrating and I am sure the forecasters want to be as accurate as possible but they are also a victim of the fickleness of nature.

Recently we had a cold spell where temperatures dipped to the mid 20’s for two nights in a row. Notice I used a weasel word, “mid.” Depending on your location and elevation that number can vary by several degrees. The damage or lack of damage to plants will also be quite variable. We do not care if the forecast is for a low of 50 degrees or 55 tonight. Those temperatures are high enough, it makes little difference to the health of the plant. But we start talking about temperatures below 30 in April, then there may be crop injury issues.

It is amazing to me how a frost means different things to various plants.

A frost occurs on nights when there is no cloud cover or wind and the temperatures are forecasted to get down to 38 degrees or below. An air inversion occurs where it becomes colder at the ground than it is higher up. Normally the higher you go the colder it gets. That is why we see snow on the mountain tops. Plants all react differently to a frost and their reaction depends on the internal temperature in various tissues of the plant. If the temperature is cold enough to break cell walls or disrupt cell constituents beyond repair, damage, wilting, and death will occur in affected tissues.

Take the case of an apple tree. Fruit damage occurs at 28 degrees F. That temperature is down into the freeze area where things like corn and tomatoes are totally killed. In fact, at 28 degrees it is estimated that 10% of the fruit buds might be damaged. In a year like this where there are plenty of flower buds, a light freeze can actually be a good thing. Causing the crop to be thinned a little.

At my place, the apples are a later blooming variety and they could withstand colder temperatures. Additionally, on the first night, they were coved with insulating snow on the flowers. In some local places, temperatures dipped lower and some damage did occur. There is such tremendous genetic variation in apples and each species could be in a different stage of growth making them more, or less, susceptible to cold.

Another plant that sets itself up for spring damage is the apricot. This is the first blooming fruit of the year and when the temperatures get cold it may already have fruit formed and they may all be lost. Cherries also can be prone to early-season cold damage.

My apples are fine, but that does not mean yours are fine. Down south around Lafayette on the Purdue orchard, the temperature dipped to 21.9F. That crop was devastated. At that temperature, there is little guesswork as to the severity of the problem.

Mark Kepler, Extension Educator- Agriculture and Natural Resources 

Purdue Cooperative Extension Service-Fulton County 1009 West Third Street, Rochester IN 46975 

574 223 3397 http://www.ag.purdue.edu/counties/fulton/pages/default.aspx https://www.facebook.com/Purdue.Extension.Fulton