Don’t React too Quickly to Cold-Injured Plants

Jan 27, 2022

Our winter temperatures go back and forth all season here in North Florida – one week it’s winter, the next week we may think spring has arrived. This back and forth with cold and mild temperatures throughout winter is typical in North Florida.

As a result of the freezing periods, the less cold-hardy tropical and subtropical landscape plants can be injured. For example, it’s normal for popular landscape plants such as oleander, hibiscus, bottlebrush and philodendron to suffer some cold damage. Then, the first impulse for many gardeners is to cut away the dead and dying leaves and branches. But, this really is not the best idea.

During winter, it’s difficult to tell how much damage has been done to these plants. If you prune immediately after a freeze, you probably will cut away live wood that does not have to be lost. Also, cold damaged leaves and branches on the outer part of the plant can help protect the rest of the plant when the next freeze strikes.

Cold-injured pinecone ginger

Cold-injured pinecone ginger.

Some of the more tender landscape plants such as banana, cassia, ginger, tropical hibiscus and many of the tropical perennials may have been severely injured with the first freeze. But, don’t give up on them too soon. These plants may surprise you by sending up new shoots come spring. Some of these plants require warm soil temperatures before they’ll produce new growth. Many of the gingers, for example, may not show any sign of life until April or May of 2022.

Some winter and spring flowering plants such as camellia and azalea may experience flower bud damage. This will be evident at blooming time when these plants have few to no flowers. Cold injured camellia flower buds will either drop off the plant or only partially open showing brown centers. Stem damage will show up in spring and early summer when some of the branches begin to die. Cold injured leaves will fall as new spring growth occurs.

Individual stems on some cold sensitive plants such as azalea and bottlebrush may split or crack during a freeze. Some of these injured branches will begin to die during spring and summer.

February and early March can bring occasional frosts and freezes. It’s not unusual to have our last killing frost toward the middle of March or even in early April in parts of North Florida.

When “spring really has sprung,” you’ll know what survived and what did not. This will be after new growth occurs and after the danger of another frost or freeze has past. That’s the time prune.

Source : ufl.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.