Fall Armyworm: Keep Looking

Oct 13, 2021

By Bryan Jensen

What a ride! This fall armyworm infestation has been unprecedented and likely (for me), a once in a career experience. Not to say this infestation has been an extremely high with over-the-top damaging population but rather one that has caused some economic problems in several cropping situation and certainly caused a lot of attention.

Here is what we do know. Fall armyworm do not overwinter in WI. The moths migrate to our state during late summer and early fall. Therefore, the problems we are experiencing will have no bearing on future years. From a crop management standpoint, they are usually a novelty insect except for some infrequent ear damage in sweet corn.

This year I have seen and heard about infestations that are now mid to late instars and some that have early to late instars. No reports of populations comprised of only small larvae. That suggests to me this problem is winding down. Ohio State Entomologist’s have also suggested that larval mortality should/could be observed with prolonged temperatures of 650 F or below. Adults may survive colder temperatures, but I have a hard time thinking the resulting larval generation could cause significant crop damage.

Field situations where I have heard of problems include pastures, alfalfa (both established and new seedings), cover crops and fall seeded small grains. There aren’t economic threshold for these situations. Rather, judge the defoliation potential and how that might impact winter survival and/or potential for forage loss if a late-season harvest were to be taken. Project ahead, don’t look at the past. You can’t resurrect damage that has already happened. Just try to prevent future damage.

If you are in a situation with multiple cover crops planted, significant damage potential, and you are going to take a late season harvest you must choose an insecticide that is labeled for all planted crops and an insecticide that has a pre-harvest interval suitable for your harvest schedule. That may be very difficult to do.

Source : wisc.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.