Fall army worm scouting

By David Jones, Broad Acre Agronomist

One of the main issues I have encountered in carrying out trials in Fall Armyworm is the difficulty in separating how effective a chemical really is, from how well it is applied and the variation in the numbers of larvae across trial plots.

We have known from the beginning of the Fall Armyworm’s arrival that the pest varies greatly across fields, often with hotspots of several meters where adult moths have laid substantial egg numbers. We also now understand the difficulty of targeting the pest inside the whorl of maize plants, which often leads to poor application technique being confused with poor control and pest resistance.

This leads to substantial errors in measuring the success of different treatments and techniques in Fall Armyworm control trials, which is why I have tried a slightly different approach…

Fall army worm

Larvae size is everything

I collected a large number of larvae from 1st instar all the way up to 6th instar stages, placed them in pots with a few maize leaves, and sprayed a known concentration of different insecticides into the pots. This achieved several aims:

  1. We know that the larvae have been exposed to the chemical and not protected under the leaves.
  2. We know exactly how many larvae were exposed, and at what stage they were when treated.
  3. We can assess mortality accurately, rather than making assumptions about the numbers of dead larvae present, or in most field experiments, the absence of larvae which makes a big assumption about whether the larvae were killed / migrated / pupated / not there in the first place!

Of course there are limitations. Some chemicals may be slightly more mobile in the leaf whorl so performance in the crop might vary. But the object of this study was to look at Fall Armyworm control from a different angle.

Fall army worm

I took four larvae from each of the 1st instar, four from 2nd / 3rd instar, four from 4th / 5th instar and four at the final 6th instar.

The results on the graph show the effectiveness of different chemicals as the size of the larvae increases.

Interestingly, chlorantraniliprole + abamectin and pyriproxyfen were the only chemicals in the study that controlled very large larvae.

No control was seen from pyrethroids (lambda cyhalothrin) which confirms the resistance to this class of chemistry. Neonicotenoids were also very ineffective except at 1st instar stage.

A word of caution

This is not an exhaustive study; just because a chemical is not included does not mean you should not use it. Emamection benzoate and acephate were not included as their function is well understood, and they are both very good chemicals.

This is also just one study, so results can and will vary in the field. The main take home message is hit the larvae when they are small. Alternate modes of action, and scout the fields thoroughly.

Wheat variety trial update

A short tour of one of the CropNuts & Agventure Centre of Excellence for Crop Rotation wheat trials:

 

No-till lessons from Israel

I visited Israel with a group of farmers from Agventure last week thanks to Amiran and Adama, to look at how they manufacture some of the products that we use, and to examine how farmers on just 350mm annual rainfall cope with growing cereals, chickpeas, forage maize and sunflowers amongst other crops.

What struck us was lack of adoption of no-till farming practices in an environment that would appear to benefit enormously from water conservation and a more resilient farming system. One farm in particular was attempting to implement no-till but was shying away from embracing the system. The reasons and the challenges were truly fascinating, and an abject lesson in understanding different farming systems.

No till farming

The rotation was typically wheat, wheat, barley then peas/clover for forage. Because of the large dairy farming sector, straw and forage crops are worth substantial amounts of money. Which leads to the first problem; residue.

The straw from every cereal crop was baled and sold, removing all organic matter and protection of the soil surface. In no-till systems this is a vital component to improve soil biology, structure and to protect the soil from temperature variation and erosion.

Straw alone is not going to prevent the soil from drying out in the 40C summer heat, but just a small amount of humidity trapped underneath can help at planting, and to seal in moisture.

The straw is worth 60% of the value of the grain. So in a 3 t/ha wheat crop with 2.5 tons of straw that represents over a third of the farm income. We can all understand the immediate need or desire for the income, but building a resilient farming system requires discipline and longer term thinking.

The second major limitation that is apparent is the lack of suitable break crops that can support the diversity needed in a notill system. Different plant families mean less disease which means better rooting and more efficient moisture use. It also improves nutrient cycling, with legumes particularly adept and providing more than just nitrogen in the system.

No till farming

 

Although the soils are less than 1% organic matter, they appear to be reasonably self-structuring, cracking clays. Planting commences in November with the arrival of rain, and erosion on cultivated fields is a serious risk.

Soils are designed to take in water, unless the capillaries and channels are blocked. On these types of soils, using controlled traffic and no-till means less run off, greater infiltration and more stored moisture. Controlled Traffic would be a sensible step; getting there needs a planned machinery replacement policy so that as equipment is replaced they are compatible with the system.

Sometimes it is useful to see a system or faming approach that is not quite working to understand the basic, building blocks of successful farming. My messages here are:

  1. You don’t have to stop baling the straw in one go; make the transition in stages around the farm to support cashflow.
  2. Work hard to find break crops that work. Israeli farms have great irrigation that could be focused on Lucerne, Vetch or Forage Sorghum that would bring in income from forage and build diversity.
  3. The growers were struggling to make Canola work. Go outside of your country or comfort zone and learn how to fix it – plenty of growers in other countries manage successfully.
  4. Weed control. Many of the famers struggle with Brome Grass. Rotation will help, as will forage cutting regimes.
  5. Organic matter. Many farms in the US and Europe have ‘straw for muck’ agreements; for every ton of straw removed, a dried or processed pellet could be brought back which would meet Israel’s environmental requirements and build fertility.
  6. Don’t dismiss cover crops or undersowing. You don’t have to use all the moisture; just take sensible opportunities to build organic matter.
  7. Years ago when I worked as an agricultural bank manager, I was always taught to look for ways to reduce the risk of change. In this example, converting part of the farm in 10 or 20% per year to notill, and using the irrigation in the first year might be unorthodox on wheat, but it is the cash earner and will support yields until the system develops.

Till next time,

Take care

David,

About David

 

David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.