By David Jones, Broad Acre Agronomist, MSc. Agriculture
What follows is the release of the results of an experiment investigating the effectiveness of various fall army worm insecticides
Earlier in the year in #ThinkAgronomy I presented the results from a study of Fall Armyworm that I undertook, examining the effectiveness of different Fall Armyworm Insecticides. One of the major challenges I found last year was how to obtain reliable and meaningful results from a randomized, replicated field trial with an insect that is highly sporadic through the crop. This means that there is a danger that we confuse good control with plots or treatments where Fall Armyworm happen to be absent.
Fall Army Worm Insecticide Experiment
So, I went back a few steps and designed an Fall Armyworm Insecticide experiment in which I collected larvae from the field, put them into batches according to size and placed them in identical containers with maize leaf and applied a known concentration of Fall Armyworm Insecticide. This achieved the following:
- We know that the larvae were exposed to the chemical and not protected under the leaves.
- We know exactly how many larvae were exposed, and at what stage they were when treated.
- There is no uncertainty as to whether a larva hidden inside a leaf whorl did or did not receive a lethal exposure to the chemical.
- 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!
All of the major approved Fall Armyworm Insecticides were examined in a fully replicated (three times) with six larvae at 1-2 instar, six at 3-4 instar and six at 5-6 instar. The results after 5 days were as follows:
Note that the 5% Confidence Interval is 27%. So anything that has achieved between 73% and 100% control is not statistically different. In other words, pyriproxyfen, emamectin benzoate, indoxacarb and acephate containing products are all very effective.
Lufenuron performed poorly even on small larvae which is what our experience in the field suggests, while flubendiamide and chlorantraniliprole + abamectin showed poor performance on larger larvae. Nonetheless the later two are still important chemicals when applied at the correct stage, and bring a different mode of action to the control program so do not dismiss them.
Of course there are limitations. Some chemicals may be slightly more mobile in the leaf whorl because of locally systemic or vapour activity, so performance in the crop might vary. But the object of this study was to look at Fall Armyworm control as objectively as possible.
A few closing remarks:
My job as an independent agronomist is not to deliberately seek controversy, but to lay out the facts in an objective and scientific manner without fear or favour. I have NO relationship or commercial agreement with any manufacturers or suppliers of farm inputs, and doubtless the above results may not be well received by some individuals in the agricultural supply industry. Yet I feel that for the greater advancement of our knowledge as farmers and society it is important to research and to lay out our findings in an open and transparent way.
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Check Soils now to finish 2018 on a high
Farmers are warned not to lose sight of the substantial amount of rain and the impact that it will have had on soil structure and nutrients. Get out now, dig holes and take soil samples to set your fields up for the coming planting season.
Center for Excellence for Crop Rotation
Farming for the future requires a change of approach. Monoculture, soil degradation and climate change and soil degradation are threats to the future of how we feed the planet. Agventure Ltd set up the Center of Excellence for Crop Rotation to help farmers diversify cropping systems and introduce techniques which have a long-term outlook to improve soil health. The Center of Excellence for Crop Rotation works extensively with Crop Nutrition Laboratory Services Ltd (CropNuts).
Till next time,
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.