Once again the hotter, drier conditions at this time of year seem to bring increased aphid pressure particularly in brassicas.
Too often I receive calls from growers confused by poor control, highlighting why it is vital to correctly identify the species before deciding on control measures.
Small, compact colonies of Mealy Cabbage Aphids are very easily identified particularly on canola, and area easily taken out with Pirimor (pirimicarb). Apply as a fine spray quality when temperatures are above 16 degrees to get the best control. Pyrethroids such as lambda-cyhalothrin and deltamethrin tend to be highly variable in their control, as is chlorpyrifos.
The Green Peach Aphid is harder to spot, and also harder to control. Most are resistant to Pirimicarb and pyrethroids, so neonicotenoid containing products such as thiamethoxam, acetamiprid and imidacloprid are usually required.
Problem is, if there are any flowers in the crops and Bees are present you should avoid these at all costs. Secondly control in my trials is 40% at best – probably due to the difficulty of achieving good coverage underneath the pods.
Sulfoxaflor has also been examined in our trials which is highly selective and safe to beneficial insects, but has rarely given above 50% control for me, even at 4.5 Bar pressure with a 015 angled nozzle. The last trial I did just last week was below 25% control in fact! Flonicamid has not been extensively trialled yet but is worth trying.
Thankfully, unless Green Peach aphids are present in particularly high numbers they are rarely worth spraying, especially if they build up towards the end of pod fill. Mealy Cabbage Aphids on less than 5% of plants can be economically damaging – just do NOT mix pirimicarb with triazole fungicides if bees are active in the crop.
Finally, remember that Ladybird larvae, Ground Beetles, Rove Beetles, Parasitoid Wasps and Spiders all predate aphids, so the more selective the product you can use, the better.
Using Sunflowers To Reduce Brome Grass Populations
I have discussed the benefits of Sunflowers in the rotation in previous editions of #ThinkAgronomy, in reducing nematode populations, building Mycorrhizal fungi and improving soil structure.
The challenge on the flip side is making them pay in their own right to contribute some cash to the operation as well as improving the profitability of the other crops.
Well here are two examples that I have seen in the last week where they have been used as a double crop, in the off season, with – largely – positive results.
This was an exceptional example where the farm only received 220mm of rain since August, but in a dryland environment it shows how one should be cautious about double cropping.
Yet the Brome control is massively improved and early on in the crop there just wasn’t the germination that occurred in the wheat after the fallow (the fallow was spotless with no weeds allowed to get past 4-5 leaf stage).
So there is clearly something happening here with Sunflowers, either an allelopathic effect, suppression from the extra residue around the wheat or perhaps the action of planting sunflowers has encouraged the Brome to germinate which we then controlled with a graminicide.
This is another very useful effect of the crop against Brome, and for drier areas you do not need to follow the crop through to harvest to benefit – our agronomist George Maweu was explaining how in Narok they used to let the Sunflowers get up above the weeds towards heading stage, then spray it off.
This is long enough to provide good soil cover, significantly reduce the number of glyphosate passes in the fallow, produce some deep roots and plenty of surface residue without it being too difficult to plant through. Planting multi species is the next step to further improve fertility and soil biology, but this vies the flexibility to take it through to a full crop if conditions look promising, or treat it as a cover crop if moisture is looking short in the soil profile.
Just remember the golden rule of cover cropping; 60-70 days is about the max before the crop starts really using moisture that may detriment the following crop.
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.