Russian wheat aphid

By David Jones, Broad Acre Agronomist, Msc. Agriculture

Growers are warned to keep a close eye out for Russian Wheat Aphid in wheat and barley crops. The small aphid around 2mm in length produces a toxic saliva when feeding on young plants, giving rise to a characteristic white and red streaking up the leaves of infected plants.

Infected tillers often roll up, revealing the aphids protected inside when opened up. Yield loss is mainly the result of plant stress and loss of tiller numbers which can be severe if populations are allowed to persist.

Thresholds for treatment range from 10-20%, but if you are seeing symptoms of damage at early tillering it is very important to respond. Clothianidin and thiamethoxam seed dressings give reasonable early control but in high pressure seasons will not be sufficient.

Russian wheat aphid

All populations that I have tested recently are susceptible to pirimicarb, which is far more selective than the alternative of chlorpyrifos which is very damaging to beneficial species. Growers are reminded that the temperature needs to be above 16C for optimum performance of pirimicarb otherwise the vapour phase and fumigant activity is much reduced leading to poor control. Lambda-cyhalothrin can be used to low populations but is less effective.

Pirimicarb is very low risk to Bees, which are unlikely to be present in fields at the time you are likely to be spraying for Russian Wheat Aphids, but if you do have hives nearby be sensible. The best method of cultural control is to eliminate the green bridge; get rid of volunteer cereal plants in the fallow leading up to planting.

Potato Seed Treatments

Current dry conditions have encouraged many potato growers to plant very deep to hit moisture. On the one hand this is the right thing to do, but it also increases the time taken for emergence and raises the risk of Stem Canker.

Clean, certified seed, close inspection of seed tubers and long rotations are very effective at reducing Rhizoctonia in potato crops, which causes Stem Canker and Black Scurf. But in most cases it pays to protect the crop properly with an approved seed treatment.

Potato seed treatement

Only problem, there do not appear to be any approved fungicides available. In a country that grows well over 100,000 hectares annually.

To qualify this let us look at the options and the evidence:

Monceren GT (imidacloprid, thiram, pencycuron)

The pencycuron loading is only 50g per litre. If you look at UK and NZ research pencycuron is applied at 250g of active per ton of seed. It is highly active on Rhizoctonia but has very little activity on Silver Scurf (I commonly pick this up in Asante and Shangi). Has the benefit of the thiram for Fusarium Dry Rots and Gangrene, plus the imidacloprid for insect pests so a good all-round product.

Maxim XL (fludioxonil)

25g/litre fludioxonil. At 1.0 lt per ton of seed this is very good on Rhizoctonia, and has activity on Silver Scurf. Of course, you need to add an insecticide, to this but when solely looking at diseases this is a solid seed treatment.

Imazalil

Cheap and widely available but not approved as a seed treatment. Just 10g per ton is a very useful addition to supress Silver Scurf but it will not cover Rhizoctonia. Be aware that you must NOT MUST USE IMAZALIL ON TUBERS WHERE AZOXYSTROBIN  IS APPLIED IN FURROW – as this can severely slow emergence.

Azoxystrobin

A very useful in-furrow treatment to reduce Black Dot and Silver Scurf, but it does not replace a proper seed treatment of the tubers. A lot of work by SRUC in Scotland has shown much faster emergence.

Think carefully about Canola fertiliser placement

Placing fertiliser near the seed to speed up establishment makes so much sense. But what are the negative consequences? Well, this recently published research from the Department of Primary Industries Southern New South Wales, ‘Research Results 2018’ gives us an insight.

This is one site, one trial, one set of weather conditions but it does highlight the effect that placing N too close to the seed can have on canola establishment (or any other seed for that matter).

Note that IBS (incorporated by sowing) where the fertiliser is not concentrated near the seed is far safer, but of course the seedlings take more time to reach the fertiliser.

The study also found that Triple Super Phosphate placed WITH the seed reduced establishment too, but placed 2.5cm below the seed showed no reduction in establishment.

canola fertiliser placement

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,

Happy farming,

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.

Till next time,

Happy farming!

David