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Don't let crop pest cut 2020 yields

Updated: Oct 8, 2020

Welcome to our first crop agronomy update for 2020. Receiving 20 -30 mm of rain throughout the district in early August has been fantastic, putting a smile on everyone’s faces.

After a dry summer, the 2020 cropping season in Kimba began ominously, with minimal soil moisture ‘in the bank’ for crops to draw on later in the year.

However, some 50mm of opening rains in March-April boosted farmer confidence early in the season, along with ample stocks of ag chemicals, fertilisers and other inputs, either held on-farm or in our store ready to go.

Impact of COVID-19

March saw the nationwide outbreak of COVID-19 - the most destructive pandemic to hit our shores in a century - with the potential to stall the entire crop production sector due to our dependence on China for imported farm chemicals, fertilisers and other inputs.

Within weeks, the Aussie dollar dropped 20% to a 17-year low, pushing up fertiliser pricing by A$100-150 / tonne during March. Thanks to early forecasting and careful planning with our supply partners, EP AGnFERT was able to minimise the risk of product shortages and avoid massive price rises for clients.

Weed & Insect Pests

Decent opening rains triggered widespread weed germinations, creating ideal conditions for knockdown weed control. Pre-emergent herbicides also delivered excellent broadleaf weed control in emerging crops which thrived in the absence of weed competition.

A mild climatic through March and April saw unseasonal flights of Moths laying eggs into pasture and stubble paddocks.

Medic pastures took the initial brunt with Weed web moth larvae (right) attacking early emerging medics, before early sown cereals.

Lesser Budworm (below) and Cutworm came next, cutting down early emerging cereal crops which had to be treated.

However, the May to July period delivered below-average rainfall with less than 100mm GSR (growing season rainfall) in most districts. Along with crop damage from cutworm, pre-frontal winds (bringing bugger all rain) have also caused serious damage to emerging crops on lighter soils. This sandblasting effect, combined with grub damage, meant some areas had to be re-sown. It seems that soil renovation in recent years has created new crop establishment challenges, relentless wind

being the main one. With excellent knockdown control prior to seeding, the few post emergent weeds have been slowed and most crops are weed-free. Most legume crops have now been sprayed for grass weeds, along with some pastures.

Due to a lack of feed for livestock, some farmers have left grass weeds uncontrolled as an extra feed source while growth of legume species (eg medic) has been slow.

Spot the Disease

Barley crops have seen SFNB (spot form net blotch) appear early this year, perhaps due to many barley crops being planted back into barley stubble, in fear of IMI residues issues. This led to early infection of SFNB with many growers now preparing for a second application of fungicide.

We have also seen boron toxicity in Compass barley, along with well-publicised SLT (Spartacus leaf tipping) which has been widespread on all EP soil types. After ruling out pathogenic and nutritional related causes, SLT remains a mystery. While barley crops appear to grow out of it by mid to late August, SLT expresses itself more potently when herbicide/fungicide applications coincide with frost. Further, SLT tends to occur on older leaves in contained areas of necrosis (see photos opposite)

Herbicide Residuals

Herbicide residuals have been a cause for concern again due to last year’s dry conditions and insufficient summer rain to breakdown the active and allow safe plant backs of various crops.

IMI herbicides (PIC, PYR, MOX) have even seen herbicide residue carryover from 2018 into Compass barley crops in 2020 (see below: IMI residual effects; Compass v Spartacus). This is concerning, not to mention the changes to crop rotations it has forced upon farmers seeking to avoid the risk of damaging crop effects.

Group I herbicides, especially LONTREL types, have created challenging issues across the district, impacting pasture establishment and legume crop performance – even with rates as low as 50ml/ha being used in previous cereal crops ie 2018/19. Therefore, we need to rethink the use of LONTREL and consider alternatives, such as spikes like Dicamba.

2021 Rotation Tips

Planning crop rotations for 2021, we need to consider the following issues associated with LONTREL (Clopyralid) and IMI herbicides:

· Avoid late applications of LONTREL to cereals

· Don’t use LONTREL if a legume eg Vetch (symptoms, below left) will be sown next year

· Be mindful of plant back restrictions if LONTREL is essential for skeleton weed control.

· Choose IMIs that have the lowest plant back periods ie Intervix or Imazamox mixes

· Use the lowest rate of IMI possible, instead of generous blanket rates.

· Keep spray records (rate, date, time) along with rainfall records from application to sowing

· Use an IMI-tolerant crop if in doubt.

Peas will tolerate IMIs better than Vetch (above ) as well as Lupins (above). Also consider Clearfield Canola, Clearfield Lentil, new Clearfield Peas or any of the Clearfield cereals available.

Finally, be mindful of soil types. Acidic sandy soils take longer than alkaline soils to break it down, mainly due to lower organic matter, reduced microbial activity and lower moisture holding capacity.


Last week saw outbreaks of Russian Wheat Aphid (RWA) south of Kimba and reports of crop damage around the Kimba region. Affected cereal crops are those that were not treated with Imidacloprid seed dressing so make sure you are closely monitoring if you did not treat. NB - a seed treatment typically costs $1.80-2.50/ha; post application treatment now is $4.50/ha (plus wages & other operating costs) so seed treatment is cheap insurance.

While monitoring crops, keep an eye out for cow pea aphid in vetch and Lupins as I have found them in volunteer crops (mainly vetch). With day time temperatures of 15-20°C presents perfect conditions for all aphid species in vetch, lentils lupins and medics.

As always, please ring me on 0499 272 544 to discuss your specific crop issues and observation. Meantime, keep your fingers crossed for a wet August-September.

Author: Troy Maitland

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