Boosting Crop Success: The Critical Reasons for Seed Treatment
Introduction
Seed retained for sowing is a highly valuable asset and the way it was treated at harvest and in on-farm storage during summer, or between seasons, is critical to ensure optimum germination potential and crop establishment in 2019.
Dry conditions across much of NSW and Qld limited winter crop plantings in 2018. The quality of seed retained from crops harvested in 2018 is also likely to be variable due to drought, frost and late rain in October in some areas. Seed supply for planting in 2019 will be scarcer than normal, especially for chickpeas due to the limited area planted in 2018. However, it is estimated that there are around 44,000 tonnes of chickpea seed from the 2017 harvest that were not planted in the northern region in 2018 (K. Moore, pers. comm.). Much of this seed has been stored on-farm under varying conditions, with some treated with fungicide in anticipation of sowing in 2018. Growers need to determine the germination and vigour of all cereal and pulse seed retained from 2017 or 2018 crops to confirm whether it is suitable for planting in 2019.
Testing retained seed
Retained seed can be tested for vigour, germination, purity/weed seeds and disease pathogens. It is advisable to undertake testing at least two months before sowing so that an alternate seed source can be organised if required. Grading to remove smaller grains which inherently tend to have reduced vigour can also improve the quality of planting seed.
Vigour and germination tests provide an indication of the proportion of seeds that will produce normal seedlings. This helps determine seeding rates. As a result of poor seasonal conditions in 2018, particular attention should be given to determining vigour of retained seed for sowing in 2019. The potential shortage of planting seed in 2019 means many growers may be in the situation of sowing seed retained from harvest in 2017. Storage conditions during this extended period are likely to have impacted on germination and vigour of retained seed which should be determined through testing. Vigour will be even more important if growers plan to increase sowing depth to capture an earlier sowing opportunity through moisture seeking.
A comprehensive GRDC Fact Sheet outlining issues with retaining seed after challenging seasons is available from the GRDC website. The fact sheet outlines how growers can test their own seed or a range of commercial providers of both germination and vigour tests are available.
NSW DPI, Tamworth provides pathology testing of winter cereal and chickpea seed for common seed-borne fungal pathogens. Germination is also noted, but this only tells growers how much of their seed is alive with the main purpose of testing to determine levels of fungal infection present. The testing does not determine vigour or emergence and germination observations should be used as a guide only.
Fungicide seed treatments
Seed treatments provide cheap and effective control of bunt and smut diseases in cereal crops. Seed should be treated every year as bunt and smut can increase rapidly, resulting in unsaleable grain. Where growers choose not to treat wheat seed for one year, it is recommended to definitely treat the following year. Good coverage of seed is essential and clean seed should be sourced if a seed lot is badly infected. Note that in-furrow fungicides on fertiliser treatments do not control bunt and smuts, so seed treatments are still required. However, due to the increasing prevalence of loose smut, it is recommended that barley seed be treated every year, especially in more susceptible varieties. Some seed treatments will also provide control of seed-borne net-form of net blotch (NFNB) infection. A comprehensive list of available products, active ingredients, application rates and efficacy against a range of diseases is published annually in the NSW DPI Winter Crop Variety Sowing Guide. A comprehensive cereal fungicide seed treatment guide is also produced by SARDI annually.
Chickpea seed should be treated every year to control seed-borne Ascochyta and Botrytisinfections. However, this does not protect plants from infection after emergence which occurs from stubble-borne sources of inoculum. It is generally considered that chickpea seed treated prior to sowing in 2018 does not require re-application of a fungicide seed treatment in 2019 (K. Moore, pers. comm.).
Impact on emergence
Seed treatments containing fluquinconazole, flutriafol or triadimenol, can reduce coleoptile length in cereals and cause emergence issues under certain conditions. These active ingredients should be avoided if sowing seed with potentially lower vigour, sowing deeper, sowing into cooler soils, in soils prone to surface crusting or where herbicides such as trifluralin have been applied.
Loose smut in barley
Loose smut, caused by the fungus Ustilago nuda, has been reportedin barley crops in the northern region since 2015. Infection has been more frequent in varieties from the Hindmarsh lineage such as La Trobe, Spartacus CL and Rosalind which appear to be more susceptible to loose smut.
Loose smut infection is obvious around flowering when infected heads bearing a mass of dark brown to black sooty spores are visible among the green heads of unaffected plants. The membrane encasing the black spores ruptures soon after heading, releasing them to be carried by wind to infect surrounding florets. Loose smut is well adapted for survival as infected plants are usually slightly earlier than healthy plants, ensuring an adequate supply of inoculum when the bulk of the crop is flowering. Infection occurs under moist conditions at temperatures around 16 – 22°C. Florets are susceptible to infection from flowering to approximately one week after pollination. Germinating spores infect the ovary and the fungus then survives as mycelium within the embryo of the infected seed where it can persist for extended periods. The resulting internal seed-borne infection is the only way loose smut is carried between seasons with infected grains appearing completely normal.
When infected seed is sown in the following season, it germinates and carries the fungus in the growing point of the plant until it is expressed as the symptomatic black spore masses at head emergence. Given that infected seed appears normal, loose smut can progress from low levels in one season to high levels in the next if infected seed is sown without treatment.
Fungicide seed treatments provide economical control of loose smut in barley. As the loose smut fungus is internally seed-borne, systemic fungicides are necessary for control. Products containing carboxin, difenoconazole, flutriafol, fluxapyroxad, ipconazole, penflufen, tebuconazole and triticonazole are registered for the control of loose smut; but their levels of control vary.
Conclusion
After a below average to poor winter crop season in 2018, recovery in 2019 starts with growers planting the best available seed possible. Seed supply will be tighter than usual in 2019, so just because a seed source (e.g. from 2017 harvest) is all a grower has on hand does not mean it will be the best choice to sow in 2019. Sowing rates can be increased to compensate for small reductions in germination, but nothing can be done to fix planting seed with poor vigour. Growers should consider certified testing of planting seed for both germination and vigour well in advance of sowing in 2019. This will ensure they plant the best seed source available or have time to organise an alternate improved seed supply if required. If using planting seed from out of your immediate region then using a quality assured seed supplier is recommended as grain quality (purity, germination and vigour) will be tested against a code of practice. Also check for freedom from weed seed, some of which may not be present on your farm or with unknown levels of herbicide resistance.
