Seed Treatments

CSD has applied a coloured polymer to cotton seed since 1989. Initially the polymer was added to bind the fungicide and insecticide to the seed and therefore improve the adhesion of the pesticides we apply to seed.

The coloured polymer also makes cotton seed easier to find in the soil and identifies the traits in transgenic cotton seed.

CSD thoroughly evaluates the treatments we apply to cotton seed before they are commercially released. In the development stage small batches of new products are assessed in the seed lab and also in the field.

CSD has not detected any adverse impact on germination as a result of the polymer applied to cotton seed.

What is a polymer?

Polymers are long chain molecules that are composed of many repeated identical subunits. Polymers can be natural or manmade. Some examples of natural polymers are sugar, cellulose and DNA. Plastics are an example of manmade polymers.

The properties of polymers vary considerably. They can be water or oil soluble or completely insoluble. They can be porous or non porous.

The seed coating polymer that CSD uses is permeable to water but is quite long lasting and may take several years to break down in the soil. It's not uncommon to find traces of the polymer several years after the cotton crop has been harvested.

CSD regularly assesses performance in the field. These trials reflect the effect of the polymers we use on the rate of seed germination in the field. Many factors interact with the seed in the soil. We all know that a shower of rain after planting can greatly assist germination and emergence. Some growers have expressed the opinion that the polymer on cottonseed inhibits germination when seed is planted into marginal moisture. It is difficult to plant and assess trials planted into marginal moisture. Our experience is that all seed including seed without any polymer struggles when the moisture is marginal and poor plants stands are often the result.

A trial at "Yarral" Narrabri in 2012 was planted into a field that was pre-irrigated and did not receive any post sowing rain for several months. Conditions were very dry and challenging. The results are summarised below.

Note that even at 10X the normal polymer rate there was no impact on the germination rate and final establishment. There was also no difference in yield between the treatments.

Capping - Persistent seed coats

When seed is planted into moisture at a depth of 4-5cm the seed coat softens, splits and is sloughed off as the cotyledons are dragged to the surface. An excavation of the seed bed reveals the discarded seed coat close to where the seed was placed during planting.

When the seed is to be ‘watered-up’ it is planted shallow. If subjected to higher temperatures the seed coat may dry out before being shed and persist as a binding on the cotyledons preventing them from developing. This persistence is generally only temporary.

The application of a polymer does not increase the percentage of capped seed but the coloured dye does increase the visibility of the seed.

CSD provides the option of insecticide treated seed. Currently Cruiser®, Cruiser Extreme® and Genero® are the registered insecticide choices available. All products are from the Neonicotinoid group and are active against a range of leaf feeding and some soil dwelling insects.

The Neonicotinoid's are synthesised molecules based on the nicotine found in tobacco. The neonic's have relatively low mammalian toxicity but are highly toxic to most insects. Just like nicotine the neonic's bind to nicotinic acetylcholine receptors in the cell. A high dose of the insecticide blocks the receptors causing a nervous shudder and finally death.

The insecticide coats the outside of the seed but the active ingredients are transported inside the seed as it imbibes water during the germination process. The insecticide then translocates throughout the young seedling but its concentration in the plant is diluted as the plant grows. Initial insect control declines over time depending on the product and the rate of plant growth.

Typically aphid control lasts for up to 4 weeks after emergence and thrips are controlled for 1 to 3 weeks. The seed treatments will give some control of wireworms but should not be relied on when high numbers are present in the soil. The current seed treatments do not give control of cutworm and other meristematic feeders.

Seed applied insecticides have the advantage of selectivity. They control pests that feed on the seedling but have minimal impact on predators. They are simple to use and have good operator safety. However none of the current seed applied insecticides give performance equal to soil applied granular insecticides such as Thimet.

CSD is continuing the evaluation and development of new insecticide options for the treatment of cotton seed. Each season CSD also evaluates the performance of the seed insecticide treatments. The results are summarised in the following graphs.

Pre-emergent and post-emergent seedling diseases are caused by fungal pathogens that are favoured by environmental conditions that slow down or delay germination, emergence or seedling growth. Pythium spp. and Rhizoctonia sp are the most common pathogens involved although several other fungi can contribute to the problem.

The NSW DPI, in conjunction with CSD and CSIRO, conduct annual field trials to compare the efficacy of the current, standard, fungicide seed treatment with the activity of potential new treatments. Each fungicide needs to be evaluated alone and in combination with other treatments. Some are specifically active against Pythium spp. or Rhizoctonia sp but have no activity against the Fusarium spp. or the black root rot pathogen.

If the seedling disease control provided by Apron alone is as good as, or better than, the control provided by the current standard then it indicates that Pythium spp. is the most significant pathogen at that site and in that season. Alternatively, if the seedling disease control provided by Apron alone is no better than untreated seed then it indicates that Rhizoctonia sp. is the most significant pathogen at that site and in that season.

The current, standard fungicide seed treatment for cotton in Australia is Dynasty which is a combination of azoxystrobin, metalaxyl-M and fludioxonil. Most seed is also treated with acibenzolar-S-methyl to add to the control of Fusarium wilt and black root rot.