CSIRO Plant Breeder Greg Constable discusses important considerations in growing Pima and CSD plant pathologist Steve Allan discusses some disease considerations. 

There has been some interest in Pima from a number of growers and consultants this year. Starting with a very basic question; ‘What is Pima and how is it different to the conventional cotton that we grow now?

Pima is a particular type of cotton, it is actually a different species to the current cotton we grow. It’s derived out of more tropical parts of the world. The interest is that it has got a longer, stonger and finer cotton and there is a substantial premium for it on the market. It’s commonly grown in Arizona, California and then there is other industries around the world but particularly Egypt, what is called Egyptian cotton is also a relative of Pima cotton.

What sort of staple length differences are there between Upland and Pima cotton?

Our upland varieties are probably around the 1.15 to 1.17 inches whereas the Pima is something like 1.4 inches. It is a substantial difference and really attractive to the spinner.

So that’s looking at say 36, 32nd’s of an inch versus say 43, 32nd’s of an inch?

Yes, 36 or 37, 32nd’s in the upland versus 43 32nd’s in the Pima.

What differences do people generally see in yield?

The old rule of thumb out at Bourke where they have been growing Pima in the past has been about 80% of the yield is upland. Its probably the better part of the yields. I think most circumstances might be a bit less than that, maybe 70 or 75%.

What would be the main considerations, especially climate and diseases that people need to take into account before growing Pima?

Pima needs a long dry season. There are a lot of affects from humidity and rain etc, either on promoting diseases or on degrading the quality of the crop towards the end of the season. So you need a long dry season; not necessarily hot but long and dry and the diseases are also quite an important consideration particularly black root rot, alternaria and in the past bacterial blight.

How is Pima managed differently than Upland cotton?

Generally the same principles. It reacts the same to each of the inputs of fertilizer, insecticides, irrigation etc. But because of the longer season it obviously needs to be managed for a longer amount of time to get the most out of it. So management wise the most important considerations really start around defoliation and harvest time making sure that the crop is treated to ensure you realise the fibre quality potential.

It is important to recognise we are dealing with a premium product so getting that quality final product is very important?

Absolutely, the length and the strength and the fineness are all very important considerations for the spinner and it stands to reason that you wouldn’t want to have a trashy, dirty sample or a degraded sample.

The CSIRO has a Pima breeding program. Can you tell me about the objectives of that and what sort of progress has been made on some of these objectives?

Fourteen years ago we started, just as an interest thing in determining if there was potential in the future for Pima as a product in our industry, and there was. It was grown commercially and still is in the western parts of NSW. But, the diseases I mentioned before were massive constraints and so our first objective was to breed bacterial blight resistance into the product and as we have been through that program we obviously have been making sure that we are trying to select for a better yield and a better quality etc.

So, to this point in time we have candidate lines that have gone into basic seed production at CSD that are immune to bacterial blight, have, better Fusarium resistance, better yield and better quality than what the material is that we have imported from Arizona that has been grown here for the last 20 years.

Pima lint needs to be handled differently through ginning. Can you tell us a little bit about that?

As a premium product the conventional saw gins affect the quality too much in a Pima product. Because Pima cotton is held on naked seed its much easier to gin so roller gins are used to gin Pima cotton so that’s treated much more gently. It’s a slower process and hence a little bit more expensive but it doesn’t damage the fibre as much.

Dr Stephen Allen, Plant Pathologist
Cotton Seed Distributors

One of the constraints to producing Pima cotton is its susceptibility to diseases. Can you tell us a bit about the diseases of Pima and how they are different from Upland?

The Pima cottons (Gossypium barbadense) have long been regarded as being a different kettle of fish completely to the upland varieties in terms of diseases.

On the good side, they are more resistant to verticillium wilt than the upland varieties. For instance we don’t have V-ranks for the S-7 but the Pima A-8 has got a V-rank of close to 194 based on 4 trials; so in terms of verticillium, good news, Pima varieties are much more resistant.

However we move onto things like Black Root Rot. Pima varieties are regarded as being more susceptible to Black Root Rot than Upland varieties and there is no sign of resistance on the horizon. About the best advice we can give in terms of Black Root Rot is that if you are growing Pima, avoid the fields with a history of Black Root Rot.

Moving further along the road to Fusarium Wilt, Pima varieties generally are regarded as being very susceptible. Much of the Pima S-7 type things and most Pima varieties have come in with an F-rank lower than 10 which is very susceptible. However, there is light on the horizon and they indicate that the Pima A-8 has an F-rank of 175 based on 4 trials. 

The same resistance that is in the Pima A-8 is proving affective against the new races of Fusarium that are appearing in California now. So generally Pima varieties are more susceptible to Fusarium but the Pima A-8 is certainly miles ahead of even many upland varieties in terms of resistance and it’s important that that resistance is maintained in new Pima varieties.

Moving on to Alternaria leaf spot, Pima varieties are regarded as being much more susceptible to Alternaria. The crops can be defoliated very quickly. A week of wet weather towards the end of the season is enough to result in the complete defoliation if the disease is present. Consequently the fungicide mancozeb has been registered as a foliar spray for Pima cotton.

It relies on complete coverage. You would not use it all the time but particularly if there is an outlook for wet weather or cool wet weather. Under those conditions, the disease can be devastating. The pathogen that causes alternaria survives on trash, it is spread in wind.

It is virtually widespread and ubiquitous, it’s always present and certainly if conditions are right it can be devastating. Maybe prior to flowering you can get away with doing nothing, but certainly once the crop starts flowering, keep a very close eye on it and it maybe necessary to apply about four sprays with Mancozeb. 

The last disease of note is Bacterial Blight which has proved a bit of a nemesis for Pima growers. There have been some terrible experiences with Pima and bacterial blight. I have seen a crop completely defoliated and with 80% of the bolls ruined by bacterial blight.

It survives and is dispersed in seed, it survives and is spread around on trash. It is important that you have a disease free source of seed and I guess we can say that we expect that current seed stocks are disease free but there is always a possibility I guess. The other issue is to make sure that the field doesn’t have a history of blight susceptible varieties.

Some of the older varieties, particularly some of the US varieties carry bacterial blight and if the field has a recent history of the susceptible varieties then the disease could be present. We have a permit for the spraying of copper sprays; copper hydroxide or copper oxychloride (APVMA permit PER7941) for bacterial blight but again it really needs to be applied by ground. It really needs to have good coverage and it’s only partially effective. It’s only protective in its effect.

The bright news for both alternaria and bacterial blight is that there are resistant varieties in the offing.

The CSIRO breeders are talking about blight resistant varieties in the next year or so and it is not too far off that we may have alternaria resistant Pima varieties as well. But for now alternaria and bacterial blight are the two things to really watch out for and keep a close eye on.

Copies are available from CSD by phoning 02 6795 0000, by faxing CSD on 02 67954 966, or by "clicking" on the graphic, right.

Further Information:
Dr Stephen Allen, Robert Eveleigh, John Marshall,  Craig McDonald, David Kelly or James Quinn