Precision will pay well with PGR regimes

30 March 2001

Precision will pay well with PGR regimes

How will you fine-tune plant

growth regulators to take

account of the wide range of

crop growth stages this

spring? Our latest detailed

look at crop inputs helps you

make the right decisions

with or without the support

of an on-farm agronomist

PLANT growth regulator decision will need to be on a field-by-field basis this spring, says Dick Neale, technical director with Cambs-based distributor Hutchinson.

"It is a case of looking at the crop and deciding on the risk. Even late-drilled crops, where the risk is much lower, will benefit from a PGR programme."

His standard PGR programme, which he recommends for the majority of crops, is an early start with a split application of Moddus (trinexapac-ethyl) and New 5C Cycocel (chlormequat + choline chloride). By early, he means GS30. "You cant regulate a stem that is not growing."

He advises using 0.1 litres/ha of Moddus and 1-1.5 litres/ha of Cycocel, which will cost £5-£7/ha depending on rates used. That should then be repeated at GS31, or within 21 days.

"Before you make the second application, go out and look at the crop. If it is racing away with long internodes, use higher rates for the second split. Try 0.2 litres/ha of Moddus and 2 litres/ha of chlormequat to bring the crop under control."

Also ensure that the chosen chlormequat has a label recommendation for the split dose and be careful not to exceed the total stated dose when using a split application.

He warns that a single application of chlormequat will have disastrous consequences. "The crop will bounce back and might end up taller than before with even weaker straw. So use a split treatment and always mix Moddus with chlormequat to prevent bounce back and improve consistency."

High risk crops will then need a follow up with Terpal (2-chloroethyl-phosphonic acid + mepiquat chloride), Satellite (chlormequat + 2-chloroethylphosphonic acid + imazaquin), Cerone (2-chloroethyl-phosphonic acid), Upgrade ( chlormequat + 2-chloroethylphosphonic acid) or similar.

"When you make this application will depend on how strongly the crop is growing. It should be done between GS33 and GS39."

An alternative strategy with lower risk crops is to make a split application with chlormequat, then follow up with Terpal. But Mr Neale prefers to mix chlormequat with Moddus. "In lower risk crops the late season PGR can often be omitted following a split application of Moddus/chlormequat."

Lodging basics

Any wheat drilled in September or October is at risk from lodging this year, unless it was sown below a seed rate of 75 kg/ha (5 stones/acre), says Mr Neale.

"Most September sowings have established really well and as there was no cold snap until January, these crops have produced high tiller numbers, putting them at risk."

The main cause of lodging is high plant population, he says. "The higher the population, the more susceptible the crop is. The tillers are small and weak."

Other lodging factors include field history, variety and site fertility. "If lodging does occur every year on a farm, the causes need to be identified," says Mr Neale. "Some farms have a history of it." Variety has an effect due to straw strength. The NIAB list rating is determined in the absence of PGR, he adds. "Things can change dramatically once a PGR has been applied, so talk to your agronomist and seed supplier if you are growing a variety for the first time."

A fertile site will add to the problem. "Any variety, no matter how strong the straw is, is at risk on a very fertile soil."

Mr Neale advises growers to work backwards when it comes to making PGR decisions this spring. "Aim for 450-500 ears/m sq at harvest. Getting out in the field and doing plant and tiller counts will show whether you need to lose or encourage tillers."

An early application of nitrogen can be one of the worst things to do, he warns. "Excess nitrogen will also cause lodging. Dont forget that a PGR will only aid standing ability. It wont stop lodging if everything else is wrong."


PGRs should be seen as insurance, believes Mr Neale. Growers must judge the risk to their crops and buy the appropriate insurance policy.

"A PGR programme will cost anything from £10/ha to £22/ha," he says. "Whether you get a yield response or not is immaterial, the aim is to stop the crop lodging to protect the investment in seed, fungicide, fertiliser and herbicides."

Mr Neale believes that a robust PGR programme costing £20/ha is good value for money with a 10t/ha potential crop. "Do not look for the cheapest solution. Buy a policy that matches the risk, the most expensive policy will still only be about 8% of the input cost.

"It will be very important this year to buy some growing season. Once it warms up, plants are going to be racing through the growth stages. Growers must help these plants to root and tiller by slowing them down. A PGR programme can do that." &#42


PGR use is not complicated, provided growers follow some basic principles, says Mr Neale.

1 To successfully thicken and shorten a stem, it must be growing. So wait until GS30 and when the temperature in the crop reaches 8C. Thats when stem extension happens and PGRs work to the greatest effect.

2 Always go with a split application of Moddus/Cycocel. Crops drilled after the middle of October are unlikely to need anything else, crops drilled before will need a further late season PGR. The timing and rate will be down to individual crops.

3 Late-drilled wheats have a far lower risk of lodging but will benefit from a PGR programme to even up tillers and aid tiller survival. Again, use a Moddus/ Cycocel split at GS30 and 31/32.

4 If only one application of PGR is to be made, then do it at GS31 using a higher dose of Moddus/Cycocel.

5 Late season use of PGRs can reduce yield by 0.2t/ha. But losses from lodging will be in the region of 1t/ha.

6 Always split stems with a sharp modelling knife to assess growth stage.

7 Match nitrogen rate and timing to lodging risk. Take account of organic manures using the new RB 209. Pig and poultry manures, in particular, can significantly increase lodging risk.

8 Lodging control starts with variety, drilling date and seed rate. With autumn 2000 fresh in the mind, most growers will favour an earlier start to drilling in 2001. Seek advice on variety and seed rate and start planning now.

See more