Herbicide Damage on Cotton Research

NSW DPI weeds research agronomist, Graham Charles, is engaged in a long-term research project aimed at examining spray drift crop damage from an extensive range of fallow herbicides.

Speaking on the weekly CSD Web on Wednesday video, Mr Charles said these herbicides can impact on crop yields by causing leaf, flower and fruit loss from which the crop may or may not recover, depending on the timing and rate of the damage.

His research over a number of seasons has looked at cotton’s exposure at four different growth stages: 6, 8, 12 and 16 nodes, to two different rates of 2,4-D; two different rates of Roundup®; and the combination of Roundup and 2,4-D.

“We did plant mapping on those plants right through the season so we knew exactly what it was doing to leaves, leaf area, squares, fruit, boll retention, and then maturity at the end.

“While the crop is at most risk the whole of its life, very early it seems to grow out of it pretty well, and very late it has already set its fruit, so you are not having a lot of damage.

“It’s that middle period, around 8-12 nodes, where the plant is really susceptible. If the season was long enough, it would still grow out of it, but the plant gets knocked for six in that period.

“You get all sorts of complications when the plant does start to recover. It grows in an uncontrollable manner almost, so it puts a heap of new fruit on and then of course it takes a long time to set that or to get the old fruit through to maturity.

“So things like maturity are quite difficult to assess on damaged plants, because you actually might end up with a lot more bolls than an undamaged plant has and it probably won’t take all of those through to maturity because the season is too short.”

Mr Charles said recent research had examined management response mechanisms that might help alleviate the problem.

“Basically, we looked at measures such as throwing on additional water, additional nutrition or a combination of water and nutrition, but it made not the slightest difference. This indicates that if the plant is damaged at a cellular level, nothing you can do externally is going to change that damage.”

He said trials this season covering a broader range of popular fallow herbicides has shown all are capable of causing damage, and it is difficult to determine which herbicides are at fault.

More detailed information on herbicide damage is available on the Cotton CRC website at www.cottoncrc.org.au. Follow the links to Industry, Publications and then Weeds, or by contacting Graham Charles at ACRI Narrabri.