The cost of less reliable technology

28 May 2015

Black-grass heads are now appearing above wheat crops. Perhaps it is too early to estimate the levels of control achieved this year but it is getting very close to the end of the window for patch spraying with glyphosate in order to prevent the setting of viable seed. In my opinion, based on field experience and limited experimentation, some of the final dates for this operation suggested in the press are far too late. It is also important to note the downside of this approach. The crop in the patches is also killed and so there is no green matter keeping the soil dry if there are meaningful summer rains. This can lead to complications in post harvest cultivations.

As the ability to control weeds with herbicides reduces, the need to be pro-active and adopt other means of control increases. No opportunity should be ignored. This spring, I noted a large field of oilseed rape where there was charlock in a small area only. It might have taken a couple of hours to hand pull the plants and put them in a bag but it would perhaps have prevented a costly problem in the future. Similarly, I have seen very small patches of black-grass which would take only a few minutes to hand pull but have been ignored. This type of activity goes against the grain for many who have become accustomed to large scale control using herbicides but the current reality means such opportunities have to be taken.

Whilst singing the praises of the opportunist hand-pulling of weeds, it is important to remember that although it is assumed that it is 100% effective, the reality is that the outcome can be disappointing unless it is done diligently. In the days of hand-roguing wild-oats, it was estimated that it was equivalent to reducing seed shed by 85% and was far more effective if the fields were re-walked a few days later.

SeptoriaThere is now the challenge of increased resistance of septoria to the triazoles. This results in all kinds of issues, including less reliance on the eradicant properties of fungicides and adopting programmes that delay resistance to the SDHIs for as long as possible. It also creates the dilemma of how much fungicide to use and also making sure that the time gap between applications is not too long. Currently, farmers are not holding back on fungicide use despite the low price of wheat. On the other hand, there are seed houses claiming that some varieties require less fungicide.

When the triazoles were providing effective control of septoria, there was a real opportunity to exploit the value of good varietal resistance through lower doses. The more resistant varieties only required two thirds of the dose normally applied to the most susceptible varieties. I suspect that in most cases this potential saving was ignored on the grounds of keeping it (too) simple or the “just in case” principle.

Nowadays, I suspect that the reason for using the more disease resistant varieties is largely to do with security of production in a difficult spraying season rather than a significant saving on inputs. There is a big financial risk to ‘getting it wrong’ when planning fungicide programmes. In high disease years, the yield penalties from using lower input programmes can be very significant compared with small potential savings in low disease years which are difficult to predict. I am sure NIAB TAG members are well aware of the options through the information they receive.

As always, it is well worth farmers and advisers keeping an eye out for all opportunities to save money in the short and/or medium term. This means being well informed and occasionally going back to practices that were commonplace a few decades ago.