SA Graan November 2015

FOCUS

Natural resources and energy

Special

You then set the application depth on the

irrigator’s controller and the variable rate

irrigation controller will pulse the valves to

lower the application depth to the percent-

age set on the map.

The capital layout of a variable rate irriga-

tion system is influenced by the number of

sprinklers on the irrigator, spacing between

the outlets and the length of the structure.

Cost estimates and return on investment

calculations show payback terms of five to

ten years. This depends on the severity of

the problem, potential of soils with the right

irrigation and the value of the crop.

Growsmart precision variable rate irrigation

is compatible with centre pivots, laterals,

pivoting laterals and reverse pivoting later-

als. It can be installed on new irrigation sys-

tems or as an add-on to existing systems.

For more information, visit

www.grow

smartprecisionvri.com

. You can contact the

author directly at the Lindsay Africa head of-

fice at 021 986 8900.

Average irrigation yields improved

Variable rate irrigation gives producers the flexibility to grow different crops under one irrigator.

Here the potatoes are getting irrigated while the wheat is left dry.

Valuable info shared

This means that there should be knowledge about the nature of the

chemicals involved, and the extent to which they can affect not only

crops, but also beneficial soil micro-organisms. Back to synthetic

herbicides…Over-reliance on a particular herbicide, in particular a

specific mechanism of herbicide action, promotes not only shifts

to dominant weed species that are hard to control, but even more

importantly promotes the evolvement of weed resistance towards

an herbicide, or to put it more accurately, weed resistance to a par-

ticular herbicide mechanism of action. Misuse (off-label usage) of

herbicides has the same consequences.

The hard lessons learned in the USA and in South American coun-

tries regarding herbicide resistance must be taken to heart and pre-

ventative measures implemented in order to contain and even avoid

the same problem from decimating profit margins of South African

crop producers. Scientific investigation the world over has proven

that containment and prevention of herbicide resistance can be

achieved only through combining different herbicide mechanisms-

of-action, e.g. by using tank mixtures of different herbicide products,

or ready-mixed herbicide formulations containing more than one ac-

tive ingredient (= mechanism of action).

From a practical viewpoint, tank mixtures give the best solution be-

cause it gives flexibility based on the weed spectrum occurring on a

particular field, at a particular point in time.

It is imperative that crop producers confront and effectively manage

herbicide resistance, because it not only poses direct financial risk,

but also indirectly through the distinct possibility that herbicides that

are currently highly effective could either be lost or at least have

their utility reduced.

The five golden rules for avoiding herbicide resistance:

Keep weed numbers low – reduce the one in a million chance

that an individual weed plant in a population could, in a natural

way, evolve herbicide resistance.

Prevent weed seed production because resistance is genetically

inherited and is spread through seed.

Do not rely on a single herbicide, or more specifically, do not be

reliant on a single mechanism of action; employ more than one

herbicide mechanism of action – this is best achieved with herbi-

cide tank mixtures.

Avoid under- and over-dosing since both promote resist-

ance.

Integrate different weed control methods (chemical, mechanical,

cultural and biological) wherever applicable.

For any enquiries, contact Dr Hendrik Smith at

Hendrik@grainsa.

co.za

or Dr Charlie Reinhardt (dean: Villa Academy) at 083 442 3427

creinhardt@villaacademy.co.za

Reference

Blignaut, J., Knot, J., Smith, H.J., Nkambule, N., Crookes, D., Saki, A., Drimie, S.,

Midgley, S., De Wit, M., Von Loeper, W. and Strauss, J. 2015. Promoting and ad-

vancing the uptake of sustainable, regenerative conservation agricultural practices

in South Africa with a specific focus on dryland maize and extensive beef produc-

tion. Asset research, booklet nr 2. Pretoria: ASSET Research.

November 2015