This week I am going to answer a few of the frequently asked agronomy questions you have sent from previous newsletters. Thanks for subscribing and talking to us! Let’s dive in..

What is the best approach for Controlling Couch Grass?

The only sure answer to Couch Grass is to apply glyphosate in the fallow period. In my experience the dose rate needs to be at least 1,500 grams of active ingredient per hectare, so 3 litres/ha for most quality glyphosate formulations.

It is best applied when the Couch Grass is actively growing which means soil moisture and not too hot or cold days.

Good coverage is essential so avoid dusty conditions, and the use of an adjuvant will improve retention and penetration on the leaf. As always, use ammonium sulphate to condition the water before putting the glyphosate into the sprayer tank, and acidify to improve activity.

I tend to use either Flat Fan nozzles for this type of spray, or 3D type nozzles are even better. The main thing is to strike a balance between an acceptable amount of drift, and good coverage of the target plant. For this reason I avoid true Air Induction nozzles.

Contact graminicides such as Fusilade (fluazifop) and Select (clethodim) do provide very good suppression, so including crops such as Peas and Canola in the rotation can be very beneficial.

For really bad localised patches of Cynodon grass, rotavating or ripping with a Chisel in January can help; the dry weather will dry out and desiccate the Rhizomes.

couch grass

The only sure answer to Couch Grass is to apply glyphosate in the fallow period

What dose rate should I use for Fall Armyworm insecticides?

As a general rule, stick to manufacturers’ recommended dose rates. This is important not only to ensure good control, but also to avoid and slow the development of resistance to the chemicals in the Fall Armyworm population.

The approved dose on the label should NEVER be exceeded; this is in place to protect the operator and the environment. Below are the typical amounts of active ingredient that I use for some common Fall Armyworm products:

Black Jack and Commelina are a serious problem in my maize!

The fact that these two very different weeds are appearing simultaneously should tell us something about the system in which they are clearly thriving.

Firstly, Blackjack is a very fast growing weed that benefits from soil disturbance and movement, and when given the opportunity can go through three generations a year. Normally it is easily controlled with herbicides but new flushes of weeds often appear shortly afterwards.

Commelina on the other hand is much slower growing but very difficult to control with herbicides; the exact opposite of Blackjack.

This leads me to two obvious conclusions, and one less so…

Number one; crop competition. If you can get the crop away ahead of Commelina and smother the weed, it is unlikely to be a problem in that crop. Blackjack also will not come through a crop of barley later after an application of Buctril, Ariane or Aurora Turbo once the canopy closes over, but with maize, this never fully happens, which is why the Blackjack also thrives even after a herbicide.

In maize pendimethalin rarely gives good persistence against Blackjack and can only safely be applied up to the four leaf stage of the crop. Stellar Star is very useful later on but has minimal residual activity. And Lumax stresses the crop the later it is applied.

For me a useful base is Adengo which has good persistence, followed by Lumax post emergence by the four to five leaf stage, no later for crop safety. Where the maize is growing healthily I have used low doses of mcpa + bromoxynil but this is at the growers own risk and can slightly hold the crop back.

Acetochlor + Sencor pre emergence is another very good mix for Blackjack.

Black jack weed herbicide

Blackjack is a very fast growing weed that benefits from soil disturbance and movement, and when given the opportunity can go through three generations a year

Beyond 8 leaf stage is certainly not sensible, but it does allow the crop canopy a few more crucial weeks to seal over. Another option if you get to the 7-8 leaf stage and have small Blackjack seedling emerging is to do a half dose of Stellar Star – the Dicamba is very strong on the weed, so as long as you are not trying to hit grasses this is effective and gentle on the crop.

For Commelina, full rates of metolochlor (Dual Gold or mixtures such as Primagran) are effective but the best is working on the weed in the fallow with a Double Knock of either glyphosate followed by paraquat, carfentrazone (e.g. Aurora Turbo) or a second glyphosate.  There are no effective herbicides in the maize crop for Commelina.

Low water volumes (50 l/ha) with a quality glyphosate have the greatest success in my experience, but maintaining ground cover is also very effective, albeit at the expense of moisture conservation. This has to be balanced against the benefit of a dense, supressing cover crop for changing the angle of attack against the weed.

Where can I access good quality Lime?

There are many good sources of agricultural lime in Kenya. The key is to ensure that the fineness or particle size is sufficiently small for the material to react in the soil, and secondly that the calcium carbonate content is sufficient.

The challenge is finding a consist and reliable source where every truck load has vast majority of the material able to go through a 0.3mm sieve. In reality the best advice is to get the lime tested on delivery, or first prize if you have a lot of liming to do is to buy a cheap crusher mill and roll it yourself so that you can be sure of the quality..

Before I finish, I would like to personally invite you to our Trials Open Day on the 8th of August at Kisima Farm. Lot’s of exciting insights to share. Hope to see you there :)

agronomy crop trials

Center of Excellence for Crop Rotation Agventures

Farming for the future requires a change of approach. Monoculture, soil degradation and climate change and soil degradation are threats to the futureof how we feed the planet. Agventure Ltd set up the Center of Excellence for Crop Rotation to help farmers diversify cropping systems and introduce techniques which have a long-term outlook to improve soil health. The Center of Excellence for Crop Rotation works extensively with Crop Nutrition Laboratory Services Ltd (CropNuts).

Till next time,

Happy farming,


David Jones cropnuts

About David

David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.