Weed out paddock problems

THE rain at this stage has not blessed us too much in many areas, however, you can bet your socks any rain we get will stimulate weed seed germinations.

It may be a large strike like I have already seen with feather top rhodes, or it may be a much lesser population of turnip or bladder ketmia.

The difficulty we all face with these little amounts of rain is that while they do germinate the weed seed bank they invariably do not contribute to the overall stored sub soil moisture levels, or even provide a planting rain.

Unfortunately finances and time is spent controlling these weeds, without the opportunity to plant a crop to offset these expenses.

Hence my attention this week to our residual herbicides again.

We have used atrazine for years and this mighty product will again be at the forefront of our weed control.

Many years ago solid research out of Hermitage Research Centre gave plenty of belief for up to 40% of atrazine to be lost from the soil surface despite incorporation efforts.

Indeed the best way to apply atrazine and retain the full weed control effects was, and still is, immediately before an inch of steady rain.

These days we really need our triazine products for broadleaf weed control, especially for Fleabane, which brings me onto Diuron.

Diuron is classified as a substituted urea in the Group C mode of action category.

I believe it is a more effective broadleaf weed control agent than atrazine, and that gets proven every year with our Diuron in regional inland Queensland's only broad acre crop registrations of chickpeas, lucerne, cotton, and Faba beans.

Rapidly adsorbed by the weeds' root system due to its very water soluble attributes, Diuron is slow to dissipate or breakdown if under anaerobic conditions. This is where there is no air or, to be specific, no oxygen for soil biota to live on.

Diuron's lengthy persistence in the soil is also dependant on levels of organic matter, with low O.M. or, more correctly, low organic carbon levels like we have around in the .5 to .75 level. Both atrazine and Diuron have brilliant residual weed control capability, however they have this large need for crop safety.

That should make us baulk at pushing the envelope for predicting and hoping for exact residual length.

There are things you will not be able to control and only be able to critically assess.

Topics:  paul mcintosh