An important reminder for this time of year is to be careful when using Group I herbicides. You have to choose the right product at the right time. Why? Because of the way they work. Group I herbicides work by mimicking indol-3-yl-acetic acid (IAA). IAA is responsible for cell division, differentiation and elongation, among other functions in plants. Group I products work by turning on all these growth ‘switches’ in a plant, causing the plant to twist and distort as rapid growth occurs that the plant can’t keep up with, causing death. Cereal crops get their selectivity as they increase in maturity, hence why it is so important to get the product and rate right.
Early in the season when doing broadleaf sprays in cereals we like to use MCPA products as they are softer on crops. These products can be mixed with a range of other products to suit your weed spectrum in the paddock. Normally the rate range will increase as the plant matures and the number of leaves on it increases. Later in the season, once the first node can be felt at the base, you can switch from MCPA products to 2,4D products.
The other differences between these products are whether they are ester or amine formulation. Esters have higher vapour pressures than amines, meaning they will have increased volatilization. Whether either provide better weed control depends on a lot of variables, however ester formulations are typically more active on weeds, due to the fact they are more soluble when in contact with the plant’s waxy cuticle.
A couple of key tips to remember going forward.
- If you struggle to get your hands on MCPA this season, don’t go in too early with a 2,4D product. Crop injury can be significant if you go too early.
- Always follow the label for rates, as well as to make sure you are using the right Group I mix partner. If you have any questions to hesitate to call our Agronomy Team.
- Remember to use the correct nozzles when applying 2,4D products.