The good, bad about weeds

Coming out of the dry season, the lush green and long grasses are both a saviour and curse to farmers, for within them pests and diseases lurk.

SO, as the rains pound throughout the country this season, crop farmers need to realise that weeds will sprout and outdo crops in the fight for growing space and uptake of nutrients. By definition, weeds are plants that grow where they are not wanted and are therefore bad news to crop farmers. Of course they are not always bad. Many weeds have luxuriant leafy growth and when buried in the soil as green manure add considerable amount of organic matter and plant nutrients.

They add about 5 to 15 tonnes of green matter per hectare depending upon weed species and their growth. When they grow on barren lands or even sloppy fields, they lower the rate of wind and water erosion thereby helping the farmer protect the environment. Some of them even have a good palatable taste that the farmer’s livestock can enjoy.

The ugly side of weeds is that as they grow, they reduce farm productivity, they invade crops, smother pastures and in some cases can harm livestock.

They aggressively compete for water, nutrients and sunlight, resulting in reduced crop yield and poor crop quality. For example, prickle bushes such as gorse, blackberries and prickly acacia can invade vast areas of grazing land preventing productive use of that land.

Weeds contaminate produce, for instance, grain milled with saffron thistle or amsinckia results in discoloured flour while animals that eat specific weeds, such as wild garlic, produce tainted milk and meat and the weed, Paterson’s curse irritates the udders of dairy cows and can kill horses.

They can also affect the operation of farm machinery and push farmers to spend a large amount of time and money managing them.

Yellowing of leaves is one sure sign that crops are losing the battle to weeds and this will eventually translate into compromised yields, as most of the vital nutrients would have been shared between the crop and the weeds.

The current incessant rains may make it difficult for the farmer to contain weeds but there are always ways of minimising the damage they may cause on crops.

Farmers can use the mechanical way of weed control, which entails the employment of methods that kill or suppress weeds through physical disruption.

Such methods include pulling, digging, disking, ploughing and mowing. Success of various mechanical control methods is dependent on the life cycle of the target weed species. Hand pulling and digging are effective on annual and biennial species and as they remove the weeds, farmers need to make sure they remove the upper 2-3 inches of tap-root to prevent re-growth. Hand pulling or digging a perennial weed such as leafy spurge can be a futile effort unless one has the time necessary to diligently dig or pull re-growth over several seasons.

Shallow tillage with a disk or sweep can also be effective for controlling annual species such as cheat grass or kochia, but can actually be counterproductive if trying to control perennial weeds such as field bindweed, leafy spurge or Russian knapweed. Perennial root systems often have meristematic buds that can set roots and produce a new plant from root segments deposited on the soil surface.

Mouldboard-ploughing (complete turnover of the top 10-12 inches of soil) disrupts underground root systems and buries seed from the surface to a depth too deep to germinate. This type of tillage is seldom feasible to practise but may become necessary depending on the levels of infestation.

It is usually not feasible to adopt the chemical method of control for the majority of the smallholder farmers, as they lack the financial muscle critical to secure the chemicals so they have to go the mechanical route, in most cases using hoes and deploying many people on a piece of land to remove the weeds.

Besides competing for almost everything on offer with crops, weeds shelter pests that can wipe out entire swathes of crops. Some of the pests that can easily find a home in the comfort of weeds include locusts, aphids and weevils to name just a few.

Interestingly, the same weeds can also help reduce the rate of moisture evaporation from the soil despite remaining the crops’ biggest nemesis that causes significant declines in yields, which eventually affects food security as well as the commercial side of farming.

The stark reality however, is that the advantages of removing weeds from a crop field outweigh the disadvantages of leaving them so they have to go no matter the cost if the farmer’s interests are to be realised.

To all crop farmers, remember as you toil on your fields, you do not want your harvest to be spoilt by weeds. So deal with them decisively and journey into 2017 with a healthy crop. HAPPY 2016 /17 FARMING SEASON!!!!