Waging war on weeds in Vanuatu

The sun shines, grass grows, cattle graze and the result is perfect South Pacific beef that fetches a premium on the international market. The trouble is that not only do the cattle and the pasture grow well, but so do weeds.

Credit: Susie Emmett

Charlie Rogers has farmed the plantation owned by the Montmarte Catholic School on the hills above Port Vila (the capital of Vanuatu) for more than 20 years. He has a battle on his hands: "You can't turn your back on the weeds here for a minute; you can't put off what needs to be done or they will win!" But, when you are running a training school for plantation managers and farmers, and a successful beef export business, plus trials for vegetable growing, time is short and the window of opportunity to solve a problem often slams shut. To illustrate his point and one of the fiercest weed problems, Mr Rogers drives his pick-up to the fence between two fields. On one side it is a picture of productive pasture; on the other side there is a dense wall of foliage and strong stems - 4 metres or more high. "Six years ago I stood here and looked through at that 50 hectare field and thought we should have a go at the patches of wild guava, but I didn't have time," remembers Mr Rogers. "Now look at it! The patches have multiplied. It's dense bush and nigh on impossible to get it back."

Wild guava (Psidrum guajava) does more than ruin the pasture. Cattle can disappear or 'go bush' in it. This makes it very hard for Mr Rogers to check on them. "Once they go in, it can be weeks before I will see them again. You can't just go in and herd them out." To get strays out and stop them disappearing into it again, Mr Rogers and his team have built a funnel-style trap, inspired by a device used to catch fish. When a stray animal is tempted to rejoin the herd and comes out of the guava forest, it follows the funnel fence and at the end comes to a one-way gate through which there is no going back.

Herbicidal control of guava is too expensive an option, but an improvised chemical control method is to paint the bark with diesel. Dieback is apparent in six weeks although it can take several applications before the guava is dead. Chemical control is not an option with another pasture weed. The low-growing wild aubergine (Solanum torvum) can establish itself very quickly and in just two or three years will have taken over the field. The only way to win against this weed is to hand pull it.

Credit: Susie Emmett

The battle against reversion to bush is only one part of Mr Roger's work. The training centre's herd of Illawara cows - put to either a Charolais, Limousin or Brahmin bull - need a rich balance of grass and legumes and it is an ongoing challenge to make sure they get it. Buffalo grass or Stenotaphrum secundatum is chosen for its resilience. It can withstand both dry and very wet periods. Two legumes - mimosa and desmodium - improve the sward's nutritional value and are also quite easily established. But another species in the mix requires a lot of effort.

Bending low to the ground Mr Rogers fingers through the pasture, checking on the growth of signal grass (Brachiaria dictyoneura) only recently transplanted into position. This pasture species is grown on to seedling stage and then transplanted every 20cm or so into the buffalo grass to improve the sward. A huge task? "Yes, it's a huge amount of work - very labour-intensive - but on some of the land it has proved the only way to get the pasture we want established." Signal grass can withstand grazing pressure and stand up to, and out-compete, a handful of highly invasive weed species. These include blue rat's tail (Stachytarpheta urticifolia), broom weed (Sida acuta), false tobacco (Elephantopus mollis) and stinking cassia (Cassia hirsuta).

In the evening, the air blows cool. Grazing peacefully beneath mature trees and coconut palms, the Illawara and Charolais suckler herd are a lovely sight. They have a near-perfect sward of grasses and patches of legumes. Does this make all the work to establish good pasture and keep it weed-free worthwhile? "Sometimes it feels like a relentless battle," says Mr Rogers. "But when you look at these animals, that's what it's all for - top quality beef that Vanuatu can be proud to export anywhere in the world."

Article submitted by Susie Emmett