Alligator weed has now been found on several kiwifruit orchards in the eastern Bay of Plenty.

Growers and contractors must take every precaution necessary to stop the spread of this invasive and almost impossible to eradicate weed.

Native to South America, alligator weed was accidentally introduced to New Zealand via ship’s ballast in the 1880’s. It spread to parts of Northland, Waikato and the eastern Bay of Plenty, initially via contaminated machinery associated with commercial kumara growing. Machinery is suspected of further spreading alligator weed between orchards in the Bay.

Alligator weed is unusual in that it grows equally well in and over water, as it does a drain, a low-lying paddock or within a kiwifruit orchard.

Dense growth can easily be 50cm high. Dark green leaves are in opposite pairs; stems are hollow; roots grow to a metre or more deep; and white clover-like flowers appear during summer and autumn.

Although alligator weed does not produce viable seed in New Zealand it can readily spread through stem fragments attached to tractor tyres or other machinery.

Herbicides have limited effect on alligator weed. If it’s a small infestation, carefully dig it out and destroy it. One of the best control methods for large areas is to peg a thick weed mat material over the entire infestation – effective until a keen orchard worker forgets the location and runs a mulching mower over it!

Prevention is the best strategy. Ensure all mowing, root pruning and other orchard machinery is pristinely cleaned between orchards. Mow clean areas of the orchard first, and infested areas last. Then clean the machinery. If you suspect you have alligator weed, contact your local regional council or KVH for further control advice.