By Mark Thomas
During prolonged dry weather some plants may begin to exhibit mysterious damage to leaves, shoots and stems. The damage can seem to appear without any apparent culprit and become increasingly more intense each day the plant is inspected. What can be most frustrating is that much of the damage appears on the fresh new growth, disfiguring foliage with irregular holes or grazing of the upper green tissue of leaves and stems. Sometimes leaf blades or stems are left hanging limp after being partially chewed through. If you have plant damage that fits this description weevils are one very likely culprit, although crickets, grasshoppers and katydids can also produce similar damage.
Weevils are stealthy plant predators that come out of the mulch at night to feed by crawling along the stems and chewing the surface of the leaf leaving white patches that dry up and become paper- like in appearance. A couple of individuals may be responsible for all of the damage to one plant with the accumulated effect being substantial. Their small size and camouflage colouring make them difficult to see, along with their nocturnal preferences. They have a distinctive elongated proboscis which makes telling them apart from other beetles easy. When frightened or touched they will pull their legs in and drop to the ground where they are nearly impossible to find and will resume feeding when danger has passed. Correa species are particularly attractive to attack although anything with soft or slightly fleshy foliage can be attacked such as Myoporum, Stylidium, Acacia and many others.
Control is probably best by hand removal at night with a flashlight and something to hold beneath the shrub to catch any that fall. Most literature also recommend Carbaryl, Maldison or Pyrethrum if numbers of weevils become too high1 2 although only in extreme situations as these chemicals can effect natural predators as well. Application of chemicals is also made more difficult due to the nomadic nature of the weevils. Such chemicals should only be used strictly as per the instructions on the container as toxicity to humans is possible also. Natural predators to weevils include lizards, frogs, birds, rodents, some marsupials, wasps, fungi and bacteria. The response time from natural predators may not be as quick as many people would like but if allowed to do their job natural predators and hand removal should usually take care of the problem and keep the natural balance in your garden.
1 Jones,D. & Elliot R. 1986, “Pests, Disease & Ailments of Australian Plants” Lothian Books, Melbourne
2 McMaugh, J.1985,” What Garden Pest Or Disease Is That: Every garden problem solved, Landsdowne Press, Sydney