Wheat Bug - Nysius

Argentine Stem Weevil (Listronotus bonariensis), often referred to as ASW, is a small weevil from South America that is now found throughout New Zealand. Adult stem weevils are hard to detect by eye being only 3.5mm long. Larvae feed in the developing shoots of many important crops including pasture, maize, sweetcorn, cereals and brassicas and it is the larvae that are responsible for the tremendous economic losses attributable to ASW in New Zealand each year. Depending upon the weather experience ASW can complete multiple life cycles each year with egg laying taking place between July and March.

Black beetle (Heteronychus arator) is a large black shiny beetle (15mm), originally from South Africa, and now found throughout the warmer parts of the North Island of New Zealand. The beetle favours light sandy or peaty soils rather than heavy clay soils as these are easier for the adult beetles and larvae to move through. Both the adult beetles and larvae cause plant damage with the adults feeding on newly emerged plants at ground level and by larvae feeding on crop roots between December - March. Beetle numbers can be very high after mild winters and also following seasons with low rainfall.

Grass grub (Costelytra zealandica) is the larval stage of the bronze beetle and is found throughout New Zealand from Southland as far north as Waikato. Grass grubs feed on the roots of pasture and autumn planted cereals and can cause extensive plant death if not controlled. Grass grubs have three larval instars and each one is capable of causing damage but the third instar, which is usually between February and spring, is the most damaging. Not all the larvae at their largest but this also coincides with plant establishment. The treatment threshold for grass grub is two grubs per spade square. Well before sowing, take a garden spade and dig ten sample squares to the depth of the spade blade in a diagonal across the paddock. Sift through the soil and if an average of more than two grubs per sample is found treat with an effective seed treatment.