Lawn Grubs

Grub out Lawn Grubs

Australian Lawn Grubs


 

We’re going to lump the three main things that attack Australian lawns into the category of lawn grubs as that is the name a lot of us know the by. They are all however the offspring of insects. They can sometimes reach plague proportions and completely destroy our lawns or farmers’ crops even though many grasses and cereals can withstand moderate feeding by a reasonable numbers of parasites. We will go through just what they are and how to get rid of them. To start off we will examine Armyworms.


Armyworms.


There are three species of these little blighters although they are all related. These are the Common Armyworm (Leucania Convecta), the Northern Armyworm (Leucania Seperata) and the Sugarcane Armyworm (Lecania Stenographa). The first stage of the lava are only about 1mm long. As they get larger they become more recognisable as they develop stripes along their sides. When it is mature it will get to about 4cms long and have  distinctive stripes along the body with three pale ones on the head and the bit just behind it as well as the tail end. There are no hairs on the smooth bodies. The moth also has a wingspan of about 4cms and is a buff colour. This description will just about fit both Common and Northern varieties with the moth of the Sugarcane species having a dark line on the forewings that are a bit more pale in colour.


The Common Armyworm is native to Australia and found pretty much all over the eastern half of the country. The Northern Armyworm is also found all over the country as well as in New Zealand and South East Asia. The Sugarcane Armyworm has been found in Asia the drier pats of the Australian mainland and sometimes it gets to Tasmania.


The Sugarcane Armyworm is a less of a problem than the others occasionally doing damage to grain crops in Western Australia. The Northern Armyworm tends to cause crop damage in Queensland to plants such as rice, barley, maize, wheat and sorghum. The Common Armyworm will have a go at native grasses in the pastures, perennial grass seed crops as well as wheat, barley and oats.


Life Cycle


All three types are similar and we will describe the Common Armyworm’s life. The adult moths will go to a place they judge to give the best chance of the continuation of their species. They will fly their and lay their eggs on what they consider the best places. This is normally in the cress of cereals or grasses that are drying out or actually dry. The eggs are laid in large clumps by the female numbering up to a thousand at one sitting, being stuck into those folds of the host plant’s leaves. When the lava emerge from their eggs they will use a thin thread of silk to be carried on the wind so as to speed out through the grasses or crops around them. Differences in temperature will control the speed of their hatching and rate of growth. At 20 degrees Celsius they will hatch after about seven days and be read to pupate in another thirty fours days. At thirty degrees these times can be reduced from  two to three days and and thirty four to thirty five respectively. 


Periods of Risk


If you are a cereal farmer, late Winter to Spring is likely to be your worst time. The winter generation can cause quite severe damage to grassland and crops when they gather in large numbers. They will eat virtually everything before moving on to another area. You should be aware that if you sow seed into stubble, the lavae may damage the new growth as it appears. There are usually three generations of Armyworms through the year and it is a good idea to check the bases of plants and under lumps of earth where they hide during the day time. 


Dealing With The Problem


There are a number of different insecticides that can be used to control Armyworms. You must be aware however that these measures are best used when the lavae are a bit smaller, say between one and two centimetres long. If they are bigger than that they are harder to kill and may need quite a bit higher concentration of chemical. As they are more active at night, the best time to spray will be later in the day in order to take advantage of the greater accessibility.


There are also parasites that can help to control Armyworm numbers but these tend to be less effective if there is already a large infestation. This is because they are obviously more slow to act than chemicals. Numbers of Green Carab Beetles will increase quite a lot when there are more Armyworms for them to feed on. Common brown earwigs, shield bugs and some fungal diseases may also help in controlling the pest.

 


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