Pulling out the trusty spade and taking a look underground has revealed an army of fluffy white spots through the soil. I have met a few consultants lately who have been misidentifying this pest as beneficial fungi; sadly it is in fact a pasture pest called “mealy bug” and in my experience it appears to be on the rise across Northland, Hawke’s Bay, Manawatu, Marlborough and Canterbury.
Using a loupe magnifying glass, the adult Pasture Mealy Bug appear headless and legless, as tiny pinkish, oval shaped insects up to 2mm long. They are often found in the crown of the plant, with the females surrounded in tufts of white waxy secretions to protect themselves. They appear to take a fancy to clover, and suck the sap from grass roots. A heavy infestation can cause death of plants in a paddock, which may be more obvious in Autumn. They like the dry, which may be why they have appeared to be worsening. Mealy bugs are also known to take up residence after grass grub vacate, so the poor pasture growth may be due to more than one insect.
The secretions made by mealy bug are waxy, this also has the double whammy for your soil by making them ‘hydrophobic’, its a sad day indeed when your soils become afraid of water! (see image below, yellow patch on hill was dying clovers, sparse grass cover and scared soils with mealy bug present)
Whats the solution?
Ultimately addressing the underlying soil conditions which have led to the infestation is the goal, however a large infestation can be slowing down your program so much, that an interim control is helpful.
I met a dairy farmer in North Canterbury early last year who was having a problem with grass pull and slow pasture recovery, we dug holes across the entire property, and sure enough mealy bug were happily grazing on his plant roots. I recommended a biological control agent called Beauveria bassiana. This entomopathagenic fungus lives naturally in healthy balanced soils in NZ. He applied the product and a few months later I had the chance to revisit, he was happy with how it had worked, as his pasture pulling had stopped within a few weeks. His only complaint was he couldn’t figure out why he had a bag left over in the shed. We dug soil spits down the length of the farm and didn’t see a single mealy bug; until we reached the last paddock, which was heaving with the little blighters. “Ahhhh so thats why there’s a bag left behind!” This farmer had actually run a very good trial, which helped him prove to himself that it wasn’t just a coincidence or a seasonal occurrence.
In my travels the more a property has biologically and minerally imbalanced soil (and more specifically humus levels) the more likely insect pressure will be. Methods which aim to get base saturation minerals in balance, improve humus levels and increase worm numbers all contribute to a reduction in pest pressures over time.