Walking the paddock to learn about pasture plants, Saturday 30 November 2013

Understanding plant relations in pastures is a big help if you are engaged in land management. It can mean the difference between healthy nutritious mixed pastures and depressing infestations of weeds such as St John’s Wort.

Knowing when to spray or not to spray St John’s Wort is also useful for avoiding expense and effort for no ultimate effect. 

The more plant species you have in a pasture, the better its grazing value for horses, apparently. Even weeds — whether grasses or broadleaved plants that you would not sow deliberately into a pasture — can be a small part of the mix, so long as they are not dominant (the patch in the photo below has at least three grass species plus the yellow Flatweed/Catsear).

Differing leaf shapes and lengths, times of flowering, annual or perennial, times of best nutritive value, hairiness, spikiness, taste (presumably), type of root, and so on, all can make for an interesting food source for invertebrates as well as stock. A varied combination of species above-ground means potentially efficient exploitation of the soil below-ground, with a range of root types and enzymes and invertebrates in action.

Soil with a complete groundcover should not erode. By definition, it has no bare patches. Bare spaces are the places where weeds (outstanding competitors) can get a ‘toe-hold’. Complete groundcover implies a rich (organic-matter) mixture of roots and their associated insect and microbial activity in the soil. Such soil has pore spaces and overall structure, which the natural plant and microbial exudates help build and maintain. Rain can infiltrate well, and the soil is better able to resist compaction — except where tracks are worn by repeated use.

These are some of the features of plant relations in pastures we learnt on 30 November, during a mild sunny and airy morning with Alison Elvin walking across paddocks on two properties in the Wallaroo area, near Canberra. About 20 local landholders attended this second workshop in the series called ‘Action on Weeds near Wallaroo’, organised by Karissa Preuss of the Ginninderra Catchment Group.

Alison not only identified every plant she saw or we pointed out to her, she also discussed how to plan to attack weeds by slashing, grazing, sowing, mapping the stands of plants in a paddock, cultivation, and the use of biocontrol, where it is available. By making careful observation and notes, a landholder can gradually build up an understanding of plant, soil and animal inter-relations, finding out what management ‘works’ and what does not ‘work’ in particular soil types, aspects and combinations.

This way, spraying with herbicide — with all the associated expense and anxiety — is needed rarely and only when absolutely necessary.

The paddocks we visited had variable proportions of grass species, and some broadleaved species. Among grasses we were shown annuals such as Fescue (Vulpia sp.; see 5th photo below, in the foreground; perennial native Wallaby Grass is near the feet) which are now (in early summer) pale brown or beige in colour . Looking across the hillside we could see patches of Fescue among the green perennials such as Wallaby Grass and Phalaris (once Alison had pointed that out to us!, e.g. in the photo below including on the hillside in the distance).

Mapping (roughly) the annual grasses as they brown off in early summer means that next year you know which paddocks or parts of paddocks to graze heavily during winter when the annuals are green. That way you take advantage of the annuals’ nutritive value, and at the same time you reduce their competitive effect on their associated perennial grasses, so the latter can get ahead.

Wild oats (Avena fatua) were prevalent around these paddocks and roadsides, usually with empty seed heads. Apart from in crops, infestations of wild oats are mostly a worry because they are a considerable fire hazard in summer when they are brown and dry, Alison told us. If you graze this grass heavily when it’s in leaf during winter, before flowering, the flowering stalks will be shorter in spring and the infestation will be less of a fire risk later.

Yorkshire Fog (Holcus lanatus; top photo below), Phalaris (Phalaris sp.; photo above), Couch (Cynodon dactylon) and Hairy Panic (Panicum effusum), Barley Grass (Hordeum leporinum; tufty, in foreground, lower photo) and Ryegrass (Lolium sp.; ridgy flowerhead, around shoe in lower photo) were other introduced grasses we saw, and of course African Lovegrass (Eragrostis curvula).

Two paddocks were well populated with Wallaby Grass or White Top (Austrodanthonia sp.; photo below, near the feet), apparently so called because the flower head has white hairs as on a wallaby’s face. Weeping Grass, Microlaena stipoides, was also seen. Both can tolerate a small to moderate level of soil phosphate: more than other native grasses, but still not much. Alison said it is preferable to build up the soil fertility gradually, over several years, by applying compost tea, rather than superphosphate.

Among broadleaved species Alison told us how to manage Capeweed (Arctotheca calendula); Paterson’s Curse (Echium plantagineum) —‘paddo’; Flatweed (Hypochaeris radicata); St Johns Wort (Hypericum perforatum) — ‘SJW’ (photo below). Alison advised that if SJW or Paddo began to invade from the denser patches visible nearby then to dig them out or cut them down quickly, or smother them with a pile of straw or similar mulch material. It’s important to act decisively at this time of year when the prolific flowers are beginning to set hundreds of seeds.

We learned that SJW has strong rhizomatous roots as well as multitudes of seeds to help it invade. Spraying it can be a huge waste of money — though it can be useful if done at a suitable growth stage. Alison says that early summer is the ideal time, when the SJW is in flower and easy to see. Although some of the flowers may have started forming immature seed, generally spraying in early summer will achieve an excellent kill rate, and the seeds will not mature further, and little or no new seed will be produced. 

(The wrong time to spray is, for instance, when the flowers are nearly finished and are full of seed. At that late stage you will not prevent the next year's 'crop' of this weed, although you would kill the plant.) 

The risk with spraying at the wrong time is that you will kill much more than just the SJW (which could leave bare patches for new weed invasions) and you could spend hundreds of dollars and end up with as big an infestation the following year.

Other control methods Alison discussed were burning, slashing and biocontrol. Burning and spraying too late (as above) can work but only because in the following wet season you can expect a thick germination of young SJW from the hundreds of unkilled seeds, which you can immediately destroy by cultivating (or perhaps spraying).

Biocontrol is an exciting possibility. The controlling beetles, released deliberately by local entomologists in one of the paddocks we saw, have killed a whole slope of SJW - the browned off plants behind the people in this photo below. Only a few individuals (flowering) remain in this stand. 

The beetle used in this area of NSW is Chrysolina quadrigemina (photo above) though other species appear to have been released in the Cooma area further south (http://www.cooma.nsw.gov.au/files/docs/environmental_
management/noxious_weeds/factsheets/St%20Johns%20Wort%20CMSC%20Factsheet.pdf). If you have the beetle, Alison advises spreading individuals as widely as you can into your own SJW patches and into your neighbours’ as well. You should let it get on with eating your SJW (the adult does the damage) and not attempt to otherwise control the SJW at the same time which would remove the beetles’ food supply.

We saw little Paterson’s Curse, but plenty of Flatweed (or Catsear). Alison pointed out its differences from Dandelion (Taraxacum sp.). Flatweed causes problems for horses (but not other stock). Dandelion on the other hand, with its distinctively hollow stem and only one flowerhead per stem, indicates good nutritional status in the soil.  

Other photos from this 'walkshop' and the previous workshop on 10 November are in the pages at the side of this blog.

Useful reference for St John’s Wort: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0010/347995/bpmg-stjohn-wort.pdf