Summer grass

Scientific name: Digitaria sanguinalis

Summer grass plant

Summer grass infestation in pasture

Summer grass plant

Summer grass seed head
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Frost-sensitive, annual grass with a large umbrella-like inflorescence, only growing over summer in warmer areas
  • Flower stems often sprawl on the ground before growing vertically, and they can root at the nodes. Between the nodes the stems are smooth and hairless
  • Seed head is up to 30 cm across with 4 – 10 racemes, (branches), each 4 – 18 cm in length
  • Emerging leaves are rolled. Blades are soft, hairy underneath when young but only a few long hairs persist at the base when the plant is mature
  • Leaves are 3 – 8 mm wide and green to greenish-purple in colour
  • Ligules membranous, 1 – 2 mm long and blunt.

Origin

  • Native to warmer regions of Europe and Asia
  • Introduced to North and South America, South Africa and Australia, and into New Zealand over 100 years ago
  • Known as crab grass in the USA
  • Summer grass is very common in northern and coastal regions of the North Island of New Zealand. It is one of the most prevalent summer-active grasses in Waikato, Bay of Plenty and coastal Taranaki dairy pastures. It is also common in parts of Canterbury and Otago but scarce elsewhere in the South Island.

Life-cycle

  • Summer grass germinates in late spring or early summer, in response to increasing temperatures
  • Rapidly produces a seed head and will continue to grow in pastures until autumn, when plants die after cooler temperatures or frosts
  • Summer-active grass species, such as Digitaria   sanguinalis, have a C4 photosynthetic pathway. This allows them to grow more quickly than other grasses in response to increasing temperatures and solar radiation, if given adequate rainfall
  • Their water-use efficiency is also higher than that of other grasses, making them more tolerant of drought conditions
  • Seeds dominate the seed banks in regions where they are prevalent, along with other C4 grass weeds like yellow bristle grass
  • Buried seed populations viability decrease by about 50% after 18 months, and after 3 years less than 1% of the seed is still alive.

Impacts on pasture

  • Summer grass competes with sown grasses and can rapidly increase after a drought year (it fills the gaps created by death of perennial grasses such as ryegrass)
  • Forage quality declines once seed heads are produced and nutritive value is much lower than that of ryegrass in mid- and late-summer.

Impacts on livestock

  • A recent study showed that the metabolisable energy (ME) of summer grass and ryegrass was similar in December, but in January and February the ME of summer grass is  lower than that of ryegrass
  • It has been estimated that a ryegrass-clover pasture, in which summer grass makes up 25% of its total dry matter, could reduce milk production by 11% due to its poor nutritive value (- see references under ‘Further Information’)
  • Dairy cattle tend to avoid summer grass once its seed heads emerge.

Grazing

  • Avoid overgrazing which opens up pastures to summer grass invasion. The seed bank in the soils of many North Island dairy pastures is dominated by summer grass
  • Avoid moving stock from infested paddocks to clean paddocks as this increases the risk of seeds being transferred in dung.

Pasture renewal

  • To prevent summer grass emerging from the seed bank and infesting new pastures, it is best to prevent summer grass seed production for two years before pasture renewal
  • During this period it must not be allowed to set seed and replenish the seed bank. Crops such as maize, chicory, turnips or lucerne and other legumes should be used as summer grass can be easily controlled in these.

Spraying

  • Roadside spraying should be timed for just before Christmas when first seed heads generally emerge
  • Glyphosate can be used to control small isolated patches of summer grass
  • Residual herbicides have the potential to prevent the germination of summer active grasses.

ALWAYS READ PRODUCT LABELS BEFORE APPLYING

Active ingredient When to apply Residual effect Grass damage Clover damage
ethofumesate When the plants are small, preferably before tillering. Spot spray only except for ethofumesate Yes Not to ryegrass Severe
clethodim Moderate Severe No
dalapon Moderate Moderate No
fluazifop-p-butyl Moderate Severe No
glufosinate-ammonium No Severe Severe
haloxyfop / haloxyfop-P Moderate Severe No
quizalofop-P-ethyl Moderate Severe No
simazine, amitrole and dalapon Severe Severe Severe

Consult your farm consultant, industry rep. or the New Zealand Agrichemical Manual for more information about chemical control.

Similar summer-growing grasses

Digitaria ciliaris, also known as summer grass, is very similar to D. sanguinalis and is found in waste and open places in the North Island but rarely in the South Island. Its leaf sheaths have hairy margins, the hairs around the collar are shorter, its ligule is irregular and the seed head has shorter branches.

Digitaria ischamum, smooth summer grass, is found on sandy or dry ground in pastures and along roadsides from the Waikato and Bay of Plenty southwards in the North Island and in Marlborough and Otago. It has hairless leaves and leaf sheaths and does not root at the nodes.

Digitaria violascens, also has hairless leaves and leaf sheaths but does not have collar hairs. It is found in waste and open places in Northland and also in the cities of Auckland, Hamilton and Tauranga.

References

  • Campbell BD, Mitchell ND, Field TRO 1999. Climate profiles of temperate C3 and subtropical C4 species in New Zealand pastures. New Zealand Journal of Agricultural Research 42: 223-233.
  • Champion P, James T, Popay I, Ford K 2012. An illustrated guide to common grasses, sedges and rushes of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 208 p.
  • Hubbard CE 1984. Grasses: a guide to their structure, identification, uses and distribution in the British Isles. 3rd edition revised by JCE Hubbard. Harmondsworth: Penguin Books, Middlesex, England. 476 p.
  • Jackson FS, McNabb WC, Peters JS, Barry TN, Campbell BD, Ulyatt MJ 1996. Nutritive value of subtropical grasses invading North Island pastures. Proceedings of the New Zealand Grassland Association 57: 203-206.
  • Young S 2013. New Zealand Novachem agrichemical manual. Agrimedia Ltd., Christchurch, New Zealand. 767 p.